Trailblazer CubeSat with SPA-1 Technology Demonstration
Trailblazer is a CubeSat mission of UNM (University of New Mexico), Albuquerque, NM, USA. The satellite will provide a proof-of-concept flight for an AFRL (Air Force Research Laboratory) sponsored bus design called SPA (Space Plug-and-play Architecture). The PnP (Plug-and-Play) type architecture is a capability that will allow for rapid development and delivery of satellite and defense systems similar to what is currently available in a home computer.
COSMIAC (Configurable Space Microsystems Innovations and Applications Center) at UNM is building the Trailblazer CubeSat. The Trailblazer mission has two key goals. The first is a proof-of-concept for SPA and the second is the flight of a series of space weather experiments. Both of these have key components for advancing the missions of NASA. UNM students are involved in the construction, testing and operation of the CubeSat project. 1) 2) 3) 4) 5)
SPA-1 (Space Plug-and-play Architecture)
SPA is defined as an interface-driven set of standards, encompassing hardware, software, and protocols, intended to promote the rapid affordable design and integration of spacecraft (busses and payloads). The SPA standards combine different data transport standards. 6)
In the parlance of “SPA”, a SPA-x interface refers to a connector that would be found on a SPA device allowing the device to join a plug-and-play (SPA) network. The suffix letter refers to a class of interface, driven usually by bandwidth. 7) 8)
• USB (Universal Serial Bus): SPA-U. This was he first SPA interface technology developed. This was because USB already embodied the essential features of plug-and-play (in the personal computer), and the other interface approaches largely did not exhibit plug-and-play characteristics. The data transport (of USB 1.1) is limited to 12 Mbit/s for the entire bus.
• SpaceWire: SPA-S (low voltage (5V) SpaceWire). SPA-S is based on the European SpaceWire standard, building upon the knowledge gained in SPA-U to add the needed plug-and-play protocols. Data rates/link of 400~600 Mbit/s can be supported.
• Optical: SPA-10, also known as SPA-O. SPA-10 is an optical fiber interconnection --in the definition/experimentation phase as of 2010. SPA-O extends the limited transport bandwidth of copper-based transports through the addition of an optical transport system consisting of a number of single- or multi-mode fibers (e.g., twelve) with an industry standard connector (e.g., "MT"). To simplify the ability to accommodate arbitrary wavelengths and protocols, SPA-S is retained in SPA-O as a control plane (as well as electrical power and synchronization signals), allowing for the structured and automated provisioning for a network of SPA-O components.
• I2C: SPA-1. SPA-1 has been commissioned to improve the efficiency of SPA for extremely simple devices.
The Trailblazer objective is to provide flight heritage to the SPA-1 protocol. A major goal is to prove the reliability and robustness of a SPA-based satellite in a space environment. Trailblazer will also show the ease of modifying current COTS parts to function on a SPA network.
Figure 1: Overview of some SPA domains (image credit: AFRL)
Table 1: Some background on SPA 9)
ASIM (Applique Sensor Interface Module): At the heart of SPA is ASIM. This module serves as the primary interface between the PnP network and the individual components. As such, it is essential that ASIM is optimized for a multitude of applications,; thus, there is no one-size-fits-all version. Based on a PIC microcontroller and a two wire data transfer protocol known as I2C, the SPA-1 ASIM is the most minimalistic of these versions. It is an ultra compact, and ultra low power option for those sensors that do not require a high bandwidth interface (Ref. 4).
There are currently three separate development teams working in close collaboration on SPA-1. Each individual effort concentrates on one of the three tiers of SPA-1. The first tier is the most simplistic, built completely from COTS (Commercial-off-the-Shelf) parts; this will be the most economical option for SPA-1. These ASIMS can be ordered for well under $100 per unit and serve the purpose of familiarizing component developers with the SPA-1 protocol. The second tier ASIM is again based on inexpensive COTS parts, but packaged in a 10 mm x 10 mm co-fired ceramic. It is electrically identical to the tier 1 ASIM. There are two companies working on the final tier of SPA-1: AAC Microtec (Sweden, see QuadSat) and Micro-RDC (New Mexico).
