HL-42 (spacecraft)

HL-42

NASA schematic from Access to Space Study
Operator	NASA
Applications	Manned spaceplane
Specifications
Launch mass	29 tonnes, including adapters
Regime	Low Earth orbit
Production
Status	Cancelled
Launched	0
Related spacecraft
Derived from	HL-20 Personnel Launch System

The HL-42 was a proposed scaled-up version of the HL-20 re-usable manned spaceplane design, which had been developed from 1983 to 1991 at NASA's Langley Research Center but never flown. Like the HL-20 ("Horizontal Lander 20"), the HL-42 would have been launched into low earth orbit mounted on top of a two-stage expendable rocket. At the end of the mission it would have re-entered and glided to a runway landing.

The HL-42 was suggested as one possible successor to the Space Shuttle in the NASA Access to Space Study of 1994. In the event another alternative, a Single-stage-to-orbit design, was chosen for further development, and work on the HL-42 was abandoned.

In the early 1980s it had been NASA policy to promote the use of the Space Shuttle for almost all launches, both civilian and military; only then, with Shuttle missions taking off almost every week, would the Space Shuttle program make economic sense. However, the Challenger disaster in 1986 forced a reconsideration, and in the following years many studies attempted to chart a way forward without reaching any consensus except for a growing feeling that "faster, better, cheaper" would be a good idea. There was also disagreement over the design (and indeed purpose) of the proposed Space Station Freedom.

Finally, as President Clinton took office for the first time in January 1993, the new NASA Administrator Daniel Goldin commissioned a major study that would reduce the multitude of possibilities to three well-defined options for launch systems.

In November 1993, while that study was still under way, an agreement was reached with Russia to develop the Freedom design into the International Space Station, so for Space Station operations the study authors were told to design for the 'worst case': Assume a 4-man Station like Freedom that would have been built and maintained solely by the USA, but put it in a Mir orbit with an inclination of 51.6 degrees (a significant change, as this would be more difficult to reach from Cape Canaveral and would reduce the Shuttle's payload by one third). On the other hand, the new era of cooperation with Russia would make it easier to buy and use the promising Russian first-stage engines of the RD-170 / RD-180 family, and the innovative tri-propellant RD-701.