Second bid to land rocket on barge
A daring second attempt to land a reusable rocket on a floating barge will be made today by a private space company.
The previous Falcon 9 launch on Tuesday was aborted a minute before take-off because of a problem with a steering thruster system.
US aerospace company SpaceX hopes the latest mission, scheduled for 9.47am, UK time, will go smoothly and mark a turning point in the way space operations are conducted.
The ability to land a rocket's first stage intact instead of allowing it to burn up in the atmosphere will slash the cost of space missions, making them more attractive to private operators such as SpaceX.
Falcon 9 is a two stage rocket designed to transport satellites and supplies destined for the International Space Station (ISS).
Today's mission will carry an unmanned Dragon spacecraft packed with more than 5,000 pounds of food and equipment to the station and its six-person crew orbiting 250 miles above the Earth.
But it is the recovery of the first stage that is the all important element of the mission.
The idea is to land the spent rocket on an uncrewed barge - dubbed an "autonomous spaceport drone ship" - 200 miles off the coast of Jacksonville, Florida.
The target measures 300ft by 100ft with wings that extend its width to 170ft.
Aiming a 138ft long rocket travelling at nearly one mile a second with such precision is an immense challenge.
On its website, SpaceX compared the problem of stabilising the rocket for re-entry to "trying to balance a rubber broomstick on your hand in the middle of a wind storm".
It added: "During previous attempts, we could only expect a landing accuracy of within 10 kilometres (six miles). For this attempt, we're targeting a landing accuracy of within 10 metres (33 feet)."
For safety, no one will be aboard the barge when the landing takes place. SpaceX accepts that the chances of success are no greater than 50-50 - but even if the attempt fails it will yield valuable data to assist further tests.
The mission is SpaceX's fifth of 12 planned under a £1 billion contract with the American space agency Nasa to supply the ISS.
Recovering the rocket involves re-lighting its engines on re-entry for a series of three burns. The first two adjust the predicted landing point and reduce its speed from 4,265ft per second to 820ft per second.
A final "landing burn" slows the speed further to around 6.5ft per second as the rocket lowers its landing legs.
Four "hypersonic grid fins" placed around the rocket are also deployed on re-entry. Each fin moves independently to help control roll, pitch and yaw.
The new launch was originally planned for yesterday evening, UK time, but was postponed.