The third stage of a Thor-Delta rocket burst into flames at Cape Kennedy yesterday injuring eleven men and destroying a satellite built by University astronomers. Three of the injured were in critical condition, two near death, due to severe burns.

Scientists were conducting pre-launch indoor tests and had just joined the rocket to its payload when the accident occurred. How the 515-pound rocket motor was ignited, causing it to spray flaming fuel throughout the experiment room, is still a mystery.

The Thor-Delta combination was to have launched an Orbiting Solar Observatory, the second of its kind, next Tuesday. Leo Goldberg, Higgins Professor of Astronomy, and William Liller, Robert Wheeler Willson Professor of Astronomy, are in charge of a Harvard team that has spent over five years building an ultraviolet spectrometer for the OSO. Their instrument, demolished yesterday, was meant to look at light waves from the sun.

Fortunately a replica of the $25,000 spectrometer has been built. But the launching will be delayed "several months," according to Liller.

The OSO satellite, when it is finally launched, will contain several experiments from government agencies and universities, in addition to the Harvard instrument. All the projects are designed to reveal more about them and study those forms of solar radiation which affect the atmosphere and magnetic field of the earth.