RØMER

1. RØMER Aalborg University, Department of Control Engineering

2. Political Boundaries Aalborg University, Department of Control Engineering

3. Industrial Boundaries Aalborg University, Department of Control Engineering

4. Financial Boundaries Aalborg University, Department of Control Engineering

5. Ansøgt beløb – detailed design fasen Aalborg University, Department of Control Engineering

6. Totalt budget – RØMER Aalborg University, Department of Control Engineering

7. Saml. Ørsted Aalborg University, Department of Control Engineering

8. AAU budget Aalborg University, Department of Control Engineering

9. AAU budget – 2 Aalborg University, Department of Control Engineering

10. AAU budget - 3 Aalborg University, Department of Control Engineering

11. Participants • Science: • Institute of Physics and Astronomy, Aarhus University • Danish Space Research Institute, Copenhagen • Copenhagen University • Technology: • Institute of Electronic Systems, Aalborg University • Ørsted.DTU, Technical University of Denmark, Lyngby • Industry: • TERMA A/S, Lystrup • Alcatel Space Denmark, Ballerup • Copenhagen Optical Company, Copenhagen • Patria Finavitec, Tampere, Finland • Auspace, Canberra, Australia • Prime Optics, Eumundi, Australia Aalborg University, Department of Control Engineering

12. Organization - Organization Chart Aalborg University, Department of Control Engineering

13. Milestones • April 1999 Kick-off of Feasibility Study of Rømer • May 2000 Funding for System Definition Phase approved • May 2000 Kick-off of System Definition Phase (SDP) • Oct. 2000 Mid-Term Review • Nov. 2000 Decision to eliminate the Ballerina PL and re-focus mission • Nov. 2000 Decision to design Rømer as a single-string mission • April 2001 System Definition Review • May 2001 Complete Report and Documentation for SDP • June 2001 Start of Detailed Design Phase • Dec. 2001 Preliminary Design Review • Dec. 2002 Satellite Critical Design Review • May 2003 Satellite Integration and Test Review • May 2004 Launch (tentatively) Aalborg University, Department of Control Engineering

14. Rømer Overall Schedule Aalborg University, Department of Control Engineering

15. Rømer Overall Schedule –2 Aalborg University, Department of Control Engineering

16. RØMER SCIENCE OBJECTIVES Study the structure, evolution and internal dynamics of a sample of stars showing stochastically excited,solar-like oscillations. This will substantially extend the very successful helioseismic studies of the solar interior. Aalborg University, Department of Control Engineering

17. Corresponding Observations (SOHO) • Note: • Extremely small amplitudes, of order parts per million (ppm). • Blue amplitude much larger than red amplitude. Hence also signal in (blue)/(red) ratio, to beobserved by MONS. • Background is entirely due to solar granulation. Aalborg University, Department of Control Engineering

18. Main MONS Observational Requirements • Photometric precision. Need detection limit below 1 ppm. • The instrumental noise must match, but be below, the intrinsic stellar granulation noise. • Requirement on precision demands strong defocusing. • Temporal coverage. Each primary target must be observed almost continuously for at least onemonth. • Sky coverage. Primary targets are distributed over the whole sky. • Hence choose orbit giving access to entire sky during the mission. • Mission duration. At least two years (baseline), to allow study of sufficient number of stars. • Exclusion of variable neighbours. Include MONS Field Monitor to detect and correct for faintvariable stars within telescope field of view. Aalborg University, Department of Control Engineering

19. RØMER Science Payload Characteristics The primary science instruments include: • MONS Telescope having a 32 cm aperture, equipped with a high-precision photometric CCD detector for measuring oscillations of stellar intensity and color • MONS Field Monitor for examining the field of view of the MONS Telescope for faint variable stars The secondary science instruments: • Forward- and aft-looking Star Trackers of the Attitude Control Subsystem, to be used for studying variable stars • The MONS Field Monitor Aalborg University, Department of Control Engineering

