Hermes CubeSat Mission
Hermes is a CubeSat technology demonstration mission of the COSGC (Colorado Space Grant Consortium) at the University of Colorado at Boulder, CO, USA. The project is completely student student-led & student student-run, the team consists mostly of undergraduate students.
The primary objective is to improve CubeSat communications through the on-orbit testing of a high data-rate communication system (S-band) that will allow the downlink of large quantities of data, making CubeSat imaging or high-data quantity science easily feasible. - In view of the primary mission goal, the project is named after Hermes, the Greek messenger god.
A further goal of the project is to create a reproducible and extensible spacecraft bus in support of future missions. This will allow future COSGC CubeSat teams to focus more on the science aspects of low-earth orbit spaceflight, rather than the logistics of designing a spacecraft. 1) 2) 3) 4)
Figure 1: Artist's view of the Hermes CubeSat in orbit (image credit: COSGC)
The spacecraft conforms to the CubeSat standard in volume (10 cm side length) and mass (≤ 1 kg). The bus structure was manufactured in-house; it features an aluminum 6061 exoskeleton design, a 5 PCB (Printed Circuit Board) internal stack configuration, and an aluminum 6061 battery box. The exterior of the bus is covered with 6 solar panels fastened with solar panel clips.
Figure 2: Illustration of the CubeSat bus structure (image credit: COSGC)
Figure 3: Photo of the interior bus configuration (image credit: COSGC)
ADCS (Attitude Determination & Control Subsystem): Use of passive magnetic control.
- Two AlNiCo Cast-5 permanent magnets are aligned with the antenna axis to provide 2-axis actuation. A magnetic hysteresis material, either in the form of rods or plates will be used for magnetic damping to prevent oscillation about the spin axis.
- 0.005 A/m2
- Size of 25 mm x 4.8 mm
- Featuring high strength and low mass.
The attitude is measured with a 3-axis magnetometer of Honeywell (HMC2003).
Figure 4: Illustration of the 3-axis magnetometer (image credit: Honeywell)
CDH (Command & Data Handling) subsystem: The CDH subsystem is based on the microchip PIC24H MPU utilizing the Pumpkin Salvo RTOS (Real-Time Operating System). The CDH features:
• I2C communication bus
• Triple redundancy on critical components
- Three SD cards for data integrity
- Three RTCs for accurate timing
• Ability to reprogram all satellite software
- Two stage boot loader
- First stage checks second stage and main code section
- Second stage checks first stage
- Main code checks communications system.
EPS (Electrical Power Subsystem): EPS is designed for high efficiency and extensibility featuring a completely autonomous base operation (does not depend on CDH for charging/power). A Li-ion / Li-Poly battery system is implemented providing automatic cell balancing, the ability to charge7discharge both batteries in parallel, and has a fully autonomous protection circuitry. The power regulation and distribution system features:
- 3.3 V, 5 V, and 7.4 V outputs to subsystems
- Less than 5% ripple on all outputs
- All regulation is performed with switching regulators
- The system can enable or disable all outputs other than 3.3 V for CDH
- Provision of redundancy on critical converters.
Figure 5: Electrical power functional block diagram (image credit: COSGC)
Launch: Hermes (University of Colorado at Boulder), KySat-1 of Kentucky Space, and E1P-1 (Explorer-1 PRIME-1) of Montana State University, are secondary payloads (all CubeSats) and part of the ELaNa (Educational Launch of Nanosatellites) initiative of NASA. 5) 6) 7)
Unfortunately, the launch of the Glory spacecraft, along with the three secondary payloads, failed to reach orbit and ended in the Pacific Ocean. Telemetry indicated the fairing, the protective shell atop the Taurus XL rocket, did not separate as expected about three minutes after launch. NASA has begun the process of creating a Mishap Investigation Board to evaluate the cause of the failure. 8)
Use of the P-POD (Poly-Picosatellite Orbital Deployer), the standardized deployer system of CalPoly for the deployment of all CubeSats.
Orbit: Sun-synchronous circular orbit, altitude = 705 km, inclination = 98.2º.
Figure 6: Schematic view of the CubeSat operations concept (image credit: COSGC)
Sensor complement: (High Speed Communications)
The primary objective is to demonstrate the feasibility of high data throughput communications for imagery data. For this purpose the spacecraft utilizes the Microhard MHX-2400 S-band modem capable of data rates of up to 50 kbit/s.
Figure 7: Photo of the MHX-2400 S-band modem (image credit: COSGC)
The TT&C communications are implemented in half duplex in the UHF band.
• Uses a Yaesu VX-3R COTS (Commercial of-the-Shelf) radio
• In-house designed TNC (Terminal Node Controller), built around the ATMega 168 MCU, MX604 for D/A conversion, data rate of 1200 bit/s.
• Communication antennas
- HSCOM monopole antenna tuned to 2.4 GHz frequency range
- PCOM monopole antenna tuned to 437.425 MHz (UHF)
- Both antennas are constructed of spring steel with a Kynar cover.
Figure 8: Photo of the spacecraft showing both antennas (image credit: COSGC)
1) “Hermes CubeSat: Testing the Viability of High Speed Communications on a Picosatellite,” COSGC, CalPoly CubeSat Developers Workshop, April 28-29, 2009, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2009/10_Missions_2/4_Martin-Hermes.pdf
3) Justin J. Likar, Stephen E. Stone, Robert E. Lombardi, Kelly A. Long, “Novel Radiation Design Approach for CubeSat Based Missions,” Proceedings of the 24th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 9-12, 2010, SSC10-III-1
4) Colorado Space Grant Consortium, Kentucky Space, Montana State University, “NASA’s ELaNaProgram and it’s First CubeSat Mission,” Portland, ME, USA, Oct. 14-16,, 2010, URL: http://national.spacegrant.org/meetings/presentations/2010_Fall/19.pdf
5) NASA CubeSat launch,” January 2010, URL: http://southgatearc.org/news/january2010/nasa_cubesat_launch.htm
6) “NASA Cues Up University CubeSats for Glory Launch This Fall,” NASA, January 27, 2010, URL: http://www.pressreleasepoint.com/nasa-cues-university-cubesats-glory-launch-fall
7) Garrett L. Skrobot, “Project ElaNa and NASA’s CubeSat Initiative,” Proceedings of the CalPoly 2010 CubeSat Developer's Workshop, San Luis Obispo, CA, USA, April 21-23, 2010, URL: http://cubesat.calpoly.edu/images/cubesat/presentations/DevelopersWorkshop2010...
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.