Yeah, it's great if you happen to have a natural lens between you and what you want to look at. However, natural lenses in a position to be useful are rare. The vast majority of the sky is inaccesible if you stick to natural lenses. It's as if you wanted to do a sightseeing tour of the US. You could either rely upon a few hundred randomly placed coin-op tourist binoculars all over the country pointed at random stuff or bring a pair of binoculars. Those coin-op binoculars might be better that your handheld ones but only if they happen to be pointed at something interesting.
While the Hubble is old, your argument isn't really that persuasive. The optics and superstructure of Hubble still sork fine and are as good as anything we'd put up now with the same general configuration. The aborted Hubble repair mission contains an entire new set of cameras and pointing control devices. BTW, we already spent $400 million on these and they're now gathering dust in a NASA warehouse somewhere. With that upgrade, Hubble would have been upgraded to the latest modern optics and the gyroscopes upgraded to where we'd probably be able to get 5-10 years of useful life out of it.
The James Webb telescope in certain ways is much better than Hubble because of the larger mirror but can't see in the blue and UV which is OK if you're looking at distant, redshifted stuff but useless for looking at a lot of intergalactic events including some star formation processes. Furthermore, the biggest limitation of the space telescopes is one of time - we've got scads of ground based telescopes that users can schedule time on. For space-based telescopes, we've only got a few and the waiting lists are long. If we've got two telescopes, it basically doubles the number of users and science that can be done. Things like this UDF shot are hard to do since the 11 or so days of exposure that it required are hard to get with all of the competing time requirements.
The line about Hubble being too dangerous to service are bunk as well. Although the spacewalk portions of the repair are hazardous, there has never, to my knowledge, been any sort of incident during a spacewalk. That seems to indicate that it is not devastatingly hazardous. Also, the ISS is actually much more dangerous to get to due to its higher inclination. Furthermore, the 20 or so further Shuttle flight needed to finish it have a vastly higher cumulative risk. The ISS is basically incapable of doing meaninful science at this point. The NSF did a study about 5 years ago where it pointed out that ISS was either incapable of fufilling its science objectives or that they could be done better on the ground. Since then, the science capability of ISS has been reduced even more. Basically, ISS is a $20 billion project to keep the US shuttle contractors in work and to keep Russian aerospace engineers from going to 3rd world ICBM programs. As such, it's not a bad use of money since the cost of those Russian engineers going abroad in terms of military expenditures we'd have to do 10 years from now are much higher. However, that said, I'd rather that our military welfare not step on the toes of actually getting science done.
And lastly, the most important reason to keep Hubble running is that the Webb telescope isn't operating yet. It uses an folding mirror which has never been operationally tested. It sits too far away from Earth to ever be serviced should it have a malfunction. What if the booster lofting Webb blows up? If we deorbit Hubble, we open ourselves up to having NO space based optical and near IR telescope. We should at least service Hubble to keep it running until Webb is up and running reliably.
According to the NASA docs, the ability to parially deflate to stop is being planned in already.
I'm wondering if there are still color cameras in the rover? An older document mentioned something about putting a pair of color cameras on the ends of the rotation axis but no mention was made in later documents.
I'm not a military aviator so this might be bunk...
I agree that not having jets scrambled really reflects poorly upon the Pentagon's ability to handle emergencies. However, I'm not sure that having those jets airborne would have made a difference.
I think the primary reason is that it's hard to intercept passenger planes if you aren't expecting them and don't know their final destination. Remember that 757's and 767's can cruise at about 600 mph for hours on end. A military fighter is designed for extremely high speed bursts but can't sustain that speed. IIRC, full military thrust is subsonic for everything but the new F-22 which isn't deployed yet. An F-15 at full military thrust runs out of fuel in something less than half an hour and is really not moving any faster than the target. To really intercept the planes, they would have to have been on afterburner and that's just a few minutes before fuel's depleted.
Jet interceptors work great if you're expecting an attack and know approximately where it's going to come from so that you can properly deploy your interceptors - eg: from the enemy's airbases. Here we had a sudden attack by planes that are blending into the rest of the commercial air traffic with unknown destinations. It's very hard to be able to scramble an effective fighter response to that kind of attack, especially in the timeframe that we had to deal with.
Well, since we did send people to the moon, this obviously wasn't a showstopper. However, the cumulative radiation in the Van Allen belts is a concern for astronauts that are parked in orbit for any extended time. Just crossing them isn't that bad.
On this topic, Tethers unlimited has proposed putting a conductive tether up into the lower Van Allen belt to basically drain the charged partices out of it. I'm not sure if their physics are completely correct (they are a well regarded company with NASA contracts, though) but they predict being able to pull the radiation out of the lower Van Allen belt in about 2 years. Note that this leaves the magnetic particle trap unaffected so the shielding effect is unchanged - it just reduces the total radiatin dose stuff in orbit will recieve.
The problem with launching nuke rockets from the moon is that you still have to loft the components including the fission core to the moon from Earth. I suppose that there's probably uranium deposits on the moon but finding them and exploiting them is going to be a long, hard process.
If you're going to loft NERVA engines from Earth, you might as well just fire 'em up in LEO.
As for Orion, the big problem I see is that the EMP effect is going to propagate for thousands of miles. IIRC, cold war calculations showed that one multi-megaton nuke in low orbit could wipe out most of N. America in one hit. I think you'd have to be a loooong way out before firing up an Orion drive which kinda makes it useless for getting to Mars since you've already expended most of your energy to get there by that point. Orion's a great way to get to Alpha Centauri but I think it's best to sit on that particular drive tech until we're ready to tackle interstellar travel.
