KySat-2 (Kentucky Satellite-2)
KySat-2 is Kentucky’s second satellite to be designed, built, and tested by students at SSL (Space Systems Laboratory) of the University of Kentucky (UKy). The primary mission is educational outreach to both the university students who worked on the satellite and to K-12 students and teachers, ultimately providing opportunities for hands-on learning in the STEM (Science, Technology, Engineering, and Math) disciplines. A goal of the KySat-2 project is to take a picture of the Earth while in orbit and return the picture to the ground. 1)
KySat-2 is a 1U CubeSat to fulfill the education and public outreach mission of the original KySat-1 CubeSat that was lost during a launch vehicle failure of ELaNa-1 and was a secondary payload of NASA's GLORY mission (launch of the Taurus-3110 vehicle on March 4 2011).
Partnerships: Kentucky Space UKy/SSL formed for KYSat-2 a partnership with COSMIAC (Configurable Space Microsystems Innovations & Applications Center), a congressionally supported space electronics center established at the University of New Mexico in Albuquerque, NM.
• Develop a standard bus, K-Bus (Kentucky-Bus), for communications for small spacecraft
• Develop a standard bus for power for small spacecraft
• Combine these into K-Bus
- Communications leverage SPA (Space Plug-and-Play) SDM-Lite (Satellite Data Model-Lite) infrastructure. SDM-Lite specifically targets limited resource SPA-1 based networks.
- Modular plug-and-play power system.
- SPA-based SDM-Lite developed by COSMIAC and the UKY/SSL.
KySat-2 will demonstrate key technologies developed by University of Kentucky and Morehead University students. These include a distributed network computing architecture, power and radio systems, and a “stellar gyroscope” for attitude determination. If successful, KySat-2 will serve as a standard on which to base future satellites built by the lab.
Figure 1: KySat-2 CubeSat in on-orbit configuration with deployed solar panels (image credit: UKy/SSL)
KySat-2 is a standard 1U CubeSat with dimensions of 10 cm x 10 cm x 11.3 cm (launch configuration) designed primarily as a test bed for the KySat standard bus with a concept of operations. The K-Bus is combination of modular, plug-and-play data and power bus for small spacecraft.
ADCS (Attitude Determination and Control Subsystem): The ADCS is designed for CubeSats on a standard PC104 board. In its basic configuration, it integrates a high sensitivity magnetometer, up to 6 sun sensors, 3 axis MEMS gyroscopes, and 3 magnetic torque rods as a 3-axis magnetic attitude control system. In its full configuration for improved attitude knowledge and pointing accuracy, a GPS receiver, a stellar gyroscope and an ADCS control computer are added on a daughter board, still within the PC104 height constraints. A momentum wheel or three reaction wheels can be added from a third party supplier. 6)
Figure 2: Block diagram of the ADCS (image credit: Uky/SSL)
Stellar gyroscope: KySat-2 will demonstrate the stellar gyroscope concept in orbit. It is a visual attitude propagation approach being researched at the University of Kentucky. The concept lies in tracking the motion of features in the camera’s view (such as stars) to estimate the changes in the satellite’s orientation. Similar to how an optical mouse observes a mouse pad to keep track of it’s position, the stellar gyroscope tracks the rotational changes of the satellite in 3 degrees of freedom. On KySat-2, the digital signal processing capabilities of the on-board the IPU (Image Processing Unit) will be utilized to acquire and process star field images to demonstrate this technology. Visual attitude propagation addresses attitude determination challenges associated with satellite miniaturization, and in turn increasing the utility of miniature spacecraft, such as CubeSats (Ref. 1).
Figure 3: Photo of the stellar gyroscope (image credit: UKy/SSL)
The stellar gyroscope complements the MEMS rate gyroscopes in eclipse to maintain an accurate estimate of attitude. However, in order to benefit from accurate propagation in eclipse, accurate knowledge in sunlight is necessary. The system utilizes sun sensors accurate within 0.5º developed by SSBV (Satellite Services B.V.), as well as a high-accuracy magnetometer that produces magnetic field vector measurements to around 1 degree of accuracy in combination with an IGRF (International Geomagnetic Reference Field) magnetic model and good knowledge of the position in orbit, which is provided by the GPS receiver. This combination results in a high quality estimate of attitude in sunlight.
