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#1
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Single Stages That Could Go All The Way
I've read that there are stages of rockets that have actually flown
that had a high enough ISP and mass ratio they could have gone to orbit if they did not need to carry a payload. In other words, if someone had fired off the first stage of the Saturn 5, it could have made orbit all by itself except it was carrying the rest of the rocket. Is this true? Can someone offer some examples? And what practical problems (like bringing along an aerodynamic shield for the nose) might one encounter in real life. Note, I'm not asking about hypothetical SSTO rockets, but real flown stages. -Charles Talleyrand |
#2
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Single Stages That Could Go All The Way
Probably the closest actual case was the original Atlas, which reached
orbital velocity with the entire fuel tank but without its booster engines. For true SSTO with nothing dropping off, the best bet would be the Delta IV core stage, because of its long burn time and extremely high ISP. It is the only rocket that can take off with hydrogen fuel alone (no strap-on boosters). Without the second stge, the core stage could probably get into orbit assuming it didn't exceed aerodynamic pressure limits on the way up: Gross Mass: 226,400 kg. Empty Mass: 26,760 kg. Thrust (vac): 337,807 kgf. Isp: 420 sec. Burn time: 249 sec. Isp(sl): 365 sec. . |
#3
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Single Stages That Could Go All The Way
I don't know of a true SSTO; Atlas approached this by dropping the mass of its booster engines and could put 3000 lbs into low orbit, a la Mercury. Saturn V could put a much larger mass into orbit doing the same thing. I've heard the claim that Titan II could do SSTO, thanks to high density propellant. Possibly either EELV could, but the payload would be relatively small for the expense and circularization of the orbit would be tricky, unless the payload could do the last 1% of the burn. Bottom line: true SSTO via existing launchers is possible, but not very practical. We're fighting the limits of chemical propulsion all the way. --Damon |
#4
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Single Stages That Could Go All The Way
Remember, they flew an entire Atlas missile into orbit in 1958.
(Whether that was SSTO depends on how you count the booster engines) Matt Bille |
#5
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Single Stages That Could Go All The Way
Charles Talleyrand wrote:
I've read that there are stages of rockets that have actually flown that had a high enough ISP and mass ratio they could have gone to orbit if they did not need to carry a payload. In other words, if someone had fired off the first stage of the Saturn 5, it could have made orbit all by itself except it was carrying the rest of the rocket. Is this true? Can someone offer some examples? And what practical problems (like bringing along an aerodynamic shield for the nose) might one encounter in real life. Note, I'm not asking about hypothetical SSTO rockets, but real flown stages. -Charles Talleyrand In order to calculate the delta-V of a rocket stage, you divide the gross weight of the stage by the weight with all fuel expended, take the natural log, and multiply by the exhaust velocity. If that stage is commonly launched with boosters, then one must remember that the liftoff thrust must exceed the GLOW. Of the flown first stages over at www.astronautix.com, I seem to find only one that exceeds the 9200 meters per second of deltaV that I find as a common limit for reaching LEO. The first stage of the Japanese H-2 rocket - http://www.astronautix.com/lvs/h2.htm - combined a 12.1% structural fraction with a high ISP (443 sec), and a 1.1:1 T/W ratio to achieve about 9220 meters per second of total deltaV, the highest I have found in their database. The Atlas CCB - http://www.astronautix.com/stages/atlasccb.htm - has a very low structural fraction when you subtract the interstage adapters, but it only works out to 8910 meters/sec of total deltaV. I have seen some studies that suggest that this would be enough, though. These studies show that lower ISP LOX/Kerosene vehicles require about 300m/sec LESS deltaV to reach orbit. The G-loads on burnout for the Atlas CCB would over 10G, even with a 50% throttle. The Saturn V first stage has an even lower structural fraction than the CCB, but the 10% lower ISP means that it won't have enough deltaV to reach orbit unless you drop four of the engines on the way up. P.S. Required deltaV is less if you launch from the equator. It is possible that the Saturn V first stage and other marginal cases might be adequate to reach LEO from a true equatorial launch. |
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