Nasa has warned the crew of space shuttle Discovery to expect rain delays as they prepare to return to Earth after their visit to the space station.

Discovery and its crew of seven are due to land at Florida's Kennedy Space Center on Monday.

In the worst case, the shuttle could always aim for a back-up landing site in southern California on Tuesday.

Discovery has spent two weeks at the space station stockpiling it with supplies, experiments and spare parts.

The shuttle's first opportunity to return to Earth would see Discovery fire its engines at 1143 GMT (0743 EDT) ahead of a landing at 1248 GMT (0848 EDT).

For the first time since 2007, the shuttle will cross North America, from Vancouver to Florida, giving observers on the ground an opportunity to see the vehicle as an orange streak against the sky and to hear its sonic boom.

This landing pattern, called a "descending node", has not been used since 2007.

Spacewalk problems

Since the Columbia disaster in 2003, when a large amount of debris fell on Texas, shuttles have generally approached Cape Canaveral from the south-west.

But since 2003, Nasa has brought in methods of checking the shuttle's heat shield for the kind of damage which led to Columbia burning up on re-entry.

Discovery left behind nearly eight tonnes of cargo and equipment on the International Space Station (ISS), including a new tank full of ammonia coolant.

The tank was successfully installed over the course of three spacewalks, but stiff bolts made the work more strenuous than anticipated.

The astronauts and ground controllers also had to deal with a stuck valve in the nitrogen tank assembly - another part of the cooling system - during the 10 days of linked flight.

In addition, a misaligned connector that delayed the removal of the Multi-Purpose Logistics Module (MPLM) cargo carrier from the space station.

Russian dependence

The nitrogen pressure valve is still jammed, but space station managers said they can live with the problem for now.

However, if flight controllers cannot open the valve by remote control, a spacewalk will be needed in the coming weeks or months to replace the entire nitrogen tank assembly.

A broken KU-band antenna meant that mission control had to send up large files of information to the space station before Discovery undocked on Saturday.

This was so that flight controllers would not have to read all the information aloud to the shuttle crew in the limited time that remains.

Discovery is hauling back more than three tonnes of rubbish and old equipment from the ISS. The MPLM anchored in the shuttle's payload bay will return to the orbiting outpost in five months to serve as a permanent storage module.

Just three more shuttle flights remain until the US fleet is retired. After that, the US will be dependent on Russia's Soyuz vehicle for ferrying crew to and from the ISS.

Weather Delays Landing; Next Opportunity on Tuesday

Continued low cloud coverage at Kennedy Space Center's Shuttle Landing Facility forced flight controllers to pass on STS-131’s second landing opportunity Monday.

This was the last opportunity for space shuttle Discovery to land today.

The next Kennedy Space Center landing opportunity is Tuesday with a deorbit burn at 6:28 a.m. EDT and landing at 7:34 a.m.

Edwards Air Force Base in California also is expected to be called up for Tuesday landing opportunities.


With Moon transiting in Gemini even tomorrow, I am of the view, there could be problem for landing, which could be cause of concern

Because of declining trends in the weather conditions, including showers within 30 nautical miles and concern for fog formation, Entry Flight Director Bryan Lunney and his team waved off the first landing opportunity at 7:34 a.m. EDT at Kennedy Space Center and advised Discovery's seven astronauts they are "no go" for the deorbit burn at 6:28 a.m.

The crew will re-target for the second landing opportunity on orbit 238 with a focus on Kennedy. Expectations are that sunlight will burn off the fog and the showers should remain offshore. For a 9:01 a.m. EDT landing at Edwards Air Force Base in California, the deorbit burn would be at 7:56 a.m. For a Kennedy landing at 9:08 a.m., deorbit burn would be at 8:03 a.m.