# Quickest time a Single-Stage-To-Orbit futuristic fighter-jet take could get into orbit?

I recently watched the rather fun anime ‘Yukikaze’ which features a futuristic jet-fighter but one which doesn’t really introduce anything completely implausible technology-wise. It got me wondering, assuming a fighter jet that was roughly the size of an F-22 Raptor but was technological advanced enough to go from a standing start into a stable low-earth orbit what would be the quickest reasonable time it could manage it without pulping the pilot (or not even as extreme as that, without compromising his/her effectiveness on the way up and once they got there).

Think of it as a rather extreme version of the old Battle of Britain Hurricane* scrambles from WW2.

*yes the Spitfires older and plainer sister needs some love as well!

Entirely ignoring the physics of how the heck you get to orbit, we can just think about g limits on the pilot. IIRC 5 g is a reasonable limit for sustained forces, and 9+ g will eventually black out even a trained fighter pilot.

In round numbers, orbital velocity in LEO is ~8000 m/s. At 5 g (50 m/s^2) it’d take 40 seconds to get up to speed.

What sort of magic rocket engine would that take? Let’s assume a rocket with a dry mass of the F-22, and propellant mass about half the normal F-22 fuel load (it’s gotta have a fair amount left for the ZOOM and the PEW PEW, after all). Also, let’s assume we need a total delta-V of 10000 m/s, to account for gravity and drag losses (and lazy calculations). Using the rocket equation, we can calculate an exhaust velocity of 10,000 m/s / (ln 24/20) = 55,000 m/s. That’s way beyond the ability of chemical rockets, but within the realm of theoretical nuclear propulsion.

And to be a debbie downer, the first problem with that nuclear propulsion is the radiation shielding you need. It needs to be a minimum thickness or you are going to be fried. The way the scaling laws work out, it means that space fighters with 1 pilot don’t make any sense, but vehicles the size of modern day destroyers do, because both need the same thickness of radiation shielidng (a shadow shield between the nuclear engine and the crew), but the much bigger ship has a lot more engine and fuel proportional to the mass of the shield.

Second, the performance numbers that lazybratsche quoted? Yeah, only fusion bombs give that kind of performance, and only in the atmosphere. The reason is each detonation would shove an immense amount of air around, and the ship could ride the shockwaves. (project Orion, of course). NERVA engines don’t have that kind of performance (ISPs of a mere 1000, which is 10,000 m/s exhaust velocity). More efficient engines like nuclear electric or (hypothetical) pure gas fusion engines would not work in the atmosphere (the air would mess up the charge gradient that ion thrusters use or contaminate the fusion reaction) and they would not have enough thrust to weight to even leave the ground.

Coming up with something like a “shuttlecraft” that can come down from space and then return, on a planet with the same gravity and atmosphere of Earth, is like, well, close to impossible. It’s the radiation from a nuclear engine with adequate performance that causes all your problems. I mean, we can posit technology that would do it - basically you drop a factory to the surface via heat shields and parachutes in a capsule that builds you a new rocket to return to orbit with. But nothing like they do it in sci fi movies like Aliens, where going down and coming back up is as easy as flying a helicopter.

17 minutes for Skylon (warning PDF), scroll down to Figure 4 on page 13.

Yes, for survival - but not if the OP’s “no compromise to pilot effectiveness” goal is to be met.

5 g makes even trivial mechanical actions (e.g. pressing a button) highly challenging.

Both lazybratsche and SamualA have provided credible answers and objections to the question of both the necessary propulsive performance and accelerations experienced (assuming no atmosphere). I can only add that the aeroelastic effects of accelerating at ~5 g from ground level would be vastly beyond any material thermal and strength capabilities, and would also pose a massive control challenge. There is also the problem of carrying sufficient propellant in an “F-22” size aircraft; even using atmosphere as the oxidizer and working fluid to the upper stratosphere (which creates substantial problems in and of itself) there just isn’t enough volume to carry sufficient propellant for any combustion or chemical detonation powered engine in that size of a vehicle. You would need some propulsion system that has both sufficient thrust to sustain that level of acceleration and the necessary propellant efficiency to achieve the necessary impulse to get to orbital speed, and there is nothing like that which exists even in theory.

