Solar Orbiter - Remote Sensing Payload Working Group

Solar Orbiter - Remote Sensing Payload Working Group

Mid-term meeting - 25-26 November 2002, ESTEC

Monday 25 November & Tuesday 26 November (Room: Einstein)

Start: 11:00

PWG Plenary #1- Welcome and introduction (Marsden)- Aims of meeting (Marsden and Rando)- Status of Solar Orbiter in ESA (Marsden/Peacock)

Remote Sensing Splinter #1- Status of PDD inputs (Appourchaux)- Discussion of each instrument PDD in turn (Harrison/Fleck) (what is needed, what is outstanding and who can supply

details?)



Remote Sensing Splinter #2Feasibility/Technical Actions and Studies- Summary of status of actions (Harrison)- Open discussion on recommendations to ESA based on

actions

- What next? Completion of remaining actions? Report? How do we relay recommendations to ESA?

- Solar Orbiter Scientific Goals

Plenary #2- Summary of Splinter Sessions (Harrison/Wimmer)- Future PWG activities

- AOB



Feasibility/Technical Studies & Actions

Aim: To demonstrate feasibility of paylaod, especially given the thermal & particle environment and the mission limitations (e.g. telemetry, autonomy). Make recommendations to ESA. Co-ordinate/request studies.

Method: By identifying the technical challenges (last meeting) and addressing specific actions. [Remember: We are demonstrating feasibility, nothing more.]

Comment: The PDD activity is an ‘extra’, parallel demand on us, but it is necessary for us to do what we can to take advantage of it.




Last Meeting: Technical challenges identified and listed. Action list set up and assigned.

Web site: Web site set up at http://www.orbiter.rl.ac.uk/solarorb/rspwg/, lists actions, provides notes from initial meeting, action spread sheet, Action Completion reports. Other documents (e.g. PDDs) can be found at http://zeus.nascom.nasa.gov/~bfleck/Orbiter/PLWG/Documents/.




Progress to date: 73 actions listed. 22 ticked off, i.e. 30 %. Not very impressive response from some – especially as some of the actions are rather basic, e.g. telemetry ‘back of the envelope’ calculations.

Next Step: Assess remaining actions; Pull out recommendations/requests; Discuss report/schedule.

Warning: Next Chair of SSWG (Peter Cargill) – ‘better demonstrate feasibility by Spring 2003’. AO June 2004 (1 year after BC)?



Recommendations:

1. Pointing: It is recommended that a hard mounted, joint-pointing policy be adopted, which is in keeping with the science goals of the mission, but will save mass and power.

2. Image Stabilisation: It is recommended that the VIM signal be used for all instruments that use an image stabilisation system, to save mass and complexity.

3. Resources: All options should be considered by the Project to maximise the payload mass, telemetry, memory capacity and power; the scientific return is increased with increased payload resource.



Other Recommendations from Actions:

Some completed actions make recommendations.

If they are concerned with critical technologies (especially involving more than one instrument) or are spacecraft-wide/mission issues, then they must be discussed and passed on to ESA – if ESA are serious about performing studies, we must request them formally now.




4. Thermal Control: Given the extreme thermal environment, it is recommended that there be a study of a spacecraft-wide approach to thermal control (Action 1.1/1.2 EUS).

e.g. What actions can be taken at a spacecraft level to dampen the thermal variations, to dissipate heat, to allow access to open space etc…




4. Thermal Control (continued):

Note: The RAL/Cranfield and MSSL studies stress that it is not so much the absolute temperatures that kill you, as the variations! (Possible actions: Reduce aphelion? Heat switches? Heaters? Adaptive optics?…)

e.g. 1500 mm CFRP will expand by 50-75 micron with variation of 100oC.

- How do you interface to spacecraft? Same materials?

- Do we use adaptive optics or is optical depth of focus OK for this?

- Note also: the use of CFRP probably means a 100-130oC upper limit (outgassing, glue)?




4. Thermal Control (continued):

However, only one instrument input has addressed the thermal ‘action’. Thermal feasibility has NOT been demonstrated for almost all insruments. This must be done a.s.a.p. if our desire to have a Solar Orbiter mission is to be taken seriously.

However, the lack of any spacecraft input on the thermal interface between instrument and spacecraft is hindering thermal modelling. It is a design driver. We need input from the Project on the thermal interface, on thermal policy and views to space. This is a request to the Project – now.




