Single-Stage-to-Orbit: The Launch Technology We Wish Was Real

Reaching orbit around Earth is an incredibly difficult feat. It’s a common misconception that getting into orbit just involves getting very high above the ground — the real trick is going sideways very, very fast. Thus far, the most viable way we’ve found to do this is with big, complicated multi-stage rockets that shed bits of themselves as they roar out of the atmosphere.

Single-stage-to-orbit (SSTO) launch vehicles represent a revolutionary step in space travel. They promise a simpler, more cost-effective way to reach orbit compared to traditional multi-stage rockets. Today, we’ll explore the incredible potential offered by SSTO vehicles, and why building a practical example is all but impossible with our current technology.

A Balancing Act

The SSTO concept doesn’t describe any one single spacecraft design. Instead, it refers to any spacecraft that’s capable of achieving orbit using a single, unified propulsion system and without jettisoning any part of the vehicle.

The Saturn V shed multiple stages on its way up to orbit. That way, less fuel was needed to propel the final stage up to orbital velocity. Credit: NASA

Today’s orbital rockets shed stages as they expend fuel. There’s one major reason for this, and it’s referred to as the tyranny of the rocket equation. Fundamentally, a spacecraft needs to reach a certain velocity to attain orbit. Reaching that velocity from zero — i.e. when the rocket is sitting on the launchpad — requires a change in velocity, or delta-V. The rocket equation can be used to figure out how much fuel is required for a certain delta-V, and thus a desired orbit.

The problem is that the mass of fuel required scales exponentially with delta-V. If you want to go faster, you need more fuel. But then you need even more fuel again to carry the weight of that fuel, and so on. Plus, all that fuel needs a tank and structure to hold it, which makes things more difficult again.

Work out the maths of a potential SSTO design, and the required fuel to reach orbit ends up taking up almost all of the launch vehicle’s weight. There’s precious mass left over for the vehicle’s own structure, let alone any useful payload. This all comes down to the “mass fraction” of the rocket. A SSTO powered by even our most efficient chemical rocket engines would require that the vast majority of its mass be dedicated to propellants, with its structure and payload being tiny in comparison. Much of that is due to Earth’s nature. Our planet has a strong gravitational pull, and the minimum orbital velocity is quite high at about 7.4 kilometers per second or so.

Stage Fright

Historically, we’ve cheated the rocket equation through smart engineering. The trick with staged rockets is simple. They shed structure as the fuel burns away. There’s no need to keep hauling empty fuel tanks into orbit. By dropping empty tanks during flight, the remaining fuel on the rocket has to accelerate a smaller mass, and thus less fuel is required to get the final rocket and payload into its intended orbit.

The Space Shuttle sheds its boosters and external fuel tank on its way up to orbit, too. Credit: NASA

So far, staged rockets have been the only way for humanity to reach orbit. Saturn V had five stages, more modern rockets tend to have two or three. Even the Space Shuttle was a staged design: it shed its two booster rockets when they were empty, and did the same with its external liquid fuel tank.

But while staged launch vehicles can get the job done, it’s a wasteful way to fly. Imagine if every commercial flight required you to throw away three quarters of the airplane. While we’re learning to reuse discarded parts of orbital rockets, it’s still a difficult and costly exercise.

The core benefit of a SSTO launch vehicle would be its efficiency. By eliminating the need to discard stages during ascent, SSTO vehicles would reduce launch costs, streamline operations, and potentially increase the frequency of space missions.

Pushing the Envelope

It’s currently believed that building a SSTO vehicle using conventional chemical rocket technology is marginally possible. You’d need efficient rocket engines burning the right fuel, and a light rocket with almost no payload, but theoretically it could be done.

Ideally, though, you’d want a single-stage launch vehicle that could actually reach orbit with some useful payload. Be that a satellite, human astronauts, or some kind of science package. To date there have been several projects and proposals for SSTO launch vehicles, none of which have succeeded so far.

Lockheed explored a spaceplane concept called VentureStar, but it never came to fruition. Credit: NASA

One notable design was the proposed Skylon spacecraft from British company Reaction Engines Limited. Skylon was intended to operate as a reusable spaceplane fueled by hydrogen. It would take off from a runway, using wings to generate lift to help it to ascend to 85,000 feet. This improves fuel efficiency versus just pointing the launch vehicle straight up and fighting gravity with pure thrust alone. Plus, it would burn oxygen from the atmosphere on its way to that altitude, negating the need to carry heavy supplies of oxygen onboard.

Once at the appropriate altitude, it would switch to internal liquid oxygen tanks for the final acceleration phase up to orbital velocity. The design stretches back decades, to the earlier British HOTOL spaceplane project. Work continues on the proposed SABRE engine (Syngergetic Air-Breathing Rocket Engine) that would theoretically propel Skylon, though no concrete plans to build the spaceplane itself exist.

The hope was that efficient aerospike rocket engines would let the VentureStar reach orbit in a single stage.

