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Paul Allen's new rocket-launching plane

arstechnica.com

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Re: Paul Allen's new rocket-launching plane

#161

Post by rbanffy »

Xixi wrote: post #148
rbanffy wrote: post #120

Earlier quoted context omitted.

That's the fuel the plane takes off with. I don't know how much this beast uses, but those six engines must be burning quite a lot of it. Also, the landing gears seem to be very robust.

The A340-600 has four engines, not six. But the point is still true with, say, a Boeing 787. Here are the figures for the 787-9: maximum takeoff weight: 560,000 lb; maximum landing weight: 425,000 lb [1]. In case of an emergency the pilot has to get rid of fuel before landing if the airliner is above maximum landing weight. [1] Figures given in pounds on wikipedia, the kg version looks like a "dumb" conversion: https…

We don't know Roc's maximum landing weight but abort is possible if the maximum landing weight is more than weight of the whole craft plus its cargo minus the fuel. I assume it takes of with a lot of fuel because it has potentially 1.5x time fuel consumption of an old 747.

Re: Paul Allen's new rocket-launching plane

#162

Post by sbierwagen »

rbanffy wrote: post #160
CydeWeys wrote: post #145

Earlier quoted context omitted.

The market would have to be really large (like way larger than the current global launch market) to justify it though. The conjoined twin 747s are gonna be good enough for any payload that they can carry.

If the cost goes down enough, new previously impractical products become practical, driving new demand.

Big if there.

The Seattle Times article says that the Vulcan rocket will have a mass of 375 tons. (Probably US tons?) Assume it's got the same payload fraction as a Soyuz, about 2.5%, which means it can put 9.4 tons into orbit. (A Falcon 9 can put 22 metric tons into orbit)

According to some comment on stack exchange, the world collectively orbited 255 tons of stuff in 2007. Assuming every payload can be launched on a Vulcan rocket, (Which they can't) and assuming a generous turnaround time of one week, (Allen says it should be faster than that) then it would take only a single plane 27 weeks to satisfy the launch needs of the entire world. You could double the amount of stuff launched, and still only need one plane.

There's probably not going to be a lot of airframes to spread development costs across.

Re: Paul Allen's new rocket-launching plane

#163

Post by neuronexmachina »

svantana wrote: post #106
iijj wrote: post #50

Earlier quoted context omitted.

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.

It would be potentially suitable for a larger payload akin to the X-37B. This would be handy if the intent isn't destruction, but rather interference or even retrieval. https://en.wikipedia.org/wiki/Boeing_X-37

Re: Paul Allen's new rocket-launching plane

#164

Post by Animats »

bergie wrote: post #147
Animats wrote: post #82

Scaled Composites built it. It should work. Although Rutan has retired, the company goes on. It's interesting that they didn't connect the tails, like the old Lockheed P-38, but there's probably some good reason for that. Launching a Pegasus XL has to be just a demo. That's normally launched by dropping it from an old Lockheed L-1011; it doesn't need this monster. They need something bigger to launch. There was a con…

> It's interesting that they didn't connect the tails, like the old Lockheed P-38, but there's probably some good reason for that. Rocket exhaust?

The Pegasus rocket ignites after being dropped.[1]

[1] https://www.youtube.com/watch?v=m7_yyvGxwrE

Re: Paul Allen's new rocket-launching plane

#165

Post by marcosdumay »

jeffdavis wrote: post #159
Tuna-Fish wrote: post #98

Earlier quoted context omitted.

Altitude is much less important than velocity.* The extra altitude you'd get from launching from a top of a mountain would not be worth the expense of having to lug the rocket up there in the first place. * https://what-if.xkcd.com/58/

Thank you, very interesting. But what is the point of a space elevator then?

A space elevator gets you velocity too.

Every time you get some altitude, you also get a minuscule amount of velocity because the Earth is rotating. A space elevator gets you so much mind blowing altitude that you'll also get all the velocity you need.

Re: Paul Allen's new rocket-launching plane

#166

Post by rbanffy »

sbierwagen wrote: post #162
rbanffy wrote: post #160

Earlier quoted context omitted.

If the cost goes down enough, new previously impractical products become practical, driving new demand.

