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A Lunar Space Elevator Is Feasible and Inexpensive, Scientists Find
- trickstra 7y ago> proposed the idea of a “lunar space elevator,” which is exactly what it sounds like—a very long elevator connecting the moon and our planet. No that's absolutely not what a space elevator is
- onion2k 7y agoA space elevator is a device that lifts things to space along a static cable. A space elevator on Earth lifts things to outside of Earth's orbit. A space elevator on Mars lifts things to outside of Martian orbit. And a space elevator on the moon lifts things outside of lunar orbit. This definitely is a space elevator by any definition of said technology.
- trickstra 7y ago> connecting the moon and our planet
- kuu 7y agoThe key point: the Columbia study differs from previous proposal in an important way: instead of building the elevator from the Earth’s surface (which is impossible with today’s technology), it would be anchored on the moon and stretch some 200,000 miles toward Earth until hitting the geostationary orbit height (about 22,236 miles above sea level), at which objects move around Earth in lockstep with the planet’s own rotation. Dangling the space elevator at this height would eliminate the need to place a large counterweight near Earth’s orbit to balance out the planet’s massive gravitational pull if the elevator were to be built from ground up. This method would also prevent any relative motion between Earth’s surface and space below the geostationary orbit area from bending or twisting the elevator
- coldtea 7y ago>instead of building the elevator from the Earth’s surface (which is impossible with today’s technology), it would be anchored on the moon and stretch some 200,000 miles toward Earth until hitting the geostationary orbit height (about 22,236 miles above sea level) Yeah, that's totally feasible and useful... /s I hope those guys are not paid with public money...
- echelon 7y ago> I hope those guys are not paid with public money... I hope they are. Engineering feats like this propel us as a species forward. Imagine the material science involved in simply achieving the correct tensile strength. Every thought that goes into this will find application in other areas. I can't imagine this will get built, especially not in our lifetimes, but I do hope that it is one of many such endeavors humans will embark upon.
- coldtea 7y ago>Engineering feats like this propel us as a species forward. Note that there are no feats thus far...
- asavadatti 7y agoWhat device did you type your comment on?
- ElFitz 7y agoProbably specifically meant the purely theoretical (and devoid of any tangible engineering feat) paper
- coldtea 7y agoNot a space elevator or anything designed by the team in the article, I can assure you of that... It's not like there can't be some research that's realistic and have tangible (even if remote) goals, like e.g. rocket research in the 20s and 30s, and some that's just theoretical filler -- and that we can never tell one from the other...
- isoprophlex 7y agoHowever wonderfully grandiose these elevator pitches sound, I'm always left wondering: what happens when some space debris hits the thing? Instant Kessler syndrome?
- ed312 7y agoI believe the traditional answer is "lasers" or "someone else will figure that out"
- extropy 7y agoNo, dual cosmic lashing. One end hitting the moon the other one earth. On earth side the atmosphere will take the worst of it, moon will hurt... Also there is hardly any space debris beyond geosynchronous.
- isoprophlex 7y agoInteresting, that makes the case for a moon -> geostationary stronger...
- marcosdumay 7y agoA part falls on Earth, another part falls on the Moon. Or a part falls on Earth and the other part is kept hanging at the same place, depends on where you cut it.
- lkbm 7y agoThis guy did some simulations on cable breakage: http://gassend.net/spaceelevator/breaks/ http://gassend.net/spaceelevator/breaks/
- isoprophlex 7y agoThis is fantastic, thanks! If that cable resist interaction with the atmosphere, some people on earth are going to be royally fucked http://gassend.net/spaceelevator/breaks/break100.gif http://gassend.net/spaceelevator/breaks/break100.gif Interestingly most debris on the tail end appears to be ejected outward rather violently
- neuromancer2701 7y agoThis a moon-GEO elevator which may have its advantages but it does not help you get out of the planetary gravity well.
- Sir_Cmpwn 7y agoWell, thanks to the bastard rocket equation, fuel savings have an exponential impact. If you can get to geostationary orbit and meet up with the elevator, then fuel up again at the moon, you save a considerable amount of weight in fuel.
- loudmax 7y agoExactly. Overcoming Earth's gravity well is the reason building a space elevator is such an exciting prospect. The geosynchronous orbit is about a 10th of the way to the moon, so this moon elevator would go 9/10ths of the way toward the Earth. That's significant but it's precisely that remaining 10th of the way where the vast majority of energy expenditure occurs. If you can make it from the surface of the Earth to geosynchronous, then making it to the moon is relatively cheap.
