GomX-4 (GomSpace Express-4) Mission
The GomSpace missions GomX-4A and GomX-4B are two 6U CubeSats with the objective to demonstrate key technologies to handle large satellite formations. Like its predecessor GomX-3, the GomX-4B mission is a collaboration between ESA (European Space Agency) and GomSpace ApS of Aalborg, Denmark to demonstrate new capabilities of nanosatellites.
In October 2016, ESA signed a contract for its biggest small nanosatellite yet: GomX-4B will be a 6U CubeSat, intended to demonstrate miniaturized technologies, preparing the way for future operational nanosatellite constellations. GomX-4B is double the size of ESA's first technology CubeSat, GomX-3, which was released from the ISS (International Space Station) on October 5, 2015. 1) 2)
"ESA regards CubeSats, based on standardized 10 cm units, as very promising for early testing of new technologies in space at a low cost," explains Roger Walker, heading ESA's technology CubeSat initiative. "GomX-4B's increased size will accommodate more technology payloads, and enables a higher level of performance."
The contract with Danish CubeSat specialist GomSpace is supported through the In-Orbit Demonstration element of ESA's General Support Technology Program, focused on readying new products for space and the marketplace. Aiming for flight in early 2018, GomX-4B will be launched and flown together with GomX-4A, designed by GomSpace for the Danish Ministry of Defence under a separate contract.
GOMX-4 is a research and development mission by GomSpace. It includes 2 satellites and 3 partners: DALO (Danish Defence Acquisition and Logistics Organization), TUD (Technical University of Denmark) of Lyngby, Denmark, and ESA (European Space Agency).
GOMX-4A is sponsored by DALO who by this mission will have their first satellite intended to contribute to surveillance of the Artic. The GOMX-4A demonstration is part of an analysis seeking to identify best-practice and future efforts reinforcing the Danish Defense's surveillance of the Artic within the Kingdom. The satellite has been named "Ulloriaq" after the word "star" in the Greenlandic language.
The two CubeSats will stay linked through a new version of the SDR (Software Defined Radio) system demonstrated on GomX-3, while their relative positions along their shared orbit is controlled up to a maximum 4500 km. Such intersatellite links will allow future CubeSat constellations to relay data quickly to users on the ground. The same radio system will also be used for rapid payload data downloads to Earth.
Nanospace of Uppsala in Sweden is contributing the highly miniaturized cold-gas thrusters for controlling the orbit, allowing future CubeSat-based constellations to be deployed quickly after launch.
Note: GS Sweden AB, the parent company of GomSpace ApS, has agreed with the Swedish Space Corporation (Svenska rymdaktiebolaget, SSC) to acquire 100% of the shares of NanoSpace AB, a wholly owned subsidiary of SSC. 3)
Additional technology payloads include a compact hyperspectral imager called HyperScout, developed by Cosine Research in the Netherlands; a miniaturized star tracker from ISIS (Innovative Solutions In Space), of Delft, The Netherlands; an in-house ESA experiment to test components for radiation hardness; and an ADS-B antenna for aircraft tracking, developed from the GomSpace system tested on GomX-3.
The GomSpace business operations are conducted through the wholly-owned Danish subsidiary, GomSpace A/S, with operational office in Aalborg, Denmark. GomSpace is a space company with a mission to be engaged in the global market for space systems and services by introducing new products, i.e. components, platforms and systems based on innovation within professional nanosatellites.
GomX flight demonstration program: The GomX-4 mission is part of GomSpace's "GOMX" flight demonstration program aiming at introducing new capabilities and acquiring in-orbit experience with these. The GOMX missions are typically implemented as a collaboration between GomSpace and project sponsors. Table 1 provides an overview.
Table 1: GomX mission overview
The GOMX-4 mission is part of GomSpace's "GOMX" flight demonstration program aiming at introducing new capabilities and acquiring in-orbit experience with these. The GOMX missions are typically implemented as a collaboration between GomSpace and project sponsors. 4)
GomSpace is the project prime responsible for the satellite platform, the intersatellite linking radio communication subsystem and integration of partner contributions . The satellites will be 6U satellites, small in size, with dimensions of 20 x30 x10 cm, each with a mass of approximately 8 kg. The two satellites will be launched together in 2018 with a planned mission to be completed within 2019.
