I am trying to device a spacecraft that is entirely fuel-less; that is it requires no reaction mass. It uses a wormhole-generator for interstellar flight and a magnetic sail for interplanetary transits, but it still needs a way of exiting planetary atmospheres.

so here is my idea: two extremely powerful air breathing engines are used to launch the craft, the momentum enabling it to breach the atmosphere, after which the magnetic sail is deployed for the ship to cruise through space. Could this system work?

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    $\begingroup$ Or, better, a fully reusable SuperHeavy booster + Starship stack carries the spacecraft out of the atmosphere and provides the initial orbital velocity. Talk with SpaceX. $\endgroup$
    – AlexP
    Commented Nov 9, 2022 at 21:23
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    $\begingroup$ Is there really a need for the ship to be able to take off/land on the surface of the planet? It could be assembled in space from ground based components and just carry a fuel using landing module for the transfer of crew and cargo to and from orbit. $\endgroup$
    – Mon
    Commented Nov 9, 2022 at 21:28
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    $\begingroup$ Extremely powerful air breathing engines imply large mass, so does does worm-hole generator which is not really compatible with magnetic sails, at least not without external assist. $\endgroup$ Commented Nov 9, 2022 at 21:35
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    $\begingroup$ Generally air breathing engines like jet turbines or propellers still require "reaction mass" in terms of fuel/energy that they burn. Also, solar sails or magnetic sails are not a free lunch, and unlike with a regular sail, you can't really "tack" against the sun making their usage limited to a very small amount of edge cases. $\endgroup$
    – Dragongeek
    Commented Nov 10, 2022 at 9:46
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    $\begingroup$ Here is an example of such a design from KSP (a space flight simulator). Is it possible? Probably yes. But is it practical? $\endgroup$ Commented Nov 10, 2022 at 12:02

8 Answers 8


The vessel would need to reach escape velocity inside the atmosphere - mach 33. It would need to be made of incredible materials to withstand the forces of that, apart from the ludicrous engines.

I don't really see any advantage of this vs. a rocket assisted ascent. Put it on top of a reuseable ascent stage which returns to earth and you have the same end result - a spacecraft that doesn't carry a rocket engine and reaction mass.

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    $\begingroup$ Also, a rocket wouldn't be hindered by the low air pressure of the upper atmosphere. You can't say the same about an air turbine. $\endgroup$ Commented Nov 9, 2022 at 22:27
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    $\begingroup$ /I don't really see any advantage of this / you neglect to consider THE AWESOMENESS!! $\endgroup$
    – Willk
    Commented Nov 9, 2022 at 22:28
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    $\begingroup$ This vessel will still require fuel to power the turbines. $\endgroup$
    – Tom
    Commented Nov 9, 2022 at 23:53
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    $\begingroup$ Depending on how quickly the magnetic sail can be deployed and how much acceleration it provides, then the ship doesn't need to reach planetary-escape velocity within the atmosphere. It just needs to get clear of the atmosphere. At most it'd need to approach or reach orbital velocity, then once it's in orbit it can deploy the sail and accelerate further. $\endgroup$
    – Salda007
    Commented Nov 10, 2022 at 8:44
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    $\begingroup$ "Put it on top of a reuseable ascent stage which returns to earth and you have [the space shuttle]". $\endgroup$
    – user458
    Commented Nov 10, 2022 at 20:35

Let's talk about this...

This is a Frame Challenge.

Are you trying to force a policy, or are you balancing technology and economics with policy?

When humans ignore economics and technology to implement policy they get... well... weird, bad, not-very-useful results. I remember back in 2003 my brother calling me and asking if it was possible to take advantage of a U.S. government grant program that sought to put retail-grade and retail-cost solar power onto (I kid you not) Walmart's shelves. The program was literally asking for what at the time was magic: a low-cost solar solution that could be bolted onto your roof with no more skill than is required by a hammer to solve your power needs and thereby get rid of all the evil coal, natural gas, and nuclear power facilities.

When I stopped laughing, I explained all that to my brother.

That grant program was an example of ignoring economics (the cost of manufacturing solar arrays) and technology (the ability to build self-contained and sufficiently efficient solar arrays small enough to solve individual household needs) to implement a policy (everything would be green today if we just convince people it's true!).

In reality (and that's a statement that starts bar fights over here in the States), policy, economics, and technology must work together to provide a solution that works today with an eye toward a better solution tomorrow.

Your question kinda feels like you're trying to ignore economics and technology to implement a policy.

