(Name: Cary Oler
Date: Thu, 19 Jun 2003 15:10:14 -0600
Subject: Re: (STD-Forum) SOHO High Gain Antenna Problems
Bob, good question. I'm not sure anyone will be able to answer your question
completely and accurately at this time. For those who aren't aware of this
problem, here's a brief summary.
The High Gain Antenna (HGA) on SOHO appears to be suffering from a
mechanical motor problem. The Flight Operations Team (FOT) is not able to
command the movement of the HGA. Requested movements are translating into
tiny motions. In other words, the FOTs ability to turn the HGA is severely
limited at the present time. It appears to be "stuck" mechanically. They are
going to try different methods of moving the antenna over the coming days,
such as boosting the temperature of the motor that is stuck, etc. Hopefully,
something will work.
This is not good news.
What does it mean for you guys? We're still not sure. If the scientific use
of SOHO is lost, communications will still be possible through the low-gain
antenna. And this would probably still allow some LASCO imagery to be
retrieved. I would imagine they would balance out the bandwidth of the
low-gain antenna for use in obtaining LASCO and EIT imagery for space
weather forecasting uses, but the cadence (frequency) of the available data
might suffer substantially.
If they are not able to correct this problem, we may lose the high return
rate from SOHO over the next week. All science teams associated with SOHO
are now being urged to prepare to safe their instruments for a possible
shut-down interval of perhaps 4 to 6 weeks.
> Cary, with the possible loss of the high res. images from the SOHO
spacecraft due to their
> antenna problem, how will this effect forecasting and is there a back-up
system that could
> be implemented? Are we going to be in the dark, so to speak when it comes
to CME
> impact predictions?
So to answer these questions: is there a back-up system that could be
implemented?
No, there really isn't anything currently in orbit that could replace the
functionality of SOHO. But there are some ground-based instruments that
would help. For example, reliance upon Mauna Loa Solar Observatory's Mark IV
K-coronameter would be heavier, which can help deduce the occurrence of
full-halo CMEs and CME profiles. But since this is a ground-based
instrument, availability of data is only when the Sun is up. H-alpha imagery
might also be more heavily relied upon. The SXI instrument on GOES-12
(soft-xray imager) would probably be very useful (as it already is), and the
TRACE spacecraft would also be useful. There are a few others as well, but
the loss of SOHO would probably degrade the accuracy of forecasts quite
noticeably.
> Are we going to be in the dark, so to speak when it comes to CME
> impact predictions?
We wouldn't be in the dark. The room would definitely be darker, but
definitely wouldn't be black. CME predictions would still be reasonably
accurate. There are a sufficient number of additional proxies to determine
(at least some hours after an event occurs) whether mass might be ejected
Earthward. But the loss would still be noticeable on impact predictions.
Cross your fingers that they are able to get the motor unstuck.