# ESA Solar Orbiter Remote Sensing Payload Working Group

[Kick-Off Meeting -- 16/17 May 2002]{.underline}

[Draft Notes -- Richard A. Harrison]{.underline}

This note outlines the main points of the ESA Solar Orbiter Remote
Sensing Working Group meeting of 16/17 May 2002, which was held at
ESTEC. It outlines the basic approach for our study and contains the
first draft of the list of 'challenges', which we compiled. [Note that
the final section lists actions which are to be tackled in the immediate
aftermath of the meeting!]{.underline}

1.  [Basic Approach of Working Group]{.underline}

-   List the instruments to consider - including any additional
    instruments which we feel should be included.

-   Consider each instrument in turn and list the challenging/problem
    areas.

-   List any mission/operational challenges/problems.

-   Classify the resulting list of challenges/problems into the
    following categories:

(i) 'Global' (mission/operatonal) challenges (e.g. pointing);

(ii) Multi-instrument challenges (e.g. detectors);

(iii) Instrument-specific challenges which are potential show-stoppers,
      and

(iv) Other instrument-specific challenges.

-   We ignore category (iv) (this is for the proposing teams!) and act
    upon the others.

-   Assess the resulting lists and assign studies or define test
    activities to be done.

2.  [List of Instruments]{.underline}

    1.  Strawman Instruments

VIM -- Visible Light Imager and Magnetograph

EUS -- EUV Imaging Spectrometer

EUI -- EUV Imager

UVC -- UV and Visible Coronagraph

RAD -- Radiometer

2.  Additional Instruments to be considered

High Energy (X-ray/gamma-ray) imager

X-ray High Temperature Imaging Spectrometer (\<10^7^K)

Heliospheric Imager

3.  [List of Instrument Challenges/Problems]{.underline}

    1.  ALL INSTRUMENTS

        1.  A thorough study of the thermal feasibility of each
            instrument is required, probably including modelling and
            test activities in some cases. In particular, it must assess
            the thermal balance, the impact of the orbital variations to
            the thermal input and the impact of (and ways to cope with)
            degradation/aging of the reflectivity of the optical
            systems. An estimate of the radiator size requirements must
            be made. *Category (iii).*

        2.  The thermal 'regulation', during the orbit, of each
            instrument must be considered, for example, using regulating
            radiators (e.g. cut/limit the radiators at/near aphelion) or
            switchable heatpipes, to damp the extremes in the
            variability. This must be studied to demonstrate that we can
            cope with a heat load varying by a factor of 25. *Category
            (iii).*

        3.  A realistic study is required to show that the scientific
            operation of each instrument is not compromised by the
            limited telemetry rate. *Category (iii).*

        4.  A realistic study of the instrument mass of each instrument
            is required. *Category (iii).*

        5.  A realistic study of the instrument power of each instrument
            is required. *Category (iii).*

    2.  VIM

        1.  Can the proposed camera system cope with the perceived
            particle environment? See detector section below. *Category
            (ii).*

        2.  Can we demonstrate that electro-optically modulated liquid
            crystal devices are not influenced by the particle and
            thermal environment? *Category (ii).* \[with UVC\].

        3.  VIM carries a sensor used for image stabilisation. It is
            suggested (below) that this be used as the image
            stabilisation signal for all instruments requiring
            stabilisation -- to save mass by avoiding duplication.
            *Category (i)*.

        4.  For the thermal and particle extremes which Orbiter will
            encounter, how do we guarantee the required levels of
            cleanliness in VIM? *Category (ii)*.

        5.  For VIM, a light-weight mirror is required. Is the
            technology available, or on the horizon for such a mirror?
            *Category (iii).*

        6.  Is it feasible to include a front filter on VIM? *Category
            (iii).*

    3.  EUS

        1.  The question of contamination and subsequent degradation of
            the optical systems must be considered, especially in the
            extreme thermal and particle environment. Consider tests
            which could be performed as well as outgassing policies
            etc... *Category (ii)*.

        2.  If we remove the independent pointing capability, can we
            include a method for image alignment? This is a general
            question for several instruments to ensure co-pointing.
            *Category (ii)*.

        3.  Can we assess the integrity of multilayers at high
            temperatures including a definition of tests to be done.
            *Category (ii)*.

        4.  Can we demonstrate that 5 micron 4kx4k APS, visibly blind
            detector systems are likely to be possible for such an
            instrument? *Category (iii) but see detector section below.*

        5.  There is some concern over the impact of the particle
            environment on optical coatings in the light of studies of
            hydrogen bubbles forming under gold coatings in the solar
            wind. This must be assessed. *Category (ii).*

        6.  The strawman EUS is too long. Can we demonstrate that a
            shorter instrument is possible. *Category (iii).*

> 3.3. EUI

## Note: Alan and Don -- produce definitive list of questions for EUI...

1.  The instrument will most likely include multilayers. Can we assess
    the integrity of multilayers at high temperatures including a
    definition of tests to be done. *Category (ii)*.

2.  The proposed EUI is too long. However, the current HRI baffle system
    is not long enough! Can we demonstrate that a shorter instrument is
    feasible? *Category (iii).*

3.  The FSI filter sees full Sun. This will, most likely, not survive at
    25 solar constants. We must assess and cater for this. *Category
    (iii).*

4.  Must assess the most realistic detector option given the particle
    environment. See detector discussion below. *Category (ii).*

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3.  UVC

    1.  With a common pointing policy, UVC must be able to cope with
        likely offsets. Assess this. *Category (iii).*

    2.  We must assess the integrity of the liquid crystal device in the
        particle/thermal environment. *Category (ii) \[with VIM\].*

    3.  The instrument will most likely include multilayers and, thus, a
        consideration and test of multilayers at high temperatures is
        required. See EUS and EUI. *Category (ii).*

    4.  The best options for detectors must be assessed, given the
        particle environment. See detector discussion below. *Category
        (ii).*

4.  RAD

*Note: Thierry to produce the list. Need list of issues/challenges.*

5.  Heliospheric Imager

Note: Clarence to contact Bernie and to take lead on this. Need list of
issues/challenges.

