Iridium NEXT (Hosting Payloads on a Communications Constellation)
In 2007, Iridium Satellite LLC announced its plans to develop its Iridium NEXT constellation and start deployment in the timeframe 2015-2017. With the announcement came the offer of hosted payloads for government and scientific organizations. Iridium NEXT, in continuity to the current Iridium system of 66 satellites, will provide 24/7 real-time visibility over the entire Earth's surface and its atmosphere. ICI (Iridium Communications Inc.) is the only MSS (Mobile Satellite Service) company offering global voice and data coverage. ICI owns and operates the constellation and sells equipment and access to its services. Satellites communicate with neighboring satellites via Ka-band ISLs (Inter-Satellite Links). Each satellite can have four ISLs: two to neighbors fore and aft in the same orbital plane, and two to satellites in neighboring planes to either side.
Hosted payloads on Iridium NEXT will provide an unmatched opportunity to meet Earth observation and government mission requirements in the near term at a fraction of the cost of designing, building, launching and maintaining dedicated platforms in space.
The Iridium NEXT system is expected to maintain Iridium's current unique architecture that provides truly global coverage, with expanded capacity, higher data speeds, new services, flexible payload architecture capable of supporting future product enhancements, cost effectiveness in maintaining and operating the network, and a design to host secondary payloads.
Major parameters of the mission are given in Table 1. Each Iridium NEXT satellite has an allocation of 50 kg in mass, 30 cm x 40 cm x 70 cm in volume, 50 W of average power, and 100 kbit/s average data rate for each hosted payload.
Table 1: Hosted payload specifications of the Iridium NEXT Constellation
Background: Iridium is a MSS (Mobile Satellite Services) provider - the only network provider offering 100% worldwide coverage. The network is a very unique, resilient LEO (Low-Earth Orbiting) satellite constellation of 66 satellites plus in-orbit spares. The original Iridium constellation of 66 satellites plus 6 spares was launched between May 5, 1997 and May 17, 1998.
A comprehensive plan to replenish the Iridium constellation, known as Iridium NEXT will launch 66 new satellites to replace the current constellation, with launches expected to begin in 2015. Also planned are 6 in-orbit spare satellites and 9 ground spares. Iridium NEXT features increased subscriber capacity, higher data speeds, and capacity for hosting payloads.
Data handling for hosted payloads: Although the satellites in the Iridium system are primarily designed to support the Iridium communications mission, they have been adapted to accommodate hosted payload missions. Mission data and sensor telemetry and command data for these missions can be transported in near real-time utilizing the K-band network of crosslinks between satellites, feeder links to the ground, and teleports connecting the satellites through earth stations to a MPLS (Multiprotocol Label Switching) cloud called the Teleport Network.
Iridium operations manage deployment and operation of the Iridium system. Iridium NEXT would retain the capability to turn off the hosted payload, in an extreme emergency situation, to preserve the health of the Iridium satellite. Iridium enables a hosted payload command and data path to an MPLS cloud. A customer designated sensor operations facility would manage the hosted payloads in-orbit on the Iridium NEXT satellite using the command and data path provided by Iridium operations. These functions include:
- Sensor operations tables
- Updating software or firmware
- Data stream management (pull or push from the MPLS cloud)
- Anomaly resolution.
This Hosted Payload Operations Center will provide the data processing capability for the sensor data. It will receive the data stream from the MPLS cloud and processes the data for end users. End users can provide feedback to sensor operations and data processing.
Benefits: The hosted payloads offer a customer the following value proposition:
• Unprecedented geospatial and temporal coverage : 66 interconnected satellites with coverage over the entire globe
• Low latency : Real-time relay of data to and from payloads in space
• User control : Data collection and hosted payload access seamlessly through Iridium infrastructure or private gateways
• Cost effective : Access to space at a fraction of the cost of a dedicated mission
• Exclusive : No other opportunity like this is likely to become available in the coming decades.
• Consistent with 2010 U.S. President's National Space Policy : Commercial capabilities, cost effective access.
Iridium Next SensorPod: A SensorPOD is a virtual container (enclosure) that is a designated subset of the total Iridium NEXT hosted payload volume and is applicable for small payloads and payload suites that only require a small portion of the available volume (Figure 1).
SensorPod "containers" can be arranged in varying configurations (i.e., stacked like blocks) to support many different customer experiments. SensorPod geometries can also be scaled on a case-by-case basis to accommodate specific customer payload needs. SensorPods are designed to be located and oriented in the hosted payload volume to provide both nadir and/or RAM FOV (Field-of-View) options. An example of a notional configuration which includes a combination of a "primary" nadir-viewing SP and multiple "secondary" SensorPods is shown in Figure 2.
Figure 1: SensorPod of Iridium Next (image credit: Iridium Satellite)
Figure 2: Schematic layout of an Iridium Next SensorPod (image credit: Iridium Satellite)
Customers may fill each SensorPod volume with one or several payloads as long as they remain within the overall sensor volume, mass, power and communication allocations. Customer payloads are provided with mechanical and thermal interface routing plates and conditioned electrical power and communications via a hub through external harnesses.
In June 2010, TAS (Tales Alenia Space) of France was awarded a contract from ICI (Iridium Communications Inc.) for the design and construction of 81 satellites — 66 operational satellites, six in-orbit spares, and an additional nine ground spares. In turn, TAS has selected Orbital ATK [former OSC (Orbital Sciences Corporation] as a subcontractor for the integration of Iridium NEXT satellites and the hosted payloads in a facility located in Gilbert, AZ. 9) 10) 11) 12) 13) 14) 15) 16)
Iridium has also signed the largest single commercial launch deal ever with Space-X (Space Exploration Technologies Corp.) to be the primary launch services provider for Iridium NEXT.
In addition, Iridium entered into two comprehensive, long-term agreements with The Boeing Company for maintenance, operations, and support of Iridium's satellite network. Under the first agreement, Boeing will continue operating Iridium's current satellite constellation and will provide support for Iridium's satellite control system. The second agreement is a new support services contract under which Boeing will become the exclusive operations and maintenance provider for Iridium NEXT. The combination of these agreements allows Iridium to benefit from having a single operator during the transition from the current constellation to Iridium NEXT.
Table 2: Specification of Iridium NEXT spacecraft (Ref. 11)
Some milestones of the program:
• December 30, 2016: The first 10 satellites for Iridium's next-generation mobile voice and data relay network have been fueled, joined with their deployment module and encapsulated inside the clamshell-like nose cone of a SpaceX Falcon-9 booster for launch as soon as next week from VAFB (Vandenberg Air Force Base) in California. 17)
- An official target launch date is pending the FAA (Federal Aviation Administration) approval of the SpaceX-led investigation into the explosion of a Falcon-9 rocket on a launch pad at Cape Canaveral on Sept. 1, 2015, which destroyed the Israeli-owned Amos-6 communications satellite awaiting liftoff a few days later.
- SpaceX missions have been grounded since the explosion. The California-based launch company, founded and headed by Elon Musk, hoped to resume launch services by the end of 2016, but the investigation, launch preparations, and the FAA's review of the Sept. 1 mishap pushed the Falcon-9's return-to-flight into January.
- The launch of Iridium's first 10 next-generation communications satellites, the first part of an eventual network of 81 spacecraft, was next in line on SpaceX's manifest at the time of the Sept. 1 explosion.
- Meanwhile, construction crews at Kennedy Space Center's launch pad 39A in Florida are finishing up modifications to the former space shuttle launch complex to support Falcon 9 flights as soon as late next month. - The launch facility used by SpaceX's previous missions from Cape Canaveral, Complex 40, suffered major damage after the Sept. 1 rocket explosion, the first such on-the-ground mishap at the Florida spaceport since the early years of the Space Age.
Figure 3: The first ten Iridium NEXT satellites are stacked and encapsulated in the Falcon 9 fairing for launch from Vandenberg Air Force Base, CA, in early 2017 (image credit: Iridium)
Legend to Figure 3: The satellites are mounted on a deployment module developed by SpaceX specifically for the Iridium missions to be flown on Falcon 9 rockets. SpaceX is under contract to launch at least 70 Iridium Next satellites through early 2018, primarily in batches of 10 at a time. The mounting system is made up of two tiers, each holding five satellites. Ground crews inside the SpaceX payload processing facility at Vandenberg have stacked the two tiers and encapsulated the satellites inside the Falcon 9's payload fairing, which is emblazoned with the Iridium logo.
• June 14, 2016: Iridium Communications Inc. announced that its first Iridium NEXT satellites have completed assembly and testing, and are now prepared for shipment to the launch site at Vandenberg Air Force Base in California. The shipment of these satellites represents a significant milestone toward the first launch of the Iridium NEXT constellation, which the company officially announced as targeted for September 12, 2016. 18)
- Assembly, integration and testing of the satellites are performed by Thales Alenia Space and their subcontractor, Orbital ATK, at the Orbital ATK manufacturing facility in Gilbert, Ariz. The production process incorporates a unique, assembly line system consisting of 18 different work stations ranging from panel integration and payload testing to full satellite integration, solar array installations and alignment checks. Each satellite features more than 5,000 individual parts assembled, culminating in one hundred thousand hours of workmanship by hundreds of engineers. A total of 81 satellites are scheduled to roll off of this assembly line, with 66 serving as the operational satellites to replace the existing Iridium® network, and the remainder serving as ground and on-orbit spares.