Personally, I think that a combination of M2P2 and ion drive driven by a nuclear reactor is the best bet for travel inside the solar system. IIRC, M2P2 gets an ISP of something like 60,000. (no, that's not a typo, I saw that in a NASA study of the drive system) The only problem is that you can't tack against the solar wind so you can't get angular velocity - the ion drive is still needed for that. Plus, you get the bonus that M2P2 creates an artificial magnetosphere which dramatically cuts down on the amount of radiation hitting the spacecraft.
Plus the fact that the M2P2 drive is about the size of a coffee can and could be built by a motivated high school student doesn't hurt either.
Also, try doing a search on dusty magnetic sails - there have been some studies of using fine dust caught up in the magnetic field lines to catch light pressure as well as the solar wind. The predicted performance of those drives is simply insane.
Ah, here's a link: http://www.spacetransportation.com/ast/presentatio ns/3j_sheld.pdf
Every 1% change in albedo gives you a 50-fold increase in thrust. The link above gives figures for a 300lb probe - assuming that it's 1/3 'propellant', 1/3 magdrive and power source and 1/3 payload. 36 days to Mars, 72 days to Jupiter, 7.4 months to Pluto. These drives actually make interstellar travel to other stars feasible.
Plus, you don't have to worry about playing catch with nuclear explosions...
IIRC, ion drives have the potential to outperform even NERVA type rockets. The fuel usage of those things is so low that there's no real reason to refuel.
As for refuelling at the moon, I've got another post around here somewhere where I go through the delta V's involved. It turns out that it takes as much fuel to get to lunar orbit as it does to go to Mars to begin with so refuelling really makes no sense. I guess that trip time tp Mars could be cut down a bit by being able to burn harder on the way to Mars but then you have to burn off that speed when you get to Mars, making for a much more dangerous aerobrake maneuver. (or using a lot of that lunar fuel to slow down)
Yeah, yeah, I'm putting a Mod parent up on my own message. I just want it to get read - there's too many people on this thread that seem to be under the impression that the Moon makes sense as a refuelling stop.
Hell, if you don't want to give me extra karma, mod it up as Funny or something - I just want to make sure it gets read so I don't have to see any more of these 'moon as a refuelling station' posts.
OK,
I keep hearing this idea of using the moon as a refueling station. If you haven't looked at the numbers, t seems like a good idea. However, a quick look at the actual orbital mechanics shows that the Moon is a big waste of time. Here's the breakdown for ow much Delta V is needed to get to the Moon and Mars:
Moon.........Mars LEO to Moon/Mars..3.2.........4.0 Orbital Insertion.......0.9.........0.1 Orbit to Surface.......1.9.........0.4 Total.............. ......6.0.........4.5
Yes, it actually takes LESS fuel to get to Mars primarily because it has an atmosphere you can use to aerobrake. The Moon has no atmosphere and so you have to carry fuel to bleed off your transorbital speed. Furthermore, Landing on Mars is assited by being able to use the aerobrake to bleed off speed on the way down unlike the Moon. Those figures even assume that you don't use a parachute and rely upon retrorockets to come to a stop.
OK, what about the idea of the Lunar refuelling station? You now lose the 1.9km/s of energy you need to get back off the lunar surface. (you still pay for it but the refuelling barge now pays that cost) The problem is that the cost of getting to the Moon and in and out of Lunar orbit is as expensive as getting to Mars to begin with. Sure, you now havea refuelled ship that can go to Mars from lunar orbit which is cheap BUT you just spent as much fuel getting to the Moon as it would have taken to go to Mars without stopping!
To use an analogy, I want to drive to New York from Seattle. Now, would it a be a good idea to send a bunch of my friends out to Washington DC to build a gas station for me so that I can drive there, gas up and then drive up to New York? NO! The only way it would make sense is if we were building a spaceship in lunar orbit which is simply insane - we can't even do that in LEO right now. Hell, we have enough trouble doing it on the ground right now.
Furthermore, as the other respondant mentioned, you can't make fuel on the Moon. All rockets that aren't ion drives (which have no need to refuel at the Moon anyways) need an oxidizer and fuel. There's plenty of O2 on the moon in the form of metal oxides. The Moon's something like 70% oxygen. There's plenty of metal and O2 if we want to expend the energy to get it. However, O2 is the oxidizer - we still need the fuel. All our fuels use (to my knowledge) carbon, nitrogen or hydrogen. That includes everything from gasoline and candle wax to hydrazine and liquid H2. The moon has no large supplies of H2, C or N. You'll have to haul all of those in anyways. It really makes no sense to refuel there.
There's plenty of good reasons to go to the Moon, refuelling on the way to Mars is NOT one of them.
Mars has native sources for water, oxygen and fuel. The atmospheric CO2 can be used to generate all of the above. Furthermore, the radiation shielding and temperature control issues of operating on Mars are far less challenging than on the Moon.
The Moon lacks a source of carbon for making rocket fuels, has a 28 day day/night cycle making the growing of plants impractical and sufers from massive temperature differentials that put enourmous amounts of stress on the structures there.
He3 is a potential fusion fuel but we can't use it until we've developed fusion reactors which is still at LEAST 10 years out. The ITER won't be completed until then and even assuming that it generates net power, it's the size of a football stadium. How exactly do you propose to put something like that on a spaceship or on the Moon? Not to mention the fact that Mars has enormous quantities of deuterium, another fusion fuel.