In the COTS versions discussed above, a physical PIC microcontroller is present in the design. The hardened parts have the unique advantage of being pin-for-pin and footprint compatible with the inexpensive COTS versions. This enables developers to design and test their boards with economical parts, then seamlessly transition to more expensive flight hardware.
SSM (SPA Services Manager): The SDL (Space Dynamics Laboratory) of USU (Utah State University) has developed a reference implementation of the SPA Standards, referred to as SSM. The SSM is responsible to component discovery, component registration, data centric queries, time distribution, and internal systems health monitoring and status reporting. These functions are accomplished by multiple SPA Subnet Managers, a CAS (Central Addressing Service) and a Lookup Service.
A SPA Subnet Manager is responsible for performing discovery on a subnet. On Trailblazer the SPA subnet that is being used is SPA-1. The SPA-1 Subnet Manager discovers each component on the SPA-1 subnet and reports it to the Lookup Service. The SPA-1 Subnet Manager also monitors the connection with each SPA-1 component and if it fails, alerts the Lookup Service which in turn alerts other components that are using the data products from the SPA-1 component that failed. This allows for fault tolerance and status monitoring.
The CAS assigns address blocks to SPA Subnet Manager. This allows to each subnet to have a unique address space ensuring that there are no duplicate addresses in the SPA Network. The Lookup Service is the core component that takes a components xTEDS (extended Transducer Electronic Datasheets) and allows other components to perform queries on it. This enables the data plug and play capabilities on SPA. If I have a component that needs temperature data, it would issue a query to the Lookup Service for temperature data, which in turn would respond with the addresses of all components capable of providing temperature data. The component would then select a data source and subscribe to the temperature data. These three core SSM components enable a system to use SPA (Ref. 4).
SPA-1 Trailblazer is a 1U CubeSat form factor with a mass of 1 kg. Use of COTS (Commercial off-the-Shelf) components. Each subsystem is either SPA compatible or has been modified to be compatible. It was the intent of the Trailblazer team to show how existing components can be converted to meet SPA standards.
Structure: The CubeSat features a Pumpkin structure and motherboard. To reduce mass, the Pumpkin skeletonized structure was chosen. The structure is a standard 1U enclosure (8051 aluminum) with space on top for the deployable antenna system. The structure contains two separation springs and two separation switches on the four corners of the legs.
Figure 2: Illustration of the 1U CubeSat structure (image credit: Pumpkin)
Spacecraft stabilization is provided by PMASS (Passive Magnetic Attitude Stabilization System) of ISIS (Innovative Solutions In Space); use of a permanent magnet and two orthogonal hysteresis rods for a reliable solution. The PMASS houses the permanent magnet and dampers for stabilization around the Z axis.
Figure 3: The ISIS PMASS configuration (image credit: ISIS)
The C&DH (Command & Data Handling) subsystem sits on top of the Pumpkin motherboard. C&DH is responsible for handling the SPA-1 network and processing the information passed along that network. The functions of a SPA manager are to discover new devices within the network, register those devices, parse through the xTEDs, and create a registry that maps out the network.
Figure 4: Illustration of the C&DH subsystem (image credit: Pumpkin)
EPS (Electric Power Subsystem). The EPS is provided by Clyde Space. An ASIM was added to the system so that it will function on a SPA-1 network. The EPS comes with an attached 20Whr battery. The power system also includes six high efficiency UTJ (Ultra Triple Junction) solar cells. This system will provide all the power information that will be used by the C&DH to make decisions relating to power usage. The system will use a battery charge management system for charging the lithium batteries. It will provide 3.3 V, 5 V and raw battery busses with over-current protection. The EPS is designed to fit into the 1U CubeSat, the solar panels are surface mounted.
