IPEX (Intelligent Payload Experiment) on CubeSat Mission
IPEX is a CubeSat mission of NASA/JPL, NASA/GSFC and Cal Poly of San Luis Obispo, CA. The mission will demonstrate the operation of autonomous instrument processing, downlink operations, and ground station operations to validate a reduction in data product downlink.
In February 2011, NASA selected 20 small satellites, including two from NASA/JPL (Jet Propulsion Laboratory in Pasadena, CA, to fly as auxiliary payloads aboard rockets planned to launch in 2011 and 2012. The proposed CubeSats come from a high school in Virginia, universities across the country, NASA field centers (GSFC), and DoD (Department of Defense) organizations. 1)
The selections are from the second round of the CubeSat Launch Initiative. The satellites are expected to conduct technology demonstrations, educational or science research missions. The selected spacecraft are eligible for flight after final negotiations when an opportunity arises.
The objective of the IPEX mission is to demonstrate operation of autonomous instrument processing, downlink operations, and ground station operations, utilizing the SpaceCube Mini payload processing unit to validate a reduction in data product downlink. 2) 3) 4) 5)
The development of IPEX is conducted by the following centers/institutions:
- JPL manages the project and develops the autonomous flight software and ground station software, CASPER (Continuous Activity Scheduling Planning Execution and Replanning) and ASPEN (Automated Scheduling and Planning Environment).
- NASA/GSFC (Goddard Space Flight Center) develops the Space Cube Mini payload processing unit.
- Cal Poly of San Luis Obispo designs the spacecraft bus (PolySat), cameras, attitude control, flight avionics software, and integrates/builds the flight unit.
IPEX will validate, in an on-orbit environment, autonomous science and product delivery technologies supporting TRL advancement of the IPM (Intelligent Payload Module) baselined for the proposed HyspIRI (Hyperspectral Infrared Imager) Earth Science Decadal Survey Mission concept providing a twenty-times reduction in data volume for low-latency urgent product generation. As the HyspIRI mission imaging spectrometer (VSWIR) and TIR (Thermal Infrared Imager) will acquire roughly 5.5 TB of data per day during global imaging with 19 day and 5 day repeat intervals, respectively, IPEX will validate the role of the IPM to produce targeted reduced bandwidth data products that can be readily available to the community while the research science quality products are processed over a longer time period. 6) 7) 8) 9)
The CASPER onboard planning software, currently used on EO-1, will demonstrate the integration into the planning schedule new activity goals based on image processing results. It will also integrate onboard telemetry with the schedule to resolve conflicts. On the ground, the ASPEN software will generate weekly schedules of primary science payload activities such as image acquisition and processing based on candidate algorithms planned for the HyspIRI mission concept. One of the new technologies introduced will be the Spacecube-Mini (SC-Mini) designed for the CubeSat form-factor as a 3-part flexible integrated circuit board design (Figure 3).
NASA/GSFC (Goddard Space Flight Center) is developing a radiation tolerant miniaturized space processor for use in a multitude of different space flight applications, from free flyers through embedded computing nodes. The SpaceCube design is based on the heritage of SpaceCube 1 that flew on the Hubble Servicing Mission and the ISS MISSE7 experiment.
The requirements of SpaceCube Mini follow the original SpaceCube and as a near functional equivalent to the SpaceCube 2, but in a 1U CubeSat form factor. The driving requirements are:
• CubeSat 1U (10 cm x 10 cm x 10 cm), < 10 W, < 1.5 kg
• Xilinx V5 XC5VFX130T commercial, or Space-grade Virtex-5QV
The new design, SpaceCube Mini, will physically conform to the volume requirements of a standard 1U (10 cm x 10 cm x 10 cm) CubeSat. It will incorporate the Xilinx Virtex-5, the latest in high speed, high density, and with the SIRF variant, radiation tolerant FPGA design.
Figure 1: Illustration of the IPEX CubeSat (image credit: NASA)
IPEX is a 1U CubeSat (of size 10 cm x 10 cm x 10 cm and a mass of ~1 kg) intended to flight validate technologies for onboard instrument processing and autonomous operations for NASA's Earth Science Technologies Office (ESTO). Cal Poly's PolySat constructed the spacecraft bus (CP8=IPEX). 10) 11) 12)
To support it's primary flight software, IPEX carries a 200 MHz Atmel ARM9 CPU with 128 MB RAM, 512 MB flash memory, a 16 GB Micro SD card, and utilizes the Linux Operating System. The IPEX core flight software is developed by Cal Poly.
