One of the things that this blog strives for is accuracy. A couple of days ago we wrote about the alternate abort system being comtemplated for ORION. The so-called MLAS originated on the back of an envelop and has since become a works project for the Langely Research Center. As we've received more data on the configuration being simulated, we want to set the record straight. Unlike the Emperor on E Street, we do take new data into account at RocketsAndSuch and give it a fair hearing!
The configuration that is being considered is a "pusher" as we mentioned before. However, the pusher rockets are actually attached to the shroud that surrounds the command module and service module, and grab the command module from underneath during an abort, leaving the service module behind. The rockets are disposed of when the shroud separates from the launch vehicle, so that parasitic mass isn't carried to orbit. The rockets can also be fired in an nominal ascent, imparting their thrust to the entire stack so that their propellant is not wasted. So the wntire system may trade better in weight that originally envisioned in our commentary.
Because the rockets are firing well behind the center of mass of the shroud/command module system, and given the aerodynamics of the shroud, the system is dynamically unstable. To get around that, canards or fins are being considered to stabilize the system. Unfortunately, those fins don't work at zero velocity, such as in the case of a pad abort. Band-aids that only work part of the time require more band-aids! So here we go again, adding more complexity to the one system that you absolutely want to be the simplest, most reliable, least susceptible to potential failures so that it might save your life on a bad day.
Unlike the Emperor, we did take the time to consider the benefits of the alternate approach and didn't dismiss it out of hand when presented with new data. So while the configuration may be a little different than we originally reported, and we've now set the record straight on that, our misgivings related to the inherent problems in pusher systems, such as giving up vital milliseconds of survival by putting the system you are depending on closer to the initiating event, still stand.
Of course, all of these issues are arising from one basic fault in the Constellation architecture: its too dang big!
Tomorrow we'll discuss why ORION is too big, how it got that way.