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GomX-4 (GomSpace Express-4) Mission

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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 late 2017, 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.





• 2U platform
• ADS-B payload

• Launched in 2013
• Very successful payload
• Platform still in operation


• 2U platform, new avionics
• Aerobrake payload
• Quantum mechanics payload

• Launch failure in 2014


• 2U platform, new avionics
• Aerobrake payload
• Quantum mechanics payload

• Launched in 2015
• Reentered in 2016
• All mission objectives successfully meet
• Payload functions extended through in-orbit upgrades


• 2 x 6U platforms
• AIS, ADS-B tracking
• Visual & hyperspectral camera
• Inter satellite linking
• Propulsion for station keeping

• On track to launch in Q1 2018

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 inter-satellite 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)


Project status:

• 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. 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 for1 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. 7)

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.

Secondary payloads:

• 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)


Propulsion system:

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: Configuration of the propulsion system (image credit: NanoSpace, GomSpace)

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. 8)



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. 9)

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.

Mass, Volume Power

1.1 kg, 1U volume compatible, 11 W

Spectral range

400- 1000 nm

Spectral bands



4096 x 1850 pixels

Swath width (@300 km altitude)

164 km

GSD (Ground Sample Distance) (@300 km altitude)

40 m

Onboard data processing

Level 2

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 8: Illustration of the HyperScout hyperspectral imager (image credit: COSINE)


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. 10)

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.

Main Features:

• 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.

Highlighted Features:

• 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 9: Photo of the NanoCom device (image credit: GomSpace)


Figure 10: 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.

Main Features:

• 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

• Interfaces:

- 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 11: Photo of the QubeAIS receiver of Satlab (image credit: Satlab) 11)

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 12: Overview of the QubeAIS hardware structure (image credit: Satlab)


1) "GomX-4B with GomX-4A," ESA, Oct. 13, 2016, URL:

2) "Arctic Surveillance and the Building Blocks of Constellations," GomSpace, URL:

3) "GomSpace completes acquisition of NanoSpace AB," GomSpace Press Release, Ocober 16, 2016, URL:

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:


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:

7) "ESA's latest technology CubeSat cleared for launch site," ESA, 23 Nov. 2017, URL:

8) "GomSpace completes acquisition of NanoSpace AB," GomSpace, October 16, 2016, URL:

9) "COSINE HyperScout," URL:

10) "Datasheet: An ADS-B receiver for space applications," GomSpace, 22 Sept. 2015, URL:

11) "Software-Defined AIS Receiver for CubeSats,
QubeAIS datasheet revision 1.4, URL:


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 (

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