This is why good managers are worth their weight in gold. Bad managers are worse than worthless.
No. This is why good systems engineers are worth their weight in gold. Dealing with the big picture, and designing large, complex systems using an engineering approach is why systems engineering came into being in the first place.
Managers are trained to deal with schedule and budget. Not with designing complex systems. Systems engineers are trained to design complex systems, and to make sure that all the pieces interact in such a way that the overall system acheives whatever goal it was designed for.
That said, decent systems engineers seem to be somewhat rare these days, or at least they seem to get overruled by management. Many of the well-known engineering blunders in recent years can be chalked up to poor systems engineering.
NASA hasn't ever had a hardware problem. Or a software problem. Ever.
Well, except for Mars Polar Lander, where the failure review board determined that the lander crashed because a flag indocating contact with the ground was not intialized to zero prior to the start of the retro-thruster loop. So the flag got set by the shock of deploying the landing legs, never got reset, and caused the thrusters to switch off as soon as they were on.
I guess maybe you forgot about Apollo 13 as well (hardware)? Or the Galileo High Gain Antenna that failed to deploy (hardware)? Or the serious telemetry system problems they had with one of the Voyagers (hardware)? Or the faulty landing bag on one of the Mercury flights (hardware)? (was it Glenn's? I don't remember) Or that funky glitch in the landing computer during Apollo 11 (software)? You know, there's a reason that most space mission tend to be heavy on redundant hardware, and invest a lot of time and effort in fault protection software.
Every problem can be directly tied to one specific person being a fscking moron.
Well yeah, but that's the case with a lot of bugs, isn't it? Mistakes tend to be people issues.
The closest you could come is that Mars probe that crashed because of mismatched units. And that was just poor communication among the software guys.
You are at least correct about that - the problem was not a software issue. Lockheed Martin Astronautics was on contract to supply everything to NASA in SI units (which is what NASA uses for everything). LMA - or at least the part the caused this problem - uses English (Imperial) units internally, and neglected to perform the appropriate conversion before they sent the data on to NASA.
You're right about L1, L2, and L3 not being stable, but L4 and L5 are. This link [nasa.gov] explains in a bit more detail , but the L4 and L5 points, despite being peaks of gravitational "hills", would be self stabilizing.
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.
In my opinion the facts you stated support the conclusion that this is a perfect next generation project for a research agency.
I'm not saying that we shouldn't be doing research in this area, just that it's very premature to be talking about putting manned platforms there.
Also, I think most people understand that the models are simplified. Eliminating all but the major variables is a useful engineering tool in understanding the problem.In your freshman physics class when you solve the ball dropping off of the building problem you don't include every possible effect acting on the ball, but you still get a very useful answer.
I agree that simplified models are a useful engineering tool (I'm an engineer by trade). My point was that the simplified models have lead to a number of popular misconceptions about what the libration points actually, and a misunderstanding of just a how complex it really is to analyze those regions of space. Also, your example with the ball dropping off of a building is not comparable to a libration point trajectory. The ball example works because, unless you are looking for a very precise answer, you can neglect everything other than gravity, which is by far the dominant force (try doing the same thing with an analysis of a feather falling:-). A libration point trajectory is a nasty problem in nonlinear dynamical systems: it is very sensitively dependent on initial conditions. If you do not correctly model some of the effects that would otherwise be neglible, you spacecraft will start in a slightly different location than you had planned, and end up in a wildly different location than you had intended. Even basic three-body dynamics are quite messy compared to the Keplerian orbits we are all used to. Throwing in all those extra bodies makes then even hairier. Not to say it can't be done (we have done it after all), just that it's much more difficult than most people seem to think (far more involved than a "normal" space mission).
And part of the reason we want to put a station there is to study the intricacies of the problem further. Having an object physically there will help us to expand our understanding of all the variables involved.