EPS (Electrical Power Subsystem): All six sides of the IPEX spacecraft feature solar panels for electrical power generation and is anticipated to have 1-1.5 W power generation. The spacecraft carries three battery packs to enable operations in eclipse and continuous processing modes.
The IPEX spacecraft will use aligned magnets for passive stabilization in LEO (Low Earth Orbit).
RF communications: The primary data link is in UHF band (437.270 MHz) with FSK modulation. The satellite will automatically beacon satellite health data which will be decodable by the amateur community. After the mission lifespan, the satellite will be put into digipeter mode for use by amateur operators.
SC Mini (SpaceCube Mini): A key part of IPEX is the SC Mini processor, developed by NASA/GSFC (Goddard Space Flight Center). This is a compact processing package carried by IPEX in addition to the above Atmel.
The SC Mini is being built to fit into the physical envelope of the CubeSat 1U form factor. The Mini physical housing is designed as a cube at just under 10 cm on each side. The housing is 100 mils thick aluminum 6061, providing strength, thermal mass, and limited radiation shielding. The printed circuit board for the SpaceCube Mini is using rigid-flex technology. This allows the SpaceCube Mini to be folded up to fit inside of the required volume. 13)
Figure 2: Photo of the Cal Poly student team involved in the development of the IPEX CubeSat (image credit: Cal Poly)
The SpaceCube Mini functionality requires three sections of PCB (Printed Circuit Board) connected by two rigid-flex sections. The printed circuit board is folded into a "U" shape, with each PCB getting attached to one wall of the mechanical housing. This provides each board with direct thermal path to the structure. An optional fourth expansion PCB can be connected internally to the SpaceCube Mini design.
The expansion I/O card can hold a custom electrical interface and does not need to be made using rigid-flex. The mechanical and PCB design are being analyzed to handle the harsh launch vibration characteristics of a sounding rocket launch vehicle. In addition a complete thermal analysis of the system will be performed when the layout and mechanical designs are complete.
Figure 3: SpaceCube-Mini board design with integration into IPEX CubeSat bus structure (image credit: NASA/JPL, ESTO)
Figure 4: IPEX bus elements (image credit: Cal Poly)
The SpaceCube Mini has many built in features easing application development and eliminating the need for additional hardware. Key internal features are:
• 512 M x 16 of SDRAM
• 96 Gbit of FLASH
• 12 bit analog to digital converter
• local power regulation
• Expansion I/O card capable
External interfaces are:
• 2 SATA interfaces
• 4 SpaceWire or 8 LVDS interfaces
• 8 RS422 interfaces
• Xilinx Multi-Gigabit Transceiver (MGT)
• 2 Passive thermistors
• 5 Analog inputs
• Power 28 V ±7 V or 5 V regulated.
The SC Mini runs a version of Linux called SC Linux. Because the SC mini will use over 10 W power, it's duty cycle will be extremely limited (5% duty cycle). Due to thermal constraints most of this SC mini operations time will be during eclipse (Ref. 10).
Figure 5: Functional block diagram of SpaceCube Mini (image credit: NASA)
Radiation-tolerant design: The SpaceCube Mini is being designed with radiation hard/tolerant components. The system is going to be very reliable to radiation upsets, even in less benign polar or geosynchronous orbits. For radiation hardness, there is really is no comparison between the typical commercial /university CubeSat and the SpaceCube Mini beyond the shared CubeSat form factor. Commercial CubeSats use commercial parts that have no radiation testing and are typically flown in very low earth orbits (450 km), where radiation effects are greatly diminished. This is in stark contrast to the SpaceCube Mini design which uses fully qualified military/aerospace components that are tested and certified to their datasheet extremes.
The inherent TID (Total Ionizing Dose) capability of the electrical components used in the SpaceCube Mini design varied from 50 -700 krad (Si). It is possible to shield the softer parts to obtain higher capability, depending on the environment. The heart of the SpaceCube Mini is the Virtex-5QV part which is designed to be radiation hard up to 700 krad (Si). Xilinx used a different transistor cell architecture than in their commercial devices in order to harden the flipflops and configuration memory within the device. NASA is planning to perform independent radiation testing on the Xilinx part sometime in the future. Finally, the onboard SDRAM is mitigated by using an EDAC memory controller inside the FPGA. Potential orbits and high value applications for the SpaceCube Mini are infinite.
