The spacecraft Magellan yesterday dived over the north pole of Venus, fired a rocket to slow down, and finally beeped word to Earth that it had slipped safely into the planet's gravitational embrace, triggering sighs of relief among its handlers and breaking the U.S. space agency's summer series of setbacks.
"We copy that. Fantastic!" said Sharon Anthony, a flight controller at the Jet Propulsion Laboratory in Pasadena, as she received word from the NASA Deep Space Network station at Goldstone, Calif., that radio communication with Magellan had resumed.
The radio signal from the craft, the first U.S. planetary mission launched since 1978, had gone silent, as expected, for a harrowing 37 minutes as it streaked down the far side of Venus. It emerged from beneath the planet's south pole about 10 seconds ahead of schedule -- at about 12:53 p.m. EDT.
"We've had a spectacular morning," said mission director James F. Scott, at the Jet Propulsion Laboratory, which is managing the mission to map the planet.
The crucial 83-second firing of the 4,700-lb solid-fuel rocket was so precise that the craft went into orbit "just like we were on a monorail," said K. Ledbetter of Martin Marrietta Space Systems, deputy program manager.
"We made it!" said Carolynn Young, a Magellan project team member. "I had goose bumps from head to toe. It's wonderful."
The anxious engineers and scientists learned about the drama unfolding almost 145 million miles from Earth after a delay of 13 minutes, the time it takes for a signal to travel that distance at the speed of light.
There was one glitch in the spacecraft's performance. A computer commanded the craft to switch from a main to a backup set of gyroscopes -- sets of spinning wheels that control the spacecraft's attitude and which are "like a child's spinning top," Ledbetter said.
The craft has four gyroscope sets on board, one of which was shut down by Magellan's fault protection system yesterday as a precaution when, just after the rocket burn, it detected that the spacecraft's attitude was slightly awry, he said.
The Magellan team plans to trouble-shoot the gyros, one set of which was indicating an electronic failure earlier in the roundabout 948-million-mile cruise to Venus, he said.
The gyroscopes must work well, and the spacecraft's egg-shaped orbit must be precisely as ordered, if the spacecraft is to carry out its 243-day, $744 million mission. Magellan is to use its advanced radar sensor to make the most detailed and complete map ever of Earth's cloud-veiled, hot and toxic sister planet.
The craft's gyros must put it through a tricky ballet on every 3.15-hour pass, turning toward the planet as it swoops to within 155 miles of the surface and collecting radar echoes from the mountains and plains below, then pivoting its antenna for transmission to Earth as it heads out to its farthest distance from the planet -- some 5,000 miles.
The mapped strips of planet surface will gradually be assembled to create a mosaic map of virtually the entire planet.
Scientists expect to collect their first echoes from the planet's surface late next week, to test and calibrate the radar sensor, but the spacecraft is not expected to begin its real mapping work until around Sept. 1.
Scott said there might be some temporary problems as the instruments are adjusted for work but he and others said they expect no horrible surprises like the flaw that has temporarily ruined the performance of the Hubble Space Telescope. Magellan's synthetic aperture radar sensor system was successfully tested during the cruise to Venus, scientists said, but without a planetary surface to provide echoes.
The successful rocket firing was the last in a series of anticipated nail-biting moments for the Magellan team since the probe was launched in May 1989 aboard the shuttle Atlantis. That launch had ended an 11-year dry spell for U.S. planetary scientists, during which no new missions had been dispatched.
"I am of course delighted," said NASA's chief scientist Lennard Fisk. "This is the beginning today of one of the most exciting eras in planetary exploration."
With Magellan at Venus, the Galileo craft bound on a looping path to Jupiter and several other explorer missions in the works, he said, the United States moves from a period of reconnaissance of the solar system to one of exploration. "From this day forward, there will be a U.S. planetary mission continuously in orbit about a body of our solar system . . . until well into the next century."