Bill Phil
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Posts posted by Bill Phil
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4 minutes ago, sevenperforce said:
That's kind of like saying that an English longbow would scale up well, so long as you had a giant to bend it.
Yeah. But WEAVs main issue is energy sources - and there are some clever workarounds that could solve the problem. But those may have their own issues.
At least in this case the giants in question could theoretically exist in the future.
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Just now, sevenperforce said:
Voltages required are far too enormous to be workable, and contrary to the inventor's claim it would not scale well at all due to the required energy density.
It “scales well” because it can be scaled up without too many changes to the flight dynamics. But to perform well it needs immense energy.
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We could, and the rocket would be much better. We can get larger specific impulses for both kerolox and hydrolox, so a similar vehicle would be even better today.
Not only that but the staging affects efficiency - SLS's use of hydrolox as a core stage hurts its performance. Using kerolox as a first stage would be more efficient.
It's entirely possible, and a modern day Saturn-V like vehicle would perform better than the original. More efficient rocket engines, smaller computers, and a better understanding of the dynamics of flight.
It wouldn't really be a Saturn V, it'd be a brand new rocket.
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Yeah that’s a common occurrence.
If it’s a documentary that’s speculating about alien life it’s not that much of a documentary - it’s more likely to be a popular science (not the specific publication, I mean the genre) production. It’s probably meant to be “infotainment” or something along those lines.
There’s a lot of meddling between what experts/science advisors say and what’s actually shown in a production.
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38 minutes ago, Spacescifi said:
Is not minimag orion just a magbetic nozzle with fusile or fissionable pellet propellant?
Pretty much beats all other nuclear tech as an orbit to orbit craft?
Mini Mag Orion isn’t an NTR. NTRs are actually a much more well understood technology as well.
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Apparently Project Rover found that DUMBO reactors could compete with chemical TWRs, but the higher complexity meant that it would be more difficult to develop and more likely to fail in flight.
However, with modern modelling software and material advances a modern DUMBO-like NTR could probably be built. And with good performance at that.
Though it probably wouldn't be used to launch unless it could be well shielded.
Though maybe a Titan III like vehicle could work - use SRBs to get the DUMBO core to a high altitude to reduce the radiation exposure on the ground and some velocity. Of course the risk of a reactor in flight would still be present in the event of a launch failure. Liquid boosters may be a better bet though.
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Nope. I’m still shaving.
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Quote
...it shall rearrange things, in which the earth is born in the heavens and the moon is born on the earth.
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1 minute ago, ThatGuyWithALongUsername said:
...except, of course, those orbits wouldn't be low anymore.
If you want a REAL low orbit then you're gonna have other problems as mentioned above.
Yes, of course.
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Reactor: Online
Sensors: Online
Weapons: Online
All Systems Nominal
Oh yeah. It's MechWarrior time. Maybe I'll finally beat MechWarrior 3...
1 hour ago, benzman said:My all-time favourite game is doom2. Of course, it will not work on win 10, nor will any of my other old games for that matter. If anyone can tell me exactly how to get it going on win 10 I would be very gratefull.
Oh, that's easy. Get DOSBox, should be able run the old doom application.
If that doesn't work try out one of the source ports - ZDoom or GZDoom are the most popular I think, but others exist.
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3 hours ago, sevenperforce said:
Once you get really close (e.g., orbits deep within the radius of the former sun), things get wonky, but the gravitational field of the Sun at any appreciable distance IS the gravitational field of a stellar-mass BH.
Same with Earth. If Earth suddenly collapsed into a black hole, it would be about the size of a dime, but the moon and the ISS would continue to orbit unchanged.
Well the oblateness of the Earth would no longer perturb the ISS (and other satellites). So precession would no longer be present in low orbits.
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Not substantially.
There might be some GR affects from it and of course the side affects of losing the light of the Sun - but the actual trajectory won’t change too much.
