On Monday NASA issued a short press release stating "The launch of NASA's DART spacecraft aboard an Orbital Sciences Pegasus XL scheduled for Tuesday is postponed. A review of projected loads data, or the G-forces the payload experiences upon ignition of the Pegasus second stage, is being re-evaluated to ensure mission success."

According to SpaceRef.com, Orbital Sciences has in fact known for months about the technical problems of the Pegasus XL rocket (which it built, as well as the DART spacecraft), but withheld that knowledge from NASA, right up until last Friday.

One year earlier, SpaceRef.com revealed, Orbital had changed the stage two igniter in the Pegasus launch vehicle that would be used to launch DART, eventually determining that the launch environment would be different, and that this would present a larger launch load - one which would damage the DART spacecraft.

At the time of this change, SpaceRef.com continues, NASA had asked Orbital Launch Division for information on the change, and how it would affect the mission. Orbital Launch Division did not elucidate, telling NASA not to worry.

Within Orbital Sciences a conflict then arose. Data told them that these new launch loads would indeed damage the spacecraft. Eventually staff felt that they could not withhold this information from NASA any longer.

In a teleconference last Friday, an Orbital Vice President finally admitted to NASA that the changes in the launch vehicle would create different launch loads than had originally been expected - and that this could indeed damage the DART spacecraft.

Responding to an inquiry from MSNBC.com's James Oberg, Orbital spokesman Barry Benesky said his company had followed "the standard procedure" for reliable space operations.

"As in any launch campaign, you review data all along, sometimes right up until launch day," Benesky said.

"In this case, some data came to light - late in the game, certainly - so with caution and diligence, we're not going to proceed to launch."

Benesky couldn't recall any past case where a launch was called off so close to the launch date on the basis of review of old data.

"It is unusually late" this time, he conceded. But he insisted that in the end, launch managers did the right thing: "We told the customer, and together we decided to take some time to review it."

NASA, meanwhile, has issued a statement, saying that a new launch date is under review.

The DART launch was initially planned for October 26 and was to be launched from the Vandenburg US Air Force base in California.

The space agency wants to test the craft as a cost-cutting measure in President George W. Bush's initiative to return humans to the moon and for manned exploration of Mars.

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