A price must be paid

Simplifying things a bit, it takes 3.29x107 joules of energy to lift just one kilogram into orbit. The Space Shuttle on the pad weighs 2,041,166 kg. So we need 6.7x1013 joules to push it into orbit.

You can't argue with that. That's physics. That's the price. What's left is to decide the economic, technological, and political balance that pays that price. If you graph the value of those three variables needed to pay the price, you'll end up with a bumpy surface that trends toward infinity1 as any of the three variables trend toward zero (even for policy... think of it as, "despite what the government wants..."). Rationally, the goal is to find the lowest point on the graph and use that combination of economics, technology, and policy to launch your craft.

Since when are humans rational?

Which brings us to your question. I upvoted @ths' answer because his is the fundamentally correct answer. But I'd like to express it with my favorite worldbuilding.SE quote:

"Can you launch an ICBM horizontally?"

"Sure, why would you want to?" (The Hunt for Red October)

Could you push a ship fast enough with air breathing engines to shoot it into space? Sure! At a price. And it's a pretty high price. Your biggest problem is that air thins with altitude, which means you need to create sufficient momentum lower to the ground, which means you're fighting air resistance longer than you have to... you get the picture.

Science is a... um... somewhat crotchety lady

Let's look at this in a cold-hearted way: you haven't created a fuelless solution. Not for any aspect of what you're doing. Fuel is being burned, you're just not who or what is burning it. In this regard your solutions are like solar power. The sun is burning the fuel, you're just taking advantage of it. And you want a solution like that, right?

Air-breathing engines ain't it. They'll require fuel. A LOT of fuel.

A better solution for you would be to create a space elevator powered with solar power. No fuel in ways similar to what you've already presented. Just attach the ship to the 37,000 km long winch and haul it up to orbit.

1In other words, if you want those joules for free (no economic payment) you need either infinitely capable technology or infinitely flexible policy or both. Do you want it with little or no tech? Infinite cash (so you can build that tower!) and/or infinitely flexible policy (so you can rob your neighbors for the cash to build that tower!). Do you want it despite what the government says? Yup, infinite tech (so you can build it w/o government assistance) and/or infinite cash (to bribe the government!). This all makes sense when you think about it.

  • $\begingroup$ Frame Challenge to your answer: It's not always everything about economics. The Space Shuttle wasn't about economics. Hubble Space Telescope wasn't about economics. The entire process of humans actually going to space weren't about economics. GPS isnt about economics. $\endgroup$
    – Hobbamok
    Commented Nov 10, 2022 at 12:44
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    $\begingroup$ Everything you describe actually is about economics. There's an entire wing of economics that studies "perceived value" and how to gauge it. All of those things exist because someone perceived enough value to talk other people into paying for it. The economic benefits of GPS more than pay the governmental cost. What JBH is describing, though, isn't economics, it's accounting. If it costs X joules to move something, then, in some manner, that many joules will have to be transmitted to that something. You think that the space shuttle came into existence without paying anybody? $\endgroup$ Commented Nov 10, 2022 at 16:29
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    $\begingroup$ @Hobbamok If you don't think the Space Shuttle and Hubble Telescope were materially affected by economics, you don't know very much about NASA. NASA must fight for every dollar it has to spend and it goes to great lengths to balance the cost of progress with the benefit of progress. Even GPS, originally developed for the military, didn't have an infinite amount of money to work with. Please take a college class in economics, then we can have a meaningful conversation. $\endgroup$
    – JBH
    Commented Nov 10, 2022 at 17:15
  • $\begingroup$ @JBH That is a strawman. I said it's not ABOUT economics. You pretend I said that economics don't matter. $\endgroup$
    – Hobbamok
    Commented Nov 10, 2022 at 21:38
  • $\begingroup$ @JBH you may want to check your numbers - nasa.gov/returntoflight/system/system_STS.html claims 2000ton is "liftoff weight", while Wikipedia en.wikipedia.org/wiki/Space_Shuttle_orbiter attributes just 110ton to orbiter itself (I don't think it changes your post materially so). $\endgroup$ Commented Nov 10, 2022 at 21:55

Every vehicle requires fuel

No matter what method it uses to move, every vehicle requires energy. For most vehicles, that energy is properly called "fuel." That's because doing work of any kind requires energy, and energy has to come from somewhere. Fuel stores energy in a compact form that can be released when energy is needed.

