TechEdSat (Technology Demonstration CubeSat)
TechEdSat is a 1U CubeSat technology demonstration mission built by students of SJSU (San Jose State University), San Jose, CA, in partnership with NASA/ARC (Ames Research Center), the Swedish National Space Board (SNSB) via AAC Microtec, Uppsala, Sweden, and JAXA (Japan Aerospace Exploration Agency). The overall objective of the mission is to evaluate SPA (Space Plug-and-play Avionics) designed by AAC Microtec, and to perform a communications experiment utilizing the Iridium and Orbcomm satellite phone network. 1) 2) 3) 4) 5)
TechEdSat will be launched to the ISS (International Space Station) aboard the HTV-3 module of JAXA on 21 July, 2012. From there, it will be deployed into LEO (Low Earth Orbit) using the JAXA J-SSOD (JEM-Small Satellite Orbital Deployer) deployer, from the JEM/Kibo.
Specific mission goals are:
· To demonstrate the SPA hardware and software from AAC Microtec
· Investigate both Iridium and Orbcomm satellite-to-satellite communication as a method of eliminating the requirement for a physical ground station in nanosatellite missions.
· Demonstrate the capabilities of the JAXA J-SSOD aboard the ISS, and be one of the first CubeSats to be deployed from the ISS. J-SSOD is new small satellite deployment system from ISS using the JEM robot arm.
Figure 1: Illustration of the deployed TechEdSat CubeSat (image credit: SJSU, NASA/ARC)
The benefits from the TechEdSat investigation include a demonstration of rapidly reconfigurable nanosatellite technologies for the development of future spacecraft. In addition, such a demonstration may ultimately reduce costs for nanosatellite bus development, eliminate the need for physical ground station interfaces for nanosatellites, and prove that the ISS is a reliable platform for CubeSat deployment.
TechEdSat has a standard 1U CubeSat form factor, using a skeletonized Pumpkin structure, with a size of 10 cm x 10 cm x 11.3 cm and a mass of 1.2 kg.
Avionics: Use of the radiation tolerant SPA (Space Plug-and-Play Avionics) architecture from AAC Microtec. The main characteristic of the TechEdSat CubeSat architecture is the division between two operational modes which is a novel approach towards efficient power usage on small satellites. While the basic operation of the satellite such as power management, housekeeping and beacon transmission requires being active during all times, more computationally demanding payloads with higher power consumption can be operated at a lower duty cycle. 6)
As the nominal mode architecture is based on the SPA standard, it is ensured that the test and integration of the nominal mode system is simplified tremendously which lowers the development cost and allows for rapid response missions.
Each of the used avionics components is available as a flight model version which includes additional protection against single event effects thanks to the implementation of error correcting code on all memories and triple modular redundancy on logic gates in the used FPGAs among others. Figure 2 is a block diagram of the SPA architecture.
Figure 2: Block diagram of the TechEdSat CubeSat (image credit: AAC Microtec)
Safe mode system: The safe-mode system consists of the power system, a safe-mode computer implemented using an AAC Microtec nanoRTUTM and a 400 MHz radio transmitter. The function of the safe-mode computer is to handle the satellite commissioning, monitor the overall satellite health status and to transmit periodic messages over the 400 MHz radio link containing the monitored data. The safe-mode system power consumption is very low and allows the batteries of the satellite to be recharged while it is in operation (Figure 3).
Figure 3: Simplified safe mode system block diagram (image credit: AAC Microtec)
The transmission of data via the 400 MHz radio link and power on the nominal mode system is only performed if the battery charge level, which is monitored as part of the system health status, is above certain thresholds. The turn-off thresholds are lower to provide hysteresis. This allows the battery to be recharged even if the average power consumption of the nominal mode system exceeds the available power from the solar arrays.
In case the safe mode computer should fail, two additional safety features are built into the safe mode system. The first is an external watchdog which will power cycle the safe mode computer unless it continuously sends a signal to the watchdog. The second feature is the under voltage lock out which will disable everything in the satellite except the battery charge regulator in case the battery voltage becomes critically low. This is to protect the satellite from complete failure in case both the watchdog and the safe mode computer should fail, or from any failure mode with an excessive current draw.
Nominal mode system: The nominal-mode system power is protected by a latching current limiter which is controlled and monitored by the safe-mode system. This allows the safe-mode computer to power on and off the nominal mode system and it also provides a level of robustness as any part of the nominal-mode system can fail in short circuit without interrupting the operation of the safe-mode system.
The nominal-mode system main computer is the AAC Microtec OBCliteTM, an OpenRISC based 32-bit computer using Linux as its operating system. On top of Linux, the SDM (Satellite Data Model) is executed which allows the nominal mode system to use the SPA standard for communication between the main computer and the payloads. In this case, the SPA-1 standard which is based on I2C communication was chosen due to its low-power characteristics. The main computer also controls the power (on/off) for the individual communication payloads.
