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Clock Ticking for Hubble
DoraLives writes "Ok then, what are we going to do with Hubble? Eventually, it MUST come down. The New York Times has a piece that addresses this less than pleasant (at least for the astronomical community) subject. Additionally "The decision about what happens then has been complicated by the breakup of the Columbia." Read all about it."
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http://news.bbc.co.uk/1/hi/world/americas/1231447. stm
In case someone was wondering about the reference.
Most satellites go up into space with a designated shelf life. They are supposed to be brought down under their own power to save the trouble of building a space-garbage collector if it died and became unresponsive.
So Hubble's self-propulsion system is supposed to go bad in 8 years so they bring it down in 7.
If sending up a Shuttle to re-establish a fresh orbit for Hubble would be cheaper than building a new and improved Hubble and launching it?
Development cost of Hubble: $2 billion
Cost of one space shuttle launch: $600 million
So you can get in excess of three launches for the same cost of the Hubble.
Toronto-area transit rider? Rate your ride.
Hubble is in Low Earth Orbit (LEO). It's got an orbital velocity of around 4KM/Sec.
To raise the orbit far enough to get to the Moon, takes a total deltaV of 7KM/S (or another 3KM/S on it's current speed).
The Earth orbits the sun at around 30KM/S, give or take. So to send something - anything - into the sun requires a deltaV of the same amount: you've got to cancel out the existing 30KM/Sec velocity, otherwise you're just going to send the object into a different orbit around the sun
The fastest any object has left the earth is around 8KM/S for the interplanetary probes (Pioneer, Voyager, Cassini, Galileo etc). That's as fast as the human race has ever gotten anything going[*]. Without a major advance in rocket technology (i.e. away from chemical rockets), that's about as fast as we're going to get anything going, too.
As a reference, the on-orbit manoever capability of the Shuttle, is a total of about 100M/S
Oh, and Hubble has much MUCH less manoever capability than this
This is why things are de-orbited, rather than "sent towards the sun" or further out. De-orbiting from LEO requires only a little "kiss" of deceleration before the orbit intersects the atmosphere, from where friction does the rest. The only exceptions are Satellites in higher orbits (e.g. GPS in the 12-hr / 12,000KM orbits, or Geostationary sats) which tend to be "retired" in slightly higher orbits because these are thought to be more stable over longer (geological) time periods than lower ones, and there's not enough residual manoever capability to lower the orbit enough to graze the atmosphere
[*] = However, we've learnt the trick of gravitational assists which lets Mother Nature (or Newton, or Einstein depending on your religious orientation :-) speed up our probes considerably at the expense of the orbital energy of the planet we're assisting from.
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I'd rather have a bottle in front of me than a frontal lobotomy
Among other things, some of the instruments (I'm thinking of the NICMOS, don't remember whether any others require this) must be cooled by liquid nitrogen in order to prevent interference from IR emitted by the instruments themselves.
If you think that's bad, COBE had to be cooled by liquid helium.
You can read more about the instrumentation here.
More speculatively, I imagine occasional physical adjustment have to be made from time to time too, like replacing lubricants, servicing gyros, replacing batteries, and replenishing propellents - space is a fairly hostile environment and you can't expect something as complex as the Hubble to work for 20 years there without some TLC.
"It is our blasphemy which has made us great, and will sustain us, and which the gods secretly admire in us." - Zelazny
The article said that Hubble can stay aloft in current status until 2013. The shuttles are not going to be grounded for a decade.
A few comments on your proposal:
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I'd rather have a bottle in front of me than a frontal lobotomy
Consider what you are suggesting for a sec, OK?
(1) Space Shuttles cannot push it up to much higher earth orbit.
(2) hence you will require a propulsion system to be attached to the HST and then launch into a new, higher orbit.
(3) however, the HST is not designed to take such ad-hoc propulsion system.
(4) and neither NASA has such convenient propulsion system sitting around (Air Force does,
IIRC).
(5) in any case, you have to do R&D to find a way to attach such system and safely launch the HST into a new orbit (consider multitude of risks; the major one that I see is supersonic vibration generated by the rocket).
(6) knowing this is NASA, it'd take a decade to get that sort of things built and launched. Waste of the limited resource. They'd rather build a new telescope (or try to build) with that resource.
In short, I guess it CAN be done. But not without additional resource and public support.