I don’t write of this in the abstract; I actually have a ‘toy model’ of a vertical two stage launch system with which I’ve played with ramjet/scramjet propulsion during the lower ascent phase of Stage 1 action time, and the weight to thrust ratio is barely sufficient to support the extra mass with even the most optimistic assumptions. A horizontal craft may get more time at useable atmospheric densities and the advantage of lift, but it doesn’t actually gain much in the way of forward velocity that translates to orbital speed performance because of the limits of how fast it can travel in atmosphere, and because it needs to be configured to optimize lift or add lift and aerocontrol surfaces (wings, canards, stabilizers) it ends up being a far less than optimal shape in terms of reducing forward drag. I have no idea how Alan Bond thinks the Skylon concept would be viable even assuming hypothetical scramjet-to-rocket phase engines because I’ve run simulations on concepts similar to the Skylon and found it to be completely unworkable with he most generous assumptions about performance.

Ground-to-orbit spaceplanes seem reasonable to the layperson because they’re familiar in layout, but once you get into the engineering details of such vehicles, even at the conceptual level, it becomes clear that they are scarcely more practicable than antigravity without assuming some kind of science fictional propulsion system which generates tons of thrust from a few liters of fuel exhausted at over a hundred thousand feet per second (which would leave a glowing contrail of ionized plasma that would be lethal to anything crossing it for minutes) and the magical material technology to build both a workable engine and thermal protection system capable of surviving the thermal energies involved. A fighter-sized spaceplane is not remotely plausible with any foreseeable technology short of an Iron Man like ARC reactor that generates essentially limitless energy with no apparent waste heat.

Stranger

Does project Orion have that kind of performance, in theory, for atmospheric flight? I am aware that in space it’s probably very inefficient, but in the atmosphere, each detonation would create a shockwave from nearby air.

Just the detonation of a nuclear device produces a shockwave (from the device casing material being heated to plasma and accelerated to hundreds of thousands of feet per second velocity), and of course in atmosphere the air will absorb X-rays and translate the resulting thermal pulse into an atmospheric shock wavefront. The effective performance of a Project ORION-type vehicle depends upon the parameters of the bomblets and vehicle, but it certainly isn’t workable as any kind of spaceplane configuration; there is a minimum practical size for nuclear pulse propulsion, and it is in the 1000 ton area which results in significantly reduced propulsive performance.

Stranger

Ok, so the reason is that the nuclear devices don’t scale linearly, right? One that gives you under a kiloton may still weigh half as much as one that is more than 10 times as powerful, right? So you have to make the spacecraft at least 1000 tons with a gigantic plate underneath and I think you’re saying it’s going to be even better if it’s 10,000 tons. An arleigh burke destroyer is 9200 tons, so that’s roughly the scale we are talking about.

And it’s not a plane, once it goes up, it never comes down, right? You just send capsules down as needed.

It’s not so much the mass of the bomblets as it is the ability of the spacecraft of a particular mass to absorb and mediate the impulse, and diameter of the pusher plate to get good utilization of the blast impulse. The ORION concept uses a two stage damper system between the pusher plate and the rest of the vehicle but if the vehicle is too light the resulting accelerations are too large for continuous operation for a reasonable sized damper. 1000 tons is about the minimum to keep the sensed acceleration at a tolerable level for sustained acceleration.

The ORION vehicle definitely never returns; for ground launch, it is intended to ascend from some remote location (Dyson et al assumed the Nevada Proving Grounds, but a better option would actually be sea launch from the low lattidute Pacific) and then proceed directly to an interplanetary destination, possibly without even entering orbit. One of the downsides is that in a propulsive failure there is not practicable abort mode; you’ll have thousands of tons of heavy steel structure falling from the sky at potentially near orbital velocities. Construction in orbit would be safer, but there is no practical way to lift that mass of material from Earth using conventional propulsion, so it would necessitate using space based resources to construct the ship, which is a massive infrastructure challenge in and of itself.

Stranger

Awesome. If the fallout you’re creating is reduced by the inverse square law, this location would mean very few people were exposed to a significant dose, since I assume you had in mind uninhabited sections of the Pacific, right?

What I was trying to say was that you could in principle scale the bomblets down to the blast of a hand grenade, but the size of them will not be proportional to the reduced energy released, so this will not work. (they wouldn’t have the size and weight of a thimble). So you have to go big, like you say.

