An American company trying to become the first private company to send a supply craft to the International Space Station has aborted its launch of the rocket.
The US firm SpaceX has aborted the lift-off of its Falcon rocket and unmanned Dragon cargo ship to the International Space Station (ISS).
The rocket's engines were shut down just as the vehicle was about to leave the pad at the Cape Canaveral Air Force Station in Florida.
Onboard computers noticed the chamber pressure in one of the nine Merlin engines under the Falcon was outside its acceptable value.
Tuesday is the next launch opportunity.
Elon Musk, the CEO and chief designer at SpaceX, tweeted: "Launch aborted: slightly high combustion chamber pressure on engine 5. Will adjust limits for countdown in a few days."
If the mission is successful - once it gets off the ground - the US space agency, NASA, hopes to contract out more of its activities.
Agency administrator Charles Bolden says NASA sees potential in that, the BBC reports.
"There's no question - this is a historic flight," said SpaceX president Gwynne Shotwell on the eve of the mission.
Garbage dump east of NZ
"There've been only four nations, or groups of nations, that have berthed or docked a spacecraft to the International Space Station: Europe, Russia, the United States of course, and Japan. So, we really stand in awe at having the opportunity to attempt this."
These re-supply tasks are usually performed by the vehicles belonging to government space agencies, such as Nasa and its European counterpart, Esa.
Many of those missions have been completed by filling the empty cargo shuttle with human waste, packaging and other garbage and then crashing the shuttle in the Pacific Ocean east of New Zealand.
But the Space-X vehicle is designed to return safely from orbit.
Although billed as a demonstration, the mission has major significance because it marks a major change in the way the US government wants to conduct some of its human spaceflight operations.
Both SpaceX and another private firm, Orbital Sciences Corp, have been given billion-dollar contracts to keep the space station stocked with food and equipment. Orbital hopes to make its first visit to the manned outpost with its Antares rocket and Cygnus capsule system later this year.
The new approach is intended to free the US space agency to concentrate more of its effort and funds on planning exploration missions far beyond Earth, to asteroids and Mars.
Unlike the Russian and European robotic freighters that drive all the way into docking ports on ISS, Dragon will move itself to a position just 10m under the platform where it will be grabbed by a robotic arm operated by astronauts inside the orbiting laboratory.
This was originally expected to happen on Tuesday, but that will now be the first chance to make another bid for a successful launch.
Since Nasa's own shuttles were retired last year, America has no means currently of launching its own astronauts into space - rides must be bought for them on Russian Soyuz rockets at more than $US60m a seat. SpaceX says Dragon could be ready to carry people in 2015 at a seat price of $US20m.