Figure 1: Artist's rendition of the GomX-4 nanosatellites in space (image credit: GomSpace) 5)
The two 6U satellites are developed to the PA/QA (Product Assurance/Quality Assurance) standards now imposed by ESA on nanosatellite missions. These are derived from the ECSS (European Cooperation for Space Standards) system, but tailored for use in innovative missions. The satellites have been qualified for 20 krad TID (Total Ionizing Dose) of radiation and single-event-upset characterization has been performed at the board level.
The satellite design reuses many products and designs flight qualified in the 3U GOMX-3 mission 6), but the architecture has now been scaled to the 6U class and the ISL (Inter-Satellite Link) and propulsion capabilities have been added to the platform. The ISL capability is based on GomSpace's modular SDR (Software Defined Radio) platform. The main SDR board performs all the modulation, demodulation and protocol functions and is connected to three active patch antennas. Each antenna provides filtering, LNA and PA functions. One forward and one aft looking antenna is used for ISL, and the final antenna is Nadir looking for ground communication. The system allows data rates up to 7.5 Mbit/s, but actual performance is limited to comply with regulatory provisions.
The propulsion capability is based on NanoSpace's flight proven cold-gas design now up-scaled to the 6U platform. A cornerstone of NanoSpace's technology is the MEMS based thrusters that allow extremely accurate thrust control.
GOMX-4B design: The two spacecraft are similar but the GOMX-4B satellite is the more complex as it packs more payloads, including the propulsion system. The Figure 2 depicts the GOMX-4 system diagram indicating the system in the configuration and their integration in the system.
Figure 2: System diagram for the GOMX-4B satellite (image credit: GomSpace)
The main communication bus in the GOMX-4 architecture is based on the CAN bus and in this aspect departing from the earlier GOMX missions that was based on the I2C bus. The CAN bus provides higher reliability and data transfer rates.
Figure 3: External configuration of the GomX-4B spacecraft (image credit: GomSpace)
The star-tracker aperture is clearly visible on the topside together with an ADS-B patch antenna. Two S-band patch antennas are visible on the sides of the satellite for ISL and ground communication.
Figure 4: Internal configuration of GomX-4 (image credit: GomSpace)
The satellite is fully "crowded" with subsystems and payloads including the relatively bulky hyperspectral imager looking out the side of the satellite.
The IOD (In-Orbit Demonstration) CubeSat Tailoring was created by ESA to apply an appropriate level of ESA requirements to the more general CubeSat standard.
The full ECSS standard is out of scope for low-cost CubeSat missions; the CubeSat IOD standard is tailored to apply a subset of the full requirements. Thus, each ECSS Engineering standard is classified as "applicable", "guideline", or "not applicable". Within standards classified as applicable, there is a line-by-line tailoring of each requirement's applicability to IOD CubeSat projects. In excluding standards (or specific requirements within a standard), a higher level of risk is accepted for these small missions. The tailored ECSS Engineering standards are supplemented by "light" Product and Quality Assurance requirements developed specifically for IOD CubeSat projects, where higher risk tolerance and extensive use of COTS components is commonplace.
The IOD CubeSat tailoring represents the expertise that ESA brings to the table when working on nanosatellite missions. It has been refined through a variety of nanosatellite projects, including GOMX-3. The refinement aims to be helpful for developers, with the goal of increasing the robustness, quality and reliability of CubeSats without excessive overhead. The tailoring is available to partners when collaborating on ESA CubeSats. For further information about the IOD CubeSat ECSS tailoring, please contact the ESA Directorate of Technical and Quality Management.
This IOD approach as been applied to the GOMX-4B project.
AIV (Assembly, Integration and Verification): AIV activities were completed by GomSpace from April to June 2017 with final environmental qualification performed at ESA/ESTEC in June 2017.
Figure 5: This photo depicts the two GOMX-4 satellites in the test facilities of ESA/ESTEC about to undergo thermal–vacuum testing (image credit: ESA, GomSpace)
• November 23, 2017: The majority of tests were made at GomSpace and other facilities in Denmark, apart from thermal–vacuum testing – ensuring that the CubeSats can withstand the hard vacuum and temperature extremes of low orbit – which took place at ESA/ESTEC in the Netherlands (Ref. 8).
