1. Spacebel, 5/04/05 Page 1 LYRA Instrument and Data Manager Software Requirements Analysis

2. Spacebel, 5/04/05 Page 2 Agenda Concept description LIM requirements presentation (SBI) LDM requirements presentation (SBI) Interface issues Open questions

3. Spacebel, 5/04/05 Page 3 PROBA 2 orbit Sun synchronous LTAN: 6:00 See emails F.Teston for details Eclipses: approximately 3 months eclipse season rest of the year: no eclipses maximum eclipse duration approx. 1100 sec. Concept description

4. Spacebel, 5/04/05 Page 4 PROBA 2 Pointing 1. Frames definitions Sun frame (Xsun, Ysun, Zsun) Xsun is spacecraft-sun axis ( = unit(Rsun – Rsc) where Rsun is the apparent sun vector from the Earth (Sun ephemeris) and Rsc is the spacecraft position vector. If S/C position is unknown onboard, Rsc is set to zero. Ysun is perpendicular to Xsun, in the plane defined by Xsun and the normal to the ecliptic plane, pointing towards the northern hemisphere. Concept description Earth Sun Rsc Rsun Xsun Ysun

5. Spacebel, 5/04/05 Page 5 S/C Fixed Body Frame Concept description Mechanical frame (Xmech, Ymech, Zmech)... With respect to S/C Payload frame (Xpl, Ypl, Zpl)... With respect to SWAP Spacecraft fixed body frame (Xbof, Ybof, Zbof)... Related to Payload frame, but origin in S/C COG. Reference frame for spacecraft attitude control.

6. Spacebel, 5/04/05 Page 6 PROBA 2 Pointing 2. Pointing in observation mode  four (baseline, up to 8 possible) large-angle rotations of 90° (or 360° / number of rotations) attitudes are commanded over one orbit in order to avoid blinding of the star trackers; For the rest of presentation: baseline number of rotations assumed)  the timing of the manoeuvres is such that the exclusion angles from the star trackers towards the earth are maximised; (performed on board -> cont. variation)  the 90° manoeuvres will take a few minutes and will be centred around these optimal switching times;  the time until the next rotation is continuously provided;  paving rotations are defined in the original sun frame. Concept description

7. Spacebel, 5/04/05 Page 7 PROBA 2 Pointing 2. Pointing in observation mode The observation mode is commanded as follows: the large rotation is commanded as a quaternion in the SUN frame: [q1 cmd, 0, 0, q4 cmd ]; the commanded large angle rotations will be taken from a list (of maximum 8) quaternions, configured by the ground; the index of the currently used large angle rotation will continuously be provided; the paving rotation is commanded as a quaternion in the SUN frame: [0, q2 paving, q3 paving, q4 paving ] Concept description

8. Spacebel, 5/04/05 Page 8 Concept description LIM mode diagram

9. Spacebel, 5/04/05 Page 9 Concept description Mode simplification: –Off (CSL/ROB survival mode -> idem SWAP) –Idle (CSL/ROB night mode -> idem SWAP) –Warm-up (CSL/ROB stand-by mode -> idem SWAP) –Acquisition (CSL/ROB nominal modes) Modes not implemented in SWIM: –First swtich on: will be performed by uploaded procedure –Bake-out mode: uploaded or onboard procedure –Calibration mode: uploaded or onboard procedure, using manually the imaging mode with different pointing configurations

10. Spacebel, 5/04/05 Page 10 Sequence diagram Nominal observation Concept description

11. Spacebel, 5/04/05 Page 11 Concept description

12. Spacebel, 5/04/05 Page 12 Concept description

13. Spacebel, 5/04/05 Page 13 Concept description

14. Spacebel, 5/04/05 Page 14 Open questions

15. Spacebel, 5/04/05 Page 15 Interace issues