Lockheed Martin also had the VentureStar spaceplane concept, which used an innovative “aerospike” rocket engine that maintained excellent efficiency across a wide altitude range. The company even built a scaled-down test craft called the X-33 to explore the ideas behind it. However, the program saw its funding slashed in the early 2000s, and development was halted.

McDonnell Douglas also had a crack at the idea in the early 1990s. The DC-X, also known as the Delta Clipper, was a prototype vertical takeoff and landing vehicle. At just 12 meters high and 4.1 meters in diameter, it was a one-third scale prototype for exploring SSTO-related technologies

It would take off vertically like a traditional rocket, and return to Earth nose-first before landing on its tail. The hope was that the combination of single-stage operation and this mission profile would provide extremely quick turnaround times for repeat launches, which was seen as a boon for potential military applications. While its technologies showed some promise, the project was eventually discontinued when a test vehicle caught fire after NASA took over the project.

McDonnell Douglas explored SSTO technologies with the Delta Clipper. Credit: Public domain

Ultimately, a viable SSTO launch vehicle that can carry a payload will likely be very different from the rockets we use today. Relying on wings to generate lift could help save fuel, and relying on air in the atmosphere would slash the weight of oxidizer that would have to be carried onboard.

However, it’s not as simple as just penning a spaceplane with an air-breathing engine and calling it done. No air breathing engine that exists can reach orbital velocity, so such a craft would need an additional rocket engine too, adding weight. Plus, it’s worth noting a reusable launch vehicle would also still require plenty of heat shielding to survive reentry. One could potentially build a non-reusable single-stage to orbit vehicle that simply stays in space, of course, but that would negate many of the tantalizing benefits of the whole concept.

Single-stage-to-orbit vehicles hold the promise of transforming how we access space by simplifying the architecture of launch vehicles and potentially reducing costs. While there are formidable technical hurdles to overcome, the ongoing advances in aerospace technology provide hope that SSTO could become a practical reality in the future. As technology marches forward in materials, rocketry, and aerospace engineering in general, the dream of a single-stage path to orbit remains a tantalizing future goal.

Featured Image: Skylon Concept Art, ESA/Reaction Engines Ltd

72 thoughts on “Single-Stage-to-Orbit: The Launch Technology We Wish Was Real

  1. Great write-up. One correction, the Saturn V was a three stage engine. Unless you count the LM and the command modules. But these two engines reached orbit on the first three stages…


  2. Combine two “normal” airplane wings plus the required fuel & “conventional” high bypass jet engines connected by a “basket” for the actual space shuttle/ship/rocket + fuel + oxidizer + payload.

    The normal wings would contain the fuel for the in-atmosphere phase of flight and drop off at the upper limit, navigating home on auto pilot. The complete airframe needs be stripped down as much as possible. Kinda like the existing concept of a space shuttle piggy-backing on a conventional plane but *without* most of the conventional plane and the shuttle literally in place of the main “original” plane body.

    The remaining space shuttle would only contain the required fuel + oxidizer and so on required to go up/faster from ~26km above ground.

    Dunno how to get it down later thou… *shrugs*

    Just a “shot in the dark” idea I got while reading this HaD article.

    1. It’s a pretty cool idea, but it’s failed each time they’ve tried it. Virgin Orbit tried to drop a rocket from a special 737 a few times and never succeed. Infighting a rocket while it’s free falling is apparently quite hard.

      The strato launch plane also tried this, but I’m not sure if any rocket was ever designed for it. I’m also not sure if the current owners are still planning to use it for rocket launches.

      Ultimately, the airplane part ends up just being a reusable first stage, which SpaceX has been doing for a while and that many other companies are also working on.

      1. Virgin Orbit had four successful launches:

        There was also Pegasus, the Orbital Sciences air-launched solid rocket, which had dozens of launches across decades.

        The problem isn’t that air launch can’t be done. The problem is that, once you’ve accounted for all the extra complexities, it ends up more expensive than just building a bigger rocket and launching that from the ground. And that was true even without recoverable rocket boosters.

      2. Trying to launch from a modified 737 didn’t really help all that much, because it didn’t go fast enough or high enough. You get less than Mach 1 and less than 10 km altitude with such a load strapped on, and then it’s just going to fall down like a rock when you drop it – before it manages to light up and start picking up some real speed.

        The point of SSTO rocket planes like the Skylon is that they’re already going several Mach and skimming the top of the atmosphere when they light up the rocket. They’re more like a souped up U2 spy plane than a 737 to get up to that altitude and speed, but they also have the ability to collect more LOX from the air than they burn, so they fill up the tank on the way up and then switch to internal oxidizer to jump out of the atmosphere.

          1. By evaporating liquid hydrogen.

            It uses ram compression to stuff air at +1000 C into a pre-cooler, where the evaporating hydrogen fuel brings it down to -150 C. The cold air is then stuffed through a compressor into the main rocket nozzle at 140 Bars of pressure. The entire point of the engine is cooling the air down very rapidly, so the compressor doesn’t melt under the massive pressure. It also uses the temperature difference between the hot air and cold fuel to run all the pumps in the system.

