I didn’t have a chance to watch either of the House subcommittee hearings today, so I’m grateful that Clark linked to the testimonies of the various witnesses.Â I really enjoyed reading Brett’s testimony, and thought one of his points in particular is worth repeating.
To me one of the more interesting points is found at the top of page 11.Â There were several misleading statements made by several people today about the relative safety of Ares-I compared to commercial crew vehicles.Â As Brett put it (my emphasis added):
Second, some have claimed that NASAâ€™s Exploration Systems Architecture Study (ESAS) shows that the current exploration vehicles are safer than commercial crew vehicles. In actuality, commercial crew vehicles were never even analyzed in the ESAS report â€“ the ESAS report only looked at vehicles large enough to carry Orion, such as Ares I and variants of the triple-core Delta IV Heavy, and did not examine the smaller, simple, single-core vehicles, such as Atlas V Medium and Falcon 9 Medium that are sufficiently sized for commercial crew missions.Â Moreover, even if ESAS had compared exploration vehicles to commercial crew-sized vehicles, the comparisons would be â€œapples vs. oranges,â€ because of the dramatically different tasks of these two types of vehicles.
When Jeff Hanley talks about how the Great Oz and supercomputers at NASA show that Ares-I is 3x safer than commercial launch vehicles, I wonder if he’s ever going to release their analyses for actually commercial crew vehicles, or if he’s being accidentally or intentionally dishonest. Because so far we haven’t been shown any data about the safety of actual commercial crew launchers. So far we have lots of data shown for the risks of using existing or modified commercial launch vehicles for launching a massive spacecraft designed to go to and return from the moon, including significant plane change maneuvers to allow anytime returns (ie Orion). It’s interesting to note that over half of the mass on Orion is the oversized launch escape system needed to get away from an SRB you can’t shutoff, and enough propellant for about 1500m/s of maneuvering to reach orbit and then to do in-space ops. That’s above and beyond the RCS propellant on the CM itself.
Most of the stuff that make Orion so massive are flat-out completely unnecessary for an earth-to-LEO crew capsule. You don’t need those kinds of delta-V capabilities. You don’t need as roomy of facilities, since by definition the flight times should be a lot shorter. Etc. There’s a reason why almost all of the proposed commercial crew systems are able to utilize single-stick launchers like Atlas V or Falcon 9–for an actual earth-to-LEO capsule you really don’t need anything bigger.
This realization that earth to LEO capsules can be much smaller than Orion leads to at least two important corollaries that I can think of:
- Smaller capsules mean higher structural margins.Â One of the existing vehicles most often suggested for commercial crew, Atlas V, was designed for the worst-case loading environment of any of its configurations (in this case I believe that would be the Atlas V 551 or 552).Â The Atlas V 552 sees much higher max-Q’s than the 401/402 do, and has a much heavier payload on top, which exerts much larger structural loads on the Centaur stage than are seen in the 401/402 configuration.Â While the Centaur structures may not meet the 1.4 magic number NASA likes in some of the bigger configurations, as I understand it, it actually exceeds that number in the 401/402 config most likely used for commercial applications.Â The Falcon 9 was designed from the start to meet NASA structural margin specs.
- No need for strapons.Â Only one of the commercial crew ideas I’ve seen so far used a vehicle with strapons for crew launch (Dreamchaser).Â This alone should make a huge difference in launcher reliability, since there are less things that can go wrong, less staging events, etc.Â Most of the commercial launcher ideas they mentioned in ESAS assumed multi-core configurations.
There’s also the possiblity on the Atlas-V of using a dual-engine Centaur configuration to allow for some upper stage engine-out capability, or running the RL-10 at a derated performance level (not sure if that’s something it can do automatically, or if you’d have to make modifications–if you have to modify it it probably isn’t worth it).Â With the much lower max-Q, and the ability to shut off the booster engine in case of an abort, I have a hard time believing that Ares-I is really that much more reliable than an actual commercial crew capsule launched on a commercial launch vehicle that has dozens of flights under its belt.
Food for thought.
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