PicosatelliteProgramming within the Constraints of the 1kg 皮卫星编程在1kg约束

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1、 Slide 1Picosatellite Programming within the Constraints of the 1kg, 10 x 10 x 10cm CubeSat Standard Andrew E. Kalman, Ph.D. Slide 2 Andrew E. Kalman President and CTO, Pumpkin, Inc. Author of Creator of the 20+ years of embedded systems design and programming experience. Contact: Introduction Slide

2、 3Outline Overview: Presentation Goals Part I: Picosatellites & CubeSats Part II: The CubeSat Standard Part III: Architectural Constraints Part IV:CubeSat Kit Architecture Part V: CubeSat Kit Programming Part VI: Architectural Extensions Slide 4Overview This presentation is targeted at programmers w

3、ho are interested in getting their work into space via new, low-cost and rapid-response opportunities. After introducing the CubeSat picosatellite standard, we present an overview of the physical, electrical, mission and cost constraints of a picosatellite conforming to the standard from a programme

4、rs viewpoint. The embedded architecture of Pumpkins CubeSat Kit a popular implementation of the standard is one reaction to these constraints. We examine the effects of these constraints on the CubeSat Kits operational software. We present extensions to the architecture to bring more “desktop-like f

5、unctionality” to a CubeSat-class picosatellite. Slide 5Part I: Picosatellites & CubeSats The CubeSat is a 10 x 10 x 10cm, 1kg public picosatellite design specification proposed by Stanford and Cal Poly San Luis Obispo universities. Low-earth orbit (LEO) CubeSat missions have typical lifespans of 3-9

6、 months. Cost to complete a CubeSat mission (inception to launch to operation to end-of-life) ranges from $100,000 to $1,500,000. Working from a standard promotes rapid development and idea sharing Picosatellites are already a hot topic in aerospace. Worldwide interest is focused on CubeSats in part

7、icular, partly because they are becoming a de facto standard. Slide 6Picosatellites & CubeSats (contd) Development, debugging & functional testing: typical lab environment. Pre-delivery and pre-launch: Temperature, vacuum and shake tests. Integration into launch vehicle. Picosatellite may remain in

8、storage for months on end waiting for launch. Launch & deployment: high g-forces (10g or more). Operation in space: vacuum, wide temperature range (-20 to +60 C), solar radiation, and remoteness. End of mission: deorbit and burn up in earths atmosphere. Slide 7 Picosatellite components: Structure. C

9、ommand & Data Handling (C&DH), with high-frequency transceiver and antenna(s). Ground Stations. Communications (COM). Electrical Power System (EPS). Attitude Determination & Control System (ADACS). Payload. Software, Software, Software.Picosatellites & CubeSats (contd) Picosatellites are often launc

10、hed in groups from dedicated launchers as secondary payloads on a rocket. CubeSats are usually ejected from a P-POD launcher. Slide 8 Available as an 8-page document from www.cubesat.org. Requirements summary: Designed to be launched from a P-POD (10 x 10cm internal cross-section) 1kg mass Nominal 1

11、0 x 10 x 10cm size to fit inside P-POD launcher +6.5mm allowed above each of the CubeSats six faces 2 separation springs Launch switch Remove-before-flight switch Location of access port area clearly defined Material & finish requirements on rail contact surfaces Safety various electrical, testing a

12、nd operational requirements Part II: The CubeSat Standard Slide 9 Things that the standard does not spell out: Payloads Antennas Electronics Programming Power sources Structural materials Operating frequencies & ground stationsIf your CubeSat satisfies the external (i.e. shape), mass, safety and reg

13、ulatory requirements, then you can “board the bus” for the next available CubeSat launch for $40,000. How you get there, and what you do with your CubeSat, is pretty much up to your imagination. CubeSat missions have included technology demonstrators, proof-of-concepts and scientific experiments.The

14、 CubeSat Standard (contd) Slide 10The CubeSat Standard (contd)Figure 1: A Picosatellite Built with the CubeSat Kit10cm10cm11.35cm Slide 11The CubeSat Standard (contd)Figure 2: Skeletonized and solid-wall CubeSat Kit structures in 1U, 2U and 3U sizes, along with an FM430 Flight Module, transceiver an

15、d user module stack. All parts are interchangeable. Slide 12Part III: Architectural Constraints The CubeSat standard essentially a mechanical & safety specification along with a typical picosat mission profile impose certain real physical & electrical constraints on the electronics contained therein

16、: Maximum planar dimensions of a PCB: 100 x 100mm, less wall thicknesses. PC/104s 90 x 96mm is practically speaking the largest common OTS form factor compatible with the CubeSat Kit. Maximum mass: From the 1kg mass budget we must deduct the structure (150 - 300g), EPS (200 400g), transceiver(s) and

17、 antenna(s) (100 200g), and payload. That doesnt leave much of a home for our IT. Maximum power consumption: A CubeSat-sized object in LEO can expect 1 - 2W on average of radiated power from the Sun. This caps our average power consumption. Maximum cost: Many CubeSat missions are done on small budge

