Switzerland’s International Space Science Institute has welcomed the launch of the space shuttle Discovery, which blasted off on Tuesday after a two-week delay.
But Rudolf von Steiger, a director at the Bern-based organisation, warned that the shuttle fleet was now showing its age.
Discovery was launched from the Kennedy Space Center in Florida shortly before 11am local time.
The United States space agency, Nasa, said it was happy with the launch, but engineers are reviewing video images which appear to show debris falling from the craft during the start of its journey.
Flight operations manager John Shannon said Nasa hoped to know by Sunday whether Discovery was damaged and whether the crew should attempt repairs.
Over the next 12 days astronauts are expected to test safety measures brought in following the loss of the Columbia space shuttle and all seven of its crew members during re-entry to Earth two and a half years ago.
Nasa will also use the mission to send urgently needed supplies to the International Space Station.
"The launch is very significant because it was a very awkward situation for the Americans to be cut off from space for two and a half years," von Steiger told swissinfo shortly before lift-off.
"They had to rely on help from other countries, mainly Russia, for access to the space station, which is quite a serious predicament," he said.
Nasa’s current mission has been seen as a test of the agency’s safety measures since the accident.
But the space agency has been criticised by some experts for downplaying the risks and for sending ageing shuttles into space. The three which are still in service were built between 13 and 21 years ago.
Von Steiger agrees that there are some problems with the current system, although he is sure that Discovery is now "as safe as it can reasonably be".
"The shuttle system was set up and designed in the 1970s, the first shuttle flew in the 1980s - it’s more than 20 years since then and the shuttle system is quite old now," he said.
"We have also found out the hard way that the system has a very fundamental and serious flaw, which is that cargo and humans are packaged in the same envelope and this makes it very large and vulnerable to security risks which are deadly for humans.
"This has to be changed in a future system."
Discovery had been due to blast off on July 13 but the launch was halted after one of the craft’s four fuel sensors failed a pre-flight test.
The sensors are designed to prevent the main engines from running too long or not long enough, in case of a fuel-tank leak or other major breakdown.
Since then Nasa experts have been working hard to find the source of the problem. On Tuesday morning the fuel-sensor system passed initial tests during fuelling for the flight.
"A sensor problem is always to be taken very seriously... even if it might turn out not to be a real problem," said von Steiger.
"In either case you have to look at it very carefully and it looks like Nasa has solved the problem."
The launch is the first since the Columbia accident when the fuel tank lost a piece of foam insulation which punched a hole through the wing, causing the spacecraft to break up as it was re-entering the Earth’s atmosphere.
swissinfo, Isobel Leybold-Johnson
Discovery blasted off at 10:39 local time on Tuesday morning. It is the first Nasa space-shuttle mission for two-and-a-half years.
The seven-strong crew is headed by veteran commander Eileen Collins.
Its mission is to test new safety and repair measures introduced after sister ship Columbia disintegrated on re-entry into the Earth’s atmosphere in February 2003.
It will also bring supplies to the International Space Station.