If I may, I'd just like to add to Philip Chien's comment: "As far as Apollo was concerned, the results of the Apollo 13 explosion were observed by engineers at the Johnson Space Center who viewed the expanding oxygen cloud from the breeched tank in a telescope." On the roof of Building 16A at the Manned Spacecraft Center, engineer Andy Saulietes with three of his colleagues, had been pointing a 14 inch telescope with a charged coupled device (CCD) hooked up to a black and white TV, at the Apollo command,service, and LEM at a distance of approx. 200,000 miles (322,000 km). They were seeing a twinkling shrinking object; it was the tumbling third stage of Apollo 13's Saturn 5 booster, speeding away from Earth at approximately 2000 miles per hour. The booster was heading for a collision with the moon, it's impact to be recorded by sensors later. The men on the rood had air to ground communication so they could track the progress of the flight and listen for key mission events. The event they were waiting for principally was a water or urine dump from the spacecraft Odyssey. When the spray of liquid vented from the side of the ship, it would crystallize on contact with space forming an icy cloud of starry flecks that Wally Schirra had dubbed "the constellation Urion". If the cloud was big enough and caught the sunlight just right, the Engineers thought they might be able to spot the spacecraft. During the course of his observations for the waste dump, Saulietes heard a transmission from Jack Swigert from his radio, at that time he seen in the middle of his TV screen a sudden an unexpected pinpoint of light appear and steadly grow. It was right where the spacecraft should have been but was way too big to be a urine dump and nothing else he had seen on previous missions could account for it. It was a huge, glassy halo, twenty or thirty miles in diameter. Saulietes was able to capture three or four stills of the event and save them for later. He thought at the time that there was a malfunction with his equipment. Dan Poeder Wyoming, Michigan