The Space Shuttle Part II: The Orbiter
Inside NASA's workhorse
Cutaway illustration of a Shuttle Orbiter. NASA Illustration.
The Space Shuttle Orbiter would be a little over 122 feet long with a wingspan of 78 feet, roughly the size of a small jet airliner such as a 727 or DC-9. Liftoff weights, including a loaded and fueled Orbiter, SRBs, and a full External Tank, would generally be in the neighborhood of 4.5 million pounds. Like all space vehicles, it featured a Reaction Control System (RCS) for control functions in space, although the Shuttle's system is more complex than most others. The Orbiter also features aerodynamic control surfaces for the approach and landing phase. During re-entry, it basically behaves like a very high-energy, high-performance lifting body aircraft, what the engineers used to call a "racehorse." Generally, it will land at 215-230 MPH and requires about a 15,000-foot runway, although runways as short as 8,000 feet can be used in an emergency (which hasn't happened yet). Information on flight characteristics and control systems gleaned from the X-15 and Lifting Body programs proved invaluable in the design of the Shuttle Orbiter, as did experience gained from high-speed aircraft such as the SR-71 and North American XB-70 Valkyrie.
BASIC LAYOUT
The Orbiter's main living area is composed of three decks. Up top was the cockpit or "flight deck," where the pilots' seats, controls, and payload bay contols are located. The mid-deck is the main living area and work area, which also contains the toilet, galley, exercise equipment, sleeping arrangements, and main hatch. The lower deck is basically an equipment bay. During launch and re-entry, the Commander sits in the left pilot's seat and the Shuttle Pilot in the right, while one or two mission specialists would ride in jump seats behind them on the flight deck. The rest of the crew, if any, rides in stowable seats on the mid-deck. This area has no windows and gets pretty noisy and shaky during launch. If anyone is gonna get a little touch of motion sickness during launch, it will probably be somebody down there.
An airlock on the mid-deck leads to the payload bay, under two massive lengthwise doors which can be opened in orbit. Many kinds of payload pallets can be carried in here; it can carry satellite launchers, space station components, large items such as big satellites and space telescopes, and habitable modules such as the European Space Agency's Spacelab module. The payload bay is also equipped with a Remote Manipulator System (RMS) "robot arm," often referred to as the "Canadarm" because it was made in Canada. The RMS, controlled from the payload bay workstation in the aft half of the flight deck, is used to grab things and move them around with precision. It can lift a large item out of the payload bay and release it, or grab a satellite or other such object and pull it inside.
The payload bay doors also contain special heat-radiating panels; for this reason, as soon as the Shuttle reaches orbit, the payload bay doors are opened, both to relieve heat and pressure built up in the payload bay during launch and ascent, and to get the radiators in the doors operating.
ENGINES
A Space Shuttle Main Engine (SSME) is tested at full throttle for 290.04 seconds at the National Space Technology Laboratories (currently called the
Stennis Space Center) in Mississippi. NASA Photo.
As far as lifting and maneuvering power, the Orbiter's 3 Main Engines combined to produce 375,000 pounds of thrust each at launch (1,125,00 lbs total), while the SRBs produce 3,300,000 pounds each (6.6 million pounds total), for a total of 7.3 million pounds of thrust at liftoff-almost as much as a Saturn V. The Main Engines can be throttled up to 109% of rated power if needed. Once in orbit, the Orbiter uses its two OMS engines for orbital insertion, orbital adjustment, and de-orbit maneuvers. The OMS engines are mounted in two pods, one on either side of the tail, and each produces 6,000 pounds of thrust, for a total of 12,000 pounds.
TILES: THE THERMAL PROTECTION SYSTEM
General diagram of the Space Shuttle Orbiter Thermal Protection System. NASA Illustration.
The program would require a lot of new technology and materials to be developed. For example, if the bird was to be really reusable, it couldn't have an ablative, burn-away heat shield for re-entry. Special heat-resistant or heat-absorbing materials had to be developed.
The highest temperatures would be encountered by the nose cap and wing leading edges during re-entry, so these surfaces were special grey-composite moldings known as Reinforced Carbon-Carbon (RCC), good for up to 3,000-deg. F.
