NASA Has Plans for 2nd Space Station at L1 439
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."
Re:5/6 is stopping short (Score:5, Informative)
Re:5/6 is stopping short (Score:3, Informative)
Re:5/6 is stopping short (Score:2, Informative)
For example:
New Planet Freeway... [cnn.com]
Re:Radiation is a solved problem (Score:4, Informative)
third brightest object in the sky (Score:5, Informative)
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 [skyandtelescope.com] (set zip code, click on almanac) shows pass times & locations, as do other websites.
Re:5/6 is stopping short (Score:5, Informative)
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.
Re:5/6 is stopping short (Score:5, Informative)
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.
Re:A more useful approach (Score:3, Informative)
Science fiction from the late 1900's aside, moon bases just don't make that much sense right now.
Re:Mixed emotions... (Score:4, Informative)
(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."
Re:5/6 is stopping short (Score:3, Informative)
That's all well and good, but you have to get TO L1 FROM the Earth or low Earth Orbit, or the Moon before you can enjoy the benefits of a low energy launch.
Wouldn't getting your launch ship there in the first place, nullify any benefits of relaunching from there?
Re:radiation shielding not so good (Score:1, Informative)
Re:Can someone explain this? (Score:4, Informative)
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.
Re:Radiation is a solved problem (Score:5, Informative)
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.
Re:Radiation is a solved problem (Score:2, Informative)
With higher energy photons than we seen, you also have the possibility of generating neutrons from exciting nuclei and spallation. Which requires other ways of shielding (in addition to what's mentioned above for photons).
Re:Why not just go to the moon. (Score:5, Informative)
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.
Re:Home on Lagrange (Score:4, Informative)
A well-known filk song in certain circles. Home on Lagrange [swarthmore.edu] by Bill Higgins and Barry Gehm in or around 1978.
Re:third brightest object in the sky (Score:5, Informative)
It covers any location in the world (not just USA and Canada). It has fly-by data for hundreds of satellites (including ISS) and my personal favorites, the Iridium flares. If you've never seen a -7 magnitude Iridium flare, do yourself a favor and check it out. It's absolutely awesome.
Heavens Above will tell you where to look (direction and azimuth) and when to look - accurate down to the second!
Re:5/6 is stopping short (Score:2, Informative)
Not a big problem. The SOHO satellite is at the Earth-Sun L1 location and it only needs to make course adjustments about once a month.
Re: What's L4,5? (Score:5, Informative)
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 [montana.edu] and there is even more detailed information to be found here [instantlearning.net]
Re:5/6 is stopping short (Score:3, Informative)
That's all well and good, but you have to get TO L1 FROM the Earth or low Earth Orbit, or the Moon before you can enjoy the benefits of a low energy launch.
Wouldn't getting your launch ship there in the first place, nullify any benefits of relaunching from there?
Well, if you are putting a ship together in space, like the ISS, then it is worthwhile. You send up pieces that get assembled in the low gravity and then *launch* from the low gravity point. You save energy by not having to break out of LEO with such a large vehicle. Otherwise, the vehicle will have to provide it's own propulsion for the breaking away - a costly proposition.
Think of getting to L1 as storing kinetic energy in the components of the vehicle. After construction, launch can entail causing the craft to drift toward the sun to use the slingshot effect for accelleration. After the craft is accellerated, onboard propulsion can be used to provide the extra impetus to extend the curve of the orbit to the point where the craft will end up at a predetermined solar destination.
Re:5/6 is stopping short (Score:2, Informative)
Not impossible, but hard.
The danger, of course, is that an L1 space station could drift so far from the actual L1 point in space that it requires more delta v to move it back than the structure can withstand. That'd be a worst-case kind of disaster, though.
Re:Gravity Simulation (Score:3, Informative)
It's pretty much indistinguishable from the real thing. The only noticable phenomenon that would indicate otherwise would be the decreasing gravity as you go 'up' towards the center of the hub.
To get the gravity simulation, do you have to be strapped into a chair?
Certainly not! Ever been on the Gravitron [optushome.com.au]? Spins around really fast and throws everything in it at the walls at a couple of G's. Same principle.