6.  High Energy Imager (Hard X-ray)

> Note: STIX presentation given by Gordon Hurford -- ideal link from
> particles at Sun (flares) and in-situ, with gamma-ray spectrometer.
>
> *Note: Gordon to list issues/concerns.*

1.  One area of concern is the STIX CCD which would probably not be the
    best option at 0.2 AU. Assess this. *Category (iii).*

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7.  Grazing Incidence X-ray/EUV Coronal Imaging Spectrometer

> Note: Discussion presented by Luca (see Tenerife abstracts). General
> conclusion was that this is an option within EUS rather than a
> separate instrument.

8.  GENERAL REQUESTS FROM SPACECRAFT STUDY

    1.  Can we assess the possibility for a payload mass increase?
        *Category (ii).*

    2.  Can we assess the possibility for a payload telemetry increase?
        *Category (ii).*

    3.  Can we assess the possibility for a payload power increase?
        *Category (ii).*

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4.  [List of Mission/Spacecraft/Operational/Multi-instrument
    Challenges/Problems]{.underline}

    1.  Pointing

> It is proposed that the instruments are hard-mounted to the spacecraft
> and that we have a co-pointing policy. This is in keeping with a
> co-ordinated JOP/pointing scenario. It is recognised that this can
> save mass, power and will simplify operations.

1.  Assess this option for UVC -- how do we compensate for this? UVC
    will need some adjustment. *Category (iii).*

2.  How do we cope with alignment -- some method is required to ensure
    that we have aligned fields. Does this simply require large areas or
    some mechanisms? *Category (i).*

> Recommend that we adopt a hard-mounted, joint pointing policy, which
> is in keeping with the science goals but will save mass, power etc...

2.  Detectors

> It is recognised that we must demonstrate feasibility, rather than
> select the 'final' detector system. It is noted that the demands on
> small pixels (down to 5 microns), array sizes (up to 4kx4k), mass, and
> the particle environment may be very restricting to CCD systems and
> this suggests that APS and Diamond detectors are appropriate. The
> different advantages of these two are noted but some areas require
> study, assessments and tests.

1.  Assess the status of the APS and Diamond systems regarding the
    requirements for Orbiter. Does this require some technological
    activity funded by ESA? *Category (ii).*

2.  Can we demonstrate that an APS system can be EUV sensitive (and
    rad-hard?) in good time for Orbiter? Should some development work be
    requested? *Category (ii).*

3.  Can we characterise the expected particle environment at 0.2 AU,
    including solar wind flux, flare/CME/shock accelerated particles,
    cosmic rays and neutrons? In particular, the anticipated neutron
    environment is of concern. Assess the impact of this on the APS and
    Diamond systems. *Category (ii).*

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3.  Image Stabilisation

    1.  For image stabilisation -- best to use signal from only one
        source, i.e. the VIM. We must assess this option fully.
        *Category (ii).*

Recommend that we use the VIM signal for all instruments that use an
image stabilisation system. Will save mass -- i.e. no duplication.

4.  On-board Intelligent Operation

> Can we have on-board target recognition for autonomous target
> selection? Note that this will most likely drive pointing of
> spacecraft (given above recommendation).

1.  Initiate target recognition, automated pointing study to assess
    fully how we cope with this for Orbiter. List what targets could be
    selected and the responses. What timing constraints exist for what
    targets? What mode changes could be envisaged? Will require
    image/data on board inspection and reaction. *Category (i).*

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5.  Operations Planning

> Treat the mission as an encounter mission with a 149 day planning
> cycle. Organise the encounter periods using JOP selections for the
> passes. Selection of some targets can be done well ahead of time and
> updated nearer to pass. Some targets need intelligent selection.

1.  Assess the operations scenario based on this encounter mission
    scenario? *Category (i).*

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6.  Instrument Safing

    1.  What are the hazards for each instrument and how should the
        instrument respond? Include an assessment of transferring data
        to warn other instruments that do not have access to such data
        (e.g. warning UVC of a flare). Include assessment of
        flare/particle storm impact and spacecraft emergency. Include
        thermal impact of closing doors. *Category (ii).*

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5.  [ACTIONS! - Next Steps -- Is everything on the list?]{.underline}

> The following people are to co-ordinate a final check on the list
> within the interested groups to ensure that everything that should be
> listed is indeed listed:
>
> VIM -- Valentin
>
> EUS -- Richard
>
> EUI -- Don/Alan
>
> UVC -- Silvano
>
> RAD -- Thierry
>
> High Energy Imager -- Gordon
>
> Heliospheric Imager -- Clarence
>
> Global/Mission Issues -- Co-Chairs
>
> Immediate Schedule of Actions:

-   Draft list from co-chairs to all by May 24.

-   Response from the above people by mid-June to confirm that list is
    complete.

-   Co-Chairs to discuss assignments of the tasks and the communication
    of the group over the coming months.

-   Co-chairs to fix mid-term meeting.

\[R.A. Harrison & B.Fleck - May 17 2002\]