Chair Force Engineer

Monday, July 17, 2006

Remora & Great White

There have been many ideas floated for a true spaceship, which is fully reusable and has a reasonable turnaround rate. It should take off and land horizontally from a runway, with little in the way of new infrastructure to support it.

Two of the ideas worth considering are two stage to orbit (like Burt Rutan's SpaceShipOne and White Knight, but on an orbital scale) and Aerial Propellant Transfer, where a dense oxidizer is loaded from a tanker aircraft onto the spaceplane after it reaches cruising altitude, which cuts down on the weight of the landing gear and possibly the size of the turbine engines. I tend to think that both of these ideas will need to be used in the same system to make a true spaceship.

My plan starts with a small, orbital, winged craft called "Remora." It uses Kerosene and Liquid Oxygen as propellants. It will be carried underneath the belly of an even larger airplane, "Great White." This mothership has two turbine engines for takeoff and climb to refueling altitude, and it has a Kerosene-Oxygen engine that is used for ascent after the Great White and Remora have taken their oxidizer load from the tanker.

On a typical mission, Remora and Great White will mate on the ground. The kerosene used for the takeoff and climb will be carried in two external fuel tanks (either expendable or recoverable by parachute) mounted tangentially to the Great White. Then Great White's turbines will start, and the duo will climb to 40,000 feet in altitude.

Great White and Remora will soon be joined in the sky by a converted airliner, with an internal dewar containing liquid oxygen. The skilled pilot of Great White will link up with a rigid "flying boom" on the tanker and take on the oxidizer load. Some oxidizer is pumped through Great White's tanks into those of Remora through a cross-feed system inside the pylon connecting the two craft. Once the propellant is off-loaded, the tanker flies a safe distance away and then serves as a chase pilot to observe the ignition.

Fully fuelled, Great White drops its external tanks, then ignites its main rocket engine and gradually transitions into a climb while picking up speed. After Great White's engine burns out and the craft ascends to a high altitude where the dynamic pressure is low, the Remora separates and ignites its own engines, sending it into orbit. Great White descends back to earth, eventually building up a sufficient amount of lift as it enters the denser atmosphere. The turbine engines allow Great White to make a powered landing with the opportunity to make a go-around.

Great White and Remora would be designed more like rockets with wings than like airplanes. That's because the spherical and cylindrical tanks used on rockets are the two most efficient shapes for pressure vessels. While most airplanes use "wet wings," the weight of the wing itself is less of a concern for the airplane; it represents dead weight on the rocket for most of its flight. The wings on Great White and Remora should be as simple as possible, and so should the landing gear.

I forsee some other problems with this system, like aborting a launch after the propellant transfer but prior to engine ignition. Escape for Remora's crew is impossible during the ascent phase of flight, but this is moot if the system can be given airliner-like safety margins (and hence avoid an escape system like airliners do.) But my proposal is at least worthy of detailed study, if for no other reason than stopping other dreamers from going down this path if it truly is the wrong one.