sevenperforce

Playing around with propellant crossfeed. Now that I've got control down, I can make orbit on a single liquid engine by using a ton of drop tanks.

I've played in sandbox and will go back shortly, but only after I do everything in Career mode that I can. But you're right, it does suck. Right now I'm just trying to get to orbit with an 18-tonne launch mass limit. The last remaining contract I have is to break 2.5 km/s and I have fallen just 120 m/s shy several times, but now that I realize how to use inline reaction control wheels, this should be a cinch. Any idea how to pick up additional science cred in career mode? I've already taken crew observations from the pad, from low flight, from space, and over the water, and I've used both the mystery goo and the science lab at launch and in suborbital flights.

I'm playing the Demo on Career mode.

Ram compression happens regardless. It's not something you can control. You could possibly reduce turbocompression while beginning to inject LOX into the combustion chamber to keep thrust up ... maybe it could gain you another half a mach or so. I mean that there is a range of airspeeds where ram compression could compensate for gradual losses in turbocompression IF there was a way to inject ram-compressed air. But injecting airflow into the nozzle still allows you to burn its oxygen. It's the same principle as an afterburner, but in reverse; instead of injecting fuel into air-rich exhaust in the nozzle, you're injecting air into fuel-rich exhaust in the nozzle. Turbofans lose thrust rapidly as you reach supersonic because they rely on mechanically forcing air around the engine using the fan. But if you inject directly into the nozzle, you don't have to rely on mechanical force to pull the air past; you're using mechanical force to compress and inject the air but the hot exhaust does the work of pushing the air out. So it's not a pure turborocket; it's a turborocket with reheat. Kinda like this. I still don't see the benefit. Remember that in a shock cone intake, the capture area is not the area between the cone and the lip, but, at least at the design condition, is the entire frontal area of the intake up to the lip (by design condition I mean that the shockwave intercepts the lip). You're not getting any more air with your geometry. Yeah, I recognize that I'm not getting any additional air...but I'm also allowing a lot of bypass to compensate for densities or speeds which would cause extreme drag. The purpose of turning it inside out was essentially to do for intakes what an annular aerospike nozzle does for nozzles. With the benefit of having a virtual aerospike on the back end.

This article gets more stuff right.... https://www.google.com/amp/m.mic.com/articles/amp/136899/spacexs-falcon-heavy-the-most-powerful-rocket-in-the-world-photos-video?client=ms-android-att-us&espv=1# But you don't need a Falcon Heavy to lift a Dragon V2 to the ISS.

Actually the CMBR only obscures the first 300,000 years, but your point remains. The only possibility for us to "see" beyond our region of the 'verse would be if there were local anisotropies present during the inflationary epoch which would be exhibited on a macroscopic scale now. But so far we haven't seen any.

Anything that would be made more efficient by the use of room-temperature superconductors.

Yeah, it's not supersonic. Basically the same concept as the SR-71: takeoff with empty tanks, refuel at modest speed, then burn to orbit from a much more optimal launch location. It's basically the same as air-launching, but you can use existing tanker aircraft rather than designing an entirely new mothership or dealing with decoupling.

Oddly, I don't have any trouble with flipping on the stages where I use SRBs. They're hard to turn, but it is doable. Only when I fire up the liquid-fueled engines do I get uncontrollable end-over-end tumbling....and that's nearly out of atmo so I doubt fins would help. Do SRBs have a force vector distributed over the whole booster body? That could explain why they don't flip as easily. I'll try doubling up my reaction wheels to see if that will give me a little more pitch control.

Try it in career mode demo. No more than 30 parts; launch mass limit of 18.

And I wasn't even using those. How do I use those, anyway? Do I need multiple ones in various axes? Why does the RT-10 seem so much more controllable than the LV-T3?

If you're going to use an airbreather as your first stage then eschew LOX altogether and just have it accelerate in-atmo on a trajectory that will take it above the Karman line. Open internal bay, release vacuum-optimized second stage+payload, and then re-enter. Should be able to beat the Falcon on a very narrow range of flight profiles. In-air refueling is by far the simplest way to get an SSTO spaceplane though.

The only engines available in career demo are the LV-T3 and the RT-10.

I started playing the demo, and I'm trying to figure out a few things. The limit on launchpad mass and part number is killer. I can't make orbit. Also, are liquid-fueled rockets notoriously difficult to control, or is it just me?

Finally got a chance to try out the demo today. Love it. Stiff learning curve...didn't kill any Kerbals yet, though. At least not outside the tutorials.