Passive magnetic stabilization: KySat-2 is equipped with a passive attitude control scheme. This passive control technique uses permanent magnets and magnetic hysteresis material fixed to the chassis of KySat-2. The permanent magnets will provide torque in attempts to align with Earth’s magnetic field (in the same fashion that a magnetic compass needle points to magnetic North). The permanent magnets will be mounted to the spacecraft’s chassis in such a way that when aligned with Earth’s magnetic field, KySat-2's camera will point at Earth while over the Northern Hemisphere, and out into space while over the Southern Hemisphere.
Permanent magnets provide the small amount of torque needed to keep the spacecraft oriented correctly, but in the vacuum of space, there is no damping effect (such as air resistance as we have on the surface). Because of this, KySat-2 would oscillate around it’s targeted orientation rather than settle into it smoothly. Also, permanent magnets can only provide control over two axes while the third axis is uncontrolled and free to rotate. To alleviate these problems, KySat-2 is also equipped with hysteresis (memory) material. This material “memorizes” the current magnetic field and thus resists changes in KySat-2's orientation. This effect is small, and much less assertive than the permanent magnets, but it provides the needed damping effect to stabilize KySat-2 on the two control axes, and resist changes on the uncontrolled axis as well.
Figure 4: Schematic view of the KySat-2's orientation in orbit (image credit: UKy/SSL)
IPU (Image Processing Unit): The IPU is based on a single board computer running Linux. University of Kentucky students have written software to provide the board with image capture and signal processing capabilities. The camera is composed of a 5 megapixel CMOS sensor and a 16mm S-Mount lens. The system is designed to be capable of star field imaging, and will be used to support research in small satellite attitude determination systems. Camera exposure control allows the IPU to image objects at varying levels of illumination, such as the Earth and its horizon. The IPU performs image acquisition, as well as several image processing and compression algorithms to maximize data return from orbit over the narrow radio down-link.
C&DH (Command and Data Handling) subsystem: The C&DH’s purpose is to command the subsystems of KySat-2. This includes commanding the IPU to perform Earth and star imaging operations, commanding the radio to beacon, receiving ground commands from the radio, transmitting data, changing settings, and commanding the EPS to power on/off the different subsystems. The C&DH is also responsible for data collection and storage from the IPU, gyroscope, magnetometer, and temperature sensors on-board. The design philosophy of the C&DH is to utilize a distributed architecture that splits interfacing and processing into two separate functions. The processing core of the C&DH interprets ground commands and schedules actions, whereas small form-factor, low power-consumption micro controllers are responsible for communicating with the satellite’s other subsystems. This design is an application of SSL’s partnership with COSMIAC to create the SDM-Lite, which is an adaptation of the SPA (Space Plug-and-Play Avionics) standard, designed to rapidly integrate spacecraft.
EPS (Electric Power Subsystem): The EPS provides power regulation for other satellite subsystems using 18650 Lithium-ion batteries. The system utilizes DET (Direct Energy Transfer) solar array interfaces to power the satellite while in orbit.
UHF radio: KySat-2 is equipped with an Astronautical Development Lithium 1 UHF Radio. As a receiver, the radio will receive RF signals from antennas and filter out the information. As a transmitter, the radio will receive data from the C&DH and transmit it out as RF signals. Communications with the C&DH subsystem is being performed using the UART protocol. The radio is directly connected to the battery for the transmitter and requires 3.3V power from the EPS. The antennas on the KySat-2 have circular polarization to provide a constant RF signal despite satellite orientation.
• Frequency: 437.405 MHz
• Modulation Scheme: FSK
• Data Rates: 9600 Baud
• Protocol: AX.25
• Output Transmit Power: ~1 W
• Beacon Period: 15-45 seconds
• Callsign: KK4AJJ.
Figure 5: Photo of the UHF radio (image credit: UKy/SSL)
Figure 6: Exploded view of KySat-2 (image credit: UKy/SSL)
Figure 7: A distributed C&DH architecture for KYSat-2 (image credit: UKy/SSL)
Figure 8: KySat-2 hardware architecture (image credit: UKy/SSL)
Figure 9: Illustration of the board stackup (image credit: UKy/SSL)
Launch: KYSat-2 was launched on Nov. 20, 2013 (01:15:00 UTC), as a secondary payload on the ORS-3 (Operationally Responsive Space-3) mission of AFRL (Air Force Research Laboratory). The launch site was MARS Mid-Atlantic Regional Spaceport), located at NASA's Wallops Flight Facility,Wallops Island, VA. The launch vehicle was a Minotaur-1 of OSC (Orbital Sciences Corporation). The primary payload on ORS-3 was STPSat-3 (Space Test Program Satellite-3), a minisatellite mission of the USAF-SMC. 7) 8) 9)
Note: The ELaNa-4 CubeSats were originally manifested on the Falcon-9 CRS-2 flight (launch of CRS-2 on March 1, 2013). However, when NASA received word that the P-PODs on CRS-2 needed to be de-manifested, NASA's LSP (Launch Services Program) immediately started looking for other opportunities to launch this complement of CubeSats as soon as possible. 10) 11) 12)
Orbit: Near-circular orbit, altitude of 500 km, inclination = 40.5º.