- Assembly, integration and testing of the satellites are performed by Thales Alenia Space and their subcontractor, Orbital ATK, at the Orbital ATK manufacturing facility in Gilbert, Ariz. The production process incorporates a unique, assembly line system consisting of 18 different work stations ranging from panel integration and payload testing to full satellite integration, solar array installations and alignment checks. Each satellite features more than 5,000 individual parts assembled, culminating in one hundred thousand hours of workmanship by hundreds of engineers. A total of 81 satellites are scheduled to roll off of this assembly line, with 66 serving as the operational satellites to replace the existing Iridium® network, and the remainder serving as ground and on-orbit spares.
- The first two completed Iridium NEXT satellites are being shipped to Vandenberg Air Force Base for processing by Iridium's launch partner, SpaceX. As the remaining eight first-launch satellites are completed, they will also be shipped two at a time to the launch site. While the satellites will be ready by August, the earliest launch date available to Iridium from SpaceX and Vandenberg Air Force Base is September 12th. During processing, Orbital ATK is responsible for fueling the satellites, while also performing software validation and testing to ensure the satellites integrate properly with the SpaceX Falcon 9 rockets. The Iridium NEXT satellites represent SpaceX's heaviest payload to date.
- All Iridium NEXT satellites are scheduled for launch by late 2017. Starting in 2018, the Iridium NEXT constellation will enable Aireon's satellite-based system to provide global aircraft surveillance in real time. Iridium and SpaceX have partnered for a series of seven launches, with ten Iridium NEXT satellites deployed at a time.
• Nov. 10, 2015: The first launch for Iridium's next-generation mobile communications fleet has been pushed back four months — from December 2015 until April 2016 — to resolve a technical problem inside the spacecraft's Ka-band communications payload. 19)
- According to Matt Desch, CEO of Iridium, the primary cause of this problem is not that complicated, nor is it difficult to fix. TAS discovered the issue during testing after assembling the component. The specific issue is an RF (radio frequency) spur that occurs at certain temperatures, which could create performance problems in the Ka-band downlinks to Iridium's Earth stations.
- The problem means the first pair of satellites will not ship to their launch site in Russia in November (Dnepr launch), but in March 2016, to begin a 30-day processing campaign leading up to liftoff.
- A "protoflight" version of the Iridium Next spacecraft bus recently completed a thermal-vacuum test at Thales' facility in Cannes, France, in a final milestone leading to the full flight qualification of the Iridium Next satellites in December, Thales said in a statement.
- TAS (Thales Alenia Space) is leading development of 81 Iridium Next satellites, and Orbital ATK is in charge of spacecraft assembly, integration and testing at a facility in Gilbert, Arizona.
• Oct. 29, 2015: TAS (Thales Alenia Space), prime contractor for the Iridium NEXT constellation, has reached a major milestone in this program with the successful completion of thermal-vacuum tests of the protoflight satellite at the company's plant in Cannes, France. This is the last milestone leading up to the qualification of Iridium NEXT satellites, which is expected to occur in December of this year. 20)
- In parallel, production is proceeding on schedule at the Orbital Sciences facility in Gilbert, Arizona, where ten satellites are currently undergoing assembly, integration and testing (AIT). The last technical issues concerning a critical supplier have now been resolved.
• June 1, 2015: Aireon LLC, developer of the world's first space-based global air traffic surveillance system, announces that Iridium Communications Inc. has completed the first successful integration of the Aireon payload on an Iridium NEXT satellite. This is a key technical milestone toward the first launch of Iridium NEXT and the first demonstration of the Aireon air traffic surveillance capability. 21)
- The forthcoming Aireon service will be deployed using space-based ADS-B (Automatic Dependent Surveillance-Broadcast) receivers built into each of the 66 satellites in Iridium NEXT, Iridium's second-generation satellite constellation. Iridium NEXT is scheduled to launch between 2015 and 2017, with full Aireon service expected to be available in 2018.
- "This milestone moves us significantly closer to being able to provide the global air traffic surveillance system that the world needs," says Vincent Capezzuto, CTO and Vice President of Engineering, Aireon. "The Aireon system will provide real value to stakeholders by enabling vast improvements in efficiency and safety of air traffic operations. Iridium continues to make good progress with the constellation build, keeping Aireon on track for full service deployment."
- "The integration of the Aireon hosted payload to the satellite platform is a major milestone for Aireon, Iridium and the aviation industry, in general," says Matt Desch, CEO, Iridium Communications Inc. "This brings the Iridium NEXT constellation one step closer to hosting the first truly global surveillance and tracking service."
• Nov. 11, 2014: Iridium reports the successful completion of the verification testing for the new solar panel design of Iridium NEXT. To verify the capabilities of the new design, the solar arrays underwent a rigorous life test and qualification program. This verification procedure allowed the project to test every mechanical and electrical configuration of the solar arrays, while testing them in simulated environments reflecting the harsh conditions into which they will be deployed. 22)
- The solar arrays were also extensively tested for longevity to ensure they would meet and exceed the lifetime expectations of the Iridium NEXT satellites. The solar cells were exposed to 75,000 thermal cycles, each one representing the Iridium NEXT satellite's movements in and out of the sun's radiating heat. The testing demonstrated that each array has a lifespan of almost 19 years of in-orbit operations — 6.5 years longer than the expected lifespan on our current satellites.
• September 15, 2014: It's "All Systems Go!" at Iridium, as the upgrade of the SCS (System Control Segment) and development of the new LEOP (Launch and Early Operations) control center has been completed. To reach this milestone, Iridium has been working closely with our Iridium NEXT Mission Team partners: The Boeing Company and L-3 Telemetry-West, whose InControl™ software suite has been integrated into the SCS. 23)
• In August 2014, Iridium Communications Inc. announced the successful upgrade of its SCS (System Control Segment) and completion of its LEOP (Launch and Early Operations) control center for Iridium NEXT, the largest new commercial satellite constellation in the world. 24)
• In October 2013, Iridium Communications Inc. has successfully completed the CDR (Critical Design Review) of the complete Iridium NEXT satellite network system, demonstrating its design is valid and on schedule for first launch in early 2015. 25)
• In Feb 2011, Iridium Communications announced that Orbital Sciences signed an agreement with Iridium that reserves hosted payload capacity on Iridium's next-generation satellite constellation, Iridium NEXT.
Orbital, as the satellite integrator and test sub-contractor for Iridium NEXT, will also be responsible for the integration of hosted payload platforms with the Iridium NEXT satellites. Orbital's role as the satellite integrator is critical to ensuring that multiple hosted payloads, including Orbital's capacity, can be accommodated simultaneously on the Iridium NEXT constellation. 26)
Launch: The first 10 Iridium NEXT satellites were launched on January 14, 2017 (17:54:39 UTC) on a Falcon-9 vehicle of SpaceX from VAFB, CA. Confirmation of a successful deployment of all 10 Iridium NEXT satellites came at about T plus 1 hour and 17 minutes after liftoff from Vandenberg. — In parallel, the first stage of the launch vehicle was recovered at sea off the coast of California. It was the seventh time SpaceX was able to land its first stage on an uncrewed ship. 27) 28)
• This is the first in a series of seven Iridium NEXT launches, which are scheduled over the next 15 months with SpaceX. Each launch will include a payload of ten Iridium NEXT satellites – the heaviest payload yet to fly on a Falcon 9 – and begin a one-for-one satellite replacement of Iridium's existing global satellite constellation, the largest commercial satellite constellation in space. This process is known as a "slot swap", and one of this scale has never been attempted before. Due to the size and complexity of this endeavor, Iridium NEXT has been referred to as one of the largest "tech refreshes" in history.
• "Today Iridium launches a new era in the history of our company and a new era in space as we start to deliver the next-generation of satellite communications," said Matt Desch, chief executive officer of Iridium. "We have been working endless hours for the last eight years to get to this day, and to finally be here with ten Iridium NEXT satellites successfully deployed into low-Earth orbit is a fulfilling moment. We are incredibly thankful for all of the hard work from our team, as well as our partners, to help us achieve this milestone."
• In addition to partnering with SpaceX for the launch of 70 Iridium NEXT satellites, the manufacturing, assembly and testing of all 81 satellites is being conducted by Thales Alenia Space and their subcontractor for production, Orbital ATK. Both partners have played integral roles in the Iridium NEXT program, including the management of an 18-station, state-of-the art assembly line production system, making today a possibility.
• The hosted payloads onboard the Iridium NEXT satellites are manufactured by Harris Corporation and will include a payload from Iridium's partner Aireon, which will for the first time provide a real-time global aircraft tracking and surveillance service for air traffic controllers and airlines, extending aircraft visibility across the planet.
• The next major milestone will be the validation that all ten satellites are receiving telemetry from our SNOC (Satellite Network Operations Center) in Leesburg, VA, and the completion of on-orbit testing of these satellites, to validate performance requirements are met. The second Iridium NEXT launch will be scheduled after this testing is completed, in April. The entire Iridium NEXT network is scheduled to be completed in 2018.
• The original Iridium constellation was launched during the 1990s and early 2000s. It provides voice and data coverage for some 800,000 subscribers through 66 active satellites.
The comeback mission kicks off a busy launch manifest with more than 20 SpaceX rocket flights expected this year as the company prepares to start launching astronauts, vital national security payloads and a slate of valuable telecommunications satellites for global broadcasters and network clients.