• In October 2016, GomSpace ApS completed the acquisition of NanoSpace AB. GS Sweden AB, the parent company of GomSpace ApS, has agreed with the Swedish Space Corporation (Svenska rymdaktiebolaget, SSC), to acquire 100% of the shares of NanoSpace AB, a wholly owned subsidiary of SSC. 7)
• Qualification Acceptance Review: June 2017
• CDR (Critical Design Review): January 2017
• PDR (Preliminary Design Review): May 2016
• Kick-off: November 2015
Launch: A launch of the two GomX-4 nanosatellites as secondary payloads is scheduled for 2 February 2018 on a Long March 2D vehicle from JSLC (Jiuquan Satellite Launch Center), China. The primary mission on this flight is CSES-1 (China Seismo-Electromagnetic Satellite-1) of CNSA. The primary mission is also referred to as Zhangheng-1. 8)
The two GomX-4 satellites are integrated together in a 12U deployer procured from Astrofein (Astro- und Feinwerktechnik GmbH) Berlin Adlershof, i.e. the satellites will be deployed in the same direction with a small time-delay between.
The CSES satellite mission is part of a collaboration program between CNSA ( China National Space Administration) and the Italian Space Agency (ASI), and developed by China Earthquake Administration (CEA) and Italian National Institute for Nuclear Physics (INFN), together with several Chinese and Italian Universities and research Institutes.
Orbit: Sun synchronous orbit, altitude of 500 km.
• ÑuSat-4 and NuSat-5 microsatellites of Satellogic S. A.,Argentina, each with a mass of 37 kg to provide commercial high-resolution imagery (1 m).
• GomX-4A and GomX-4B 6U CubeSats (each with a mass of 8 kg), a technology tandem mission of the Danish Ministry of Defence and ESA, respectively.
• Fengmaniu 1, an Earth observation satellite of CNSA.
• YouthSat sponsored by CNSA, a 2U CubeSat, referred to as Shaonian Xing, roughly translating to 'Junior Sat' or 'Youth Sat', a result of China's Teen Satellite Project.
Sensor/experiment complement: (ISL, Propulsion System, HyperScout, ADS-B, AIS receivers)
ISL (Inter-Satellite Link):
The ISL demonstrator payload is based on GomSpace SDR (Software Defined Radio) platform product based on the Xilinx Zynq7000 FPGA (Figure 6). The SDR is connected to an active (integrated LNA & PA) S-band patch antenna and the SDR implements a special waveform to allow ISL communication at up to in theory 6 Mbit/s – in practice bit rates are restricted by distance and regulatory aspects.
Figure 6: Photo of the SDR platform (image credit: GomSpace)
ESA's next miniature satellite will be its first able to change orbit. Thanks to a compact thruster resembling a butane cigarette lighter, the cereal box-sized satellite will fly around its near-twin to test their radio communications. Much quicker to build and cheaper to launch than traditional satellites, ESA is making use of CubeSats for testing new technologies in space. 9)
The main goal is to test the radio link at varying distances, routing data from one satellite to the other, then down to the ground. GomX-4A, from the Danish Ministry of Defence, will remain in position while ESA's GomX-4B maneuvers up to 4500 km away.
"We have two pressurized fuel tanks linked to two pairs of thrusters," explains Tor-Arne Grönland, head of NanoSpace. "Rather than burning propellant, these are simpler ‘cold-gas' thrusters designed specifically for such a small mission. And simpler means cheaper and smaller."
"The fuel is stored under pressure, then released through a tiny rocket nozzle. Even though it's cold gas, we achieve a substantial velocity change by using liquid butane that turns to gas as it exits. Storing it as a liquid allows us to pack as many butane molecules as possible inside the small available volume – its liquid form being some 1000 times denser than its gas."
Each thruster will provide only 1 mN – the weight you would feel holding a feather in your hand – but enough to move the 8 kg satellite over time.