Using turbines is not going to make your vehicle fuel-less. Plenty of vehicles today are driven by turbines, and they all require fuel to power those turbines. Some aircraft use turbines, and they need jet fuel. Submarines are driven by propellers, which are just underwater turbines, and they need nuclear fuel.

The truth is that even if your vehicle simply floated in space and never tried to move, it would require some kind of fuel to power the electronics and life-support. Your wormhole generator sounds like it will need fuel, because creating a wormhole probably requires a lot more energy than could be captured using solar panels, even if the panels have 100% efficiency. The magnetic sail will probably require energy because your astronauts will not want to have to venture outside the craft to adjust the sail.

I suspect that what you're really trying to avoid is anything like a rocket engine, which blasts fuel out of a nozzle to generate thrust. That might be doable. But if it is, the resulting vehicle will still require fuel aboard, adding mass and taking up space. And since igniting the fuel and blasting it out the back is the most efficient way to convert the fuel to thrust, and you're avoiding that, your vessel will require more fuel than a rocket.

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    $\begingroup$ What about turbines that are turned by a coiled spring that you wind up before launch? Where is the fuel then, hmm? HMMM?? $\endgroup$
    – Willk
    Commented Nov 10, 2022 at 22:15
  • $\begingroup$ @Willk Phooey! Harumph!! $\endgroup$
    – Tom
    Commented Nov 12, 2022 at 0:01

I think I see what you're getting at. Let's presume you're getting zero-point energy from your wormhole generator, so you don't need a power source.

Re-wrote based on the comments

Air pumped scram jets

The trick is to get the PSI out the back end greater than what you plow into at Mach 33. The advantage that fuel gives you is that a small amount of liquid gets expanded into 500x the volume when it burns, creating a very high PSI within the reaction chamber.

Yes, jet engines contain turbines. They don't propel the exhaust, they are spun by the exhaust. Their role is to makes sure the energy of the expanding gasses is pushing everything in the correct direction. Also, they leverage the pressure of the initial expansion to keep the gasses moving when they're pushed out the back, and to compress the air on the way in.

In order to push a vehicle hard enough without the explosive expansion advantage, you'd basically need to compress air into a liquid, then forcefully ejecting it from the backside. Without the heat generated by burning fuel, your turbines would freeze up from the expanding gasses, so you'd need to radiate some of your zero-point energy into the expansion chamber.

Once your doing that, you are basically imitating a scram jet, except that you're compressing the gas more on the way in, and using magic, ahem, advanced technology to heat it instead of relying on the heat of combustion.

Overall, it's not impossible with unlimited energy. You won't be able to use it to launch your ship from a standstill because you need a high pressure flow of air to get the turbines started.

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    $\begingroup$ You suggest putting energy into compressing the air and getting thrust from its subsequent expansion? Like a continuous bottle rocket? Wouldn't it be more efficient to heat the air up to plasma temperatures with some sort of extreme microwave/RF generator and blow it out the back? Higher temperatures -> greater exhaust velocity -> greater thrust. $\endgroup$
    – BMF
    Commented Nov 10, 2022 at 17:54
  • $\begingroup$ @BMF, No, the bottle rocket thing wouldn't work. Not nearly enough PSI. If you heat normal air up to plasma, then you have less reaction mass to work with, but it would work. What we're describing here is essentially a "scram jet" that uses the supersonic speed of the movement to compress the air for you. My suggestion is that, since you want it to continue working where there's almost no atmosphere, you pre-load tanks with compressed air that will supplement it when it gets out of the lower atmosphere. $\endgroup$ Commented Nov 10, 2022 at 18:12
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    $\begingroup$ I see now what you're suggesting. I think you could do both at the same time and get the most bang for your buck. Cool/compress loads of air into pressure tanks, and then when you want to expel it for thrust, super-heat it to a plasma. (With unlimited zero-point energy, you could get seriously hot temperatures while using magnetic nozzles.) $\endgroup$
    – BMF
    Commented Nov 10, 2022 at 18:20
  • $\begingroup$ I am digging this. You will use compressed hydrogen as lightest. It is a gas as any other so the expansion on relieving compression should do the same work as any gas. Expansion turns the turbines via gears. The gear chamber in which expansion is occurring is not directly contiguous with the atmosphere so there is no water vapor to freeze up. Exhaust is at some distance and sited to prevent ice buildup. $\endgroup$
    – Willk
    Commented Nov 10, 2022 at 22:22
  • $\begingroup$ @Willk, if you're venting hydrogen in an atmosphere, then you might as well burn it. Also, "light weight" isn't a goal when you're talking about reaction mass. The trick is to do the whole thing without actually needing fuel tanks. The compressed air is just what's readily available. $\endgroup$ Commented Nov 11, 2022 at 0:16

If a truly fuel-less launch mechanism existed, don't you think we'd be using it right now?