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1 hour ago, Nuke said:
for launchers i tend to make the case leave the reactor on the ground, make hydrolox. you can always build bigger rockets. especially large multi-stage reusable rockets. once in space all bets are off and you can use whatever you want from the nastiest of hypergolics to the cleanest fusion drives. though you might have a nuclear exclusion zone for really nasty drives like fission fragment and orion (for the latter we might be talking in a solar orbit no closer than mars).
actually im curious how far actual exclusion zones would be for various drives. not just to keep fission products from entering the atmo, but also to protect satellites. i dont think there has ever been a study as no one has ever flown a dirty drive in space to the best of my knowledge.
Starfish Prime messed with a bunch of satellites but I think it wouldn’t be impossible to harden future satellites against such a thing - robust in-space infrastructure would make deploying higher mass satellites easier.
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2 minutes ago, KSK said:
Not sure about the details but there's a table further up the page with various engines and (where applicable) different propellants used in the same engine type. Fairly sure that the 410 was for DUMBO with water propellant but I may have misread.
It's a table with ISPs for different propellants assuming 3200 Kelvin.
410 was for water.
I'm not sure how hot DUMBO's core is but nonetheless the thrust would be higher if you were to use water.
Though methane actually has good ISP and would also have higher thrust to weight than LH2. Approximately 600 seconds at 3200 K and higher molecular weight. So higher specific impulse without much sacrifice for thrust.
Though it's probably less environmentally friendly. A specific ratio of LOx to LH2 can probably achieve the same performance.
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6 hours ago, KSK said:
If you just want to get to orbit, water will do fine.
Assume we're using DUMBO nuclear thermal engines.
Using water as a propellant, and assuming the Project Rho figures are correct, a 5 ton engine will give you a thrust-to-weight ratio of a little over 71 and an ISP of 410. That T/W appears to be an average - three different DUMBO versions are listed with T/Ws of 20, 55 and 130. But lets roll with 71 for the sake of argument.
From that link it appears that DUMBO uses liquid hydrogen - which would imply a higher T/W when using water. 130 may be much more realistic in that sense.
However the 410 ISP may be a bit high. Nuclear Thermal generally operates at lower temperatures than chemical rockets - so the ISP will be lower as well than a comparable rocket with water exhaust - that is the performance may be closer to kerolox.
But perhaps a LANTR DUMBO system would work where the oxygen/hydrogen mix is changed as it gains altitude and velocity - losing thrust but gaining ISP. All of the LOx is used up like a first stage, and then it continues with just hydrogen past some point. So really good engine T/W for launch and the early ascent where fighting gravity is the most important aspect and then good T/W but really high ISP for when getting up to orbital speed is the priority.
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25 minutes ago, wafflemoder said:
I've only ever seen Orion figures above 10000s when using thermonuclear hydrogen bombs, which do get really efficient with size. Pure fission weapons are pretty terrible, which is why they were quickly superseded by thermonuclear weapons.
Looking through some of the papers on Mini-Mag Orion, they seem to top off at 25000s using Curium 245 as the fissile material, with values around half that for plutonium and uranium based charges.
The 482 ks value for NSWR probably represents the theoretical maximum, in much the same way H-bomb orion can have a theoretical maximum ISP of 100 ks.
The Mini-Mag Orion papers don't use fusion boosting in the pulse units - which would boost the fission yield significantly. Many fission bombs do the same. They do use a small amount of fusion for the initial neutron source, but not a large amount.
Fusion boosting is essentially having a hollow fissile core with fusion fuel inside that undergoes fusion during the explosion - releasing more neutrons and thus causing more fission. This would benefit Mini-Mag quite well. The papers assume a 10% burnup fraction for the Curium target - this can be theoretically increased much more, likely to 30% or even 40%. This would greatly increase the available energy, and thus the specific impulse.
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45 minutes ago, wafflemoder said:
Nuclear saltwater rockets can actually be made much smaller than orion drives, as like minmags they are not limited to the minimum size of self contained explosives.