Secondary Payloads: The secondary technology payloads on this flight consist of 26 experiments comprised of free-flying systems and non-separating components (2 experiments). ORS-3 will employ CubeSat wafer adapters, which enable secondary payloads to take advantage of excess lift capacity unavailable to the primary trial. 13) 14)
NASA's LSP (Launch Services Program) ELaNa-4 (Educational Launch of Nanosatellite-4) will launch eight more educational CubeSat missions. The ELaNa-4 CubeSats were originally manifest on the Falcon-9 CRS-2 flight. When NASA received word that the P-PODs on CRS-2 needed to be de-manifested, LSP immediately started looking for other opportunities to launch this complement of CubeSats as soon as possible. 15)
Table 1: ORS-3 manifested CubeSats & Experiments (Ref. 12)
ORS and CubeStack: 16)
• ORS (Operationally Responsive Space) partnered with NASA/ARC and AFRL to develop & produce the CubeStack
• Multi CubeSat adapter provides “Low Maintenance” tertiary canisterized ride capability
• ORS-3 Mission: Will fly 2 CubeStacks in November 2013. This represents the largest multi-mission launch using a Minotaur I launch vehicle (26 free flyers, 2 experiments).
Figure 10: Illustration of the CubeStack, (consisting of wafers) configuration (image credit: ORS, Ref. 12)
The CubeStack adapter structure is a design by LoadPath and Moog CSA Engineering. 17)
Figure 11: Photo of the ORS-3 launch configuration with STPSat-3 on top and the integrated payload stack at the bottom (image credit: AFRL)
• The stations at both Morehead State and the University of Kentucky are both working to get consistent uplink commands to the spacecraft. 18)
• According to Kentucky Space, data packets from KySat-2 were received on its first orbit in Montana and in the UK. The decoded packets showed the batteries at 12.47 V and the C&DH drawing 90 mA, which is nominal operation. 19)
Sensor complement: (Camera, Additive Manufacturing/3D Printing)
The stellar gyroscope on the ADCS system consists of a low-cost camera assembly and processing hardware and is designed to require little mass and volume. The camera is based on the Aptina MT9P031 5 Mpixel CMOS sensor and a miniature S-mount lens with a focal length of 16 mm. This configuration results in a 15° x 20.2° FOV. Table 2 summarizes the camera specifications. As it is only to be used in the orbital eclipse phase in this application, it is not required to operate in sun light and does not need a baffle.
The camera is designed to register stars of magnitude 4 and brighter. With the selected optics, field of view, and an exposure time of 800 ms, at least 4 stars are visible in 97% of the sky, and at least 3 stars are visible in 99% of the sky.
Table 2: Parameters of the stellar gyroscope
By tracking the motion of stars in the camera field of view, and solving the relative attitude problem, the stellar gyroscope propagates the spacecraft attitude in 3 degrees of freedom, as long as the camera is viewing the sky.
Figure 12: Photo of the single board Linux computer running OpenCV image processing library and the camera system (image credit: UKy/SSL)
Additive Manufacturing/3D Printing and Materials for Space Applications
There were several 3D printed components on the KySat-2 made by CRP USA from CRP Technology’s proprietary material Windform XT 2.0. One of the subsystems, is the camera systems that acts as an attitude determination system called Stellar Gyro. The 3d printed parts, were produced using the additive manufacturing technology Selective Laser Sintering and Windform XT 2.0 material. The additive manufactured process 3D printed the mounting hardware for the camera system, extensions for the separation switches, clips for holding the antennas in their stowed position, and the mounting bracket for the on board batteries. The process and the material were critical to achieve the right components for KySat-2. 20) 21)
CRP USA together with CRP Technology produced five Windform XT 2.0 parts that are incorporated into the deployable solar panels on the KySat-2; camera annulus, lens cover, deployable extensions, antenna clips, and battery holders. One of the highest levels of Windform materials, Windform XT 2.0 is a high performance material filled with carbon fiber and offers maximum mechanical performance for 3D printed parts. The material combines maximum toughness and robustness, yet produces an extremely light, final part that doesn’t impact the overall production weight of the KySat-2 unit. Utilizing the additive manufactured technology, SLS (Selective Laser Sintering), and Windform XT 2.0 material final parts for small productions can easily replace parts that are usually produced with traditional technology, or are otherwise unmanufacturable.
