Friday, 13 January 2012

Background to the Space Shuttle

The Space Shuttle Story” was the title of a recent public lecture at Nottingham University. The talk covered a lot of ground and gave an interesting overview of the subject, and provoked NSB to dig a little deeper into the background of the Shuttle program. . .

One can trace the origins of the Space Shuttle program back to US military projects such as the plane-like Dyna-Soar project in the late 1950s. At the time, manned space travel was the domain of NASA which was designed to be re-usable and have good manoeuvring capability during re-entry, in contrast to other spacecraft being developed at the time. Unfortunately for the Air Force, they focussed so much on the controlled re-entry aspect of the project that they forgot to develop any useful missions for the craft do perform while it was in space. So the project got canned in 1963, before any flight tests had taken place. Doh!

Too late, it became clear that Vaseline had not been the best choice to seal the underside of the Dyno-Soar

Incidentally, the Dyna-Soar used a high performance Nickel alloy called “Rene41”. You can get a feel for the detailed way in which metal alloys are characterised by checking out the data for Rene41 here.

The Air Force remained interested in spaceplanes, however, and ran a series of tests on so-called “lifting bodies” in the 1960s and 70s. These craft investigated the handling and landing characteristics of small wingless planes and were dropped from carrier aircraft before firing a rocket motor, climbing to altitudes well above 70,000ft and then gliding back to earth. Examples of lifting craft were the X-24B and the HL-10

The X-24 was a lean mean lifting body. . .

. . . while the HL-10 was a lifting body that had eaten all the pies.

Those of a certain age will recognise the tubby lifting body as the craft that crashes spectacularly in the opening sequence of the Six Million Dollar Man. A sequence that NSB is only too happy to link to below. . .

A review of NASA’s activities in the early seventies resulted in the organisation focussing on two projects - the Shuttle and a Space Station. NASA decided to develop the Shuttle first and, in 1972, that President Nixon formally announced that NASA would proceed with the program.

There were many competing designs in the early stages of the program (see below). It is noticeable that many of the early designs featured a carrier vehicle that was piloted and returned to land conventionally under its own jet power. Further development demonstrated that the extra weight associated with the engines, wings and pilot compartment of these carrier planes had an adverse effect on the payload that the actual shuttle could carry. These concerns, together with budget pressures moved the design towards that of the “Star Clipper” (top right in image below). This proposal used an expendable fuel tank and analysis of the design showed that this was a particularly efficient approach to designing the craft.

I'm not saying that the designers were dropping acid, but . . . .

Amongst other concepts, the above image contains the following :
SERV+MURP (top left)
Star Clipper (top right)
North American DC3 (centre right)

Eventually the design was refined into a vehicle that we recognise today. The first Shuttle, Enterprise, was completed in 1976, without engines or a real heat shield, and used for testing, including atmospheric flight tests (Enterprise was carried aloft on a modified 747 from which it separated and then glided back to earth). Famously, Enterprise was originally intended to be named “Constitution” - until a letter campaign by Star Trek fans led to the change of name to Enterprise.

The flight tests were not without incident. In particular, during the fifth test Enterprise suffered from severe “Pilot Induced Oscillation” during landing - a problem that was cured by a modification to the control computer system. You can read a NASA report about the incident, and the work undertaken to develop a solution, here.

By the early 1980s the program was ready for its first orbital flight. This was performed by Shuttle Columbia on 12th April 1981. This was the first of 135 missions, including 37 missions to build the International Space Station.

Image Sources : HL-10, X24B, Columbia, Dyna-Soar, Shuttle Concepts

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