guest blogger john hare
The increasing tempo of VTVL development flights and the recent success of the Falcon 9 lead to possibilities for a different type of cooperative venture. Two companies have VTVLs testing that are pretty much gas-n-go while SpaceX has vehicles that are quite difficult to get back. Using gas-n-go boosters to improve an expendable rocket payload might be a viable business.
Two VTVLs are built proportionate to the Falcon 9 and used as strap on boosters with propellant cross feed so that the Falcon 9 is fully fueled up when the VTVLs stage off and return to launch site for a pinpoint landing. What I propose that is different than what I have seen before is that the VTVLs separate at about a minute into the flight before transonic flight and maxQ is reached. By separating at high subsonic, the VTVL vehicles and the coop vehicle clusters never have to be designed for or subjected to the stresses of transonic and supersonic flight.
Subsonic flight is a far more forgiving and understood aerodynamic problem than the higher velocities and leads to considerably less problems, though also with less results. By staging at high altitude the Falcon’s engines are attaining near vacuum thrust and the vehicle could be considerably heavier than on a ground take off. A small tank stretch and a subsonic boost should get about 40-50% more payload to orbit. While the Falcon would be the main player, the supporting cast could improve the bottom line considerably with benefits for all.
The benefits for Falcon would be of the same order as the subsonic air launch scenarios that so many have studied. The VTVLs just do the airplane’s job. It is the emergence of the fast turnaround rocket vehicles that make it possible to virtually airlaunch in unlimited sizes.
The VTVL players would have a market for a fairly low velocity vehicle with a high dollar (compared to the suborbital field) market that doesn’t require high flight rates. It would give them early experience with a larger vehicle than would fit in their normal course of development, and a large launch assist platform in the bargain. Though the vehicles developed for Falcon assist would not go supersonic in their booster role, they would have plenty of size margin for modifications to allow them to carry relatively large VTVL upper stages to mach 3-4 and still do an RTLS maneuver for another flight or two that day.