Its End Near, Galileo Takes NASA on Wild Ride

[Susan L Gawarecki <loc@icx.net>]

Going where no astronaut could survive....



Its End Near, Galileo Takes NASA on Wild Ride 



By William Harwood

Special to The Washington Post

Monday, January 6, 2003; Page A06 



CAPE CANAVERAL -- NASA's Galileo spacecraft, crippled by old age,

suffering from hellish doses of radiation and nearly out of fuel, has

completed its last major objective, all but closing out one of the most

successful voyages of planetary exploration ever.



In November, seven years after braking into orbit around the solar

system's largest planet, Galileo streaked past Amalthea, one of

Jupiter's inner moons, and dipped deeper into the planet's seething

radiation belts than ever before for a final death-defying flyby.



The radiation scrambled Galileo's computer timing circuits, sent the

spacecraft into electronic hibernation and caused its tape recorder,

loaded with priceless data, to freeze up. But in one more display of

technical virtuosity, engineers at NASA's Jet Propulsion Laboratory in

Pasadena, Calif., brought the spacecraft back to life and got the

recorder working in time to play back a final treasure trove of data, a

task they hope to complete this week.



Over the next few weeks, engineers expect to finish the job of

retrieving additional data that was stored earlier. At that point, 13

years after launch and seven years after arrival at Jupiter, the Galileo

mission will come to a fiery end.



The three-ton spacecraft is sailing through the outbound leg of its 35th

and final orbit of Jupiter. It will crash into Jupiter on Sept. 21, a

deliberate plunge into the dark side of the planet -- out of view from

Earth -- at 108,000 mph.



The robotic suicide is designed to eliminate any chance that a hardy

microbe, possibly alive in the radiation-shielded bowels of the

spacecraft, could contaminate one of Jupiter's moons, where subsurface

oceans may harbor life.



"The spacecraft is aging, propellant is almost gone, and we continue to

dose it with radiation," said Eilene Theilig, Galileo project manager.

"It's the right thing to do, to have a controlled end to the mission

before we lose that control."



For the hundreds of men and women who built, launched and cared for

Galileo over the course of its long and productive life, Sept. 21 will

mark the end of an era.



"People note things like when they got married and when they had kids

during, you know, which orbit Galileo was on," said project scientist

Torrence Johnson. "When we really get down to September, when the

spacecraft is just going to go away, there will be a few moist eyes

around."



The nuclear-powered $1.5 billion Galileo was launched from the space

shuttle Atlantis on Oct. 18, 1989. To reach Jupiter, the spacecraft had

to fly once past Venus and twice past Earth, using the planets' gravity

to boost its velocity.



On the way to Jupiter, its camera made a movie of Earth spinning in

space, collected high-resolution images of two asteroids and provided

the only pictures of the impact of a comet fragment crashing into

Jupiter's atmosphere in 1993.



Major problems cropped up, as well.



On April 11, 1991, its $3.7 million 16-foot-wide "high-gain" antenna,

needed for high-speed data transmission to Earth, jammed and failed to

open. That forced engineers to redesign the mission using the

spacecraft's smaller -- and slower -- low-gain antenna. Later,

mysterious electronic glitches periodically sent the spacecraft into

protective "safe mode." Galileo's software ultimately was modified,

directing the main flight computer to ignore such crippling anomalies.



Then in October 1995, as Galileo closed in on Jupiter, its tape recorder

jammed. Engineers ultimately fixed that problem and another potential

glitch.



Finally, all was ready, and on Dec. 7, 1995, a 747-pound atmospheric

probe it had released the previous July slammed into Jupiter's cloud

tops at 106,000 mph -- 50 times faster than a rifle bullet.



The hardy probe survived for nearly an hour. Descending by parachute,

its instruments collected unprecedented data about Jupiter's atmosphere,

beaming it up to Galileo 133,000 miles overhead.



Over the next seven years, flight controllers used the main engine and

the gravity of Jupiter and its major moons to repeatedly alter Galileo's

trajectory, setting up multiple flybys of the planet's four major

satellites: Io, Europa, Ganymede and Callisto.



Galileo also measured Jupiter's space environment, and charted its

powerful magnetosphere, radiation zones and the planet's tenuous ring

system. 



The effort was so successful that the original two-year mission was

extended three times to collect additional data about icy Europa,

believed to harbor a vast subterranean saltwater ocean, and Io, racked

by gravitational stresses responsible for about 120 known "hot spots"

and active volcanoes.



The flyby of Amalthea marked the closest Galileo had ever flown to

Jupiter.



"Galileo wasn't going to let us go without having some fun on the last

pass," Johnson said. "The spacecraft went into [safe mode] at closest

approach to Jupiter, about 30 minutes after Amalthea.



"That appears to have resulted from just very high radiation doses

causing the timing circuits to go crazy."



The problem was traced to a radiation-soaked light emitting diode. After

running current through the diode for more than 50 hours, engineers

boosted its output enough to get the recorder running again.



Not bad, considering that the circuits in question were aboard a

spacecraft orbiting a planet a half-billion miles from the sun, so far

that radio commands from Earth, traveling 186,000 miles every second,

need 45 minutes to get there.



"The number of anomalies and the magnitude of them that the spacecraft

took at our Amalthea flyby was just completely unprecedented," said

Duane

Bindschadler, the spacecraft and sequence team chief.



In that single flyby, Bindschadler said, Galileo received the equivalent

of 70,000 rads, about half the radiation dosage the spacecraft was

designed to survive in its lifetime and a more-than-lethal level for an

astronaut.



Because of earlier mission extensions and repeated high-priority flybys

of the volcanic moon Io, also deep in Jupiter's radiation belts, Galileo

has absorbed about four times the radiation it was designed to

withstand. But it has survived, thanks to the ingenuity of the jet

propulsion laboratory's flight control team.



In September, Galileo engineers and scientists, past and present, plan

to gather at the laboratory to mark the spacecraft's passing.



Whether the gathering will be a party or a wake is a matter of

definition.



"I consider a wake to be a celebration of somebody's life," Theilig

said. "And so I consider that a party. It's not a sad wake, by any

means. It's a celebration."

-- 

.....................................................

Susan L. Gawarecki, Ph.D., Executive Director

Oak Ridge Reservation Local Oversight Committee

102 Robertsville Road, Suite B, Oak Ridge, TN 37830

Toll free 888-770-3073 ~ www.local-oversight.org

.....................................................

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