Figure 13: 3D printed mounting hardware for camera system built with Windform XT 2.0 (image credit: CRP Group)
1) “KYSat-2,” SSL (Space Systems Laboratory), University of Kentucky, URL: http://ssl.engineering.uky.edu/missions/orbital/kysat-2/
2) Jason Rexroat, Chris Mitchell, Max Bezold, Marc Higginson-Rollins, Steve Alvarado, Zachary Jacobs, Samir Rawashdeh, James Lumpp, “ A Distributed Command and Data Handling Architecture for KYSat-2,” 10th Annual CubeSat Developers’ Workshop 2013, Cal Poly, San Luis Obispo, April 24-26, 2013, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2013/Rexroat_KYSat-2.pdf
3) Chris Mitchell, Zachary Jacobs, Max Bezold, James Lumpp, “Implementation of SDM-Lite for Space Plug and Play Avionics (SPA) CubeSats,” 10th Annual CubeSat Developers’ Workshop 2013, Cal Poly, San Luis Obispo, April 24-26, 2013, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2013/Mitchell_SPA_CubeSats.pdf
4) Zachary A. Jacobs, “Providing a persistent Space Plug-and Play Avions Network on the International Space Station,” Theses and Dissertations-Electrical and Computer Engineering, Paper 16, University of Kentucky, March 2013, URL: http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1016&context=ece_etds
6) Samir A. Rawashdeh, James E. Lumpp, Jr., James Barrington-Brown, Massimiliano Pastena, “A Stellar Gyroscope for Small Satellite Attitude Determination,” Proceedings of the 26th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-IX-7, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1078&context=smallsat
7) “Orbital Successfully Launches Minotaur I Rocket Supporting ORS-3 Mission for the U.S. Air Force,” Orbital, Nov. 19, 2013, URL: http://www.orbital.com/NewsInfo/release.asp?prid=1876
8) Patrick Blau, “Minotaur I successfully launches STPSat-3 & record load of 28 CubeSats,” Spaceflight 101, Nov. 20, 2013, URL: http://www.spaceflight101.com/minotaur-i-ors-3-launch-updates.html
10) Garrett Lee Skrobot, Roland Coelho, “ELaNa – Educational Launch of Nanosatellite Providing Routine RideShare Opportunities,” Proceedings of the 26th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-V-5
11) Garret Skrobot, “ELaNA - Educational Launch of Nanosatellite,” 8th Annual CubeSat Developers’ Workshop, CalPoly, San Luis Obispo, CA, USA, April 20-22, 2011, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2011/21_Skrobot_ELaNa.pdf
12) Peter Wegner, “ORS Program Status,” Reinventing Space Conference, El Segundo, CA, USA, May 7-10, 2012, URL: http://www.responsivespace.com/.../Dr.%20Peter%20Wegner.pdf
13) Peter Wegner, “ORS Program Status,” Reinventing Space Conference, El Segundo, CA, USA, May 7-10, 2012, URL: http://www.responsivespace.com/.../Dr.%20Peter%20Wegner.pdf
14) Joe Maly, “ESPA CubeSat Accommodations and Qualification of 6U Mount (SUM),” 10th Annual CubeSat Developer’s Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 24-25, 2013, URL: http://www.cubesat.org/images/stories/workshop_media/DevelopersWorkshop2013/Maly_MoogCSA_ESPA-SUM.pdf
15) Garrett Lee Skrobot, Roland Coelho, “ELaNa – Educational Launch of Nanosatellite Providing Routine RideShare Opportunities,” Proceedings of the 26th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-V-5
16) “CubeStack: CubeSat Space Access,” 9th Annual Spring CubeSat Developers’ Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2012/Maly_CubeStack.pdf
17) Joe Maly, “6U Mount for CubeSats on ESPA,” CubeSat 9th Annual Summer Workshop, Logan UT, USA, August 11-12, 2012, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/SummerWorkshop2012/Maly_6U_ESPA_Mount.pdf
18) “KySat-2 Update: Beaconing Strong,” Kentucky Space, URL: http://www.kentuckyspace.com/index.php?option=com_content&view=article&id=601:kysat-2-beaconing-strong&catid=45:kentuckyspaceblog&Itemid=194
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.