Figure 5: The EPS with solar panels and batteries not shown (image credit: Clyde Space)
RF communications: UHF (435 MHz) downlink with a data rate of 9.6 kbit/s; the transmit power is 0.2 to 3 W. VHF is being used for the uplink. The subsystem consists of an AstroDev Helium 100 radio and an ISIS deployable antenna. Again, each component has been fitted with an ASIM to be SPA-1 compliant.
Figure 6: Schematic view of the various subsystems on SPA-1 Trailblazer (image credit: COSMIAC)
Launch: UNM’s Trailblazer satellite was launched on Nov. 20, 2013 (01:15 :00 UTC) as a secondary payload from the MARS (Mid-Atlantic Regional Spaceport) on Wallops Island, VA on a Minotaur-1 vehicle of OSC (Orbital Sciences Corporation). The launch was part of the ORS-3 (Operationally Responsive Space-3) enabler launch mission. The primary payload on this flight was STPSat-3. 10) 11) 12)
Orbit: Near-circular orbit, altitude = 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 2: ORS-3 manifested CubeSats & Experiments (Ref. 13)
ORS and CubeStack: 18)
• 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 8: Illustration of the CubeStack, (consisting of wafers) configuration (image credit: ORS, Ref. 13)
The CubeStack adapter structure is a design by LoadPath and Moog CSA Engineering. 19)
Figure 9: Photo of the ORS-3 launch configuration with STPSat-3 on top and the integrated payload stack at the bottom (image credit: AFRL)
Sensor/experiment complement: (Dosimeter, 3D PCB)
In addition to the SPA main mission, Trailblazer will also contain a SPA-1 Dosimeter to measure the effects of the SAA (South Atlantic Anomaly); and a SPA-1 rapid prototyped analog to ADC (Digital Converter) control board to test new advancements in 3D PCB (Printed Circuit Board) design for space applications.
The PnP (Plug-n-Play) dosimeter monitors the accumulation of ionizing radiation. This is accomplished with a depletion mode, p-channel RADFET from REM which is fabricated with a thick oxide to maximize its sensitivity to radiation. An ASIC from Nu-Trek Corporation, called the NuDose, is configured to force a specified current through the RADFET.
As radiation penetrates the oxide in the RADFET, electron-hole pairs are created and then separated via the electric field in the dielectric. The positive charge drifts toward the conduction channel and becomes trapped in the oxide. This modifies the threshold voltage of the device, and consequently changes the resistance between the source and drain electrodes.
The NuDose must maintain the selected current through the RADFET and thus, the voltage across the source and drain must increase to compensate for the increased channel resistance. This voltage is sent out to and external ADC on the SPA-1 ASIM. The ASIM can be configured to periodically transmit the 10 bit binary number corresponding to this voltage via the SPA-1 I2C bus. If a periodic message is not desired, the user can set up a request message that will only transmit data upon a request command (Ref. 4).
3D PCB (3-D Printed Circuit Board):
The experiment is a rapid prototyped IMU (Inertial Measurement Unit). The objective is to test a new 3-D PCB design methodology. A 3-D PCB design can improve the limited volume available found on each CubeSat mission by filling in the open space with critical electronics. In addition, the IMU may provide a low power, low cost solution to position acquisition. As with the rest of the satellite, these payloads have been fitted with an ASIM to make them SPA-1 compliant and to facilitate their use in future satellites.
The W. M. Keck Center for 3D Innovation of UTEP (University of Texas at El Paso) is a premier lab focusing on Additive Manufacturing, a technology that was invented almost 25 years ago in order to fabricate three-dimensional prototypes, but more recently is evolving to be used in manufacturing highly-customized 3D finished products. - Another term for 'Additive Manufacturing' is '3D printing' and an analogy can be made between printing a 2D picture from a home computer. As a common printer today will print a 2D image on paper, Additive Manufacturing allows one to print a CAD model of a 3D object (say a coffee mug for instance) layer by layer in a 3D printer and have the mug custom-fit - specifically with the imprint of the fingers in the handle. One could then print a customized coffee mug for each member of one's family with the same printer.
