Slide 26 of 125
General Dynamics also received a $0.15-million Phase-A extension from NASA/Marshall to further
study its shuttle concepts. The Triamese design was abandoned in September 1969 after more
detailed analysis indicated that the development cost showed no considerable advantages vs.
traditional two-stage systems. It had proven difficult to to have one aerodynamic shape serve
both as booster and orbiter; too many compromises had to be made. The designers then tried
to “stretch” the Triamese orbiter but this, in turn, reduced the design commonality and hence
cost savings. The company finally settled for a similar "FR-3A" two-stage design (bottom left)
with V-tails to provide hypersonic roll control and aerodynamic stability. The booster/orbiter
staging point was at 56.7km altitude and 193 seconds after launch when the vehicles were flying
at 3325 meters/second. The straight-sided bodies were designed to accommodate cylindrical
propellant tanks efficiently. Variable geometry switch-blade wings would still be used for
subsonic flight and landing only, so they would have to be optimized only for this part of the
flight regime. The variable-geometry system would also have reduced the thermal protection
system requirement on the wings (GD was the only company that still proposed a “hot
structure” metallic TPS at the end of Phase A) and a very good crossrange capability, although
it unfortunately also produced a high vehicle weight-to-planform ratio which in turn resulted
in higher average base temperature relative to the straight- or delta-wing shuttles. The
additional weight and complexity of the swing-wing system was of some concern to NASA, who
feared it would be costly to maintain and produce the required hardware.
Payload capability to a 550km 55 deg. orbit: 22,680kg.
Liftoff Thrust: 3,083,900 kgf. Total Mass: 2,557,880 kg. Core Diameter: 11.2 m. Total Length: 86.0 m.
Stage Number: 1. 1 x Shuttle FR-3-1 Gross Mass: 2,169,691 kg. Empty Mass: 234,467 kg. Thrust (vac): 3,068,166 kgf. Isp: 442 sec. Burn time: 275 sec. Isp(sl): 392 sec. Diameter: 11.2 m. Span: 25.7 m. Length: 71.8 m. Propellants: Lox/LH2 No Engines: 15. SSME Study
Stage Number: 2. 1 x Shuttle FR-3-2 Gross Mass: 388,189 kg. Empty Mass: 130,159 kg. Thrust (vac): 463,874 kgf. Isp: 459 sec. Burn time: 251 sec. Isp(sl): 359 sec. Diameter: 7.5 m. Span: 21.8m. Length: 54.6 m. Propellants: Lox/LH2 No Engines: 2. SSME Study
“Progress in Technology for Space Shuttles”-- Rainey, AAS 1970/vol.28/p. 3
“Characteristics of the Space Shuttle” -- Jean & Scott, AAS 1970/vol.28/p.141
“Space Group Readies Proposal Requests” -- AW&ST 1970/January 19/p.18
”Space Shuttle” -- Dennis R. Jenkins, 1981, ISBN: 0963397451