Hacker News Reader

Comment by kitd | Hacker News Reader

Interesting post. I'd never thought of it that way. Not consciously anyway.

Might that make an air-launched system more reliable? Even if it's less efficient, the TCO would be lower using a winged system for the initial phases of launch.

View on HN

Several air launch systems have been tried, with limited but non-zero commercial success. The altitude and speed you get from the plane is very small compared to the total work the rocket needs to do, so the benefit in terms of "the rocket can be smaller" is minimal. The main benefit in practice has been launching from ~wherever you like, since regular fixed launch sites usually have strict limits about the direction you have to fly to avoid people. But the economics of reusability are pushing rockets to get bigger, and no air launch system can fly anything nearly as big as a Falcon 9, much less a Starship + Super Heavy. Other scattered problems:

- Hanging under-wing is a totally different set of forces than standing vertically, especially for a big rocket with thin walls. You're more like a bridge than a tower, or rather like a bridge one moment and then a tower the next. You need reinforcement for that, which makes the vehicle heavier.

- Modern reusable rockets do quick "load and go" filling to keep their propellant as cold and dense as possible. You can't do that if you need to fuel on the ground and then hang off an airplane for ~an hour while it climbs.

It wouldn’t help much, sadly. Getting to orbit is about speed, not height — you need 27000 kph to get to orbit, and having an air launched platform would shave off 1k kph off it at most, perhaps 5k with some insane hypersonic engineering.

It helps a bit more than you imply, though: if you can launch from a higher altitude, you have less atmosphere to plow through. That lets you use more of your propellant to speed up instead of to push air out of the way.

You've just got the problem of building a fixed wing aircraft which can carry your rocket full of explosive propellant, successfully release it pointing in the right direction and then get the hell out of the way....

You're extremely limited by the amount of mass you can even launch from a mothership aircraft.

There's no future in this idea outside of small sat, and probably not even there.

That isn’t very helpful considering rocket launches only spend a few seconds in atmosphere mostly going vertically to get above the majority as quickly as possible .

Main advantage of air launch is that you can better match your target inclination or perhaps even orbit timing - just drop the rocket at the right time in the right direction over the ocean. With a fixed launch site you always need to adjust for some difference of your point of origin versus the orbit you want to achieve.

Sure but the main disadvantage that you need another highly complex vehicle. Best case its a existing commercial platform like Virgin Orbit, but then you are limited by the size. Or you design another whole vehicle that more complex then the rocket itself.

And even then you need to have all the infrastructure flying and integrated rather as nice static pad.

You are also putting human in bigger danger unless you want to have another autonomous highly complex vehicle.

The benefits are simply better addressed by having 2-3 launch pads.

How big a trebuchet would be needed to chuck a cubesat directly into LEO?

100 or 200 km tall at point of release ought to do it.

The tip would still have to be doing 7 km/s.

cubesat + small rocket. Orbital mechanics require a burn at a later time in the orbit, to avoid coming back to say hello again to Mr. Trebuchet (Ignoring Earth's rotation)

Lookup SpinLaunch.

There are some companies working on that and / or there have been some experiments with it, but there's two factors there; the one is of course how much weight an aircraft can carry. The other one is the altitude and / or angle; a big plane goes to about 10 kilometers (maybe more, idk), but that's a 'flat' flight, ideally you launch while angled upwards and that's a bit more involved.

But that's how a lot of the X projects were / are done.

There’s actually been commercial launch services using air launch - Virgin Orbit, which went bankrupt, and Northrop Grumman’s (acquired as part of Orbital ATK) Pegasus, which hasn’t launched since 2021 and has one launch planned in 2026.

That’s what Virgin Galactic was.

No, Virgin Orbit. Virgin Galactic is still in business and does sub-orbital tourist flights.

Reply on news.ycombinator.com