20. Ground Segment Architecture • One or more Ground Stations • A Control Center which shall have total control of the mission and shall provide data processing, storage and display • A Science Data Center which shall prepare the specified user data products and disseminate them to the involved research institutes and organizations Aalborg University, Department of Control Engineering

21. Orbit Requirements • Maximize time outside the trapped proton radiation belts • Allow momentum unloading using only magnetorquers • The operational orbit shall be delivered by the upper stage of the launch vehicle. • Visibility from a ground station in Denmark • Frequent launch opportunities to the proposed orbit (1 per year) Aalborg University, Department of Control Engineering

22. RØMER in Molniya Orbit • Largest separation from Earth (Apogee): ~40000 km • Smallest separation from Earth (Perigee): ~600 km • Angle between orbit and Equator (Inclination): 63.4° • Period: 11 hours 58 min. 02 sec. (= ½ siderial day, ideal) • 10 hours of observations outside the radiation belts. • A satellite in Molniya orbit is subjected to a large dose of radiation from high-energy protons and electrons trapped in the Earth’s radiation belts. Aalborg University, Department of Control Engineering

23. SOYUZ/FREGAT Launcher FREGAT Upper Stage FREGAT with Cluster II Satellites RØMER is foreseen to be launched with a Russian SOYUZ/FREGAT rocket in mid 2004 from Plesetsk Cosmodrome The SOYUZ rocket has been launched more than 1650 times and its reliability exceeds 97% Aalborg University, Department of Control Engineering

24. Launch Configuration Aalborg University, Department of Control Engineering

25. Satellite Specification • Configuration, Mass and Envelope, Orbit • Nominal sun facing diagonal [+X,-Y] • – Solar panels on [+X] and [-Y] • – Single payload, MONS • – Main telescope, FOV in [+Z] • – Field monitor, FOV in [+Z] • – Radiators on [-X] and/or [+Y] • – Communication antennas on the exterior of the satellite, [±X], [±Y] • – Launch Vehicle I/F on [-Z] • – Mass: <120kg, Envelope: 600x600x710mm • – Orbit baseline: Molniya Aalborg University, Department of Control Engineering

26. Structure, Mechanism and Thermal Requirements • Accommodation of payload and platform subsystems • Accommodation of various CCD radiators (cold faces) • Accommodation of solar panels (hot faces) assuring optimal power input • Accommodation of battery assembly (with easy access) • Accommodation of COM antennas assuring 4p coverage • Accommodation of the PAA • Platform and payload electronics shall be enclosed in a common structure • Fundamental lateral/longitudinal frequency requirements: >45Hz />90Hz Aalborg University, Department of Control Engineering

27. CDH requirements • The CDH on-board computer shall act as satellite brain • Task requirements: • C&DH • ACS • Star Tracker handling • Parallel Star Tracker science if possible • Packet Utilisation Standard • SW patching and dumping • Power safe mode • Command loss timer • HW/SW watchdogs Aalborg University, Department of Control Engineering

28. Autonomous Control (requirements) – MONS observation Þ three axis control – Modes: – Fine pointing (science observation) – Coarse pointing (target slew) – Momentum unloading – Safe mode (startup, sun acquisition) – Sensors: – Primary: Star Tracker (2), Rate sensors (4) – Secondary: Sun sensors (4p steradian), Magnetometer (3 axis) – Actuators: – Reaction wheels (4) – Torquer coils (3) – Fault detection and management (SW) Aalborg University, Department of Control Engineering

29. Platform network structure Aalborg University, Department of Control Engineering

30. Design Philosophy • Model philosophy • EBB (subsystem level) • E(Q)M (subsystem level) • STM (subsystem and satellite level) • RF model (satellite level) • FM (subsystem level) • FS (subsystem level, optional) • Proto-flight satellite • Satellite simulator (EM setup) • Cleanliness TBD • Satellite magnetic stray field <1Am2 Aalborg University, Department of Control Engineering

