Invited Paper

Polish-made payload for the Brite-PL2 "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 , "", 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.

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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: ->

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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. data lines ..11. RF lines

Figure 10 BEACON block diagram

It uses one boom antenna that will be located on the opposite side from the main mission UHF antennas.

Proc. of SPIE Vol. 8454 84540D-8 4. CONSTRUCTION OF THE PROTOTYPE A novel approach to prototype building was taken: a CAD model with accurately rendered cabling was produced so all details pertaining to cabling were incorporated into the new model. The information from the virtual model containing a harness was then transferred to the prototype created with a 3D printing technique. Those stages are shown in Figure 11.

Figure 11 Wirtual model with a harness (left) and 3D-printed prototype parts on the right.

The challenge in adding an extra payload is to find an optimal location of the harness in an already tightly packed original structure. The integration procedure previously used on several BRITE spacecraft has to be redefined in order to adapt to different requirements imposed by added hardware.

5. RESOURCES Table 1 Power resources

Voltage Max Curent Max Power Expected [mA] [mW] Average Power [mW] 1.2V 200 240 60 1.8V 300 540 100 3.3V 120 396 120 Total 1176 280

With assumed power supply efficiency of 80% the total average power consumption will not be more then 0.4 W and maximum power will not exceed 1.5 W.

Proc. of SPIE Vol. 8454 84540D-9 5.1. Mass and Volume All the additional experiments will be controlled with electronics located on a single multilayer printed circuit board. It will be square-shaped with a side of 8 cm long and maximum component height of 1 cm. Mass including additional shielding of control elements will be 200 g. The total added mass of the add-on experiments is 640 g.

5.2. Bit Rate UHF transmitter with OOK modulation and Morse coding will guarantee that the additional radio system will be independent of the communication system link used on the "Hewelusz" satellite. Maximum bit rate of the additional system will be 1.2 bps. . The experiment will minimize the data stream and the expected bit rate is to be 100 B/h.

6. CONCLUSION Polish-made payload of the BRITE-PL 2 "Heweliusz" satellite will complement the advantage gained from this purely scientific mission. New technological experiments developed in Poland will underline the goal defined at the outset of the project: to build expertize in constructing satellites. The technological experiments that will be installed on the "Heweliusz" spacecraft will get flight heritage, which is an important issue in the future selection of instruments for space exploration missions.

REFERENCES

[1] Scharzenberg-Czerny, A., Weiss, W, Moffat, A., Zee, R.E., Rucinski, S., Mochnacki, S., Mathhews, J., Breger, M., Kuschnig, R., Koudelka, O., Orleanski, P., Pamyatnykh,A., Pigulski, A., Grant, C., 2010, [The BRITE Nanosatellite Constellation Mission], COSPAR 38th Sci Assembly, 38, 290 [2] Piotr Orleanski, Rafał Graczyk, Mirosław Rataj, Aleksander Schwarzenberg-Czerny, Tomasz Zawistowski, Robert E.Zee,[BRITE-PL – the first Polish scientific satellite],4th Microwave and Radar Week MRW-2010 Conference, Vilnius, 2010 [3] Grant.C, [SFL-GNB-SYS-R004 Systems Requirements], v.1.4.3. Feb 26, 2008

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