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ASCA Guest Observer Facility

Mission Operation

--Tadayasu Dotani, ISAS

Daily Planning

Two duty scientists, a staff member and a graduate student, work Monday through Saturday at ISAS to prepare the daily command plan. Following is the sequence of events established during the PV phase when we make an attitude/observation plan.

  • Nagase-san announces the weekly observation plan two weeks or at least 10 days before the start of observations.
  • The ISAS duty scientist establishes the attitude and mode requirements.
  • The attitude duty scientists makes the attitude plan a week before the start of observations.
  • The ISAS duty scientists make the command plan.

The information is gathered by the duty scientists at ISAS from Japanese PIs and by the duty scientists at NASA/GSFC from US PIs. A brief description of the purpose of the observation, if supplied by the PI, is useful to make an optimized command plan.

We usually try to take as much data as possible in high bit rate. However, in most cases, nearly half of the data are taken in medium bit rate due to the limitation of the onboard data recorder. Low bit rate usually is not used for the purpose of observations. It is often required to change the SIS observation mode (e.g. faint/bright or 4-CCD/2-CCD/1-CCD) according to the bit rate to avoid telemetry saturation. Therefore, it is recommended that PIs specify the SIS mode for both high and medium bit rate, respectively. If the information supplied by the PI is not enough to make the command plan and the duty scientists cannot contact the PI, the default observation mode, which may not always be appropriate, is used.

The command plan prepared at ISAS is sent to KSC (Kagoshima Space Center) through the dedicated network.

Tracking Stations

The only ground station used for up-link is KSC, whereas KSC and three DSN stations (Canberra, Goldstone, and Madrid) are used for down-link. Most of the acquired data are stored in the onboard data recorder, and are reproduced later, when the satellite is in contact with these ground stations. A small number of the data are transmitted directly to the ground station (which is possible only at KSC). New data cannot be recorded while down-links to the DSN stations are in progress. This introduces a small gap of about 10 minutes in the data.

Five up-/down-links at KSC and 6-7 down-links at DSN stations are available every day, except for Sunday, at KSC. Because of these frequent contacts to the ground station, we can use high bit rate for more than half of the data; the rest are acquired in medium bit rate. We have no operation at KSC on Sunday. The satellite is controlled by the onboard program and the observations are carried out as usual. However, because KSC is not available and because the capacity of the onboard data recorder is limited, data coverage is a little poorer on Sunday.

Operation at KSC

Two duty scientists and 5 company personnel work at KSC. All the command plans sent from ISAS are checked by the duty scientists at KSC once again. They also check the satellite's condition and the quality of data after every contact. All the data acquired at KSC go through the quick-look analysis to check the condition of the detectors. Details of the daily operation are summarized in the operation report, which is circulated within the operation team.

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