Author Topic: Atlantis STS-30 – One Touch of Venus  (Read 56701 times)

Offline Ares67

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #360 on: 08/17/2012 04:11 PM »
Working Magellan’s Magic

(by J. Kelly Beatty)

Of all the dates stashed away in Stephen Saunders’ memory, none is more indelible than August 16, 1990. NASA’s Magellan spacecraft had recently slipped into orbit around Venus after a 15-month cruise from Earth. A crucial test on the 16th would determine how well the craft’s radar-imaging system could reveal the landscape that lay hidden beneath Venus’ mantle of dense clouds. As Magellan’s project scientist, Saunders was more anxious than eager to see what the spacecraft could deliver.

For its debut Magellan was to transmit home radar echoes recorded over two orbits; once received they would be converted into narrow image swaths of the Venusian landscape. But after firing off one and a half orbits of data, the spacecraft fell silent. The flight team was stunned. “It was a mixed feeling as we waited for that first image,” Saunders recalls. “It looked fantastic, the whole length of it. But at the same time we knew the spacecraft wasn’t functioning right and that maybe we’d lost it.”

Offline Ares67

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #361 on: 08/17/2012 04:13 PM »
A lot was riding on Magellan. NASA managers were still reeling from the discovery two month before of flawed optics aboard the Hubble Space Telescope. Moreover, Magellan represented the first U.S. planetary probe launched in more than a decade, and Voyager 2’s triumphant march through the outer solar system was a tough act to follow. Even the Soviet Union had unexpectedly taken some of the gleam from Magellan’s mission, by dispatching a pair of radar orbiters to Venus in the mid-1980s.

But Saunders had faith in his spacecraft, an unwavering dedication he’d maintained since getting involved in the program during the 1970s. Back then it was called the Venus Orbiting Imaging Radar, a cumbersome mouthful that represented a larger, beefier machine for studying both the surface and atmosphere of Venus. However, officials in the Reagan administration balked at the mission’s high cost and canceled it outright. From those programmatic ashes and a frenzied redesign effort came Magellan, a smaller, single-purpose mapper that drew heavily upon spare parts from existing spacecraft like Voyager and Galileo.

Magellan was incommunicado for 14 hours before flight controllers tracked down its distress call. The spacecraft had been staring off into space due to a runaway program in its attitude-control computer, an electronic fit that would recur several more times before being diagnosed and corrected nearly a year later. In time the team would learn to take these “walkabouts” in stride, but concern after the first outage and a second, longer one on August 21 delayed the start of the mapping effort for weeks.

After August’s surprises, Magellan settled into its programmed routine. As the spacecraft cruised around Venus its radar mapper looked to one side, deviating from the nadir by 12° to 45°. Each time a radar pulse reached the surface, the resulting echo would be spread into a spectrum of delay times (defining range from the receiver) and Doppler-shifted frequencies (defining locations ahead of or behind the moving spacecraft). This delay-Doppler checkerboard of raw data uniquely identified each spot illuminated by the radar beam and yielded an average resolution of 120 meters. A second, smaller antenna clocked the roundtrip times of separate radar pulses sent straight down and in doing so traced out the vertical relief of the landforms below to within ten meters. It also paused from pinging periodically to record the microwave energy emitted naturally by the hot Venusian landscape.

Mission planners knew there would be plenty of data, for never had an interplanetary probe undertaken so vast an assignment: to map an entire world with even finer detail than is available for much of Earth. But the spacecraft’s output proved so prodigious that the processing computers at the Jet Propulsion Laboratory in California were swamped with a week-long backlog. By November 29, after just ten weeks of mapping, Magellan had already amassed a trillion bits of data.