31. Structure • Solar panels • Star tracker • Radiator • S-band antenna • Sun sensors • Radiator for the MONS telescope • The MONS telescope • Field Monitor • Sunlight protecting lid (closed during launch) Aalborg University, Department of Control Engineering

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33. Aalborg University, Department of Control Engineering

34. Key Specification • Mass: 80 kg, 100kg incl. 25% Margin. • Size: 60 x 60 x 71cm in Launch Configuration • S/C Power: 70 W avg. • Battery: 33V, 4.5Ah, Li-ion • Mission Life Time: 2 years Aalborg University, Department of Control Engineering

35. Aalborg University, Department of Control Engineering

36. Attitude Control Precision • Attitude movements have a dramatic effect on photometric precision, due to small spatialvariations in CCD sensitivity (pixel-to-pixel and sub-pixel). • Need to design the instrument, telescope and platform carefully. • Detailed computer simulations include: • effects of flat-field structure • ACS jitter and shape of telescope PSF (including off-axis aberrations). • readout and photon noise. • Results: photometric errors from ACS errors form a non-white noise source whose powerspectrum has the same shape as the ACS errors themselves. Aalborg University, Department of Control Engineering

37. Required ACS power spectrum • Assumed flat at frequencies below 10 mHz (should be true if the control loop is operatingcorrectly). • Assume power spectrum falls off as frequency squared (i.e., as 1/f in amplitude), asseems likely. The spectrum can then level out at frequencies higher than 10 Hz. • If ACS power spectrum shape is significantly different then further simulations will beneeded to specify new requirements. • Preliminary study by the Rømer ACS group shows feasibility of reaching 1.2 arcmin RMS Aalborg University, Department of Control Engineering

38. Required ACS precision Aalborg University, Department of Control Engineering

39. ACS Requirements What is the ACS Supposed to do? • Stabilise Satellite from tumbling situation (2 deg/ sec) • Stop the tumbling and, • Perform Sun Acquisition Maneuver • Provide a three axis stabilised attitude for commandedattitudes • Orient to desired attitude and keep it fixed (coarse) • Provide a stable platform for science observations • Requirements to attitude error spectrum • Provide sufficient onboard autonomy to handle fault eventsrelated to ACS • Handle one fault to prevent loss of mission • Environment: • Molniya Orbit Aalborg University, Department of Control Engineering

40. ACS Requirements 95% confidence numbers: Pointing Error: - P/ Y: 2 arcmin - R: 60 arcmin RMS Stability Error: - 1.2 arcmin Slew Capacity - 180 deg in 10 minutes Sun Exclusion: - 60 degrees - max 30 seconds with Sun <3 deg from MONS boresight Earth/ Moon Exclusion: - 55 degrees Aalborg University, Department of Control Engineering

41. Hardware Config and concept diagram Aalborg University, Department of Control Engineering

42. Disturbance Environment Aalborg University, Department of Control Engineering

43. Rømer Overall ACS Architecture Aalborg University, Department of Control Engineering

44. Optimal estimator update both the spacecraft attitude and the gyro drift rate. Kinematic gyro based prediction. Attitude Estimator Concept DesignSingle axis analysis Aalborg University, Department of Control Engineering

45. Attitude and attitude rate from dynamic modelof the spacecraft’s angular motion. (uncertainty due to RWA etc.). Gyro data are observations. Attitude Estimator Concept DesignSingle axis analysis - 2 Aalborg University, Department of Control Engineering

46. AD Structure Aalborg University, Department of Control Engineering

47. ACS concept diagram Aalborg University, Department of Control Engineering

48. AD modes Aalborg University, Department of Control Engineering

49. AC modes Aalborg University, Department of Control Engineering

50. ACS Workpackage breakdown Aalborg University, Department of Control Engineering