Updated: 23 March 1998
ISO's liquid Helium depleted! (09/Apr/98)
This document aims at presenting a top-level summary of the status of those elements of ISO directly of interest to an Observer. As the status evolves, this posting will be updated. The topics currently included are:
A number of tools have been placed on the WWW to enable Observers to track the progress of their own observing programmes. An overview is given on the page, "How to Manage an ISO Observing Programme". These tools include:
For further information on the latest status of the various instruments, access the periodically-updated instrument specific pages:
| CAM | LWS | ISO | PHT | SWS |
|---|
Details of the implementation of the data rights proprietary rights policy are available here.
The following observing modes have been released for general use:
No observing modes remain un-released.
Release Policy: The policy of the Observatory is not
to release any observation for scheduling until the Observer has given an
explicit go-ahead by agreeing to a "PH" (proposal handling) report.
The Observer has the responsibility for ensuring that the user-entered
parameters
are correct.
HELPDESK: All communications should be made via
the ISO HELPDESK (https://support.cosmos.esa.int/iso).
This account is checked regularly, logged and an automatic acknowledgment
of each mail is made to confirm receipt. If you do not receive this
acknowledgment
within 24 hours, please re-send.
Updating Programmes: Observers may update the un-executed
parts of their proposals. Contact should be made with the ISO HELPDESK,
either to specify the changes or to arrange a visit or remote login. About
half of the updates are made by Observers specifying the changes to the
SOC via an e-mail to HELPDESK, about one-third by a remote login and the
remaining one-sixth via a visit to PDEC in ESTEC or to IPAC.
Execution Status: Observers may check the
ISO Observing Log for the status of their programmes. As of 21 March, ISO
had successfully carried out 25937 observations, totalling 10237 hours,
during the routine phase.
Cryo-system: Behaving as predicted with the temperatures
and helium mass flow rates being nominal.
Lifetime: ISO's useful in-orbit lifetime
depends on the amount of liquid helium remaining on board. The technique
used to determine the remaining mass is to inject a known quantity of heat
into the liquid and to measure the temperature rise. The first direct
measurement
of the remaining liquid helium was made on 5 September 1996 and a second
one on 14 May 1997. Taken together, these two measurements yielded an estimate
of 10 April 1998 (+/- 2.5 weeks) for the date on which the liquid helium
coolant would run out. A third measurement was sucessfully carried out on
11 December but did not improve the accuracy of the prediction. However,
it gave indications that the remaining lifetime might be at the upper end
of the measurement accuracy, i.e. up to the beginning of May 1998. This
predicted in-orbit lifetime exceeds the specification of 18 months by some
10-11 months, thereby significantly enhancing the scientific return of the
mission.
Optical: No indications of defocus or aberrations. Analysis
of an ISOCAM image taken at a wavelength of 15 microns shows the first
6 Airy rings!
Pointing: Better than specifications; figures are given
in the table below. Two dedicated periods of observing time (on revolutions
137 and 264) were devoted to investigations of possible systematics in the
absolute pointing error. Having completed the analysis of this data, various
fine tunings were made to the system. The absolute pointing error has been
reduced to less than 1.5 arc seconds.
| Units | Spec. | Now | ||
|---|---|---|---|---|
| Relative Pointing Error (short term jitter) |
2 sigma, half cone, over 30 secs |
arc secs | < 2.7 | 0.5 |
| Absolute Pointing Drift | 2 sigma, half cone, | arc secs per hour | < 2.8 | < 0.1 |
| Absolute Pointing Error (blind pointing) |
2 sigma, half cone, | arc secs | <11.7 | <1.5 |
The third station-keeping manoeuvre was successfully executed on 11 December 1997; this stopped the eastward drift of the satellite and induced a small westward motion. Over the course of time, the westward motion will slowly decrease and reverse.
The Mission Planning system within the SOC is routinely producing and
executing very efficient scheduled of highly-graded observation. About 90-95%
of the available science window is being used for observations.
ISO averages around 40 observations a day and carries out about 400 hours
of science observations per month.
In the routine phase to date, around 4% of the observations have been
"lost"
and needed repeating.
Scientifically-Validated Products: As of version 6.0 of the "pipeline" processing, the following products had been declared "scientifically valid":
Further information is contained on the README file which accompanies
the data products when shipped.
Pipeline Update: Version 6.3 has been used for processing
since revolution 739 on 27 November. Version 6.2 of the pipeline, containing
many minor updates, was first used for processing with revolution 691 on
10 October. Version 6.1 of the pipeline became operational on 1 August 1997
and, compared to 6.0, had better reconstruction of the pointing information
for observations made between revolutions 79 and 451. (For revolutions later
than 452, the improved information was already included).
The next major update foreseen is to version 7.0, currently planned to
become operational on 18 May 1998.
Data Shipment:
There exists a small pool of time for "observations which could not have been foreseen at the time of the proposal process". The procedure for applying for this Discretionary Time may be found at the "Discretionary Time Policy" page.
The Observing Time Allocation Committee Panel Chairs met on 16 September 1997 to consider the overall status of the programme and to make recommendations concerning use of time originating from the expected longer lifetime of ISO. The principal conclusions were: that the amount of discretionary time should be significantly increased for the rest of the mission; that an additional ~200 hours should be made available to the previously-approved large surveys; and that some 300 hours should be devoted to observations of general interest which should be placed in the public domain without the usual 12 months proprietary period. A separate WWW page addressing these "general interest" observations (also known as 'solicited proposals' ) contains information to the community on how to access the data.
Martin F. Kessler,
ISO Project Scientist
ISO Science Operations, Astrophysics Division, Villafranca, Spain.