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #362 on: 08/17/2012 04:14 PM »

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #363 on: 08/17/2012 04:16 PM »
Meanwhile, cloistered deep inside a windowless building behind three sets of security doors, Saunders and radar principal investigator Gordon Pettengill had assembled a hundred researchers to attack the avalanche of imagery. “We set them up like SWAT teams,” Pettengill says, to analyze distinct groups of features like impact craters, tectonic fractures, and volcanoes. There was no shortage of things to look at, and Saunders encouraged the mission’s scientists to bring their post-doctoral and graduate students along to assist in the effort. Throughout late 1990 and much of 1991 the small army of analysts slaved over the data every day in double shifts. NASA brass had even named three Russian scientists as official participants, an acknowledgement of the scientific cooperation that had blossomed in the final days of the Cold War. “The mode of selection was very Russian,” observes team member Aleksandr Basilevsky, a veteran researcher from Moscow’s Vernadskiy Institute. “Our director handpicked who would go.”

Saunders’ chief task was to make sure the mission data were properly organized, calibrated, and archived for future use. But the geologist inside him relished the chance to join his colleagues around the worktables. “I set an objective for myself – to map Venus – quite a long time ago,” he reflects. Seen in that context, he doesn’t consider the weeks and months of 14-hour days to have been much of a sacrifice. Besides he likes being caught up in all the scientific debates that Magellan’s data have spawned. The team’s findings, though initially released in a slow trickle, have been the dominant theme at planetary meetings for the past two years. In late 1992 a pair of special issues of the Journal for Geophysical Research, weighing in at more than two kilograms, offered more than 1,100 pages of insights on the “new” Venus. Indeed, many researchers feel the study of the Venusian landscape has essentially begun anew, despite the leaps in knowledge represented by prior spacecraft and ground-based radar efforts. “In some areas, our resolution has gone from 20 kilometers to 100 meters,” says Pettengill. “That’s a big jump, and it looks like a different planet.”

Healthy and sometimes emotional scientific debates continue now that all of Magellan’s imagery, altimetry, and radiometry have been given the once-over. For instance, why do the landscape’s radar properties change dramatically at an altitude precisely four kilometers above the planet’s mean radius, at which point the temperature falls below 730° Kelvin? “As you reach 6,055.5 kilometers,” says radar specialist Peter Ford, “you are guaranteed that the reflectivity goes up and the emissivity drops.”

Did the planet really get a completely new surface some 500 million years ago, or does it only look that way? How does a massive “continent” taller than Mount Everest remain so high when its rocks are halfway to their melting point? And of course, is Venus still geologically alive? Initially the lava flows that blanket the face of Venus fueled expectations that Magellan might record before-and-after views of an eruption or some other ongoing geologic phenomenon. An embarrassing false alarm occurred in August 1991, when a surface change was noted in two views taken eight months apart. However, what the team initially announced as a recent landslide turned out to be an illusion caused by the vagaries of radar imaging.

As Saunders notes, “There are students not born yet who will use this data and come up with things that I never dreamed of.” But the team still has one analytical trick up its collective sleeve. As you read this (August 1993), Magellan is ending a risky aerobraking maneuver and settling into a smaller, nearly circular orbit. From there the spacecraft can conduct a global survey of the planet’s gravity, a final result that should help resolve many thorny issues.

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #364 on: 08/17/2012 04:17 PM »

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #365 on: 08/17/2012 04:18 PM »

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #366 on: 08/17/2012 04:20 PM »
However, getting the gravity data requires funding that neither the project nor NASA currently has. Project managers initially estimated they’d need $80 million and a staff of 200 to circularize Magellan’s orbit and complete two 243-day cycles of gravity mapping. But last year NASA administrators flatly rejected the proposed extension and announced that the mission would end this September 30. Some serious belt-tightening ensued back at the Jet Propulsion Laboratory, saving enough money to conduct the aerobraking experiment with existing funds. Moreover, project manager Douglas Griffith now thinks the gravity mapping can be had for no more than $7 million in fiscal 1994 and a little more in 1995 using a “lean, mean” staff of just 32.