The reason that NASA wants to put a station there is that the people involved in planning the station do not have a clear understanding if the difficulties involved - they believe the "simplified model", and don't even seem to fully understand that. Someone in the NASA HEDS program needs to talk to some of the folks at JPL or Goddard who do libration points for a living. We would do much better to place unmanned objects in libration point orbits if we want to "expand our understanding of all the variables involved". That said, it's not so much the actual environment that we don't understand, it's the math needed to characterize and predict what things will do in these regions. In a Keplerian orbit we can use standard conic sections as a first cut, and perhaps include the effects of the major perturbations if necessary. At a libration point we don't even fully understand the motion: there's nothing comparable to a conic section. It's all numerical explorations, with no firm grasp of the underlying character of the trajectories. Right now operating a spacecraft in the vicinity of a libration point is akin to what it would have been like if someone tried to compute a free-return to the moon in the days before Kepler pointed out that "it's all just ellipses".
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.
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:-)
Didn't we just have this story a few days ago? Oh well - guess we can talk about it again:
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.
You raise some good points. Unfortunately, the problem is not the control laws. The problem is that for a spacecraft to control its trajectory so that it will stay at L1 it must burn propellant (there are no propellantless drives yet, unless you count solar sails - which haven't yet flown). Since L1 is unstable, you will constantly drift away, which means that you will constantly have to burn propellant, which is a finite resource. Thus, your mission will be over very quickly. Even a highly efficient propulsion system like an ion engine will not be enough to keep you at L1 for any reasonable amount of time. An unstable fighter does not face the same kind of constraints in terms of consumables for control - the amount of energy (==fuel) required to actuate its control surfaces is miniscule in comparison to the energy needed to provide thrust.
Your points regarding some kind of transfer out to L1 would be correct if we were referring to conventional orbital mechanics. But as I stated in my previous post, the dynamics in the vicinity of the libration points is significantly more complex than the regular two-body dynamics we are used to thinking of. In particular, the so-called "unstable manifolds" that emanate from the periodic orbits surrounding the libration points are groups of trajectories that will, for relatively low cost in propellant, send you zipping away from the libration point. Yes, if the targeting to get you to a libration point orbit is wrong, you most likely will fall into an orbit around the earth or moon. But if you correctly insert into a halo around L1, and then try to move to a slightly different halo, a mistake in your maneuver is quite possibly going to throw you onto one of those unstable manifolds. Which was the point of my original post.
You must admit, though, there's a world of a difference between saying "libration points are very complex" and calling NASA scientists stupid yahoos who "didn't bother to check with anyone who actually knows anything about libration points".
I agree that there is a world of difference between those two statements. But I did not call NASA scientists stupid yahoos. You have again misinterpreted my post. I called the NASA HQ people a bunch of yahoos, not the scientists. I know several people who work at the cutting edge of libration point dynamics, and they are most assuredly not stupid, or yahoos. They also do not work at NASA HQ. The scientists are the people that should have been consulted before the NASA bureaucrats made their grand pronouncements. But, bureaucrats will be bureaucrats.
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. 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.
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. 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.
You misinterpret my post (or "smug troll"). I'm not saying that we should put stuff at L4 or L5. I'm saying that putting something at any libration point is going to be tough. Three body dynamics are not easy. Even NASA (if you talk to the people who actually understand trajectories) admit that libration point trajectories are far more complex than your typical conic section.
Regarding SOHO, it was not teh first, and is not the only spacecraft at a libration point (I believe that the first was ISEE-3 - the most recent I know of is Genesis). But it is a far different proposition to place a spacecraft in a single, carefully pre-planned orbit and keep it there than it is to jump between halos, and perform proximity operations or rendezvous and docking (which would be needed for a manned platform, or even an autonomously assembling spacecraft). I'll say it again: the dynamics in the vicinity of a libration point are very complex, and presently our understanding of them is limited.
Who said anything about putting something at L4 or L5. Personally, I think putting manned stuff at any libration point is beyond our capabilities right now. Three-body dynamics are not something to be trifled with, and they are still far from being understood.