            The extra hydrogen used to cool the air is burned off with bypass air in a ramjet to provide extra thrust. The SABRE engine doesn’t actually liquefy the air, but the earlier LACE concept does simply by using more hydrogen, and so the SABRE too could – but it comes with an efficiency penalty. Whether it pays off or not remains to be tested.

          2. The efficiency penalty in collecting liquid oxygen along the way comes from the ratio of hydrogen fuel that you will burn in the rocket engine vs. the ramjet. When you cool the intake down to the point of liquefying air, more of the hydrogen fuel ends up in the ramjet, which gives you less bang for the buck than the rocket engine.

        1. NASA looked at the concept of air launching a follow up to the shuttle in the 1980’s.
          One concept uses a 747 as the launch vehicle, containing LOX and hydrogen tanks to top off the space craft, and also used some of the hydrogen as an afterburner for the 747’s engine, so it could release the spacecraft in a zoom-climb. An alternative was installing a SSME (the engine from the Shuttle) in the tail to add more boost.
          Probably not a sensible plan, but a really cool idea.
          (more info

      3. There’s other versions of air launch which seem more reasonable. For reference, the U.S. worked out how to launch anti-satellite missiles from f-15’s (which is interception, not orbit), and while I don’t know what the true limits of the yf-12’s would be for short hops, they were well known to be able to sustain at least mach 3 at quite high altitudes. But while even a modern more conservatively designed launch jet with a larger payload would probably be slower and lower than we’d like, it should be higher and faster than a passenger jet. Was Virgin just cruising along like a normal flight, or building up speed and then climbing outside their envelope temporarily to launch?

        While it would probably be limited to smaller rockets and therefore likely smaller LEO sats, air launch might still be able to win against other reusable first stages in some circumstance, just given the advantages everyone acknowledges. I’d expect the rocket stage could skip straight to a fairly highly expanded nozzle and not need to throttle down for max-q as it’d be long since past the sort of altitudes where dynamic pressure would be so intense by the time it built up enough speed to matter. Might help if the rocket could be ignited while still attached, if that’s a pain point?

        1. Current anti-satellite system use staged rockets not air launch; 30 foot long SM-3 missiles with 3 stages. Anti-satellite only needs much less delta V since the don’t have to orbit. They just cross the orbit of a much faster moving satellite at just the right time.

          1. Okay? I was only bringing up the old f-15 example because having one launch a ASM-135 is a successful example of everything but the delta-v for orbit. The jet launched a missile that was able to begin acting like a rocket, including staging and plotting a course for rendezvous/interception which ended in a high speed (but precise) impact. Not bad at all for being strapped to a fighter jet 40 years ago instead of a hypothetical modern launch plane.

          1. So it reads like the two problems were a) you mostly didn’t need suborbital cameras like that and b) they didn’t build those planes around this purpose, so while the performance was great, achieving high speed and altitude, it was awkward to make it physically fit around the landing gear and such.

            Looking at some of the other planes we’ve had, we’ve had other planes go higher, rocket planes go faster, and bombers with more capacity go fairly high. So in general, seems like we could probably make a decent stab at it if we wanted, though after thinking it over, I guess just getting a larger mass up to a lower altitude at best possible speed would be better after all.

            I guess you do want to get the speed up a bit more before losing the benefit of the wings. (Since without wings, you have to spend one gee of your acceleration on fighting gravity, but winged aircraft can support their own weight without making one gee of thrust.) The less time spent with a rocket at a low speed, the better, because energy spent fighting drag and gravity is energy not spent making you go faster. Once you’re high enough that the rocket doesn’t need to have engines optimized for thick atmosphere, even if you’re lower and slower than normal for switching to a second stage, it seems like that’s probably still the time to light the rocket engines.

            The SpaceShipOne example seems to have gone for a more moderate altitude, but the rocket portion was launched at a slow speed and the engine was not nearly as strong as regular rockets, although that part is understandable. I can’t really prove that this would work, but it’d be a fun flight profile in Kerbal space program :P.

  3. When I was 6 years old, I remember seeing a drawing of a proposed rocket that looked exactly like the Skylon. The proposed rocket had air breathing engines that transitioned to rocket power just like the Skylon. I am almost 68 years old now. I don’t see this happening any time soon.

  4. You skipped one of the big reasons. Engine expansion ratio. A sea level expansion ratio engine is very inefficient in vacuum due to being under expanded. A vacuum engine at sea level is over expanded, which tends to lead to explosions, but even if it didn’t, the rockets width would have to massively increase, which increases air resistance.

    For example: the falcon 9’s sea level and vacuum engines are basically the same thing but one has a bigger bell. If you replaced all 9 of the first stage engines with the vacuum variant, they wouldn’t fit, so, you’d have to make the whole rocket wider, about 3 times wider. That’s almost as wide as the falcon heavy, but all the way around. And once you did make it out of the atmosphere, you’d have way more thrust than needed, which means you’d probably want to leave most of the engines turned off and not contributing.

