Ulysses: 12 extra months of valuable science (Forwarded)

ESA News
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30 June 2009

Ulysses: 12 extra months of valuable science

In 2008, Ulysses was expected to cease functioning due to weakening power.
But solid engineering know-how and on-the-fly innovation have eked out an
additional year of important science returns, which came to an end today.

Ulysses, the joint ESA/NASA solar orbiter mission, finally ended today when
ground controllers sent commands to shut down the satellite's
communications. The event marks the conclusion of one of the longest and
most successful space missions ever conducted.

The mission had been predicted to end in July 2008, when the satellite's
weakened power supply was expected to fall below the minimum required to
keep fuel lines from freezing, without which Ulysses would be
uncontrollable. At that time, the ESA/NASA operations team planned to
continue operating the spacecraft in a reduced capacity for a few more
weeks.

However, through smart engineering and realtime innovation, controllers
determined they could keep the lines from freezing by briefly firing the
thrusters every few hours. In fact, Ulysses has continued gathering valuable
scientific data throughout most of the past year -- until today, after a
decision was taken to end the mission due to continuing weak power and the
unavailability of ground station time.

No further contact planned

Today's final communication pass via NASA's 70-m Deep Space Network started
at 17:35 CEST [1535 UTC] and the satellite's radio communications switched
into receive-only mode at 22:10 CEST [2010 UTC]. Last telemetry was received
as expected at 22:15 CEST [2015 UTC]. No further contact with Ulysses is
planned.

The joint ESA/NASA mission operations team under Nigel Angold, ESA Mission
Operations Manager, monitored the final activity from the Ulysses Mission
Support Area (MSA) at NASA's Jet Propulsion Laboratory (JPL), California,
USA.

Launched by Space Shuttle Discovery on 6 October 1990, the 18-year, 8-month
mission has returned a wealth of scientific data on the space environment
above and below the poles of the Sun. The spacecraft and its suite of nine
instruments had to be highly sensitive yet robust enough to withstand some
of the most extreme conditions in the Solar System, including a close fly-by
of the giant planet Jupiter.

Final ground station communication

During today's final activities, ESA and NASA mission controllers radioed up
a series of instructions that progressively switched off systems on Ulysses,
including:

* Switch off instrument high voltages
* Deschedule the 'Loss of Command' programme
* Perform a last Earth-pointing manoeuvre
* Switch on the redundant receiver
* Switch off the tape recorder
* Switch to the 64-bit-per-second communication rate
* Configure the S-band radio communications
* Switch off the transmitter

At the time of sending the last commands, Ulysses was located approximately
1.5 astronomical units from Earth and the one-way radio signal time was
approximately 45 minutes.

An amazing adventure

"This has been an amazing adventure. Although we have said a sad farewell,
Ulysses will remain a unique landmark in the exploration of space, something
we can all be incredibly proud of," said Richard Marsden, ESA's Ulysses
Project Scientist and Mission Manager.

During its life, Ulysses made nearly three complete orbits of the Sun. The
probe revealed for the first time the three-dimensional character of
galactic cosmic radiation, energetic particles produced in solar storms and
the solar wind.

Not only has Ulysses allowed scientists to map constituents of the
heliosphere in space, its longevity enabled the Sun to be observed over a
longer period of time than ever before.

"The Sun's activity varies with an 11-year cycle, and now we have
measurements covering almost two complete cycles," said Marsden. "This long
observation has led to one of the mission's key discoveries, namely that the
solar wind has grown progressively weaker during the mission and is
currently at its weakest since the start of the Space Age."

First commands sent in 1990

Nigel Angold, ESA's Ulysses Mission Operations Manager, said that a lot has
changed since the first commands were sent to Ulysses as it orbited the
Earth inside Discovery's payload bay back in October 1990.

"But what's remarkable is that many of the people involved then are here
today to send the last commands," he added. "A half-dozen of the team have
worked on Ulysses for its entire life -- this mission has been sufficiently
challenging and inspiring for talented people to dedicate significant
portions of their careers to it. Also, a number of those who have moved on
to other jobs at JPL are joining us to celebrate the end of this unique
mission."

Longest-running ESA-operated spacecraft

Earlier in June, the Ulysses Mission Team received a NASA Group Achievement
Award. Another milestone was reached on 10 June when Ulysses, having
operated for 18 years and 246 days, became the longest-running ESA-operated
spacecraft, overtaking the International Ultraviolet Explorer (IUE).

Following today's shutdown, Ulysses flight data will be archived and
available to future ESA and NASA mission teams for reference; the mission's
scientific data are already being stored in the Ulysses science data
archives at ESTEC, ESA's technical centre, and at NASA's National Space
Science Data Center (NSSDC).

Notes for editors:

During its life, Ulysses was operated by a joint ESA/NASA team at NASA/JPL.
ESA managed the mission operations and provided the spacecraft, built by
Dornier Systems, Germany (now Astrium). NASA provided the Space Shuttle
Discovery for launch and the inertial upper stage and payload-assist module
to put Ulysses in its correct orbit. NASA also provided the radioisotope
thermoelectric generator which powers the spacecraft and payload, and the
NASA Deep Space Network (DSN) was responsible for communicating with the
satellite. Teams from universities and research institutes in Europe and the
United States provided the nine science instruments.

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