The propulsion system is provided by NanoSpace and based on their flight proven 3U cold gas based system scaled up to the 6U mission. The Figure 7 shows how the dual tanks take up 0.5U height of the platform. The system provides around 15 m/s ΔV capability delivered through 4 x 1 mN thrusters based on NanoSpace's MEMS thruster technology allowing extremely accurate thrust control.
Figure 7: GomX-4B's cold-gas thruster system takes up two half-CubeSat units at one side of the nanosatellite, with two spherical titanium tanks filled with liquid butane. It has four 1 mN thrusters, typically to be fired in pairs while keeping one set in reserve (image credit: NanoSpace)
Figure 8: Thruster chip for the GomX-4B CubeSat's propulsion system, designed by Nanospace in Sweden. Elements such as flow channels and sensors, chamber and nozzle are fitted into a 1 x 2 cm chip, just 1 mm thick by using microelectromechanical systems technology, otherwise known as MEMS. In terrestrial terms, MEMS is already a very mature technology platform: there are such devices all around us, in our cellphones, watches and cars (image credit: Nanospace)
The thrusters will typically be fired in pairs although they can also work individually, for a few minutes at a time and up to an hour. "Compared to a typical half-ton satellite with 1 N hydrazine thrusters, we are almost a hundred times lighter and a thousand times weaker," adds Tor-Arne.
NanoSpace already has flight experience behind its cold-gas thruster, with a smaller version carried on China's TW-1 in 2015.
The company plans to demonstrate a great many different operating methods during the GomX-4B mission: "We'll do different kinds of burns: long, short, pulsing and throttling up and down. It's important to do these things early in the mission then again late on, to show it can survive and perform well in space."
NanoSpace began as a commercial spin-off from Sweden's University of Uppsala, and was acquired last year by Danish company GomSpace, builder of the GomX-4 satellites. The companies are currently working together on a constellation of more than 200 CubeSats for a commercial customer.
NanoSpace is also developing an ESA thruster for flying several satellites in formation, rendezvous and docking, and for controlling the orientation of CubeSats in deep space.
HyperScout, provided by COSINE Measurement Systems, Warmond, The Netherlands, is the first ever miniaturized hyperspectral imager with its own brain. It is designed to be operated upon nano-, micro- and larger satellites. The extremely compact reflective telescope ensures high optical quality in the VNIR range. The onboard data handling system is made for realtime data processing, enabling Level-2 generation onboard and therefore drastically reducing the amount of data to be downloaded and processed. 10)
Due to rapid price drops and miniaturization of the instruments, HyperScout can be turned into a commercially exploitable platform bringing enterprise solutions by real-time earth inspection. HyperScout will enable countless companies and organizations to use real-time Earth observations in different applications for their insights and decisions.
If used onboard larger satellites, the wide swath, the Level-2 realtime data processing, and the minimal impact at system level, make the HyperScout attractive as an ancillary instrument providing real time phenomena information either to the larger primary payload, or to a ground control room. This enables smart operational planning for large payloads.
Table 2: HyperScout specifications
• Land survey and management, e.g. illegal dumps
• Early warning, e.g. flooding, forest fire, landslides
• Land cover and land use classification
• Monitoring of vegetation conditions (drought)
• Water logging
Figure 9: Illustration of the HyperScout hyperspectral imager (image credit: COSINE)
Color equals information, so the more spectral bands an Earth-observing satellite sees, the greater quantity of environmental findings returned to its homeworld. Now ESA is ready to fly a hand-sized hyperspectral imager – small enough to fit on its next nanosatellite. Hyperspectral instruments divide up the light they receive into many narrow, adjacent wavelengths to reveal spectral signatures of particular features, crops or materials, providing valuable data for fields such as mineralogy, agricultural forecasting and environmental monitoring. 11)
These cameras are typically bulky items of 100 kg or more, requiring costly full-sized satellites. But advanced electronics, new materials and optomechanical manufacturing techniques have opened up new possibilities for miniaturizing payloads, with lower but still acceptable performances in terms of radiometry and spatial/spectral resolutions, when comparing to their bigger cousins.
ESA worked with industrial partners for years to shrink the complex assemblage of precisely curved ‘three-mirror anastigmat' mirrors needed to achieve a hyperspectral imager small enough to fit in the palm of a hand.
