Fwd: SOHO Gets New, More Robust Computer Sofware
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Subject: SOHO Gets New, More Robust Computer Sofware
Date: 30 Sep 1999 15:06 UT
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ESA Science News
http://sci.esa.int
28 Sep 1999
SOHO gets new, more robust computer software
Just like personal computers on Earth, ESA's Solar and Heliospheric
Observatory is getting a software upgrade of its own. After SOHO
vanished in space in June 1998, engineers on two continents struggled
for several weeks to regain control of the spacecraft. In December
1998,
the loss of the last working gyroscope caused major orientation
problems
and rapid fuel depletion. But once again, engineers and ground
controllers
put the satellite back in working order. By February 1999, an
unprecedented
solution -- emergency software rushed up to SOHO -- allowed it to
reorient
itself. Yet that fix, which has been working perfectly ever since, was
only
meant to be temporary.
"It was the equivalent of an emergency-room procedure to stabilize a
patient," said Michel Verdant, ESA's SOHO Programme Manager. "But now
we have new software. This is the medicine we need to cure the patient
once and for all."
Indeed, the new software will make SOHO much more robust and reliable
in case orientation problems ever happen again, Verdant said. On 27
September, ground controllers beamed the new software up to SOHO. Both
software and spacecraft were developed mainly by prime contractor
Matra
Marconi Space. Now even if SOHO loses sight of the guide star it needs
to
orient itself to remain stable on all three axes, it won't have to
resort to
the Emergency Sun eacquisition mode (ESR), which up to now
automatically
meant halting all scientific observations.
"It's a major accomplishment to be out of this situation," said
Bernhard
Fleck, ESA's SOHO Project Scientist. "Before this new software, losing
the guide star would have meant that we had no way of measuring the
spacecraft's roll rate or of controlling it."
In case of trouble, the new software will now allow engineers to
determine
SOHO's drift by measuring the slight changes in the speed of the so-
called
momentum wheels. In a way, these wheels, which are normally used to
impart the necessary force to point the spacecraft, will be used as if
they
were gyroscopes and to return SOHO to its correct orientation.
"It is very similar to using the gyroscopes, but here we are using the
whole
spacecraft as a gyroscope," said Verdant. And this sets a real space
record.
For the first time, a spacecraft is operating in space without the
gyroscopes
it was designed to rely upon.
To avoid possible problems with other programs already installed, the
software was uploaded to a part of the spacecraft memory never before
used. "The software is something we must always respect," said Francis
Vandenbussche, SOHO System Engineering Manager. "I am very confident
everything will work fine."
"This new software will provide an extra safety net to the satellite."
In
fact, if SOHO now lost its guide star, the spacecraft would
automatically
switch to others loaded in its memory. Should that method fail,
control of
the spacecraft would be regained by using the momentum wheels as
reference. And that would still allow the satellite to continue its
observations.
Finally, there will always be ESR mode, as a last resort. Besides
halting all
observations, it takes several days to bring the spacecraft back to
top gear.
"With this new software, we'll sleep much better," said Verdant.
About a week of so-called flight commissioning will be required before
scientific observations -- which had been partly suspended -- can
resume
in full.
"What really amazes me is the competence and skills of these engineers
who are capable of coming up with solutions to solve incredible
problems,"
said Fleck.
Barring unforseen problems, SOHO should continue its mission until at
least 2003, seven years after its launch, Fleck said. "But what I
would
really like to see is the spacecraft carry out observations for a full
solar
cycle of 11 years."
SOHO, the most sophisticated satellite ever to study the Sun, is part
of a
joint programme between ESA and NASA.
USEFUL LINKS FOR THIS STORY
SOHO web site
http://sohowww.estec.esa.nl
[IMAGE CAPTION:
http://sci.esa.int/image.cfm?TypeID=1&ContentID=6871&table=ContentTable&Storytype=12]
This EIT full sun image, taken on 14 September 1999 in the He II
emission
line at 304 A shows the upper chromosphere/lower transition region at
a
temperature of about 60,000 K. The bright features are called active
regions.
A huge erupting prominence escaping the Sun can be seen in the upper
right
part of the image. Prominences are "cool" 60,000 K plasma embedded in
the
much hotter surrounding corona, which is typically at temperatures
above
1 million K. If an eruption like this is directed toward the Earth it
can cause
a significant amount of geomagnetic activity in the Earth's
environment
with a following spectacular aurora.
Instrument: EIT; Taken: Sept 14 1999, 07:19UT