ENGINEERS SUCCESSFULLY REGAIN CONTROL OF SOHO SPACECRAFT
Spacecraft controllers successfully regained control of the Solar and Heliospheric Observatory (SOHO) spacecraft yesterday after sending a series of commands directing the spacecraft to fire thrusters and turn its face and solar power panels fully towards the Sun.
The SOHO flight operations team reported success in the maneuver, which is called attitude recovery, at 2:29 p.m. EDT Wednesday, the first time the joint European Space Agency (ESA) and NASA spacecraft has been controlled from the ground since SOHO spun out of control and communication was lost on June 24.
"It's a big step forward in our recovery plan for SOHO," says Dr. John Credland, ESA's head of scientific projects. "We were never quite sure that we would manage to make the spacecraft point back towards the Sun, which is essential for its proper operation. I congratulate our joint ESA-NASA team, helped by our industrial contractors, who have accomplished it."
"This is the best news we've had from SOHO in a long time," said Dr. George Withbroe, Director of the Sun-Earth Connection science theme at NASA Headquarters, Washington, DC. "Despite the gloomy early days after the loss, we always stayed hopeful that the resourceful people on the team could save the day. We're not there yet -- we still have to see if the scientific instruments survived. But this gives us reason to hope."
"Now we start a comprehensive check of all the spacecraft's systems and scientific instruments," said Dr. Bernhard Fleck, ESA's project scientist for SOHO. "We shall take our time and go step by step, in consultation with the 12 scientific teams in Europe and the United States, who provided the instruments. In some cases the instruments have been through an ordeal of heat or cold, with temperatures approaching plus or minus 100 degrees Celsius (212 degrees Fahrenheit). But I'm cautiously optimistic that SOHO can win back much of its scientific capacity for observing the Sun."
SOHO operates at a special vantage point 1.5 million kilometers (about one million miles) out in space, on the sunward side of the Earth. The spacecraft was built in Europe and it carries both American and European instruments, with international science teams. NASA launched SOHO and has responsibility for operations at NASA's Goddard Space Flight Center, Greenbelt, MD.
After its launch on Dec. 2, 1995, SOHO revolutionized solar science by its special ability to observe simultaneously the interior and atmosphere of the Sun, and particles in the solar wind and the heliosphere. Apart from amazing discoveries about flows of gas inside the Sun, giant "tornadoes" of hot, electrically charged gas, and clashing magnetic field-lines, SOHO also proved its worth as the chief watchdog for the Sun, giving early warning of eruptions that could affect the Earth.
In April 1998, SOHO's scientists celebrated two years of successful operations and the decision of ESA and NASA to extend the mission to 2003. The extension would enable SOHO to observe intense solar activity, expected when the count of sunspots rises to a maximum around the year 2000. It would remain the flagship of a multinational fleet of solar spacecraft, including the ESA/NASA Ulysses and Cluster II missions.
More details about the operations, and about SOHO in general, can be found on the Web at:
http://sohowww.estec.esa.nl and http://sohowww.nascom.nasa.gov
-end-
NASA press releases and other information are available automatically by sending an Internet electronic mail message to domo@hq.nasa.gov. In the body of the message (not the subject line) users should type the words "subscribe press-release" (no quotes). The system will reply with a confirmation via E-mail of each subscription. A second automatic message will include additional information on the service. NASA releases also are available via CompuServe using the command GO NASA. To unsubscribe from this mailing list, address an E-mail message to domo@hq.nasa.gov, leave the subject blank, and type only "unsubscribe press-release" (no quotes) in the body of the message.
Subject: SOHO Spacecraft Contacted
Date: Tue, 4 Aug 1998 15:47:49 -0400 (EDT)
From: NASANews@hq.nasa.gov
To: undisclosed-recipients:;
Don Savage/Doug Isbell
Headquarters, Washington, DC August 4, 1998
(Phone: 202/358-1547)
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5017)
Franco Bonacina
European Space Agency Headquarters, Paris, France
(Phone: 33-1-5369-7713)
RELEASE: 98-145
SOHO SPACECRAFT CONTACTED
Contact has been re-established with the European Space
Agency (ESA)/NASA Solar and Heliospheric Observatory (SOHO)
spacecraft following six weeks of silence.
Signals sent yesterday through the NASA Deep Space
Network (DSN) station at Canberra, Australia, were answered by
SOHO at 6:51 p.m. EDT in the form of bursts of signal lasting
from two to ten seconds. These signals were recorded both by
the NASA DSN station and the ESA station at Perth, Australia.
Contact is being maintained through the NASA DSN stations at
Goldstone, CA; Canberra; and Madrid, Spain.
Although the signals are intermittent and do not
contain any data information, they show that the spacecraft is
still capable of receiving and responding to ground commands.
"This is an excellent sign," said Dr. Joe Gurman, NASA
SOHO Project Scientist at the Goddard Space Flight Center,
Greenbelt, MD. "It means the spacecraft still has a heartbeat
and gives us added optimism that we may be able to restore
SOHO to scientific operation. Our next step, already
underway, is to continue the careful process of attempting to
re-establish control of the spacecraft. We will be
attempting, in the near future, to begin data transmissions in
order to get an assessment of SOHO's condition."
More information, images and status reports from SOHO
can be found on the Internet at:
http://sohowww.nascom.nasa.gov/
- end -
* * *
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03:51 PM ET 06/10/98
Scientists solve 50-year-old astronomy mystery
LONDON (Reuters) - Astronomers and mathematicians have
solved a mystery that has perplexed scientists for half a
century -- why the atmosphere of the sun is so much hotter than
its surface.
They have known that the sun's surface is barely 6,000
degrees Centigrade but they could not explain why its outer
atmosphere called the corona, where temperatures climb to
several million degrees, is so much hotter.
Nobody, until now, knew what was causing the dramatic
increase in temperature.
In a letter to the scientific journal Nature Wednesday,
Professor Eric Priest of St Andrews University in Scotland and
colleagues in Britain and France said a clash of magnetic fields
was heating giant, super-hot loops that extend over the sun's
surface to produce the extreme temperatures.
Priest said the finding was absolutely central to the rest
of astronomy.
``The sun is our closest star and if we want to understand
what is going on in the rest of the universe we have to
understand our sun,'' he said in a telephone interview.
The researchers used a telescope on a space satellite called
Yohkok to measure, for the first time, how the temperature
varies along the giant loops.
``Once we had measured the temperature profile, it was
exciting to compare the observations with predictions from the
three main theoretical models previously put forward,'' he said.
The findings matched one model that showed the heat was
uniformly released, probably by a clash of magnetic field lines
causing dozens of explosions that release energy along the loop.
Priest said the explosions occur in tiny regions of intense
electric current that heat the atmosphere in the same way as an
electric current in a light bulb or electric fire.