Regarding specific impulses: Pure fission Orion can have isps between 1800-4500s, Thermonuclear Orion can push this up to 7500-12000s, MinMag Orion can do 9500-16000s, NSWRs can do 4000-8000s (though I've also seen values of 67000s and 482000s)
Pure fission Orion can potentially reach 12000s. This is because the bomb yield per kilogram actually improves with higher bomb masses.
Mini-Mag can reach 16000s, yes, but it can actually exceed 20000s and likely 30000s if fusion boosting is used (increasing the fission burnup rate).
I've never seen anything to indicate NSWR ISP that high, though if it does exist the temperature would be immense and would require magnetic confinement, and potentially have low thrust unless you have really good radiators.
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27 minutes ago, wafflemoder said:
In terms of surface to orbit applications, nuclear saltwater is probably the best you can get for a self contained launch system. It has better performance than orion (traditional, thermonuclear, or min-mag), operates under continuous thrust (to vastly reduce structural and aerodynamic loads), and would have far simpler plumbing.
Nuclear Saltwater doesn't actually perform as well as Orion, depending on the chosen Orion vehicle. Remember, NSWR gets around 6000 seconds of ISP, and advanced Orions can easily double that assuming the original papers were correct. It may be possible to improve NSWR performance, but it's also possible to improve Orion performance. And it certainly doesn't outperform Mini-Mag, which is theoretically capable of even higher ISP if it used fusion boosting.
It's also much more difficult to build - at least Orions don't try to actually contain their nuclear detonations or if they do they use magnetic nozzles and much, much smaller detonations.
32 minutes ago, wafflemoder said:Of course vacuum cable maglevs of various sorts (launch loops, orbital rings, startrams, etc) would be far superior options, but it seems non-rocket launch methods don't count for whatever reason.
Those are methods of getting stuff into space, not actual space vehicles. That said, they're vastly superior to rockets in many ways, provided we actually build them. But we don't call seaports ocean-going ships. Infrastructure is not the same as a vehicle - at least for now. Orbital skyhooks and other such things do combine vehicles with infrastructure.
24 minutes ago, Spacescifi said:Yes... but my ideal version of a scifi spaceship can takeoff to orbit and land on an Earth world repeatedly.
Your question is what is the best we could build now. And the best we could build now just can't do that. Even Mini-Mag is stretching the "now" part a bit far. Now, theoretically, if we could build gas-core fission rockets then we can have closed cycle gas core rockets for landing and some kind of Z-Pinch drive like Mini-Mag for space. You don't need much delta-V since the Mini-Mag can slow you down over the target - maybe 2 km/s.
Basically two engine systems:
1.) Closed Cycle Gas Core NTR: Take off and landing
2.) Fusion Boosted Mini-Mag Orion: Finalizing orbit and some in-space maneuvering
This vehicle would suffer the worst of both worlds, however, as it would need to stow its space drives and other things to land. A separate dedicated landing vehicle would be far more appropriate.
Now if you just want to take off and land and use some other system to get around space itself and not a realistic drive, you can just use number 1 above.
QuoteBased on my accumulated knowledge so far, the best option would be an antimatter thermal saltwater rocket.
Basically have a rocket that is mostly water tank, with some payload and crew space to spare, and a sufficient amount of anti-iron suspended in magnetic fields to add to the water propellant as needed.
1.) This thread is about the now. Antimatter is out of the question except for - and this is a very big stretch - antimatter initiated nuclear systems.
2.) Saltwater isn't the best choice. The reason it works for nuclear salt water is that the specific salt used contains fissile material, and is not the same kind of saltwater found in Earth's oceans. Either use normal water or some other propellant.
3.) Anti-iron is even more difficult than anti-hydrogen and has worse performance than electron-positron annihilation because you will not get perfect annihilation due to the more complex atom.
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20 minutes ago, Spacescifi said:
Mini-mag works best in space. In air heat will conduct and probanly damage the magnetic metal lattice nozzle.