Figure 4: Picture perfect blastoff of the SpaceX Falcon-9 on Jan. 14, 2017, Return to Flight launch from Vandenberg Air Force Base in California carrying a fleet of ten advanced Iridium NEXT satellites to low Earth orbit (image credit: SpaceX)
• In June 2010, SpaceX was awarded a contract by Iridium Communications to launch 70 Iridium NEXT satellites aboard the Falcon 9 launch vehicle, between 2015 and 2017.32)
• Note: This launch is contingent upon the FAA's approval of SpaceX's return to flight following the anomaly that occurred on September 1, 2016, at Cape Canaveral Air Force Station, Florida. The investigation has been conducted with FAA oversight. Iridium expects to be SpaceX's first return to flight launch customer. 33)
• However, the first two Iridium Next satellites were set to launch on a Dnepr rocket of ISC Kosmotras, a Moscow-based company with joint Russian-Ukrainian ownership (Ref. 19).
- In June 2011, Iridium Communications signed a contract with ISC (International Space Company) Kosmotras as a supplemental provider of launch services for its next-generation satellite constellation, Iridium NEXT. The contract enables ISC Kosmotras to provide Dnepr launch services for the Iridium NEXT program in 2015 and beyond. Iridium has the capability and flexibility to launch the Iridium NEXT satellites on Kosmotras Dnepr and SpaceX Falcon 9 rockets to successfully deploy the Iridium NEXT constellation. 34)
- Note: Iridium Communications has pushed back the inaugural launch of its second-generation constellation to October 2015, saying payload-software issues need more time to validate. Iridium Communications said the delay will have no effect on the in-service date for the 66-satellite Iridium Next constellation. 35)
• Iridium has contracted with SpaceX to launch the constellation on Falcon-9 FT (Full Thrust) vehicles in the timeframe 2016-2017. Ten satellites are on each launch and seven missions are planned (see Table 4 for update information). 36)
Table 4: The Russian government delays satellite launches of western nations indefinitely — a consequence of economical sanctions imposed onto Russia by western nations due to the Crimean conflict 37)
Orbit: Circular polar orbit, altitude = 780 km, inclination = 86.4°, period = 101 minutes (the spacecraft of the constellation will be positioned in 6 orbital planes).
However, the first ten Iridium NEXT satellites were delivered to a 625 km temporary parking orbit where they will be tested and exercised by Iridium over the coming weeks. Upon meeting testing and validation requirements, the satellites will then be moved into their 780 km operational orbit and begin providing service to Iridium's customers.
Figure 5: Artist's rendition of the deployed Iridium NEXT spacecraft (image credit: Thales Alenia Space)
The 66-satellite main constellation (+6 in-orbit spares), configured in 6 orbital planes with 11 evenly spaced slots per plane, provides continuous global coverage as demonstrated by the RF footprints in Figure 6. This is achieved though cross-linked satellites operating as a fully meshed network that is supported by multiple in-orbit spares to provide real-time data downlink to the Iridium operated ground station network. The constellation has a design lifetime greater than 10 years in a polar orbit at 780 km with an inclination of 86.4°.
Figure 6: Illustration of RF overlapping footprints of the Iridium NEXT satellite constellation (image credit: Iridium)
Figure 7: Orbital coverage of the Iridium NEXT constellation of 66 spacecraft (image credit: Iridium Satellite)
• May 26, 2017: For an unusual change, a launch date just got moved forward. Usually date changes are to push the event further out ... not so for Iridium Communications second launch for the Iridium NEXT satellite constellation. The date is now targeted for June 25, 2017 at 1:24:59 p.m. PDT with an instantaneous launch window. 38)
- SpaceX informed Iridium that range availability had opened up at VAFB (Vandenberg Air Force Base) in California, where SpaceX's west coast launch facility is located, and planned to target Iridium's launch four days earlier than originally scheduled. This launch will deliver the second payload of 10 Iridium NEXT satellites to orbit, bringing the total to 20 Iridium NEXT satellites in space.
• May 2, 2017: Iridium Communications Inc. has announced that the first set of Iridium NEXT satellites have been integrated into the operational constellation and are providing excellent service to Iridium customers. Prior to achieving this major program milestone, the new satellites went through a rigorous testing and validation process that demonstrated that they met all performance requirements and even exceeded many. The Iridium NEXT satellites are already providing superior call quality and faster data speeds with increased capacity to Iridium customers. In addition, the Company has announced the targeted launch date for the second payload of ten Iridium NEXT satellites as June 29, 2017, at 1:02pm PDT, with an instantaneous launch window. 39)
- The testing and validation process for the Iridium NEXT satellite constellation involved a thorough test of each of Iridium's services, an assessment of each satellite's performance against established metrics, and a formal acceptance process between Iridium and Thales, thus ensuring a smooth integration into Iridium's existing network architecture. Once completed for each new satellite, a precisely orchestrated process of replacing the original Iridium® satellite with a new Iridium NEXT satellite, known as a ‘slot swap' is completed. To date, the team at Iridium's SNOC (Satellite Network Operations Center) has successfully completed three individual slot swaps, and two dual slot swaps. Two of the new satellites are currently drifting to their assigned orbital plane.
- "To say that I am proud of the Iridium satellite network operations team is an understatement," said Scott Smith, chief operating officer at Iridium. "Conducting multiple slot swaps to replace a network of this magnitude is an incredible task, and only Iridium has the team and technical capacity to manage this project. We have been preparing for this process for years, and since first launch the team has worked non-stop to manage each maneuver to successfully integrate the new satellites into the active network. We are thrilled to say that these new satellites are exceeding expectations and are already delivering faster speeds to our customers."
• April 28, 2017: Eight of Iridium's first ten upgraded communications satellites launched in January started providing voice and data relay service ahead of schedule, and SpaceX says it can launch up to 40 more Iridium spacecraft by the end of the year, Iridium officials reported on 28 April. "I'm happy to report that our initial batch of Iridium Next satellites are now fully operational and working very well," said Matt Desch, CEO of Virginia-based of Iridium Communications. 40) 41)
- Engineers are repositioning the other two new-generation Iridium spacecraft in orbit to replace other satellites, part of a "highly-choreographed process" to complete a refresh of the company's entire constellation by mid-2018, Desch said Thursday in a quarterly earnings call with investment analysts.
- The first eight Iridium Next satellites entered service in March and early April, taking the place of aging first-generation spacecraft launched in the late 1990s.
- After their deployment from the second stage of a SpaceX Falcon 9 rocket launched from Vandenberg Air Force Base in California, the satellites boosted their altitude from a 625 km drop-off orbit into the operational constellation at an altitude of 780 km alongside the craft they were intended to replace. - Ground controllers then instantaneously switched off the inter-satellite communications links on the old satellite and turned on the links on the new craft, a procedure Iridium calls a slot swap.
- The Iridium fleet consists of 66 operational satellites distributed in six orbital tracks, with 11 slots in each plane. The remaining two Iridium Next satellites, deployed into Plane 6 on Jan. 14, are drifting into a different plane, a movement that will take around 10 months.
- "We completed the commissioning of these Iridium Next satellites about one week ahead of schedule, which is a real testament to the planning and preparation of our satellite operations team," Desch said. "What's important is that our experience with in-orbit testing, slot swaps and the new satellite performance gives us confidence that we'll be able to manage the roughly 60-day launch cycle (we're) targeting following the second launch."
- Iridium's next 10 satellites are set for launch June 29 aboard another Falcon-9 booster. Desch said the spacecraft will begin shipping from their factory in Gilbert, Arizona, to the Vandenberg launch base in mid-May for fueling and attachment with the rocket's multi-payload dispenser, which accommodates the 10 satellites inside the Falcon-9 nose cone.
- The Iridium Next assembly line in Arizona, managed by Orbital ATK in partnership with satellite-designer Thales Alenia Space, is producing spacecraft at a rate to manufacture all of the Iridium Next satellites by the end of 2017, Desch said.
- Iridium originally planned to launch 70 of the Iridium Next satellites on seven Falcon-9 rockets by the end of 2017, but SpaceX launch delays caused by rocket failures and production bottlenecks have pushed that target to mid-2018.
• February 23, 2017: Since the first 10 Iridium NEXT satellites were successfully launched and deployed on January 14th, they have undergone a series of rigorous testing and validation in preparation for their insertion into the network. Today Iridium announced the first satellite, space vehicle (SV) 106, is now active in the network, carrying live voice and data communications within our global network. 42)
• February 15, 2017: Iridium Communications Inc. announced it has received a targeted launch date of mid-June 2017 for the second mission of 10 Iridium NEXT satellites. Originally anticipated for mid-April of 2017, the date has shifted due to a backlog in SpaceX's launch manifest as a result of last year's September 1, 2016 anomaly. This second launch will deliver another ten Iridium NEXT satellites to LEO on a SpaceX Falcon-9 rocket. SpaceX is targeting six subsequent Iridium NEXT launches approximately every two months thereafter. 43)
- "After such a successful first launch, we are eager to maintain the momentum until our network is completed," said Matt Desch, chief executive officer at Iridium. "Even with this eight week shift, SpaceX's targeted schedule completes our constellation in mid-2018."