Special ceramic tiles were used all over the orbiter's skin. The tiles were made of extremely pure sand (99.7% pure at least), crushed into silica fibres, mixed in ceramic binder, fired in a furnace, and made into blocks that are machined into the proper size and shape. These came in several varieties, differing in the amount of heat they could withstand; the outer coating of each tile is high-strength refractory glass, the color of which signalled its temperature range. Next-highest on the temperature scale, behind the nose cap and leading edges, would be the Orbiter's belly and the leading edge of the tail, along with some trim areas around the RCC on the wing leading-edges. These areas were adorned with heat-absorbing black tiles called High-temperature Reusable Surface Insulation (HRSI), which were 6x6-in tiles varying from 1/2-in. to 5 in. thick. HRSI was good for between 1,200-deg. F and 2,300-deg. F. The rest of the Shuttle's skin was covered with white tiles that radiated heat rather than absorbing it, in order to keep the cabin and payload bay cool. These came in two varieties: Low-temperature Reusable Surface Insulation (LRSI), good between 700-deg. F and 1,200-deg. F, and a Nomex-felt quilt known as Fabric Reusable Surface Insulation (FRSI), good for up to 700-deg. F. FRSI was also used to cover areas that were too small (gaps were no bigger than 1.6mm) or too curved for LRSI tiles, which also allows the tiles and airframe some room to expand and flex as temperatures vary. This Thermal Protection System keeps the Orbiter's structural temperature below 350-deg. F.
Of all the Orbiters built, Columbia had the most tiles. Challenger replaced a lot of the LRSI with thicker, higher-temperature FRSI, and the remaining Orbiters replaced all of the LRSI with this material.
Each tile is bonded to the structure with room-temperature vulcanizing silicon adhesive. As no two of the thousands of tiles are exactly alike, each is labeled with a serial number. After each mission, each tile is painstakingly examined, and if need be, repaired or replaced.
BIG PLANS
NASA had intended to fly the Shuttle by the end of the 1970s-indeed, before the end of 1978 if all went well. They had big plans for it, most of them having to do with either commercial and military satellite deployment-and manned space stations. As NASA envisioned it, the Shuttle would spend much of its operational life flying back and forth to a permanent manned space station, as its name implies. Initially, it was planned to use the Shuttle to support Skylab. There were some problems with that scheme, though; Skylab was designed and built as part of the Apollo Applications program, back when the Shuttle was just a concept. The S-IVB-derived station was designed to be compatible with Apollo CSMs and other hardware of that era, and the Shuttle was set up differently. Still, NASA was working on ways of adapting the Orbiter for Skylab operations via payload-bay modules, and they were also planning to use the Shuttle to deliver a booster engine to the station, to move it to a higher and more stable orbit. One of the very first missions, the proposed STS-2A with Fred Haise and Jack Lousma, was supposed to do this.
What they hadn't counted on was that one of the biggest opponents of the manned space program, Walter Mondale, would be elected Vice President in 1976, and be placed in charge of said manned space program. Mondale, with typical politician's vision, had stridently tried to kill the space program after Apollo 1 and Apollo 13. Shuttle funding was delayed and cut and scrutinized. As a result, there wasn't enough R&D money, and there were delays, which gave Mondale more ammunition to cancel it. But Congress wouldn't cancel the program. So the Shuttle was just delayed-with the inevitable cost overruns-and Skylab was left to rot, finally burning up over Australia in 1979. Mondale wasted many times as much money as he had hoped to save.
Four Shuttle Orbiter Vehicles (OVs) were to be built: OV-99, to be called Challenger, OV-102 Columbia, OV-103 Discovery, and OV-104 Atlantis. The first vehicle built, Challenger, was originally just a structural test article, but it was decided to go ahead and outfit the vehicle for spaceflight and place it into service. In addition to these vehicles, one flying test vehicle would be built to evaluate the Orbiter's flying characteristics; this was to be called Constitution in commemoration of the upcoming Bicentennial in 1976, but a write-in campaign by fans of the TV show Star Trek persuaded NASA to rename it Enterprise, after the starship in that series. Additionally, a facilities validation article called Pathfinder was built to check out the ground hardware.
On September 17, 1976, cast members of the TV series Star Trek attend the rollout of the first Shuttle test vehicle, Enterprise, at the Palmdale, CA plant. From left: NASA Administrator Dr. James D. Fletcher, DeForest Kelley (Dr. Leonard "Bones" McCoy), George Takei (Mr. Sulu), James Doohan (Cdr. Montgomery Scott), Nichelle Nichols (Lt. Uhura), Leonard Nimoy (Mr. Spock), Star Trek creator Gene Rodenberry, unidentified, and Walter Koenig (Ens. Pavel Checkov). The Big Question: Where is William Shatner?!?!? NASA Photo.
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