    P.S. aerospike rockets still have to have the same cross section because they need the same expansion ratio to avoid loosing efficiency due to being under expanded, but they don’t have to worry about exploding when over expanded. A falcon 9 with 9 aerospike engines would still be triple the diameter of the normal 2 stage falcon 9.

  5. SSTO sounds cool, a spacecraft like an aeroplane that just needs to be refuelled and can take off again. The problem is that even with better materials as described in the article, the payload capacity will be small and the complexity high. I think the SSTO dream is pretty much dead and the killer is fully reusable multi-stage rockets.

    SpaceX has shown that fully reusable multi-stage rockets are not only feasible with current technology, their performance is competitive.

    The Falcon 9 or Falcon Heavy rockets are not too far away from being fully reusable. The first stage (or the first three stages for the Heavy) is fully reusable, using fairly conventional technology. The second stage is not reusable, but analysis has shown that it is realistically possible with current technologies and only moderate weight/capacity penalties.

    With Starship, SpaceX wants to not only scale up the design, but also make the second stage reusable. Starship is an ambitious project that has other advantages from its size, but I don’t think the size is really necessary for reusability alone.

    I think we’ll see a lot more partially or fully reusable multi-stage rockets of all sizes in the future, which don’t have many disadvantages compared to SSTO or spaceplanes.

    1. I agree that an SSTO is pretty much a dead idea. I would be interested in a hypersonic, air-breathing mother ship (like Virgin Galactic’s 747 or the Roc, but fast) with a rocket-propelled orbital stage. It’s starting to get within reach of current technology. It only gets you maybe a quarter or third of the way to orbital velocity, but that’a not nothing.

      1. Re-usable traditional rockets are the steam cars of rocketry. They push old concepts to their breaking point, but don’t really provide the revolutionary benefits they claim. They’re just somewhat cheaper rockets.

        If the SSTO space plane concepts – more importantly, their engine concepts – can be made to work, they would provide 8-10 times the specific impulse at launch, which is a true game changer. It means you can get to orbit with a fraction of the fuel, so your whole vehicle can be a fraction of the size for the payload, and cost a fraction of the money in the long run. It’s not just about shaving a few tens of percents off – it’s taking the whole infrastructure cost down, because you no longer need fragile launch pads that disintegrate under the sheer power of your skyscraper-sized rocket.

        1. What rocket engine provides 8-10 times the specific impulse while still having reasonable thrust (and not being air breathing)?

          (Note: I’m genuinely interested in this, since I haven’t heard of any engine with those numbers that don’t have a glaringly huge downside)

          The only engine I know of that is even close to that ISP without being air breathing is the NERVA rocket engine.

          (There are ion engines and similar systems, but none of them provide enough thrust to work on the earths surface)

          Comparing an air breathing engine’s ISP to a rocket’s ISP is apples to oranges. A turbo fan engine can have an ISP that’s 25+ times higher than the most efficient Rocket engine, but it wouldn’t work for most of the flight to orbit.

          1. With that kind of ratio he’s either comparing a turbofan to a rocket engine or he has an inside line on the first honest-to-god perpetual motion machine. Either way, he glossed over the SSTO limitation in the article, the tyranny of the rocket equation. ISP isn’t everything.

          2. >and not being air breathing)

            The SABRE is air breathing, but it switches to internal oxidizer when it runs out of air. That’s the entire point – it doesn’t need to lift massive first (and second) stage LOX tanks, which reduces the weight of the vehicle, which again reduces the need for fuel, which again reduces the weight of the vehicle… it’s the rocket equation going in the other direction.

            Ordinary rockets burn straight up for about a minute and consume most of their fuel just gaining altitude before they can turn and start picking orbital speed. They’re enormously inefficient machines. A space plane using an air breathing rocket engine, with wings, going sideways, runs longer with less power and gets more than 10x the lift for the fuel, so obviously it needs less than 10% of it. With smaller fuel tanks and engines to lift, even less of the fuel is spent on just lifting the rocket, which is why they can afford to launch the entire thing to orbit without shedding stages.

            >the SSTO limitation in the article

            It applies to conventional rockets which carry all their fuel and oxidizer from the start, and don’t use aerodynamic lift (wings).

  6. >> Saturn V had five stages
    Technically, only 3 of those were used to reach Earth orbit (S-IC, S-II, and S-IVB), with the 3rd stage also sending the combined CM/SM and LM off to the moon (TLI). I presume the 2 additional stages you are referring to are the service and command modules, but only one of those had an actual engine. The LM had a descent stage and an ascent stage.

    So technically, six stages from the Earth to the Moon and back.

      1. Maybe if you wanted to get an empty tank into orbit (and probably a nosecone to cover the big hole where the next stage should attach on top). Still pretty impressive

  7. I’m not a rocket engineer. So maybe I’m way off.
    But as I see it a rocket goes from zero to super fast then back to zero. The part from super fast to zero requires slowing down which is nearly all accomplished by atmospheric drag. Which means it gets hot-hot-hot. So what is the reason for re-entry to be so short? Can that phase be lengthened (a week? Way longer?) where it just warms up instead of needing to be crazy hot? For military or whatever without people in there that would decrease or eliminate the need for ablative heat shields and all that.

