Slide 40 of 125
In June 1975, NASA's Langley Research Center began a 12-month study to determine what RLV
technologies might be available in the 1990s and which ones would be the most economical.
Boeing and Martin Marietta received contracts to study fully reusable VTHL & HTHL SSTO concepts
capable of launching the same type of manned spaceflight-related "priority payloads" (18.3 x
4.5m envelope, 29,484kg mass) as the Space Shuttle by 1995. Single-stage-to-orbit was chosen
because of the potential for simplied operations & lower costs relative to TSTOs, e.g. because
recovering a flyback TSTO booster appeared to be quite difficult without cruise/landing jet
engines. Other significant assumptions included a technology readiness date of 1986 and the
use of 4500psia high-pressure SSME-derived engines; Langley initially regarded tripropellant
propulsion as too risky. Both linear aerospike as well as conventional two position bell-nozzle
engines were however included. Compact, high pressure engines were regarded as essential because
the RLV base area only increases by the square as the weight increases by the cube. The
estimated cost to build four Langley SSTOs and fly 1710 missions by the year 2009 was only
$8 billion [1976 rates] and the launch cost could be as little as $20 per pound. Langley felt no
major breakthroughs were required, but only a number of subtle improvements in design, design
techniques and technology. Although the SSTO payload capability for a given gross liftoff
weight is less than for a TSTO, the configuration offers many compelling advantages (e.g. no
downrange staging constraints, incremental airplane type testing becomes feasible) but also
requires technology advances (mainly propulsion & structural mass). The overall conclusion was
that single-stage-to-orbit appeared to be clearly feasible in the 1990s due to significant
improvements occurring in applicable technologies.
Martin Marietta focused on VTHL SSTOs; the company initial design from September 1975 had a dry
weight of 203,000kg and gross liftoff mass of 1,925,000kg. This represented a 25% weight
reduction in vehicle structures from the existing Shuttle, thanks to new materials that likely
would be developed in the 1980s and '90s. Uprated SSMEs with multi-position nozzles would be
used to optimize performance. The vehicle also utilized an advanced external insulation thermal
protection system derived from the existing Shuttle Orbiter TPS, and separate load-carrying
propellant tanks with stand-off TPS carrier panels. NASA/Langley predicted the gross liftoff
mass of a 29.5-tonne payload capability VTHL SSTO could be reduced from 4000t to 1633t (171t
dry) by 1995 thanks to expected improvements such as two-position engine nozzles & 25% lighter
structures.
The "normal technology growth" Martin Marietta VTHL SSTO (200t/1920t mass) would have cost
$6 billion [1976] to develop and the cost per flight would be $2.6M. A similar "accelerated
technology" tripropellant concept could be made much smaller (83t/1000t) and the cost would be
less as well ($5.3B development + $1.2M/flight).
"Looking Beyond the Space Shuttle" -- Dooling, SPACEFLIGHT 1976/p.68 & p.367
"Advanced Launch Vehicle Systems and Technology" -- Bell, SPACEFLIGHT 1978/p.135
"Advanced Technology and Future Earth-Orbit Transportation Systems" -- Henry & Eldred, Space Manufacturing Facilities II (Proceedings of the Third Princeton/AIAA Conference, May 9-12 1977) p.43
"Space Transportation Systems 1980-2000" -- Salkeld,Patterson & Grey, AIAA Aerospace Assessment 1978/Vol.1