Sun probe mission finally burns out

Ulysses comes to a natural end

vnunet.com, 25 Feb 2008

A long-running mission to study the Sun's poles and its influence on surrounding space is finally coming to an end after more than 17 years.

The Ulysses mission is finally succumbing to its harsh environment and is likely to finish in the next month or two.

The joint mission between Nasa and the European Space Agency was launched in 1990 from a Space Shuttle and was the first attempt to study the environment of space above and below the poles of the Sun.

Originally designed for a lifetime of five years, the probe has surpassed all expectations.

Data from the probe has "forever changed" the way scientists view the Sun and its effect on the space surrounding it, according to the ESA.

Ulysses is in a six-year orbit around the Sun carrying it out to Jupiter's orbit and back again. The further it ventures from the Sun, the colder the spacecraft becomes. If it drops to two degrees C, the spacecraft's hydrazine fuel will freeze.

The decision to switch the transmitter off was not taken lightly

Richard Marsden Ulysses project scientist and mission manager

This has not been a problem in the past because Ulysses carries heaters to maintain a workable onboard temperature.

The spacecraft is powered by the decay of a radioactive isotope and, over 17-plus years, the power it has been supplying has been steadily dropping.

The spacecraft no longer has enough power to run all of its communications, heating and scientific equipment simultaneously.

"We expect certain parts of the spacecraft to reach two degrees C pretty soon," said Richard Marsden, ESA's Ulysses project scientist and mission manager. This will block the fuel pipes, making the spacecraft impossible to manoeuvre.

In an attempt to solve this problem, the team approved a plan to temporarily shut off the main spacecraft transmitter. This would release 60 watts of power that could be channelled to the science instruments and the heater.

When data was to be transmitted back to Earth, the team planned to turn the transmitter back on. Unfortunately, during the first test in January, the power supply to the radio transmitter failed to turn back on.

"The decision to switch the transmitter off was not taken lightly. It was the only way to continue the science mission," said Marsden.