    1. That means you’ll need to slow it with thrust, which necessitates bringing along enough fuel/engine to do so. You’ll have to have gotten this up there first which would be even more weight and even less payload to carry to orbit, which only adds to the original problem.

    2. Nope. As soon as you start slowing down a little, gravity brings you down into the thick air real quick. Using aerodynamic lift to stay up in the thin air longer and decelerate more gently does help a little, but not as much as you might hope. And at near-orbital speeds, interacting with the air enough to develop lift still means crazy high surface temperatures.

      1. Having a larger lifting body that is mostly empty helps here. It’s got a larger surface for the heat, and more lift, but not much more mass, so the kinetic energy is dissipated over a larger surface area and it comes down slower and cooler.

      2. Combine it with a trebuchet to lose momentum :)

        I hereby release this idea to be freely used by anybody.
        This includes SciFi producers because I bet this would be fun in a SciFi show/movie.

    3. Orbital mechanics. Speed and orbit height are linked. So if you slow down beyond a certain speed your orbit is now in the atmosphere and you will keep slowing down due to drag. They already try to minimize this as much as possible, but even then you got enough speed to heat up to crazy amounts

    4. One way to help with the crazy heat loads is to spread it out: a light winged vehicle re-entering can spread the power to dissipate over a large area, as well as generating a bit of lift to prolong the duration over which to dissipate the energy.

      A dense or heavy bullet-like re-entry vehicle has a large power density on its heatshield, requiring very high temperature or an ablative material to dissipate the high peak power.

      A paper airplane is speculated to be able survive re-entry just fine. There was a Japanese plan to drop a bunch from orbit a few years ago. Dunno whatever happened to that.

    5. Scott Manley has an analysis brought on by this exact question. He shows why no matter what combination of orbits you use you get trapped in a particular solution to the equations and the family of solution curves all have the same shape so to speak.

      If you had some sort of scifi engines you could slow down while directing some thrust towards the Earth until you are hovering then drop at your leisure – like in every comic book movie and Star Wars, etc.

    6. This can work for highly elliptical orbits, where you pass through the atmosphere to slow down some, then back into orbit to cool off. But, unless you are flying to the moon or Geostationary orbit, you don’t normally fly a highly elliptical orbit.

      As others have mentioned, you can “create lift’ but that’s limited in what you can do. I’m fairly sure that’s basically what the space shuttle did for re-entry.

      Counterintuitively, going through the atmosphere quickly results in less heating of the space ship than taking it slowly. (I’m sure there are some good YouTube videos that explain this better than I ever could)

    7. Other than what others covered, there’s an ability to make multiple passes and cool down in between, which may also have been called “skipping” off the atmosphere, but eventually you do run out of speed and come in for a fiery last pass. I believe one thing I’d seen as a concept was an absolutely massive inflatable heatshield – I don’t know if it was intended to be filled with some kind of ablative foam just before reentry or what – which allowed more drag up high and better eventual temperatures.

      1. In the movie “2010” the Russians used a “ballute” to slow their spaceship to orbit Jupiter.
        It was a cluster of heat resistant balloons that surrounded the ship while it skimmed Jupiter’s upper atmosphere.

        1. NASA’s Low-Density Supersonic Decelerator project, back around 2015 I think, was doing engineering development for this concept. it was mostly focused on Mars entry, though. The scale for Earth reentry gets ridiculous quickly. But if you need a very small reentry payload, it apparently could work quite well, even given very high initial reentry velocities.

          And, at least for the very small payloads, a ballute sufficient for reentry is also a ballute sufficient for a pretty soft landing even absent any other parachute system.

          On the other hand, the size and weight of the reentry module rapidly scales out of control as the payload scales. If I remember correctly, a Gemini-scale human capsule would require a ballute system nearly the size of a Soyuz cargo craft, and an Apollo-scale capsule’s ballute system would have cubage and mass more like an ISS module.

          But, if the materials had been available at the time, a reentry payload such as the film cannisters on the Discover/CORONA satellites would have been really easy to do, and quite effective. They would also probably been easier to recover in flight, because a ballute appropriate for that weight and reentry velocity would have had a fall rate similar to a normal parachute, and would have been much easier to snag with the fish hook ropes, without tearing something or risking parachute reinflation after it was successfully snagged.

          The cannisters also could have held significantly more film, because the big challenge was heat propagation into the film compartment, and a ballute is a much better insulator while also keeping the hot interface much further away from the delicate payload. On the other hand, the total volume-to-orbit addition to the CORONA would have been larger because the ballute cannot pack down into as compact a volume as that taken up by the heat shield plus parachute.