- narag 7y agoNot orbit, the Moon doesn't orbit the Earth in one day, but a month. The cable would be almost stationary compared to orbit. That needs less power.
- 7y ago
- 34679 7y agoWhat cable weighs less than half a pound per mile? 200,000 miles 88,000 lb cable No friggin way.
- binarymax 7y agoWell since it's in pounds, that's an earth gravity weight measurement. Maybe they're talking about moon weight :) Actually, not using a measurement of mass is a bit of a red flag. EDIT: Perhaps I should read the paper and not rely on science-journalism. At first glance paper looks pretty good in terms of mass measurement and estimation.
- mkl 7y agoYes, that seems to have been misunderstood. The cable that weighs 88,000lb (in the paper, 40,000kg), has a cross-sectional area of 10⁻⁷m²! That won't stand up to much use. If I'm reading (skimming) right, they say "this would only allow transport of weights up to 100kg".
- jandrese 7y ago100kg seems like a barely usable amount of lift. It means you need an in-orbit assembly system for most things you want to launch and I'm pretty sure you're not going to be able to launch a person with life support gear.
- mkl 7y agoYes, it's hard to imagine a cable-crawling machine and its power source being under that mass limit, let alone a payload.
- jandrese 7y agoI had assumed the cost of the crawler was already included in that 100kg figure, but if not then yeah, that's even more marginal. It really can't bring its own fuel source along, it needs to work on beamed power or maybe a current between two parallel tethers.
- m4r35n357 7y agoGlanced through the paper quickly, couldn't find _any_ references to elasticity or strain, just the breaking stress. I would have thought that would be in the calculations somewhere, considering this thing would be a quarter of a million miles long! Maybe I'm just being a killjoy . . .
- sathackr 7y agoIf one end is tethered to the moon, and the other end is in geostationary orbit...you're gonna have a bad day. The moon is not in geostationary orbit. Not an orbital scientist but doesn't seem that will work out very well.
- deleted 7y ago[deleted]
- empath75 7y agoI think it’s at geostationary orbit height.
- mkl 7y agoI don't really understand how it can stay at geostationary orbit height without being at geostationary orbit speed. Can someone explain?
- Majestic121 7y agoWell it's anchored on the moon at the other side
- extropy 7y agoIt's dangling down from the moon. Going at moons speed - 28 days per revolution instead of geostationary 1 day. So less centrifugal force form rotation that is compensated by the cable strain.
- brians 7y agoThe end is at that height. Its center of mass is much higher, and it's rigid enough to hold together. It's also not orbiting—its other end is nailed to the lunar surface.
- sathackr 7y agoWell I started thinking about it more. If it's orbiting at the speed of the moon, it's going slower than geostationary orbit speed. So its tendency will be to fall towards the earth. But since it's attached to the moon, this won't happen. Not sure how much station keeping would be needed to hold this in place. Also will have to deal with collision risks with objects in geostationary orbit. Though I don't think geostationary orbit is a particularly important factor. Could probably be a few thousand Km above geostationary orbit without any significant adjustment to their plan.
- sfjailbird 7y agoWonder how fast the 'elevator cart' would be able to move. Considering that it takes a rocket several days to reach the moon.
- ed312 7y agoMost of the time the rocket isn't firing - you have a few minutes of burn to change your delta v, then you just gotta sit and wait before decelerating into orbit (or landing). Assuming the cart was attached to a powered cable you could in theory constantly accelerate until half way, then constantly decelerate. Possibly this would allow you to make the trip faster (unless you had humans on board, then you're probably stuck with short accelerating bursts).
- brians 7y agoI'm pretty sure humans can take 1 g continuous.
- pmontra 7y agoI'm not sure if the cable can take it: 1 g yields pretty large speeds quickly. Somebody already made the math at [1] [1] https://space.stackexchange.com/questions/840/how-fast-will-1g-get-you-there/5016#5016 https://space.stackexchange.com/questions/840/how-fast-will-...
- black6 7y ago> it takes a rocket several days to reach the moon That's using an unpowered transfer orbit. Burning the whole time would be considerably quicker (and be extremely inefficient).
- wbhart 7y agoDoes someone know what the difference in deltav would be to get to geostationary orbit from earth vs getting to lunar orbit from earth? A citation would be helpful. I've tried looking this up, but from previous comments on this paper, I infer that I am misunderstanding something.