So.... based on your and my info, the best ship we could build is... two.
My concept would be to use chemical rockets to loft the Mini-Mag to a suitable altitude where it can then enter orbit under its own power.
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5 minutes ago, Dragon01 said:
Yes, it is. Robots can function a long time, but they work very slowly. For all that time, you need to keep a fully staffed mission control team on station. You need to factor in these costs, too. There's a lot more to space mission costs than just the launch. Humans can get more done, faster, than anything robotic we can currently design. Even if we've had a Saturn V's payload, and were going to the moon.
And you need hundreds of thousands of workers to get the manned mission off the ground to begin with, with another few thousand (maybe even more than ten thousand) on standby for whatever problems might crop up.
A probe on the other hand? You just need to design and build it. Then you just need to operate it and have the DSN talk to it and keep track of it - and not even that if you have autonav. Then you just need to talk to it. A small team for trajectory analysis. The rest of the team on the ground would be scientists. Maybe a few hundred for a big mission like Cassini.
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3 minutes ago, Terwin said:
The classic Orion will blow itself up in an atmosphere due to the atmospheric over-pressure wave that can go around the pusher plate and crush critical components, not to mention the atmosphere causing the sheet of metal being sprayed at the pusher plate being disturbed by atmospheric effects. (the first bomb does not take the Orion super-sonic, so that blast-wave *will* engulf the craft in a fireball and over-pressure wave if in an atmosphere. The pusher-plate only works as a shadow-shield if there is nothing else around to carry/reflect the wasted nuclear energy)
While a nuclear pusher-plate looks like a great idea for deep space, I am trying to convince @Spacescifi that an antimatter fueled pusher-plate surface-to-orbit design is unneeded, incredibly wasteful, and will probably irradiate your launch site.
I've never seen any indication that the classic Orion will blow itself up due to over pressure.
Not only that but the first explosion was intended to be a smaller chemical explosion to push the vehicle into the air and not a nuclear explosive. The "first bomb" is chemical.
And even if that were the case many proposals called for using chemical boosters to loft the vehicle to a higher altitude where air is much less dense, which completely voids the problem of over-pressure provided sufficient altitude is reached.
Antimatter is more suited for magnetic nozzles - especially since if you've mastered antimatter containment then a magnetic nozzle is likely easy to do.
QuoteChemical Rockets benefit tremendously from increasing the scale of the vessel. While a chemical rocket will be larger than a pusher-plate design with a similar payload, I am not aware of anything that would prevent a chemical launch vehicle for any payload that could be handled by a pusher-plate design. And if you are using antimatter for the pusher-plate fuel, Chemical will be cheaper and probably safer.
Rockets need to be large enough for Steel to make sense, see Starship and Super-heavy for rockets finally getting large enough that steel makes sense over aluminum and composites.
Pusher-plate designs use steel because they are large enough for it to make sense, and any chemical rocket made to deliver the same payload to orbit will be large enough to warrant similar materials.
Surface to orbit has lots of issues for Orion, and is well within the capabilities of chemical rockets. While Orion may be the only option for a rapid transit to Pluto, it is a sub-standard option for reaching orbit, and an expensive calamity waiting to happen when you power it with anti-matter for a surface-launch.
Chemical rockets do benefit from scale. But so do Orions. In fact, Orion vehicles only get more efficient the bigger they are. Millions of tons becomes easy when you have nuclear bombs pushing your spacecraft.
There are actually quite a few limitations on chemical rockets. Even SLS, a rather sensibly sized rocket compared to Sea Dragon, has issues with hydrostatic pressure. It's too large for the engines. This can be overcome. However, the hydrostatic pressure will eventually increase the hoop stress of the propellant tanks, potentially beyond the yield stress of the materials used. There is a size limit for chemical rockets. And that limit is much lower than the millions of tons that are at least theoretically possible with nuclear pulse. The square cube law means more propellant yes, but it does not mean you don't have to have more structure. Indeed, the structural mass percentage of the fuel tanks will increase with size past a certain point due to the large hydrostatic pressure and the immense forces involved.