Having spent some time doing research on libration point dynamics (as part of a group that works for NASA to figure out how to "send space probes galavanting around the solar system slingshotting around the sun, planets, moons etc... to reach their final destination"), I am fully aware of the gravitational advantages of placing something at L1. I just think it's extremely premature to talk about doing that with manned platforms (or anything that requires proximity operations and short term changes in trajectory).
Putting a space station at the Earth-Moon L1? snort What yahoo at NASA HQ came up with that one? They obviously didn't bother to check with anyone who actually knows anything about libration points.
Why is this stupid? Here's why:
The Earth-Moon L1 is an unstable point. Put something there (if you can), and it will immediately drift away.
Yes, there are these things called halo orbits and lissajous orbits, that are essentially periodic orbits around the libration points, but their dynamics are very complex.
Did I mention that the dynamics in this region is very complex? Actually getting onto a halo or liss is not anywhere near as simple as computing a hohmann transfer - it takes a lot of careful precalculation. The region around the L1 point (and all libration points) is governed by three-body dynamics - highly nonlinear, potentially chaotic, very messy to deal with.
Even assuming that you successfully put your space station at L1, how the hell are you going to get anything else to rendezvous with it? (see previous point) I can't even imagine trying to carry out docking maneuvers in that kind of gravitational environment.
The reason it's cheap to get to a halo (the efficient "superhighway" they keep talking about) is that you can hop on the stable manifold associated with the halo (essentially a sheaf of trajectories that asymptotically approach the halo) where it passes near the earth. But this cuts both ways, since the halos also have unstable manifolds that lead away from the halo (and are also cheap to get onto). One small burn in the wrong direction, and "whoops!", you're on the unstable manifold leading away from the halo and off to who knows where.
So what do you have when you break it down: A dynamically complex region of space that will make proximity maneuvers extremely difficult to perform. And if you make one small mistake in those difficult maneuvers, you're basically headed for Pluto. Bottom line: L1 is just about the stupidest place to put a space station that you could pick.
Not exactly, yes, L1 is an "unstable" Lagrange (or libration) point, however if you put an object in ORBIT around the L1 point it is extremely easy to keep it there. It is analagous to the motion of a top, yes, the top is unstable and will fall, but if you spin it it will remain upright. The difference is that very little fuel is required to maintain the orbit about the libration point.
True. But the dynamics in that halo orbit are very messy. Just getting to the orbit is a pain - the trajectory requires a lot of work before the mission - and if you need to perform a maneuver while you're in your halo (e.g. to rendezvous and dock), well, good luck. One small delta-v in the wrong direction and you're on the unstable manifold of the halo and an express elevator to whoe knows where.
There are plans for a probe at the Earth-Sun L1 point (about 4 times farther than the moon)that will similiarly orbit that L1 point but for different reasons. If it were precisely at the L1 point, then we would have point our antenae directly at the sun to communicate with it. The noise from the sun would make it essentially impossible to communicate with, hence the offset.
Actually, I can almost guarantee that the reason the probe is going to a halo or lissajous orbit is that it is well nigh impossible to stay at the Sun-Earth L1 without burning an insane amount of fuel. The Sun-Earth L1 is unstable. I would however not be surprised to find that the particular orbit selected (the size of the halo) was driven by the need to achieve a certain angular separation from the sun.
The SOHO satellite isn't interacting with other objects, though. Any manned-- or even occasionally manned-- space station will have to dock with visiting spacecraft and whatnot, which will involve significant transfers of momentum. Keeping an L1 space station on station will be a harder job than simply keeping the SOHO on station.
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.
I have a feeling that keeping something at L1 long-term is easier than keeping that same something in LEO. Gravity is easier to deal with than atmospheric drag.
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.
Many scenes of the forest were cut for looking too jungle-like (LOTR was filmed in New Zealand)
I don't know what parts of New Zealand you've been to, but I can assure you that most of the forest looks like forest. It certainly doesn't look like jungle. You may be thinking of New Guinea, or some other island somewhat closer to the tropics.
