Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Paul Allen's new rocket-launching plane

arstechnica.com

Post reply on HN
Print view View original

101–110 of 170 posts

Re: Paul Allen's new rocket-launching plane

#101

Post by grkvlt »

bamboozled wrote: post #6
Analemma_ wrote: post #3

I'm confused as to what this thing can accomplish. It can probably fly very high, but I assume it can't fly very fast (relative to orbital speed), and I thought the overwhelming majority of the delta-V to get something into orbit was for forward momentum and that just launching from higher up wouldn't help much. Clearly there's something I'm missing here (or they wouldn't have built it), can anyone fill me in?

Checkout the photo gallery, it seems to launch a rocket from between the two hulls while flying very high in the atmosphere (less drag and gravity).

Not really that much less gravity, certainly not enough to notice, let alone have a difference to a rocket launch. Gravity varies as 1/R^2 where R in this case is distance from the earth, so it's the difference between that at ~6380 km and ~6400 km (for a 20 km altitude) which is not much - you have to be well into space, at over 1000 km up, before gravity drops to less than 7 km/s^2 for instance.

Re: Paul Allen's new rocket-launching plane

#102

Post by MPSimmons »

gernerz wrote: post #58
mLuby wrote: post #55

Earlier quoted context omitted.

I haven't actually seen anyone mention it, but it shouldn't be much more risky than taking off fully-fueled. That said, landing with the rocket still on board might break some fuel-balancing assumptions.

Peagus rockets aren't cryogenic, they are solid monopropellant rockets. Not really all that dangerous.

Anyone who suggests to you that hydrazine isn't dangerous shouldn't be trusted.

Re: Paul Allen's new rocket-launching plane

#103

Post by [deleted] »

SkyMarshal wrote: post #79
kashkhan wrote: post #52

Earlier quoted context omitted.

it's a proven design. scaled composites, which built this also built the GlobalFlyer with similar configuration. https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer

Well, proven at small scale. I'm sure the new bigger one will work fine too under most anticipated conditions, but I wonder what its structural safety factor is.

[deleted]

Re: Paul Allen's new rocket-launching plane

#104

Post by kashkhan »

JumpCrisscross wrote: post #100
kashkhan wrote: post #52

Earlier quoted context omitted.

it's a proven design. scaled composites, which built this also built the GlobalFlyer with similar configuration. https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer

> it's a proven design No. This is breakthrough science. Scaled proofed a specific implementation of one of its materials.

Almost every aircraft Burt Rutan has built is a breakthrough. Mostly asking questions that other designers weren't, like does a twin need to be symmetric.

twin tail booms have a long history.

e.g p38 with twin engines.

Burt Rutan's key realization was that the connected skinny horizontal tail doesn't really add much torsional stiffness and it's easy to obtain the required stiffness with the wing center box.

Re: Paul Allen's new rocket-launching plane

#105

Post by blorsh »

renega3 wrote: post #47
jeffdavis wrote: post #35

Dumb question: why don't they launch rockets from the tops of mountains?

Rockets require cryogenic fuels, workers and large launch complexes. In contrast, Everest is a mere 9km and the first stage of a rocket will take it to something along the lines of 100km at 2000m/s. It is much easier just to throw more fuel in the first stage (or move to the equator) than try and relocate around the relatively smooth surface of Earth.

Cryogenic fuel is a reason to use a mountain.

Florida's air is humid and dense. You get lots of heat gain from that. The density itself matters. Condensation is a huge source of heat. Freezing is another huge source of heat. So you boil off cryogenics and maybe worse. We lost a space shuttle due to a chunk of ice hitting the wing. Falcon 9 rockets need unusually cold filler; if it warms then it expands and won't even fit in the rocket. It probably pours out and gets drained away, the alternative being a rupture.

The USA would do better launching from near Tuscon, Arizona. It's decently high up and dry, which helps keep the cryogenic content cold. We used to do this in fact, before the Mexican embassy complained about defective rockets crashing in Mexico. We chose to move to Florida instead of making a liability payment deal with Mexico.