Even air-breathing engines require fuel to heat and expand the air for thrust.

Option 1:

Your spacecraft deploys a space elevator down onto the planet. This'll probably require some preparation time. If your spacecraft has some manufacturing capability, it may harvest materials in asteroids and such to construct the cable and counter-balancing mass at +geostationary altitude (which could probably just be a raw, unprocessed asteroid tethered to the cable).
The spacecraft may aerobrake in the atmosphere if it is capable of doing so, but would need to ride the space elevator for perhaps a day or so to reach orbital altitude + velocity again.
For a fuel-less ride, the space elevator could have a matrix of solar panels at GEO for solar energy.

Option 2:

Your spacecraft deploys a rotating sky hook. Sky hooks are a type of momentum exchange tether. They are similar to space elevators but require much less cable & mass to build. They also require a large counter-balancing mass to exchange momentum with which, like the space elevator, could also be a captured asteroid. Your spacecraft must simply be able to reach a target altitude & speed well below orbital and the tether carries you the rest of the way (no simple feat, but any competent spaceplane could make the rendezvous). If you don't care about the sky hook's orbit eventually decaying (possibly leaving you stranded if you can't reach it in time), you don't have to build any thrusters into it for orbital corrections (although there are a number of electrodynamic tethers that use the geomagnetics of planets for orbital corrections).
This is IMO the best option. The cable can be coiled-up and reused for later planetary excursions, and all one needs to do is find a large enough counter-mass (such as an asteroid) and to place the thing into the correct orbit.

Option 3:

You leave your spacecraft in orbit and take a hypersonic airship down to the planet. This is JPAerospace's Airship-to-Orbit proposal for space launch & return missions. A mile-long, solar-powered hydrogen airship slowly decelerates to suborbital speeds over the course of a couple days, coming to rest several miles above sea level. (The airship is delicate due to mass constraints and must remain floating in the upper stratosphere to avoid high barometric pressures and weather conditions.) Smaller balloons/airships or heavier-than-air vehicles could then deploy from the orbital airship's cargo bay to peruse the planet at will.
To return to space, the orbital airship gradually builds up orbital speed & altitude over 2-3 days using solar-powered ion engines, rendezvousing with the main spacecraft.

  • $\begingroup$ Bah! Option 3 stole my answer. +1 :-) I've met John Powell. It's a viable solution. It's just not as "sexy" and launching rockets since you can't get research grants for "blimping" a nuclear warhead at an enemy. $\endgroup$
    – ShadoCat
    Commented Nov 11, 2022 at 0:59
  • $\begingroup$ @ShadoCat Oh you have? That's really cool! Loved the orbital airship concept the moment I heard of it. It's grand yet elegant. Personally, I think the slow scenic ride to space is sexy as hell. $\endgroup$
    – BMF
    Commented Nov 11, 2022 at 3:21
  • $\begingroup$ as JP once said, if you have an emergency, you have time to put on a pot of coffee since nothing happens fast. His plan calls for 3 parts: The Ascender gets the load up to the very thin atmosphere, the Dark Sky Station floats up there, the Airship to Orbit spins out and can get enough DeltaV to get to Mars. It works out that the pressure at it's minimum altitude on Earth is the pressure at ground level on Mars. $\endgroup$
    – ShadoCat
    Commented Nov 11, 2022 at 18:00

You can, but the engines wouldn't be called turbines. The whole setup will also be extremely energy-inefficient, which might be irrelevant to you, though.

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. In colloquial use, this term is also applied to some engines used in aircraft. These engines can be put in two categories: turbojets use a turbine to drive a compressor, note that the actual thrust is usually produced by the exhaust gases of such engine; turboshaft engines produce thrust via turbine-driven propellers.

Both these types are internal combustion engines that burn fuel in (compressed) air atmoshpere to produce thrust. They need fuel, and go against your fuel-free concept.

