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NASA Has Plans for 2nd Space Station at L1
Keith Gabryelski writes "New Scientist has an article on NASA's unveiling of a "blueprint for the future" of space exploration. It entails a Space Station 5/6ths of the way to the moon. In other news, radiation sheilding on the space station isn't so good."
From a physics standpoint, getting men and material to and from the Lagrangian points would be vastly cheaper than getting them to and from the moon. Until we could utilize the raw materials of the moon to produce things, it isn't going to be cost-effective to have a moon presence.
Perhaps it has to do with the fact that lead is heavy, and heavy things cost more to get into space?
Hey kids, there's only 5 days left 'til Yak Shaving Day!
After the Sun and Moon. Its been fascinating to watch it get brighter as they add more cylinders and panels every year.
The station is visible in the evenings about one week a month and mornings one week a month, so the orbit can wobble over the US, Russia, Europe, and Japan. Sky & Telescope (set zip code, click on almanac) shows pass times & locations, as do other websites.
Why not just build on the moon? Why stop at 5/6 the way to the moon?
Because the whole point of staging at L1 is that it allows low-energy transfers to other points in the solar system. Launching a trip to Mars, for example, from L1 would require much less energy than from either the surface of the Earth, or low Earth orbit, or the surface of the moon.
Of course, this ignores the biggest problem with the L1 point: it's unstable. A body placed at L1 will tend to either fall inward toward the Earth or outward toward the moon at the slightest push. Any space station at L1 will have to correct its position regularly, probably using simple chemical rockets. These rockets will have to be refueled periodically and so on, making for a nontrivial amount of effort to keep an L1 space station in position.
The L4 and L5 points, on the other hand, are gravitationally stable. If a body at L4 or L5 starts to drift out of position-- due to a collision or outgassing or whatever-- the Earth-moon system will tend to pull it back to the point of stability again. But since L4 and L5 are farther from Earth than L1 is, it takes more time and energy to get there from LEO.
I write in my journal
a space station at a LaGrange point (in this case L1) wouldn't have to use thrusters to maintain a stable orbit and would never leave it's stable orbit around the earth
That's not true. L1, L2, and L3 are all gravitationally unstable points. A space station at L1, if nudged out of position even slightly, will tend to spiral inward toward Earth or outward toward the moon. The L4 and L5 points are the only stable Lagrangian points in a two-body system.
I write in my journal
(which is not to say that they didn't precipitate in quite a little jolt for this nation's capitalists)...
Clearly there's a bit of saliency to the argument that a little "push" by the govt. can jump-start some of these "market forces."
the most mysterious thing you'll see today
They aren't global attractors. Meaning that if I stick something on the other side of the solar system, it's going to be pulled towards Earth, not the two stable Lagrange points.
However, they are locally stable. Meaning that anything put in that general area gets pulled into the Lagrange point. The 'general area' is mathematically defined by the gravitational equations, but you can think of it like a dip in the side of a bowl. A marble placed in the bowl rolls toward the bottom. But if you put the marble close enough to the dip, it will settle there instead.
Fair question, but one with a fairly simple answer. Lets do some numbers...
To within a factor of a few, what matters in radiation shielding is "surface density", i.e. how many grams of material per square centimeter there are in your shield. So you can have a thick shield of light material, or a thin shield of dense material; for the same area they will provide the same shielding effect if they have the same mass.
Say for a moment that you want as much shielding as provided by the Earths atmosphere; that works out to be about 10 tons/square meter. (If you SCUBA dive: remember that the pressure goes up by 1 atmosphere for every 10 meters of depth. A 10x 1x1 meter column of water weighs 10 tons.) Those ten tons/m2 can be in any form you want: a 10 km thick air shield, 10 meters of ice, 2 meters of rock, or a meter of lead.
So, you want to put a couple of guys in a spaceship and send them to Mars? Well, put them in a cramped tube, say 10 meters long and 3 meters in diameter. That gives you about 100 square meters of surface area.... or 1000 tons of shielding.