  8. I am surprised the strange case of the original Atlas was not mentioned. In essence, it was a 1 and 1/2 stage launch vehicle, able to reach orbit by shedding two of its 3 engines along the way to save weight. However, the tyranny of specific impulse will always limit what we can do with chemical propulsion. Similar to the Atlas cheat, we may get a little further with hypersonic jet engines using atmospheric oxygen, but even that may leave us just short of SSO systems with large orbital payloads…

  9. USAF Captain Mitch Burnside Clapp had the great SSTO(-ish) idea of using dense non-cryo fuels in a light spaceplane: it would burn hydrogen peroxide and ordinary jet fuel. It would take off horizontally under its own power, and refuel at high altitude from a more-or-less conventional air tanker, then re-enter and land like the space shuttle. It had a small cargo capacity, but the numbers worked. He called it the Black Horse:

      1. Excellent point! There is a good reason for Clark’s description of H2O2 in “Ignition!” “Always a bridesmaid, never a bride.” Peroxide decomposition is catalyzed by transition-metal compounds. And non-transition-metal compounds. And random mixtures. Dirt. Asphalt. Human tissue, especially blood…….. Yes, it’s room temperature store-able, but even under ultra clean prep and storage, high-purity H2O2 still does the slow ‘bloop…..bloop….bloop…..”

    1. Have you calculated how much energy it takes to suck all the air out of a huge tube like that?
      And since you let the air back in to launch the rocket, you have to pull it back down to vacuum every time.
      And most of the velocity a rocket needs is sideways, rather than upwards.

      1. “Have you calculated how much energy it takes to suck all the air out of a huge tube like that?”

        I bet our Vice-president could do it with one hand behind her back!

  10. OK, now I’m an idiot, but if I look at a ramjet and a rocket engine they look similar, except the ramjet gets it’s oxidizer from the air and the rocket from storage what if we built an engine that combined the two? So here’s the idea, launch a winged SSTO from a land based launcher similar to (but larger) than that on an aircraft carrier to get it up to a speed where the ramjets start, then when the air gets too thin the engine inlets close and the onboard oxidizer takes over until the SSTO reaches orbit. To deorbit, well the Shuttle has done it so that part is figured out. So I know that this is stupid, but I don’t know why so could somebody give me the technical reason for the stupidity?

    1. Getting a scramjet that works at the altitude and hypersonic speeds that would be best for a launcher is hard. If someone managed to make an engine that has the right capabilities, then I expect it would get strapped into rockets.

      Note: Ramjets and scramjets have different operating speeds.

        1. This probably falls under the concept of “Rocket Based Combined Cycles” or RBCC of which there has been plenty of literature research. The short summary is making a high performance rocket engine which manages to contain its desire to spontaneously disassemble is incredibly difficult. Then trying to combine it with flight through many different aerodynamic regimes with variable atmospheric properties which you are trying to feed into your combustion chamber or exhaust tends to give nightmares to propulsion and aerodynamic engineers.

          I think it might be possible but it’s a horrendous engineering challenge.

  11. Fusion energy. One we have an effectively unlimited small, power dense enough energy source *everything* becomes possible. (oooh, Iron man’s ARC reactor!!)
    Combine that energy source with ‘room temperature’ superconductors and we’ll have a path to plasma propulsion tech that from the outside, whilst squinting will resemble something like an anti-gravity system.
    You’ll have enough energy to enter the atmosphere slowly over a longer time, negating the significant heat shielding needed.
    You’ll have enough energy to ‘shoot straight up’
    could the source of the plasma ions be the fused particles being ejected from the fusion reactor?

    1. Unfortunately, fusion won’t work in atmosphere, especially any direct fusion thrust concepts.

      The atmosphere, even when at very high altitude & very thin/low pressure will just wreck the fusion reactions from happening.

      And the other issue is that while the exhaust velocity (Specific Impulse – Isp) for fusion is quite high, the total thrust is miniscule.

      Imagine you have two pressurized water rocket motors to push a car, like the red plastic pump-up kids toys. One shoots a squirt gun needle of water out at supersonic speeds. But it only pushes an ounce of water. The other just barfs out 1000 gallons constantly, but at only 20mph.

      You might understand what will actually at least get the car rolling forward, or actually slow it down if you let it roll backwards down a hill.

      And the supersonic needle jet of water would be handy for long distance cruising on a freeway road trip once you’re up to speed, because it’ll actually last the whole way, and you won’t run out of water.

      Obviously, “get both” barf out a ton of mass at really high speed to truly “get moving” is a natural idea, but there’s really not a lot in physics or engineering that can do that.

      And if there is actually something like that ypu can come up with, and you got it working, it might be a decent deep space engine. But anywhere near a planet, to take off or land, it acts a lot like a Death Star laser, and starts drilling a hole a thousand miles deep…

      Somebody might get mad at that.

      Otherwise, nuclear propulsion is just using that energy to get stuff hot for “fast barfing” to push you. Even if you don’t combust the “stuff,” you still run out of it as your tanks empty, and you’re going to need “more stuff to move the extra stuff.”

