The entire big throat solid Titan experience actually argues for solid motor reliability when compared to liquid rockets. There were 123 flights of Titan 3C/D/E and 4 rockets, using 246 big throat solid motors. Two of those solid motors suffered failures (a 99.19% success rate). An additional 13 of these solid-boosted Titan-launched missions were thwarted by failures that affected the liquid stages or upper stages, lowering the overall mission success rate to 87.80 %.
Quote from: edkyle99 on 09/04/2011 04:37 pmThe entire big throat solid Titan experience actually argues for solid motor reliability when compared to liquid rockets. There were 123 flights of Titan 3C/D/E and 4 rockets, using 246 big throat solid motors. Two of those solid motors suffered failures (a 99.19% success rate). An additional 13 of these solid-boosted Titan-launched missions were thwarted by failures that affected the liquid stages or upper stages, lowering the overall mission success rate to 87.80 %. But that's the whole point! Using solids forces you to use bigger and more extreme second stages. You can't decide the reliability of the whole vehicle by using only a part that individually might have less failure occurrences, but that forces a higher complexity in the rest of the stack (namely, second stage and LAS).
Ares I would have used one solid motor and one gas generator engine powering two stages. Show me a simpler rocket that can orbit as much mass.
Slavish devotion to "simple" is exactly what led down the Ares I path. And the end result was a whole system which was NOT simple.
Quote from: Lars_J on 09/04/2011 11:50 pmSlavish devotion to "simple" is exactly what led down the Ares I path. And the end result was a whole system which was NOT simple.The pretty much sums it it up.The people running the project would not change the design when it became obvious it was the wrong direction.If the people doing Apollo had the same stubborn mindset we may have never landed on the moon and certianly would not have done so before the end of the decade.Apollo originally was going to use a direct landing LOR was the underdog at first.Kinda like Direct vs Ares.
Quote from: Lars_J on 09/04/2011 11:50 pmSlavish devotion to "simple" is exactly what led down the Ares I path. And the end result was a whole system which was NOT simple.It was simpler than the alternatives. - Ed Kyle
Quote from: Patchouli on 09/05/2011 03:39 amQuote from: Lars_J on 09/04/2011 11:50 pmSlavish devotion to "simple" is exactly what led down the Ares I path. And the end result was a whole system which was NOT simple.The pretty much sums it it up.The people running the project would not change the design when it became obvious it was the wrong direction.If the people doing Apollo had the same stubborn mindset we may have never landed on the moon and certianly would not have done so before the end of the decade.Apollo originally was going to use a direct landing LOR was the underdog at first.Kinda like Direct vs Ares.Nothing like "Direct vs. Ares". If it were, NASA would be planning a lunar landing right now, using Direct. It isn't. Instead, the clamor for alternative ideas like "Direct" helped kill NASA's lunar landing program.It wasn't about the rocket. It was about the lack of funding from the outset. There still isn't enough funding for a lunar landing even with Ares dead. - Ed Kyle
Quote from: Downix on 09/04/2011 07:00 amYes it is, considering how many SRB's failed after Challenger. While they did not fail on the Shuttle, they still failed. [like] this: Titan 4 A-20 was not a solid motor failure. It was an electrical (wiring harness short circuit) failure in the liquid core stages that caused loss of guidance/flight control.The entire big throat solid Titan experience actually argues for solid motor reliability when compared to liquid rockets. There were 123 flights of Titan 3C/D/E and 4 rockets, using 246 big throat solid motors. Two of those solid motors suffered failures (a 99.19% success rate). An additional 13 of these solid-boosted Titan-launched missions were thwarted by failures that affected the liquid stages or upper stages, lowering the overall mission success rate to 87.80 %. - Ed Kyle
Yes it is, considering how many SRB's failed after Challenger. While they did not fail on the Shuttle, they still failed. [like] this:
