BEOSAT (BRUNSWICK-EARTH-OBSERVATION-SATELLITE)

Transcription

1 ABSTRACT BEOSAT (BRUNSWICK-EARTH-OBSERVATION-SATELLITE) Rolf Kluge Jörn Pfingstgräff ExperimentalRaumfahrt-InteressenGemeinschaft e.v., Germany BEOSAT is a microsatellite designed by students from the Technical University of Brunswick, Germany. The satellite has a weight of 45kg and an edge-to-edge length of 40cm. The project started with a satellite design workshop in summer 2003 which was organised by the ExperimentalRaumfahrt-InteressenGemeinschaft - ERIG - which means experimental-space-interest-group. By now this group is a registered association with nearly 40 members. The ERIG is completely organized by students but we also get support from the University of Brunswick, some institutes and industrial partners. Since we are all students our first aim of this project is to learn how to construct a satellite and how to handle the project organisation. But we are also interested in scientific issues. That is why our payloads are more then just a camera. One is µscia which is a micro-spectrometer for measuring tropospherical nitrogen dioxide with a high scale ground resolution of 10 by 10km². The other one is AIDA which stands for Advanced Impact Detector Assembly. This is an impact detector for space debris and meteoroids. Both instruments represent a new generation of technology in their particular areas. They are built by cooperational partners. µscia is a project of the Institute of Environmental Physics in Bremen. AIDA will be built by eta_max space GmbH in Brunswick. The satellite will fly a sunsynchrous orbit (10.00h) with a maximum altitude of 650km. The satellite bus is designed and built by the BEOSAT team. The bus consists of a combination of COTS and space hardware. The project's timeline schedules a possible launch readiness for late In July 2004 the project has successfully passed the Preliminary Requirements Review held by the DLR (German Aerospace Centre) and experts from German space companies and research institutes. By now we have finished our first full scaled mock-up and in summer 2004 there will be the Preliminary Design Review. BEOSAT BEOSAT stands for Brunswick-Earth-Observation-SATellite. It is a project of the ERIG which is an association of students from the Technical University of Brunswick. The ERIG was founded in 1999 by students who develop and launch experimental rockets. It is a registered association with nearly 40 members. Most of them are still students but there are also some graduates from the Technical University of Brunswick. There are students from many different fields of study. There are mechanical, electrical,

2 computer and industrial engineering students but there are also physicists and media scientists. In 2003 some of them had the idea to build a student satellite. The question was how to initiate such a project. There were a lot of difficulties. No one knew how a real satellite looks like neither how to handle such a complex project. So the first step was to find a lot of answers. They decided to organise a workshop of two weeks for about 40 students of our university. In the first week there were many lectures about all fields of satellite technology held by space experts from EADS Astrium, GFZ, ZARM, OHB System, the DLR and universities. During the second week we could define our aims together with the new students who joined the workshop. Thus this was the kick-off for BEOSAT, a microsatellite for earth observation. ORGANIZATION Beside MEPHISTO a two staged experimental rocket to reach 10km altitude and HYDRA an innovative hybrid motor, BEOSAT is the third big project of the ERIG. The ERIG is fully organized by students. There is no technical interference by university, but we get support by the Institute of Aerospace Systems (ILR) and the Institute for Computer and Communication Network Engineering (IDA). Furthermore we could find many supporting partners in German space related companies. The BEOSAT project group is divided into six subsystem groups: Payload, AOCS, Structure/ Thermal Systems, Electrical Systems, Systemengineering and Finance/ Marketing/ Organization. PAYLOAD As mentioned, BEOSAT carries two payloads. µscia is developed by the Institute of Environmental Physics (IUP) in Bremen. It consists of a microspectrometer and a telescope. It will reach a ground resolution of 10km by 10km. µscia will measure the concentration of nitrogen dioxide (NO 2 ) in the atmosphere. NO 2 is an indicator for air pollution. It is emitted by all kinds of burning processes as in cars, aircrafts, households and factories. NO 2 causes acid rain and supports the production of troposhperical ozone. µscia will only measure nadir-orientated so we get information about the entire concentration and no height-dependable information. The question is what is the improvement? There are existing systems like SCIAMACHY on the satellite ENVISAT which measures with a ground resolution of 60km by 30km. BEOSAT will have a ground resolution of 10km by 10km, which is an improvement by a factor of 18. All data that µscia will collect shall be posted on web, so that everybody can take a look of his local air pollution. AIDA is an impact detector for space debris and meteoroids. There are two concepts of assembling AIDA on BEOSAT. AIDA is built by eta_max space GmbH in Brunswick which is the main contractor for ESA's MASTER model. Our dates can be used to compare them with MASTER and depending on the results it can be used for an update for our orbit. So what types of assembly are possible? The AIDA concept consists of a base plate with thermal sensors. In front of the base plate there are two laser curtains or two thin grids.