The moon is a great place to put an observatory but really is not where we should be going first.
Well, most climbers would consider something like this an anathema but that's never stopped the lazy.;) These days, the 'in' thing is to climb w/o oxygen which requires you to be a superhuman mutant like Meissner or Veisturs (sp?). Although I can see rich people using something like this to ascend a mountain, they'd be the laughingstock of everyone else there - kinda defeats the purpose of climbing the mountain.
I see two reasons why this would get used. One: letting disabled people climb mountains. Two: rescue work.
Unfortunately, even though these suits would be pretty good on paper, I can't see them being used in reality. Mountain climbing is about much more than pure strength - there's a lot of things like crossing snow bridges and ascending steep snow slopes where an additional 300 pounds of metal on you will get you killed regardless of the amount of strength you have.
While the cheap glasses in Africa are a wonderful idea (IMO, engineers spend too much time on expensive, gee-whiz stuff and overlook simple, cheap ideas that would potentially raise the quality of life for hundreds of millions of people), this is a different beast.
The cheap glasses are basically a pair of tensioned water balloons in a cheap frame. (50's fashions appear to be 'in' for the third world, I guess.;) ) A syringe is used to add or remove water until the person can see clearly - no need for expensive glass grinding or optometrists. Of course, they're crap glasses but it's better than nothing.
This new lens uses electrostatics to manipulate the meniscus between two liquids of different refractive indices. I guess that it's a similar basic idea in the same way that any variable focus lens is the same basic idea but these really aren't the same thing.
Actually, gravity influences were one of the first things that popped to mind but the size scale of these things (3mm) makes the influence of gravity pretty minimal. I'm thinking of a 3mm water drop on a mirror - even though the water is unsupported, the distortion is suprisingly small. This is two liquids - they don't really even need to be that closely density matched - in a closed container. Vibratiosn and shocks are probably a much bigger problem.
I'd guess that the front and back surfaces of the lens are hydrophobic and hydrophillic respectively to keep the two fluids properly oriented in the cannister. Even if the lens gets dropped, I think that you're looking at most ramping the lens back and forth a few times to get the meniscus properly reset and the lens should be ready to go.
Re: Prandtl/Tietjens - thanks for the heads up, it's already on my Amazon wish list.
I agree - these lenses seem analagous to the magnetic lenses in an electron microscope - variable focus but lousy from an optical standpoint. Since the curvature is purely determined by the interplay of surface tensions, I'm not sure how one could make the lenses better optically. Perhpas by changing the curvature of the outer wall (instead of using a straight-walled cylender, using a curved cylender like those old-fashioned barrels out of Westerns) That would change the initial contact angle of the fluids with the wall depending on where the meniscus is located and give you an additional term under your control to modify the meniscus curvature.
I'm not an optics jockey, my knowledge is relatively superficial, does anyone know how many terms are needed to generate a good lens? It might be possible to generate a fairly decent lens with the idea I just outlined, at least on the order of a single sperical glass lens in terms of optical quality.
Yes, the lens can refocus in basically no time but that's not the primary limitation. What presently limits the speed of taking picutres is the time it takes for the processor to determine whether the image is in focus. Although your lens might be able to change focus in 10 ms, it'll still take a second or two of focuss fiddling for the camera to lock down the focus range for either of those focus ranges. If high speed image processing comes along with a similar time scale, yes, this would be practical.
Actually, an idea just occured to me - you could do all the autofocussing first, establishing the various focal lengths and then hammer out the different shots as fast as the CCD can pull down the data. If you did things that way, your idea might actually work. However, its tempered by the fact that these lenses are very low quality, optics-wise. (they may be flawless but they don't have the optimal curvature for a lens and they're pretty small to boot) Any scheme would have to take into account that these lenses are going to be strictly disposable camera and cell-phone camera material.
For the other respondants:
A tripod would be useful for taking two shots with different focus but relys upon the photographer to take both shots which probably involves a significant delay between those shots. (hence the tripod, I assume) However, it is quite likely that objects in the shot will move in that time period, making it impossible to composite the shots. If the camera can be used to grab two sequential shots within a fraction of a second of each other, the need for a tripod is greatly reduced.
Yes, a small aperture will increase depth of field but at the expense of incoming light. A pinhole camera has everything in focus but requires a very brightly lit scene or long exposure times. IIRC, Ansel Adams used this techniques to get his photos and they required him to use obscenely long exposure times.
I'm not sure where this 'air bubble' comes into play here. According to the diagrams, there's no air involed in the lens at all. There's a plastic cylinder that contains two different liquids that form the lens. Of course, underwater, you'll have different focal lengths due to the different refractive indexes of water and air but that simply requires refocussing - which this lens is nicely adapted for.
There are no moving membranes involved. The only moving parts are the two fluids. The lens is formed by a moving interface between the two. Even if some sort of mechanical shock causes this interface to break up, simply wait and the system will eventually re-equilibrate. If you take a container with water and oil and shake it up you just wat a few hours or days and the two fluids will seperate back out again. Since there really *are* no moving parts, this lens should be able to operate over an infinite number of focussings without trouble. At the least, it will be able to refocus a number of times orders of magnitude beyond what a mechanical system could handle.
