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SOHO data loss not nearly as bad as expected!

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  • David
    (In fact, the LASCO imagery has already resumed on the SOHO website!) Science News Release Wed, 02 Jul 2003 15:05:26 GMT SNR 5-2003 SOHO s antenna anomaly:
    Message 1 of 1 , Jul 3 9:45 AM
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      (In fact, the LASCO imagery has already resumed on the SOHO website!)

      Science News Release
      Wed, 02 Jul 2003 15:05:26 GMT

      SNR 5-2003

      SOHO's antenna anomaly: things are much better than expected

      2 July 2003 After a number of tests and new insights, SOHO engineers
      now say there will be no 'blackout' periods for SOHO science data.
      "We're now talking only moderate fractions per day every day during
      the 2-3 week periods," says Bernhard Fleck, ESA's SOHO Project Scientist.

      High-rate transmissions from the Solar and Heliospheric Observatory
      (SOHO) were initially interrupted on 27 June 2003. The interruption
      was expected due to a recent malfunction in the pointing mechanism of
      the spacecraft's high-gain antenna (HGA). The loss of signal occurred
      on a 26-metre station of NASA's Deep Space Network (DSN). Until 30
      June 2003, however, the spacecraft continued beaming down its science
      data, which were successfully picked up by larger 34-metre DSN
      stations (when available). In addition, dumping on-board recorder data
      during these contacts has further reduced data losses so far.

      On 30 June 2003, the 70-metre DSN station in Madrid, Spain,
      successfully transmitted high-rate science data through SOHO's
      omnidirectional on-board low-gain antenna. SOHO normally uses this
      antenna only for low-rate telemetry in emergencies, and the antenna
      does not need to be repointed.

      Even better, when high-rate telemetry was lost on 1 July 2003, during
      a 34-metre station pass, engineers successfully switched SOHO into a
      medium-rate telemetry mode, using the low-gain antenna. In medium
      rate, all real-time science telemetry can be downlinked during station
      passes. However, on-board recorder dumps are not possible in this mode.

      The relatively late occurrence of the initial loss of contact means
      that the effective SOHO's HGA antenna beam width is larger than
      anticipated. Also, since the 34-metre stations are much quieter than
      the smaller stations, you can use them for longer time periods than
      expected. Being able to transmit science data through the on-board
      low-gain antenna using 70- and 34-metre stations therefore means that
      there will be no hard blackout periods for SOHO science data, given
      sufficient ground station resources. However, 34- and 70-metre
      stations are in higher demand than the 26-metre stations that SOHO
      normally relies on. Minor data losses are therefore inevitable every
      day during the 2-3 week periods.

      SOHO scientists expect full high-rate telemetry coverage, even on
      26-metre stations, to resume on or about 14 July 2003. To achieve
      this, they will make the spacecraft roll 180 around its Sun-pointing
      axis in a manoeuvre currently planned for 8 July 2003.
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