"Having got the payload working from an optical point of view, the next challenge we faced was the sheer quantity of data that hyperspectral imagers produce, potentially terabytes per orbit," explains Alessandro Zuccaro Marchi of ESA's Optics section. "Each line of each view is observed in many different wavelengths, building up into a complete image ‘cube'. The problem is that the available bandwidth downlink back to Earth faces fundamental limitations, set by the CubeSat's small size, threatening onboard data bottlenecks."
The answer was to make HyperScout as smart as possible, to perform as much image processing as possible onboard, to turn raw radiance measurements into corrected, georeferenced geophysical parameters. Such Level-2 results comprise less data, but contain much more useful information.
"In addition, HyperScout will be sufficiently intelligent that it will be able to perform automated comparisons of images of the same location taken in different moments, such as subsequent orbits," adds Alessandro. "It can then flag any variations that might indicate important changes such as flooding, drought or fire hazards, going on to decide an alert needs to be sent to Earth. So only really important, actionable notifications will need to be returned."
Gomx-4B's main goal is to demonstrate intersatellite communication techniques and micropropulsion orbit control with near-twin GomX-4A, but time is being made available to make repeat acquisitions over areas of interest, in combination with airborne observational campaigns using another HyperScout.
HyperScout was developed by a consortium led by cosine Research in the Netherlands, who stressed the value of this early chance to demonstrate the technology in orbit for the technology's commercial future.
"HyperScout is a unique combination of hardware and software," comments Marco Esposito of cosine Research. "Bigger instruments can make more precise measurements of different components of ecosystems, but require years of development. "Mass produced, this compact instrument could instead be flown as a secondary payload on numerous different missions, potentially to be used as an early warning viewfinder – providing realtime alerts of changes on the ground to cue up larger instruments for detailed follow-up observations."
cosine Research worked with TU Delft and VDL ETG in the Netherlands, Belgium's VITO Remote Sensing and S&T in Norway.
Figure 10: The compact HyperScout hyperspectral imager, small enough to fit aboard CubeSats, was developed by this team from cosine Research in the Netherlands (image credit: cosine Research)
Figure 11: Illustration of a hyperspectral image 'data cube' (image credit: University of Texas at Austin, Center for Space Research)
ADS-B (Automatic Dependent Surveillance – Broadcast)
ADS-B is a cooperative surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. Usually it is ground stations and other airplanes receive the information, but when flying over large bodies of water, no receiver might be in the vicinity. 12)
Today, most civil passenger aircraft are equipped with ADS-B transponders operating at 1090 MHz and transmitting information about aircraft ID, position and status. On-board intelligent database allows recorded data to be queried and searched in many ways e.g. tracking specific flight IDs or providing regional overviews.
GomSpace refers to its ADS-B system as NanoCom. The system has been flight tested on GOMX-1, and performed as planned.
• Flight-proven ADS-B (Automatic Dependent Surveillance - Broadcast) receiver for aircraft tracking
• Consists of a reconfigurable FPGA Cube Sat kit compatible board
• Fits in less than a 0.3U volume in a nanosatellite / cubesat and uses less than 1 W of power
• Reconfigurable FPGA (in flight)
• Max ADS-B packages per second: 800.
• Sensitivity down to –103 dBm (NB) and -99 dBm (WB)
• CSP data interfaces over I2C-bus
• Low power consumption: ~500 mW
• Operational temperature: -40 °C to +60 °C
• Dimensions: 92.0 mm x 88.9 mm x 12.5 mm (without stack connector)
• UART console interface for easy use in lab setup
• SSMCX antenna connector
• Integrated EMI shield
• Fits standard PC104
• PCB material: Glass/Polyimide 4+4 twin stack ESA ECSS-Q-ST-70-11-C
• IPC-A-610 Class 3 assembly.
Figure 12: Photo of the NanoCom device (image credit: GomSpace)
Figure 13: Block diagram of NanoCom (image credit: GomSpace)
AIS (Automatic Identification System)
Ship Tracking with Space based AIS Receiver. The Satlab QubeAIS is a fully self-contained SDR based AIS (Automatic Identification System) receiver, which is suitable for LEO satellite missions. Weighing less than 55 g and using only 800 mW during full load. This versatile SDR offers excellent performance given the typical constraints of a CubeSat - or as an additional payload on larger satellites.