      And, that talk of the “rocket equation” and how you need “fuel to move the extra fuel to go faster” thing, that’s true for more direct-thrust fusion and fission propulsion concepts too. You’re still throwing/barfing stuff in one direction to move the other. It’s also true when coasting in space and wanting to move to someplace else. Going from orbit around Earth to Mars, or floating as freely as one wants to choose to do rhe math.

      The rocket equation is indeed the worst when taking off of a higher gravity planet with substantial atmosphere like Earth, but it never goes away, ever.

  12. X-33/Venturestar was kind of a scam from the beginning, even if the linear aerospike is super cool… It’s too bad.

    SSTO is one of those ideas that is like a loose tooth, you know you shouldn’t poke at it but it is irresistible. The optimal designs for a sea level vehicle versus an orbital vehicle are just too different, it makes more sense to stack two or more vehicles up. Especially if you can catch the bottom ones and re-use them, like SpaceX does. At that point, there’s not any great reason to go for SSTO. You’d get everything done less efficiently, essentially for vanity.

    Unless you want to revoke nuclear treaties and bring back the great GOD Orion. Blast yourself from sea level to Saturn in the same hulk by shoving nukes out the back at one to two Hertz. Designate whatever country you like the least as the launch site, and make sure there’s no wind

  13. SSTO doesn’t need to carry much or even any payload on the way up to be very useful if its cheap enough to cycle and can come down carrying loads picked up in orbit. There is lots of junk to tidy up with some of it being very beneficial to bring down intact, and more than a few satellites that are only going to be junk because they are stuck up in orbit while needing a simple fix, which might be as minor as a refuel.

    1. And that is part of the gotcha. Any engine system with sufficient performance is unlikely to have maintenance costs and mean times between major work similar to a turbofan. If we’re lucky, it won’t be similar to current reusable liquid fuel rocket engines, but it’s more likely to be.

      And the SSTO vehicle itself is a likely source of routine and extensive maintenance costs and delays.

      People tend to hope for something that goes to orbit and back, with the operating costs of an airliner. But any SSTO is probably going to be significantly more complicated and prone to damage than a Falcon 9 or a Starship.

      For that matter, consider the significant maintenance time and cost of any glide-reentry vehicle to date, not just the Shuttle. The Shuttle program was delayed long enough that by the time it flew, it was extremely old technology. But that’s not really true on Dreamchaser, the X-37B, etc.

      SSTO, to be useful, has to get back down, and a lot of the unavoidable maintenance cost and repair delays come from the “back down” part…

      1. Really can’t say any of that with great certainty, though I don’t really disagree. However with effort you find its usually possible. And then being possible it might actually be a good idea – the engineering and research just has to be done first.

        I’d suspect the technologies and materials for a SSTO space shuttle type concept (be it capsule or space plane) that can lift small payloads and people to work on stuff in orbit and recover even large old satellites and junk are largely already in existence. Just have to have to put enough money and time into combining them to make it happen. In much the same way Falcon 9 seemed completely impractical, hardly covered itself in glory early on, but suddenly has become the default launch vehicle for nearly everything it seems. Being now both cheap and reliable, where to start with it was pretty terrible…

        Also if a Starship can re-enter and re-launch cheaply that same heat protection system can almost certainly be applied to a single stage vehicle, and nobody says the single stage has to be consumable free – could just strap a wooden (probably ply) plank to the cooking side, sacrificial ablative and cheap. Bolt on the new one, same engine work as the SpaceX stuff if not less (being lighter and likely landing aerodynamically the engines probably wouldn’t get as much use in each flight), refuel, and good to go cheaply…

    2. There are other forms of SSTO feasible, but they have their own problems.

      If you have the budget (cryofuels are very much not-cheap), you could even easily do something like a Falcon 9 first stage using aerospikes. The aerospike would remain thrust-efficient throughout the flight profile, and the required much larger diameter would allow enough fuel to cover the inefficiency of having to accelerate and decelerate the whole craft, rather than just a light upper stage. In effect, it would turn it into a well-understood solved problem, and would avoid the complexity and maintenance burden of an aerodynamic glide vehicle, in exchange for losing any chance at air breathing.

      But, anything that it might do well, something like a Starship would probably do equally well, nearly as cheaply, and a lot more flexibly.

  14. To those who have herein presented ‘novel’ suggestions that could make SSTO practical, I refer to a quotation from an engineer who was far ahead of his time, ‘Wheels’ Axlebolt (a guest star on The Flintstones):

    “Every new idea sounds great…….until you do the math.” ;-) :-D

  15. Functional and economical SSTO is extremely unlikely. Winged HTOL is just… impossible. And anyone mentioning the X37B, or Dream Chaser, they need to remember both utterly sidestep the problem by being rather small, and riding atop a plain old staged rocket under a payload fairing…

    There’s really just no savings to be found. And if one actually was produced in a workable fashion, SpaceX Falcon 9, & Falcon 9 Heavy, cost, payload, & launch cadence have already left it in the dust. Starship hasn’t even entered the picture yet…

    Imagine what lofting 150 tons at-will, with theFalcon 9 launch cadence looks like. Something bigger than Saturn V, lifting off once or more a week.