-b
First please read some post on the Low earth orbit issue above.
The HST orbits at a low earth orbit, which means the space environment is nowhere near "vacuum" like we'd expect in the deep space. There is a very thin air
(much, much thinner than that on the top of Mt. Everest) up there that would drag the HST body. The drag eventually slows the satellite; and when the satellite slows down, it starts to decend.
And now the HST does NOT have self-propulsion system. I.e., it is not designed to fly. So if you
leave it up there, it'd eventually come down and
burn in the atmosphere.
-b
Hubble is an overgrown version of a digital camera. As CCDs improve, you eventually want to replace the ones up there with better ones. This has already been done a couple of times, but electronics keeps improving.
It also has batteries and solar cells that provide power, and these wear out and have to be replaced.
Hubble needs to point itself at things, and it does so using heavy spinning rotors, which are
turned one way, and by Newton's Law, Hubble
turns the other way. There are 5 of these
"Control Moment Gyros", or CMGs. Being mechanical devices, they wear out and break over time.
You need 3 out of 5 to be working to point Hubble, and if they have an MTBF of 12.5 years (which is pretty good for a mechanical device), then you need to visit every 5 years and replace 2 to keep Hubble running.
Hubble has no propulsion and you don't want any until you are ready to kill it. Fluids sloshing in tanks will mess up your pointing of the telescope, and any exhaust from a rocket will contaminate the optical surfaces. When the Shuttle visits, the thrusters are 50-75 feet away, which is much less of a problem than if your booster pack is on the back end of the telescope only 2 feet from the science instruments.
And yes, IAARS, in fact the first group I worked at at Boeing back in 1981 supplied the graphite/epoxy frame that holds Hubble's mirrors in place.
Daniel
We just have to move on and produce a successor.
A successor to Hubble is already in the works. See this article on Yahoo! news.
From the article:
But its days (and nights) have always been numbered. NASA has long planned to end Hubble's spectacular run and bring it down in 2010 to make way in the budget for the James Webb Space Telescope, scheduled to be launched in 2011.
SiO2
How do you think the shuttle launches sattelites from 300 miles to 1300 miles into orbit? Onboard PAM rockets! It's in "The Space Shuttle Operator's Manual." Great book, if a bit outdated and expensive.
It's got some stuff about Spacelab, and Endeavour hadn't been named yet. Also, it refers to Heading Alignment Cylinders. They use Cones now, I believe.
The Columbia was the only shuttle capable of holding the Hubble in the cargo bay -- the other 3 orbiter have the airlock in the front portion of the bay, which gives extra room in the crew area. When they built the Hubble, they literally had about 3 inches of extra space to fit it in the shuttles.
The four orbiters are not identical, they've been upgraded and changed as time went on. It was years after the Hubble was launched that they upgraded the airlocks in the other orbiters, purposely keeping the Columbia with the old design so it could be used on Hubble service missions.
Recursive: Adj. See Recursive.
Here the the correct link.
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Amtrak is a government operation. Worldcom and Enron are insignificant compared to the great mass of successful, productive businesses. And at least Worldcom and Enron go OUT of business when they fail, unlike failed government operations which go on, and on, and on, and on, and on.
You have to pay to read the offline version.
Well, calling JWST a successor to HST is a bit of a stretch, actually. JWST will be great for its intended mission of studying high-redshift galaxies, but it is a specialized instrument; not the general-purpose workhorse that HST exemplified. Plus, it will be at a lagrange point, and therefore completely unserviceable. So much for upgrades.
Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
Discovery was also the shuttle that did the 1999 maintenance (STS-103). Endeavor did the 1993 maintenance (STS-61), and finally Columbia did the 2002 maintenance (STS-109).
The maintenance can be preformed by any of the shuttles as long as they have the Payload Deployment and Retrieval System (the robotic arm).
The retrieval (as it appears that they may want to do) is another story, but I believe that they can remove the upgraded airlock.
There is a ton of debris in space, there is no reason to bring all of that down
Actually, there is. It's a hazard to satellites and orbiting spacecraft. A few years back, one of the shuttles had a small crater made in its windshield when it was hit by an orbiting *paint chip*.