Big if there. The Seattle Times article says that the Vulcan rocket will have a mass of 375 tons. (Probably US tons?) Assume it's got the same payload fraction as a Soyuz, about 2.5%, which means it can put 9.4 tons into orbit. (A Falcon 9 can put 22 metric tons into orbit) According to some comment on stack exchange, the world collectively orbited 255 tons of stuff in 2007. Assuming every payload can be launched on…

Either that, or we will launch a lot more stuff, 9 tons at a time.

The biggest thing going against it is it's not clear this scheme can drive the costs down enough to double or triple the launched mass per year. There is a limited number of things we can do in space. A significant part of the cost of any single probe is the launch.

If we can reduce launch costs enough (maybe making the booster reusable) and through building a standard probe with pluggable sensors, drive down the building costs, we could have dozens of probes going places we currently can't afford to go. We spend enormous effort in shaving off every single gram from anything that goes to space. If going to space gets cheaper, we can spend a lot less time shaving probes and more time probing.

Re: Paul Allen's new rocket-launching plane

#167

Post by SkyMarshal »

blunte wrote: post #144
endorphone wrote: post #81

Earlier quoted context omitted.

Clearly Allen and his team did the necessary engineering work, but I'm not sure the GlobalFlyer is a good example. It had a single mid-mounted engine, and had a gross, fully loaded weight of 22,000lbs. This thing has 70,000+ lbs of engines alone. The torque has to be absolutely colossal. Again, I know that much smarter people did the math, but from the eye check this does not look like a tenable design.

I agree. There are so many forces at such incredible potential levels of torque that the center wing must be almost entirely full of structural elements... and those probably pass through to the outer wings. Imagine differing oscillations of pitch or yaw from each fuselage happening at the same time... and at just the right/wrong frequency for the connecting structure. I'm sure I'm just overly paranoid, but often we…

>Imagine differing oscillations of pitch or yaw from each fuselage happening at the same time... and at just the right/wrong frequency for the connecting structure.

Exactly. I expect they have real-time computer control of all control services that quickly adapt the relative attitude of both fuselages to prevent over-stressing the wing, but what about "rogue waves" of turbulence hitting each fuselage differently. What's the safety factor on both the adaptive controls and, as a backup, the structural integrity of the wing?

Re: Paul Allen's new rocket-launching plane

#168

Post by gruturo »

jeffdavis wrote: post #35

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

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

Not a dumb question at all. It would actually give you some non-trivial advantage - but altitude matters considerably less than speed when trying to achieve orbit.

Starting a mile higher would allow you to avoid the densest parts of atmosphere, giving you less air resistance and helping with the Max Q, or maximum dynamic pressure (rockets sometimes need to reduce their engine output until they have cleared the denser atmospheric layers, or they would break up due to air resistance stresses).

This does unfortunately not outweigh the cost and complication of moving your launch site on top of a mountain. If you're really after every scrap of advantage, moving your launch site closer to the equator is way better than moving it up (until you already have it at the equator, that is).

Re: Paul Allen's new rocket-launching plane

#169

Post by vadym909 »

mabbo wrote: post #133
vadym909 wrote: post #91

Any more billionaires feeling left out of the space race?

Should we worry that every billionaire seems highly intent on building ways to get the heck off the planet? ... Do they know something we don't?

Except Musk and Branson who've been doing this before it was the cool new thing- it feels the newcomers are just doing it for legacy. Having hospitals and colleges named after you isn't special enough anymore. Space is the new frontier for ego battles.

Re: Paul Allen's new rocket-launching plane

#170

Post by Gravityloss »

Gravityloss wrote: post #44
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…

You can also fly towards the equator before the launch for more boost. Further from the Earth's axis. For example Cape Kennedy is 28 degrees north. If you fly to the equator, you get another 200 m/s. Depends a bit to which orbit you're launching though. Another good thing is flexibility if you are more constrained by launch windows in a stationary launch location. Hard to explain.

I had a big mistake in the comment above, it's 220 km/h or about 60 m/s.

    cos(28)=0.88 
    0.12*(2*pi*7000 km) = 5300 km
    5300 km / 24 h = 220 km/h
    220 km/h / 3.6 m/s/km/h = 61 m/s
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