Long Term Science

working group statusLSWT Venice, 30/03-01/04/2009

2 LSWT meeting, Venice, 30/03-01/04/2009

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 LSWT meeting, Venice, 30/03-01/04/2009

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 , latitude ), from which 28 cases are simulated and 14 cases can be extracted (choosing the right hemisphere)

R

4 LSWT meeting, Venice, 30/03-01/04/2009

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 LSWT meeting, Venice, 30/03-01/04/2009

COMET ENVIRONMENT IMPLICATIONS

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

6 LSWT meeting, Venice, 30/03-01/04/2009

COMET ENVIRONMENT IMPLICATIONS

Optimisation of Philae orientation:

X

Y

X

200 ° 330 °Sun illumination

W3

W1W2

W4W5

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 LSWT meeting, Venice, 30/03-01/04/2009

COMET ENVIRONMENT IMPLICATIONS

Optimisation of Philae landing site (values after orientation)

3,96 0 8,9 8,74 7,86 15,12 4,26 17,47

4,58 2,82 8,1 10,4 6,89 15,9 7,4 15,13

4,32 4,9 4,67 7,44 8,91 12,4 8,55 8,73

3,57 5,66 4,5 4,9 4,65 2,81 7,42 0

OBLIQUITY (°)

0 30 60 90

LATITUDE

(°)

90

60

30

0

3,96 17,64 22,98 21,73

7,4 18,5 22,79 22,53

7,42

9,22 12,11 21,31 17,28

9,23 9,4 7,46

3 AU

8 LSWT meeting, Venice, 30/03-01/04/2009

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 LSWT meeting, Venice, 30/03-01/04/2009

CDMS – PHILAE BASIC MODESPROPOSAL

Philae Wake-Up mode: this mode is required when Philae shutdown is mandatoryDuring 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

LSWT meeting, Venice, 30/03-01/04/2009

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 excessPower: 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 excessPower: 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

LSWT meeting, Venice, 30/03-01/04/2009

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

LSWT meeting, Venice, 30/03-01/04/2009

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