Rosetta comet chaser on hold

" What we have to do right now is study back up options "
Dr Gerhard Schwehm, Rosetta project scientist

A formal announcement suspending all preparations of the Rosetta spacecraft is expected from the European Space Agency (Esa) later on Tuesday.

There has been concern over the mission following the explosion of a rocket at the probe's launch site in French Guiana last month.

It is understood the review of systems ordered at the spaceport following the rocket failure will not now be completed in time to allow Rosetta to catch up with Comet Wirtanen.

The mission will have to be redesigned as a result.

Review board

The news will come as a major blow to the scores of scientists and engineers who have been working on Rosetta for more than 10 years.

The lead researcher on the project, Dr Gerhard Schwehm, told the BBC: "It's a decision we have to live with because there are good arguments to delay the launch. What we have to do right now is study back-up options and come up with a viable scenario."

The original plan was for the spacecraft to go into orbit around Comet Wirtanen and then drop a lander on to the icy body's surface.

Such was the complexity of the mission, it would have taken until 2011 for Rosetta to reach its target.

The one-billion-euro probe should have flown at the weekend but was put on hold because of ongoing investigations into the failure of Europe's new super rocket, the Ariane 5-ECA, at the Kourou spaceport on 11 December.

" Yes, it's disappointing, but we need to wait and make sure that this is safe "
Dr Ian Wright, Open University

The BBC understands investigators want more time to complete their review of rocket components and systems and this work will not be completed until February.

Extra cost

But this will be too late for Rosetta which must get off the ground no later than 31 January.

The reason for the deadline lies in the detailed space manoeuvres that are needed to get the probe to within touching distance of Wirtanen.

This involves swinging past Mars once and Earth twice to build up the speed required to catch the comet near Jupiter.

If Rosetta loses its launch window, it misses its target.

Esa will not abandon Rosetta - it has spent too much on the project to just throw it away.

Project scientists have already begun looking at alternative targets but this will mean a redesign of the mission, which is likely to add millions more to the total cost, and a delay of a year or more.

One of the principal researchers, Dr Ian Wright from the UK's Open University, said: "We want Esa and the rocket launcher people to be absolutely certain that this is going to be successful. So, yes it's disappointing, but we need to wait and make sure that this is safe.

"The project's been in the making 10 years already, so I guess what difference will another few months make."