SOHO data loss not nearly as bad as expected!
- (In fact, the LASCO imagery has already resumed on the SOHO website!)
Science News Release
Wed, 02 Jul 2003 15:05:26 GMT
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.