How would/if at all/ laser propulsion help? I see futuristic calculations giving a three days to Mars scenario:rolleyes:

Could our theoretical plane be “pushed” by ground lasers and conserve its fuel to the orbital/suborbital portion of flights (the pew-pew part)?

You didn’t mention catapults, but given that carrier-based fighters use them regularly, I think we should consider them to be in play.

Let’s build a giant electromagnetic accelerator, angled so that the exit is at 30 km altitude (roughly 1% of atmospheric pressure). We’ll make it 200 km long so that it’s not too steep. It’s powered from the ground so there’s no exotic tech needed there.

We want to be at close to orbital velocity at exit so that only a circularization burn is needed later. But we can accelerate more quickly, if we want. Humans can take up to 50 gees without serious injury, if properly supported, and accelerated “eyes in”. They’ll black out, of course, but they should recover if it doesn’t go on too long. 8000 m/s takes only 16 seconds at 50 gees. That seems like it’s not too long to cause permanent damage.

The acceleration will take 64 km, so the craft will coast the rest of the way through the tube, exiting through a shutter system. It takes around 160 seconds to get to a 200 km orbit, which is low but acceptable if the craft has active thrust. The craft needs to burn off around 1200 m/s of upward velocity to circularize, which we might do at just 10 gees, taking 12 seconds. Overall we’re in the ballpark of 200 seconds.

A lot of this time is coasting up to altitude, so you could do a tad better if you made the catapult steeper, but that places higher (and probably unreasonable) demands on the craft.

There’s nothing in this proposal that requires way-out-there exotic tech; the electromagnetic accelerator is feasible, and can be powered by ordinary ground electrical plants. The fighter only has a modest delta V budget, and doesn’t need any exotic heat shielding, given that it goes through the dense parts of the atmosphere in a vacuum tube. It would be ridiculously expensive, of course.

As already mentioned, a fighter-sized SSTO seems impossible given current or near-future technology. The X-15 was that size and it could not remotely achieve orbit, even given an aerial launch and if using external drop tanks: http://www.astronautix.com/graphics/x/x15a2.jpg

The X-33 was a planned 1/3-scale prototype of the VentureStar SSTO. At 285,000 lb gross weight it was not fighter size but at least it was smaller than a bomber. It was not manned, and despite this would only have achieved suborbital velocity: Lockheed Martin X-33 - Wikipedia

Using air-breathing scramjet propulsion is the only conceivable way current or near-future technology could achieve orbit using anything remotely like a large fighter or small bomber-size aircraft. However the research to date shows this is much harder than was first envisioned, and may never be achieved. This is clear from this free online NASA book, Facing the Heat Barrier: A History of Hypersonics (PDF, part 1): history.nasa.gov/sp4232-part1.pdf

That said, some using the Kerbal simulator claim they have built a small SSTO spaceplane. But I tend to doubt the simulation is very rigorous or representative of available materials, propulsion and thermal protection technology. Otherwise there wouldn’t be such a vast difference between that vs all real-world efforts to date.

But your main question involves time-to-orbit and g force. Given a futuristic propulsion system able of achieving orbit in a fighter-size vehicle, there might be no (or few) limits on fuel or specific impulse or thermal protection. IOW to achieve your premise requires such advanced technology it would be essentially like Star Trek.

If you have no real limits on materials, propulsion or thermal protection, the question is really one of human physiology and g tolerance. A key issue is whether human consciousness is required or simply survivability without permanent damage.

You could just boost constantly at 4 g or so and you’d be at orbital velocity and altitude within about 200 seconds: Uniformly Accelerated Motion Calculator

If boosting at 20 g, you could be in orbit in 41 seconds. If in a supine position, this NASA graph indicates roughly 20 g might be survivable for 60 seconds. The person would probably not be conscious after that but he would not be damaged : https://history.nasa.gov/conghand/fig15d5.gif

For a direction injection orbital insertion, no circularization burn (or impulse) is needed, so the above time periods are time to stable orbit.

There are two types of laser propulsion that could help a craft to get to orbit; the first is laser-energized rocket, where a propellant is heated by a groundbased laser and produces thrust. This isn’t all that different to a rocket, since you have to take your propellant with you. But the propellant can be quite varied; one scheme I have seen described used ice dyed black to absorb heat better.

