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Astronaut Group Endorses Commercial Spaceflight
FleaPlus writes "Buzz Aldrin and twelve other astronauts have published a joint endorsement of commercial human spaceflight, stating that 'while it's completely appropriate for NASA to continue developing systems and the new technologies necessary to take crews farther out into our solar system, [the astronauts] believe that the commercial sector is fully capable of safely handling the critical task of low-Earth-orbit human transportation.' They are confident that commercial systems (which NASA already relies on for launching multibillion-dollar science payloads) can provide a level of safety equal to the Russian Soyuz and higher than the Space Shuttle, while strengthening US economic competitiveness. They also support the expected endorsement of the White House's Augustine Commission regarding NASA's use of commercial spaceflight — the Commission's final report will be released today." And here's the Augustine report itself (PDF).
The Real link is here:
Final Report
None that wouldn't have turned up in any other new rocket design.
There are three big safety issues that appear precisely because of the choice of an solid rocket motor (SRM) derived from the Shuttle solid rocket boosters (SRB). First, thrust oscillation is a problem with solid rocket motors because of their design. The SRM has a chamber prior to ejection through the nozzle. Certain vorticies resonate with this chamber and this vibration is then transmitted to the rest of the vehicle.
Now you may ask, if all solid rocket motors have thrust oscillation and the SRM is Shuttle-derived, why isn't the Shuttle affected? The answer is that it would be except for the clever way in which the SRBs are attached to the rest of the Shuttle stack. Effectively, both SRBs are attached to each end of a giant bar. The external tank only connects to this bar at two points which as I understand it are null points of the thrust oscillation vibration (which is very predictable). So as a result, little of the vibration is actually transmitted to the rest of the Shuttle. This only works because we have a pair of boosters that are attached only in a couple of spots to the rest of the vehicle. It doesn't work for the Ares I because the second stage has to be mounted on top of the SRM. End result is a great deal of vibration (how much we'll see in a few days). There are various solutions for dampening the vibration, but these cost mass or thrust. Neither is a problem with liquid propellant rockets like the EELVs.
Moving on, the second problem is the aspect of the Ares I. It has a wide second stage and a narrow first stage. This is precisely a consequence of the choice of the SRM as the first stage. The problem is that since SRMs have to go through a railroad tunnel when they're being shipped from Utah, they cannot be wider than they currently are. So the Ares I has an increased chance of bumping the launch tower at launch due to wind gusts. The limited width of the first stage also limits the performance of the vehicle leading to the third problem.
The third problem is that the launch of the Ares I has been made safer at the expense of the rest of the mission. This doesn't have much consequence for LEO missions since there is some performance margin to use up. But lunar missions are very tight on mass. So the performance loss from thrust oscillation mitigation or other problems comes by taking weight away from the payload, here the Orion vehicle. Further, the first stage is already as large as it can be, so there's no additional performance to be gained from the first stage. That means in turn that compromise of the safety of the Orion vehicle, namely removal of some redundancy of the vehicle, has to occur in order for the Ares I to lift it. Since for lunar missions, most of the risk is in the mission not in the launch, this means that we're increasing the overall risk of the mission merely to continue to use the Ares I.
The Launch Abort System didn't even exist on the Shuttle or Saturn rockets. It may not be 100% effective, but it doesn't need to be to at least provide a measure of additional safety.
This reminds me that there is a fourth safety advantage of other rockets than solids. In case of full rupture and conflagration of the first stage, a liquid rocket burns slower than a solid. That means lower heat on the escape vehicle and a greater chance of survival for the crew.
There are much better arguments against the Ares I. Like why it needs to be done at all when it has similar capabilities to the Delta IV, Falcon 9, or one of the number of shuttle-derived concepts out there.
This is my primary objection to the Ares I as well. There are two near future commercial rockets, the "EELVs", Delta IV Heavy, which flies now, and Atlas V Heavy (which would be based on a modification of the Atlas V which flies now). So we're ignoring rockets which fly now in exchange for paper rockets which as we've seen don't work as advertised. NASA should never be in direct competition with private launch services. It gives them too much incentive to undermine the competition.