Proposed Next-Generation Space Station 153
WallytheWalrus writes "This NewScientist.com article discusses the proposed next generation of telescopes and space stations. The concept presented with little fanfare by the NASA Exploration Team (NEXT) consists of placing a space station about 5/6ths of the way to the moon at one of a handful of local Lagrangian Points. This station would act as a springboard for constructing new telescopic mirrors, maintaining the telescopes that use them, and as a haven for future manned exploration missions. If only NEXT's budget was more than $4 million a year...."
Repeat from Wednesday (Score:3, Informative)
Raise Taxes (Score:3, Informative)
In other words: raise taxes.
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Bush's Argument: Raise children, not taxes
lagrangian points (Score:5, Informative)
These are points where the gravitational pull of two bodies, such as the Earth and the Moon, cancel each other out, providing a stable location to position spacecraft.
I am very surprised The New Scientist makes such a mistake. These points are stable mainly because of rotation. In a nonrotating system, there is only one equilibrium point, and that is unstable.
Deja vu all over again (Score:5, Informative)
While the concept of placing a space station at a libration (or Lagrange) point seems nice on the surface, it's a very tough proposition in reality.
The problem is that the myth of a libration point as simply some kind of nifty stable point in space where gravity balances has been propagated for a while now. I've seen this mistake turn up in countless places, including some otherwise reputable textbooks. The reality is far more complex, and difficult to analyze.
For starters, the L1, L2, and L3 are unstable. That means that anything put there will tend to drift away over time. Not only that, but the L points don't even exist in reality - they are an artifact of a simplified gravitiational model (three bodies only). Once you incorporate the eccentricity of the primaries, and the effects of the other planets, you find that the L points are not so much points as variable regions of space with rather messy dynamical properties that we still don't fully understand. Oh, sure, you can mess around with numerical explorations and experiments, and there are a couple of series approximations that give reasonable first guesses at some particular solutions, but we are still a long way from being able to characterize and predict the full dynamics in one of these regions.
So, placing some thing actually at a libration point is out. But, as it turns out, you can establish periodic or near-periodic orbits around the approximate region of the libration "point" (so-called halo or lissajous orbits). We still don't really undertsand these orbits that well either, but we know enough to be able to have successfully put some unmanned probes out at the Sun-Earth L1 point (e.g. ISEE-3, SOHO, and most recently Genesis). Note that these are all Sun-Earth L1 missions, not Earth-Moon which would add another layer of complexity due to the influence of the Sun's gravity of the Earth-Moon system.
At present, the process of designing a new trajectory for a libration point mission consists of a fair amount of trial and error, and iteration. Techniques have improved some in the last decade (check out the work by Martin Lo at JPL and Kathleen Howell at Purdue on using dynamical systems theory to find transfers to/from halos), but it's still a lot of work to generate a finished trajectory that meets all of the necessary constraints. Trying to do this kind of thing with a manned, maneuvering spacecraft is going to be extremely difficult. In particular, any kind of rendezvous between two or more spacecraft will be difficult, since it's tough to predict where your spacecraft is going to go (very non-linear dynamics). Planning L point trajectories in real time really isn't that feasible until techniques improve a lot more.
This is a very active field of research, but there's still a long way to go before we're likely to be really ready for manned missions that do anything other than hang around on their own at L1 for a while.
Re:lagrangian points (Score:5, Informative)
You are correct about the contribution of rotation to teh formation of the libration points. However, these points are not all stable. L4 and L5 (the triangular points) are stable (at least in a linear sense). L1, L2, and L3 are unstable. That said, you can establish periodic orbits around the unstable points, so they aren't completely useless :-)
It's time to leave LEO (Score:1, Informative)
To think that technological advance is blazingly fast in this day in age is misleading. We're not doing too well at hitting the important targets. NASA might just now be waking up to this, but it's yet to be seen if their budget wakes up to it. (Nasa funding was 4% of the national budget at the height of the Apollo program, it's less than 1% now)
So I applaud their very recent efforts to finally mention some vague goals away from Low Earth Orbit. L1 is a fine stepping stone, but Mars is where the public eye is. Nasa administrator Daniel Goldin had some brave words about the possibility of sending men to Mars in this decade or the next, but Bush put a bean counter in charge of Nasa pretty quickly to throttle cost overruns from the ISS.
What we really need is a president giving NASA a kick in the pants, and the funding to follow, as Kennedy did. Either that or wait around for private space exploration to become worthwhile, and we're going to be waiting quite a while in that case. Another space race? maybe China? I hope so. Because the current NASA schedule is anything but ambitious.
Re:Yeah, right... (Score:3, Informative)
They seem to have fun messing around with stuff [nasa.gov]. Don't ask me what the heck they're up to on the picture.
Re:Deja vu all over again (Score:2, Informative)
Actually, if you read the paper you link to you will find that the L4 and L5 points are stable in a linear sense (i.e. using a linear analysis). However, it is not clear how far out from the libration point this linear approximation is valid. It may require extremely precise targeting to get your spacecraft into the linearly stable region.
That aside, the reason we were talking only about the co-linear points (L1,2,3) instead of L4 and L5 is that L1 was the focus of the New Scientist article. The most likely reason for that is that L4 and L5, being (as you point out) at least linearly stable, have accumulated a lot of dust and debris over the millennia (see also the Trojan asteroids at Jupiter's L4 and L5 points). This makes them unattractive as a location for sensitive scientific instruments, or space stations. Hence the focus on L1.
Re:Repeat from Wednesday (Score:3, Informative)
Ok, while the story is reposted, I don't think that's the worst of your problems.
Re:lagrangian points (Score:4, Informative)
The center of gravity of the Earth-Moon system is about 1000 miles below the Earth's surface.
The point where the Earth and the Moon would exert an equal gravitational force on a third body is in space, much closer to the Moon than to the Earth. I think the actual balance point, the L1 point, is somewhat closer to Earth because of the contribution of rotation -- "centrifugal force", which of course isn't really a "force" unless you use a rotating frame of reference