Invited Paper Polish-made payload for the Brite-PL2 satellite "Heweliusz" Tomasz Zawistowski Space Research Center of the Polish Academy of Sciences, ul. Bartycka 18a, 00-716 Warszawa ABSTRACT Two institutes of the Polish Academy of Sciences, Space Research Centre and Nicolaus Copernicus Astronomical Center cooperate on the project to build and place in orbit the first Polish scientific satellite. The BRITE (BRight Target Explorer) mission formed by Austria, Canada and Poland will send to space a constellation of six nanosatelites, two from each country. They will be observing star pulsations with fotometric methods gathering data that will verify thermodynamic models of bright, massive stars of our Galaxy, delivering information on their structure, formation and evolution. The first of two Polish satellites, "LEM", will closely resemble its international kin, while the second, "Heweliusz" will carry Polish flavor to space – delivering additional technological experiments. They will use commercial-off-the-shelf components. Keywords: satellites, BRITE, star oscillations, COTS 1. INTRODUCTION The BRITE mission represents a new approach in space research – the use of small, cheap, specialized nano-satellites that will monitor minute changes in the brightness of stars, in order to study their behavior [1]. While observation from orbit has an advantage – no disturbances caused by the Earth’s atmosphere influence the optical image acquired by the telescope, additionally the constellation of satellites offers the continuity of observations . The basic systems of a nanosatellite used by the BRITE mission comprise: the telescope computers (House Keeping Computer (HKC), Attitude Control System Computer (ACSC), Instrument On Board Computer (IOBC) communications system (radio receiver and transmitter) power system (control boards, photovoltaic cells, regulators) Attitude Control System (ACS) (magnetometer, star tracker, sun sensors, magnetorquers, reaction wheels) The total mass of a BRITE nanosatellite is about 7 kg and it is encased in a cube-shaped box, having a side 20 cm long [2]. It is covered with thermal tape protecting it from overheating by the SUN at the Low Earth Orbit. The first of the two Polish satellites will be launched in November 2012, the second will be placed in orbit in the second half of 2013. The satellite is to be controlled from the ground-based command station with radio communications: the uplink will be realized with the frequency of 437.625 MHz, while downlink will be transmitted at 2.2 GHz. The Polish ground station will be one of 3 principal stations and will be located at the Nicolaus Copernicus Astronomical Center in Warsaw. The Generic Satellite Bus (GSB) is common to all 6 spacecraft in the BRITE constellation. Most of the components were designed at UTIAS SFL (University of Toronto Institute of Aerospace studies Space Flight Laboratory) or its Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2012, edited by Ryszard S. Romaniuk, Proc. of SPIE Vol. 8454, 84540D · © 2012 SPIE CCC code: 0277-786/12/$18 · doi: 10.1117/12.2000424 Proc. of SPIE Vol. 8454 84540D-1 subcontractors. Most of the parts used were COTS. One of few non-Canadian made parts were structural parts (panels and brackets). BRITE PL 2 "Heweliusz" will differ from BRITE-PL 1 "LEM" in the payload contents. It was decided that additional features will be built into it: it will consist of several technological experiments, all of Polish origin. Figure 1 The First Polish Scientific Satellite-BRITE-PL 1 "LEM" 2. TECHNICAL APPROACH All add-on experiments will be controlled by the control and measuring system. It will monitor the state of all experiments, conduct testing procedures, analyze and process test data and prepare them for downlink. Depending on the available power the component tests will be done in parallel or separately with an option of turning the power off. 2.1. Technologies to be verified on the electronic components As far as some of technologies to be tested on the electronic components of the control and measuring system they are: BGA assembly corrective coding, partial reconfiguration or using quartz resonators as generators in FPGA. 2.2. Electronic components to be tested The criteria cited below were followed during the selection of components to be flown on Heweliusz: usefulness for low budget space missions low power consumption long term availability no record on susceptibility to damage by radiation availability of units with wide range of operational temperatures Proc. of SPIE Vol. 8454 84540D-2 The following parts were picked for the test: SDRAM DDR2 Memories (IS43DR16664A-3DBL), NOR FLASH Memories (S29GL01GP11TFIR10), programmable FPGA Spartan-6 family (XC6SLX45- 2CSG324I), Analogue to Digital Converter (ADC128S102). Commercially available off the shelf components, preferably with space heritage provide reliable service with substantially lower costs compared to those used on missions requiring certified parts. From the experience of SFL – COTS provide quite reliable alternative to thoroughly screened parts. 