The electrodes shouldn't have problems with corrosion. First, they don't even have to be in contact with the solution - the interaction is electrostatic and so a Teflon coating could be used. Furthermore, when working with a known solvent, corrosion issues are trivial. It's when making stuff that interfaces with the outside world and biological interfaces with all the associated uncontrolled variables that we still hit problems.
The curve should actually be as perfect as you want*. The interface is created by two imiscible liquids - while there will be some transient ripples from vibration, etc, the overall lens interface will be scratch free. It doesn't matter what the manufacturing quantities are - the lenses will be near perfect - the physics of the liquids will smooth out minor manufacturing defects. The only big concern would be defects in the electrodes (unlikely to be big enough in actuality to significantly affect the lenses) and making sure the correct volumes of both liquids are added. (again a trivial matter with modern liquid handling technology) Even if you do get some defects - its easy to correct. Simply automate an optical testing station where each lens has a light pattern run through it. A sensor looks for abberrations in the otpput light and calculates if the problem is fatal. If not, it calculates the necessary compensation to get proper optical performance. (eg: more or less charge on the elecgrodes for a given focus.) have an EEPROM associated with each lens that stores the correction value - problem solved. * Note: your point holds in that the curve generated by the liquids doesn't form a perfect lens so you'll get hit with some nasty chromatic and spherical abberrations. These lenses definately WON'T be used for high quality optics.
Light loss should be a non-issue. I might be wrong here but surface reflection is primarily at air/liquid and air/solid interfaces because of the large refractive index mismatch. Here, all of the internal interfaces are liquid/liquid and liquid/solid interfaces. Reflective losses shouldn't happen, making anti-reflective coating unnecessary.
Color balance will only be an issue if the liquids absorb a particular color preferrentially. Since both liquids (at least from the pictures) appear colorless, this isn't an issue. The UV degradation you mention is an issue but simply putting a UV absorbing front coating on the lens should prevent degradation. Overall, the problem should be no worse than what one sees with low cost optics with plastic lens components.
I do agree that this lens won't be practical for anything but low-quality optics. The size is limited by the surface tensions and won't get much bigger than what is being demonstrated. Also, the lens shape is non-ideal and will give poor optical performance regardless of the size since it's shape is purely determined by the interacting surface tensions of the liquids. What this lens will be wonderful for is low-cost disposable cameras, cell phone cameras and small security cameras where image quality isn't essential and cost/size are the determining factors. A potential killer app is machine vision. A robot can easily compensate for the lens aberrations computationally. Furthermore, replacing the continuous ring electrode with a segmented one gives the ability to cahge the curvature
It's not going to be possible to scale these things up much beyond what they've already demonstrated. The reason is that the curvature is solely determined by the interaction of the liquids with the electrodes on the edges. If the lens gets much larger, most of the liquid will be minimally affected. Look at a glass of water, for example: the water has a meniscus edge where it curves upwards to meet the glass. It looks as if most of the water is flat and the edges are curved but this is not true. In actuality, the entire surface is curved but only the water right by the edge of the glass has enough curvature for it to be visible.
If you want the lens to have a uniform curvature so that it is useful as a lens, the overall diameter of the lens must be less that a certain critical length scale which is the length at which the surface tension effects of the edge are still dropping off in a relatively linear fashion. This is determined by the relative surface tensions of the liquids and the electrodes around the edge. While you can tweak those parameters a bit there will be a practical limit to the lens size and I'm guessing that this model is probably pushing that limit already.
Furthermore, the lens is gonna be kinda crappy - it's actually analagous to the lenses in an electron microscope - magnetic lenses that bend electron paths. You can change the current level to change the focus but the lens itself is not shaped properly for good optics - as a result, electron microscopes don't have nearly the resolution they could have on paper. (by about a factor of 100 or so). This new lens has its shape determined by the interplay of surface tension and it's fairly certain that this shape won't make an ideal lens. The result is that you'll have awful sperical aberration. (probably nasty chromatic aberration as well) The result is that the image quality will be poor.
However, that said, these lenses are pretty cool. For point 'n shoot cameras, cellphone cameras and webcameras, these things would rock. Also, security cameras would probably benefit from being able to focus in a reduced total size as well. Any application where fantastic picture quality isn't necessary would benefit from this.
Another potential application is machine vision. There, the machine can easily be programmed to compensate for the lens distortions. Also, if you replaced the ring electrode with a ring of small electrodes around the circumference of the lens, you could set up an uneven charge distribution. This would allow a lens that has a focal point than can be moved off the optic axis. Not only can you focus, you can also bend the light coming through the lens - an electronic equivalent to a gimbal mount. A robot using these eyes can focus and 'look around' with 10 ms speed. This is a potential killer app for these things.
While it's true that the elements above and Methionine (and several other amino acids as well) are required for humans, most free-living organisms can generate all of the amino acids from scratch.
Aside from sulfur, iron, phosphorus, monovalent and divalent cations most of the other trace elements are required in levels so low that just about any random location will have enough to suffice.
Actually, the standard line for several years is that the polar ice caps are a mix of CO2 and water ice. It's fairly clear that there is still a very significant amount of sold water on Mars. The contention these days is how prevalent liquid water is.
Slashdot Mirror
Futhermore, the risks of going to ISS are actually GREATER than Hubble:
f f
http://www.marssociety.org/docs/Hubblerisk1a.pd
http://www.marssociety.org/docs/Hubblerisk2a.pd
Those are a pair of leaked NASA documents that got sent to the Mars Society. Basically Hubble is being killed for political reasons.
