Escape tower: Ares I vs. Ares V

[radarredux]

NASA's current plans has the CEV only launching on the Ares I, and it containing a small rocket to pull the CEV away from the Ares I should an abort be necessary during boost.<br /><br />My question is this: <font color="yellow">Would there be any difference in the success/failure of using this escape method if the CEV was placed on the Ares V instead of the Ares I?</font><br /><br /><br />The reason I ask is that there has been some grumblings about the cost and technical issues of the stick for the Ares I, and some have suggested doing away with it and just go with a Apollo-style launch with the CEV on top of the Ares V. This has got me thinking about safety issues.<br /><br />It seems that the Ares I would be simpler than the Ares V, and therefore a failure is less likely for an Ares I (fewer things to possibly fail) during the boost phase. Similarly, it seems that the pulling a capsule away from the Ares I would be more likely to be successful than pulling the capsule away from the larger Ares V.<br /><br />However... I also know intuition is often wrong. Any thoughts?

 

[PistolPete]

The main reason for the two vehicles is to separate the crew from the cargo. The reason for this is two-fold:<br /><ol type="1"><br /><li> The separation is for safety purposes. After the Challenger and Columbia accidents it became painfully obvious that having the two combined meant a large and complex vehicle. This leaves designers with fewer choices on how to safely extract the crew in case of an accident. For example, if the Shuttle suffers another Challenger-like incident, there is still no way for the crew to survive, period. Separating the two means less that can go wrong, and higher likelyhood that the crew survives in case something does happen.<br /><br /><li> Separating crew from cargo also means more payload to the Moon because the Ares V doesn't have to lift the extra weight of the CEV into space. Docking in LEO means more weight for fuel for the TLI stage, which translates to an increase in mass to the Moon which means more crew/cargo to the surface. <br /><br /></li></li></ol> <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[josh_simonson]

Separation of cargo and crew and cargo is achieved by having the CEV be separable from the rest of the rocket. The escape tower works more or less the same wether there is 100t of cargo between the rocket and CEV or not.<br /><br />Rather, the 'separation of crew and cargo' meant the death knell for shuttle and venturestar type vehicles in which the crew, cargo and propulsion are wrapped up into one contiguous vehicle and the crew goes down with the ship.<br /><br />The larger Aries V will be more accident prone due to it's higher complexity, leading to a slightly worse safety rating over the simpler Aries 1, but it's still orders of magnitude better than STS. Squeezing 20% more performance out of the Aries V will certainly be cheaper than another LV. A 2 launch Aries V architecture would also be cheaper.

 

[PistolPete]

Separating crew from cargo is safer because when you do that you have a smaller spacecraft, which means having a smaller LV, which means a simpler, safer LV.<br /><br />So, in other words... what you said.<br /><br />So... uh... nevermind. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[henryhallam]

There is an argument that cost savings can be made by only "man rating" the CLV and allowing the CaLV to run at a slightly lower reliability. I'm not really sure how much merit there is in this idea.

 

[edkyle98]

"The main reason for the two vehicles is to separate the crew from the cargo. The reason for this is two-fold:<br /><br /> 1. The separation is for safety purposes. After the Challenger and Columbia accidents it became painfully obvious that having the two combined meant a large and complex vehicle. ..."<br /><br /><br />Separating crew from cargo was done after Challenger only because the accident made it apparent that most shuttle payloads of that day (commercial and military satellites, mostly) could have been launched by unmanned rockets. The missions weren't worth the lives of NASA's astronauts. Challenger's crew essentially died for a TDRS communications satellite, for example.<br /><br />But that argument has no merit outside the STS system. There is no equivalent "cargo" on the lunar missions. Astronauts will have to dock with, and use, the components launched by the Ares V once they reach orbit. Ares V will have to be very reliable, or the lunar program will never work. A CEV escape system could be made to work just as well atop Ares V as Ares I. *Any* launch escape system will make CEV an order of magnitude more survivable than space shuttle.<br /><br /> - Ed Kyle

 

[josh_simonson]

In the ESAS report the stick variants had an LOM/LOC of around 4 (75% escape success), while the shuttle derived HLVs were more around 6-7. Appearantly they felt that the added space between the SRBs and the CEV improved it's odds of survival. All liquid EELV derived boosters had LOM/LOC between 6-8. <br /><br />Appearantly the LES works better on the HLV than the CLV, but not enough to make up for the lower reliability of the HLV. But really, we're talking the difference between 1/1000 and 1/2000. 0.05%, at 6/year that's one LOC every 166 years vs 333.