Slashdot Mirror
Chandra Losing Its Sight To Grease
lgreco writes "The new scientist has this article about NASA's Chandra X-Ray Observatory that is losing part of its sight due to grease built up on one of its optical filters. I guess it will take a space shuttle mission to clean the filter or install one of these mini windshield wipers ..."
after working for a gas stations for a few years.. i am more than qualified to be sent to clean its lense. ill check it's oil and tire pressure too :P
Wouldnt you like to be a pepper too?
Heavens dimmed for Chandra space telescope
17:15 07 November 03
Exclusive from New Scientist Print Edition. Subscribe and get 4 free issues.
One of NASA's highest profile space telescopes is losing its sight. The $2 billion Chandra X-Ray Observatory is suffering from a mysterious build-up of grease on an optical filter in front of one of its cameras, blocking almost half the light at some frequencies.
Since being placed in orbit by the space shuttle in 1999, Chandra has been studying X-rays emitted by astronomical objects such as quasars and black holes. It is expected to carry on working for up to 15 years.
Jane Turner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, was one of the first scientists to spot something strange in her data. She compared data from an instrument on Chandra called the Advanced CCD Imaging Spectrometer (ACIS) with similar data from a European spacecraft called the X-ray Multi-Mirror (XMM) telescope, and found some discrepancies in the low-energy region of the X-ray spectrum.
Chandra x-ray telescope
This low-energy data is useful for determining how much gas there is between the instrument and an X-ray source because it can show how much light is absorbed. If you did not know about the contamination, she says, it could look as if there was a gas cloud in front of the object of study.
Scientists soon identified a problem with a filter in front of the instrument, which allowed them to add a correction factor to their data. "It slowed everyone down at first, but these things happen," she says.
Evaporate and condense
Astronomers had expected to see a certain amount of contamination on the filter. Some materials used on spacecraft evaporate in a vacuum and tend to settle on the coldest surfaces nearby. ACIS is at about -100 C. But the level of contamination is much higher than anyone anticipated.
"There is 10 times as much contamination as we expected at launch," says Herman Marshall, an astrophysicist with the Center for Space Research at MIT. In the three years since the launch, a layer of grease 0.37 micrometres thick has built up on the filter. That's thicker than the filter itself, he says.
Scientists are not yet sure what is causing the build-up. Analysis of the contamination shows that it contains carbon and fluorine, which points to a problem with a fluorocarbon lubricant called Braycote used on the spacecraft or with other sources of fluorine such as Teflon-coated screws.
Braycote was chosen because it does not normally evaporate at low temperatures. But Marshall thinks the contamination may have occurred when molecules in the lubricant were broken down by mechanical stresses and then bombarded with radiation. These breakdown products could then have evaporated and settled on the filter.
Bake out
The contamination only affects a small percentage of the data Chandra is collecting. "The issue is mainly with sources at lower energies and lower temperatures," says Dan Schwartz, a physicist at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
But in this region of the spectrum the contamination is absorbing about half of the light, he says. "I would guess about 20 to 25 per cent of people have added uncertainty in their data, but it probably doesn't affect scientific conclusions."
Now engineers are working out how to remove the grease. In December, they may heat up the instrument in the hope of boiling away the contaminants.
A "bakeout" has its own risks, because too much heat could damage the camera or the filter. Or the contamination could settle somewhere worse, says Chandra programme manager Keith Hefner. So far, the other instruments on board are unaffected. "The vehicle is still performing well," says Hefner.
Emily Singer
Return to news story
(C) Copyright Reed Business Information Ltd.
Unfortunately Chandra's orbit is way out of reach of the shuttle -- orbiting between 133,000 km (82,646 mi) and 16,000 kilometers (9,942 mi) from the Earth.
Two wrongs don't make a right, but three lefts do.
Space.com, Spacedaily.com, and some more from Google.
The Space Shuttle Columbia delivered Chandra to a low Earth orbit. Then, the Inertial Upper Stage rocket boosted Chandra up to a higher altitude where a built-in propulsion system took Chandra to its final orbit.
I'm wondering whether there's some juice still left in Chandra's propulsion systems. If so, we can still launch a repair shuttle mission, have Chandra go to the shuttle with whatever's left in it's rockets, and get a repair done. Then, boost it back out. IANARS (I Am Not A Rocket Scientist) but usually NASA leaves some rocket fuel in it's satellites and stuff so they can reorientate themselves if necessary, etc.
install one of these mini windshield wipers ...