Overpriced products (they just paid another $70M for price-fixing - again!!!!!) are the problem here.
If it's too expensive, don't buy it. If everyone did that, then the RIAA wouldn't sell any CDs at all, and the price would abruptly drop. CDs are clearly not overpriced, since people still buy 'em. The RIAA and their cronies have found the price point that gives them maximum profits in terms of price per unit x units sold. They'll stick to that price point come hell or high water.
The problem the RIAA is facing is that the mp3 explosion has messed up their price point equation, and they don't know how to react. Note that I'm not necessarily claiming that the mp3 craze has decreased CD sales, but rather that it has upset the equilibrium so that it is now unclear what the correct CD price point should be. How do you factor in the free distribution? The increase (or decrease) in sales volume? Do you charge more for a CD in an attempt to recoup lost sales (assuming every download is a lost sale)? What if people are actually buying more CDs as a result of mp3 "advertising" and you scare them off by raising the price? How do you know how many people will buy vs download (or do both), and at what price point? Maybe you charge less and hope to encourage people to go back to buying CDs (or just get them to buy more CDs and make up on volume what you lose on unit price)? Or do you try to maintain the same price as before mp3s?
The RIAA is scared becuase their stable little setup has been all screwed up and they don't know what to do. So they are trying to get the dynamics of the system back to the way they were pre-mp3.
I have read that the airbag parts actually weighed more than the equivalent in a fuel-based landing system. They originally didn't think it would weigh as much as it did.
Some engineers say that fuel-based landing systems still look like a better design in their opinion.
Don't know about the weight thing, but from what I've heard, the airbag system has been a royal PITA for the new Mars mission just in terms of getting it to work. The public perception is that the airbag system is simple compared to a rocket-based system, and that isn't necessarily true. It's not just a case of "Enter Mars atmosphere. Deploy airbags. Land". There's a fairly complex landing sequence involving the parachute, bridle, and airbags, plus some little solid rocket motors. Gettting it all to work together can be hairy, plus you have minimal control during the actual landing, so if something does go wrong you're screwed.
My beef with NASA is that once they find a brilliant solution to a problem that works perfectly, they rarely, if ever, use it again.
Actually, JPL is using a Pathfinder-like airbag landing system for the 2003 Mars Exploration Rover.
Of course, this hasn't been without its problems - for starters, they really were lucky that Pathfinder worked: there were problems with the bridle deployment, and several other potentially catastrophic things that could have happened, but luckily didn't. Also, trying to redesign the somewhat limited airbag/parachute system to deal with the larger, more complex MER mission has not been without difficulties.
The airbag system worked well for its intended purpose (ultra-cheap, quick 'n dirty mission), but a rocket based system is inherently more flexible and provides much more control during the landing phase. That's why it was selected for Polar Lander, which had to land in some fairly constrained terrain. Incidentally, the problem with MPL was a flag variable that was not reset prior to entering the loop controlling rocket firing, not a units issue. You are conflating the MPL failure problem with the earlier Mars orbiter that had a units problem during its approach to Mars (and that problem was actually the fault of the contractor, Lockheed Martin, not NASA or JPL - the contract specified metric units, the contractor used English units anyway).
NASA has heard of economies of scale. Congress has not. Building 10 identical Pathfinders may be cheaper than building 10 separate missions, but trying to pitch a single program that costs 10 times as much as most other missions is a losing battle. Congress does not care what things cost in the long run, they care about the current years budget. They will consciously make decisions that will cause programs to cost more in the long run if it will save money this fiscal cycle.
Takes a reasonably large amount of computing horsepower and a good idea of the initial conditions but a useful approximation can be calculated.