Yeah, it's great if you happen to have a natural lens between you and what you want to look at. However, natural lenses in a position to be useful are rare. The vast majority of the sky is inaccesible if you stick to natural lenses. It's as if you wanted to do a sightseeing tour of the US. You could either rely upon a few hundred randomly placed coin-op tourist binoculars all over the country pointed at random stuff or bring a pair of binoculars. Those coin-op binoculars might be better that your handheld ones but only if they happen to be pointed at something interesting.
While the Hubble is old, your argument isn't really that persuasive. The optics and superstructure of Hubble still sork fine and are as good as anything we'd put up now with the same general configuration. The aborted Hubble repair mission contains an entire new set of cameras and pointing control devices. BTW, we already spent $400 million on these and they're now gathering dust in a NASA warehouse somewhere. With that upgrade, Hubble would have been upgraded to the latest modern optics and the gyroscopes upgraded to where we'd probably be able to get 5-10 years of useful life out of it.
The James Webb telescope in certain ways is much better than Hubble because of the larger mirror but can't see in the blue and UV which is OK if you're looking at distant, redshifted stuff but useless for looking at a lot of intergalactic events including some star formation processes. Furthermore, the biggest limitation of the space telescopes is one of time - we've got scads of ground based telescopes that users can schedule time on. For space-based telescopes, we've only got a few and the waiting lists are long. If we've got two telescopes, it basically doubles the number of users and science that can be done. Things like this UDF shot are hard to do since the 11 or so days of exposure that it required are hard to get with all of the competing time requirements.
The line about Hubble being too dangerous to service are bunk as well. Although the spacewalk portions of the repair are hazardous, there has never, to my knowledge, been any sort of incident during a spacewalk. That seems to indicate that it is not devastatingly hazardous. Also, the ISS is actually much more dangerous to get to due to its higher inclination. Furthermore, the 20 or so further Shuttle flight needed to finish it have a vastly higher cumulative risk. The ISS is basically incapable of doing meaninful science at this point. The NSF did a study about 5 years ago where it pointed out that ISS was either incapable of fufilling its science objectives or that they could be done better on the ground. Since then, the science capability of ISS has been reduced even more. Basically, ISS is a $20 billion project to keep the US shuttle contractors in work and to keep Russian aerospace engineers from going to 3rd world ICBM programs. As such, it's not a bad use of money since the cost of those Russian engineers going abroad in terms of military expenditures we'd have to do 10 years from now are much higher. However, that said, I'd rather that our military welfare not step on the toes of actually getting science done.
And lastly, the most important reason to keep Hubble running is that the Webb telescope isn't operating yet. It uses an folding mirror which has never been operationally tested. It sits too far away from Earth to ever be serviced should it have a malfunction. What if the booster lofting Webb blows up? If we deorbit Hubble, we open ourselves up to having NO space based optical and near IR telescope. We should at least service Hubble to keep it running until Webb is up and running reliably.
For 18 grand, it *should* be made of platinum.
According to the NASA docs, the ability to parially deflate to stop is being planned in already.
I'm wondering if there are still color cameras in the rover? An older document mentioned something about putting a pair of color cameras on the ends of the rotation axis but no mention was made in later documents.
Even worse, we'd have to breed a strain of giant space hamster to put inside of it...
...Martian Fun Ball.
I'm not a military aviator so this might be bunk...
I agree that not having jets scrambled really reflects poorly upon the Pentagon's ability to handle emergencies. However, I'm not sure that having those jets airborne would have made a difference.
I think the primary reason is that it's hard to intercept passenger planes if you aren't expecting them and don't know their final destination. Remember that 757's and 767's can cruise at about 600 mph for hours on end. A military fighter is designed for extremely high speed bursts but can't sustain that speed. IIRC, full military thrust is subsonic for everything but the new F-22 which isn't deployed yet. An F-15 at full military thrust runs out of fuel in something less than half an hour and is really not moving any faster than the target. To really intercept the planes, they would have to have been on afterburner and that's just a few minutes before fuel's depleted.
Jet interceptors work great if you're expecting an attack and know approximately where it's going to come from so that you can properly deploy your interceptors - eg: from the enemy's airbases. Here we had a sudden attack by planes that are blending into the rest of the commercial air traffic with unknown destinations. It's very hard to be able to scramble an effective fighter response to that kind of attack, especially in the timeframe that we had to deal with.
Well, since we did send people to the moon, this obviously wasn't a showstopper. However, the cumulative radiation in the Van Allen belts is a concern for astronauts that are parked in orbit for any extended time. Just crossing them isn't that bad.
On this topic, Tethers unlimited has proposed putting a conductive tether up into the lower Van Allen belt to basically drain the charged partices out of it. I'm not sure if their physics are completely correct (they are a well regarded company with NASA contracts, though) but they predict being able to pull the radiation out of the lower Van Allen belt in about 2 years. Note that this leaves the magnetic particle trap unaffected so the shielding effect is unchanged - it just reduces the total radiatin dose stuff in orbit will recieve.
The problem with launching nuke rockets from the moon is that you still have to loft the components including the fission core to the moon from Earth. I suppose that there's probably uranium deposits on the moon but finding them and exploiting them is going to be a long, hard process.
o ns/3j_sheld.pdf
If you're going to loft NERVA engines from Earth, you might as well just fire 'em up in LEO.
