sevenperforce

Note -- in testing, aero forces tend to break exposed radiator panels at around 60 m/s at SL. Just for reference.

The Ridiculously Oversized Space Telescope has arrived at Kerbal Space Center just in time to catch the anticipated merger of two black holes near the Kerbol system. However, during payload integration, tragedy strikes! The telescope turns out to be too large to fit into the prefabricated fairing. With no time to order another fairing, the Kerbals must find a new way to get the telescope into orbit. CHALLENGE: Launch an oversized payload -- something too large to fit into a fairing -- into LKO at the lowest possible airspeed. Airspeed is defined as the surface-relative speed below 70 km. To complete this challenge, you'll have to lift your payload completely through the atmosphere before accelerating it to orbit. The orbit must be anything over 70x70 km. Scores are based on your highest speed during the ascent. Be sure to keep your navball set to Surface relative tracking until you're over 70 km, or you'll show orbital speed, which includes the velocity of Kerbin's rotation. No performance mods. You can use a mod to track your highest speed, or you can just use the honor system. Bonus/tiebreaker: keep your orbital acceleration under 1.5 gees. I'll submit my entry shortly!

Yeah, you can pretty much just go arbitrarily high.... The real question is, what's the goal? What are we trying to lift?

.........wow. That was amazing.

I used to play Demo only. Here are a few you can do:

My entry: 16,704 meters. Probably could have done better, but my first attempt kept breaking up over and over, so I ended up sacrificing mass fraction and going super-modular.

I've seen video of a fifty-cal firing through a house of cards without knocking it down. One relevant note is that supersonic jets are designed with the equal-area rule in mind, which reduces the size of the sonic boom. A less streamlined object will produce a much more violent sonic boom. Also, the energy in a sonic boom is a function of the speed, so Mach 1.5 is many times less violent than Mach 3.

What do you mean by "ONLY FOR SEPARATING STAGES"? Do you mean the Separatrons need to be pointed retrograde and activated at decoupling, or what?

As a means of repurposing Shuttle hardware and personnel, the original DIRECT/Jupiter HLV was a great idea. It just didn't have a payload, which meant development crawled and crawled. By now, there's little or no advantage to repurposing Shuttle hardware, and SLS has evolved to use fewer and fewer actual Shuttle parts. IIRC, the early flights may not actually reuse mothballed RD-25s at all. An aluminum-lithium monocoque-body eight-meter Raptor-derived Falcon X with ten Raptors on the booster and two Raptor Vacs on the upper stage, flying expendable, would be able to deliver 125 tonnes to LEO with a ten-meter-wide fairing. A three-core expendable variant would be able to deliver a whopping 292 tonnes to LEO. And that, for cheaper than a single SLS launch.

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.