Material Marvels – To Boldly Go…

Materials World magazine
,
24 Sep 2018

The Space Shuttle Enterprise stands as a testament to the human need to explore and seek answers. Ceri Jones looks at its construction and the journey from build to retirement.

Inspired by intergalactic adventures on the television programme Star Trek in the 1960s, the American public petitioned to name the country’s revolutionary new space shuttle after the show’s beloved starship, the USS Enterprise.

Launched in the mid-1970s, the shuttle, in turn, inspired generations of explorers, technicians, engineers and myriad others, all enraptured by the possibilities of space travel and discovery.

However, unlike its namesake, the indefatigable Space Shuttle Enterprise (OV-101) was destined never to travel into space. While it captured the public’s imagination and kicked off the USA’s 30-year space shuttle era, NASA used the Enterprise to conduct flight and landing tests imperative for informing the designs of other spacecraft.

Reusable rockets made for an entirely new type of spacecraft, and this research became the foundation of the Columbia, Challenger, Discovery, Atlantis and Endeavor crafts, intended to rack up more than 100 missions each, carrying crews that would perform satellite maintenance and build the International Space Station.

So the Enterprise prototype didn’t boldly go into space, but did make it possible for a pioneering fleet to go beyond what had been done before. As NASA describes, it’s a shuttle that ‘launches like a rocket, manoeuvres in Earth orbit like a spacecraft and lands like an airplane’, presenting a tantalising degree of versatility – along with a whole host of design and operational problems.

A model spacecraft

An entire space shuttle system consists of an orbiter – the ‘rocket’ – and two rocket boosters, all of which are reusable, plus a single-use external fuel tank that burns up in the atmosphere. But the public eye is inevitably drawn to the orbiter, the unit that carries the crew into space and, hopefully, safely home again.

Enterprise was constructed at the Rockwell International manufacturing facility in Palmdale, California, USA, on the site of the renowned United States Air Force Plant 42, which famously provided the construction sites for the Grumman and the Blackbird, as well as many other recognisable planes.

The shuttle was constructed from aluminium and graphite epoxy. Originally 122ft (37.2m) long with its tailcone, later removed following flight tests, making the final length 137ft (41.76m), 57ft (17.25m) wide with a 78ft (23.8m) wingspan. Initial tests informed structural design changes, whereby the bodies of Columbia and Challenger were improved, and the Enterprise deemed unworthy of retrofitting for space flight.

As such, Enterprise contained no engine, fuel lines, tanks, air-propulsion or guidance systems, and had an empty crew compartment. And having no payload to carry or eject, the payload bay had explosive bolts in place of mounting infrastructure and hydraulics, and aluminium covered panels where later models would have windows. Therefore, testing periods required additional weight to be added for more accurate real-event simulations.

As well as the reduced load, Enterprise had no surface heat shield, it being a costly and laborious process. For the space-ready orbiters that followed, shuttle surface temperatures would need to withstand the -150°C of space, as well as up to 1,600°C due to friction upon re-entry.

Installing heat shields consisted of covering specific outer skin surface areas with reinforced carbon-carbon (RCC) panels, white low-temperature (LRSI) and black high-temperature reusable surface insulation tiles, fibrous refractory composite insulation tiles, felt reusable surface insulation blankets, and any surface gaps were filled with an array of thermal barrier materials. Later developments included replacing the LRSI tiles with advanced flexible reusable surface insulation – a quilted composite fabric.

The RCC panels alone required 22 uniquely sized and shaped panels per leading wing – the graphitised rayon fabric impregnated with a phenolic resin was layered one ply at a time, before being cured, trimmed, drilled and inspected, and to prevent oxidation, the outer layers of the substrate were covered in a 0.5–1mm-thick layer of silicon carbide – all of which was carried out in an argon-filled chamber at up to 1,600°C.

Instead, the Enterprise shuttle’s surface was covered in polyurethane foam tiles.

Testing times

After five years of planning and construction, in February 1977 the prototype was ready to start approach and landing tests (ALT) at NASA’s Dryden Flight Research Center in Edwards, California, USA. It was used to monitor and validate design decisions, flight, ALT, and to refine operational procedures.

For this, the orbiter was mated to a Boeing 747 Shuttle Carrier Aircraft (SCA) and performed three captive-carry flights with no crew, followed by five free flights piloted by astronauts Fred Haise, Gordon Fullerton, Joe Engle and Richard Truly. Haise had been a Dryden research pilot and part of the Apollo 13 mission. On each free flight, the shuttle was released at between 17,000–24,700ft and with no engine or crew, where it would glide to a controlled landing. During these phases, the rocket reached top speeds of more than 470mph in carrier-captive mode and 310mph during ALT.

In August 1978, the complete shuttle system was setup for its first vertical mating to undergo vertical ground vibration testing. Over the years, the Enterprise orbiter was wheeled out for additional rounds of tests with new equipment and procedures, including supporting operational processing systems at the Kennedy Space Centre. In 1979 it was taken to Rockwell plant in Palmdale, where some of its parts were recycled for other shuttles. Later, the shuttle was used to test a landing arresting barrier concept following the Challenger accident, and then put into long-term storage.

During the 1980s Enterprise travelled to numerous world fairs, where the public could get a close-up look at the famous orbiter rocket, before it was retired to the Smithsonian Steven F Udvar-Hazy Center in Virginia.
At this point in its life, the shuttle had been left in storage for 19 years, so in March 2004 it required a thorough restoration, where three specialists and a team of volunteers washed the orbiter inside and out with detergent and cotton rags, before sanding the paint, repairing the vertical stabiliser and rudder, and the orbital maneuvering system, then repainting the body with aerospace paint containing an additive to help it appear like a plush spray on, and fixing up the polyurethane tiles before its unveiling in October. Names, logos and design work were hand-painted according to 1985 versions.

Multiple makeovers

But this too was not to last and the shuttle was signed over to New York City’s Intrepid Sea, Air & Space Museum – a converted WWII aircraft carrier – in December 2011. It made the incredible journey flying from the Smithsonian in Washington to JFK airport in New Jersey, where it was towed by a barge along the Hudson River to the museum, for a welcome that included former pilot Joe Engle, and Leonard Nimoy.

Prior to this, the rocket had endured weeks of outdoor storage, including exposure to heavy rainstorms. Resulting paintwork damage and flooding required restoration work before the shuttle could be put on display.

‘This was facilitated through removable stress panels in the primary structural components accessible through the main landing gear wheel wells,’ Eric Boehm, Aviation Curator at the Intrepid Sea, Air & Space Museum, told Materials World. ‘For example,’ he said, ‘the main fuselage structure is typical of aircraft construction with a modified monocoque type with formers, longerons, stringers and stressed skins.’   

Boehm explained that the right-side wheel well’s inboard structure is the main fuselage skin, with a removable stress panel allowing access to the internal payload bay. A further stress panel at the engine compartment opens up to the internal structure, tail cone and wing interiors – creating a full chord wing rib structure allowing access all the way to the tips.

‘A plywood catwalk was constructed and installed in the payload bay. After the catwalk was installed, our primary requirement was to preserve the vehicle. We did this by applying commercially available corrosion inhibiting compounds to all internal surfaces.

‘Enterprise is now listed in the National Registry of Historic Places and will serve as an educational artefact for generations to come.’