sevenperforce
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Everything posted by sevenperforce
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Not if their weight cost makes them prohibitive. An engine which can using air as its primary working mass from launch to beyond its exhaust velocity makes reusable SSTO not only realizeable, but economical. If it can be lightweight enough.
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What happens at the edge of the universe
sevenperforce replied to Starshipcaptain16's topic in Science & Spaceflight
Statistically, none. -
What happens at the edge of the universe
sevenperforce replied to Starshipcaptain16's topic in Science & Spaceflight
There's no reason to think that any edge exists. -
Moving parts are heavy, particularly when you're trying to redirect a flow of superheated air moving at ten times the speed of sound. The thrust-to-weight ratios of scramjet designs are their undoing already. If the increasing speed of the airflow ends up focusing itself, then you don't have to worry about moving parts and the same engine can function from launch to orbit.
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Moving parts.
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The "moving inlet spike" is the part that I'm trying to avoid. It's (relatively) straightforward to use an inlet spike to move the shock; it's a little trickier to figure out a way to let increasing Mach numbers move the shocks automatically as the shock angle narrows.
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If the shock angle decreases as a function of Mach number, then it should be possible to design an asymmetric intake which will focus shock convergence at the appropriate point for each target speed. I was wanting to have the precooler double as an inlet ramp to save weight and space; at high speeds, the pressure between the slits will be so high that it is effectively a flat surface. But the precooler and compressors can be entirely cylindrical rather than integrated with the inlet ramp; that's not a problem. The goal is merely to have high intake flow at low speeds without intake obstruction at hypersonic speeds. Then ram compression can do whatever it can to improve ISP via air augmentation and/or fuel-rich afterburning.
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How do we know it was still on three engines? I thought it was standard to do the re-entry burn on three engines and the landing burn on one engine.
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You seem quite knowledgeable on the subject, so let me ask this: does the deflection angle of an oblique shock change as a function of Mach number, or is it a constant? It's hard to tell from looking at shadowgraphs and diagrams alone. The idea is to have the precooler and compressors buried behind the drag shadow of the engine cowling and intake ramps. At a standstill, the compressors pull air out radially from the center of the inlet, with an effective intake surface area far greater than the axial inlet cross-section and an induced axial flow component apart from the compressor exhaust itself. As forward velocity increases, the compressors pull air in as it rushes past. At transonic and low supersonic speed, inlet shocks slow the airstream enough that it can still enter the compressors at optimal Mach numbers. Then, upon transition to hypersonic speed, less and less air enters the compressors because it simply goes straight through the engine, but at that speed it's no longer possible to get the air slowed down enough, so that's fine because the compressors aren't actually in the flow path. At least that's the theory.
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"Constant air flow for ventilation" of orders of magnitude less of an energy drain than "constant air flow for drag compensation on a gigantic suspended centrifuge". I think his example involved air jets as the driver of the rotation, which would tend to produce net torque. But sure, you can set it up in such a way as to zero out transfer of angular momentum. A tethered arrangement, with the hab on one end and the counterweight on the other end, is probably the simplest arrangement.
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"No signal" is not in and of itself problematic; the landing is a highly...energetic...affair, and has a tendency to mess with communications. But Musk has already announced it was an overly-hard landing. We don't know whether it missed or crash-landed or broke apart or what, though, since SpaceX hasn't yet released the full video from the barge. More interested in whether the ISS resupply mission at the end of the month will be a barge landing or a return-to-launch-site landing.
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I like the idea of a planet with less hospitable zones more suited to launch....
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The RB545 lists an ISP of 2000s. But in any case, trying to identify specific performance for specific engines is kind of missing the point. The thrust of an engine depends on one thing and one thing only: instantaneous change in propellant momentum. For a rocket, this is simply your fuel consumption (in mass flow) times your exhaust velocity. But for airbreathers and air-augmented engines, it's more complicated. An airbreather collects the airstream (a net loss of thrust, equal to the mass flow of the airstream times the forward velocity of the engine) and then burns it with a small amount of fuel to accelerate it out the back at a higher speed than it came in; the net thrust is the difference between the momentum going out and the momentum coming in. An air-augmented engine, on the other hand, has a higher fuel mass flow, but doesn't have to slow down the airstream as much, meaning that it can continue to operate with enhanced thrust at far higher forward speeds.
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The JASON mission was actually a successful landing, but they lost the rocket in an "unrelated" mount accident a few seconds later.
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What happens at the edge of the universe
sevenperforce replied to Starshipcaptain16's topic in Science & Spaceflight
If the universe is finite, then it is something like at least fifty times greater in volume than the observable universe, since we can detect neither local curvature nor any edge anywhere we look... -
IIRC it has to do with a complex relationship between the angle of repose for sedimentary rock, the buoyancy of the continental plates, and so forth... More likely: a world where the poles have some sort of crystalline extrusion process that produces hollow, pyramidal structures reaching into space.
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I was thinking of how a world with very, very high prominences could form...
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Not necessarily. Orbital resonances are possible. In this particular case you'd probably have a resonant precession.
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Look again; the LACE has an ISP of 1200s, not 600s, and can operate in or out of atmo. And the LACE has a lower ISP because liquifying air is dumb.
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What happens at the edge of the universe
sevenperforce replied to Starshipcaptain16's topic in Science & Spaceflight
That would imply an edge of the universe at the sphere surface. -
Yeah, this will cause the outer shell to spin in the opposite direction, which will spin the whole spacecraft. Also, constant power supply required to keep pumping air through.
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...right. Which is why adding liquid oxygen tanks to jumbo jets would not be a good idea, even if thrust-specific fuel consumption might be lower.
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It would depend on how you set it up, whether you were using a reaction wheel, etc.
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Aerodynamic drag is the primary problem. You want the thing to keep spinning without loss; otherwise you have to constantly add energy to keep rotating.
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Here's a stripped-down diagram of SABRE: And here's what I mean by an inside-out engine: The flow following the red airstream need never be choked at sufficiently high speeds in the lower case.
