Los Angeles - Jul 09, 2002
Galileo - a spacecraft originally designed to work for just two years during a 12 flyby tour of the Jovian system is still working over five years and 33 flybys later.
But with Galileo having taken several times the dose of Jovian radiation it was designed to endure, NASA has basically said no to a science campaign during the final flyby opportunity on Nov 5 this year of Jupiter's little inner moon Amalthea, a potato-shaped lump of dark reddish rock 270 by 150 kilometers, which up to now has only been seen at distances of 100,000 km or more by Galileo and the Voyagers.
Galileo will fly within a mere 500 km of Amalthea, which would seem to present a splendid opportunity for closeup photos of it. There's only one problem: NASA currently has no plans to do so. The reason, as usual: NASA's funding problems.
The current plan is not to use the instruments on Galileo's pointable scan platform at all (the only one relevant to Amalthea being the camera). Instead -- while the spacecraft will record high-speed science data on its tape recorder -- it will only utilize its various magnetic, radiation and dust detection instruments, which need not be pointed.
These will provide some data on the effect Amalthea has on Jupiter's complex radiation belts -- including the unlikely possibility that the little moon has a magnetic field -- but their main purpose is to provide new information on Jupiter's inner magnetosphere itself (which has only been observed by spacecraft a few times) and on Jupiter's faint rings (Galileo will actually fly through the very faint, dusty "gossamer ring").
The main goal of the Amalthea flyby, though, is simply to track the effect the moon's gravity has on Galileo's trajectory, allowing the first good calculation of its mass and thus the density of the rock composing it.
Closeup photos would certainly greatly add to the data from the flyby. They've consistently revealed surprises about all of Jupiter's four main moons. And it will be a very long time -- perhaps decades -- before another spacecraft has a chance to get this close to Amalthea.
But Galileo, throughout its 3 1/2- year extended mission, has been operating on a shoestring, as NASA continues to whittle the costs of its other activities to a minimum in a desperate effort to try to feed the ever-growing financial maw of the Space Station.
And if the usual procedure for photography during one of its moon flybys was followed, photographing Amalthea would cost 1 to 1.5 million dollars -- a mere crumb compared to the hundreds of millions that each individual Solar System mission costs, but enough to make the agency determine that Amalthea photos are simply not quite worth it in its current financial travails.
There's another reason: all that Jovian radiation, which increases to savage intensities as one gets closer to the planet, is finally starting to have serious effects on the spacecraft.
After considerable debate, the agency finally reluctantly decided to shell out for photography and other scan-platform studies of Jupiter's volcanic moon Io during the spacecraft's final flyby of it last January 17 -- only to have the spacecraft go into emergency "safe mode" due to a temporary radiation-triggered electronics malfunction just 28 minutes before the flyby, so that it could make no active science observations of Io at all, and could only reset itself the next day in time for some observations of Jupiter's own cloud patterns.
Galileo is becoming more and more susceptible to these safe modes during its flights through Jupiter's inner radiation belt, and it unexpectedly suffered one while far from the planet in February.
Moreover, its camera suffered a radiation-triggered problem that kept it from photographing Io during a flyby last August, although a software fix allowed it to obtain beautifully clear photos during the next flyby in October.
And its IR and UV spectrometers both broke down from the radiation back in 1999, preventing it from getting any closeup mineral mapping of Io during its six optional flybys of that world. The radiation level is even more ferocious for Amalthea than for Io; any attempt to photograph the little moon would be a definite gamble.
But there's a possible alternative, described by "Aviation Week"magazine in its forceful July 8 editorial ("Quit Fiddling and Image Jupiter Moon"). That $1 million-plus bill for Amalthea imaging is based on the Jet Propulsion Laboratory maintaining Galileo's 12-member science team and data distribution system for another year (during much of which they would be idle).
But this, strictly speaking, is not required. The science team does not have to be on hand, and distribution and analysis of the photos could easily be delayed, with the photos simply being stored for later distribution to scientists.
The JPL technicians who actually design the sequence of camera instructions are still there and could very easily design a sequence of pointing and shuttering instructions for the camera adjustable to its final calculated flyby trajectory.
Indeed, with a flyby that close, it isn't even necessary to have the camera precisely pointed -- during Galileo's flybys of two asteroids and the NEAR spacecraft's flyby of asteroid Mathilde (all of them more distant flybys of much smaller targets than Amalthea), it was not even certain that the asteroids would be in the viewfield at all; but the photography attempts were considered well worth the effort anyway. And they all did pay off very well scientifically, repeatedly revealing unexpected things of major scientific importance.
Such a minimum-price photography team, according to Aviation Week, would cost only "a small fraction of the full-blown proposal". Indeed, it could be extended to other targets as well during that last orbit.
Had NASA decided to fully fund such imaging, it would also have included what a paper by the Galileo imaging team earlier this year calls "two very high-value" (though distant) observations of the Jupiter-facing side of Io.
Even with a resolution of only 1/2 km per pixel, these would "provide critical tests of the lava-lake hypothesis for [the gigantic volcano] Pele... allow us to determine if the [huge recent] eruption at Pillamn involved magma moving up the same faults that are ripping the nearby mountain apart... provide the best view ever of [Loki], the Solar System's most powerful volcano, and a much better look at the most likely site of sulfur volcanism on Io". A useful consolation prize for the loss of photography during Galileo's final close Io flyby.
The original plan also called for Galileo to make the closest and most detailed images and infrared maps yet of Jupiter's weather patterns, with a photo resolution of only 0.7 km per pixel. Perhaps it could also make additional closeup observations of Jupiter's ring structure. And all or any of this could be done without the need for super-precise scan platform pointing.
As mentioned, it would be risky -- Galileo could very easily undergo another "safing event" that would cause it to lose some or all of its observations. But this would also cause it to lose its observations of Jupiter's magnetosphere and ring dust, and JPL nevertheless regards them as worth the risk. If the cost of imaging can be trimmed to a few hundred thousand dollars, the gamble looks worth the price.
On the advice of a scientist, this reporter enquired several months ago of JPL why they had rejected such a cut-rate plan -- and no one could give me any answer whatsoever except that it would be "violating established procedure".
Unless NASA can come up with a better reason that that, it seems ridiculous -- and scientifically irresponsible -- to be passing up such a possible final hurrah for Galileo for a cost only a few millionths the cost of the International Space Station.
Amalthea at PlanetScapes
Galileo at JPL
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The Next Four Weeks on Galileo
June 17 - July 14, 2002
The Galileo spacecraft has now rounded the corner in its longest looping orbit around Jupiter and is again heading back in toward the giant planet and a close flyby of the tiny moon Amalthea in November.
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