Actually, it really doesn't take all that much computing power. I did a bunch of work on 3-body trajectories during graduate school, and my workhorse computer for that research was my home-PC at the time - a K6-2 (400MHz) running debian. As well, I was computing much more than just the trajectory. I was simultaneously computing a 6x6 matrix differential equation that provided a linearization around the trajectory. Even then, it was only when I got into doing large runs involving hundreds of trajectories that I found I needed to shift things to a server-level machine.
You are correct that a good idea of the initial conditions is essential. Without it, you are basically flailing blindly in the 6-dimensional phase space - it's unlikely that you'll find the trajectory you want. That's why Lagrange (libration) points are so popular. They are analytical "particular" solutions that provide a starting point for finding initial conditions. In addition, there are approximations for various periodic trajectories near the libration points that also give a nice place to start. From the periodic solutions it is relatively easy to use numerical methods to map out stable and unstable manifolds to/from the periodic solutions. Next thing you know, you're on the interplanetary superhighway...
Socialism means trying to give everybody a fair shot.
Uh... no.
Capitalism means trying to give everyone a fair shot (I mean real capitalism, not the bureaucratically entangled, over-regulated, politically corrupt system they call capitalism in the US).
Socialism means trying to give everyone an equal outcome. Which is a different animal entirely. To give everyone an equal outcome you either need to lift the under-achievers up, or keep the over-achievers down. As it turns out, the latter is far easier than the former, and tends to get pretty healthy support from the under-achieving masses as well. But it doesn't do good things to your country in the long run...
So if indeed the third world consumes a large factor (an order of magnitude!) less "footprint" than the Western nations, it would seem to me that the world might actually be better off by 2050 : they are, quite simply, more efficient at using existing resources.
Take a look at this comment. It's not so much that the third world is more efficient, as that they have higher mortality rates, shorter lifespans, more disease, less literacy, and a generally worse set of living conditions. It has nothing to do with efficiency. If anything a technological nation is a more efficient user of resources - that's what technology is, efficient use of resources.
Re:Didn't here the E or T words..
on
Cradle to Cradle
·
· Score: 1
My understanding is that they at least as robust as Si cells. They get used a lot in space applications, so you have to figure that they're pretty tough.
Re:Didn't here the E or T words..
on
Cradle to Cradle
·
· Score: 1
The best photovoltaic panels currently in the laboratory are about 15% efficient.
Actually, the best PV cells in production right now are multi-junction GaAs/Ge cells that run at around 26%-28% efficiency. I've heard that there are already 30%-32% cells in the labs.
Slashdot Mirror
No. This is why good systems engineers are worth their weight in gold. Dealing with the big picture, and designing large, complex systems using an engineering approach is why systems engineering came into being in the first place.
Managers are trained to deal with schedule and budget. Not with designing complex systems. Systems engineers are trained to design complex systems, and to make sure that all the pieces interact in such a way that the overall system acheives whatever goal it was designed for.
That said, decent systems engineers seem to be somewhat rare these days, or at least they seem to get overruled by management. Many of the well-known engineering blunders in recent years can be chalked up to poor systems engineering.
Otherwise they become managers
Or systems engineers...
Well, except for Mars Polar Lander, where the failure review board determined that the lander crashed because a flag indocating contact with the ground was not intialized to zero prior to the start of the retro-thruster loop. So the flag got set by the shock of deploying the landing legs, never got reset, and caused the thrusters to switch off as soon as they were on.
I guess maybe you forgot about Apollo 13 as well (hardware)? Or the Galileo High Gain Antenna that failed to deploy (hardware)? Or the serious telemetry system problems they had with one of the Voyagers (hardware)? Or the faulty landing bag on one of the Mercury flights (hardware)? (was it Glenn's? I don't remember) Or that funky glitch in the landing computer during Apollo 11 (software)? You know, there's a reason that most space mission tend to be heavy on redundant hardware, and invest a lot of time and effort in fault protection software.
Every problem can be directly tied to one specific person being a fscking moron.
Well yeah, but that's the case with a lot of bugs, isn't it? Mistakes tend to be people issues.