Figure 4: Schematic view of the nominal mode subsystem (image credit: AAC Microtec, Ref. 6)
EPS (Electric Power Subsystem): A PnP scalable power architecture is used providing the following features (Figure 5):
· SPA (Space Plug-and-Play Avionics) compatible
· RadHard with short circuit protections of LCLs (Latch-up Current Limiters)
· Galvanic isolation
· Li-ion BCD (Battery Charge/Discharge), a Canon BP-930 Li-ion battery
· Solar array management
· Safe mode and mission mode.
Figure 5: The PnP scalable power architecture (image credit: AAC MicroTec)
The solar array provides an average power of 1.8 W. The power consumption in nominal mode is 3.9 W (0.35 W in safe mode).
Figure 6: Photo of the TechEdSat engineering development unit (image credit: NASA/ARC)
RF communications: UHF and VHF communications with monopole antennas (and a 1600 MHz patch antenna).
- StenSat radio beacon (437.465 MHz beacon transmitting 1 W to 1/4 wave monopole). Commanding is via the commercial networks and there is a 2 week watchdog timer to stop the beacon in the event of no commands being received.
- Quake Global Q1000 Modem (communications with Orbcomm constellation spacecraft)
- Quake Global Q9602 Modem (communications with Iridium constellation spacecraft).
TechEdSat features a StenSat amateur beacon with a 12 cm antenna for communications. Four rod magnets stabilized the satellite so that the Orcomm antenna faced the sky while the beacon antenna looked down.
Launch: TechEdSat was launched as a secondary payload on July 21, 2012 from Tanegashima, Japan aboard JAXA's HTV-3 (H-II Transfer Vehicle-3) ISS resupply mission. The HTV-3 module was launched by the H-IIB launch vehicle of Mitsubishi Heavy Industries. The HTV-3 module is nicknamed Kounotori-3. 7) 8)
Further CubeSats on this mission are:
· Raiko (Drum of the Thunder), a 2U CubeSat of Wakayama University, Japan
· FITSat-1 (Fukuoka Institute of Technology), Fukuoka Prefecture, Japan
· We-Wish of Meisei Electric Co., Ltd., Tokyo, Japan
· F-1 (F Space Laboratory) of FPT University, Hanoi, Vietnam.
In addition, the J-SSOD system will be delivered on this flight to the ISS and installed in JEM/Kibo. The deployment of all CubeSats is planned for Sept. 2012.
Orbit: The ISS is in a near-circular orbit in the altitude range of 350 -400 km, inclination = 51.6o.
Deployment of CubeSats:
The deployment from the fairly low orbit of the ISS will limit the operational life of the CubeSat to a few months due to the encounter of atmospheric drag.
On October 4, 2012 five CubeSats were successfully deployed from the new J-SSOD (JEM-Small Satellite Orbital Deployer) aboard the ISS. The first pod contained RAIKO and We-Wish, while the second pod contained FITSat-1, F-1 and TechEdSat. 9) 10)
Figure 7: Artist's rendition of the CubeSat deployment from JEM/Kibo (image credit: JAXA)
Figure 8: An Expedition 33 crew member captured this image as three CubeSats were released from the ISS with the solar array structure of the ISS in the background (image credit: NASA) 11)
Figure 9: High resolution image of three CubeSats after deployment with planet Earth as the background. TechEdSat is the satellite to the right (image credit: NASA) 12)
The payloads that were integrated in the first satellite built using this architecture, TechEdSat-1, was a Q1000 Orbcomm modem and a Q9602 Iridium modem. The goal of this satellite is to demonstrate ISL (Inter-Satellite Communication) from a 1U CubeSat (Ref. 6).
Each integrated payload is connected to an AAC Microtec nanoRTUTM which is used to enable the SPA communication between the payloads and the main computer. This way, payloads that do not support the SPA standard can be easily adapted to function in a plug-and-play system.
The Satellite Data Model software on the OBCliteTM consists of two modules, the SPA-1 manager which handles the low-level SPA-1 protocol on the I2C links and the data manager, which is responsible for setting up the internal data paths between payloads and software applications. In addition, several SPA application modules are run which take care of the payload data processing:
· FDIR (Fault Detection, Isolation and Recovery) application which queries the housekeeping data from all entities on the satellite and publishes exception notifications if exceptions in the housekeeping data are observed.
· Data Gatherer application which collects all data from all connected payloads and stores the data in a file.
· Comm application which accesses the data file which was created by the Data Gatherer creates data packets and prepares them for transmission over one of the two inter-satellite communication links.
Status of mission:
· In summary, the TechEdSat-1 mission has been very successful. The project has verified the error correcting code of the fault tolerant avionics on orbit. SPA has been demonstrated and the project has also demonstrated the rapid integration possibilities using the avionics concept. 13)
The AAC Microtec group has shown that it can build a satellite in 4 months. During the mission it was also confirmed that AAC Microtec's components stand the extreme conditions of a rocket launch and operations in space. The key factors for the success of the mission were the good and fruitful cooperation with NASA, the fantastic commitment from our dedicated employees, and the support from the Swedish National Space Board. 14)
The results of this mission mark a stepping stone for the company. Trust into satellite avionics is built up through flight heritage - the actual use of technology under real mission conditions. The results of the TechEdSat mission are being used in the design of the next satellite, ORS-3/STPSat-3 (Operationally Responsive Space-3/Space Test Program Satellite-3) of DoD, which is 6 times bigger than TechEdSat and it will be launched in the fall of 2013.