5. ESA Study of LCVRs: Liquid Crystal Variable Retarders (LCVRs) may be critical to the operation of VIM & UVC - (as polarization modulators). No LCVR has been in vacuum for a long period & put into extended operation after a long time, & the radiation impacts must be considered. Is this a spacecraft issue or just for the instrument(s) involved? (Action 2.2).




6. Contamination Control:

(i) Instrument teams must adopt a stringent contamination policy in the laboratory, but also in operations (e.g. long out-gassing period) (Action 3.1).

(ii) A test activity on the degradation of selected optical surfaces under high irradiation and particle flux levels should be recommended as part of a Solar Orbiter development programme (Actions 3.1 & 3.5). Can we define such a test and the materials to test?




6. Contamination Control (continued):

Test 1: Contamination of optical surfaces under high irradiation levels.

Basic test – EUV/UV reflectivity of optical surfaces at normal incidence under extreme temperatures, under vacuum.

Surfaces: SiC, SiC gold coated, what else?…

Temperatures: 0oC to 100oC, perhaps higher? Cycles to represent orbit.

What facilities are available for this? Who can do it?

Action to define test: Udo, Luca?? To be relayed to ESA now.




6. Contamination Control (continued):

Test 2: Degradation of optical surfaces from particle impacts.

Basic test – Examine optical surfaces/coatings after exposure to selected particle environments, perhaps also under high temperatures. Look for blistering and sputtering effects.

Surfaces: e.g. SiC gold coated, what else?… (see note on multilayers later)

Particles: Proton and ion beams.

What facilities are available for this? Who can do it? Extend previous CDS study? Action to define test: Harrison? To be relayed to ESA now.




7. Detector Development: Most instruments call for detector systems now under development, e.g. 4kx4k 5 micron back-thinned APS or diamond. (Actions 10.3-10.5). Does this require any effort from ESA or is it all under control?




8. Autonomous Target Selection/Pointing: After a feasibility study (Action 10.7), we recommend that this facility be adopted for Solar Orbiter, to ensure the best scientific return. Concerns over instrument/mission safety must be addressed.

9. Planning and Operations Cycle: A study of the possible planning and operations scenario (Action 10.9) has recommended a 150-day planning cycle, possibly with a dedicated science centre. ESA must examine the study report and decide on an approach prior to the AO.




10. Operations Scenario & Memory: It is recommended that the Solar Orbiter mission is run with a full 150-day observation period and that on-board memory is maximised in order to obtain the best encounter observations. (Action 10.9).

11. Solar Orbiter Goals: The Solar Orbiter goals are NOT well/properly defined. This is beginning to ‘hurt’ – i.e. potential proposing groups are not really able to ‘tune’ their instruments to the priority goals. (See post-Tenerife document). It is recommended that the SOPWG address this now.




12. Multilayers: Action 1.6 not completed. However presentation by David Windt (Columbia, New York) at MSSL on multilayer stability:

(i) For ‘traditional’ multilayers, e.g. Mo/Si, Mo2C/Si, have tested to high temperatures (see Stearns et al. J. Appl. Pys. 67, 2415, 1990). No effects up to 100oC. No real concerns up to 150oC but degadation seen at 200oC. Can we arrange repeat tests with 0-100oC cycling to mimic orbit and long-term effects?

(ii) No reports of degradation due to radiation (e.g. Kortright et al., J. Appl. Phys. 69, 168, 1991).




12. Multilayers (continued):

(i) The effects of particles have not really been tested. Possibly a problem is the multilayers are not well protected. Should we include multilayers in the particle test activity on surfaces?



Real Concerns:

1. Thermal feasibility has NOT been demonstrated for most instruments

2. Thermal policy/interfaces from S/C required to progress beyond basics

3. Multilayer and optical surface integrity at high temperatures and particle fluxes needs to be established

4. Instruments must be able to cope with latch-up

5. We must have an automated instrument safing policy/plan/procedure

6. We really need a set of focused goals for Solar Orbiter!



Schedule/Remaining Activities:

Refine PDDs as much as possible - because that will influence the mission we get!

Complete action studies by end of February 2003.

Write final report by April/May 2003 (based on Action Response Forms) - including all recommendations.

Any clear recommendations MUST be passed to ESA as they come up.

Define any studies/test activities as agreed, and pass on to ESA now!

Recommend a set of focused goals for the mission!