- This announcement comes as Iridium has successfully connected the first Iridium NEXT satellite via its crosslinks into its global LEO constellation. The new satellite is expected to begin providing service to Iridium customers in the coming days. This marks a major milestone for the Iridium NEXT program as the testing and validation phase is ahead of schedule and the satellites are working well.
- "Our team at our Satellite Network Operations Center has been working around-the-clock to confirm the health and performance of these new satellites," said Scott Smith, chief operating officer at Iridium. "Since their perfect orbit injection and deployment by SpaceX, our satellite testing process has progressed ahead of schedule, a testament to the rigorous development program they've undergone on the ground."
- The upcoming mid-June launch will mark the second mission of eight Iridium NEXT launches with SpaceX, including the recently announced satellite rideshare with NASA and GFZ's (Potsdam, Germany) GRACE-FO (Gravity Recovery and Climate Experiment Follow-on) mission. In total, Iridium currently has plans to launch 75 Iridium NEXT satellites — 66 to serve as operational satellites and nine as on-orbit spares.
• January 18, 2017: On the heels of a successful launch of the first ten Iridium NEXT satellites on Saturday, January 14th, Aireon announced today that it has signed a data services agreement with Isavia, the Icelandic Air Navigation Service Provider (ANSP). Isavia will deploy Aireon's spaceborne ADS-B (Automatic Dependent Surveillance-Broadcast) service throughout the Reykjavik Oceanic Control Area (OCA). In addition to providing enhanced redundancy to existing terrestrial surveillance resources in the southern part of the airspace, the AireonSM service will, for the first time ever, provide real-time surveillance and tracking in the region extending from 70º north to the North Pole. 44)
- With control of more than 5.4 million square kilometers of airspace, Isavia is looking to improve safety, and efficiency (through reduced separation) of operations by expanding the ADS-B service area. Continuity of service will be enhanced through use of Aireon's technology in airspace where line-of-sight surveillance is already.
• January 19, 2017: SpaceX was able to celebrate a successful return to flight this week with a picture-perfect launch of the Falcon-9 rocket on January 14, 2017 that successfully delivered a fleet of ten advanced Iridium NEXT mobile voice and data relay satellites to orbit. But the icing on the cake was the dead-center landing and recovery of the Falcon-9 booster on their drone barge in the Pacific Ocean, off the west coast of California. 45) 46)
Figure 8: A stunning view of the Falcon-9 rocket just before landing on a barge in the Pacific Ocean, on January 14, 2017 following the launch of 10 Iridium NEXT satellites into orbit (image credit: SpaceX)
Hosted Payload Missions:
In 2008, GEO (Group on Earth Observations) — an international intergovernmental initiative with the goal of furthering the creation of a comprehensive, coordinated, and sustained Earth observing system or systems — concluded that four missions stand out as prime candidates for flying on the Iridium NEXT platforms which would also be of benefit for climate observation. These are altimetry, broadband radiometry (Earth's radiation budget), multispectral imaging (ocean and land) and GPS radio occultation. 47) 48) 49) 50)
There are several additional missions which could provide additional climate/weather observations of interest to various groups. The consensus was that a constellation approach to sensing, using the real-time communications backbone of Iridium, will enable unprecedented geospatial and temporal sampling, with a move from R&D-driven space programs to operational monitoring of the effects of global climate change. 51)
Figure 9: Timeline of the Iridium NEXT hosted payloads (image credit: Iridium Satellite, Ref. 50)
• Earth observation, atmosphere, and climate 52)
- GPSRO (GPS Radio Occultation). One or two instruments can be hosted in each plane (with GPS, GLONASS and Galileo tracking capability) 53)
- Ocean color
- Forest fire
- Earth radiation budget
- Ozone profile monitoring
- Solar irradiance
• Space weather and space situation awareness
• AMPERE for monitoring of the magnetosphere
• Low light imaging and cloud observations
• SensorPOD – small payloads 1-5 kg class in a 3U Cube volume, hosted on NEXT providing significantly more capabilities and longer mission life at low cost
• Aircraft monitoring –ADS-B receiver for next generation ATC/ATM
• AIS for maritime monitoring
On March 27-30, 2011, a GEOScan Planning Workshop was held in Annapolis, MD, USA. The dual theme concept of GEOScan involves System Science (SS) sensors on all 66 Iridium NEXT satellites as well as Hosted Sensor (HS) suites that can accommodate unique payloads in a standard, 14 cm x 20 cm x 20 cm [5.6 U] SensorPOD.
Each Iridium NEXT satellite has a total hosted payload allocation of 50 kg in mass, 30 cm x 40 cm x 70 cm in volume, and 50 W of average power. GEOScan is designed to fit into a hosted payload module, which has been allocated 5 kg in mass, 14 cm x 20 cm x 20 cm in volume, and 5 W of average power. In addition to these resources, the Iridium satellite design provides for an unimpeded 75° half-angle nadir FOV (Field of View), nadir pointing control to within 0.35° (pointing knowledge within 0.05°), spacecraft altitude control within 10 m, and spacecraft position control within 15 km (position knowledge within 2.2 km). 54)
Table 5: Iridium NEXT hosted payload specifications and resource allocation for GEOScan
Figure 10: Allocation of the hosted payloads on the Iridium NEXT spacecraft (image credit: Iridium)
GEOScan (GEOscience Facility from Space) - a sensor suite of hosted payloads
GEOScan is a grassroots effort, envisioned as a National Science Foundation (NSF) globally networked orbiting observation facility utilizing the Iridium NEXT satellites, that will create a revolutionary new capability of massively dense, global geoscience observations. GEOScan capitalizes on the once-in-a-generation opportunity presented by Iridium with a facility that will benefit both society and a broad cross section of the scientific community through dramatic advancements in Earth and Space science. 55) 56)
GEOScan, proposed as a globally networked orbiting facility utilizing Iridium NEXT's 66-satellite constellation, will provide revolutionary, massively dense global geoscience observations and targets questions scientists have not been able to answer, and will not answer, until simultaneous global measurements are made. GEOScan dramatically lowers the logistical and cost barriers for transmitting "big data" from 66 satellites by using Iridium's communications platform and COTS (Commercial-Off-The-Shelf )components. 57) 58) 59)
Background: A consortium led by researchers at JHU/APL ( Johns Hopkins University / Applied Physics Laboratory) is proposing a geoscience program that would give scientists the first continuous real-time look at the Earth's surface and atmosphere through a global network of sensors. GEOScan includes a "Hosted Sensor" program that provides an opportunity for university researchers and students, as well as small businesses, to address novel science topics and test new instruments and technologies in space at a low-cost. 60)
More than 100 volunteer scientists and engineers are working to implement the GEOScan program through a proposal to NSF. This committee, led by JHU/APL, is made up of scientific experts from a variety of geoscience disciplines including space, atmosphere, oceans and Earth science.
Four primary factors make this an unprecedented opportunity for geoscience discovery, while holding the potential to affect a paradigm shift in the way we conduct science from space: 61)
1) Truly global coverage provided by the constellation.
2) Massively dense-space-based measurements enable revolutionary new techniques such as tomographic imaging.
3) Because Iridium Inc. is a telecommunications company, the logistical and cost barrier of transmitting massive amounts of data from 66+ satellites is REMOVED.
4) Because the project plans to build nearly 70 2.5U GEOScan pods, advantage can be taken of the cost savings of scale for science from space instead of the highly costly "one of a kind" methods of the past.
Table 6: Key GEOScan advantages (Ref. 61)
Geoscience is at the dawn of a new era. Scientists are realizing that future discovery and understanding in geoscience research will rely on viewing the Earth as a complete and interactive system, rather than as a series of isolated observations of natural phenomena. There is growing scientific opinion that many of the open geoscience questions cannot be answered without global and continuous coverage of key measurements.
GEOScan science objectives: GEOScan will enable the next generation of discovery with the first globally networked orbital observation facility. GEOScan will:
• Measure Earth's outgoing radiation budget on a global scale with the temporal and spatial resolution necessary for studying the causal relationship between the Earth's infrared radiation and fast-evolving phenomena like clouds, dust storms and volcanic eruptions, as well as their effect on long term climate trends.
• Measure global mass flux variations at temporal and spatial resolutions that relate the flow of water mass in the oceans and atmosphere to secular trends in the global water cycle, cryosphere and climate.
• Image the Earth's radiation belt and plasma environment with an unprecedented temporal and spatial resolution that provides the details of the governing physical processes for large-scale global reconfigurations that drive space weather events and resultant societal effects.
Iridium's Hosted Payload Program facilitates the effort, but it could be executed using any small-sat constellation. Each GEOScan sensor suite consists of 6 instruments:
1) a Radiometer, to measure Earth's total outgoing radiation
2) a GPS Compact Total Electron Content Sensor, to image Earth's plasma environment and gravity field;
3) a MicroCam Multispectral Imager, to provide the first uniform, instantaneous image of Earth and measure global cloud cover, vegetation, land use, and bright aurora
4) a Radiation Belt Mapping System (dosimeter), to measure energetic electron and proton distributions
5) a Compact Earth Observing Spectrometer, to measure aerosol-atmospheric composition and vegetation
6) MEMS Accelerometers, to deduce non-conservative forces aiding gravity and neutral drag studies.