- t_fatus 7y agoGTO: ~11.5 km/s GEO: ~14 km/s (but you don't need that speed since the end of the cable is much slower, orbit period of ~28days instead of 24 hours) GEO <-> moon surface ~3.2km/s superbe reddit source: https://www.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/ https://www.reddit.com/r/space/comments/1ktjfi/deltav_map_of...
- wbhart 7y agoThanks but that's not what I asked. I asked what is the difference in delta-v between getting from the surface of the earth to GEO vs getting from the surface of the earth to Lunar orbit. The answer is, there is almost no difference.
- t_fatus 7y agoWithout considering the fact that the orbit of the Moon is not circular, this only helps reduce the delta-v needed to go from the surface of the earth to the surface of the moon by ~3.2km/s, but we still need ~12-14km/s to go to GTO/GEO.
- Barrin92 7y agoi think the bigger upside here is that getting humans into orbit and then to the moon via elevator is likely safer than repeated landings back and forth.
- t_fatus 7y agoHowever since the moon period is not the same as a GEO period, maybe the fact that you could juste 'catch' the end of the cable before falling back to earth without having the speed to maintain at GEO could help you save some delta-v.
- extropy 7y agoThat's essentially what GTO is - an orbit going close and fast at one side and going high and almost stopped at high side. Going directly up means over 1h of fighting earth gravity. So need Isp > 3600. Much cheaper to go for orbit.
- logfromblammo 7y ago
- ColinWright 7y agoThe comment[0] I made a previous time this was submitted[1] > One major problem with the classical Earth based Space Elevator is the problem of security. It wouldn't take much (relatively speaking) for a terrorist organisation to create a credible threat. > A Moon-based Space Elevator wouldn't have that problem. [0] https://news.ycombinator.com/item?id=20977269 https://news.ycombinator.com/item?id=20977269 [1] https://news.ycombinator.com/item?id=20977142 https://news.ycombinator.com/item?id=20977142
- jobigoud 7y agoThe cable is held by tension from the Moon anchor point right, so I wonder about ramming a satellite a few hundred kilometers above the endpoint. If the cable is severed in this way, will the loose end fall straight to Earth causing damage? It's not itself in GEO orbit, it's moving at Moon orbital speed and pulled by Earth gravity. So I feel it should fall pretty much straight down.
- ColinWright 7y agoYes, clearly there are failure modes that can be provoked, and breaking the cable close to the Moon's surface will result in this thing falling to Earth from a great height. But most terrorist organisations short of governments won't have the capability to provoke such damage, and it's likely that most of it will burn up on re-entry, and possibly can be designed explicitly to do so.
- s1artibartfast 7y agoI think it would easily burn up in the atmosphere. With <1mm in diameter it has a huge surface area.
- SaturateDK 7y agoWas on HN 10 days ago: https://news.ycombinator.com/item?id=20895443 https://news.ycombinator.com/item?id=20895443
- timthorn 7y agoZephyr Penoyre (one of the paper's authors, then at the IoA in Cambridge) gave a talk about his proposal for a Moon-tethered spaceline earlier this year, and is available here: https://upload.sms.cam.ac.uk/media/2921572 https://upload.sms.cam.ac.uk/media/2921572 The talk starts with a polemic about the way research is done, but the physics starts about 16:40.
- dkrudy 7y agohttps://what-if.xkcd.com/157/ https://what-if.xkcd.com/157/ A fire pole would be slightly cooler.
- yk 7y agoFrom the paper [0]: > Values taken straight from Wikipedia. :) [0] https://arxiv.org/pdf/1908.09339.pdf https://arxiv.org/pdf/1908.09339.pdf
- kerkeslager 7y agoI have only been following space elevator research cursorily, but it seems to me that this proposal lacks the most compelling reason for building a space elevator: breaking the bonds of Earth's gravity well. The most expensive part of space travel now is getting from the earth's surface to a stable orbit, and a space elevator from the moon does exactly nothing to reduce this cost. It does still have some benefits, i.e. if I'm not mistaken you could still use this elevator to "slingshot" spacecrafts on interplanetary trips, and it would make it cheaper to get to and return from the moon. But it's unclear (to me) whether these benefits could actually be realized when the cost to get to the space elevator in the first place is still so prohibitive. I guess what I'm saying is that this is just the cost analysis, not the full cost/benefit analysis. The costs may be a lot less than a space elevator from the surface of the earth, but the benefits are a lot smaller too.
