The National Aeronautics and Space Administration yesterday reversed itself and said a Soviet satellite was not to blame for drowning out radio transmissions from Pioneer 11 as the spacecraft flew by Saturn's giant moon, Titan.
In fact, NASA may have all the data it thought had been lost.
"The way it looks now, there was no radio interference from any Soviet satellite in Earth orbit," Pioneer chief scientist John Wolfe said yesterday from the Ames Research Center in Mountain View, Calif., from where the flight of Pioneer is directed. "The reason this story keeps changing is that the information we get keeps changing."
On Tuesday, NASA said it lost all the temperature measurements Pioneer 11 took of Titan because signals were drowned out by the broadcast Monday of a Soviet satellite as it circled the Earth. NASA identified the satellite as Cosmos 1124, which was put into orbit last week.
At the same time, however, NASA blamed itself for not having asked the Soviets to turn off the satellite's radio during the time Pioneer would be transmitting back to Earth.
The space agency had asked the Soviet Union to keep three of its satellites in radio silence during the four hours Pioneer would be transmitting on Sept. 1 and 2. The Soviets obliged and silenced Cosmos 1024, 1109 and 1124 during the four crucial hours on Saturday and Sunday. Broadcasting was resumed Monday because there was no request to continue radio silence.
"It was NASA mistake," Wolfe said. "It was a case of too many hands getting involved."
The way these things work, NASA's Office of Space Science in Washington alerts the State Department to the possibility of radio interference, then sends a cable through the State Department to the Soviet Academy of Science in Moscow, asking for radio silence for a specific time period on a specific day.
These requests are made only when a spacecraft is broadcasting from another planet and can run into radio interference when its signals arrive at Earth, where numerous satellites are in orbit and are broadcasting back along similar frequencies.
Yesterday, Pioneer scientists said they have discovered that they had not lost their measurements of Titan, whose atmosphere is believed to be rich enough to support some primitive kind of life.
Poring through the data they received from Pioneer Monday, scientists discovered at least two minutes' worth of information on the temperatures of Titan that had been sent back to Earth later than scientists originally thought.
"The data was ratty, make no mistake about that," Wolfe said yesterday. "But it's there, and it may all be there, all 20 minutes of it, ground up in some scrambled data that was fouled in the communications link between Madrid and California."
Wolfe and the California Institute of Technology's Dr. Andrew Ingersoll said the Titan temperature information appeared to have been lost when computers in California which were supposed to receive it began spewing out dollar signs, a standard computer signal that it is receiving information it cannot understand.
However, all the incoming signals are taped, and scientists have since been able to extract the Titan data from the jumble of material on the tape.
One additional complication was that scientists were not sure exactly when Pioneer would be looking at Titan. They guessed wrong at first, and when they looked at that part of the tape the data was not there.
"It's nobody's fault, except it may be mine," Ingersoll said. "The trouble was we failed to see Titan at the time we thought it was there."