2.3. Measuring and Control system Measuring and control system will be based on ATMEGA microcontroller, which will be the basis of the experimental power system and UHF transmitter with OOK modulation. The processor will monitor voltages and currents through DS2438 battery monitor convertors, while temperatures will be measured with DS18B20 digital thermometers. Additionally a total radiation dose will be measured with an eloctroluminescent dosemeter, that will be precalibrated before flight. 3. POLISH-MADE PAYLOAD DESCRIPTION Polish payload will consist of two parts: scientific and technological. The scientific payload comprises the red-filter telescope which was designed from scratch at SRC and will be part of the major payload of the satellite. Thus it will not be considered an "additional payload". However since it has a smaller number of lenses compared to the telescope inserted in "LEM", it will save mass compared to the previous design. The technological payload is composed of: • Power Supply Unit, solar cells, battery (PSU) • Lock and Release Mechanism (L&R) • Micro Antenna Boom (MAB) • Radiation Dosemeter • Beacon Figure 2 Internal configuration of the Polish payload Proc. of SPIE Vol. 8454 84540D-3 The total mass increase connected with the technological payload is 640 g. The components of the Polish payload are shown in Figures 2, 3 and 4. z Figure 3 Remaining technological payload BATTERY Figure 4 Beacn and PSU All add-on technological experiments are extras that should not interfere with the main BRITE mission objectives. In order to implement that philosophy, the additional payload will be turned on by the command from the main on- board computer, BRITE PL HKC. The system architecture is shown in Figure 6. Proc. of SPIE Vol. 8454 84540D-4 MAIN PAYLOAD SWITCH Figure 5 System architecture of the additional payload Another example of the risk mitigating approach regarding the deployment and operation of the additional payload is the micro antenna boom test handling (Fig. 7) Figure 6 Antenna Boom - the configuration before deployment The antenna boom made of beryllium copper tape and shaped into a 6 mm diameter cylindrical tube is unfolded from a motor-driven spool. Initially it was to be deployed 1 m into space, but questions were raised regarding the influence the boom might have on the optical performance of the telescope (reflections, etc) and its impact on the Proc. of SPIE Vol. 8454 84540D-5 spacecraft stability and pointing accuracy [3]. In order not to interfere with the mission objectives the deployment of MAB was to be delayed till some imprecise moment which is supposed to define the end of the BRITE mission. Finally a different approach was assumed: the MAB would deploy the boom within spacecraft structure, thus it will not affect the BRITE mission. A confinement tube is to protect the boom during and after its deployment. It will also facilitate the layout of the harness within the spacecraft during the integration process. The PSU architecture is presented in Figure 7. -> -> -> I -> :1: -> > Figure 7 PSU block diagram PSU will receive power from experimental 3 junction photovoltaic cells that will be prototypes made in Poland. Their efficiency is expected to be better than 30%. There will be 2 patches of 8 cm x 8 cm of experimental photovoltaic cells installed on the "Heweliusz" spacecraft. Additionally there will be thin photovoltaic cell foil of much smaller efficiency placed on the Yplus panels of the satellite. Its purpose is to test the external protection layer rather than deliver consummable power. Proc. of SPIE Vol. 8454 84540D-6 THIN FOIL SOLAR CELLS SOLAR CELL -1 Figure 8 Experimental Photovoltaic Cell location on the satellite panels SRC has long developed mechanical devices that were stowed at launch and released in orbit. They all used release mechanisms that were purchased from commercial sources. The recent decision to standardize that sort of equipment and develop an in-house lock and release mechanism led to the development of the unit shown in Fig. 9. It uses a rope that melts when subjected to contact heat from a nearby resistor. 2 of such units will be flown on "Heweliusz". Figure 9 Lock and release mechanism Proc. of SPIE Vol. 8454 84540D-7 Radiation dosemeter was designed with the following objectives: • Verification for LEO radiation simulations (RadFET, LED-dosimetry) • Evaluation of fault mitigation techniques • To provide flight heritage opportunity to some potentially interesting COTS components (future SRC missions) – FLASH, SDRAM, ADC, FPGA It uses the operation mode listed below: • FLASH, SDRAM, FPGA retention(SEU) (80mW) • FLASH read/write tests (350mW) • FPGA(LFSR, RAM, SEFI, (300mW) • SDRAM read/write (350mW) • ADC tests (280mW) Its only electrical interface is a connection to the payload PSU’s MCU (UART LVTTL, 5V supply). All the telemetry data from the add-on experiments will be delivered to the ground by a beacon. PSU 3V PSU SV Voltage stabilizer r r AVR 2.4GHz RF match 2.4GHzRF uC Transmiter Frontend CC2550 CC2591 4 TI UART TTL CW keying line (digital) ,,,,,, power lines -3111.
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