Well, the goal is markedly different. Their engine wasn't intended to operate in a vacuum. The beautiful engine on the sr-71 answered a different question: how fast can an air breather go? That isn't the same question that SABRE is trying to answer. SABRE is asking: how long can an orbit-capable airbreathing rocket use a turbocompressor? The question I'm asking is different still: how much of an orbital rocket's propellant mass fraction can be air? Because that is the question that will get you to SSTO.

Negative, ghostrider. A rotating hab doesn't need to consume any energy over time. In fact, it can serve as part of the reaction control system for the ship. And heating is not the typical problem; cooling is. Getting rid of waste heat is a much bigger problem.

If the SABRE's operating speed is limited by compressor heating, then it would benefit by gradually shifting compression off of the turbocompressor and onto a ram compressor. But it can't do that, because it can only accept air in the combustor (spill ramjets aside). Well, "real engines" is a bit of a tricky consideration; there haven't been any airbreathing SSTO engines of any kind ever successfully built. But that depends on what constitutes a turborocket. A rocket engine which runs fuel-rich and accepts compressed air solely in the nozzle may well be more efficient than an engine which does not use its own oxidizer and accepts compressed air solely in the combustion chamber, simply because the former can accept a greater air/propellant ratio. The central bypass approach seemed to be the best way to get "high-bypass turbofan" performance. You can have a large intake because you can have a really, really ridiculously large effective nozzle. In a craft which was too heavy to take off under its own weight unless its fuel tanks were all but emptied.

Eh, just trying to solve the problem of being able to use ram compression and turbocompression in the same engine.

The purpose of having a central bypass rather than an annular bypass is to keep the compressor out of the flow path. That way it can still massively augment thrust at low speeds, but does not produce drag at high speeds. I also suspect that its maximum operating speed will be slightly higher, since it is pulling in air perpendicular to the airflow vector rather than bearing the full brunt of stagnation pressure. On the topic of (sc)ramjets vs (sc)ramrockets... We have a few choices for a partially airbreathing rocket engine capable of vacuum operation. You can put the fuel, LOX, and compressed-air inputs directly into the combustion chamber, as SABRE has done. Alternatively, you can put the fuel and LOX inputs into the combustion chamber and put the compressed-air input in the exhaust bell. The former choice has the attractive option of switching between pure airbreather and pure rocket, which seems like a major advantage. However, since it's possible to run the combustion extremely fuel-rich, comparable performance should be attainable with the latter choice, particularly because the use of pure LOX will result in a more efficient reaction than if your airbreathing mode is damping combustion with nitrogen. The latter choice also allows a much higher air flow than the former, which should significantly offset any of the former's advantages. So there needn't be bypass jets, just a bypass flow path opening into the exhaust bell.

I'm not averse to the thought of a lightweight sliding cover to seal off the precooler inlet, but if bleed air (which already would be used to run the compressor) can be used to form a smooth layer without moving parts, that ought to be simpler. What do you think, generally, about having a cylindrical turbocompressor mounted into the sidewalls of the intake, to allow mechanical compression of the airstream at subsonic and low-supersonic speeds without impeding ram compression at mid-to-high-supersonic speeds? SABRE depends on slowing down the airflow to allow turbocompression even at prohibitively high speeds where ram compression (while generally less efficient) would be more realizable and result in less drag. But if you can put the turbocompressor in the sidewalls then you can have both. An additional supersonic-flow scramjet/scramrocket mode would be nice, I suppose, but it's not necessary; the gains are rather low.

What are the differences between using a short three-engine suicide burn and a longer one-engine suicide burn? It's the same total dV, right?

How smooth of a surface are we talking about needing? Are allowable irregularities on the order of cm? mm? micrometers? So no chance of bleeding exhaust out into the flow path to smooth the surface?

How smooth does the parallel wall need to be in order to maintain supersonic flow with minimal pressure loss? E.g., given the following: As I understand it, a supersonic airstream entering from the left will be deflected parallel to the lower wedge, then flow horizontally (with shock compression) through the portion with parallel walls. From what you're saying, it seems the wedge itself must be perfectly smooth in order to have proper deflection. Would the parallel section (i.e., what is highlighted in green) also need to be perfectly smooth? Or could it have axial slits forming a precooler, flush with the wall?

Before it was spun up, yes. I think the case he's suggesting is where the ring is already in motion, and the vessel applies a reaction force only to counteract drag. In such a case, the torque on the force is only as much as is needed to offset the drag torque, so they cancel out.