3 If a particle hits the sensor, it first goes through the two curtains. When the particle hits a curtain a flash is occurring. These flashes are measured by optical cameras which give a time signal and storage the location of the flash. The same happens at the second curtain. So we get information about the particle's direction and velocity. Then the particle hits the base plate and all his kinetic energy is converted into heat energy. Considering E=1/2mv² we can get a good estimation about the particle's mass with measuring the temperature. If the sensor is assembled with the grids they will measure the ionisation energy of the particle when it hits the base plate. With this information and the thermal energy that you can measure on the base plate the sensor can calculate the velocity and the mass of the particle. It does not matter which version will flight on BEOSAT, the satellite will detect the space debris and meteoroid's flux and the velocity of the particles with a higher resolution than every other sensor does it at the moment. AIDA will have a fully assembled mass of 4kg and it requires 4W of power. The sensor will be working all over the orbit. MISSION BEOSAT is intended to fly a 650km sunsynchrous orbit (10.00h). Regarding being only a secondary payload this is our best purposed orbit. The design must be that robust that a wide range of orbits might be possible. A launcher has not yet been identified. There had been contacts with DNEPR and ArianeSpace. The main driver for choosing the launcher is the launch costs. Since this is a student satellite project we will have to find a sponsor. During the eclipse, BEOSAT is flying nadir-pointed. When the satellite is leaving the eclipse the solarpanels will be sun-pointed as long as there is no measurement campaign. That is why BEOSAT is three-axis stabilized. Furthermore µscia is the main design driver for BEOSAT s attitude control system. µscia needs a high pointing accuracy and stability. For µscia's operational mode a highly accurate sun sensor is needed. SUBSYSTEMS Attitude Control System (ACS) Besides the high accurate sun sensor the attitude control system (ACS) is quite standard. BEOSAT will use six coarse-earth-sun-sensors (CESS), a three-axis magnetometer, three gyros and a GPS receiver. As actuators there are three reaction wheels and magneto-torquers. Because BEOSAT will not use a cold gas system there will not be the possibility of an orbit control. A micro processor will control all ACS work. The controller is only working for ACS and it is cold redundant. On-Board Data Handling (OBDH) The main computer - a FPGA - is the heart of the On-Board-Data-Handling-System. All computers on BEOSAT are identical and use the same software. So it is ensured that

4 one computer can take over the other's jobs, too. For data storage 1GB of Flash will be used. Communication The communication system consists of an S-Band system. There will be a high- and a low-rate for up- and downlink. It will have a maximum data rate of 0,15MBit/s. The high-rate system uses a helix antenna. If everything is working well this system is used for the communication of the payload and the housekeeping data. The low-rate communication is a back-up system which will be used in terms of malfunctions. As groundstation it is foreseen to use a 3m parabol antenna which receives the high-rate data and which is placed at an institute of the Technical University of Brunswick. The low-rate link uses a yagi antenna which is also situated at an institute in Brunswick. Electrical Power System (EPS) For generating electric power BEOSAT uses high-efficient solar cells. They are placed on a body-mounted and on one deployable panel. They deliver up to 125W, due to the satellite s orientation. For power storage it is foreseen to use Lithium-Ion batteries with a capacity of 9Ah. The working voltage of the electrical bus will be 28V. Thermal A very sophisticated design for thermal system is needed because µscia has a very small bandwidth of operational temperature. µscia will be thermal decoupled from the satellite's bus. That is why the thermal system is divided into two parts; one for the bus and one for µscia. The bus system is intended to be passive. µscia needs a Peltier element for active cooling and maybe a heating element. µscia will be placed on the cold site of the satellite so that the instrument box is directly connected to his own radiator. Furthermore the box with the CCD-Chip will be isolated with multi-layer insulation (MLI) and eventually thermally isolated mounted on the panel. The passive system of the satellite itself is comparable to standard systems. The satellite will be insulated with MLI and gets its own radiator. Structure The structural concept of BEOSAT is called FIPS, which stands for Function- Integrated-Primary-Structure. That means that the whole structure of the satellite is used to absorb the strains of the launch as well as all the parts will be fixed directly on this structure. It consists of a massive aluminium base plate where four corner stiffeners are mounted. The bars are holding the panels on which all instruments are placed. The panels are set up with honeycomb and carbon fibre plates. All instruments are assembled directly on

5 the panels with inserts. The deployable solar panel is mounted at the satellite's back and is released by pyros and arrests in a fixed position. PROJECT PHASES BEOSAT is a pure student project. At the moment the students work mostly in their spare time. But there is also the possibility for the students to do BEOSAT related projects for their studies. There are two main challenges. Like in the most student projects these challenges are money and continuity. Furthermore such a complex project needs a lot of time for its realisation. To build up partnerships and sponsoring activities we have the group finances/ marketing/ organization. To ensure a continuous work and to guarantee a sufficient team size every year a BEOSAT satellite design workshop takes place. The project timeline is orientated on the ECSS project phases. The project has passed the Preliminary Requirements Review (PRR) in June and July The PRR has been organized together with the DLR. Therefore we could win 14 experts from the DLR, space companies and research institutes. They have reviewed the documentation and confirmed the feasibility of our concepts. Phase B started in August 2004 and is intended to be finished with the Preliminary Design Review (PDR) in July For design, assembly, integration and tests (Phase C/D) there are three years of work planned so that we can launch the satellite at the end of By now the first full scaled mock-up is finished. The next steps are the STM (structurethermal-model) which shall qualify the thermal and structural design in the second half of 2005 and the first functional models of the OBDH and communications systems. CONCLUSION BEOSAT is a project which is completely organised by students. Even the satellite will be constructed and built by us. Our primary aim is to learn more about space technology and that is what we do, every week a little bit more. Besides the technology we get in contact with project management, international conferences and many industrial partners. If the project continues like it does at the moment the satellite will reach its launch readiness at the end of So in about 4 years many people can also profit from BEOSAT when we will get the results of the first measuring campaign.