The Zenit 3SLB has a takeoff weight of a mere 1,038 klb, but the RD-171 engine provides 1,641,100 lbf of thrust at sea level. http://www.astronautix.com/lvs/zent3slb.htm The Atlas V has a takeoff weight of ~335 tons, but has an RD-180 engine, with a thrust of ~860 klbs, close to half of the RD-171. It would seem economical to expand the Zenit's first stage fuel tanks to carry more fuel, to carry more payload into orbit. Why hasn't the Zenit been expanded, like the Falcon 9 v1.1 has been? Want to avoid competition with Proton?I know payload to orbit is not this simplistic, but the Zenit 3SLB seems like it has much untapped potential.
The current Zenit served the Soviet purposes well. With the fall of the Soviet Union and Energia, and the increased focus on cost, I would expect a tank stretch, to get increased payload, like the Falcon 9 v1.1. There have been ~20? Zenit launches since the fall of the Soviet Union. Maybe the launch market is really driven by large nations that want to ensure their access to outer space and pork.
I can think of a number of reasons. First, Russian rockets have always tended to have higher liftoff thrust to weight ratios than all-liquid U.S. rockets. Zenit is nearly 1.6, Proton nearly 1.5, Soyuz nearly 1.4, while the U.S. EELVs can be as low as 1.17 or so.
There can't be a stage stretch due to logistics.
Quote from: quanthasaquality on 10/26/2012 02:20 am Maybe the launch market is really driven by large nations that want to ensure their access to outer space and pork.Huh? How the heck did you come to that conclusion? Especially in face of the post above.
Maybe the launch market is really driven by large nations that want to ensure their access to outer space and pork.
Quote from: Jim on 10/26/2012 02:32 amQuote from: quanthasaquality on 10/26/2012 02:20 am Maybe the launch market is really driven by large nations that want to ensure their access to outer space and pork.Huh? How the heck did you come to that conclusion? Especially in face of the post above.Ok. There is not enough evidence in this thread to conclude the launch market being driven by large nations. It is off topic for this thread, and would be a different thread.Russia's transportation system might not be able to handle a stretched rocket. Heck, America's highways might not be able to handle the Falcon 9 v1.1, and Spacex intends to move the first stage by air or sea.Zenit also served as a booster for the Energia rocket during Soviet times.A different second stage would be needed to maximize payload to orbit. ULA has proposed a dual RD-180 Atlas V. http://www.ulalaunch.com/site/docs/publications/EELVPhase2_2010.pdf A new upper stage on a stretched Zenit, maybe from a foreign partner, could produce a rocket with 10 mt to GTO. Arianespace is able to find payloads for 10 mt into GTO.
Stretch Zenit on left:
Quote from: Salo on 11/14/2012 08:43 pmStretch Zenit on left:I ran into ULA's study of options regarding the Atlas V Phase 2 awhile back. They had one figure that really caught my eye. (http://www.ulalaunch.com/site/docs/publications/EELVPhase2_2010.pdf) On page 5, they listed 79 expected stage failures per 100,000 flights due to engine problems with a single RL-10 engine. The 4-engine stage in contrast was considered likely to fail at a rate of only 5 in 100,000 flights. The failure rate in other words was 15.8X as high with only one engine as with four. When I look at the Zenit's RD-171 and then at its quarter-size cousin, the new RD-191, it sure seem like using four RD-191 engines would be an easy change. The question I have is, if the Zenit's major problem has always been reliability and not price, why not consider replacing the RD-171 with its quarter-size cousin? Is there anything besides price that would stop such a change?
RL-10 upper stage is completely different thing than RD-171/RD-191 first stage.
On first stage T/W is much more important than second stage so losing one engine would propably be too much unless it happens at quite high altitude.
And those RD-171/RD-191's are very high-pressure staged combustion cycle engines, there is much higher risk of them failing in catastrophical way instead of having nice clean shutoff.And with 4 RD-191's there are more turbopumps that can fail.And those 4 RD-191's would also be more expensive than 1 RD-171.
There's also the Atlas V, which looks likely to start sending up American astronauts in a few years' time. Its RD-180 engine, unlike the RD-171, has proven extremely reliable. It has proven so reliable that ULA floated plans of an Atlas V Phase 2 with the exact same number of engine chambers as the Zenit. Yet with two RD-180 engines why doesn't ULA even appear to blink at the dangers of "catastrophic failures" you mention? Why would they even consider an Atlas V Phase 2 Heavy with six of those engines (12 engine chambers and considerably more turbopumps) on three cores? The answer, I think, is that dual RD-180 engines is a more reliable and safer setup than one RD-171.
Quote from: Hyperion5 on 11/25/2012 05:44 pmThere's also the Atlas V, which looks likely to start sending up American astronauts in a few years' time. Its RD-180 engine, unlike the RD-171, has proven extremely reliable. It has proven so reliable that ULA floated plans of an Atlas V Phase 2 with the exact same number of engine chambers as the Zenit. Yet with two RD-180 engines why doesn't ULA even appear to blink at the dangers of "catastrophic failures" you mention? Why would they even consider an Atlas V Phase 2 Heavy with six of those engines (12 engine chambers and considerably more turbopumps) on three cores? The answer, I think, is that dual RD-180 engines is a more reliable and safer setup than one RD-171. Wrong. The reason they use RD-180 for advanced designs is because they have a source for engine.RD-17X problems have nothing to do with the number of chambers. It has to do with manufacturing quality.