The closest you could come is that Mars probe that crashed because of mismatched units. And that was just poor communication among the software guys.
You are at least correct about that - the problem was not a software issue. Lockheed Martin Astronautics was on contract to supply everything to NASA in SI units (which is what NASA uses for everything). LMA - or at least the part the caused this problem - uses English (Imperial) units internally, and neglected to perform the appropriate conversion before they sent the data on to NASA.
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.
I'm not saying that we shouldn't be doing research in this area, just that it's very premature to be talking about putting manned platforms there.
Also, I think most people understand that the models are simplified. Eliminating all but the major variables is a useful engineering tool in understanding the problem.In your freshman physics class when you solve the ball dropping off of the building problem you don't include every possible effect acting on the ball, but you still get a very useful answer.
I agree that simplified models are a useful engineering tool (I'm an engineer by trade). My point was that the simplified models have lead to a number of popular misconceptions about what the libration points actually, and a misunderstanding of just a how complex it really is to analyze those regions of space. Also, your example with the ball dropping off of a building is not comparable to a libration point trajectory. The ball example works because, unless you are looking for a very precise answer, you can neglect everything other than gravity, which is by far the dominant force (try doing the same thing with an analysis of a feather falling :-). A libration point trajectory is a nasty problem in nonlinear dynamical systems: it is very sensitively dependent on initial conditions. If you do not correctly model some of the effects that would otherwise be neglible, you spacecraft will start in a slightly different location than you had planned, and end up in a wildly different location than you had intended. Even basic three-body dynamics are quite messy compared to the Keplerian orbits we are all used to. Throwing in all those extra bodies makes then even hairier. Not to say it can't be done (we have done it after all), just that it's much more difficult than most people seem to think (far more involved than a "normal" space mission).
And part of the reason we want to put a station there is to study the intricacies of the problem further. Having an object physically there will help us to expand our understanding of all the variables involved.
The reason that NASA wants to put a station there is that the people involved in planning the station do not have a clear understanding if the difficulties involved - they believe the "simplified model", and don't even seem to fully understand that. Someone in the NASA HEDS program needs to talk to some of the folks at JPL or Goddard who do libration points for a living. We would do much better to place unmanned objects in libration point orbits if we want to "expand our understanding of all the variables involved". That said, it's not so much the actual environment that we don't understand, it's the math needed to characterize and predict what things will do in these regions. In a Keplerian orbit we can use standard conic sections as a first cut, and perhaps include the effects of the major perturbations if necessary. At a libration point we don't even fully understand the motion: there's nothing comparable to a conic section. It's all numerical explorations, with no firm grasp of the underlying character of the trajectories. Right now operating a spacecraft in the vicinity of a libration point is akin to what it would have been like if someone tried to compute a free-return to the moon in the days before Kepler pointed out that "it's all just ellipses".
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 :-)
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.
Your points regarding some kind of transfer out to L1 would be correct if we were referring to conventional orbital mechanics. But as I stated in my previous post, the dynamics in the vicinity of the libration points is significantly more complex than the regular two-body dynamics we are used to thinking of. In particular, the so-called "unstable manifolds" that emanate from the periodic orbits surrounding the libration points are groups of trajectories that will, for relatively low cost in propellant, send you zipping away from the libration point. Yes, if the targeting to get you to a libration point orbit is wrong, you most likely will fall into an orbit around the earth or moon. But if you correctly insert into a halo around L1, and then try to move to a slightly different halo, a mistake in your maneuver is quite possibly going to throw you onto one of those unstable manifolds. Which was the point of my original post.
You must admit, though, there's a world of a difference between saying "libration points are very complex" and calling NASA scientists stupid yahoos who "didn't bother to check with anyone who actually knows anything about libration points".
