sevenperforce

It doesn't need to be too perfect. You just need to parallel-stage Fleas in duplex around your capsule, with decouplers in separate stages. You can use RCS to maintain retrograde attitude and suicide burn with a pair of Fleas, then decouple them while they're still running when you no longer need them. Subsequent pairs can then be used, giving you several chances at the suicide burn. Re-entry would probably require that you hold on to the empty SRBs and use them as disposable heat shields.

Then by all means let's replace it with an SSTO-capable airbreathing VentureStar.

The difficulty is that this is not a constant-acceleration trajectory.

No indication yet that the launch is actually scrubbed.

Right. Beamed power would assumptively be coherent/in-phase (think laser). So power drops off due only to scattering, not as any consequence of geometry. That is why I was thinking that dropping power by 1/3 over the course of a Martian transfer would possibly correlate to the gradual attenuation of a beamed power arrangement.

How have I not seen StarClipper before? That is beautiful. More beautiful would be a StarClipper setup, but with an airbreathing VentureStar core and a pair of F9 boosters in place of the ET.

The ideal velocity is what gets you there fastest. And you don't thrust prograde the entire way; you thrust prograde to the halfway point and then thrust retrograde to brake the rest of the way. At least in a constant-thrust brachistochrone. This is different; hence the mathematical conundrum.

I think SpaceX has a decided advantage due to the versatility and flexibility of their launch platforms. Between Falcon Heavy reusable, Falcon Heavy expendable, Falcon Heavy core expendable, and the various options for Falcon 9, they can service just about any combination of launch requests. They are also small, and are able to fit their launches to the specific requests and requirements of their customers, as evidenced by the last mission. Price per kilogram isn't everything, or we would already be using Big Dumb Boosters. A better metric would probably be price per kilogram for a specific mission profile.

The thought occurred to me that if you had an engine with sufficiently high energy to pull a brachistochrone (thrust prograde halfway to your destination, then retrograde until you arrive) to Mars, the ideal plan for a manned Martian mission would be to start from LEO at 1 gee, then gradually taper off thrust through the full transfer to 0.3 gees to Martian orbit. That way, your crew would be smoothly acclimatized to Martian gravity and have no adjustment period. The same could be done in reverse, starting at 0.3 gees and thrusting harder and harder (no innuendo intended) until you reached Earth at exactly 1 gee retrograde. Unfortunately I have absolutely no idea how much dV would be required for such a maneuver, nor how long the transfer would take. It would require like four nested integrals, and trying to set it up for iterative solution in Excel would be a nightmare. I don't even know if outgoing dV would equal incoming dV, due to the influence of old Oberth. Any ideas on how to calculate that? Notably, such a thrust profile would be a prime candidate for beamed power...

Gorgeous photos. The only reason they planned wings and turbofan engines was because they didn't have the computer control or deep throttling they needed for sitting down on the tail.

I have yet to see any advantages in such a design over using something like the Falcon 9R as the first stage.

This is basically what I expected to see: "The thing that shocked me was that at the beginning, this reusable flyback booster was just a cylinder with engines and little wings, just a turbo fan in the back. And three years later these were complete Airbuses in terms of size with four engines in each of them." Your designs really really burgeon.

Footage from Shuttle re-entries as well...even one from Columbia's last mission, though it ended well before the breakup. But no footage from something not intended to survive re-entry.

Hey all, I've been playing the Demo for a while now, and there's a challenge I'd like to propose. Can you make it into orbit and back using only solid-fueled boosters (specifically, the RT-5 and the RT-10) without a parachute? Rules: You don't have to use Demo, obviously, but you have to limit to the Demo toolbox. No mods. It has to be manned. The capsule must return intact. You have to reach a stable orbit outside of the atmosphere before returning. I was thinking more "can you do it" than a particular winner, but we can say that whoever can do it with the lowest launch mass wins. I'll try it too. Good luck! EDIT: @*MajorTom* proved this was possible by making a glider and ditching it into the ocean, which wasn't what I had expected but is definitely a win! So good job. For further submissions, I'll additionally specify that a soft landing on land is required, with or without landing legs. This is supposed to be an exercise in suicide burns, haha.

Which you can do because burning close to the planet leaves your exhaust with much less gravitational potential energy, allowing you to keep that extra kinetic energy.

That's why I still have a warm place in my heart for small SSTO concepts, despite how difficult they would be to design. Launch vehicle costs can be brought quite low by reusing separate stages, but the only way to significantly decrease workforce is to go to a single launch vehicle with minimal refurbishment.

Hear, hear. Here. Yeah, as others have said, it's a barge landing. With the BEAM in the trunk weighing them down, I think they would be cutting awfully close on a RTLS. It wouldn't make sense to attempt a risky RTLS when they have a very good chance of sticking the barge landing. Another barge landing failure, while disappointing, would not be the end of the world. A RTLS failure would be devastating; it would make the former landing look like a fluke while potentially messing up FAA approval for future attempts.

Yeah, that's an issue. There are two other challenges I can see -- one is that adding a pair of vacuum engine nozzles might end up spraying some exhaust from the other engines onto the outside of the vacuum engines, which is less than ideal. Another challenge is changing center of mass/center of thrust because you don't have a balanced launcher. But those are solvable. Crossfeed might not be necessary; your core booster is firing fewer engines than your strap-on booster, and can be downthrottled past maxQ. Plus, once altitude is high enough, the higher-thrust vacuum engines can be ignited and the other engines can be shut off entirely, which further decreases fuel consumption. So it might even work without crossfeed. If so (or if crossfeed can be implemented), then it's quite possible that the booster would have enough remaining dV in orbit to burn off a good deal of speed prior to re-entry. Particularly because it can RTLS without a boostback burn, simply by doing AOA.