As for Orion, the big problem I see is that the EMP effect is going to propagate for thousands of miles. IIRC, cold war calculations showed that one multi-megaton nuke in low orbit could wipe out most of N. America in one hit. I think you'd have to be a loooong way out before firing up an Orion drive which kinda makes it useless for getting to Mars since you've already expended most of your energy to get there by that point. Orion's a great way to get to Alpha Centauri but I think it's best to sit on that particular drive tech until we're ready to tackle interstellar travel.
Personally, I think that a combination of M2P2 and ion drive driven by a nuclear reactor is the best bet for travel inside the solar system. IIRC, M2P2 gets an ISP of something like 60,000. (no, that's not a typo, I saw that in a NASA study of the drive system) The only problem is that you can't tack against the solar wind so you can't get angular velocity - the ion drive is still needed for that. Plus, you get the bonus that M2P2 creates an artificial magnetosphere which dramatically cuts down on the amount of radiation hitting the spacecraft.
Plus the fact that the M2P2 drive is about the size of a coffee can and could be built by a motivated high school student doesn't hurt either.
Also, try doing a search on dusty magnetic sails - there have been some studies of using fine dust caught up in the magnetic field lines to catch light pressure as well as the solar wind. The predicted performance of those drives is simply insane.
Ah, here's a link: http://www.spacetransportation.com/ast/presentati
Every 1% change in albedo gives you a 50-fold increase in thrust. The link above gives figures for a 300lb probe - assuming that it's 1/3 'propellant', 1/3 magdrive and power source and 1/3 payload. 36 days to Mars, 72 days to Jupiter, 7.4 months to Pluto. These drives actually make interstellar travel to other stars feasible.
Plus, you don't have to worry about playing catch with nuclear explosions...
IIRC, ion drives have the potential to outperform even NERVA type rockets. The fuel usage of those things is so low that there's no real reason to refuel.
As for refuelling at the moon, I've got another post around here somewhere where I go through the delta V's involved. It turns out that it takes as much fuel to get to lunar orbit as it does to go to Mars to begin with so refuelling really makes no sense. I guess that trip time tp Mars could be cut down a bit by being able to burn harder on the way to Mars but then you have to burn off that speed when you get to Mars, making for a much more dangerous aerobrake maneuver. (or using a lot of that lunar fuel to slow down)
Yeah, yeah, I'm putting a Mod parent up on my own message. I just want it to get read - there's too many people on this thread that seem to be under the impression that the Moon makes sense as a refuelling stop.
Hell, if you don't want to give me extra karma, mod it up as Funny or something - I just want to make sure it gets read so I don't have to see any more of these 'moon as a refuelling station' posts.
OK,
. ......6.0.........4.5
I keep hearing this idea of using the moon as a refueling station. If you haven't looked at the numbers, t seems like a good idea. However, a quick look at the actual orbital mechanics shows that the Moon is a big waste of time. Here's the breakdown for ow much Delta V is needed to get to the Moon and Mars:
Moon.........Mars
LEO to Moon/Mars..3.2.........4.0
Orbital Insertion.......0.9.........0.1
Orbit to Surface.......1.9.........0.4
Total.............
Yes, it actually takes LESS fuel to get to Mars primarily because it has an atmosphere you can use to aerobrake. The Moon has no atmosphere and so you have to carry fuel to bleed off your transorbital speed. Furthermore, Landing on Mars is assited by being able to use the aerobrake to bleed off speed on the way down unlike the Moon. Those figures even assume that you don't use a parachute and rely upon retrorockets to come to a stop.
OK, what about the idea of the Lunar refuelling station? You now lose the 1.9km/s of energy you need to get back off the lunar surface. (you still pay for it but the refuelling barge now pays that cost) The problem is that the cost of getting to the Moon and in and out of Lunar orbit is as expensive as getting to Mars to begin with. Sure, you now havea refuelled ship that can go to Mars from lunar orbit which is cheap BUT you just spent as much fuel getting to the Moon as it would have taken to go to Mars without stopping!
To use an analogy, I want to drive to New York from Seattle. Now, would it a be a good idea to send a bunch of my friends out to Washington DC to build a gas station for me so that I can drive there, gas up and then drive up to New York? NO! The only way it would make sense is if we were building a spaceship in lunar orbit which is simply insane - we can't even do that in LEO right now. Hell, we have enough trouble doing it on the ground right now.
Furthermore, as the other respondant mentioned, you can't make fuel on the Moon. All rockets that aren't ion drives (which have no need to refuel at the Moon anyways) need an oxidizer and fuel. There's plenty of O2 on the moon in the form of metal oxides. The Moon's something like 70% oxygen. There's plenty of metal and O2 if we want to expend the energy to get it. However, O2 is the oxidizer - we still need the fuel. All our fuels use (to my knowledge) carbon, nitrogen or hydrogen. That includes everything from gasoline and candle wax to hydrazine and liquid H2. The moon has no large supplies of H2, C or N. You'll have to haul all of those in anyways. It really makes no sense to refuel there.
There's plenty of good reasons to go to the Moon, refuelling on the way to Mars is NOT one of them.
Ummmm, yeah.
And Republican Senators look for any excuse to criticize the sitting Democratic President during an election year too. Since when is this news?
Just how does something like this get modded Insightful?!
Oh, yeah, it's Slashdot, nevermind...
With all due respect, what are you smoking?
Mars has native sources for water, oxygen and fuel. The atmospheric CO2 can be used to generate all of the above. Furthermore, the radiation shielding and temperature control issues of operating on Mars are far less challenging than on the Moon.
