1. Introduction
EXOSAT's orbital operations will terminate in the latter half, of 1986 due to
orbit decay and/or loss of attitude control gas. IUE's orbital operations, from
an ESA viewpoint, will terminate either following catastrophic satellite failure,
or should funding for further mission extension not be approved.
Both missions represent a very significant investment of the Scientific Programme
and both have generated and are continuing to generate invaluable data-bases,
which will be used by researchers long after the termination of mission
operations.
The advisory bodies, the Astrophysics Working Group and the Space Science
Advisory Committee, and the SPC have emphasized, particularly in discussion of
the long range plans for a 'European Space Information System', the need, not
only to preserve eventually such data in an archive but to keep them readily
accessible and useable in the shorter, post-operational term.
This paper outlines the Executive's plan for the
development and maintenance of the EXOSAT data-base, together with the
necessary scientific competence, to support the scientific
community. The SPC is requested to approved this plan.
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2. The needs of post-operational support and timescale
After the transmission from EXOSAT of its last bit, (the situation for IUE being
broadly similar) there will be a backlog of production of final observation
tapes and auto-analysis production to be cleared. There will also be
considerable tidying-up of documentation, including the need for an analysis of
the operations themselves for feed-on to future missions, e.g. ISO and the X-Ray
Cornerstone, etc. While the data remain proprietary to the observer for one year
after despatch, it will be necessary to continue support to the 'last' observers
as is done for current observers. On a longer timescale it can be anticipated
that updating of instrument calibration, software modifications
etc. will be required.
The EXOSAT interactive analysis system is providing a major
facility to observers not only at a time close to the observation but more
importantly for later analysis. Since its availability to the community, it has
been almost continuously fully booked. It will be necessary to continue to
provide this support if the EXOSAT mission is to be fully exploited.
Data from early in the mission are now entering the public domain and eventually,
of course, all data will be publicly available and support will be required to
enabledata-base access. Again the need for tile interactive facility be reinforced.
It will be essential to provide the infrastructure, equipment, and scientific
personnel for the proper support of the scientific communty wishing to
exploit the EXOSAT data. This infrastructure must include the scientists of tile
Observatory Team familiar with EXOSAT's instrumentation and the data analysis
systems. For the support to the community to be of the right calibre these
scientists will pursue their research activities (based on their own observations
and archive retrieval) which, during tile orbital operational phase have had to
take second place to the support role.
It will be essential for the data in the data-base to be brought to a common
standard, e.g. with respect to current instrument calibration, format etc., bad
or insignificant data sets will have to be purged and the data-base properly
structured for long-term archive retrieval as needed, for example, by a 'data
centre', see ESA/SPC(85)17. This can best be done by scientists actively working
with the data.
Defining the time of arrival of the last bit as To the best estimate for the
clearing of backlogs, finalising documentation etc. is of tile order of six
months to a year, i.e. TO+1 . During this interval the requirements on those of
the Observatory Team dealing solely with operations will reduce to zero.
It is very difficult to predict the rate of decay of tile interest in EXOSAT
data, but the next major international missions, fully accessible by the world
community, AXAF and the ESA X- Ray Cornerstone, will not fly until the
mid-1990's. In the meantime specialist missions, (ROSAT, ASTRO-C and SAX) will
fly. Observations with these satellites will, without any doubt, lead to
the question - what did EXOSAT see? - if only because of the ubiquitous property
of most X-ray sources - time variability.
The response to a questionnaire to the IUE 'community' indicated that intensive
use of the HE data should be foreseen for at least 5 years after termination
of orbital operations and this has been used as a guide for EXOSAT.
For present purposes for EXOSAT it is planned that, in tile period up to TO+4
years, the scientific manpower level of the Observatory Team would gradually
reduce and that support is provided to the 'level-of-effort' available. The
Executive limits the scope of this activity to 4 years at the present time, it
being assumed that after this period the
'European Space Information System' or something similar will
be in place. In this four year period it is the intention to use the ESIS
Network, to be established, to provide catalogue and eventually data access to
remote users.
The Executive will monitor the use of the EXOSAT data-base and report back to the
SPC as TO+4 years approaches.
3. Staffing and budget
The Observatory Teams performing the Scientific Operations of EXOSAT and IUE
comprise scientific supernumeraries, contract staff and with support from some
regular staff members. Currently for full operations the EXOSAT Team comprises
some 24 persons. This number would reduce to about the 50% level at TO+1 year and
to 25% level at TO+4 years. Associated with staff costs would be the running
expenditure for missions etc.
The computer systems utilised for data reduction and analysis are, in the Case of
EXOSAT, largely stand-alone and fully dedicated to the programme. However,
capital expenditure for upgrading and/or replacement of certain items must be
foreseen together with, of course, the necessary consumables. Some use is made of
the ESA main frame computers.
A budgetary estimate is given below for the activities of the Observatory Team
over the period from TO to TO+4. Some uncertainties exist, coming from precise
dates of staff redeployment, use of main frame, level of staff support and
associated overheads etc.
Year |
1(1987) |
2(1988) |
3(1989) |
4(1990) |
Yearly total (MAU) |
1.44 | 1.10 | 0.91 | 0.80 |
The total figure for the years is 4.25 MAU
The financial situation of the scientific programme (ESA/SPC(85)6 of 10 June 1985
under headings 'EXOSAT' and 'D/Sci Planning Reserve Extensions') foresaw EXOSAT
operated fully through to mid-1987 with a nominal run-down, corresponding to and
limited to the immediate clearing of backlogs etc. through to mid-1988. The
budget earmarked internally was 4.75 MAU. With EXOSAT operations terminating
earlier, it is the Executive's proposal to use these funds to support the
post-operational phase over the four years as described herein.
Recommendation
The Executive proposes the course of action described here to support EXOSAT in
its post-operational phase and invites the SPC to approve the funding as
indicated.
EUROPEAN SPACE AGENCY
ASTRONOMY WORKING GROUP
Recommendation on the EXOSAT post-operational phase
The Astronomy Working Group supports the proposals by the Executive for the post
operational phase of the EXOSAT mission as described in ESA/SPC(86)3. The AWG
considers it absolutely essential that the invaluable resource represented by the
EXOSAT data base be preserved and worked on and the scientific community
supported in its use in the years after orbital operations are completed. (The
AWG pointed to the intensive ongoing Use of the Einstein data base and the
excellent science now coming out. The same could be expected for EXOSAT.) The AWG
considers that such post-operational phase support should be foreseen by tile
Executive for IUE (currently still operational) and ISO (currently at the
beginning of the development phase).
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