Long Journey's End
Pioneer 10 Not to Phone Home
After more than 30 years, it appears the venerable Pioneer 10 spacecraft has sent its last signal to Earth. Pioneer’s last, very weak signal was received on Jan. 22, 2003.
|NASA hopes to launch a Europa Orbiter mission in 2008, with the primary goal of determining if there indeed is a global, subsurface ocean.
NASA engineers report Pioneer 10’s radioisotope power source has decayed, and it may not have enough power to send additional transmissions to Earth. NASA’s Deep Space Network (DSN) did not detect a signal during the last contact attempt Feb. 7, 2003. The previous three contacts, including the Jan. 22 signal, were very faint with no telemetry received. The last time a Pioneer 10 contact returned telemetry data was April 27, 2002. NASA has no additional contact attempts planned for Pioneer 10.
"Pioneer 10 was a pioneer in the true sense of the word. After it passed Mars on its long journey into deep space, it was venturing into places where nothing built by humanity had ever gone before," said Dr. Colleen Hartman, director of NASA’s Solar System Exploration Division, NASA Headquarters, Washington. "It ranks among the most historic as well as the most scientifically rich exploration missions ever undertaken," she said.
"Originally designed for a 21-month mission, Pioneer 10 lasted more than 30 years. It was a workhorse that far exceeded its warranty, and I guess you could say we got our money’s worth," said Pioneer 10 Project Manager, Dr. Larry Lasher.
Pioneer 10 was built by TRW Inc., Redondo Beach, Calif., and was launched March 2, 1972, on a three-stage Atlas-Centaur rocket. Pioneer 10 reached a speed of 32,400 mph needed for the flight to Jupiter, making it the fastest human-made object to leave the Earth; fast enough to pass the moon in 11 hours and to cross Mars’ orbit, about 50 million miles away, in just 12 weeks.
On July 15, 1972, Pioneer 10 entered the asteroid belt, a doughnut-shaped area that measures some 175 million miles wide and 50 million miles thick. The material in the belt travels at speeds up to 45,000 mph and ranges in size from dust particles to rock chunks as big as Alaska. Pioneer 10 was the first spacecraft to pass through the asteroid belt, considered a spectacular achievement, and then headed toward Jupiter. Accelerating to a speed of 82,000 mph, Pioneer 10 passed by Jupiter on December 3, 1973.
The spacecraft was the first to make direct observations and obtain close-up images of Jupiter. Pioneer also charted the gas giant’s intense radiation belts, located the planet’s magnetic field, and established Jupiter is predominantly a liquid planet. In 1983, Pioneer 10 became the first human-made object to pass the orbit of Pluto, the most distant planet from the Sun.
Following its encounter with Jupiter, Pioneer 10 explored the outer regions of the solar system, studying energetic particles from the Sun (solar wind), and cosmic rays entering our portion of the Milky Way. The spacecraft continued to make valuable scientific investigations in the outer regions of the solar system until its science mission ended March 31, 1997.
Since that time, Pioneer 10’s weak signal has been tracked by the DSN as part of a new advanced-concept study of communication technology in support of NASA’s future Interstellar Probe mission. At last contact, Pioneer 10 was 7.6 billion miles from Earth, or 82 times the nominal distance between the Sun and the Earth. At that distance, it takes more than 11 hours and 20 minutes for the radio signal, traveling at the speed of light, to reach the Earth.
"From Ames Research Center and the Pioneer Project, we send our thanks to the many people at the Deep Space Network (DSN) and the Jet Propulsion Laboratory (JPL), who made it possible to hear the spacecraft signal for this long," said Pioneer 10 Flight Director David Lozier.
Pioneer 10 explored Jupiter, traveled twice as far as the most distant planet in our solar system, and as Earth’s first emissary into space, is carrying a gold plaque that describes what we look like, where we are, and the date when the mission began. Pioneer 10 will continue to coast silently as a ghost ship into interstellar space, heading generally for the red star Aldebaran, which forms the eye of the constellation Taurus (The Bull). Aldebaran is about 68 light-years away. It will take Pioneer 10 more than two million years to reach it. Its sister ship, Pioneer 11, ended its mission September 30, 1995, when the last transmission from the spacecraft was received.
Galileo Set to Join Jupiter, Literally
The flight team for NASA’s Jupiter-orbiting Galileo spacecraft will cease operations on Friday, Feb. 28 after a final playback of scientific data from the robotic explorer’s tape recorder.
The team has written commands for the onboard computer to manage the spacecraft for its short remaining lifetime. Galileo will coast for the next seven months before transmitting a few hours of science measurements in real time, leading up to a Sept. 21 plunge into Jupiter’s atmosphere.
|Observations of Io by Galileo spacecraft. Click image for higher resolution black and white. The image has a resolution of 335 meters (1,100 feet) per picture element. North is to the top of the image. Credit: Arizona/ Galileo images NASA/JPL. False color. BW Image produced by: Zibi Turtle, Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL), University of Arizona|
"This mission has exemplified successful team efforts to overcome obstacles to make outstanding discoveries," said Dr. Eilene Theilig, Galileo project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "While the team is sad to see it come to an end, there is great pride in Galileo’s remarkable accomplishments."
In the years since astronauts deployed Galileo from the cargo bay of Space Shuttle Atlantis in 1989, the mission has produced a string of discoveries about asteroids, a fragmented comet, Jupiter’s atmosphere, Jupiter’s magnetic environment, and especially about the geologic diversity of Jupiter’s four largest moons. The prime mission ended six years ago, after two years of orbiting Jupiter. NASA extended the mission three times to continue taking advantage of Galileo’s unique capabilities for accomplishing valuable science.
Now, the onboard supply of propellant is nearly depleted. Without propellant, the spacecraft would not be able to point its antenna toward Earth nor adjust its trajectory, so controlling the spacecraft would no longer be possible. Before that could happen, the flight team last year put Galileo on course for disposal by a dive into the crushing pressure of Jupiter’s atmosphere. This strategy eliminates any possibility of an unwanted impact between the spacecraft and the moon Europa. Galileo’s own discovery of a likely subsurface ocean on Europa has raised interest in the possibility of life there and concern about protecting it.
On Nov. 5, 2002, the orbiter passed closer to Jupiter than it had ever ventured before, flying near an inner moon named Amalthea and through part of Jupiter’s gossamer ring to begin its 35th and last orbit around the giant planet. This elongated farewell loop will take Galileo farther from Jupiter than it has been since before it entered orbit in 1995, to a point more than 26 million kilometers (16 million miles) away on April 14 before heading back in for impact.
Scientific data recorded on the tape recorder during last November’s flyby have been gradually played back for transmission to Earth since the flight team repaired radiation damage to the tape recorder in December. Transmissions during a communication session with a NASA Deep Space Network antenna at Goldstone, Calif. Thursday night and early Friday will finish the playback.
"After this month, we have no further activities planned until the day of impact," Theilig said.
The Galileo flight team numbered about 300 people at its peak during the prime mission, but has run much leaner in recent years, with about 30 since the Amalthea flyby. That smaller team is now disbanding, mostly to work on other JPL-managed NASA missions that are in development or already flying.
JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA’s Office of Space Science, Washington, D.C. Additional information about the mission and its discoveries is available online at http://galileo.jpl.nasa.gov.