Author: Frank Adam
Date: December 2005
"We must sail sometimes with the wind and sometimes against it', said Oliver Wendell Holmes, 'but we must sail, and not drift, nor lie at anchor'. So with man's epic voyage into space - a voyage the United States of America has led and still shall lead."
On January 5, 1972, it was with these words that President Richard Nixon ushered in a new era in manned spaceflight. The president charged NASA with the task of designing and developing a novel spaceflight vehicle, one that would more than simply follow in the footsteps of the famous Apollo missions of the preceding decade, but would blaze a trail into the future. Ingenuity and creativity melded with a desire to bring spaceflight to the masses, a union which borne the Space Transportation System (STS), better known as the Space Shuttle. The novelty and power of the system is its reusability, as is evidenced by the latest July 26 flight of Discovery, a craft built in 1983 and used for over 30 previous missions. Unfortunately, the STS program has not been without tragedy and loss, manifested in the Challenger and Columbia explosions. However, the Space Shuttle, as a step out of Apollo and into the future, has played an invaluable role in the history of space travel. Though now the time has come for an heir to succeed the Shuttle and again launch America forward into the future and forefront of space exploration.
From Humble Beginnings
Figure 1. Original Design Sketch for Space Shuttle.
In the wake of the grand successes of the Apollo program, the realm of space science and spaceflight opened wide and secrecy among nations became a relic of the bygone Cold War era. Thomas Paine, then acting administrator at NASA, held an interest in advancing the technology used to launch astronauts into orbit. His desire for change found an outlet in President Nixon who appointed a Space Task Group to research and develop comprehensive ideas for the next 10 years of space exploration. Paine and his group put forth a number of potential initiatives in their September 1969 report to the President; however, the Space Shuttle was the standout concept. With an administrative change that placed James Fletcher in the driver's seat of NASA, the Shuttle concept was reviewed and reworked to reduce the budget necessary for its development and eventually won approval from Nixon in 1972.
Figure 2. Orbiter Enterprise is ferried from test site to test site using a modified Boeing 747. Image courtesy NASA.
Though the future for manned spaceflight looked bright for NASA, the road ahead was not without potholes and speedbumps. In fact, before construction began, major overhaul of the Shuttle was needed: the initial design for the Space Shuttle called for an aircraft style take-off from a conventional runway, acceleration and climb to orbiting speed and altitude, and a typical horizontal aircraft landing. Unfortunately, the budget for space research was slimming down in the early 1970s and multiple revisions of the Shuttle left only the horizontal landing as a hallmark of its original conceptual design. The lowered price tag, from $10 to $5.5 billion, altered the fundamental functioning of the shuttle; its "take-off" morphed into the more conventional vertical rocket "launch" used for previous spacecraft. The need for reusability of the Shuttle's engines provided a technical challenge which required tinkering before an optimal system was produced. Further tribulations came in the form of heat shielding; materials were needed able to withstand the extreme temperatures due to air friction at speeds reaching Mach 24 during reentry. Though previous spacecraft such as those of the Apollo project had overcome this challenge, their heat shields, known as ablative tiles, were designed to be destroyed during reentry as a means to dissipate heat. Again, the issue of reusability challenged NASA scientists to expand the boundaries of engineering and material sciences and develop a wholly novel insulation material. However, this arena of shuttle engineering would return to haunt the STS program.
However, despite the trials of design and production, on September 27, 1976 Orbiter Enterprise was rolled out of the assembly plant to begin testing. Months of rigorous data collection began on Enterprise: did the finished model fly as designed; could the orbiter actually perform a gliding landing; were the mathematical stress models used for design consistent with real-world stresses due to liftoff? These questions and others were tested and retested over a nine month period during which the shuttle was ferried from one test center to another on the back of a modified 747.
Interestingly, Enterprise never reached space; rather this first orbiter served only as a test vehicle and made a final ferried voyage to Dulles International Airport on November 18, 1985 where it became the property of the Smithsonian Institute. However, Enterprise made an invaluable contribution to the shuttle program by showing that the design plans were functional and that future orbiter modules would perform as expected.
Components and Features of the Space Shuttle
Figure 3. Launch of STS-1, Shuttle Columbia on April 12, 1981. Image courtesy NASA.
Following hot on the heels of Enterprise was the first fully functional Orbiter Columbia which flew its maiden voyage on April 12, 1981. Three other shuttles were originally commissioned for construction by NASA and are all named for historical sailing ships: Challenger, Discovery, and Atlantis. The newest shuttle, Endeavor, which became operational in May of 1991, was named through a competition in elementary schools nationwide and was constructed from spare parts.