18、ts with considerable free / donated materials and labor. COTS components are used whenever possible. Slide 13Architectural Constraints (contd) In addition to the more obvious / external constraints, mounting and interconnect issues bring system integration constraints. This suggests that a high leve

19、l of electronics integration is required. Some OBC candidates:CandidatePC/104 SBC + peripheralsSmaller SBCs (e.g. gumstix, FOX)Pumpkins TI MSP430-based FM430Custom / roll your ownProslarge variety, powerful, very PC-like, inexpensive, rugged, -40 to + 85 Cvery inexpensive, small & light, very PC-lik

20、e, runs Linuxdirect support for transceiver, USB, RBF, LS, SD card and latchup protection, extremely low power (25mW), rugged, -40 to + 85 Cdelivers exactly what you (think you) wantConspower-hungry (2 - 20W), inefficient packaging / form factor1 2W, not as rugged as PC/104, only 0 to +70 C, limited

21、 peripheralsmore expensive, advanced functionality (e.g. image processing) not possible with this CPUnews design costs time & money & more time Slide 14Architectural Constraints (contd) Not only must the OBC provide a base computing engine, but it also must provide a variety of peripherals to interf

22、ace to the rest of the picosat, including: General-purpose I/O A/D & D/A Timers Communications (async serial, SPI, I2C) Mass storage Given these constraints esp. power consumption, operating temperature and level of integration we chose TIs MSP430 8MHz 16-bit RISC microcontroller for the basis of th

23、e CubeSat Kits electronics architecture. Slide 15Architectural Constraints (contd)Figure 3: MSP430 x16x Block Diagram Slide 16Part IV: CubeSat Kit ArchitectureFigure 4: FM430 Block Diagram Slide 17CubeSat Kit Architecture (contd)Figure 5: FM430 Flight Module Rev B Slide 18Part V: CubeSat Kit Program

24、ming How does the choice of 16-bit MSP430 affect the programming environment of the CubeSat Kit? 64KB memory space MSP430F1612 has 5KB RAM and 55KB Flash. RAM is especially limited, as is typical of microcontrollers. C rules here. C+ is generally ill-suited to this small embedded programming space.

25、Assembly language is not required. HLLs are not an option due to memory & speed limitations. Tools (compiler, linker, debugger, IDE, both commercial and free) are very good, standard C libraries are all present, multitasking RTOSes (e.g. Salvo) are available. As a CubeSat programmer, youre never too

26、 far from the on-board hardware, at least at the early stages of development. Since much of the hardware in each CubeSats payload is unique and requires drivers & support, there are many opportunities for real-world learning when programming a CubeSat. Slide 19CubeSat Kit Programming (contd)Figure 6

27、: A CubeSat Kit Development Board with a UHF/VHF Radio Module Slide 20CubeSat Kit Programming (contd)Figure 7: Screen Capture of Programming / Debugging IDE on CubeSat Kit Slide 21CubeSat Kit Programming (contd) Detecting the presence of USB: void TaskDetectUSB ( void ) for (;) /* proceed if USB/MHX

28、 I/F is not in use */ OS_WaitBinSem(BINSEM_USB_MHX_AVAIL_P, OSNO_TIMEOUT); OpenUSBMHXIF(USB); if ( !FM430status.USBpresent & (P1IN & BIT7) ) FM430status.USBpresent = 1; FM430Msg0(DetectUSB: USB connected.); else if ( FM430status.USBpresent & !(P1IN & BIT7) ) FM430status.USBpresent = 0; FM430Msg0(Det

29、ectUSB: USB disconnected.); CloseUSBMHXIF(USB); /* release USB/MHX I/F */ OSSignalBinSem(BINSEM_USB_MHX_AVAIL_P); OS_Delay(25); /* come back in 25 ticks */ Listing 1: Sample Task to Detect Presence of USB Connection Slide 22CubeSat Kit Programming (contd) Code modules developed for CubeSats include:

30、 Interfaces to various I2C devices to measure currents, voltages, etc. I2C is very popular because its a two-wire bus with a wide choice of supported devices. Interfaces to various SPI devices (e.g. magnetometers, MMC cards, other / slave processors). Interfaces to various asynchronous serial device

31、s (e.g. transceivers and cameras). Watchdog / reset code (both internal and external). On-board fault detection, collection and correction. Multi-processor intercommunications. Sun- and attitude-sensing algorithms. Deployment & release mechanisms. End-of-life / deorbit mechanisms. In-flight reprogra

32、mming. Active attitude control. Slide 23CubeSat Kit Programming (contd)Figures 8 & 9: Final Exam for Stanfords AA236A class semi-autonomous, remotely-controlled rovers based on the CubeSat Kit Slide 24CubeSat Kit Programming (contd) In CubeSat programming, the challenge is to do more with less. More

33、 functionality, more reliability and more versatility with less mass, less power and fewer components. Example: The KatySat project has an on-board VHF/UHF AX.25 transceiver operating at 1200 bps. The VHF receiver presents ASCII data to the CubeSat Kits MSP430 Flight MCU at 4800bps. Figure 10: KatyS