Figure 10: Illustration of a UTEP 3D project: Image credit: COSMIAC)
2) Craig Kief, Brian Zufelt, “Trailblazer, SPA and Radiation Testing Overview for CubeSat Workshop,” Summer CubeSat Developer's Workshop, USU, Logan, UT, August 6-7, 2011, URL: http://www.cosmiacpubs.org/pubs/Trailblazer_CSworkshop.pdf
3) Craig Kief, Brian Zufelt, “Trailblazer: Proof of Concept CubeSat Mission for SPA-1,” 8th Annual CubeSat Developers’ Workshop, CalPoly, San Luis Obispo, CA, USA, April 20-22, 2011, URL: http://www.cubesat.org/images/2011_Spring_Workshop/fri_p1.00_zufelt_cosmiac_cubesatws.pdf
4) Craig J. Kief, Brian K. Zufelt, Jacob H. Christensen, Jesse K. Mee, “Trailblazer: Proof of Concept CubeSat Mission for SPA-1,” AIAA Infotech, March 29-31, 2011, St. Louis, Missouri, USA, URL: http://www.cosmiacpubs.org/pubs/AIAA_Trailblazer.pdf
5) Craig J. Kief, Brian Zufelt, Scott R. Cannon, James Lyke, Jesse K. Mee, “The Advent of the PnP Cube Satellite,” Proceedings of the 2012 IEEE Aerospace Conference, Big Sky, Montana, USA, March 3-10, 2012, URL: http://www.cosmiacpubs.org/pubs/06187237.pdf
6) Jim Lyke,, Don Fronterhouse, Scott Cannon, Denise Lanza, Wheaton Byers, “Space Plug-and Play Avionics,” AIAA 3rd Responsive Space Conference, April 25–28, 2005, Los Angeles, CA, USA, paper: RS3-2005-5001
7) Keith Avery, Nathaniel (Shane) Francis, James Lyke, Patrick Collier, “Optical Networking for Aerospace Systems Provisioned through Plug-and-play Avionics,” Proceedings of the 24th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 9-12, 2010, SSC10-XI-9
8) Louis Marketos, “Leveraging the Space Plug-and-Play Avionics (SPA) Standard to Enable Constellation-Level Collaborative Autonomy,” URL: http://www.amostech.com/TechnicalPapers/2009/Space-Based_Assets/Marketos.pdf
9) L. J. Hansen, P. Graven, D. Fogle, J. Lyke, “The Feasibility of Applying Plug-and-Play Concepts to Spacecraft Guidance, Navigation, and Control Systems to meet the Challenges of Future Response Missions,” 7th International ESA Conference on Guidance, Navigation & Control Systems 2-5 June 2008, Tralee, County Kerry, Ireland, URL: http://www.smad.com/analysis/ESA%20GNC.pdf
10) “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
11) 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
12) Roz Brown, “Ball Aerospace's STPSat-3 to Fly Solar TIM Instrument for NOAA,” BATC, July 19, 2012, URL: http://www.ballaerospace.com/page.jsp?page=30&id=478
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) “NASA Helps Launch Student-Built Satellites and latest PhoneSat as Part of CubeSat Launch Initiative,” NASA, Nov. 18, 2013, URL: http://www.nasa.gov/content/nasa-helps-launch-student-built-satellites-and-latest-phonesat-as-part-of-cubesat-launch/#.UphFWSeFcyW
17) “CubeSat ELaNa IV Launch on ORS-3,” NASA fact sheet, Nov. 2013, URL: http://www.nasa.gov/sites/default/files/files/ELaNa-IV-Factsheet-508.pdf
18) “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
19) 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
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.