sevenperforce

The original purpose of the SLS was to repurpuse Shuttle-era hardware and personnel. That won't happen.

Alternately, I wonder if a partially-airbreathing first stage would ever be worth developing. VTOL style.

If the Raptor engine really does end up being as amazing as expected (TWR > 200 and vacuum isp over 380 seconds), then honestly it really only makes sense to use it for everything. Especially because methane is so cheap. Not being a SpaceX fanboy here; just saying. Hence Raptor-derived Falcon X.

That would also be good for a second stage.

Ah, well, look who was incorrect.

Hence folding back. Maybe all the way into a cowling.

Well, nothing REQUIRES maneuver nodes, but maneuver nodes make everything way easier. That video is precisely why I said "nearly impossible".

One can assume that landing gear would be approximately equivalent in weight to landing legs, but unless the wings are wet, the wings themselves are almost definitely going to outmass propellant landing reserves...at least for ASDS recovery. And that's not even accounting for the additional body reinforcement you need for dual-axis operation. On the flip side, I've had a reasonable amount of success with this design: feathered tail canards and very small wings work wonders. Aux engines mostly because the low-atmospheric L/D ratio isn't enough for a horizontal landing. Of course, it's more an upper stage design than a booster design. The original SLS proposal, pioneered by the guys (and gals) from the NSF forums, was all about reusing Shuttle hardware and staff. That is no longer really part of SLS; thus, SLS is useless.

Protip: play around in sandbox until you've taught yourself to dock. Direct ascent to Duna or Eve landing is hard enough; direct ascent with return is almost impossible for Duna and definitely impossible for Eve. Use the debug menu and turn on infinite fuel and use that to play around with docking until you get the hang of it. I assume you've at least gone through the motions before? E.g., setting target, using RCS translation, etc.? With infinite fuel enabled and the navball set to target tracking mode, you can simply wait until closest approach and then translate toward retrograde until you cancel velocity. Then, translate toward target until you pick up speed. Wait again for closest approach and repeat. It will work, eventually.

Glide back or boostback? I think the latter is more fuel efficient. But yeah, for Falcon X I'm thinking something roughly New Glenn sized, or slightly larger, with ten Raptors. But lithium-aluminum bodies rather than composite, to save cost and permit expendable missions. One nice thing about the Raptor family is being able to use methalox for RCS and optional upper-stage landing thrusters. I'm a sucker for biconic reentry and dual-thrust-axis landing of the upper stage but that's probably not realizeable. This whole topic is interesting given that the SLS is derived from a design that our buddies over at NSF originally proposed.

Raptor-derived Falcon X, and devote a bunch of funding to orbital prop transfer. With reliable orbital prop transfer and a single HLV, you can send anything anywhere.

I wonder if something like a propfan would work for this. LB turbojet core, variable-pitch geared pusher prop in the back of the engine cowling. The propfan would give it good takeoff and landing efficiency at low speeds, but would be windmilled or simply fixed at high speeds. Or folded back completely.

Probably either this: or this: But I'm working on a design right now which is particularly neat.

Well, for one thing, the higher your TWR is, the less of an impact gravity drag will have. But when we are talking about near-orbital velocities, it's definitely going to be a factor. Another issue is the Coriolis effect, which the previously-discussed math models.

The rotation of the Earth has a lesser effect for ICBM launches, because you're not going to orbit; you're going to a target that is on the Earth's surface so it is also rotating. However, if your ICBM is large enough to hit a meaningful fraction of orbital velocity, then the centrifugal element can negate part of Earth's gravity, decreasing gravity drag on your ICBM during the boost phase. However, I'm afraid that calculating this is extremely difficult. I've done it before, in advanced classical mechanics, but it involves creating a system of equations to model the differential rotation of the Earth as a non-inertial reference frame. Physicists were doing it with slide rules back during the Cold War. It's extremely advanced math and it's different for every possible trajectory. Adding staging to the mix makes it even more complicated.

There shouldn't be any differences in drag between eastward and westward launches. The problem you're probably running into is the rotation of the Earth. Just give it enough dV for westward launches, and then use a higher parabola for eastward launches.

