We went off on adventures with the upper stage, and left our booster alone in the night. This kind of launch may take the unmanned craft on quite a trajectory, possibly making a skip across the ocean or a return to base. At some point it needs to be called home for reentry and a landing.
Engines may be closed by the inlet cones for thermal protection. With the orbiter gone the leading edges are largely rounded for thermal loads and drag to slow reentry speeds.
Will it be on final approach to the old shuttle landing strip? To save mass our landing gear is reduced to a nose wheel and two skids, per the X-15. Like that craft it will have a dedicated launch vehicle, but not one you might expect.
Gear down and near the ground. We may again use thrusters to slow the craft and aid ground effect for a soft touchdown. Now we can look at ground service and propulsion needs before the next mission.
We illustrate a simple cylindrical engine installation in part for fast service removal, replacement, and servicing between missions.
For a prototype, engine development may be part of the early missions. There have been many air breathing propulsion designs proposed, but this is not an easy performance realm. We are illustrating turbine based systems in the outboard positions for low speed and takeoff operations. These have been reliable and efficient in the past, but they may also be a bit heavy and complex. This may be just our crude image here, but the Concorde, XB-70, and SR-71 are all complex installations.
THAT INLET MESS? DON’T ASK!
Even a greatly simplified view of Concorde engines suggests sophisticated understanding of shock wave and flow management. This delivered supersonic speeds with greater fuel efficiency than rockets.
The SR-71 is a lot more complex to achieve Mach 3 performance. this also challenges thermal loads on the airframe, so we would not want to go beyond this. Here again, mechanisms are building a lot of mass and complexity
In 1999 Orbital Sciences did a study of modification of a D-21 drone to use for space launch. This study proposes a cheap reuse of old tech for space launch. It again validates Hydrogen Peroxide instead of liquid oxygen. The proposal would use avionics from their Pegasus launcher and the X-34 for economical development. The X-37 also demonstrates autonomous operation, so the guidance capacity is out there. A ram jet engine is often considered for these missions. These still require a rocket or turbine to reach operational speeds, and may still be a bit complex, but possibly lighter. The D-21 offered enough fuel economy to reach China, where at least one crashed and is now in a museum there.
We illustrate another slightly silly vision of an ejector ramjet, which features a rocket surrounded by a ram duct. This may increase the efficiency of a rocket and offer that propulsion when ram air is no longer available. Ours shows a little rocket in the inlet for air compression and ignition of fuel, and a larger one aft for more thrust. The aft engine may share an aerospike with the upper rockets for vacuum efficiency. Don’t copy this design unless you have money to waste…it is fantasy art!
Without striving for unobtanium or hypersonic engines there may be value in the idea of applying lessons learned in historical technical solutions. As such we have illustrated cylindrical engines where cones may be easier to manage shock and inlet issues during development. For ease of servicing these engines are installed individually. The possibility of various combinations of test engines remains here.
Gangs of engines in square inlet configurations are seen on the XB-70 and the Concorde. The SR-72 has inlets and airframe configured and tuned for Aerojet turbine and scramjet engines. Our goal is not extreme speeds until leaving the atmosphere. To harvest atmospheric oxygen cannot come at the cost of a massive fuel burn penalty or huge development costs. To field a serviceable test bed that can climb at supersonic speed and switch to rockets is a better goal. Identifying efficient air breathing propulsion may require flight testing. Our platform proposes to deliver variable test opportunities.
Engineering software and wind tunnels may not deliver all the variables that these engines will experience. Engine performance can vary with weather, altitude, speed, and thermal loads. In Wyoming your barbecue may be smothered without a breeze and a good hot start. But on some days here the 80 mph winds may share your meal and glowing embers with the neighbors. I read about a physics professor who started his barbecue with liquid oxygen. High test peroxide would work too, but you may not be able to find your meat!
WITH SUFFICIENT THRUST, BBQ PIGS FLY JUST FINE!