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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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Reality has a liberal bias
http://news.bbc.co.uk/1/hi/world/americas/1231447. stm
In case someone was wondering about the reference.
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
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
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
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.
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.
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.