A moon base could have a banked rotating surface to help enhance the puny natural gravity of the moon, couldn't it?
Quite correct. Not sure it's worth the trouble on a large scale, though. It would have to spin nearly vertical (relative to Luna's surface). I estimate that you'd have to spin it up to 0.91 G at the edge to augment the puny gravity there to a full 9.8 m/s^2. And the 'floor' of the habitat would be at a good 66 degrees relative to the ground. Changing the spin rate would actually change where 'down' pointed to (faster->more lateral, slower->more vertical). Any attempts to get in or out of the hub would have to be done right at the center, which is fine for a space station but would suck for a surface colony. It'd certainly be useful as an exercise gym or maternity ward, though.
Re:5/6 is stopping short (Score:3, Informative)
If you have a station at L1 you can launch the pieces of the spacecraft up from earth in parts and assemble it there, and it only has to be able to withstand whatever gravity or thrust you expect it to experience during it's mission.
On the other hand, if you build it on earth, it has to be able to survive the many G launch from the surface of the earth up into space, which would require it to be built much heavier and therefore be less efficient once it leaves earth's gravitational field.
Why carry all that extra weight around when you can construct it in orbit instead and dodge the whole issue?
Re:5/6 is stopping short (Score:2, Informative)
Actually, the reverse is true. Drag is a fairly simple thing to correct for. The dynamics in the vicinity of a libration point are hairy at best. Keeping something actually at an unstable libration point (such as L1) is well nigh impossible without thrusting all the time. It is possible to put things into orbit around the libration points (so-called halo orbits), but theie dynamics are also complex, they have to carefully pre-planned in advance, and trying to use them for manned ops (where things are coming and going all the time) would be extremely hard.
Re:5/6 is stopping short (Score:2, Informative)
The other catch is just getting there. Generating a trajectory to a halo or lissajous orbit is still a fairly labor intensive task. The probes that head out to the libration points have carefully calculated trajectories that are worked out years in advance (and then recomputed like mad a few months in advance when the launch date changes :-).
As Han Solo once said: "Traveling through hyperspace ain't like dusting crops, boy". And traveling to a libration point ain't like doing a patched conic around the moon.
Telescopes for high-energy radiation. (Score:5, Informative)
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.
Re:Telescopes for high-energy radiation. (Score:2, Informative)
Frequency is _directly_ proportional to angle of incidence. Teaches me to post at 2am.
Re:5/6 is stopping short (Score:3, Informative)
Even then the actual L4 and L5 points are not entirely stable in the real solar system, because the solar system has a lot more that two bodies and nothing is a point mass. This also means thet the "points" are actually regions. Which is why Jupiter can capture many asteroids in it's L4 and L5 points with Sol.
Re:5/6 is stopping short (Score:3, Informative)
SOHO is at Earth/Sol L1, this station would go at Luna/Earth L1. Different points. The size of the "points" is a function of the mass and mass distribution of the larger 2 objects. In the case of the proposed location these objects are Earth and Luna.
Re:5/6 is stopping short (Score:3, Informative)
Re:5/6 is stopping short (Score:3, Informative)
So, I'm wondering if the LaGrange (sorry bout the spelling folks) points are completely stable
In a perfect two body system. The lagranian point is stable. In our solar system, not even a normal orbbit is stable. So any station at L1 would need to correct it's possition once in a while. But this is already true for ISS. No problem.
Cheers
Re:5/6 is stopping short (Score:2, Informative)
The moon was original part of Earth that was torn off.
Most likely, but not proven AFAIK.
It's not a perfect sphere so one side was pulled on more than the other
This is wrong. Tidal locking requires dissipative effects, i.e. the moon must have become solid after the locking was finished. rotational energy was transfered to intrinsic energy, i.e. heat.
Cheers
Re: What's L4,5? (Score:2, Informative)
The "missing" force you are looking for might be thought of as the "centrifugal" force, which isn't a "real" force but feels real to someone going around in a circle.
Re:5/6 is stopping short (Score:2, Informative)
Re:5/6 is stopping short (Score:5, Informative)
GiliadGreene has made some [slashdot.org] good [slashdot.org] points [slashdot.org]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.