There's just so much space junk and it's moving so fast, that it's tough if not impossible to safely intercept and capture. NORAD actually tracks and catalogs every piece of it large enough to get a radar return. When a shuttle is up, they constantly monitor its path for errant debris so it can maneuver if necessary. I believe they do the same for the ISS.
~Philly
The number is 4B per month.
It's actually worse than that. Orbits at altitudes reachable by the Shuttle decay rapidly, because the atmosphere's a little too thick up there - satellites like the Hubble, with big solar arrays, are particularly vulnerable.
The most important thing that happens on Hubble servicing missions has nothing to do with fixing hardware. The Shuttle catches the Hubble, then fires its maneuvering engines and carries the Hubble up to a higher orbit.
I know this because my company did some computer modeling for NASA to help them predict how often these reboosts would be needed. The amount of atmospheric drag varies with sunspot activity - increased solar output makes the atmosphere "puff up" and makes orbits decay faster.
And guess what? The Space Station is in an orbit reachable by the Shuttle, and also has big solar panels, so it needs reboosting by the Shuttle too.
To a Lisp hacker, XML is S-expressions in drag.
I can read the paper version completely anonymously, but I have to go through the hassle of registering, and remembering passwords etc, so that NYT's marketing department can collect entirely bogus statistics on usage. They'd be better off creating a "My NYT" and assuming anyone who doesn't register with that is a casual visitor.
You are not alone. This is not normal. None of this is normal.
When you're trying to aim an optical system accurately, people moving around the ISS would cause totally unacceptable vibrations. Not to mention station orientation thrusters and the occasional docking maneuver by visiting spacecraft
To put it in perspective, imagine trying to compose a picture and while someone is smacking your camera with a nerf hammer(people moving) and sledge hammers(docking maneuvers). It's just not gonna happen.
I'm an individual! Just like everyone else!
Sadly not, for a start the JWST will orbit the L2. Secondly, it's currently planned to be launched on an Ariane 5.
It doesn't include anything to bring it back, and we don't have anything that can go out there and get it. Seems like a major problem to me, since Hubble wouldn't be nearly as useful as it is today if it couldn't be serviced.
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The lagrange point in question is Lagrange Point 2 (L2) of the Earth-Sun system. A notable characteristic of L2 is that it is always on the night side of Earth orbit (ie. the Earth is always in between L2 and the Sun). Clearly, this is advantageous for a telescope like the James Webb.
As a side note, L1 is opposite to L2 and is therefore, always on the day side. As might be expected, L1 is currently occupied by The Solar and Helioscopic Observatory, or SOHO
Further, the reason why satellites at either of these points are (currently) unservicable is simply a consequence of distance; approx. 100th of 1 AU, or, 4 times the distance of Earth to Moon.
Depending on what L-point, it would more or less make it unserviceable. The LAgrange points are very far away from LEO (Low Earth Orbit)
The closest L-point is the one between the Earth and the Moon, which would make it possible to service, if NASA still had spacecraft able to carry people to the moon...
The Trojan points (30 degrees ahead and behind in orbit) are other L-points. There's the Earth Sun L-point, which is where the Helios Solar Probe is IIRC. There's the behind the Earth-Sun point, which is where the JWST (NGST) is supposed to go, IIRC. The trojan points have some space flotsom in them... the Moon's Trojan points have them also.
An actual reactor would have too many parts (moving, and otherwise) to be reliable in the environment and over the lifespan of a Voyager-type mission. And lets not even get into the complexities involved with the liquid coolent of a reactor.
Rathar, an RTG is simply a source of heat in a decay much slower than that in a reactor. Said heat is then converted into electricity by a thermocouple (Actually, a battery of many thermocouples, but who's counting?) And while there's no danger of the plutonium ceasing to give off heat anytime soon, even the best thermocouples wear out. And in the hostile environment of space, and under bombardment of particle radiation (from the plutonium, and the solar wind) they wear out even faster.
Incidently:
> These things have a half-life of several thousand years.
Nope.
Plutonium 238, the radioisotope used in the Cassini space probe (I'm not sure about Voyager.), does not have a half-life of "several thousand years". Pu-238's half-life is 87 years. Strontium 90, another radioisotope commonly used in RTGs has a half-life of 28 years. A half-life in the range of "several thousand years" would actually be a *BAD* thing in these applications. You WANT a significant amount of decay to take place. That's where the HEAT comes from!
cya,
john
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