34、at ConOps Slide 25CubeSat Kit Programming (contd) The challenge with the KatySat VHF/UHF module lies in the fact that we would like to be able to listen on the VHF uplink 100% of the time. This requires a dedicated serial UART. But the FM430s UART1 is dedicated to the 2.4GHz TT&C, and UART0 is share

35、d among UART, I2C and SPI devices in the CubeSat. So the hardware UARTs are spoken for. The solution was to bit-bang the UART in software, using a TI example as the base code. During testing, it was found that a CPU clock of 800kHz (the nominal DCO frequency) was insufficiently fast to guarantee rel

36、iable operation. Therefore the MSP430s CPU clock was sourced from the HF crystal (7.3728MHz). Careful choices of timer modules, interrupt vectors and interface to the overlying RTOS ensure reliable operation within the larger multitasking framework of the SC software. PD was deemed acceptable. Slide

37、 26 What about more advanced functionality? uIPs embedded TCP/IP stack provides web and Telnet servers over CubeSat Kits wireless or USB interfaces via SLIP. HCC-embeddeds EFFS-THIN small-footprint PC compatible file system provides easy interfacing between on-board SD card mass storage and developm

38、ent PCs. As long as memory requirements are not too extravagant, high-level functionality can be ported to the FM430 via a simple cut-and-paste or by linking to a library.CubeSat Kit Programming (contd)MSP430F149 CubeSat KitDemonstration ApplicationRAM UtilizationApplication variables66uIP TCP/IP st

39、ack, SLIPcode & web server 293FM430 USART0 buffers(256 Tx & 256 Rx) &control 539FM430 USART1 buffers(256 Tx & 256 Rx) &control 539Salvo RTOS (10 tasks &2 events) 107Stack 90Free 414MSP430F149 CubeSat KitDemonstration ApplicationFlash Utilizationmain() & Salvo tasks3880FM430 utility functions1136uIP

40、TCP/IP stack, SLIPcode & web server5654uIP web server files(*.html, etc.) 8700Salvo RTOS 1890ISRs & interrupt vectors190C library functions(printf(), etc.) 1906Free 37828Figures 11 & 12: Flash and RAM utilization of a uIP-enabled Salvo application on the FM430 Slide 27 All of the MSP430s I/O is on t

41、he CSK bus connector. The FM430s ultralow power requirements mean that it can run 24x7 during the entire mission. Additional processors (e.g. Linux SBCs) can be added due to a variety of architectural features: Multiple pins on CSK bus connector reserved for user. MSP430s NMI input enables simple ha

42、ndshake with other processors. SPI, I2C and UART all available for inter-processor communications. Up/downlink transceiver can be accessed directly via CSK bus connector. Due to the SBCs higher power consumption, its on-time duty cycle will necessarily be 100%. The FM430 can manage it as an “on-dema

43、nd coprocessor.”Part VI: Architectural Extensions Slide 28This presentation is available online in Microsoft PowerPoint and Adobe Acrobat formats at: and: SMC-IT-2006.pdf Notice Slide 29 Q&A SessionThank you for attending the workshop! Slide 30Notes & References1.CubeSat Design Specification, www.cu

44、besat.org .2.MSP430 x16x block diagram from TIs MSP430F1612 datasheets, .3.CubeSat Kit User Manual, Pumpkin, Inc. 2005, .4.Connex-xm platform spex, .5.FOX Board Documentation page, Acme Systems, www.acmesystems.it.6.AXIS ETRAX 100LX MCM 4+16 product brochure, Axis Communications AB, 2004, . 7.The uI

45、P Embedded TCP/IP Stack, Adam Dunkels, http:/www.sics.se/adam/uip/.8.EFFS-THIN product specification, HCC-embedded, www.hcc-. Slide 31Appendix Speaker informationDr. Kalman is Pumpkins president and chief technology architect. He entered the embedded programming world in the mid-1980s. After co-foun

46、ding Euphonix, Inc the pioneering Silicon Valley high-tech pro-audio company he founded Pumpkin to explore the feasibility of applying high-level programming paradigms to severely memory-constrained embedded architectures. He holds two United States patents and is a consulting professor at Stanford

47、University. AcknowledgementsStanford Professor Bob Twiggs continued support for the CubeSat Kit, and his input on enhancements and suggestions for future CubeSat Kit products, are greatly appreciated. Pumpkins Salvo and CubeSat Kit customers, whose real-world experience with our products helps us im

48、prove and innovate. Salvo, CubeSat Kit and CubeSat informationMore information on the Pumpkins Salvo RTOS and Pumpkins CubeSat Kit can be found at http:/ and http:/ respectively.More information on the open CubeSat standard and the CubeSat community can be found at http:/www.cubesat.info/. Copyright

49、 notice 2006 Pumpkin, Inc. All rights reserved. Pumpkin and the Pumpkin logo, Salvo and the Salvo logo, The RTOS that runs in tiny places, CubeSat Kit, CubeSat Kit Bus and the CubeSat Kit logo are all trademarks of Pumpkin, Inc. All other trademarks and logos are the property of their respective owners. No endorsements of or by third parties listed are implied. All specifications subject to change without notice.First presented at the 2nd IEEE International Conference on Space Mission Challenges for Information Technology in Pasadena, California on July 17, 2006.