The launch of a European satellite to take precise measurements of Earth’s gravity field has been delayed by at least three months, to August, because its Rockot launch vehicle uses the same hardware that failed on a larger Russian Proton rocket in March. The satellite also may need to be placed into a different orbit because of the delay, program managers said here April 3.


The Goce satellite, which will measure Earth’s gravity field and study ocean circulation, is designed to fly in an unusually low orbit of 250 kilometers in altitude.


Goce is scheduled for launch on a Russian Rockot vehicle from the northern Russian Plesetsk Cosmodrome. The planned March launch already had been moved to late May following last-minute tests on the spacecraft and coordination with the launch-services supplier, Eurockot Launch Services GmbH of Bremen, Germany.


That May launch date
now has slipped at least until August following the March 15 failure of a heavy-lift Proton rocket’s Breeze-M upper-stage engine.


Rockot uses a modified version of the Breeze-M engine and has been grounded pending a Russian government investigation into the Proton failure. Preliminary findings are expected to be announced in mid


Peter Freeborn, commercial director of Eurockot, told a press briefing here April 3 that Eurockot will await the conclusions of the Proton investigation before setting a Goce launch date. But he said early indications are that an August Rockot launch is possible.


Goce’s mission depends on being able to keep relatively vibration-free in orbit. It is designed with rigid solar arrays and tail fins to give it an aerodynamic advantage when flying at an altitude where residual atmospheric drag could disturb the instruments. It is equipped with a xenon-ion propulsion system at its rear to deliver soft pulses of thrust.


Goce managers also had hoped that a spring launch would permit the satellite to conclude its 20-month mission at a time of relative solar calm. But as the launch date shifted from March to May and now to August, mission managers are considering whether to raise the orbit, according to Reiner Rummel, chairman of the Goce Mission Advisory Group and a professor at the Technical University of Munich, Germany. Solar activity heats the atmosphere causing it to expand, which then creates atmospheric drag at higher altitudes.


Goce is the first of the European Space Agency’s series of Explorer satellites. The satellite
, which
originally was planned for launch in early 2006, proved more difficult to build than anticipated, causing delays and cost overruns.


now is expected to cost around 340 million euros ($53
7 million), a figure that includes its construction by a 45-company team led by Thales Alenia Space Italy, its launch and operations for 30 months –
10 months more than its basic mission.


Program managers said the 1,100-kilogram satellite’s gradiometer, composed of six accelerometers –
each taking measurements on three axes – developed by France’s Onera aerospace research institute, will permit Goce to measure the gravity field with an accuracy of one-millionth of the gravity on the Earth’s surface.