Re: Paul Allen's new rocket-launching plane

#106

Post by svantana »

iijj wrote: post #50
mLuby wrote: post #27

IANARS but this plane should give the remaining stage(s) four advantages: 1. +230m/s orbital velocity [1] 2. +9km launch altitude [1] 3. can launch in more weather conditions 4. 1st stage can abort mid-launch without loss of payload. Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies: A. a vacu…

The primary advantage of airplane launch is that you can fly to into a launch window for an orbital rendezvous. Otherwise you'd have to wait for the target's orbit to be just right w/respect to the launch site, or do a long orbit matching process. This is very useful if say you want to very quickly and quietly launch something towards another satellite. People are making comparisons with the Spruce Goose, but the Glo…

> This is very useful if say you want to very quickly and quietly launch something towards another satellite.

Surely you could already do that with Orbital ATK's Pegasus? 1000 lbs is plenty of explosives. It seems to me this is just a bigger version of that.

Re: Paul Allen's new rocket-launching plane

#107

Post by PhantomGremlin »

synicalx wrote: post #92

I can just imagine him up there in the plane, listening to Huey Lewis and the News.

I'm confused by this. I don't know if Paul Allen is a Huey Lewis fan. What I do know is that he's a big Jimi Hendrix fan.

Allen basically built a museum to (mostly) Hendrix. It's since been re-purposed somewhat, and Wikipedia doesn't have much of the history. But originally the museum was mostly Hendrix. Here are links to a few early articles that make it clearer:

http://www.independent.co.uk/travel/americas/in-search-of-ji...

http://www.voodoohendrix.com/jimi-hendrix-museum/

Re: Paul Allen's new rocket-launching plane

#108

Post by yakshaving_jgt »

PhantomGremlin wrote: post #107
synicalx wrote: post #92

I can just imagine him up there in the plane, listening to Huey Lewis and the News.

I'm confused by this. I don't know if Paul Allen is a Huey Lewis fan. What I do know is that he's a big Jimi Hendrix fan. Allen basically built a museum to (mostly) Hendrix. It's since been re-purposed somewhat, and Wikipedia doesn't have much of the history. But originally the museum was mostly Hendrix. Here are links to a few early articles that make it clearer: http://www.independent.co.uk/travel/americas/in-searc…

It's a reference to American Psycho.

https://www.youtube.com/watch?v=vzN3qO-qc8U

https://www.youtube.com/watch?v=cISYzA36-ZY

Re: Paul Allen's new rocket-launching plane

#109

Post by arethuza »

mikeash wrote: post #32
Analemma_ wrote: post #9

Earlier quoted context omitted.

Is it really that dramatic a difference? I suppose it must be, if they're building it, but it's strange that no one has done this before if it really helps.

It is a pretty big difference. In vacuum you want a huge nozzle to extract as much energy as possible from the engine's exhaust. In atmosphere, there's a limit to how large the nozzle can be before the exhaust flow separates from the sides and you get asymmetric thrust or worse. Since the nozzle can only be optimized for one particular altitude, that means that rockets which launch from sea level spend a good portion…

There was also the cancelled Skybolt ALBM from the early 1960s:

https://en.wikipedia.org/wiki/GAM-87_Skybolt

Re: Paul Allen's new rocket-launching plane

#110

Post by InclinedPlane »

curtis wrote: post #45

It seems like air launch doesn't buy you a whole lot, but it turns out that a small win on delta-v can result in a fairly big win on payload. This might seem counter-intuitive, but you have to remember that in orbital class rockets, payload is only 5% or so of total mass at take-off.

It's a small win on delta V, a small win on gravity losses, and a small win on Isp (due to atmospheric pressure). The delta V and Isp wins are exponentially related to stage mass fraction so they actually become very big wins.
Post reply on HN