This is a nice idea at first blush, but in practice it won't work. In space, the rubber will get solid and shatter--anyone who has dipped rubber in liquid nitrogen has seen it happen.
It sounds like a silly idea, but it is the kind of thing that space roboticists think about. Mars rovers can have problems with dust getting on the lenses, and getting it off is not as easy as it seems. (Actually, I don't know how or even if there's a way right now.)
--Tom
MAN SHOOTS ROVER!
The problem only shows up with only one filter at the lower end of the filter's spectral range. The amount of buildup and its effect on various frequencies has been measured. There is even a model for how the buildup has increased over time. A review of older data and instrument calibration may be able to further validate and refine this buildup model. In most cases old data that used this filter can be corrected to a reasonable degree. In nearly all cases, this buildup has a nil impact on the scientific conclusions that have thus far been produced.
NASA is examining a potential correction to the buildup. They are considering what is known as a "bakeout": going through a warm-up and cool-down cycle to boil off the contamination. They are going through a risk / reward analysis at the moment. The reward of a buildup reduction is being compared to the risk that the bakeout will move the contamination to other instruments. It is possible that the bakeout will happen in mid December, or it will be moved from mid-December to a later date or canceled altogether.
So while the buildup is not good / unfortunate, it appears to be neither fatal nor mission threatening at the moment.
P.S. To those who asked about the using the remaining on-board fuel to lower the bottom of the orbit to a shuttle serviceable level. The remaining on-board fuel is insufficient to do that ... a rough calculation shows that it
is 1-2 orders of magnitude too small.
chongo (was here)
I commented a preview of the New Scientist article several days ago. And just in case Chandra's camera filters cannot be cleaned, my overview included a a picture of a composite Chandra X-ray and optical image of the massive star HD 192163.
If you send a robot up to do the same job, you need it to have an auto-switching socket wrench set, crescent wrench, squeegee in this case, holding clip.. the list goes on and on. Plus, the robot has to know ahead of time exactly where each screwhead will be, because robotic vision is nowhere near up to snuff for figuring out that the robot attached 2mm to the left of where it should, and everything in the program has to be changed.
Robots in factories are effective because each robot arm does one or two jobs, and because everypiece coming down the line is put in eaxactly the same place. Robots that are somewhat adaptable, like Asimo, or to a much greater extent research robots with neural nets that do nothing but wander about, have nothing like the precision, nor the computational space, to also do a very complex repait task.
It's going to be many years before we bring those two sides of our robot expertise together. In the meantime, expensive as it is to send a man into space, it's vastly more expensive to imagine creating flexible repair robots, and universal robots are just impossible.
> > The Space Shuttle Columbia delivered Chandra to a low Earth orbit. Then, the Inertial Upper Stage rocket boosted Chandra up to a higher altitude where a built-in propulsion system took Chandra to its final orbit.
> I'm wondering whether there's some juice still left in Chandra's propulsion systems.
Sadly, no. Changing orbits between the Shuttle's LEO and Chandra's large elliptical orbit (it moves almost one third the way to the moon) requires massive amounts of fuel. The Inertial Upper Stage is actually a large two-stage solid-fuel booster with over 25,000 lbs of fuel and 40,000 lbs thrust. This rocket is discarded along the way. Chandra, itself, has some fuel and some tiny thrusters (105 lb thrust each), but that is completely inadequate for a big job like moving back to LEO.
As Douglas Adams said, "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the drug store, but that's just peanuts to space." Unfortunately, this harsh reality means that moving in space is expensive, mind-bogglingly expensive.
Two wrongs don't make a right, but three lefts do.
A fried of mine was in the coast guard in the early 60's, one of his duties was changing the light bulbs on the large marker bouys, he would change about 24 bulbs on a rotating mount that would turn a new bulb in place when the previous one burned out. This way only a once a year visit to the bouy was needed. perhaps this could be used on a satalite with one or two extra lenses. More weight and expense but longer life. His story was pretty cool he described being on a 20 foot tall bouy in high seas and ocean spray hanging on with one hand and bulbs in the other, though he did not care for it, scared out of his wits most of the time.
I eat my grapes at room temperature, cuz the cold ones hurt my teeth