The other scheme uses the atmosphere itself as propellant, heating the air behind the craft until it expands. The Lightcraft is an example of this.
https://en.wikipedia.org/wiki/Lightcraft
…note that the highest this sort of craft has ever flown is 236 feet.

It’s actually really, really easy to build a SSTO spaceplane in vanilla Kerbal Space Program. This is because orbital velocity of Kerbin is a mere 2.3km/s. So, you build a plane capable of hitting ~1.2km/s at an altitude of about 17km on air-breathing engines and only need a rocket-powered delta-V of another 1.5km/s.

If on the other hand you mean people have built SSTO spaceplanes using the Real Scale Solar System mod, then to the extent that’s possible it’s probably by building what amounts to a conventional SSTO and slapping a few wings on it for show, because air-breathing in RSS is only going to get you to ~1.2km/s @ 30km leaving another 7.5km/s of delta-V required on rockets. A rocket-powered craft with 7.5km/s of delta-V isn’t going to be anything like an F-22. It’s going to be a ginormous fuel tank with a tiny, tiny payload.

The other big advantage of this is that you can make the spacecraft propellant velocity much higher by tuning the laser pulses appropriately. You could probably in fact meet the requirements of this thread and have an F-22 sized fighter, with an F-22’s normal fuel load, make it to orbit. This is because all the energy is coming from a gigantic apparatus on the ground, and if there’s a nuclear reactor providing the power, you left it on the ground. Extremely good (and expensive) mirrors can in principle focus the beam onto a 1meterx1meter sized patch inside the engine bell, and essentially as propellant (it’s a solid) ablates off, some kind of internal mechanism pushes more forward. It’s going to cost you a lot of energy, but you could probably in fact get the exhaust velocity to the point that you only need a little bit of propellant.

The catch is, the spacecraft just rides the beam, and is totally dependent on the ground station to be anything more than a falling brick. Not remotely sexy like the anime, and if you want to go into orbit any other way but launching from dead center of the laser array, it isn’t going to happen.

200 km long? And necessarily engineered to perfect tolerances over that length because of the very unforgiving speeds involved? And that doesn’t wear out in a relatively few shots or need constant major overhauls every few firings to make sure everything is still in alignment?

And then we suspend the thing’s exit point 30 km in the sky? Are we to build a mountain 3.4 times the height of Everest, the last 70% of which is in air that is not breathable? And don’t forget the 200 km long ramp that has to be built to support not just the far end but the rest of the accelerator as well? And none of this mountain range collapses under gravity?

And any alternative support system like struts at 30 k vertical height are going to have impossible stability problems at the very least. You have, after all, just built a space elevator the hard way (no cable and counterweight system here).

“No exotic materials necessary?” Seems to me that both your accelerator and your supports, whatever the supports be, are pretty much the definition of unobtainium.

Yeah, this is pretty much always the case whenever a someone decides that SSTO or some other not-yet-relalized conceptual technology is “just an engineering problem”. A vertically launched rocket propulsion SSTO is just possible (hypothetically) with current technology, but hasn’t been realized because of major technical challenges (largely thermal protection systems, and practically application of more efficient altitude compensating plug and aerospike nozzle propulsion systems), but the idea of a 200 km long, 30 km high electromagnetic catapult is not long beyond the state of the art, it would represent a macroengineering challenge to dwarf all existing engineering construction projects notwithstanding the difficulties in maintaining such a system. It would literally be more feasible to construct an orbital elevator than it would to build such a catapult, and the elevator would be more practical in terms of being able to recapture a fair portion of energy used on the trip back down.

Stranger

MagLev space launch in evacuated tubes has been discussed for decades, including some small-scale prototype testing: StarTram - Wikipedia

The OP’s basic premise essentially requires a revolutionary breakthrough in physics, materials and propulsion. Stranger was simply postulating the most achievable system given current physics and attainable materials that might conceivably permit something remotely like OP scenario. There was no requirement that this be economic, or maintenance free.

If the scenario is relaxed from SSTO to TSTO, and from F-22 size to XB-70 size, there are some vaguely fighter-like concepts that might have a remote chance of working, given sufficient funding and development: https://photos.smugmug.com/photos/i-2tBk3CN/0/L/i-2tBk3CN-L.jpg