- skj 7y ago> and a space elevator from the moon does nothing to reduce this cost. How do you figure? My extensive Kerbal Space Program experience tells me that freeing oneself from the moon's gravity well is far cheaper than doing the same from the earth, and then you're approximately MGH of the way to freeing yourself from Earth's well.
- luxuryballs 7y agoPerhaps you jest but clearly we can’t launch anything from the moon until we bring it there, from Earth.
- flopunctro 7y agoUnless it's something that was mined there, like Helium-3 or some other mineral resource that we may find it's cheaper to extract from the moon.
- wallace_f 7y agoYou need more dv to get to the moon than to leo. An elevator helps with this.
- davidhyde 7y agoOne disappointment with space elevators is the speed at which you can safely travel along them. For example, if you were to travel at 1000 km/h it would take 15 days to get to the moon and just under 2 days to get to geostationary orbit (if there was also an elevator for that)
- gameswithgo 7y agoThat might be disappointing for human travel, but for cargo its great. As long as throughput is high the latency is no big deal.
- perl4ever 7y agoBut you can't get high throughput unless you have a large capacity in terms of mass. It's easy to say "cargo", but if the only cargo it can carry is a flea, not so much.
- toss1 7y agoDisappointing in one way, but in another, it seems like it would be extraordinarily pleasant to be able to enjoy such a journey for a while, perhaps like old trans-oceanic cruise ships...
- extropy 7y agoyou don't need to hold on to the tether all the time. Linear motors on the car and embedded metal strips every 1 km and you have a Lunar rail gun :) In practice the rotational speed difference at different altitudes will make it a bit more complex. But nothing that cannot be solved.
- deleted 7y ago[deleted]
- drakythe 7y agoNon scientific observation: The Earth and Moon are not a consistent distance apart. XKCD What-If 157 (https://what-if.xkcd.com/157/ https://what-if.xkcd.com/157/) neatly illustrates this with the idea of connecting a pole from the earth to the moon, noting that "it's enough that the bottom 50,000 km of your fire station pole would be squished against the Earth once a month". I realize XKCD isn't precisely accurate, but even if 50,000 KM is a /rough/ estimate Geostationary Orbit Height is still around 35,785 km, significantly less. As the moon and earth move closer this Lunar Space Elevator would need a winch capable of taking in 50,000 KM (or perhaps less, but not much or the earth's gravity would become much stronger on the 'station' end and the rope's strength calculation would be off) of "rope" or we're all gonna have a bad time.
- andyford 7y agohow to get to moon without a rocket: 1. go to moon and install thin wire on moon and dangle it toward earth 2. use a rocket to reach wire
- danschumann 7y agoLet's not call a 200,000 mile, multi billion dollar cable "easy", but let's say it's doable, important, and absolutely necessary!
- tiku 7y agoIs there a sweet spot where both gravity's will pull it towards eachother?
- jacquesm 7y agoThe 'sweet spot' is called the Lagrange point. https://en.wikipedia.org/wiki/Lagrangian_point https://en.wikipedia.org/wiki/Lagrangian_point
- adhoc32 7y agoHow about moving stuff _from_ the Moon back to Earth. Harvesting the Moon for rare materials is going to be relatively cheap.
- jacquesm 7y agoWhat rare materials would these be? The only thing that comes to mind at the surface would be Titanium but even there the economics would probably not make sense if your goal is to use the material on Earth.
- adhoc32 7y agoI have no idea. Just trying to make a point for the utility of the project. Maybe rare earth elements or something else yet to be discovered?
- MagnumOpus 7y ago> What rare materials would these be? Every material is rare outside of gravity wells. Even plain steel, aluminium or magnesium cost >$1000/kg if you want them delivered to geostationary orbit. So this material would not be for earthbased construction, it would be for space factories, space-based solar microwave powerplants, spaceships etc.
- kerkeslager 7y agoSo if the elevator from the moon extends toward earth and is held in place by Earth's gravity... why stop at geostationary orbit height?[1] Wouldn't you want to extend the elevator as close to the earth as you could go? It seems to me that the closer to the earth the elevator goes, the more Earth's gravity keeps its location stable, and the easier it is to get from Earth's surface to the tip of the elevator. It seems to me you'd want to stop the elevator just shy of the strength limitations of the cable material (with some margin of error). [1] I suspect the article may just be wrong about this, since as others have pointed out, the moon has an elliptical orbit that is not geostationary.
