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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
(not the little masked animals that rob garbage cans)
Im intrigued by a small company and a persistent individual here in my state of California. He and some others advocate for balloon assisted to orbit rockets.
im interested in the mass fraction of propellent that would differ, between launch of 1kg at earth surface, and 1 kg at 150,000 feet. im pondering the usual math, but i wonder with a normal fraction for the shuttle being 0.799. im wondering at the same latitude, how much propellant can be reduced.
It seems most propellent is consumed just after ignition, when velocity is low, mass high and altitude low. So obviously changing those factors to be slightly more favorable, should change things considerably, As a 150,000 vertical head start would, also minimizing drag. Im not sure how to calculate it though.
This may really make single stage to orbit (not counting the balloon) practical, unlike Al Gores "venture star" which totally collapsed, figuratively and literally.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
This has been successfully done in the past. However, the payload was comparatively quite small for a lift vehicle. For example, the cost per kg of payload drops from around $4k/kg to under $1k/kg, but does not scale up due to high-altitude balloon volume limits. The lift capacity is constrained by the thickness of the balloon, and the lift gas expansion volume. While someone could get a conventional multistage solid fuel rocket into orbit for fun, its usable payload gets proportionally small rather quickly.
The early Russian space program had numerous engine failures, but focused on perfecting the metallurgy for an in-line turbo pump. While North American liquid fuel engines still dump 25% of the fuel out the side while driving engines like they did in the 1960s. Simply put, the same class of Russian engines can put 25% more payload into orbit for less upfront cost. Therefore, the overall $/kg payload-mass cost is substantially less.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Patrick wrote ...
(not the little masked animals that rob garbage cans)
Im intrigued by a small company and a persistent individual here in my state of California. He and some others advocate for balloon assisted to orbit rockets.
im interested in the mass fraction of propellent that would differ, between launch of 1kg at earth surface, and 1 kg at 150,000 feet. im pondering the usual math, but i wonder with a normal fraction for the shuttle being 0.799. im wondering at the same latitude, how much propellant can be reduced.
It seems most propellent is consumed just after ignition, when velocity is low, mass high and altitude low. So obviously changing those factors to be slightly more favorable, should change things considerably, As a 150,000 vertical head start would, also minimizing drag. Im not sure how to calculate it though.
This may really make single stage to orbit (not counting the balloon) practical, unlike Al Gores "venture star" which totally collapsed, figuratively and literally.
Altitude is not an extremely significant thing.
Much more important is sideways speed; rockets spend most of their delta-v going sideways very fast.
Rockets put most of their thrust at an angle to the horizontal; due to pythagorus this reduces the sideways acceleration only marginally, while giving good thrust upwards as well.
Therefore, starting at high altitude has only a very modest effect.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Carbon_Rod wrote ...
There was a documentary made about some of the commercial models:
Well, that doesn't surprise me, crafty Russians always need to be watched... the Russians always came up with clever ways of equaling or besting the west, since they didn't have a silicon valley.
They were always good at heavy lift for example, but once in orbit, their craft had little maneuver capability. I dont know how they would have got to the moon and then back off again, MIT and others were pressed to the limit for NASA's solution.
I'm trying to figure out, approximately, how much payload a 30,000 lb rocket can push to orbit from 150k ft. The Pegasus air launched vehicle weighs 41 k lbs, and carries 997 lbs to orbit. So im thinking a 30,000lb all up rockoon, putting 1000 lbs in orbit is plausible.
EDIT: Carbon Rod,
Carbon_Rod wrote ...
Simply put, the same class of Russian engines can put 25% more payload into orbit for less upfront cost. Therefore, the overall $/kg payload-mass cost is substantially less.
This means the space shuttle was really on the losing end of the 25% problem, for 25+ years! thats a lot of lost productivity and lost value.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
You mean the "silicon valley" where $140k/yr job is minimum wage after you deduct the cost of actually living there. LOL... sad but true...
I forget the mathematical proof, but there is an optimal number of booster stages to reach orbit. IIRC it is 3 or 4 based on current fuel energy density.
At the start, NASA was full of people who really wanted to build something new. Toward the end, it had too many meritocratic politics with ties to conventional partisan politics.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Carbon_Rod wrote ...
You mean the "silicon valley" where $140k/yr job is minimum wage after you deduct the cost of actually living there. LOL... sad but true...
yeah but now were surrounded by more communists from San Francisco then the soviet block ever had. In any case, the "silicon priarie" and "silicon valley" were huge advantages the US military had, which the Soviets had no equivalent of. But I digress.
As for stages, its probly 2 in this case. One solid fuel, the other a polyurethane/LOX hybrid. Then on payload verniers for circularizing the orbit.
EDIT: NASA's management has a bad habit of undermining there own really good experts. those management/administrative idiots cant wait to screw things up (see venture star, Challenger and Columbia for examples.) High ranking idiots get other people killed, not themselves, thats why i didnt join the military after 9/11. but i digress.
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Rockoons and Propellent Mass Fractions.