The GEOScan system sensor suite is comprised of 6 instruments packaged to take advantage of the Iridium NEXT hosted payload allocation. This suite of instruments is designed to be batch manufactured to meet the cost and schedule constraints of the Iridium NEXT launch schedule and reduce costs through volume procurement, manufacture, integration, and test. The conceptual packaging of the suite of sensors is shown in Figure 11.
Figure 11: Illustration of the GEOScan sensor suite (image credit: GEOScan consortium)
Legend to Figure 11: GEOScan's payload design uses a modular configuration for efficient assembly and testing. It also includes additional mass, power, data, and volume allocation for sensors proposed by scientific and government stakeholders.
CTECS (Compact Total Electron Content Sensors):
CTECS are GPS instruments that utilize a COTS receiver, modified firmware, a custom-designed antenna, and front-end filtering electronics. In a 24 hr period, a single GPS occultation sensor can provide several hundred occultations or total electron content (TEC) measurements distributed around the globe. Even with this number of occultations, latitude and longitude sectors still remain that are undersampled at any given instant because of the geometry of the GPS constellation.
GEOScan's 66 CTECS will provide an unprecedented continuous global snapshot of Earth's ionosphere and plasmasphere. The data will allow us for the first time to see the temporal and spatial evolution of the ionosphere/plasmasphere from 80-20,000 km with a 5 minute temporal resolution and 10 km height resolution with a measurement error < 3 TECU (Total Electron Content Unit) globally.
Furthermore, the gravity field will be derived using the satellites' trajectories determined from the onboard CTECS GPS receivers, as well as from ancillary data from the MEMS accelerometers and Iridium star cameras. In short, the positions and velocities determined from the CTECS receiver can be differentiated to reveal the accelerations caused by the various dynamic (mass transport) processes that occur at the surface and in the atmosphere. By accurately tracking the orbit of each Iridium NEXT satellite and removing non-gravitational influences, the project can infer changes in Earth's gravity field and learn about the processes that create these changes (e.g., large-scale water mass movement). Global diurnal water motion maps at 1000 km resolution, accurate to 15 mm of equivalent water height can be created on sub-weekly time scales with a time-integrated monthly resolution that matches the GRACE (Gravity Recovery and Climate Experiment) satellites.
Instrument: The CTECS sensor is a GPS receiver that has been designed to specifically make TEC (Total Electron Content), electron density altitude profiles, and ionospheric scintillation measurements. The CTECS sensor tracks the GPS L1 and L2 signals as they are occulted by the Earth. CTECS consists of a custom designed antenna, LNA (Low Noise Amplifier), and the NovAtel OEMV-2 GPS receiver.
Table 7: CTECS specifications for GEOScan
The CTECS data downlink budget is customizable to the limitations of the spacecraft telemetry and is based on conservative estimates (e.g. scintillation occurs only at night but the calculation uses the mode at all times).
Note: The PSSCT-2 (Pico Satellite Solar Cell Testbed -2) nanosatellite served as a low-cost risk reduction for the upcoming SMC SENSE (Space Environmental Monitoring Nanosat Experiment) because it contained the Aerospace Corporation's CTECS (Compact Total Electron Content Sensor ) that characterizes the ionosphere by measurement of the occultation of GPS signals - a precursor of an instrument with the same function on SENSE. The PSSCT-2 nanosatellite of The Aerospace Corporation was deployed from the Space Shuttle flight STS-135 on July 20, 2011 (reentry on Dec. 8, 2011). After early orbit checkout, CTECS began normal operations mid August 2011. 62)
GEOScan will measure Earth's outgoing radiation simultaneously and globally with a constellation of heritage-driven, two-channel radiometers carried by the Iridium NEXT commercial constellation of satellites. This constellation, each with a 127º field-of-view radiometer, will provide a global view of the Earth's TOR (Total Out-going Radiation) every 2 hours with better than 0.15% accuracy. The shortwave channel (0.2-5 µm) and total channel (0.2-200 µm) along with the longwave (determined form differencing the two channels) is calibrated to a precision of 0.09 Wm-2 with an accuracy of 0.3 Wm-2 using a NIST (National Institute of Standards and Technology) traceable calibration standard.
The GEOScan radiometer design draws direct heritage from the NISTAR instrument (TRL8) aboard DSCOVR (Deep Space Climate Observatory - aka Triana). NISTAR (National Institute of Standards and Technology Advanced Radiometer) is a high sensitivity, cavity-based radiometer, designed to measure the solar reflected and long-wave thermal emission from the full disk of the Earth as viewed from L1 (Lagrange point located on the Sun-Earth line 1.6 x 106 km from the Earth). The materials and construction techniques of the cavity detectors for GEOScan are based on those of the NISTAR detectors (TRL8).
Table 8: Radiometer design specifications for the GEOScan mission
Figure 12: Illustration of the radiometer (image credit: JHU/APL, Ref. 59)
CEOS (Compact Earth Observing Spectrometer):
CEOS can provide spectrally resolved information on the outgoing shortwave radiation from the Earth's surface and atmosphere, which is critical fo calibrating climate models. CEOS can also determine the concentration of various aerosols and their effect on radiative transfer. As such, it will play an important role in achieving GEOScan's goal of collecting high-quality data regarding the ERB (Earth's Radiation Budget).
Aerosols represent an area of uncertainty within the climate modeling community. The IPCC (Intergovernmental Panel on Climate Change), in their 2009 report declared aerosols to be "the dominant uncertainty in radiative forcing." Aerosols have direct effects on ERB, affecting atmospheric absorption, transmittance, and scattering of incoming and outgoing radiation. They also have indirect effects on ERB, as they act as condensation nuclei and affect cloud formation.
CEOS consists of an exceptionally small crossed Czerny-Turner spectrometer, a linear CCD array, and read-out electronics. Its modular design allows for easy substitution of optical elements, electronics, and optical sensors to rapidly and confidently customize the optical performance to meet a wide range of science goals. This design provides spectral measurements from 200 to 2000 nm with approximately 1 nm spectral resolution from 200 - 1000 nm and 3 nm from 1000 - 2000 nm. The foreoptics design provides a 1º FOV, which allows 14 km resolution.
CEOS has flight heritage on the O/OREOS CubeSat mission (launch Nov. 20, 2010) of NASA/ARC as part of the SEVO (Space Environment Viability of Organics) experiment, where it has been operating successfully on orbit so far. CEOS also shares heritage with the spectrometers on LCROSS and LADEE, two lunar science missions.
Figure 13: Photo of the CEOS spectrometer on the O/OREOS CubeSat (image credit: NASA/ARC)
MMI (Multispectral MicroCam Imager):
MMI is designed to provide multispectral images on both regional and global scales. The MMI provides multispectral imagery in the same footprint within a time of 30 s, each with a spatial resolution of ~450 m at nadir. The spacing of the satellites in the constellation (11 satellites per orbital plane), and the fact that one MMI is placed on every satellite, will allow complete multispectral global imagery to be acquired every 2 hours.
GEOScan's MMI is a visible to near-infrared WFOV (Wide-Field of View) imager that uses a STAR-1000 CMOS imaging 1024 x 1024 array detector. MMI will use custom-designed strip filters oriented in the across-track direction. This will allow the imager to be used in a pushbroom mode. The attitude of the Iridium NEXT constellation will be carefully controlled because each of the satellites has cross-linked communication receivers and transmitters.
MMI uses refractive optics and will have a FOV of 33º x 33º to provide global coverage over a 2 h time interval. Each FOV footprint on the surface of the Earth is 465 km x 465 km. Images will be acquired every 29 s to provide continuous imaging in the along-track direction of the satellite. The trailing satellite in a given orbital plane lags the leading satellite by ~9 minutes. In this time interval, the relative drift in longitude between a spot on the Earth and Iridium is 250 km.
MMI requires a single 5 V power supply drawing 0.11 amp (0.55 W). This is lower power than typical cameras of this type. The MMI receives commands and transmits telemetry across an LVDS serial interface, which is commonly used between instruments and spacecraft. An Actel FPGA drives the detector control signals based on the command inputs, accepts detector image data and converts it to serial form to transmit. The FPGA is also capable of performing automatic exposure control, FAST compression or other simple algorithms. The camera produces a 1024 x 1024 pixel image with 10 bit pixels at one frame per second.
Figure 14: MicroCam with C-mount commercial optics (image credit: JHU/APL)
Dosimeter-based RBMS (Radiation Belt Mapping System):
GEOScan's dosimeter payload will image radiation belt dynamics, including relativistic electron micro-bursts, global loss to the atmosphere, and variations in geomagnetic cutoffs of solar energetic particles. Each GEOScan payload will contain one pair of Teledyne micro dosimeters; one is an electron dosimeter with a 100 keV electronic threshold for registering a count, and the other is a proton dosimeter with a 3 MeV electronic threshold. A common thickness of shielding covers both dosimeters. Five unique lid-shielding choices will enable aggregating over multiple vehicles to obtain a dose-depth curve and electron and proton spectra. Shielding will be chosen to provide electron energy resolution from 0.3 to 5 MeV and proton resolution from 10 to 50 MeV. The dosimeter has more than sufficient dynamic range to measure the dose rate due to galactic cosmic rays at the geomagnetic equator for the most intense solar particle events and deep within the inner radiation belt.