- ARandomerDude 7y ago*Assume the ball and the man are point masses, the man is standing on frictionless ice, and there is no drag when the ball is thrown.
- deleted 7y ago[deleted]
- marcosdumay 7y agoI imagine it's because stopping upper than GEO clears the plan from any thinking about debris. A lower cable would cross GEO twice a month at a huge relative speed. There are a lot of things there to hit the cable.
- excalibur 7y ago1. Build a space elevator anchored to the moon. 2. Mine raw materials on the moon. 3. Send them over the elevator piece by piece to earth orbit. 4. Assemble the counterweight for an earth-space elevator in orbit. 5. Have TWO space elevators, one to get you to orbit, another to take you to the moon. 6. Colonize the solar system or whatever.
- Apofis 7y agoThe moon has a ton of deuterium which could be used for all sorts of things, nuclear power plants and possibly future propulsion tech for example.
- wolfram74 7y agoDeuterium is abundant on earth as well. It's tritium and helium3 that's unusually abundant on the moon. But it's the result of solar wind deposition over copious amounts of time. And it's one of the dumbest reason to mine the moon. You can run the math the flux of those elements from the solar wind is minuscule. The area you'd need to harvest for a reliable steady state is huge. You'd be better off putting up solar panels, energizing a rail gun and launching more solar panels into space made from lunar silica.
- Apofis 7y agoOkay, railgun it is.
- vinaypai 7y agoGetting the counterweight to orbit is not the hard part of building an earth space elevator. The hard part is the 36,000 km cable from the surface of the earth to geostationary orbit that can support its own weight against earth's gravity. There are a few experimental materials like carbon nanotubes that have the right tensile strength to weight ratio, but we aren't anywhere close to making them in more than microscopic lengths.
- 7y ago
- codesnik 7y agoif the tether would be visible in sun light, and because of eccentricity of moon orbit not always pointed directly to earth, it could look interesting from earth.
- detcader 7y agoSo inexpensive: Only a few billion dollars not going to people and communities who actually need it.
- jaimex2 7y agoThey'd just blow it on booze and drugs right?
- detcader 7y ago"And you know lately, I've been thinking about how I love Jesus / Because Jesus was a dirty homeless, hippie peace activist / And he said, 'Drop out and find God' to anybody who would listen / While turning water into space bags..."
- HenryKissinger 7y agoI'll believe it when I see it.
- umvi 7y ago> Future moon travelers will still have to ride a rocket, though, to fly up to the elevator’s dangling point, and then transfer to a robotic vehicle, which would climb up the cable all the way up to the moon. And... how long is that going to take? A few months? A year? 200,000 miles is like going the circumference of the earth 10 times and I can't imagine a machine attached to a pencil-thin cable could go very fast
- hguant 7y agoIf you assume the cable car is moving at a constant 60 miles per hour, about 4 and 1/2 months (138 days). The current fastest elevator in the world (in the Burj Khalifa) moves at 22 mph; taking that up would take you about a year. However, I'm told by a friend who used to work at Otis (the company that made the Burj Khalifa elevator) that the limiting factor on elevator speed is the comfort factor - there's a hard cap on the acceleration a standing person can comfortably take, and the course of the elevator is generally pretty short, so you don't have time to build up a decent head of speed. Presumably we can do a little better than that
- jaclaz 7y agoAs a side note, usually cables used in lifts/cablecars/cranes/etc. have a 5x (or even in some cases higher) factor of safety, i.e. the cable needs to resist at least 5,000 Kg of traction in order to be used for a 1,000 Kg weight. Part of this high factor is because cables wear down during use (and they are usually inspected for all their length every 6-12 months), particularly when relatively high travel speed is used.
- codeulike 7y agohttps://what-if.xkcd.com/157/ https://what-if.xkcd.com/157/
- vinaypai 7y agoIt is not the fault of the students who wrote the paper, but this is an exceptionally good example of terrible science reporting in popular media. Practically every sentence of the article is wrong including multiple errors in the title. > Feasible & Inexpensive The paper says "Building a spaceline would be a huge engineering challenge, stretching the limits of current human capacity - but not exceeding them" which is a far stretch from "feasible and inexpensive" > Scientists Find Second year graduate students > In a paper published on the online research archive arXiv An as yet un-peer-reviewed pre-publication draft that is being prepared for submisson --- it says that right on top of the first page. > After doing the math, the researchers estimated that the simplest version of the lunar elevator would be a cable thinner than a pencil and weigh about 88,000 pounds They they actually said: "Let’s say such a line was made of a cable with a0 =10−7m2: its total mass would then be around 40,000 kg.". So yes, they're right that it would be "thinner than a pencil". A cable with diameter section of 0.36mm is definitely "thinner than a pencil". (They are misquoting them saying thinner than a pencil lead... presumably referencing the lead in a 0.5mm mechanical pencil, not the lead in the regular pencil). So yes, you could spend billions of dollars to build an elevator that could lift ~100kg off the surface of the moon to GEO, and take months to years to do it any any speed you're likely to achieve with a solar powered elevator tethered by a 0.36mm thick line.