The Moon lacks a source of carbon for making rocket fuels, has a 28 day day/night cycle making the growing of plants impractical and sufers from massive temperature differentials that put enourmous amounts of stress on the structures there.
He3 is a potential fusion fuel but we can't use it until we've developed fusion reactors which is still at LEAST 10 years out. The ITER won't be completed until then and even assuming that it generates net power, it's the size of a football stadium. How exactly do you propose to put something like that on a spaceship or on the Moon? Not to mention the fact that Mars has enormous quantities of deuterium, another fusion fuel.
The moon is a great place to put an observatory but really is not where we should be going first.
Well, most climbers would consider something like this an anathema but that's never stopped the lazy. ;) These days, the 'in' thing is to climb w/o oxygen which requires you to be a superhuman mutant like Meissner or Veisturs (sp?). Although I can see rich people using something like this to ascend a mountain, they'd be the laughingstock of everyone else there - kinda defeats the purpose of climbing the mountain.
I see two reasons why this would get used. One: letting disabled people climb mountains. Two: rescue work.
Unfortunately, even though these suits would be pretty good on paper, I can't see them being used in reality. Mountain climbing is about much more than pure strength - there's a lot of things like crossing snow bridges and ascending steep snow slopes where an additional 300 pounds of metal on you will get you killed regardless of the amount of strength you have.
While the cheap glasses in Africa are a wonderful idea (IMO, engineers spend too much time on expensive, gee-whiz stuff and overlook simple, cheap ideas that would potentially raise the quality of life for hundreds of millions of people), this is a different beast.
;) ) A syringe is used to add or remove water until the person can see clearly - no need for expensive glass grinding or optometrists. Of course, they're crap glasses but it's better than nothing.
The cheap glasses are basically a pair of tensioned water balloons in a cheap frame. (50's fashions appear to be 'in' for the third world, I guess.
This new lens uses electrostatics to manipulate the meniscus between two liquids of different refractive indices. I guess that it's a similar basic idea in the same way that any variable focus lens is the same basic idea but these really aren't the same thing.
Actually, gravity influences were one of the first things that popped to mind but the size scale of these things (3mm) makes the influence of gravity pretty minimal. I'm thinking of a 3mm water drop on a mirror - even though the water is unsupported, the distortion is suprisingly small. This is two liquids - they don't really even need to be that closely density matched - in a closed container. Vibratiosn and shocks are probably a much bigger problem.
I'd guess that the front and back surfaces of the lens are hydrophobic and hydrophillic respectively to keep the two fluids properly oriented in the cannister. Even if the lens gets dropped, I think that you're looking at most ramping the lens back and forth a few times to get the meniscus properly reset and the lens should be ready to go.
Re: Prandtl/Tietjens - thanks for the heads up, it's already on my Amazon wish list.
I agree - these lenses seem analagous to the magnetic lenses in an electron microscope - variable focus but lousy from an optical standpoint. Since the curvature is purely determined by the interplay of surface tensions, I'm not sure how one could make the lenses better optically. Perhpas by changing the curvature of the outer wall (instead of using a straight-walled cylender, using a curved cylender like those old-fashioned barrels out of Westerns) That would change the initial contact angle of the fluids with the wall depending on where the meniscus is located and give you an additional term under your control to modify the meniscus curvature.
I'm not an optics jockey, my knowledge is relatively superficial, does anyone know how many terms are needed to generate a good lens? It might be possible to generate a fairly decent lens with the idea I just outlined, at least on the order of a single sperical glass lens in terms of optical quality.
Yes, the lens can refocus in basically no time but that's not the primary limitation. What presently limits the speed of taking picutres is the time it takes for the processor to determine whether the image is in focus. Although your lens might be able to change focus in 10 ms, it'll still take a second or two of focuss fiddling for the camera to lock down the focus range for either of those focus ranges. If high speed image processing comes along with a similar time scale, yes, this would be practical.
Actually, an idea just occured to me - you could do all the autofocussing first, establishing the various focal lengths and then hammer out the different shots as fast as the CCD can pull down the data. If you did things that way, your idea might actually work. However, its tempered by the fact that these lenses are very low quality, optics-wise. (they may be flawless but they don't have the optimal curvature for a lens and they're pretty small to boot) Any scheme would have to take into account that these lenses are going to be strictly disposable camera and cell-phone camera material.
For the other respondants:
A tripod would be useful for taking two shots with different focus but relys upon the photographer to take both shots which probably involves a significant delay between those shots. (hence the tripod, I assume) However, it is quite likely that objects in the shot will move in that time period, making it impossible to composite the shots. If the camera can be used to grab two sequential shots within a fraction of a second of each other, the need for a tripod is greatly reduced.
Yes, a small aperture will increase depth of field but at the expense of incoming light. A pinhole camera has everything in focus but requires a very brightly lit scene or long exposure times. IIRC, Ansel Adams used this techniques to get his photos and they required him to use obscenely long exposure times.
I'm not sure where this 'air bubble' comes into play here. According to the diagrams, there's no air involed in the lens at all. There's a plastic cylinder that contains two different liquids that form the lens. Of course, underwater, you'll have different focal lengths due to the different refractive indexes of water and air but that simply requires refocussing - which this lens is nicely adapted for.