Wesley Huntress, NASA’s Associate Administrator for Space Science, likes what he’s seen, “I think what JPL has done to get the cost down is excellent, and I’d love to be able to reward them for that.” But unless Congress feels equally sympathetic, Magellan may soon become the first American interplanetary spacecraft ever to be switched off for lack of funds. (J. Kelly Beatty, “Working Magellan’s Magic,” Sky & Telescope, August 1993)

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #367 on: 08/17/2012 04:21 PM »

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #368 on: 08/17/2012 04:24 PM »
August 3, 1993: MAGELLAN’S HISTORIC AEROBRAKING MANEUVER NOW COMPLETE
The Magellan Venus mapper’s historic aerobraking maneuver is now complete. During the so-called transition experiment from May 25 to August 2, Magellan altered its orbit from a 170-by-8,460-kilometer ellipse to  amore circular 197 by 540 km. The orbit change used only a small amount of fuel, most of the work being done by drag in the Venusian atmosphere. The trajectory was carefully calculated to ensure that the spacecraft would not overheat. Magellan now begins a more detailed mapping of Venus’ gravitational field. The success of this experiment, and that of a less ambitious one carried out in Earth’s upper atmosphere by the Japanese Hiten probe in 1991, make it likely that aerobraking will become standard practice in future missions, just as gravity-assist flybys first done by Mariner 10 and Pioneer 11 are now part of virtually every planetary mission. (Sky & Telescope, October 1993)

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #369 on: 08/17/2012 04:26 PM »
September 1994: MAGELLAN - THE FINAL DAYS OF THE GREAT NAVIGATOR
And with the aerobraking maneuver successfully completed in August 1993 there came another reward: The Magellan team got a fifth cycle approved and – more importantly – funded. They even were able to begin a sixth and final cycle, which began in April 1994 and produced additional gravity, radio science and radar data. During the final days of its life, Magellan’s orbit was lowered further into the outer reaches of the dense Venusian atmosphere. The so-called “windmill experiment” involved using the probe’s solar arrays like the blades of a windmill. The scientists gathered data on the amount of molecules in the upper atmosphere of Venus and the torque control required keeping Magellan in a stable orientation. Future low-orbiting spacecraft and probes conducting areobraking maneuvers could benefit from the results.


October 12, 1994: DEATH DIVE INTO VENUS
NASA ground controllers gave final commands Tuesday (Oct. 11) that sent the Magellan space probe crashing to its death in the searing atmosphere of Venus. The $900 million robot mapping probe, one of the most successful space missions ever, has been in Venus Orbit since 1990. But with failing solar panels and worn-out gyroscopes, the spacecraft will now begin its death dive.

Magellan has sent back more data than all previous U.S. planetary missions combined. “It’s been successful beyond our expectations,” chief scientist Moustafa Chahine said. The images sent back “gave us unprecedented information to study the planet.” Magellan, deployed in 1989 from shuttle Atlantis, spent 15 month looping the solar system before reaching Venus. It mapped 98% of the surface and found volcanoes taller than Mount Everest and canyons longer than the Nile River. Venus is often called Earth’s twin; they are roughly the same size, age and composition. But somewhere along the way, Venus suffered a runaway greenhouse effect that left it with an acidic atmosphere and a surface temperature of 900 degrees. (USA Today, Oct. 12, 1994)


AND NOW: MISSION TO PLANET EARTH
Last contact with Magellan was recorded at 3:02 a.m. PDT on October 12, 1994. And while the highly successful radar mapping Venus probe broke apart and probably was vaporized, back home six astronauts aboard Space Shuttle Endeavour conducted the second Space Radar Laboratory mission of 1994 (SRL-2), using a powerful radar antenna to scan swaths of terrain on Planet Earth. The goal was to produce topographic maps unrivaled for accuracy, similar to those obtained of Venus’ surface during the Magellan mission.

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #370 on: 08/17/2012 04:28 PM »
What have we learned? Where do we go?

(by Ellen Stofan, Deputy Project Scientist for Magellan at JPL)

For me, Magellan’s time at Venus has passed far too rapidly, and it has been difficult to find time to sit down and truly try to fathom the significance of its findings or to ponder future discoveries hidden in the mountain of data returned. It is clear that we have uncovered a world both incredibly similar and dissimilar to Earth. Venus might not exhibit plate tectonics, but perhaps we have found a planet dominated by catastrophes, showing us a path that the Earth, for reasons unknown, has avoided – at least to this point. We have learned that the greenhouse around Venus, as expected, has operated for at least the last 500 million years and probably much longer. But the hot, inhospitable surface should serve as a warning that planetary atmospheres should not be abused.