Quote from: baldusi on 09/04/2011 08:14 pmQuote from: edkyle99 on 09/04/2011 04:37 pmThe entire big throat solid Titan experience actually argues for solid motor reliability when compared to liquid rockets. There were 123 flights of Titan 3C/D/E and 4 rockets, using 246 big throat solid motors. Two of those solid motors suffered failures (a 99.19% success rate). An additional 13 of these solid-boosted Titan-launched missions were thwarted by failures that affected the liquid stages or upper stages, lowering the overall mission success rate to 87.80 %. But that's the whole point! Using solids forces you to use bigger and more extreme second stages. You can't decide the reliability of the whole vehicle by using only a part that individually might have less failure occurrences, but that forces a higher complexity in the rest of the stack (namely, second stage and LAS).I don't follow. The alternatives to Ares I were more, not less, complex than Ares I. Atlas V Heavy, for example, would have used four liquid propulsion units using a total of four or five or more complex liquid rocket engines (including three staged-combustion engines). Ares I would have used one solid motor and one gas generator engine powering two stages. Show me a simpler rocket that can orbit as much mass. - Ed Kyle
There's a lot more to consider than the plain number of engines. You can have drastically different designs that both have two engines. In Ares 1's case the issue is compounded by a very poor first stage decision. (And looking at the number of small thrusters that have to fire during its ascent, and for its stage separation - one could actually argue that it has a LOT of engines that HAVE TO work)
Both Ares I and V had serious design issues that made them unviable designs.
Quote from: Patchouli on 09/05/2011 05:56 amBoth Ares I and V had serious design issues that made them unviable designs.I don't see the Ares I design in particular as nonviable.
Quote from: edkyle99 on 09/05/2011 06:58 pmQuote from: Patchouli on 09/05/2011 05:56 amBoth Ares I and V had serious design issues that made them unviable designs.I don't see the Ares I design in particular as nonviable.It was. The premise behind Ares-I was to take two existing engines and use their extensive flight experience to make a simple, reliable rocket for Orion. Then they discovered their choice for the second stage engine (SSME) wouldn't work and that they'd have to design a new second stage engine. Then they discovered that the new engine wasn't going to give the performance of the original so they'd have to design a new first stage engine as well.
So the entire premise was falsified and the entire project should have been re-evaluated at that point.
This is not correct.
One logical, attractive approach to providing the launch capabilities necessary to support the overall exploration vision would be to leverage the existing Space Transportation System (STS) components andinfrastructure....Since STS hardware has already been demonstrated in a human-rated environment, the cost associated with qualifying components for future human-rated applications would be significantly reduced.Additionally, the proven aspect of that hardware would significantly reduce the risk and improve the safety of future missions involving human exploration and presence in space....The baseline Inline CLV configuration, represented in Figure 1, is a 4 segment Reusable Solid Rocket Motor (RSRM) booster first stage and a LO2/LH2 Space Shuttle Main Engine (SSME) upper stage engine modified for air start capability with 385,000 lbm of propellant.
Quote from: Lee Jay on 09/05/2011 07:38 pmQuote from: edkyle99 on 09/05/2011 06:58 pmQuote from: Patchouli on 09/05/2011 05:56 amBoth Ares I and V had serious design issues that made them unviable designs.I don't see the Ares I design in particular as nonviable.It was. The premise behind Ares-I was to take two existing engines and use their extensive flight experience to make a simple, reliable rocket for Orion. Then they discovered their choice for the second stage engine (SSME) wouldn't work and that they'd have to design a new second stage engine. Then they discovered that the new engine wasn't going to give the performance of the original so they'd have to design a new first stage engine as well. This is not correct. ESAS recommended the four-segment booster and SSME stage 2 design, but also described a five-segment booster and J-2 derived alternative. The alternative was selected soon after ESAS. It was selected not for any of the reasons you describe. Instead, it was selected to speed up development of five-segment booster and J-2X for Ares V - a choice that was expected to save development costs for Ares V down the road. In addition, the five-segment booster design actually outperformed the four-segment SSME design. It's all right there in the ESAS report.