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Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Having a 747 or its equivalent to get you to 35000 ft with 500mph on the clock is a very good start to getting into orbit, I think some early rocket planes were launched like that. Or is it such a good start? Could a stripped-out 747 lift a Saturn V minus the first stage? I think the first stage delivers rather more energy than 35kft+500mph though. If 35k + 500mph is only 10% of a first stage, then it's not worth fiddling about with. If it's 50%+, then maybe it is worth redesigning the 2nd stage up to launch from there. Just musing, anyone want to run some figures? Any kerbal fans here?
To make it a bit more apples with apples comparison a) what's dV for LEO and escape from earth's surface (yeah, I know I could look this up) b) what's dV for either from 35kft and 500mph c) what's dV for either from burnout of a Saturn V first stage
Isn't Branson's space toy launched with a re-useable first stage that's basically a plane?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
yep, Dr. Slack, im pretty much wondering if first stage replacements are possible or practicable. it sure looks like some reduction in take off mass is doable.
Id like to compare lift mass and cost of flight, of a balloon vs. B-52 drop.
The C5A Galaxy was used to test drop ICBMs, but that was for the benefit of a unkown launch posistion to an enemy.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Yes, but as you said with the closed loop engines, thier force is integrated over longer time, and the "lost" American H2 is really more like lost payload capability toward the 6th, 7th and 8th minute near shut down. right?
(less propellent, for same force with same duration = lower cost to orbit)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The Space Shuttle main engines did not "dump 25% of the fuel over the side", they used staged combustion just the same as the Russian ones. The advantage of the Russian engines was (and still is) an oxygen-rich preburner combined with higher chamber pressures than any Western rocket engine ever achieved.
SpaceX's Merlin series of engines still work on the open cycle. In launch and test footage, you can see the turbopump exhaust coming from a small nozzle next to the main one. This is not really wasted propellant, it's just discharged at somewhat sub-optimal conditions, in that it generates less thrust than if the same fuel had been preburnt and then passed through the main combustion chamber.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve Conner wrote ...
This is not really wasted propellant, it's just discharged at somewhat sub-optimal conditions, in that it generates less thrust than if the same fuel had been preburnt and then passed through the main combustion chamber.
this changes things, ok so theres some efficiency gain.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
I've found the answer to my own question of a few posts back.
Quantatively, how does the Saturn V first stageS-1C and a 747 leg-up compare?
747 - 10km altitude and 200m/s velocity S-1C - 67km altitude and 2300m/s velocity
I think the phrase is square root of fa!
To make it a bit more apples with apples comparison a) what's dV for LEO and escape from earth's surface (yeah, I know I could look this up) b) what's dV for either from 35kft and 500mph c) what's dV for either from burnout of a Saturn V first stage
Hi I think your confusing deltaV with velocity, 9 or 18m/sec is enough to get into orbit, another 9 or 18m/sec is enough to leave the solar system, dV is impulse times fuel mass, and means that you could throw it out the back at any speed, and the rocket would travel the same distance.
95% of rockets today are fuel, for orbit, at a impulse of around 400 or 250, 400 being the top for solid fuel and maybe 800 for H2
if the impulse is the same, but the weight of the craft goes down....
NOTE, the numbers are from memory I wouldn't quote them
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Andy wrote ...
I've found the answer to my own question of a few posts back.
Quantatively, how does the Saturn V first stageS-1C and a 747 leg-up compare?
747 - 10km altitude and 200m/s velocity S-1C - 67km altitude and 2300m/s velocity
I think the phrase is square root of fa!
To make it a bit more apples with apples comparison a) what's dV for LEO and escape from earth's surface (yeah, I know I could look this up) b) what's dV for either from 35kft and 500mph c) what's dV for either from burnout of a Saturn V first stage
Hi I think your confusing deltaV with velocity, 9 or 18m/sec is enough to get into orbit, another 9 or 18m/sec is enough to leave the solar system, dV is impulse times fuel mass, and means that you could throw it out the back at any speed, and the rocket would travel the same distance.
95% of rockets today are fuel, for orbit, at a impulse of around 400 or 250, 400 being the top for solid fuel and maybe 800 for H2
if the impulse is the same, but the weight of the craft goes down....
NOTE, the numbers are from memory I wouldn't quote them
yeah, it seems the extra altitude allows the rocket to be smaller for a LEO, compared to same payload leaving sea level.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
No, I'm not confusing deltaV with velocity, I'm confusing people by referring to one in one post, and the other in another. The question I was answering was 'is a sub-sonic heavy-lift conventional plane worth 10%, or more than 50%, of a conventional rocket first stage?' If 10%, then there's too much to do to be worth mucking about with the second stage. If more than 50%, then it could be worth it.
If a 747 can get the 2nd stage to 10km and 200m/s, and a S-1C to 67km and 2300m/s, without any detailed sums it's obvious that we are down at the 10% end, and using it would require a total redesign, ie not worth it for existing rockets.
Taken into account at the start of the design, Branson's space plane to sub-LEO rather than the Moon, that's worth doing.
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