I agree that there is a world of difference between those two statements. But I did not call NASA scientists stupid yahoos. You have again misinterpreted my post. I called the NASA HQ people a bunch of yahoos, not the scientists. I know several people who work at the cutting edge of libration point dynamics, and they are most assuredly not stupid, or yahoos. They also do not work at NASA HQ. The scientists are the people that should have been consulted before the NASA bureaucrats made their grand pronouncements. But, bureaucrats will be bureaucrats.
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. 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.
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. 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.
Regarding SOHO, it was not teh first, and is not the only spacecraft at a libration point (I believe that the first was ISEE-3 - the most recent I know of is Genesis). But it is a far different proposition to place a spacecraft in a single, carefully pre-planned orbit and keep it there than it is to jump between halos, and perform proximity operations or rendezvous and docking (which would be needed for a manned platform, or even an autonomously assembling spacecraft). I'll say it again: the dynamics in the vicinity of a libration point are very complex, and presently our understanding of them is limited.
Having spent some time doing research on libration point dynamics (as part of a group that works for NASA to figure out how to "send space probes galavanting around the solar system slingshotting around the sun, planets, moons etc... to reach their final destination"), I am fully aware of the gravitational advantages of placing something at L1. I just think it's extremely premature to talk about doing that with manned platforms (or anything that requires proximity operations and short term changes in trajectory).
Why is this stupid? Here's why:
So what do you have when you break it down: A dynamically complex region of space that will make proximity maneuvers extremely difficult to perform. And if you make one small mistake in those difficult maneuvers, you're basically headed for Pluto. Bottom line: L1 is just about the stupidest place to put a space station that you could pick.
True. But the dynamics in that halo orbit are very messy. Just getting to the orbit is a pain - the trajectory requires a lot of work before the mission - and if you need to perform a maneuver while you're in your halo (e.g. to rendezvous and dock), well, good luck. One small delta-v in the wrong direction and you're on the unstable manifold of the halo and an express elevator to whoe knows where.
There are plans for a probe at the Earth-Sun L1 point (about 4 times farther than the moon)that will similiarly orbit that L1 point but for different reasons. If it were precisely at the L1 point, then we would have point our antenae directly at the sun to communicate with it. The noise from the sun would make it essentially impossible to communicate with, hence the offset.
Actually, I can almost guarantee that the reason the probe is going to a halo or lissajous orbit is that it is well nigh impossible to stay at the Sun-Earth L1 without burning an insane amount of fuel. The Sun-Earth L1 is unstable. I would however not be surprised to find that the particular orbit selected (the size of the halo) was driven by the need to achieve a certain angular separation from the sun.
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.
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.
I don't know what parts of New Zealand you've been to, but I can assure you that most of the forest looks like forest. It certainly doesn't look like jungle. You may be thinking of New Guinea, or some other island somewhat closer to the tropics.
If it's too expensive, don't buy it. If everyone did that, then the RIAA wouldn't sell any CDs at all, and the price would abruptly drop. CDs are clearly not overpriced, since people still buy 'em. The RIAA and their cronies have found the price point that gives them maximum profits in terms of price per unit x units sold. They'll stick to that price point come hell or high water.
The problem the RIAA is facing is that the mp3 explosion has messed up their price point equation, and they don't know how to react. Note that I'm not necessarily claiming that the mp3 craze has decreased CD sales, but rather that it has upset the equilibrium so that it is now unclear what the correct CD price point should be. How do you factor in the free distribution? The increase (or decrease) in sales volume? Do you charge more for a CD in an attempt to recoup lost sales (assuming every download is a lost sale)? What if people are actually buying more CDs as a result of mp3 "advertising" and you scare them off by raising the price? How do you know how many people will buy vs download (or do both), and at what price point? Maybe you charge less and hope to encourage people to go back to buying CDs (or just get them to buy more CDs and make up on volume what you lose on unit price)? Or do you try to maintain the same price as before mp3s?
The RIAA is scared becuase their stable little setup has been all screwed up and they don't know what to do. So they are trying to get the dynamics of the system back to the way they were pre-mp3.
