Special Orbits: January to May 2001

A.Fazakerley, 14 December 2000
Last Updated: 20th March 2001 (primarily revision of discussion of orbit - tbc)

Introduction

This discussion document contains a list of the currently proposed (by JSOC) special orbits, and describes where and when the data is acquired, and in what telemetry mode. It discusses possible uses we may choose to make of Special orbits in general, and proposes some possibilities for the particular orbits proposed by JSOC. Other teams may wish to propose different alternatives. Note that detailed instrument mode definitions are not made in this document.

Proposed Uses of Special Orbits

1. Co-ordinated Science Operations using instrument modes other than those used on standard orbits (some more specific ideas are included in this document)
2. Co-ordinated Interference Testing; repeat already attempted tests if necessary, carry out successful tests in different environment as needed.
3. In-flight Calibrations between different instruments on the same spacecraft
4. Instrument specific calibration or similar (e.g. may want to ensure that no interfering instruments are running).

Summary of orbits and one set of possible uses

(see also the following discussion)

Note, these currently exclude the option of BM operations at both a quasi-perpendicular and a quasi-parallel bow-shock crossing and the (electron or otherwise) foreshock option may not be ideally placed (?). Perhaps this should be addressed in a further plan modification?

Some Dayside-related Special Orbit Proposals from 1996   (summarised; these are a subset of those that I am aware of)

Note, PEACE non-standard operations could mean using non-standard energy range coverage from the sensors as well as non-standard data product return.

1. Solar Wind Turbulence

2. Foreshock Structure, Waves/Related Particles

3. Bowshock Physics Studies (single point, and multi-point for surface shape & motion)

4. Magnetopause Structure (single point, and multi-point for surface shape & motion)

5. Nightside Auroral Field Lines

(subject to perigee constraints - possibly prohibitive of lowest altitude operations at present)

6. Wave-Particle Interactions (for both Passive and Active variants)

7. Cold Plasma Studies

Other teams are invited to propose additional scenarios, and to comment on those proposed here.

Orbit 90

Planning Period 37

Orbit from January 23 15:50 approx. to January 26 01:00 approx (perigee to perigee)

LT apogee 14.5

LUNAR ECLIPSE SPECIAL OPERATIONS

Rationale

The solar photon flux is reduced during the partial lunar eclipse. The spacecraft potential must change as the photo-electron flux from the spacecraft falls, and the local electron cloud will change correspondingly. The event occurs in the solar wind (unlike other spacecraft eclipses which occur in the magnetosphere). The event may provide valuable measurements of the solar wind electron population to the lowest energies, while the spacecraft potential is lower than is usually seen in the solar wind, so that a significant part of the spacecraft-generated electron population that is seen when the spacecraft is in full sunlight may be absent.

Telemetry Return

Current planning has an N-B-N interval consisting of [0.5hr NM1 -1.2hr BM1 - 0.5hr NM1].

The following table of eclipse data is based on information from JSOC dated 07 Jan 2001 (based on ESOC Event Files). The Entry and Exit times refer to the boundary between full sunlight and the penumbra. The spacecraft are not expected to enter the full shadow (umbra).

JSOC plans to start BM1 coverage at 06:05:53 and finish it at 07:17:53, giving about 10 minutes of margin before and after the eclipse boundaries are encountered.

Overview of Instrument Modes

These are suggestions by PEACE and JSOC, as placeholders for firm statements from the other Teams, unless otherwise indicated.

The intention is to make good low energy plasma measurements and otherwise monitor the natural variation of the spacecraft potential and the surrounding electron sheath as the spacecraft moves in and out of shadow. Instruments which might perturb the spacecraft potential are thus proposed not to do so, although this is open for discussion.

Note that it is important to verify which instruments need the spacecraft sunpulse for normal operations, and which of those have alternate modes of operation allowing them to operate during the eclipse.

Further remarks

At the October 2000 SOWG, JSOC and ESOC announced that the spacecraft would experience a lunar eclipse on Orbit 90, while outside the magnetosphere. PEACE requested that this rare lunar eclipse become a Special Orbit activity.  Several other instrument teams expressed interest as well.

JSOC responded with a plan at the  November 2000 SWT for which Orbit 90 had three acquisitions in standard operational modes:

1. NM across perigee
2. N-B-N with NM coverage of the Magnetopause and BM coverage targeted on the Bowshock
3. NM coverage of the Lunar Eclipse.

PEACE requested a further change at the December IFC Review Meeting, to permit BM1 coverage of the eclipse interval, to allow the return of detailed 3 D distributions. This was agreed, and JSOC achieved this by taking a portion of the BM TM resource from the Bowshock interval.

Orbit 114

Planning Period 45

Orbit from (DoY 80) March 21 18:50 approx. to (DoY 83) March 24 04:00 approx (perigee to perigee)

LT apogee 11.25 (High chance of Cusp)

The plan is for one acquisition:

N-B-N starting above the Radiation Belts, with BM coverage of the Magnetosheath and continuing into the Solar Wind

 INSTRUMENT CALIBRATION/TECHNICAL MODES

1. FGM Calibration Activity.

FGM data on IEL to RAPID, CIS, PEACE, EDI does not describe the local plasma environmental magnetic field.

Time: (DoY 81) March 22 10:46 to 10:53

Region: Expected to be Solar Wind

2. PEACE Operational Level Test.

PEACE varies MCP level in one sensor while the other monitors the environment, and vice versa. Moments  data to be interpreted with care. PAD data not available.

Time: (DoY 81) March 22 13:40 to 14:10

Region: Expected to be Solar Wind

SPECIAL INSTRUMENT SCIENCE MODE

1. PEACE Telemetry in BM1

PEACE sends COR, PAD, LER as usual, plus 3DX-apl-60w08, plus 3DR-h

BM1 is from 02:46 to 07:16 on March 24

Orbit 115

Planning Period 45

Orbit from (DoY 83) March 24 04:00 approx. to (DoY 85) March 26 13:08 approx (perigee to perigee)

LT apogee 11.25 (High chance of Cusp)

The plan is for one acquisition:

N-B-N starting above the Radiation Belts, with BM coverage of the Magnetosheath and continuing into the Solar Wind

SPECIAL INSTRUMENT SCIENCE MODE

1. PEACE Telemetry in BM1

PEACE sends COR, PAD, LER as usual, plus 3DX-apl-60w08, plus 3DR-h

BM1 is from 11:56 to 16:26 on March 24

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Last Updated: 20th March 2001