The engines were on the correct side of the CoM, but there was a bigger problem -- the engine plumes were impinging (just barely) on the cargo bay doors. It wasn't enough to overheat them, but it was cutting my effective thrust to almost zero. It's a shame that KSP doesn't allow you to use differential thrust in place of gimbal when you have a large engine cluster or a situation like this. I realize that with the current engine placement, there's virtually no meaningful pitching torque on the ship as a whole. Differential thrust would be much more effective because the horizontal distance from CoM would be an advantage instead of a hindrance. I'll try rearranging the engines, cargo bay, and fuel tanks so that CoM is 100% balanced at all times during the landing burn.

With yaw authority turned off for the Thuds and roll authority turned off for all but the rearmost pair, I can now throttle up gradually without flipping over. I think that attempts to correct minor variations in yaw were misaligning the Thuds and causing it to flip. However, on the landing approach I am telling SAS to hold the internal docking port to retrograde, so that it will try to make the belly face prograde. So constant nose angle isn't the problem. Since nose-down is my main problem right now, I think I'll try turning off pitch authority for the rearmost Thuds and see if that helps. EDIT: Going to try some Grasshopper tests:

Actually, that was happening at about 4 km. Anyway, starting with the canards feathered up for entry and then down for descent solved the nose-down problem completely, if you look at the most recent photo examples. I've got entry and descent licked; the only remaining problem is the actual landing approach. I go from level, stable flight with no control input other than SAS: ...to opening the bay doors, still stable despite a little added drag: ...to throttling up the Thuds slowly, with corresponding instability: ...and then suddenly I roll to one side (which makes no sense; the gimbaled Thuds should have tons of roll authority): ...and dropping like a brick: Maybe the Thuds are trying to control yaw and are throwing everything out of whack. I'll try it again with yaw authority off on all engines and roll authority only on one pair of the tail engines. I'll need to account for the fact that roll is yaw and yaw is roll for this control scheme, incidentally.

A few changes. Going at it with the canards inverted for landing approach.

Yeah, exactly. Although I was thinking it would stay nosed up a little on landing approach; basically, stable at a high angle of attack due to body lift. Hmm, I had been trying to punch the vertical engines, suicide-burn style. I'll try throttling them up more gradually and seeing if I can do a more controlled landing approach. I don't open the main cargo bay on EDL. Though yeah, it's a touch unstable in yaw. Going to more level flight rather than trying to do a straight-down drop has helped with that. I'm intentionally not using any RCS or reaction wheels during the descent or landing approach. If I'm throttling up the aux thrusters slowly, I might kick on the RCS at that point, just to help a bit.

Hmmmm, interesting. What if I try flying it at a very high AOA rather than truly belly-first? E.g., gliding like a brick. That might be able to give me passive stability, and since the Thuds have a decent gimbal range, I can cancel my horizontal velocity pretty easily. Doing some redesign work... Okay, here, this seems to work a bit better. Seems like I'm making progress...

With on-orbit refueling, I have plenty of dV for pretty much anywhere. The Vector's aren't ideal for space, true, but I can replace them with Darts once I get the design perfected; I just need the Vectors to get off the ground. First goal is second stage to LKO and propulsive biconic EDL. The notion of using the same design for executing propulsive EDL followed by SSTO on Duna is secondary.

With the rocket equation. 348 seconds of specific impulse times one gee times natural log of 316 million short tons divided by the mass of the Earth equals 104.6 km/s. https://www.wolframalpha.com/input/?i=(gravity+of+Earth)*(348+seconds)*ln((316+million+short+tons)%2F(mass+of+Earth)) EDIT: 348 seconds was a vacuum specific impulse for kerolox off the top of my head. That's the MVac D. I think the maximum theoretical specific impulse of kerolox is something closer to 358 seconds, which gives you 107.6 km/s. If you want to do something exciting, like going nuclear with a notional specific impulse of 900 seconds, you get a much more impressive 270.5 km/s. To get to galactic escape velocity from our current location and orbital velocity, you'd need to throw your "fuel" at around 1,060 seconds of specific impulse. ANOTHER EDIT: Of course, if you have a perfectly-efficient mass-to-energy conversion engine, you can accelerate Earth to galactic escape velocity for the low, low price of just 0.11% of its mass. Which is 6.33e21 kg, or roughly half the mass of Pluto. Given the influence of relativistic effects at this scale, your mileage (literally) may vary.

I did the same thing. I had my sound muted and so I didn't ever realize it was on a loop.