Yes, rockets need to be large for steel to make sense. But eventually the structural mass required increases faster than the benefits of increasing the size. Eventually the rockets start to perform worse. Far worse.
Pusher plate designs use steel because they are less sensitive to weight. Shaving off as much mass as possible isn't the priority. So steel is useful and cheap to use. The classic 4000 ton Orion is roughly similar in mass to the Saturn V - yet it uses steel. This is because nuclear propulsion is that much more powerful.
Orion is explicitly amazingly good at surface to orbit - that's what it's best at. High thrust and specific impulse in the thousands of seconds means huge payloads to orbit. It's actually a somewhat mediocre interplanetary drive - it's just the easiest one to build. Mini-Mag is better, though, and Medusa should perform well too.
Anti-matter is a bad idea period for vehicles - there are almost always better options.
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9 hours ago, IncongruousGoat said:
I find the Antarctica comparison not particularly compelling, for several reasons. First, Antarctica is actually worse (i.e. less habitable) than Mars by some measures. There's less available sunlight, especially during the winter months, meaning less consistently available solar power, and Earth's atmosphere is much thicker than Mars's, which corresponds to faster heat loss.
When we start discussing the habitability of places like Mars or the Moon we inevitably reach the crux of the issue - the amount of protection required to keep a human alive. With no protection, a human on the Moon is dead in minutes. A human on Mars has a similar fate. A human in Antarctica will likely be dead in minutes as well, depending on their specific location - but not from lack of oxygen. Rather, a human will die from the cold. Thus, keeping a human alive in Antarctica is measurably easier than on Mars - no need for a pressure suit, just temperature regulation.
But even then - moderate temperatures have been recorded in Antarctica, nearly room temperature at that though those are record highs. Average coast temperature is just -10 Celsius, which is warmer than winter in Siberia and the Yukon territory.
This is why Antarctica is more habitable than Mars - human beings can technically survive there for at least some time. We don't need a pressure suit nor an oxygen supply, just protection from the cold, to survive. At least in the short term.
You mention the lack of solar power - which is true. But solar isn't our only option. In fact, the colder environment at Antarctica can probably be useful for making heat engines more efficient than in other locations. A nuclear reactor would be a great option. And if the usability of solar power is a measure of habitability, then where I live isn't that habitable either - because it's too darn cloudy most of the time.
Essentially the lack of solar is practically a non-issue, and the faster heat loss can be dealt with by using clothes and heating.
QuoteBeyond that, though, there are several international treaties preventing any and all exploitation of Antarctic resources for economic gain, by public or private entities. The population of Antarctica is low because, beyond anything else, it's illegal to do anything there other than research. Were that not the case, I'm sure we would see mining and oil towns in Antarctica, and at least one settlement that could be described as a city (to function as a port of entry, among other things). The population wouldn't be high, by any means - but it would be a lot higher than what it is today.
I doubt it. Settling Antarctica would be difficult and expensive. There are resources there, but there are also resources that aren't in Antarctica.
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1 hour ago, Terwin said:
The only thing a pusher-plate launch vehicle does better than a chemical launch vehicle of the same payload capacity is to make your origin uninhabitable. And chemical rockets can be made with greater maximum payload capacity then a pusher-plate using the same materials, because a chemical rocket puts less stress on the materials than a pusher-plate will.
I'm having trouble seeing your reasoning for this.
1.) Pusher plate vehicles do not have to use antimatter, and the classic Orion designs would release radioactive fallout of course. But the amount is manageable, indeed the total environmental damage per kg of payload may be less as similar amounts of "fallout" are released to the environment by other industrial processes (such as oil extraction and refinement - which is necessary for kerosene) and no one bats an eye. It seems unlikely that the Earth can even be made uninhabitable even with a fairly decent NPP launch rate over long periods. Maybe, maybe, there will be a higher rate of cancer. But some models seem to suggest mild benefits for the population as a whole (hormesis models), and nonetheless we do far more damage to human lives with much less useful endeavors.