There are no moving membranes involved. The only moving parts are the two fluids. The lens is formed by a moving interface between the two. Even if some sort of mechanical shock causes this interface to break up, simply wait and the system will eventually re-equilibrate. If you take a container with water and oil and shake it up you just wat a few hours or days and the two fluids will seperate back out again. Since there really *are* no moving parts, this lens should be able to operate over an infinite number of focussings without trouble. At the least, it will be able to refocus a number of times orders of magnitude beyond what a mechanical system could handle.
The electrodes shouldn't have problems with corrosion. First, they don't even have to be in contact with the solution - the interaction is electrostatic and so a Teflon coating could be used. Furthermore, when working with a known solvent, corrosion issues are trivial. It's when making stuff that interfaces with the outside world and biological interfaces with all the associated uncontrolled variables that we still hit problems.
The curve should actually be as perfect as you want*. The interface is created by two imiscible liquids - while there will be some transient ripples from vibration, etc, the overall lens interface will be scratch free. It doesn't matter what the manufacturing quantities are - the lenses will be near perfect - the physics of the liquids will smooth out minor manufacturing defects. The only big concern would be defects in the electrodes (unlikely to be big enough in actuality to significantly affect the lenses) and making sure the correct volumes of both liquids are added. (again a trivial matter with modern liquid handling technology) Even if you do get some defects - its easy to correct. Simply automate an optical testing station where each lens has a light pattern run through it. A sensor looks for abberrations in the otpput light and calculates if the problem is fatal. If not, it calculates the necessary compensation to get proper optical performance. (eg: more or less charge on the elecgrodes for a given focus.) have an EEPROM associated with each lens that stores the correction value - problem solved.
* Note: your point holds in that the curve generated by the liquids doesn't form a perfect lens so you'll get hit with some nasty chromatic and spherical abberrations. These lenses definately WON'T be used for high quality optics.
Light loss should be a non-issue. I might be wrong here but surface reflection is primarily at air/liquid and air/solid interfaces because of the large refractive index mismatch. Here, all of the internal interfaces are liquid/liquid and liquid/solid interfaces. Reflective losses shouldn't happen, making anti-reflective coating unnecessary.
Color balance will only be an issue if the liquids absorb a particular color preferrentially. Since both liquids (at least from the pictures) appear colorless, this isn't an issue. The UV degradation you mention is an issue but simply putting a UV absorbing front coating on the lens should prevent degradation. Overall, the problem should be no worse than what one sees with low cost optics with plastic lens components.
I do agree that this lens won't be practical for anything but low-quality optics. The size is limited by the surface tensions and won't get much bigger than what is being demonstrated. Also, the lens shape is non-ideal and will give poor optical performance regardless of the size since it's shape is purely determined by the interacting surface tensions of the liquids.
What this lens will be wonderful for is low-cost disposable cameras, cell phone cameras and small security cameras where image quality isn't essential and cost/size are the determining factors.
A potential killer app is machine vision. A robot can easily compensate for the lens aberrations computationally. Furthermore, replacing the continuous ring electrode with a segmented one gives the ability to cahge the curvature
It's not going to be possible to scale these things up much beyond what they've already demonstrated. The reason is that the curvature is solely determined by the interaction of the liquids with the electrodes on the edges. If the lens gets much larger, most of the liquid will be minimally affected. Look at a glass of water, for example: the water has a meniscus edge where it curves upwards to meet the glass. It looks as if most of the water is flat and the edges are curved but this is not true. In actuality, the entire surface is curved but only the water right by the edge of the glass has enough curvature for it to be visible.
If you want the lens to have a uniform curvature so that it is useful as a lens, the overall diameter of the lens must be less that a certain critical length scale which is the length at which the surface tension effects of the edge are still dropping off in a relatively linear fashion. This is determined by the relative surface tensions of the liquids and the electrodes around the edge. While you can tweak those parameters a bit there will be a practical limit to the lens size and I'm guessing that this model is probably pushing that limit already.
Furthermore, the lens is gonna be kinda crappy - it's actually analagous to the lenses in an electron microscope - magnetic lenses that bend electron paths. You can change the current level to change the focus but the lens itself is not shaped properly for good optics - as a result, electron microscopes don't have nearly the resolution they could have on paper. (by about a factor of 100 or so). This new lens has its shape determined by the interplay of surface tension and it's fairly certain that this shape won't make an ideal lens. The result is that you'll have awful sperical aberration. (probably nasty chromatic aberration as well) The result is that the image quality will be poor.
However, that said, these lenses are pretty cool. For point 'n shoot cameras, cellphone cameras and webcameras, these things would rock. Also, security cameras would probably benefit from being able to focus in a reduced total size as well. Any application where fantastic picture quality isn't necessary would benefit from this.
Another potential application is machine vision. There, the machine can easily be programmed to compensate for the lens distortions. Also, if you replaced the ring electrode with a ring of small electrodes around the circumference of the lens, you could set up an uneven charge distribution. This would allow a lens that has a focal point than can be moved off the optic axis. Not only can you focus, you can also bend the light coming through the lens - an electronic equivalent to a gimbal mount. A robot using these eyes can focus and 'look around' with 10 ms speed. This is a potential killer app for these things.
While it's true that the elements above and Methionine (and several other amino acids as well) are required for humans, most free-living organisms can generate all of the amino acids from scratch.
Aside from sulfur, iron, phosphorus, monovalent and divalent cations most of the other trace elements are required in levels so low that just about any random location will have enough to suffice.
Actually, the standard line for several years is that the polar ice caps are a mix of CO2 and water ice. It's fairly clear that there is still a very significant amount of sold water on Mars. The contention these days is how prevalent liquid water is.