Table 9: Teledyne UDOS001-K chip Dosimeter parameters
MASS (MEMS Accelerometer for Space Science):
MASS is a micromechanical, silicon-based accelerometer with unprecedented sensitivity compared to current accelerometers of similar size and power that can be used for Earth science applications. Current spaceborne accelerometers on GRACE and GOCE (Gravity field and steady-state Ocean Circulation Explorer) require more power (tens of watts) and mass (+50 kg) than can be accommodated within the GEOScan payload allocation. The GEOScan approach utilizes a constellation of low-noise MEMS accelerometers, which would assist in aggregately measuring the variations in Earth's gravitational field as well as satellite drag for neutral density studies. Current commercial MEMS devices have demonstrated sensitivities in the 10 ng/√Hz range, with potential for 1 ng/√Hz — clearly suitable to compensate for the non-gravitational forces of 10-7 to 10-8 m/s2. The performance of this class of MEMS accelerometers has shown a consistent white noise floor on the order of 10-11 g2/Hz, making the device ideal for gravimetric measurements.
The GEOScan facility allows and encourages community users to propose for customized data acquisition from the facility system sensors. This is in addition to community user open access to standard system sensor data products through the NSF-JHU/APL Data Centers. Community users can customize data collection by acquisition date range and locations, measurement time and frequency, and parameters specific to the system sensors, such as integration time and compression for the optical imager, or a higher repeat rate measurement of certain bands by the spectrometer. GEOScan provides the ability for community users to tailor system sensor data to their research goals using measurements from anywhere on Earth taken at any time.
The data storage, processing, and downlinking process for GEOScan allows for continuous data collection from all instruments with less than 4 hours delay on data retrieval. A 2 GB SSR (Solid State Recorder) will provide ample data storage for a day's worth of raw, compressed, and engineering data. Studies are being performed to support data storage options which cover one day up to a week. Currently, there is a 64.7% margin on data retrieval, and 20% margin on all SSR sizing calculations. All of this analysis requires that the PI hosted payload produce no more than 20 kbit/s of raw data that can be compressed into a 2 kbit/s data stream.
Furthermore, the project notes that in order to create a cyber infrastructure for the geosciences that enables transformative research and new understanding of the entire system, an architecture must be created that relies on synergy between measurement, data system, and user. To facilitate this approach, a broad effort requiring community input, scalable data management and web-based tools must be implemented. APL has been actively involved in meeting the future challenges of the geosciences by developing flexible, scalable, platform independent data management architectures for ingesting, processing, and serving out higher level data products to the community for the various NSF and internal programs that are actively managed, including: AMPERE, SuperDARN, SuperMAG, and GAIA.
A goal of existing programs is to create tools that reduce cost and save user/provider time through common interfaces and flexible applications, which have been instrumental in producing synergistic discovery.
Constellation system science:
GEOScan employs a full constellation approach to answer outstanding system science questions about the Earth and remote sensing of space environment state variables. Equipping the full constellation provides homogeneity of observation, thus simplifying analyses and reducing error in inherently global calculations. This suitably dense, homogeneous network enables the use of modern reconstruction techniques to image state variables and persistent measurement of global change across a wide range of temporal and spatial scales.
GEOScan climate science-measuring Earth's energy balance:
GEOScan addresses Earth's current state of energy balance and climate change via a homogeneous constellation of satellites observing the Earth 24/7 with hourly temporal resolution and spatial resolution ranging from 500 km for the broadband radiometer to 450 m for the imager. This revolutionary coverage will enable discoveries concerning many open science questions critical to our ecosystems and our habitability — notably how highly spatially and temporally variable phenomena aggregate to contribute to global change, and how global long-term changes affect smaller scales and surface processes where human beings live and work.
GEOScan's most central climate instruments are extremely well calibrated radiometers, which will measure, for the first time, the ERI (Earth Radiation Imbalance). ERI is the difference between incoming radiation from the Sun and the TOR. TOR is the sum of reflected solar radiation and emitted longwave radiation. How ERI and TOR change regionally and globally, and on timescales from hourly to annually, is critical for understanding climate change.
According to climate models, current climate change, including the dramatic melting of Arctic sea ice and Greenland glaciers, results from an ~0.1–0.2% imbalance between incoming solar energy and TOR. Currently, space instruments measure incoming solar radiation to >0.03%. However, TOR has never been simultaneously, globally sampled, and is accurate to no better than 1% — not good enough to resolve the imbalance predicted by climate models. GEOScan's global coverage of highly calibrated radiometers (0.3 Wm–2) will measure TOR at the necessary 0.1% accuracy level.
GEOScan's time-variable gravity measurements focus on the large-scale, high-frequency spectrum of the gravity field that GRACE and other dedicated gravity field missions inherently cannot observe. These other missions cannot observe the high-frequency variations solely because of the limited sampling possible resulting from single satellite ground track (or satellite pair in the case of GRACE) measurements. The error caused by under sampling (independent of measurement accuracy) dominates any gravity solution at the daily to weekly timescales for a small number of satellites. This highlights the fact that with only one satellite pair, higher spatial resolution compromises temporal resolution and vice versa; the only way to improve both is to dramatically increase the number of satellites involved. GEOScan, with its 66 satellite constellation approach, addresses this short-coming in traditional gravity science investigations. The GPS measurements will track the orbits of the satellites to an accuracy of 2-3 cm, which, along with the data from the MEMS accelerometers, makes it possible to recover large-scale (>1000 km) gravity variations, which result mainly from the large scale movement of water mass.
Transformational space weather nowcasting and forecasting with the GEOScan constellation:
Significant progress has been made in the study of the Earth's geospace environment over the last few decades. We have a firmly established understanding of the system dynamics on a climatological basis along with a basic understanding of the universal physics of smallscale processes of waves, instabilities, magnetic reconnection, and ENAs (Energetic Neutral Atoms). Yet accurate nowcast, much less forecast, of the details of individual space weather events remains elusive. We lack an understanding of the fundamental global properties of our system, such as determining what is the total energy input into the thermosphere, whether Hall or Pederson currents are primarily responsible for auroral current closure, and which mechanisms dominate radiation belt losses and their longitudinal extent.
Nowcasting and forecasting the global electron density field for space weather applications are difficult research operational challenges that have not yet been met. Operational requirements for electron density [Air Force, IORD-II (Integrated Operational Requirements Document-II)] include profiles of electron density from ~80 – 1500 km altitude, with ~ 5 km vertical resolution, and ~ 50-100 km horizontal resolution with errors in electron density < 10%. That is a global 3D electron density field from 80-1500 km altitude with 5 km vertical resolution and 50-100 km horizontal resolution. First principle models cannot achieve such resolutions and accuracy. Data assimilative models can achieve all the above requirements, but only with sufficient amounts of data.
In order to meet such stringent requirements over the entire globe, all the time, it is clearly necessary to have continuous global data coverage. This data coverage must be sufficient to sample the entire ionospheric profile with the required vertical resolution, and have the necessary horizontal resolutions. No existing data set, nor even combination of existing data sets, can meet this requirement. Thus, while in principle we have the theoretical understanding and numerical tools in place to provide required global nowcasts and forecasts of electron density, we do not have the necessary observational data. In addition to ionospheric nowcasting, there is a need for imaging the plasmasphere on a global, temporally updating scale. Plasmaspheric imaging is important since plasmaspheric densities impact the physics of the radiation belts. Plasmaspheric imaging to 20,000 km combined with radiation belt mapping of energetic electrons and protons will allow us to understand which loss processes dominate at different temporal and spatial scales. However, up until now there are almost no available direct measurements of plasmaspheric density.
GEOScan provides a transformative capability by providing the global data coverage necessary for the aforementioned investigations. GEOScan radio occultations will sample the ionosphere from 80 km altitude to the IRIDIUM satellite altitude of 780 km, Topside TEC observations provide information from the satellite altitude to the altitude of the GPS constellation (~ 20,000 km). Each GEOScan satellite will continuously monitor 10-15 topside TEC measurements to different GPS satellites, providing an almost overwhelming amount of topside and plasmaspheric data that can be used in tomographic imaging algorithms to obtain accurate, time evolving images of plasmaspheric density. For the radio occultations, each GPS receiver sees ~ 3 occultations at a time. Each occultation lasts ~ 1 minute. Over a 5 minute period a total of 66 x 3 x 5 = 990 occultations / 5 minute period are observed. While this data alone only provides ~ 600 km horizontal resolution, when combined with the copious amounts of ground GPS TEC data available (currently > 4000 sites and growing), we can easily achieve the required horizontal resolutions necessary to meet Air Force IORD-II requirements. A beautiful aspect of this constellation design is global continuous data that can be streamed to ground systems in near real-time. This allows, for the first time, global high-resolution, high accuracy nowcasts of electron density to be provided continuously in time. This is accomplished using global tomographic or data assimilation imaging methods such as IDA4D (Ionospheric Data Assimilation Four Dimensional. When combined with first principle models, where the global density field is used to reinitialize the model, it becomes possible to provide accurate forecasts that are only limited by the accuracy of the forward model.
GEOScan gratity imaging:
The time-variable gravity products created from GEOScan seek to provide new insights into the large-scale (>1000 km), short-term (< 1month) mass transport processes governing the global water cycle. Any process that involves the transport of water, such as the melting of glaciers in the cryosphere, changes in continental hydrology (e.g., groundwater), or other processes in the oceans and atmosphere, creates a change in Earth's gravity field. By precisely measuring the variations of Earth's gravity over time, the project can exploit this link and understand more about the behavior of these processes.