2.) Chemical rockets can not be made with a higher payload capacity than pusher-plate vehicles unless the pulse units are chemical explosives. Nuclear Pulse Propulsion has specific impulses around 10x chemical even in a rather crude design. With more advanced designs it can be 30x chemical if not higher. And since Orion vehicles were intended to use steel... no one in their right mind would build a chemical rocket out of steel. Except the Sea Dragon - a big dumb booster that deliberately sacrifices performance for simplicity and just uses shear size to overcome the performance losses. And its total mass would have been on the order of 18 thousand tonnes and only deliver around 500 tonnes to LEO. Compared to the 4000 ton Orion design which was 4000 tons and capable of putting 1600 tons into LEO assuming a rather crude Orion drive. Or 14.4 times more payload as a percentage of the vehicle mass. An Orion as big as Sea Dragon with the same isp as the 4000 ton Orion would deliver over 7000 tons to LEO.
Pusher plate drives can be made to put reasonable stresses on the vehicle structure, the performance is so huge that you can afford the mass to reinforce the vehicle. That's the point. Instead of "Every Gram Counts" it's "Every Hundred Kilograms Count", maybe "Every Tonne Counts". Higher specific impulse and high thrust is just that good - the Tyranny of the Rocket Equation is an exponential relationship. Double the specific impulse, and the mass ratio falls by the square root. This means if your vehicle needs a mass ratio of 16 to reach a desired Delta-V, then doubling the specific impulse reduces this to 4. So even if the Orion reports are too optimistic, they are not likely to be any worse than nuclear thermal, and can be expected to outperform nuclear thermal by a factor of 2 reasonably. That still outperforms chemical even with the large mass of the pusher plate.
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2 hours ago, mikegarrison said:
That will happen when the energy required for interplanetary flight is the same as a domestic airplane flight, which is to say, "never".
It's not the absolute energy requirement, it's the energy cost. And the labor cost, and everything else.
And even ignoring that, as humanity accesses more and more energy, the relative energy cost of interplanetary flight will eventually approach the relative energy cost of domestic airplane flights.
Once we have more energy, our options expand.
1 hour ago, Dragon01 said:Actually, I'm not sure about the cost efficiency of unmanned probes. People overestimate their capabilities and data output. Just look at how much, in terms of raw data, we got out of Apollo landings, compared to all unmanned lunar probes before or since. Automation had progressed, but so had manned research equipment. If we could set up a lab on Mars, the sheer amount of data that we'd get, pre-processed on site and transferred at a vastly higher rate than any unmanned mission could hope for, would dwarf everything we'd have learned so far. To gather that data using unmanned probes, it would require years, possibly decades of unmanned operations, and these have their costs, too, which may seem lower, but spread over such a long time, might end up totaling just as much as a manned mission.
Cassini alone provided 444 gigabytes of scientific data. And newer probes will only be better at providing scientific data.
Apollo isn't actually a good example - it was never a scientific program as its main focus. Yes experiments were done, but they weren't the reason they went to the Moon. With an infrastructure that allows regular spaceflight to the Moon we could do far more science there, with or without crews. Only one scientist went to the Moon on an Apollo mission. But if we could actually deploy a few hundred scientists, maybe thousands, to the Moon, along with research equipment? Then we'd be cooking with gas.
Crews will be faster than unmanned rovers, and they have advantages for some specific scientific enquiries. But in general probes are better at gathering data.
However, as preparation for a manned mission and during the manned mission itself, a lot of science will be done to support the mission. This alone would provide immense science. And we get a manned mission to boot.
Whatever Happened To Wingless Electromagnetic Air Vehicles?
in Science & Spaceflight
Posted
Same case for planes and helicopters though.
Of course planes can at least glide. Choppers might be able to try and glide with autorotation, or at least slow their fall.