On the other hand, your ship seems to have nigh-infinite (by modern standards) energy generation capabilities - it can power its wormhole generator, after all. Thus, it could theoretically propel itself via plasma jets using atmospheric gases as reaction mass - like in this article. These engines are in very early stages of development, and their reported energy efficience is much lower than that of conventional jet engines; moreover, there is some serious doubt that they will scale well from current 28 Newtons of thrust the experimental device puts out to hundreds of kN needed to match the power of turbojets. But with the energy generation capacity of your ship, a bruteforce solution might just be viable.

P.S. There is a question of how your ship manages to generate all that power without any fuel, but that's on you.


Laser ablation propulsion: Or just laser propulsion could be your answer.

In a nut shell. Step one: Cram a bunch of air into a rocket nozzle shaped bell. Step two: Shoot a high powered beam laser into the nozzle from a ground based laser. Step three: well that's it.. you didn't ask, hope you have breaks!

enter image description here

Most proposals work by filling the reaction chamber with some kind of solid or liquid reaction mass that when hit by the laser is ablated away and the expanding plasma thrusts the rocket forward. But there is no reason the reaction mass can't be air. It would be far more complicated with the need to supply the reaction with enough air gathered from the atmosphere as it accelerates through thinning layers. Than to just carry a jettisonable inert fuel only stage.

All power and thrust adjustment is carried out by the laser, independent of the craft at a ground facility where mass and volume in no issue. Thus for all intents and purposes the specific power of the craft is only limited by your laster technology.

Hard Science Reference: Beamed Energy Propulsion


So, consider your average turbojet engine. It brings in air from in front of it, compresses it via several turbines, sprays fuel into it, ignites it, and then lets the heated air and combustion products expand out the back through several more turbines, which also power the ones compressing the air up front.

Your ship seems to have some sort of handwavium energy source, given that it's generating wormholes via some means or another. Theoretically, you could replace the "spray in the fuel and ignite it" part with "use your sci-fi energy source to superheat the compressed air even further", so that your only working mass is the air you're bringing in.

This was studied in the US back in the late '50s, using a nuclear reactor on the aircraft to provide the heat source, in order to power bombers that could potentially stay aloft for extended lengths of time. They got as far as ground tests of the engines and flying a nuclear reactor (operating but not hooked up to the engines) before Kennedy pulled the plug. From https://en.wikipedia.org/wiki/File:HTRE-3.jpg

As you can expect, the thrust-to-weight ratio of that setup isn't exactly want you'd want for a high-speed application like you're considering. But again, you're using some sort of sci-fi energy source, which hopefully is either a lot smaller than that reactor or is tied to much more powerful engines than the J47s in that picture.

As far as exiting the atmosphere goes, if you're on Earth, you're unlikely to reach space without some sort of actual rocket. The fastest that a real-world air-breathing (as opposed to rocket-powered) aircraft has reached is Mach 9.65 at about 33,500m altitude, set by the X-43 unmanned aircraft in 2004. The absolute highest that an air-breathing aircraft has reached is 36,240 m, set by a MiG-25 pilot in 1973 via a "zoom climb", where he accelerated to top speed at a lower altitude, then pulled back and "traded speed for altitude", to the point where the engines flamed out due to lack of air and he coasted on a ballistic arc to the peak, where his airspeed was a whopping 75 km/h. The records for the highest level-flight altitude (~26,000 m) and fastest speed (3,530 km/h) by a manned air-breathing aircraft were both set by pilots of the SR-71 Blackbird. I don't know if any Blackbird pilots ever tried zoom climbing one, but if they did, it's not recorded anywhere.

The lower edge of space on Earth is variously defined, but the FAI defines it at 100 km altitude. So the best we've managed by air-breathing aircraft to date is only a third of the way there. Beyond that point, the air is too thin to support combustion, but too dense to allow for a free orbit. Given that your handwavium heat source is just directly heating the air without burning a fuel in it, you might get a bit higher before it's too thin to provide any useful propulsion, but you're still going to have a ways to go.

So here's the flight profile that I can picture. Your spaceship flies up to 30km or so, then levels off and kicks the handwavium engine into scramjet mode, accelerating to Mach 10 or so. Once it's going as fast as it can, its pilot pulls back on the stick and zoom climbs. Mach 10 at that altitude is roughly 3 km/s, so you just have to hope that its momentum is enough to carry it upwards the remaining 70km.

Just keep in mind that it's not going to have much forward speed remaining by the time it reaches the peak of its climb. I hope your magnetic sails are quick to deploy and can accelerate the ship to orbital speeds before it descends back down into the atmosphere. They can take it from 0 to 8 km/s in just a few seconds, right?


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