Slide 2 of 100
Both NASA and the military investigated various reusable TSTO launch vehicle concepts during
the early 1960s. In November 1962, the heads of the military and civilian future space transportation efforts signed an agreement to coordinate their hypersonic research vehivle programs.
The U.S. Air Force initially was very interested in airbreathing HTHL SSTO
aerospaceplanes -- General Dynamics and North American received $1.5-million contracts for
preliminary USAF concept studies in June 1963 and the Department of Defense had spent some $46 million on advanced airbreathing vehicle research by FY 1963
-- but quickly concluded that scramjets and other
propulsion systems were not yet sufficiently lightweight and efficient for single-stage vehicles. Airbreathing
propulsion and rocket propulsion on HTHL TSTO boosters, on the other hand, would be bigger
since they require large wings and huge hydrogen fuel tanks and consequently have a higher
dry mass which translates to higher cost. For these reasons, NASA preferred all-rocket TSTO
boosters for its "Space Transporter" class of vehicle, since the required engines already had
been developed for the Saturn program. The Space Transporter studies were based on the
following specifications: (1) 10 passengers + crew of 2 with 3,000kg of cargo to LEO,
(2) reduced payload into polar orbit, (3) maximum acceleration of three G, (4) 95% mission
reliability and 99.9% probability of passenger survival, and (5) launch rate options of four,
eight and sixteen per month over an operational period of 10 years. In general, the 1960s RLV
studies were focused on mission/technology requirements rather than detailed vehicle design.
NASA's main priorities for the 1970s were large space stations and manned lunar & planetary
missions; the reusable ”space transporters” and post-Saturn heavy-lift rockets were simply
regarded as necessary adjuncts to reduce the transportation cost.
NASA initially regarded horizontally launched TSTOs as safer for passenger transport than
vertically launched systems, since the launch G-loads are reduced and the abort characteristics
are better than for VLs. However, the US Air Force had more flexibility with respect to G limits
and was willing to consider both vertically and horizontally launched Aerospaceplanes.
Martin's "Astrorocket" would have been launched vertically because the designers felt the VL
mode frees design from gross liftoff weight constraints (Martin regarded about 450t as the
upper limit for a HTHL TSTO). The vertical takeoff mode would provide additional mission
flexibility since no rocket powered horizontal launch sled would be required. The Astrorocket
would have used less efficient but storable hypergolic propellants on both stages so
consequently the liftoff weight was high: 1134t. The payload capability to a 555km orbit was
only 2.27t and the crew of three astronauts could stay in orbit for up to two weeks. Both
stages carry turbojets for powered landing and self-ferry between launch sites. The liftoff
thrust would be 13,350KN and stage separation would occur at an altitude of 64km while the
vehicle is travelling at 9600km/h.
Liftoff Thrust: 1,320,820 kgf. Total Mass: 1,133,786 kg. Core Diameter: 7.0 m. Total Length: 78.0 m. Flyaway Unit Cost $: 36.00 million. in 1985 unit dollars.
Stage Number: 1. 1 x Astrorocket-1 Gross Mass: 981,859 kg. Empty Mass: 132,000 kg. Thrust (vac): 1,500,000 kgf. Isp: 293 sec. Burn time: 164 sec. Isp(sl): 258 sec. Diameter: 7.0 m. Span: 40.0 m. Length: 65.0 m. Propellants: N2O4/Aerozine-50 No Engines: 9. LR87+
Stage Number: 2. 1 x Astrorocket-2 Gross Mass: 151,927 kg. Empty Mass: 23,500 kg. Thrust (vac): 220,000 kgf. Isp: 345 sec. Burn time: 181 sec. Isp(sl): 230 sec. Diameter: 3.0 m. Span: 20.0m. Length: 30.0 m. Propellants: N2O4/Aerozine-50 No Engines: 1. LR87+
”Reusable Launch Vehicles” -- Osmun, Space/Aeronautics 1964/September/p.43
”Space Transporter Study” -- SPACEFLIGHT 1965/p.124
"Frontiers of Space" -- Bono & Gatland, Macmillan, New York, 1969.