- m3at 7y agoGood points. For anyone interested in skipping the superfluous and sensationalizing article, here is a direct link to the paper, avoiding the embedded tracking link: https://arxiv.org/abs/1908.09339 https://arxiv.org/abs/1908.09339
- phil248 7y ago"stretching the limits of current human capacity - but not exceeding them" That means "feasible". As for inexpensive, it may be a poor word choice, but the alternative is launching rocket after rocket in to space, which is one of the most expensive things humans do.
- opencl 7y agoThis is not an alternative to a rocket. It goes from geosynchronous orbit height to the moon, so you still need a rocket from earth to the elevator. It enables the use of smaller rockets rather than no rockets. With a probably optimistic ~billion dollar pricetag for something able to move 100kg. You would need to launch an awfully large number of rockets with tiny payloads to the moon for this to be a net cost savings.
- lidHanteyk 7y agoWouldn't a skyhook work better on the Moon?
- mLuby 7y agoLot of talk about how 1. a Moon elevator is pointless without an Earth elevator, and 2. we can't build an Earth elevator with today's technology. However we can build an orbital ring around Earth with today's technology, and it'd be much better than space elevators. [Video] https://youtu.be/LMbI6sk-62E?t=254 https://youtu.be/LMbI6sk-62E?t=254 [Paper] https://jenda.hrach.eu/f2/Low%20cost%20design%20of%20an%20orbital%20ring%20-%202017-1.pdf#page=5 https://jenda.hrach.eu/f2/Low%20cost%20design%20of%20an%20or...
- empath75 7y agoThat paper doesn't strike me as being particularly credible.
- dghughes 7y agoWould the Earth end still be in geostationary orbit even with a variation of the Moon's orbit by 43,000 km? And if the Moon end snapped would that mean the entire 380,000km cable would crash to Earth? How much weight and what velocity would it be? Crazy!
- sudhirj 7y agoIt's 40,000kg, so about 400 heavy people or a handful of elephants. Might not be fun if you're under it, but not particularly damaging to the planet.
- dghughes 7y agoBut what velocity would it be traveling? Project Thor aka "the Rods from God" concept is a satellite with 20'x1' 76,000 lb (34,000kg) tungsten rods. No explosives just pure mass and kinetic energy. From low Earth orbit they would travel at Mach 10. Supposedly at impact each rod would release the same energy as a small nuclear bomb.
- ethagknight 7y agototally unrelated but is there an opportunity or reason to tow a load to space via cable behind a "rocket tractor-trailer" instead of rockets pushing from behind? Maybe the tractor is a quadcopter or octocopter but rockets instead of electric props. Rocket engines would need to aim their exhaust plumes outward slightly to avoid melting the tow cable, but it would seem like a tow cable could provide some level of suspension (stretch) to the load, reduce structural requirements since materials dont require stiffness in tension. Maybe there is no benefit compared to just pushing the load as is traditional.
- mesozoic 7y agoOk could be good but the real issue is leaving earths atmosphere.
- dmckeon 7y agoFirst sentence of the paper: > 1.INTRODUCTION For a vehicle travelling in empty space it’s momentum, as well as it’s energy, comes from it’s fuel. His, hers, its - are all possessives. This is why one should have papers for publication, a CV, or a résumé proofread by someone who can spell correctly and understands grammar. Spell-checking software is fine, but it will not catch everything. If it is important, read it aloud to yourself, then get a friend to read it aloud to you. Yes, here the intended meaning is obvious, but this left me wondering about the accuracy of the rest of the paper, which is not a good start for any reader of anything written.
- thecleaner 7y agoI think given the lack of precision in this article it is better to replace the sensational news article with the actual arxiv paper.
- Alex63 7y agoNow that's a zip line!