Power: The SpaceCube Mini is on the leading edge of the MIPS to Watt performance metric for spaceflight computational engines. When the SpaceCube Mini is populated with the commercial Xilinx V5, it has two power PC processors coupled with a huge sea of gates. The gates can be programmed as accelerators to further speed up any CPU intensive operation. This set-up provides the highest computing power per watt. When configured with the commercial Xilinx V5, radiation tolerance (scrubbing, watchdog functions) are managed through an onboard radiation hard one time programmable Aeroflex FPGA. Instead, if radiation susceptibility is the most critical requirement for a mission, then the radiation hardened Space-grade Virtex-5QV can be used. The downside of this part is that the embedded PowerPC processors are factory disabled. To compensate for this, one or more Xilinx soft core MicroBlaze processors can be embedded to provide substantial computational resources for a Virtex-5QV design.
Figure 6: Photo of the SpaceCube 2.0 Mini CubeSat processor (image credit: NASA)
Figure 7: Photo of the assembled IPEX rapid prototype (image credit: Cal Poly)
Figure 8: Exploded view of the IPEX CubeSat (image credit: NASA/JPL)
Figure 9: Photo of the IPEX flight module (image credit: Cal Poly)
Figure 10: Functional diagram of the IPEX electronics (image credit: NASA/JPL)
Launch: The IPEX CubeSat was launched as a secondary payload on Dec. 6, 2013 (07:13:40 UTC) on an Atlas-5-501 vehicle from VAFB, CA. The primary payload on this flight was the classified NROL-39 reconnaissance mission of NRO (National Reconnaissance Office). The launch provider was ULA (United Launch Alliance). 14) 15) 16) 17)
Note: The NROL-39 is reported to be a Topaz radar-imaging reconnaissance satellite with the FIA Radar-3 payload of the cancelled FIA (Future Imaging Architecture) program. FIA was a program to design a new generation of optical and radar imaging US reconnaissance satellites for NRO. Despite the optical component's cancellation in 2005, the radar component, with a code name of Topaz,has continued, with two satellites in orbit as of November 2013; these are: NROL-41, launched on Sept. 21, 2010, and NROL-25, with a launch on April 03, 2012. A total of 5 radar satellites are in the Topaz program (Ref. 15). 18)
Secondary payloads: Next to the NROL-39 primary payload, the Atlas-5 hosts the GEMSat/ELaNa-2 mission for the NRO and the NASA/LSP ( Launch Services Program), lifting 12 CubeSats/nanosatellites to orbit as secondary payloads. All 12 CubeSats/nanosatellites are considered to be technology missions. 19) 20)
• AeroCube-5a and -5b, two 1.5U CubeSats of The Aerospace Corporation.
• ALICE (AFIT LEO iMESA CNT Experiment), a 3U CubeSat of AFIT (Air Force Institute of Technology)
• CUNYSAT-1 (City University of New York-1), a 1U CubeSat of Medgar Evers College, Brooklyn, N.Y. of the City University of New York.
• FIREBIRD-A and -B (Focused Investigations of Relativistic Electron Burst, Intensity, Range and Dynamics), two 1.5U CubeSats of Montana State University, University of New Hampshire, Los Alamos National Laboratory, and The Aerospace Corporation.
• IPEX, also known as CP8, is a 1U CubeSat of Cal Poly (California Polytechnic State University) and NASA
• MCubed/COVE-2, a 1U CubeSat of the University of Michigan, Ann Arbor, MI and of NASA/JPL
• SMDC-ONE-2.3 (Charlie) and SMDC-ONE-2.4 (David), two 3U CubeSats of the U.S. Army SMDC/ARSTRAT (Space & Missile Defense Command/Army Forces Strategic Command) of Huntsville, AL (Redstone Arsenal)
• SNaP (SMDC NAnosatellite Program), a 3U CubeSat of the U.S. Army SMDC/ARSTRAT
• TacSat-6 (Tactical Satellite-6), a 3U CubeSat of the U.S. Army SMDC/ARSTRAT. TacSat-6 will be operated in conjunction with the ORS (Operationally Responsive Space) Office; it forms part of the TacSat program of technological research satellites.