Don't know about the weight thing, but from what I've heard, the airbag system has been a royal PITA for the new Mars mission just in terms of getting it to work. The public perception is that the airbag system is simple compared to a rocket-based system, and that isn't necessarily true. It's not just a case of "Enter Mars atmosphere. Deploy airbags. Land". There's a fairly complex landing sequence involving the parachute, bridle, and airbags, plus some little solid rocket motors. Gettting it all to work together can be hairy, plus you have minimal control during the actual landing, so if something does go wrong you're screwed.
Actually, JPL is using a Pathfinder-like airbag landing system for the 2003 Mars Exploration Rover.
Of course, this hasn't been without its problems - for starters, they really were lucky that Pathfinder worked: there were problems with the bridle deployment, and several other potentially catastrophic things that could have happened, but luckily didn't. Also, trying to redesign the somewhat limited airbag/parachute system to deal with the larger, more complex MER mission has not been without difficulties.
The airbag system worked well for its intended purpose (ultra-cheap, quick 'n dirty mission), but a rocket based system is inherently more flexible and provides much more control during the landing phase. That's why it was selected for Polar Lander, which had to land in some fairly constrained terrain. Incidentally, the problem with MPL was a flag variable that was not reset prior to entering the loop controlling rocket firing, not a units issue. You are conflating the MPL failure problem with the earlier Mars orbiter that had a units problem during its approach to Mars (and that problem was actually the fault of the contractor, Lockheed Martin, not NASA or JPL - the contract specified metric units, the contractor used English units anyway).
NASA has heard of economies of scale. Congress has not. Building 10 identical Pathfinders may be cheaper than building 10 separate missions, but trying to pitch a single program that costs 10 times as much as most other missions is a losing battle. Congress does not care what things cost in the long run, they care about the current years budget. They will consciously make decisions that will cause programs to cost more in the long run if it will save money this fiscal cycle.
Time traveling production crew? Or did you mean "descendant"?
Actually, it really doesn't take all that much computing power. I did a bunch of work on 3-body trajectories during graduate school, and my workhorse computer for that research was my home-PC at the time - a K6-2 (400MHz) running debian. As well, I was computing much more than just the trajectory. I was simultaneously computing a 6x6 matrix differential equation that provided a linearization around the trajectory. Even then, it was only when I got into doing large runs involving hundreds of trajectories that I found I needed to shift things to a server-level machine.
You are correct that a good idea of the initial conditions is essential. Without it, you are basically flailing blindly in the 6-dimensional phase space - it's unlikely that you'll find the trajectory you want. That's why Lagrange (libration) points are so popular. They are analytical "particular" solutions that provide a starting point for finding initial conditions. In addition, there are approximations for various periodic trajectories near the libration points that also give a nice place to start. From the periodic solutions it is relatively easy to use numerical methods to map out stable and unstable manifolds to/from the periodic solutions. Next thing you know, you're on the interplanetary superhighway...
Uh... no.
Capitalism means trying to give everyone a fair shot (I mean real capitalism, not the bureaucratically entangled, over-regulated, politically corrupt system they call capitalism in the US).
Socialism means trying to give everyone an equal outcome. Which is a different animal entirely. To give everyone an equal outcome you either need to lift the under-achievers up, or keep the over-achievers down. As it turns out, the latter is far easier than the former, and tends to get pretty healthy support from the under-achieving masses as well. But it doesn't do good things to your country in the long run...
Take a look at this comment. It's not so much that the third world is more efficient, as that they have higher mortality rates, shorter lifespans, more disease, less literacy, and a generally worse set of living conditions. It has nothing to do with efficiency. If anything a technological nation is a more efficient user of resources - that's what technology is, efficient use of resources.
My understanding is that they at least as robust as Si cells. They get used a lot in space applications, so you have to figure that they're pretty tough.
Actually, the best PV cells in production right now are multi-junction GaAs/Ge cells that run at around 26%-28% efficiency. I've heard that there are already 30%-32% cells in the labs.