That's silly. "Our planned heavy-lift launcher will match your operating medium-lift launcher in per-kilogram costs!" Apples and oranges. Never mind that Falcon Heavy is much further along than Ariane 6.

Here's an idea. If Elon wants 100% stage reuse, why not offer a tandem launch with crossfeed? Call it Falcon TT. Take a standard Falcon 9 FT first stage and replace one opposing pair of its outer engines with Merlin 1D Vacuum engines: Strap it to a standard Falcon 9 first stage capped booster and add your payload on top. On launch, fire all nine Merlin 1Ds on the strap-on booster and fire the seven SL-optimized Merlin 1Ds on the payload booster, keeping the pair of Merlin 1D Vacuum engines turned off. Crossfeed fuel from the strap-on booster to the payload booster up past Max-Q, then throttle down the engines on the payload booster while keeping the strap-on booster at full throttle. Within moments, the vehicle will be high enough to ignite the vacuum-optimized engines at full throttle, downthrottling the other seven or even cutting off several of them entirely. Continue until the strap-on booster is down to its boostback and landing reserves, then separate. Allow the two Merlin 1D Vacuum engines to carry the remaining stage and payload all the way into orbit. With the two vacuum-optimized engines, the stage will have a much higher remaining delta-v in orbit and can deliver its payload with enough remaining dV for an extended re-entry burn. It can RTLS without a boostback burn because it is already in orbit. It can touch down on the SL-optimized engine. I think that would work, anyway. No one said it couldn't be done. It can just be done with higher payloads and lower booster cost if you stick with tail-first RTLS landings. Those StarBoosters would be insanely expensive.

And maybe even a drop tank, with a side-slung spaceplane, eh? No, it wouldn't be an SSTO. But it would be closer. I wouldn't want to use SRBs, though; the whole point of an SSTO is rapid reuse, and SRBs are anything but. What about a triad of kerolox engine clusters wrapped in a shroud around the base of the core rocket, carrying LH2 tanks for crossfeed and forming a duct for air augmentation of the core engine? Even the simplest duct can increase thrust (and decrease thrust-specific fuel consumption) by 15% at start and by up to 50% during ascent. The ring would be dropped when its LH2 was depleted for a propulsive RTLS landing. The ascent would be short enough that it would be virtually refuel-and-refly. Not unlike the Falcon 9 first stage, the core would be theoretically capable of zero-payload SSTO; the launch assist ring would serve merely to allow the core to carry a large payload into orbit. You could use launch assist rings of various sizes and capacities while retaining the same core stage for simplicity.

I wonder if it would be useful to explore a smaller parallel-staged first stage with a larger SSTO-capable main spacecraft. Sort of a "launch assist" stage, but one which carries a substantial amount of fuel for crossfeed to the main spacecraft. Basically, the smaller parallel stage would compensate for gravity drag and aerodynamic drag while "gifting" the main spacecraft with a substantially decreased dV requirement for orbit, allowing it to sustain dramatically higher payload fractions. The launch assist stage would need to be high-thrust, but would not need to reach particularly high altitudes or velocities compared to typical stacked first-stages, so recovery would be extremely easy.

The mass penalty to strengthen the booster for horizontal landing is severe. You're no longer just supporting a single column against a single stress; you're supporting wings (which aren't axisymmetric) and pitch stress and yaw stress. You're also supporting far heavier landing gear, and since it needs to retract inside the body, that's less space inside the body for fuel. The landing gear is heavier because the booster is heavier, and on and on in a punishing cycle. You have extra weight due to the need for control surfaces; unlike grid fins, the weight of movable aerodynamic control surfaces is significant, and you need a lot of control authority because of how small your wings are. You'll easily triple the dry mass of your booster.

How sure are you? I am almost certain that the Shuttle had internal tanks for the SSMEs. Watch this video of the External Tank separation -- there is no MECO before separation and the plume remains throughout. EDIT: After reviewing more info it seems you're right; MECO came before separation. In any case, I was just presenting a potential design for full reuse.

This seems the same as a Falcon 9R arrangement with an expendable upper stage, except that it has to carry a cargo bay up and back, and has useless wings. Four legs or three legs, doesn't matter from a weight perspective. The Falcon 9 first stage could land with three legs easily; they would just be larger individually. Four legs is slightly more stable than three legs. The tank is empty at vertical landing, too, so there isn't any difference there. Horizontal makes no difference either. The landing gear needs to be fairly wideset so that the rocket body won't tip over either way horizontally. Plus, you have to factor in control surfaces, and you need to be able to extend the gear from inside the body because landing gear cannot fold up aerodynamically. The side boosters couple so that their thrust is transferred through their central axis just like the core booster. Horizontal landing would introduce radial/lateral forces far greater than those experienced during takeoff, even though axial forces are comparatively minimal. They are called grid fins... but they probably doesn't weight much. The grid fins are used for hypersonic aerodynamic control during and after re-entry. Landing stability during the suicide burn uses cold gas RCS.