A typical high key pattern for an unpowered approach to landing.Īt the same time these studies were going on on how to save weight with Orbiter and flyback booster-mounted jet engines, with NASA there was a group at the Flight Research Center at Edwards AFB where unpowered landings were routine for many high speed research aircraft going back to the X-1 (the X-15 program being the most recent one at the time) and the graduates of the co-located Aerospace Research Pilot School had as a requirement that students demonstrate proficiency in unpowered landings using the school’s Lockheed F-104 Starfighters which were throttled down to idle for the practice sessions. Both companies showed that liquid hydrogen fueled jet engines saved about 2500 lbs of weight per jet engine compared to conventionally-fueled jet engines. Pratt and Whitney also got a similar contract to study the use of liquid hydrogen fuel in the F401 engine, the planned naval derivative of the USAF’s F100 engine planned for the F-15 Eagle. In June 1970, NASA issued contracts to GE to study the feasibility of using liquid hydrogen in the F101 engine being developed for the B-1 bomber. Consideration was then given to using liquid hydrogen as fuel for the jet engines which would cut out the need for jet fuel tanks. Many of the flyback booster designs would need approximately 150,000 lbs of jet fuel (for comparison, a Boeing 777-200ER has a fuel capacity of roughly 300,000 lbs). The weight of up to twelve jet engines and the necessary jet fuel cut into the payload of liquid hydrogen and liquid oxygen for the booster’s rocket engines. Soon the design of the flyback booster itself began to take on technical challenges that rivaled that of the Orbiter design itself. Some of the designs for the flyback booster were massive with a need for as many as twelve jet engines. Even if designers went with an Orbiter design that was unpowered on its landing, the 19 design studies prominently featured a fully reusable two stage Space Shuttle with a big flyback booster that would have to have its own jet engines. But in the ascent and in orbit, jet engines and fuel for those engines was dead weight that subtracted from potential payload. Some designers envisioned the Orbiter rendezvousing with a tanker for additional jet fuel. Having its own jet engine propulsion also gave the Orbiter cross range capability upon return from orbit. The engines also facilitated ferry flights, repositioning the Orbiter amongst various facilities (landing, launch, overhaul, etc.). Having its own air breathing engines offered three advantages- they would allow atmospheric flight testing much like any other aircraft was tested and pilots could practice landings in the run up to an orbital mission. Avgeekery contributor JP Santiago tells us why.Īs design work by various aerospace companies began on the Space Shuttle program in the late 1960s, it was a given that the Orbiter would have its own jet engines. The concept proved unfeasible and too costly. Similar in concept to the USSR’s shuttle-clone Buran, the US Space Shuttle went through many design iterations including a concept where jet engines could be attached to the space vehicle for ferry and/or powered approaches.
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