guest blogger john hare
There is an increasing discussion of launch escape systems in the last few months. Most of them seem to focus on developing some sort of high acceleration tower to yank the capsule free in event of booster malfunction. The financial numbers involved get quite entertaining, with the added dangers of a seldom used system a close second.
If the second stage could just do an early high acceleration staging event, it would seem desirable to do that and save the whole upper stage by having it land at the launch site under it’s own power. This would also have the advantage of using regularly used engines that would almost certainly be more reliable than the every several year operation of the units now proposed. Unfortunately, that would require oversizing the upper stage engines for a major cost and mass hit as they would be normally operated at far below their designed thrust.
Unless you steal borrow a page from the orbital refueling proponents. Stretch the tanks on the first stage some so they hold as much propellant as both stages normally would. At take off, the second stage has only 20 seconds or so of on board propellant. If the upper stage has a normal mass ratio of six, then if it has to stage early, it can have a thrust to weight ratio of well over five, which should be sufficient to clear the lower stage debris field with adequate failure warning
Just before staging, the upper stage is fueled up from the first stage tanks. This puts the entire mass penalty of the LES in the first stage tank stretch and reusable high volume/low pressure transfer pumps. IMO, this would be faster and cheaper that an LES tower that is expended every flight or carried all the way to orbit. If it saves the upper stage as well as the cabin, it could be better as well. It might also reduce the insulation requirements for the upper stage tanks as they would be topped off just seconds before lighting the engine(s).