At current prices it costs about $20,000 to put a kilogram of material into low Earth orbit. The biggest rocket flown to date can put about 100 tons into orbit. With current technology you either hit up Bill Gates for the 20 billion, or you can skimp on the shielding. The space station skimps by a factor of 300 (you get a years ' worth of background radiation in a single day). You could also play games like have most of the spacecraft lightly shielded, but have a lead-lined "storm shelter" for the times when solar flares erupt. This works because much of the radiation comes in bursts. However, it isn't useful for going to places with continuous high levels of radiation, like Jupiter.
That's why we need a new and cheaper space launch system.
Human genome = 3 billion base pairs = 6 GBit. Windows + Office = 20 Gbit. Which is more impressive?
I thought Lagrange points collected a lot of dust, which would be bad for optics.
L4 and L5 are gravitationally stable points, so there may be collections of dust there. (In the Jupiter-Sun L4 and L5 points, there are collections of asteroids.)
But L1, L2, and L3 are all gravitationally unstable. A body at one of those three points will tend to fall away from the point rather than staying in it.
L4 and L5 are like being at the bottom of a depression: whichever way you go, gravity tends to pull you back toward the middle. L1, L2, and L3 are more like being at the top of a hill. If you're right at the very center, you're fine. But if you're even slightly off-center, gravity will pull you down the hill.
In theory, L1 ought to be the cleanest point between the Earth and the moon. Nothing can stay in orbit at L1 without active station-keeping.
I write in my journal
A well-known filk song in certain circles. Home on Lagrange by Bill Higgins and Barry Gehm in or around 1978.
[
L1 is about 5/6 of the way to the moon, along a direct line from the earth to the moon.
L2 is opposite the L1, over the far side of the moon from the earth.
L3 is close to the moon's orbit around the earth, but on the opposite side of the earth from the moon.
L4 and L5 are also in the orbit of the moon around the earth, but one is 60 degrees ahead of the moon in its orbit and the other is 60 degrees behind.
You can find more information at this web site and there is even more detailed information to be found here
Sapere aude!
My take on the subject is that we don't have any materials heavy/stable enough to reflect high energy radiation.
The problem is that conventional materials of all types misbehave as photon energy substantially exceeds the chemical binding energies. You go from having materials acting like ideal classical conductors or dielectrics interacting with photons that act more or less like classical EM waves [normal reflection and transmission], to having materials that act like a set of quantum energy levels and photons that act like particles [photoelectric effect], to having materials that act like a diffuse sea of particles that scatter photons which also behave like particles [Compton scattering].
As the valence shell binding energies in atoms are at most on the order of a few tens of eV, there is a hard upper limit on the frequency of radiation that conventional optical elements made of normal matter can handle.
The limit's mushy in one respect, in that grazing-incidence devices see an effective frequency that's inversely proportional to the angle of incidence. However, practical devices limit the benefit of this to between a factor of 10 and a factor of 100 (so you can see some x-rays, but gamma rays are still tricky).
Non-conventional optics made of normal matter can still work under some conditions. Because the inter-atomic spacings in crystals are in the same ballpark as high-energy photon wavelengths, you can get diffraction occurring when an x- or gamma-ray beam passes through a crystal (due to scattering off of inner-shell electrons and the nuclei). This is commonly used to identify materials (x-ray diffraction patterns have been used to image atoms in everything up to and including crystals of viruses). Gamma ray telescopes using crystalline blocks to construct diffractive optics have been built.
Lastly, the final and most difficult way to cheat involves using plasma as a mirror. As it's a gas of free ions, it should have near-perfect reflection even at high wavelengths (subject to a few probably-nontrivial conditions). Keeping a cloud of ions confined to an optically flat surface is left as an exercise for the reader.
GiliadGreene has made some good points already about SOHO being in a halo orbit around the L1, not at the actual L1 "point".
Orbit corrections are performed every 17 weeks (four months, not one).
The halo orbit is much saner than trying to stay at the L1 point, and it attenuates solar interference. Ironically, the COMSAT link that DSN uses to get data from Madrid to California gets more solar interference than the spacecraft to ground link.
I hold it, that a little rebellion, now and then, is a good thing. -- Thomas Jefferson