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Long Term Science working group status L SWT Venice , 30/03 -01/ 04 /200 9

Long Term Science working group status L SWT Venice , 30/03 -01/ 04 /200 9. OBJECTIVES.

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Long Term Science working group status L SWT Venice , 30/03 -01/ 04 /200 9

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  1. Long Term Science working group status LSWT Venice, 30/03-01/04/2009

  2. OBJECTIVES • The objective of this working group (2 workshops held on 10-11/02 and 04/03) is to set up the lander functioning when the primary battery is fully discharged, that is when available energy is minimal • For that we have to: • Study the external conditions on the comet between 3 and 2 AU • Check the individual sub-system constraints in these conditions of T° and power (CDMS, PSS and secondary battery, TCS and absorbers, TxRx, …) • Set up Philae and CDMS modes to cope with all kind of conditions • Check if all test means are available to test this phase • Make that all is feasible before end of 2009

  3. R  COMET ENVIRONMENT IMPLICATIONS • Comet at 3 AU means a limited power received by 2 ways inside the thermal controlled compartment: • Solar panels redistributed in thermal and electrical energy • Absorbers redistributed in thermal energy only • The different conditions of illumination are depending on 2 parameters only (co-obliquity q, latitude f), from which 28 cases are simulated and 14 cases can be extracted (choosing the right hemisphere)

  4. COMET ENVIRONMENT IMPLICATIONS • Thermal environment gives constraints to: • the lander total dissipation • the external wall temperatures : T° cells and cell efficiency • Cold temperatures are favourable (first calculations made by CNES with the SABER tool show from +25°C to -100°C the cell efficiency is increased of about 25%) • Radiation dose effects are not favourable (first PoliMi results) • Other effects as dust or ice covering, shadows • AI on CNES for gas refreezing • AI on PoliMi for cell tests • Total dissipation and particularly by the absorbers during nights has to be precisely determined • AI on DLR

  5. COMET ENVIRONMENT IMPLICATIONS • First thermal map at 3 AU (LAM/ O. Groussin) -40°C sub-solar point, -140°C night side

  6. Y W1 W2 W3 X X W4 W5 200 ° 330 ° Sun illumination COMET ENVIRONMENT IMPLICATIONS • Optimisation of Philae orientation: • Confirmation of best attitude: to turn Wall3 (W3) to Sun highest elevation (generally South direction in northern hemisphere, North in southern) • When to do this pointing ?

  7. COMET ENVIRONMENT IMPLICATIONS • Optimisation of Philae landing site (values after orientation) 3 AU

  8. SUB-SYSTEMS CONSTRAINTS • Primary and secondary working ranges • SB maximum charge (around 95%) and maximum discharge (double protection) • SB best working temperatures in charge / discharge (AI on CNES) • Charge level measurement (CDMS measures worst case) • Solar arrays performances (AI on PoliMi) • At cell level, T° tests • At array level, shadowing and radiation effect • Shunts and MPPTs performances (AI on MPS) • Consolidation of power required by each sub-system (LUM values verified by each responsible)

  9. CDMS – PHILAE BASIC MODESPROPOSAL • Philae Wake-Up mode: this mode is required when Philae shutdown is mandatory During nights, shutdown. During day, when SA are illuminated enough, this mode is automatically switched on and compartment heating starts • CDMS Super-Low power mode: DPUs are alternately ON and OFF with regularly the 2 DPUs OFF, TCS heating and SB charging possible with power in excess, Minimal power: 2,4 W • CDMS Low power mode: DPUs are alternately ON and OFF, TCS heating and SB charging possible with power in excess, Minimal power: 3,6 W • CDMS Nominal mode: 2 DPUs ON, TCS heating and SB charging possible with power in excess, Minimal power: 4,8 W

  10. CDMS – PHILAE BASIC MODES PROPOSAL • Philae quiet mode: CDMS in nominal mode + 1 Rx ON every 30 mn for 2 mn, TCS heating and SB charging possible with power in excess Power: 7,3 W (peak value) • Philae nominal mode: CDMS in nominal mode + TxRx working during visibilities, TCS heating and SB charging possible with power in excess Power: 10,8 W (for visibility periods) -> SC TM retrieval only possible in this mode -> if the landing site is correctly chosen, if landing is nominal (operational LG / orientation possible, nominal attitude, no shadowing), possibility to achieve PQM at 3 AU (TBC)

  11. OPEN POINTS ON PHILAE WORKINGDURING LTS • 23 open actions • Decisions to be taken at the next workshop on 27/04 • Confirmation of CDMS and Philae working modes (rationale: to remain as simple as possible) • Check if all contingency cases have been taken into account • Check what has to be monitored / commanded by Ground Segment according to modes (list of HK and TC parameters, strategy of MM EEPROM use, strategy of TxRx use) • Assess the possibility to do science in CDMS modes below the nominal modes (on solar panels immediate power, on SB during comet nights) • Determine the nominal operational loop when Philae nominal power mode is achieved for day and night (science every day)

  12. LTS SPECIFIC TESTS • The current Solar Array Simulator is not usable at GRM because of too small currents • Specification of a new SAS on-going between PoliMi and LCC • Delivery of new SAS planned in autumn • In parallel to SDL tests, LTS tests will be done after CDMS V8.0 delivery end of September and before delivery to ESA in January 2010 • only 3 months • Priority to SDL phase testing in case too much work

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