The most exciting thing about the Magellan data has been discovering features we never expected: channels extending for thousands of kilometers, beautiful outflows surrounding impact craters, and odd volcanic constructs like the steep-sided domes. Whatever else may lie hidden in these data, future geologists will have an Earth-size planet available to study at incredibly high resolution. In truth our investigation of Venus with the Magellan data has barely begun.

So should we leave Venus now? Is our work collecting data finished there? The answer is most definitely no. As with any scientific endeavor, Magellan has left us with more questions than when we began. Venus still holds important information on the evolution of planets. The composition, structure, and dynamics of its atmosphere, in particular, await further elucidation. These were addressed in only the most basic fashion with Magellan’s U.S. predecessor, the Pioneer Venus mission, and the Venera probes sent by our colleagues in the former Soviet Union.

Concerning the Venusian surface itself, the Veneras provided very limited chemical information at only a few sites and nothing at all in the high-reflectivity regions. Certainly, we suspect that Venus’ interior is active. Seismic data acquired by a network of landers could tell us volumes about the planet’s interior structure.

All these types of missions are currently under study, with a whole new generation of scientists standing ready to test their theories and analytical skills. One day soon, we will be back on our way to Venus. (Ellen Stofan, “The New Face of Venus,” Sky & Telescope, August 1993)

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #371 on: 08/17/2012 04:30 PM »
And that’s all for now. I hope you’ve enjoyed our journey, from close-up shots of the U.S. Gulf Coast and the Florida peninsula by the crew of Atlantis, to exciting views beneath the clouds of Venus, and then a jump to the outer solar system, taking a first look into the dark eye of Neptune. We’ll continue that trip in the upcoming new STS-34 thread.

L2 high-res STS-30 photo source:

http://forum.nasaspaceflight.com/index.php?topic=13657.0

But first we’ll witness the return of an “old lady,” and in addition to that all the other space-related events during the summer of ‘89 – we’ll see a load of expendable rocket launches, a comeback in Earth orbit, a match made in heaven in the name of the Roman goddess of marriage, a snowstorm in Paris, a continued fight for Freedom and a tragic loss. And of course we’ll remember the achievement of a major goal within eight years two decades earlier and relive the announcement of new goals we haven’t even achieved today… 23 years later!

Columbia STS-28 – Called Back to Duty

Coming soon to your favorite space site…

;)

Offline Beemer

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #372 on: 08/18/2012 12:38 AM »
Another great job Ares.

You should be designated NSF's Official Historian :)
Ride, Sally Ride! In memory of Sally Ride [1951-2012] America's first woman astronaut

Offline Ares67

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #373 on: 08/18/2012 11:57 AM »
Another great job Ares.

You should be designated NSF's Official Historian :)

Thanks for your nice words, Beemer.  - But remember, when I'm presenting my shuttle flashbacks, I'm always standing on the proverbial shoulders of giants - and several of those giants are also members of NSF/L2.

Nevertheless I'm glad to share the results of my three-decades-long hunter/gatherer efforts and really appreciate the positive feedback, since I'm really kind of a history buff.


:)

Offline Beemer

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Re: Atlantis STS-30 – One Touch of Venus
« Reply #374 on: 08/20/2012 11:38 PM »
Another great job Ares.

You should be designated NSF's Official Historian :)

Thanks for your nice words, Beemer.  - But remember, when I'm presenting my shuttle flashbacks, I'm always standing on the proverbial shoulders of giants - and several of those giants are also members of NSF/L2.

Nevertheless I'm glad to share the results of my three-decades-long hunter/gatherer efforts and really appreciate the positive feedback, since I'm really kind of a history buff.


:)

So am I. I followed the space program very closely when I was younger but sadly fell away from it. Now I have a lot of catching up to do  and threads like this are very helpful :)
Ride, Sally Ride! In memory of Sally Ride [1951-2012] America's first woman astronaut

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