The Satlab QubeAIS has flown on several successful missions. Aalborg University have public data from their AAUSAT3 mission.
• AIS Receiver Board features:
- Easy to configure stand-alone AIS receiver
- Monitors both AIS channels simultaneously
- Possible to download raw IF spectrum samples
- Low Power
• RF Features:
- -113 dBm sensitivity
- LNA and SAW filters onboard
- Multiple connector and placement options
- Delivered with SW library for easy integration
- CSP (CubeSat Space Protocol)
- UART and CAN
• Mechanical Features:
- PC/104 form factor
- MCX or SMA antenna connector.
Figure 14: Photo of the QubeAIS receiver of Satlab (image credit: Satlab) 13)
The Satlab QubeAIS is a fully self-contained SDR based AIS receiver, suitable for LEO satellite missions. Using less than 1 W during full load, this versatile SDR offers excellent performance given the typical constraints of a CubeSat - or as secondary payload on larger satellites. The receiver is software configurable for simultaneous reception of either AIS channels 1 & 2 (162 MHz) or the long-range channels 3 & 4 (156.8 MHz).
The trade-off between a reconfigurable hardware down-converter and a DSP based SDR algorithm, enables a large amount of processing power at a minimal power consumption. The demodulation algorithm uses per-packet adaptive filtering and center frequency estimation, which ensures good reception even at >3000 km line-of-sight and at a large Doppler frequency offset.
Support for the CSP (Cubesat Space Protocol) on CAN-bus or UART, eases integration and reduces the buy-to-fly-time significantly.
Figure 15: Overview of the QubeAIS hardware structure (image credit: Satlab)
1) "GomX-4B with GomX-4A," ESA, Oct. 13, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/10/GomX-4B_with_GomX-4A
3) "GomSpace completes acquisition of NanoSpace AB," GomSpace Press Release, Ocober 16, 2016, URL: https://gomspace.com/news/gomspace-completes-acquisition-of-nanospace-a.aspx
4) Lars K. Alminde, Morten Bisgaard, Igor A. Portillo, Daniel Smith, Laura Leon Perez, Tor-Arne Grönland, "GOMX-4: Demonstrating the Building Blocks of Constellations," Proceedings of the 31st Annual AIAA/USU Conference on Small Satellites, Logan UT, USA, Aug. 5-10, 2017, paper: SSC17-III-04, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3612&context=smallsat
6) David Gerhardt, Morten Bisgaard, Lars Alminde, Roger Walker, Miguel Angel Fernandez, Anis Latiri, Jean-Luc Issler, "GOMX-3: Mission Results from the Inaugural ESA In-Orbit Demonstration CubeSat," Proceedings of the 30th Annual AIAA/USU SmallSat Conference, Logan UT, USA, August 6-11, 2016, paper: SSC16-III-04, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3347&context=smallsat
7) "GomSpace completes acquisition of NanoSpace AB," GomSpace, October 16, 2016, URL: https://gomspace.com/news/gomspace-completes-acquisition-of-nanospace-a.aspx
8) "ESA's latest technology CubeSat cleared for launch site," ESA, 23 Nov. 2017, URL: http://m.esa.int/Our_Activities/Space_Engineering_Technology
9) "ESA's next satellite propelled by butane," ESA, 21 December 2017, URL: http://m.esa.int/Our_Activities/Space_Engineering_Technology
11) "Hand-sized hyperspectral camera to fly on ESA's next CubeSat," ESA, 8 Jan. 2018, URL: http://m.esa.int/Our_Activities/Space_Engineering_Technology
12) "Datasheet: An ADS-B receiver for space applications," GomSpace, 22 Sept. 2015, URL: https://gomspace.com/UserFiles/Subsystems/datasheet/gs-ds-nanocom-adsb-10.pdf
13) "Software-Defined AIS Receiver for CubeSats," QubeAIS datasheet revision 1.4, URL: https://gomspace.com/UserFiles/Subsystems/datasheet/SLDS-AIS-14.pdf
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).