· The TechEdSat CubeSat reentred and decayed in Earth's atmosphere on May 5, 2013. 15) A short mission life of 7-8 months was expected due to the relatively low deployment altitude of < 400 km from the ISS.
· Preliminary mission results (Ref. 6): After six months of continuous operations of the safe mode subsystem on orbit (in April 2013), it can be concluded that the mission succeeded. The nanoRTUTM safe mode computer has not encountered any problems so far and is regularly sending data packages through the 400 MHz radio.
Thanks to several radio amateurs around the world, regular beacon messages, which were sent out over the amateur radio band, were forwarded to the TechEdSat development team. These beacon messages contained information about the health status of the satellite such as temperatures, voltages, single event effects counters, etc. AAC Microtec is currently analyzing these packets in order to draw conclusions from the long-term operation of the avionics on orbit which will improve future generations of the power and data handling subsystems.
- As an example, the received temperature curve shows an interesting periodicity which will be further investigated.
Figure 10: Plot of the CubeSat temperature during the first 154 days on orbit (image credit: AAC Microtec)
- Another very interesting mission result is that one single event effect on the internal SRAM was detected and corrected by the error detection and correction procedure of the nanoRTUTM after 87 days of operation. This shows that the single event mitigation functionality in the digital parts of the AAC Microtec avionics products functions as expected (Ref. 6).
· On December 27, 2012, TechEdSat reached 2000 hours of continuous operations.
· TechEdSat came to life according to plan 60 minutes after deployment and has now demonstrated the function of AAC's pioneering miniaturized electronics for low cost satellites by sending down data. 16)
Some background: The TechEdSat CubeSat was constructed in less than 6 months by a team from NASA Ames Research Center, San Jose State University and AAC Microtec [built within only 6 months from mission capture to launch pad delivery thanks to the use of AAC Microtec's RIA (Rapid Integration Architecture) products]. What makes TechEdSat unique is that NASA uses electronics from Swedish AAC Microtec for control and operation of the satellite. Normally the countries only exchange scientific instruments and data. AAC Microtec was chosen for its innovative architecture and product portfolio for autonomous systems, which is based on PnP (Plug-n-Play) protocols, and the company's leading electronics integration ability.
In June 2011, the SNSB (Swedish National Space Board) and NASA signed a ten year collaboration agreement, concerning the development, testing and use of small satellites, with the Uppsala-based company AAC Microtec as the designated strategic supplier of technology solutions. Under the terms of agreement, SNSB and NASA make equal investments in their respective countries and share the end results on equal terms, with the stipulation that NASA handles trials and testing, and SNSB supplies the technology through AAC Microtec.
2) Fredrik Bruhn, "TechEdSat - CubeSat Technology demonstration mission featuring Plug-and-play and radiation hardened electronics," 9th Annual Spring CubeSat Developer's Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2012/Bruhn_TechEdSat.pdf
4) Rachel Hoover , "NASA, JAXA to Send Small Satellite into Space from Space Station," NASA/ARC, Release: 12-52AR, July 18, 2012, URL: http://www.nasa.gov/centers/ames/news/releases/2012/12-52AR.html
5) "Technology Education Satellite (TechEdSat)," NASA, July 31, 2012, URL: http://www.nasa.gov/mission_pages/station/research/experiments/
6) Henrik Löfgren, Jan Schulte, Per Selin, Johan Bäckström, Jorge Freyer, Fredrik Bruhn, "TechEdSat - A minimal and robust 1U cubesat architecture using plug-and-play avionics," Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013
7) "Launch of the H-II Transfer Vehicle "KOUNOTORI3" (HTV3) Aboard the H-IIB Launch Vehicle No. 3," JAXA Press Release, March 21, 2012, URL: http://www.jaxa.jp/press/2012/03/20120321_h2bf3_e.html
8) "Cube Satellite Launches to International Space Station," SJSU, URL: http://blogs.sjsu.edu/today/2012/
10) Ann Marie Trotta, Rachel Hoover, "NASA's TechEdSat Launches from International Space Station," NASA News, Oct. 4, 2012, URL: http://www.nasa.gov/centers/ames/news/releases/2012/12-72AR.html
11) "SJSU Satellite Launches From International Space Station," NASA, Oct. 4, 2012, and SJSU Oct. 10, 2012, URL: http://blogs.sjsu.edu/today/2012/
13) Information provided on June 3, 2013 by Jan Schulte of AAC Microtec, Uppsala, Sweden.
14) "AAC Microtec celebrates successful satellite mission," AAC Microtec Press Release, June 17, 2013, URL: http://www.aacmicrotec.com/index.php?option=com_content&view=article&id=95&Itemid=215
16) "Swedish breakthrough in space on NASA satellite with electronics from AAC Microtec," AAC Microtec, Oct. 11, 2012, URL: http://www.aacmicrotec.com/
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.