5 ms·

It seems like a neat idea but it really doesn't save money, though. The hard part, as in the vast majority of energy & fuel needed, is to get horizontal velocit

by ptmcc 4y ago

It seems like a neat idea but it really doesn't save money, though. The hard part, as in the vast majority of energy & fuel needed, is to get horizontal velocity not altitude. The complexity and cost of a 747 carrying a rocket up for an additional maybe ~3% of orbital velocity just doesn't pencil out in the end And reusable boosters sway the calculus even further toward ground-based launches, both in cost and launch system simplification.

simonh 4y ago
Indeed. As usual XKCD is helpful here. https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/ It's similar to why launching from a mountain top isn't worth it. If you're launching to a few hundred km altitude, a 2km or even a 10km head start is peanuts. And altitude is only a small fraction of the problem, compared to orbital speeds large jet aircraft are barely even moving. If you're launching anti-satelite missiles that's different. Getting altitude is the main aim, and military jets can get reasonably high with a small missile as payload.
- hoseja 4y ago
  The major savings is in exponentially less air to go through, so you can do more aggressive gravity turn so you have less gravity losses. And he didn't even address the reentry questions, both of which are actually plausible - if you somehow have the fuel to drastically reduce your orbital velocity, you're suddenly no different than a sounding rocket, indeed not needing a heat shield. And if you cleverly slow down your reentry over many orbits, it can be very gentle.
  - SonicScrub 4y ago
    The benefits of the "exponentially less air" diminish once you have to slap an aerosurface on the vehicle (added weight + drag) to perform the pitch up maneuver Coupled with the fact that on deployment the vehicle is gaining velocity in the wrong direction until the engines ignite, accelerate forwards, and the vehicle begins the turn. The theoretical benefits of air launch quickly fade away given these practical realities. Nevermind the much more complex operations that comes with air launch. There's a reason why air launch has more or less died as an idea. The theoretical savings don't typically manifest once the additional complexities are accounted for.
jojosbuddy 4y ago
Pros and cons. You can instead of using that 747 with more optimized aircraft for this purpose. And you can make the boosters reusable. Stratolaunch was on a good path long term but ran out of cash. The dilemma with VO's approach was the same as OSC, thinking that reusing parts made for something else is cheaper short term and long term, where in fact more $ short and long. Yes the carrier was too expensive to maintain and material tech wasn't there yet to stop boil on the upper stages during staging. But the tradeoff was you can launch (nearly) anywhere, anytime, but regs/politics killed that benefit. I think we had potentially 8 locations at one point, ended up with 3. And thus, here we are. Sad VO couldn't keep the idea innovating.
hotpotamus 4y ago
I've seen it pushed as a potential way to launch into orbits that are harder to achieve via current launch sites; in theory, a plane-launched rocket can start from anywhere in the world.
sidewndr46 4y ago
So how fast & high would the carrier aircraft have to go for it to make sense?
- IshKebab 4y ago
  Very. Orbital velocity is like Mach 23 or something. The X-15 could apparently go to Mach 6, but probably not if it was carrying a rocket!
  - aidenn0 4y ago
    The x-15 was a rocket
ta1243 4y ago
The benefit of a plane based launch is the flexibility Want to launch from say Israel, currently you can only launch retrograde (to the west), as you can't launch over land (especially countries with questionable friendliness) You could in theory launch via Virgin One, fly south along the red sea and then launch over the Indian Ocean Same with launches from the West Coast US -- want to launch Polar, that's fine, you can launch south out of LA (and that's what they do). You can't launch East though, you have to move the rocket from California to Florida to launch. You don't need to worry much about bad weather at the launch site either. Got rain and lightning in Florida? Unless it's really bad you can still take off in a plane, then launch from above or away from that bad weather
- CydeWeys 4y ago
  Though non of this applies to Virgin Orbit, which is a US-based company.
- deleted 4y ago
  [deleted]

by ptmcc 4y ago

simonh 4y ago

Indeed. As usual XKCD is helpful here. https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/ It's similar to why launching from a mountain top isn't worth it. If you're launching to a few hundred km altitude, a 2km or even a 10km head start is peanuts. And altitude is only a small fraction of the problem, compared to orbital speeds large jet aircraft are barely even moving. If you're launching anti-satelite missiles that's different. Getting altitude is the main aim, and military jets can get reasonably high with a small missile as payload.

hoseja 4y ago
The major savings is in exponentially less air to go through, so you can do more aggressive gravity turn so you have less gravity losses. And he didn't even address the reentry questions, both of which are actually plausible - if you somehow have the fuel to drastically reduce your orbital velocity, you're suddenly no different than a sounding rocket, indeed not needing a heat shield. And if you cleverly slow down your reentry over many orbits, it can be very gentle.
- SonicScrub 4y ago
  The benefits of the "exponentially less air" diminish once you have to slap an aerosurface on the vehicle (added weight + drag) to perform the pitch up maneuver Coupled with the fact that on deployment the vehicle is gaining velocity in the wrong direction until the engines ignite, accelerate forwards, and the vehicle begins the turn. The theoretical benefits of air launch quickly fade away given these practical realities. Nevermind the much more complex operations that comes with air launch. There's a reason why air launch has more or less died as an idea. The theoretical savings don't typically manifest once the additional complexities are accounted for.

jojosbuddy 4y ago

Pros and cons. You can instead of using that 747 with more optimized aircraft for this purpose. And you can make the boosters reusable. Stratolaunch was on a good path long term but ran out of cash. The dilemma with VO's approach was the same as OSC, thinking that reusing parts made for something else is cheaper short term and long term, where in fact more $ short and long. Yes the carrier was too expensive to maintain and material tech wasn't there yet to stop boil on the upper stages during staging. But the tradeoff was you can launch (nearly) anywhere, anytime, but regs/politics killed that benefit. I think we had potentially 8 locations at one point, ended up with 3. And thus, here we are. Sad VO couldn't keep the idea innovating.

hotpotamus 4y ago

I've seen it pushed as a potential way to launch into orbits that are harder to achieve via current launch sites; in theory, a plane-launched rocket can start from anywhere in the world.

sidewndr46 4y ago

So how fast & high would the carrier aircraft have to go for it to make sense?

IshKebab 4y ago
Very. Orbital velocity is like Mach 23 or something. The X-15 could apparently go to Mach 6, but probably not if it was carrying a rocket!
- aidenn0 4y ago
  The x-15 was a rocket

ta1243 4y ago

The benefit of a plane based launch is the flexibility Want to launch from say Israel, currently you can only launch retrograde (to the west), as you can't launch over land (especially countries with questionable friendliness) You could in theory launch via Virgin One, fly south along the red sea and then launch over the Indian Ocean Same with launches from the West Coast US -- want to launch Polar, that's fine, you can launch south out of LA (and that's what they do). You can't launch East though, you have to move the rocket from California to Florida to launch. You don't need to worry much about bad weather at the launch site either. Got rain and lightning in Florida? Unless it's really bad you can still take off in a plane, then launch from above or away from that bad weather

CydeWeys 4y ago
Though non of this applies to Virgin Orbit, which is a US-based company.
deleted 4y ago
[deleted]