The CubeSats are integrated into 8 P-PODs (Poly-Pico Orbital Deployers ), which are contained in the NPSCuL (Naval Postgraduate School CubeSat Launcher), built by NPS students of Monterey, CA. The NPSCuL, together with the 8 P-PODs and 12 CubeSats, is referred to as GEMSat (Government Experimental Multi-Satellite), and is attached to the Centaur upper stage's ABC (Aft Bulkhead Carrier), Figure 12. The assembled GEMSat is shown in Figure 11 ready for mate to the launch vehicle along with the members of the various institutions from NPS, OSL (Office of Space Launch), ULA (United Launch Alliance) and Cal Poly. 21)
Figure 11: Photo of the GEMSat/ELaNa-2 secondary payload along with all team members (image credit: GEMSat Team)
Orbit: The primary payload was launched into a Sun-synchronous near-circular orbit, altitude of ~1075 km x 1089 km, inclination of 123º (deployment ~07:32 UTC).
• The Centaur AV-042 upper stage then made two orbit lowering burns to a SSO of 467 km x 883 km at an inclination of ~120.5º. Attached to the AV-042 was GEMSAT, the second NPSCuL CubeSat launcher, which ejected 12 CubeSats between around 10:22 and 10:38 UTC. 22)
• The last transmission heard from IPEX was on January 30, 2015 (IPEX was launched December 6th, 2013). IPEX completed its mission, autonomous image processing and data reduction, fairly early after launch. During the remainder of its functional life, it continued to transmit down health data. With nearly a years worth of health files, the team has been able to observe how the electronics behave in harsh environments. We have learned a great deal from IPEX. 23)
• The IPEX CubeSat is operational in the spring of 2014 (Ref. 12).
Figure 13: CASPER/JPL mission status (image credit: Cal Poly, JPL)
• Feb. 2014: IPEX is on orbit, undergoing initial checkout. Over 50 packets have been received. 24) 25)
The successful capture, storage, and downlink of the recent IPEX images represents an important milestone for PolySat's technical and operational capabilities. IPEX is the first CubeSat to use PolySat's new avionics suite, comprised of a variety of custom PCBs and a Tyvak Intrepid systemboard/comm board package. The timely and efficient downlink of one of IPEX's high-resolution deployment images such as the one of Figure 15 adequately verifies not only PolySat's new avionics bus, but the recent upgrades to the Cal Poly ground station as well. The project team is excited to continue IPEX operations!
Figure 14: A shot of the Hawaiian Islands, the picture was taken by IPEX on Dec. 12, 2013 (image credit: Cal Poly, JPL)
• December 10, 2013: The payload processor and software have been activated.
Figure 15: First picture of IPEX acquired on Dec. 6, 2013 using the -Z camera while IPEX was traversing over the Australian coast, pointed southwest towards the terminator line (image credit: Cal Poly, JPL)
Sensor complement: (Camera experiment)
IPEX carries five Omnivision OV3642 cameras, each producing images at approximately 2048 x 1536 pixel resolution, 3 Mpixels in size, with an IFOV (Instantaneous Field of View) of 0.024º. With currently manifested orbit, the project hopes to get approximately 200 m/pixel imagery of the Earth's surface (Ref. 8). The cameras are a stand in for actual science instruments on future NASA missions. Figure 16 shows imagery from a balloon test flight in July 2012 acquired approximately 31 km above sea level. 27)
Figure 16: Image from a balloon test flight acquired in July 2012 (image credit: NASA/JPL)
What makes IPEX unique is its five cameras used by NASA's JPL software. The system analyzes collected images and reports back to NASA on which items may be of particular interest and worth further analysis. "I'm particularly proud of the camera on the board that I built. Since the satellite launch in December, the camera on that board has produced amazing pictures of the Earth," says Jeff Weaver, electrical engineer undergraduate student at Cal Poly. "Knowing that something I've designed and built is in space and taking pictures is a good feeling." 28)
With both a primary and secondary payload processor, the IPEX's primary processor, along with all critical electrical components, are integrated onto a single system board. Weaver's specific involvement was in the creation of the power system and signal breakouts from the primary processor, as well as an integral side panel attached to the main processor.
"This panel connects all of the solar power to the batteries, manages the data buses from external sensors, and includes one of the five cameras on the satellite," explaines Weaver.