How the time-variable gravity field can be measured by GEOScan's sensor suite is relatively straightforward, and is driven by the fact that changes in Earth's gravity field, however small, will alter the trajectory of an orbiting satellite. Using the CTECS GPS receiver, the absolute position of each Iridium NEXT satellite will be precisely determined, down to the cm level. These positions can then be differentiated to create a time series of satellite accelerations that represent both gravitational and non-gravitational forces. Those accelerations caused by non-gravitational forces, such as atmospheric drag and solar radiation pressure will be accounted for by the information provided by the onboard MEMS accelerometers, leaving as a final product only those accelerations due to Earth's gravity.
The GRACE mission was the first to highlight the value of time-variable gravity data; however, despite its tremendous success, GRACE suffers from the measurement sampling limitations related to having only a single satellite pair. Since gravity observations are essentially point measurements, the spatial and temporal coverage of a single satellite will never permit the observation of high-frequency events, and this is why the temporal resolution for GRACE is approximately one month. While GEOScan will not be able to match the spatial resolution of GRACE, the time variable data collected from the full constellation of Iridium NEXT satellites will allow the monitoring of large-scale processes at the Earth's surface at time scales as short as one day. Global gravity data at this temporal resolution has never been collected before, and should be especially valuable to the ocean and atmosphere communities. Figure 15 demonstrates the potential quality of the GEOScan gravity products (bottom panel) from a single day's worth of measurements, compared to the full high-resolution signal (top panel) over the same timeframe, as derived from a recent coupled Earth system model. As can be seen, a number of terrestrial and oceanic/atmospheric mass transport processes are clearly observed, with the spatial resolution corresponding to approximately 1000 km.
Figure 15: Illustration of the daily resolution expected from the GEOScan gravity products (bottom panel), as derived from a high-resolution coupled Earth system model (top panel). Units are in equivalent water height (image credit: GEOScan consortium).
Figure 16: Iridium NEXT mission timeline (image credit: JHU/APL, Ref. 59)
GEOScan's development timeline is mated to Iridium NEXT's development and launch schedule.
Figure 17: Iridium's global coverage (image credit: Iridium/NASA)
Hosted payloads of other customers on Iridium NEXT
ADS-B (Automatic Dependent Surveillance - Broadcast):
Satellite operator Iridium, through its new joint venture Aireon LLC, will be putting ADS-B (Automatic Dependent Surveillance-Broadcast) receivers on its next-generation satellite constellation as hosted payloads, aimed at bringing global, real-time aircraft surveillance for ANSP (Air Navigation Service Providers).
In June 2012, NAV CANADA and Iridium signed a contract for a joint venture to be run under the company Aireon LLC (McLean, VA, USA) with support from the U.S. FAA (Federal Aviation Administration) and suppliers Harris Corporation and ITT Exelis. The objective of Aireon is to take advantage of Iridium's hosted payload services using ADS-B receivers and to deliver a surveillance capability to ANSPs (Air Navigation Service Providers) around the world and their commercial airline customers. 63) 64) 65) 66) 67)
ADS-B is a next generation commercial surveillance technology that supports radar-like separation standards. The system brings significant safety and efficiency benefits, offering properly-equipped and certified aircraft more flexible, fuel-saving routes through airspace previously managed using only procedural air traffic control. Aircraft with ADS-B automatically transmit accurate position reports with integrity every second to ATC (Air Traffic Control). As a result, ADS-B will reduce separation minima for equipped aircraft and allow more aircraft to follow the most efficient flight trajectory.
NAV CANADA corporation owns and operates Canada's civil ANS (Air Navigation Service), providing for the safe and efficient movement of aircraft in Canadian domestic airspace and international airspace assigned to Canadian control. Through its coast-to-coast operations, NAV CANADA provides air traffic control, flight information, weather briefings, aeronautical information, airport advisory services, and electronic aids to navigation. NAV CANADA is the second largest air navigation service in the world by traffic volume and provides air traffic management for 1,200 flights per day, the busiest oceanic airspace in the world. -NAV CANADA will be Aireon's first customer to deploy the new satelliteborne surveillance capability in its North Atlantic airspace operations most of which is without surveillance at the moment.
In November 2012, Iridium Communications Inc. announced that it has finalized an agreement with NAV CANADA regarding Aireon LLC, a joint venture that will allow air traffic management agencies around the globe to continuously track aircraft anywhere in the world. For the first time ever, ANSPs (Air Navigation Service Providers) around the world will be able to track aircraft from pole-to-pole, including oceanic airspace and remote regions. The new capability will provide significant benefits to the aviation industry, including substantial fuel savings, a reduction in greenhouse gas emissions and enhanced safety and efficiency for passengers. 68) 69)
The ADS-B receiver payloads, to be mounted on each Iridium NEXT satellite, will operate independently and perform the air traffic surveillance function separately from the main mission of the spacecraft. The power for the ADS-B payloads will come from the main satellite bus and will be designed to work with the other subsystems, such as thermal management or communications systems. By sharing Iridium's spaceborne capability and ground infrastructure, these commercially hosted payloads illustrate how to avoid the cost of building and launching separate satellites, thereby reducing the expense and time required to put mission capabilities into space for government and private organizations via a public-private partnership model, says a representative. 70) 71) 72)
The spaceborne ADS-B surveillance solution is set up as a joint venture between Iridium and NAV CANADA with support from the U.S. Federal Aviation Administration (FAA) and several other partners:
• Iridium will host the ADS-B receivers on its next-generation Iridium NEXT constellation.
• NAV CANADA is Aireon's first customer and an investor in Aireon. The venture will be operated under a PPP (Public Private Partnership) between industry and the world's major ANSPs.
• Harris Corporation is supplying 81 ADS-B payloads for the venture.
• ITT Exelis is providing systems engineering support.
Figure 18: The spaceborne ADS-B concept of operations (image credit: Aireon)
The Iridium architecture is unique in that all of the satellites are cross-linked, communicating with their neighboring satellites, allowing signals to be relayed from any point on the globe to a central ground location in Tempe, AZ (USA) in near real-time, with back-up locations in Alaska and Norway. The real time nature of relaying ADS-B surveillance data through the Iridium network is critical to achieving radar-like surveillance and reduced oceanic separation minima down to 15 NM (Nautical Miles) for aircraft equipped with appropriate communication and navigation avionics – enabling the full potential of benefits from such operations. No other existing or planned LEO-constellation has an equivalent capability. The Iridium architecture with built in redundancy and backup would provide a seamless experience to the Air Traffic Controllers when utilizing the Aireon surveillance capability. 73)
The Iridium NEXT LEO constellation is the world's largest with 66 operational satellites, plus six on orbit and nine ground spares, providing a level of redundancy and system availability that is unprecedented. The Iridium satellite design has significant built-in redundancy and high reliability. The planned ADS-B payload receivers will have even higher reliability requirements and the design will include the ability to make on-orbit software updates to adapt to future changes in ADS-B formats, if required. No other LEO constellation has a comparable global coverage, system availability, redundancy or flexibility.
The Aireon global space-based ADS-B surveillance system is being developed under a joint venture between Aireon and NAV CANADA and will be operational in 2017. This transformational new global surveillance system will offer far reaching capabilities and benefits to the global aviation community. The global aviation community would benefit by early interaction and participation in the development and deployment of this capability.
Background: In the timeframe 2010, ADS-B is a land-based system and deployed primarily in high air traffic areas such as North America, Australia and Europe. Vital airways over oceans, mountains, remote areas and polar regions remain largely uncovered.
In the ground-based ADS-B system concept, each aircraft broadcasts its own GPS position along with other information like heading, ground track, ground speed, altitude. Receivers on the ground then receive this information and send it to air traffic control displays. The ADS-B information can be used to augment existing primary and secondary (transponder-based) radar or used in lieu of those radar technologies. Aircraft that broadcast this information are considered to be equipped with ADS-B Out. ADS-B is all about communications between aircraft, and also between aircraft and ground. Both are vital in ensuring safe flights and efficiency in terms of fuel use, time and emissions. ADS-B is an integral part of the planned efficiency drive towards 2020. 74) 75)
Taking advantage of the latest technology, ADS-B is designed to be retrofit on aircraft flying today. In its final form, ADS-B is designed to ease ATC (Air Traffic Control) as the number of approaches grows, enhancing safety and increasing airport capacity. In the air, the information provided by ADS-B enhances the pilots' traffic awareness, allowing more optimal flight levels leading to fuel savings. ADS-B is designed in two parts:
• ADS-B OUT provides a means of automated aircraft parameter transmission be tween the aircraft and the ATC.
• ADS-B IN provides automated aircraft parameter transmission between aircraft themselves.
Ground-based systems primarily use radar to provide aircraft surveillance. As part of the global ATM modernization, ANSPs (Air Navigation Service Providers), such as the U.S. Federal Aviation Administration (FAA) and NAV CANADA, are implementing new ADS-B systems. On-board ADS-B transmitters broadcast GPS position and other useful data; yet, ADS-B networks are limited by ground-based ADS-B towers, which collect this data for the ANSPs. The ground-based ATM infrastructure cannot monitor flights over oceans or remote regions of the globe where placing an ADS-B tower is not feasible, adds the representative.
