Spacecraft Matters

Telemetry Increase

Following EIT's request to redistribute telemetry, Matra found out that they could allocate 16 additional packets (approx. 3.5 kb/s) to the science data stream. In addition to the previous request for increased bandwith from EIT (see minutes SWT-20) there was a new request from LASCO.

G.Br"uckner presented the scientific case for an increase of the LASCO telemetry rate:

1. Cadences need higher frequencies.
   Corona changes faster than anticipated.
2. Advanced Discrete Cosine Transform (ADCT) compression scheme does not work.
   Compression is 2:1, was supposed to be 10:1.
   
   Reasons:

   1. Strong gradients in corona, not anticipated.
   2. Strong gradients near occultors.
   3. Number of stars and cosmic rays much larger than anticipated.

J.-P.Delaboudiniere repeated the arguments why EIT needs a higher bandwith (see annex 4 in minutes SWT-20).

It was agreed that the EIT and LASCO teams first discuss this internally at their upcoming consortium meeting in France and present a proposal to the SWT.

SWAN Request for Maneuvers

W.Schmidt requested a S/C roll twice a year for crosscalibration of the two SWAN sensors which was accepted by the SWT.

P.Scherrer asked about the impact of S/C rolls on the S/C which is run in gyro mode during these exercises. J.-P.Olive commented that so far the gyros have run approximately 900 hours. The design lifetime for the 2 year nominal mission is 1500 hours, but one can expect a lifetime of about 5000 hours. There is an action on ESA/Matra to study the effect of S/C rolls on the lifetime of the gyros in detail and report back to the SWT at the next meeting (Action 21-5). P.Scherrer then made a request for a 360 S/C roll consisting of 16 steps à 22.5 with 30 min dwell times at each step, except at the 90, 180, and 270 position where the dwell time should be 1 hour. Target date: 3-4 months from now, i.e. February/March. This request was also accepted by the SWT.

CELIAS, UVCS, LASCO Thermal Disturbances

CELIAS and LASCO colleagues stated that the new operational modes of CELIAS/CTOF and the heater cycling of LASCO will not cause any thermal disturbances for the other experiments or the S/C. The instrument teams were reminded that they should inform the SOT at the daily meeting (or the SOCs by e-mail) well in advance of any planned changes in the operational mode of their instrument which might cause a disturbance to other instruments or the S/C. The three helioseismology instruments are extremely sensitive to temperature changes and disturbances should be kept to an absolute minimum. If they can't be avoided at all, one of the ESA/Matra engineers should have a look into it prior to the implementation to evaluate potential consequences.