The highly condensed single panel board design posed a challenge in incorporating all the power and data signals branching out from the single system board. Five of IPEX's six panels hold cameras, all of which feed into the system board through shared data lines. Furthermore, each of the six panels include solar cells.
• Focal length (f): 4mm
• Integration time: 67 ms
• Pixel diameter: 1.75 µm
• Detector size: 3 Mpixels (2500 x 1600)
• FOV: ~50º.
Payload CPU – Gumstix EarthStorm:
• Computer on module
• Widely used in terrestrial applications
• 800 MHz OMAP (ARM) CPU
• 512 MB RAM
• 512 MB Flash
• SD card slot (8 GB used)
• < 1 W typical power
• Runs Linux
Figure 17: Overo EarthSTORM COM (board) 29)
Figure 18: The Gumstix EarthSTORM solution (image credit: Cal Poly, Ref. 12)
IPEX Ground and Flight Operations:
IPEX is intended to demonstrate automated ground and flight operations of onboard autonomous processing of instrument data. In order to achieve this end, a range of capabilities and software are required (Ref. 10).
The ground mission planning software for IPEX uses the CLASP (Compressed Large-scale Activity Scheduling and Planning) system to determine the processing and downlink requests based on the projected overflight of the spacecraft (Ref. 8).
These requests are then handled in a priority-based fashion by the ASPEN system to generate a baseline schedule for several days operations in advance. ASPEN (Automated Scheduling and Planning Environment) must manage the ground contact schedule, eclipse schedule, observation activities, and onboard image processing activities. The onboard image processing activities can involve a range of constraints including CPU usage, RAM usage, and downlink product size. The primary activities of image acquisition and image processing can also require significant data storage resources based on when the image is acquired versus when the SC mini can be powered on (thermal & power constrained) to process the image.
Onboard the spacecraft the CASPER (Continuous Activity Scheduling Planning Execution and Replanning) planner will be used to manage spacecraft resources. CASPER will model all of the same resources and constraints as ASPEN but will be able to modify IPEX operations in response to deviations from the ground predicted plan such as: using more or less power than expected; activities taking longer or shorter than expected; or image products being larger or smaller than expected. CASPER will also be able to respond to onboard analysis of instrument data such as detection of features or events in imagery. Onboard processing will also be used to detect data of little value (e.g. images of dark space) early in processing activity. This analysis will save processing time, data-storage, and energy that would have been spent processing these less interesting images. In response, CASPER can schedule follow on acquisitions from event or feature detection, or previously unscheduled lower priority data acquisition goals.
The IPEX spacecraft will have a number of driving operations constraints. IPEX is extremely power limited. The solar power generation will be approximately 1/10th of the maximum power draw (when the SC mini is powered on). The peak power of the SC mini also limits its use to times of eclipse for thermal reasons.
The base flight software on IPEX is based on extensions and adaptation of the Linux Operating System. The well-known System V init process is used directly to start, and restart if necessary, the principal components of the flight software: system manager for health monitoring, watchdog, beacon for real-time distribution of telemetry, datalogger for logging and archiving of telemetry and a sequence execution processes for real-time, time-based, and event-based commanding of the spacecraft.
IPEX Onboard Instrument Processing:
IPEX will be validating a wide range of onboard instrument processing algorithms. The vast majority are variations of pixel mathematics, e.g. normalized difference ratios, band ratios, and similar products. For example, many flooding (surface water extent) classifications are based on band ratios. Snow and ice products also use simple band processing formulae. Thermal anomaly detection algorithms such as for volcano and active fire mapping also involve computationally efficient slope analysis of spectral signals. Finally, a wide range of vegetation indicators also involve difference ratios or similar computations.
IPEX will also fly more computationally complex image processing technologies. These include: Support Vector Machine Learning Techniques, spectral unmixing techniques, and TextureCam Random Decision forest classification techniques.
IPEX is expected to have an extremely limited downlink data rate (less than 9.6 kbit/s). As a result, most of the IPEX onboard processing validation will come from running algorithms on the same images on the Atmel, PPC, and FPGA, and comparing the results. Only in cases where the results do not compare will full images be likely to be downlinked (Ref. 10).
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11) CP8 (IPEX), Cal Poly, URL: http://polysat.calpoly.edu/in-development/cp8-ipex/
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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).