    Rapid at-will unusual inclination small payload business models… those start looking unrealistic when F9 lofts a deck of 30, 50 Starlinks, or whatever it is, at once, and maybe parasite carried a few university cubesats, or a HAM radio club “gratis.”

    Making staged rockets robust & reusable and more “SSTO-like” has proven far more effective than chasing pipe dreams of actual SSTO. And fuel & oxidizer costs, especially LH2, LOX, Kerosene, CH4, or Hydrazine/Nitric Acid derived hypergolics… those are all a pittance. It’s the dumped/destroyed stages that’s the cost sink.

    Then, one day, SpaceX actually said: “Let’s just tailstand suicide-burn & land one.. no really stop laughing and watch this…”

    Aircraft-like flight profiles to hypersonic, before a final burn up & out for orbit at high altitude, lose all the “savings” of atmospheric O2 on the mass penalty, as air breathing ramjets, scramjets, etc. become dead weight the instant space is reached. Just as your friction/atmospheric losses end.

    Skylon’s SABRE that can actually “switch modes” and effectively change to vacuum rocket, and actually collect supersonic atmospheric O2 and chill/liquefy it… that is damn impressive. However, the plausible payload is still pathetic.

    And, when one does posit some “secret sauce” engineering, fuel, engines/propulsion, better Isp, new ultra lightweight materials… whatever it is, thay they insist makes SSTO “workable,” if one thinks about that critically and objectively… a “traditional” staged rocket uses that “new fancy thing” even more efficiently. Or, it never needed it in the first place.

    So say that some super lightweight & strong alloy is discovered, literally MAGIC… and it even eliminated the need for TPS on reentry. It’s got compresssive/tensile strength better than titanium, it’s thermal & refractory properties exceed Tungsten, it weighs/masses less than Lithium, and costs as much as low grade Aluminum.

    Simultaneously, the “plumbing burden” for turbopump rocket engines suddenly evaporates with a rotating detonation aerospike design, and a Thrust/Weight ratio double of anything that came before…

    Guess what? A staged rocket built with those things will still throw more mass to LEO than the SSTO would, and it’ll scale to arbitrarily large sizes too, meaning it’s payload is exponentially better.

    Once one lets go of the subjective (and flawed) impression a “spacecraft” can be a “sort of fancy airplane that can just go even higher…” the actual “use case” for SSTO almost completely evaporates. Because an “aircraft” is about as useful a conceptual basis for a spacecraft as an automobile is. There is no air up there, nor is there any roads or ground.

    And other non-winged SSTO concepts, or vertical launched ones, they all fail as being practical well, the moment that capture/landing boosters, & reusable staged rockets are possible.

    To be fair, it’s a very potent fallacy. So much so that even scientists & aerospace engineers that should “know better” fall for it. And they could correct themselves with a bit of “bar-napkin math too.”

    1. >Aircraft-like flight profiles to hypersonic, before a final burn up & out for orbit at high altitude, lose all the “savings” of atmospheric O2 on the mass penalty, as air breathing ramjets, scramjets, etc. become dead weight the instant space is reached. Just as your friction/atmospheric losses end.

      Which is why you define that aircraft as a launch vehicle and resist letting anyone call it a stage, so that you can leave it behind as soon as the weight is no longer worth carrying as you rocket into orbit on your vacuum-optimized engine(s). Remember that even at high altitudes, it takes more thrust to hover against gravity than to use wings and only need to fight drag, so the heavy aircraft may still be of some use for its wings, even once its engines are useless. Though, the appropriate aero may be so much different at the top end than it was at takeoff that it is hardly worth doing with many launch craft options. Certainly a 747 seems like a poor fit, so maybe there’s a balance where the rocket can have some aero features without turning into the shuttle again and wasting mass.

  16. The final trajectories for VentureStar I simulationed never achieved a stable orbit. Those trajectories simulated launching and landing at KSC with one trip around the earth. The trajectories were optimized to stay within the reentry heating limits while placing the maximum payload in low earth orbit. The payload was not in an internal payload bay (as shown above). The payload was carried on the top of the VentureStar and had its own propulsion to achieve orbit. The VentureStar was essentially the first stage of a two stage vehicle.

  17. Titan II was very nearly a SSTO.

    SLS, Shuttle and Atlas were stage-and-a-half-to-orbit designs.

    This could allow wet workshops:

    No Adama maneuver, no tiles, no Starship.

    I want a dedicated Shuttle 2 with Merlin engines.

    Orbiter uses X-33 metal heat-shield, and contains kerosene.

    External Tank is all LOX…leftovers used for oxy-torch—ET made from start to be left in orbit.

    Strap-ons like Falcon or winged.

    Returning orbiter like the jet equipped Buran analog.

    Kerosene allows standard jets, not unlike OK-92

    I want self-ferry, so big jet engines.

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