ADS-B mission status:
• May 3, 2017: Aireon announced that NAV CANADA has completed a successful flight test of spaceborne ADS-B (Automatic Dependent Surveillance-Broadcast) technology. The test was conducted to collect ADS-B data used for validating Aireon's satellite aircraft surveillance and tracking service. The NAV CANADA flight occurred on March 7, 2017 and utilized a specially equipped Bombardier aircraft with both top and bottom mounted 125 W ADS-B antennas. It was the first of two scheduled flight tests by the Canadian ANSP (Air Navigation Service Provider). Additional flight tests were done by the FAA (Federal Aviation Administration) and Polaris Flight Systems. 76)
- During the flight test, 6,935 ADS-B messages were received and decoded by a single Aireon payload, and after rigorous analysis, were found to exhibit comparable results to that of terrestrial ADS-B stations. Traveling through the Montreal, Winnipeg and Edmonton FIRs (Flight Information Regions), the flight test was a highly choreographed exercise requiring the aircraft to position itself in the correct airspace while the appropriate Iridium NEXT satellite carrying the Aireon ADS-B receiver was overhead.
- An additional flight test with the FAA took place on March 30, 2017, utilizing the FAA's specially equipped "flying laboratory" Bombardier jet with three Aireon payloads available to receive data. A total of 2,462 ADS-B messages were received and decoded while also exhibiting comparable results to that of terrestrial ADS-B stations. The FAA flight test took place in the Washington and New York FIRs.
- Aireon also conducted a flight test with Polaris Flight Systems, a private vendor, on March 20, 2017. The aircraft, a Beechcraft Bonanza, was outfitted with a top and bottom mounted 200 W ADS-B antenna and flew solely through the Albuquerque FIR, where more than 1,050 ADS-B messages were received from two Aireon payloads during the flight.
- "The flight tests coordinated with NAV CANADA, the FAA, and Polaris Flight Systems have been remarkable successes and further enable our team to thoroughly validate the capabilities of our system," said Vinny Capezzuto, chief technology officer and vice president, engineering at Aireon. "Through multiple flight information regions, with various levels of aircraft traffic, these tests were able to put our system through some challenging environments, and the data we've received is incredibly strong."
- "NAV CANADA is excited to play such an important role in helping to bring the next-generation of air traffic surveillance and aircraft tracking to the world," said Rudy Kellar, executive vice president, service delivery at NAV CANADA. "Aireon will fundamentally change the way the world flies, increasing safety, efficiency and reducing greenhouse gas emissions. The benefits will find their way right down to the individual traveler who will benefit from more predictable flight times and more efficient airport ground operations."
- Aireon's spaceborne ADS-B system will be operational in 2018, providing ANSPs with global air traffic surveillance and airlines with real-time flight tracking. The first ten Iridium NEXT satellites carrying the Aireon hosted-payloads were launched into low-Earth-orbit from Vandenberg Air Force Base on a SpaceX Falcon 9 rocket on January 14, 2017. Seven additional SpaceX launches are scheduled to take place over the next 12 to 15 months, including the second launch targeted for June of 2017. In total, the operational constellation will consist of 66 satellites, with an additional nine serving as on-orbit spares.
• March 2, 2017: Aireon announced today that they have formally received control from Iridium Communications Inc. of the first ADS-B (Automatic Dependent Surveillance-Broadcast) payload hosted on an Iridium NEXT satellite. This is a major milestone on the path towards 100 percent global air traffic surveillance. Aireon now begins a rigorous, in-depth testing and validation process, verifying the capability of the ADS-B payloads. 77)
- Known as an IPV (Initial Performance Verification), this process will last approximately two weeks before transitioning to a DPV (Detailed Performance Verification) that will focus more specifically on calibrating the payloads for optimal performance. Procedures for the IPV were under development for over a year with valuable insight provided by Iridium, Harris Corporation, NAV CANADA and the Federal Aviation Administration.
- "When we first turned on the payloads after they reached orbit, we received an unexpected surprise – aircraft were immediately being seen in real-time," said Aireon CEO, Don Thoma. "We've already seen commercial aircraft, general aviation aircraft and helicopters, in oceanic and remote airspace that have never before had real-time surveillance. The real fun for us now begins as we take control and push the performance to see just what spaceborne ADS-B can do."
- In late January, the first "power-on" for the AireonSM ADS-B payload was performed to validate launch survival and run a self-diagnostic systems check. During this systems check, Aireon did not expect to see any aircraft, however the payload antennas were active and 150 ADS-B aircraft were detected over multiple-passes with thousands of ADS-B messages received and decoded. Among some of the firsts for the Aireon system are:
a) The first officially received ADS-B message was Korean Airlines 530
b) The first full ADS-B position message decode was SAS 4576
c) The first U.S. carrier ADS-B message was UA 86 to Shanghai
d) The first aircraft detected landing at an airport was NextJet 594 in Sweden.
- "Detecting NextJet 594 was an added bonus," said Vincent Capezzuto, CTO for Aireon. "This is an early proof-point of the power of the Aireon ADS-B payload and its ability to detect aircraft close to the ground and in terminal airspace."
Global AIS (Automatic Identification System) Realtime Services provided by COM DEV and Harris Corporation
Harris Corporation and exactEarth Ltd., a subsidiary of COM DEV, have formed a strategic alliance to offer new advanced data services that will help track maritime vessels faster and more accurately than ever before. The AIS (Automatic Identification System) services will, for the first time, provide constant, realtime, global coverage — enabling customers to reliably track the location of vessels anywhere in the world. This helps improve efficiency, safety and security. 78)
The services take advantage of exactEarth's proven and patented signal de-collision detection technology and Harris' expertise in satellite hosted payloads, advanced radio frequency communications, and satellite antenna solutions. ExactEarth Ltd. is a majority-owned subsidiary of COM DEV International. The services are made possible by a sensor that is based on Harris' AppSTAR™ reconfigurable payload technology and hosted on the Iridium NEXT satellite constellation — which will have 66 satellites to greatly expand global maritime traffic coverage versus the eight satellites used today.
New AIS-based data products and services are expected to be available in 2018, once the Iridium NEXT satellites are on orbit. Harris becomes the exclusive provider to the U.S. government of AIS products and services produced under the alliance, including exactEarth's exactAIS product portfolio, while exactEarth serves all other global markets.
exactView RT (Real Time) powered by Harris will leverage the persistent global coverage and realtime connectivity of the Iridium NEXT constellation through the implementation of 58 hosted payloads covering the Maritime VHF frequency band. This new service will provide the user community with the fastest, most accurate vessel information available with both global average revisit times and customer data latency less than one minute. 79) 80) 81)
This new satellite AIS architecture encompasses the complete maritime domain with realtime, continuous satellite coverage. The satellites are networked together with crosslinks and constantly communicate with multiple ground stations, customers receive AIS data in real time. 82)
• On May 30, 2017, exactEarth Ltd. announced the launch of exactView™ RT powered by Harris, the world's first global, persistent real-time Satellite AIS service. exactView RT consists of a system of more than 60 maritime satellite payloads, designed, built and operated by Harris Corporation – a world leader in satellite payload technology - which are hosted onboard the Iridium NEXT constellation of satellites. These advanced maritime payloads cover the entire maritime VHF radio band and leverage the unique cross-linked architecture of the global Iridium NEXT satellite constellation to deliver AIS and other vessel-based VHF data services from any vessel, anywhere on the globe, relaying that data securely to customers in real-time. Today the first four of these advanced real-time maritime payloads are being put into service with the completion of full system deployment expected in 2018. 83)
- Initially, the system is tracking more than 250,000 AIS-equipped vessels around the world including Class B AIS device transmissions utilizing exactTraxTM technology. With the continued growth of the highly successful global AIS system, this tracked population is expected to grow to more than one million vessels worldwide in the next decade. Real-time global AIS data unlocks huge possibilities and enables significant advances in maritime safety, security and efficiency. Advantages include the ability to provide automatic alerts when vessels veer off course; real-time route optimization can provide substantial fuel savings and emissions reductions for vessel owners and operators; logistics and port operations will run more efficiently with highly accurate location and arrival predictions; and, fishing activity can be more effectively managed and enforced. In addition, the ability of the exactView RT system to address the full maritime VHF frequency band combined with the full capabilities of the Iridium NEXT system to transmit data to anyone, anywhere opens up the potential for a wide range of future real-time vessel data services, which will further improve vessel safety, efficiency, and navigation in support of the major smart vessel and e-Navigation initiatives of the global maritime industry.
• January 16, 2017: Four payloads in the exactView RT powered by Harris system made their way successfully into orbit on January 14, 2017. These four advanced payloads are the first of many additions to the revolutionary exactView RT system which will, for the first time ever, deliver real-time global continuous coverage of shipping activity. 84)
exactView RT will consist of more than 60 payloads aboard the Iridium NEXT constellation with all satellites set to be in orbit by 2018. Designed to deliver significant enhancements to current and future customers.
exactView RT powered by Harris provides:
- Global average revisit under one minute
- Customer data latency under one minute
- Reliable detection of both Class A and Class B AIS messages
- Tracking of large populations of small vessels with exactTrax™ equipped AIS transceivers
- Support for the future evolution of AIS to support VDES and other initiatives in the maritime VHF band
These advancements allow for:
- Immediate awareness of maritime incidents in your waters
- Maximum efficiency of your resources using the most complete and up-to-date vessel picture available
- The single source of truth for all your AIS data needs.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).