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Comment by MrSkelter | Hacker News Reader

This would be used in something like Starraker. That design can get 100 tons to orbit with a single stage much more efficiently than any rocket. Take off like a plane, climb to high altitude. Enter a supersonic dive. Pull up and ignite your rockets from high in the atmosphere when travelling relatively fast. You need much less fuel that way. The wings get you the first 30k mètres.

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Orbit is a different beast than space.

> The extra energy needed to make an object travel fast enough to stay in orbit is more than 30 times as much as the energy needed to lift it to an altitude of 100 km.

https://www.sciencelearn.org.nz/resources/272-launching-sate...

> with a single stage

SSTO is driven by the notion that staging is dangerous and worth avoiding. I think the SpaceX experience shows that effort was better spent making staging reliable rather than trying to make SSTO work.

Eh, winged SSTO has some very practical potential advantages! (To wit: you can use existing airfields for your turnaround).

This is not me advocating for winged SSTO every day of the week. But I can definitely see the lure.

Are those advantages worth inherently worse amortization costs on the first stage though? A TSTO can have one first stage for ~10ish orbiters since it's only used for 10 minutes while the orbiter has to do all it's supposed to do before coming back into the soup. An SSTO definitionally has to have all parts of the vehicle involved at all stages of operation.

I think a more complicated ground facility is fine if you're doing enough flights.

> Are those advantages worth inherently worse amortization costs on the first stage

If you can launch from and land at any airfield, even if just any military airfield, absolutely. You've opened the market for point-to-point ballistic transport.

> point-to-point ballistic transport.

What does ICBM early warning look like in a world with point-to-point ballistic transport?

What does tracking incoming nuclear-capable enemy aircraft look like in a world with commercial air transportation?

The difference is that when a C-17 comes up on radar, there is not a predefined protocol in RU or CN to prepare all of their ICBMs for a rapid response.

What I was getting at, is do all ICBM early warning systems sit on edge more often? That would be my assumption.

We have come close to annihilation from mistakes before, this seems like a path towards more possible mistakes.

Then I guess the answer might include ADB-S and other information-sharing channels. Perhaps only accepting incoming ballistic transports from predefined friendly launch sites. Perhaps only accepting manned ballistic transports.

Ballistic vehicles do not have much cross-range capability, so knowing both where they came from and where they are going is easier than with aircraft. But of course real-time human-seeming communication could be faked with good AI, and even if that were not an option I'm sure some kamakazi pilots would volunteer if necessary. Anything could be faked, but the barriers are not unsubstantial.

And, of course, MAD remains a deterrent.

Existing airfields will have safety and noise limits. As a result, most would support only very small launchers, if they could support any at all.

And TSTO has some very practical advantages. The mass ratios of the stages are much less constrained, the payload mass is less sensitive to overrunning the mass budget, and most of the mass of the launcher is recovered at much lower speed, making handling entry much easier. The first stage does have to be returned to the launch site but that's not a terribly hard problem.

Orbit is not about height, it is about speed. You have to get to almost 30km/s otherwise you aren't in orbit and you fall back into the atmosphere.

I think you are confusing the speed at which the earth orbits the sun (~29.8km/s) with the speed at which an object needs to travel to maintain earth orbit (~7.8km/s).

Whoops, you are right. I think it's too late to edit my original post.

The point still stands, though, you have to get to nearly 8km/s otherwise you aren't in orbit and you fall back into the atmosphere.

You can't get to anywhere near that speed while still in the atmosphere - SR-71s only manage about 1km/s, and because kinetic energy is proportional to the square of the speed, at that point you are only 1/64th of the way there.

To get to an appropriate speed, you need to accelerate eventually. But it's easier to do that at a higher altitude, where you have thinner air to travel through: less drag, less severe transonic effects to mitigate and, on the way up, a wider variety of air-breathing engine types to choose from (including the Astro Mechanica one).

The wider variety of air-breathing engines points out a problem: the launcher necessarily goes through a wide variety of aerodynamic regimes where different engines work. Making a single engine that works over a wide range of speeds is difficult. And for what? Using more fuel in a larger first stage just so you can save on cheap oxidizer (LOX at $.10/lb)?

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