Despite differences in their construction dates, each shuttle system shares the same basic features and components. The most important of the three constituents of a functional STS vehicle is the Orbiter, the actual vessel in which the astronauts travel. The orbiter is a veritable limousine in size and stature compared to any previous manned spacecraft; for instance, the Apollo command module in which a three member crew would live and work had an approximate volume of 650 cubic (about the size of a college dorm room) while the crew compartment of the orbiter has a volume of over 2,300 cubic feet (closer to the size of a living room); though the orbiter typically houses seven crew members. The length (122 feet) and wingspan (78 feet) of the orbiter also dwarf the Apollo space module. In total, the orbiter is approximately the size of a DC-9 jet. In addition to the crew quarters, a pivotally important aspect of the orbiter is the large payload bay able to tote 65,000 pounds into space. Using the orbiter to launch satellites and other space-bound objects (such as sections of the International Space Station) has the advantage of providing a much smoother ride for the cargo than conventional rocket launch.
The shuttle system is not complete with just an orbiter. In fact, an orbiter alone could not make the trek into space. It was due to budget restrictions that the design of the shuttle necessitated vertical liftoff, much in the fashion of previous rocket launches. Thus, the most striking external features of a fully assembled shuttle system are the massive external fuel tank and two solid rocket boosters. The external fuel tank stores approximately 143,000 gallons of liquid oxygen and 383,000 gallons of liquid hydrogen fuel, close to the size of an Olympic swimming pool! The fuel is sent to the orbiter main engines during liftoff and ascent where it ignites to produce a whopping 375,000 pounds of sea-level thrust. Overall, the shuttle has about 15 million horsepower at liftoff, that's like 46,000 Hummers strapped together. Reusability is a constant thread running through the shuttle program and again appears in the context of the appendages to the shuttle: both rocket boosters are jettisoned from the shuttle and parachute into the ocean where they are recovered and refurbished for use at a later date. The external fuel tank, however, is destroyed in the atmosphere after jettison and is therefore a single use component.
An Aging Hero
Figure 4. Cut-away diagram of the orbiter component of the STS. Image courtesy NASA.
Imagine driving a 24 year old car, say an '81 Plymouth Reliant, over a long haul, perhaps from New York to Los Angeles. Naturally, there might be a few worries: is the transmission still functioning, will the steering be responsive, will the brakes work? Now imagine the little car cruising at Mach 24; you might reconsider the scope of your worries. Unfortunately, this is the nature of the dilemma that stares NASA in the face: they are relying on spacecraft and flight technology that is approaching antique status. But if something isn't broken, don't fix it, right? Well, that may be true, but what qualifies as "not broken?" NASA has had a number of tragic and devastating accidents manifested in the Challenger explosion of 1986, which killed seven crew members, and the Columbia re-entry catastrophe of 2003, which killed another seven crew members. Both of these incidents raise questions about the safety of the shuttle in general, but the later of the two also opens a debate about the structural integrity of all of the aging orbiters.
Over the course of the shuttle program, manned spaceflight became a commonplace occurrence; major news networks gave the launch of a shuttle minimal coverage. In one sense this speaks very highly for the success of the program inasmuch as Americans felt comfortable and confident with spaceflight, an initial goal during shuttle development. However, the risks always inherent with such an endeavor were forgotten, or rather never truly realized as an entire generation had grown up without experiencing the Challenger disaster and thus not knowing that danger did lurk hidden in the background.
This situation changed dramatically with the flight of the former shuttle Columbia on mission STS-107. Following a seemingly normal launch and mission for scientific research, Columbia pilot William McCool performed the usual maneuvers to remove the shuttle from orbit and begin the sequence of events necessary for re-entry and landing. Re-entry appeared to proceed normally except for a heat sensor alarm from one wing. This alarm turned out to be of critical importance, and with only 15 minutes of flight time left, the Columbia orbiter was ripped into millions of pieces, killing all seven crew members. The cause? The strike of the carbon-carbon heat shields of the wing by a piece of insulating foam that had broken loose from the orbiter during its launch. The hole created by the strike allowed superheated plasma to enter into the shuttle and literally melt away vital components. Could the tragedy have been averted? Perhaps: information was present from video surveillance on the ground that a strike had occurred, though the decision was made not to further explore the situation. Beyond this NASA folly, one must wonder why the strike occurred at all. Could it be that the orbiters are simply reaching an age when they should be put out to pasture?
In fact, as early as 1986 NASA had foreseen the eventual retirement of the shuttle and stated so directly in a commission report: "The shuttle fleet will become obsolescent by the turn of the century" (Launius 288). Again, in 1992, internal governmental warnings were sounded, this time by the President's Space Policy Advisory Board: "the system is fragile, not as reliable or safe as it should be, more expensive than it need be, and inefficient in its operations. [However, the] report concluded: It is the unanimous view of the Task Group that now is the time to initiate an aggressive effort toward the development of a new generation space launch vehicle" (Launius 293).
An Exciting Future
Figure 5. Diagrams and Statistics of the fully assembled Space Shuttle. Image courtesy NASA.
"Engage hyperdrive!" Exclamations such as these have filled the pages of science fiction for years; from Star Trek to Star Wars our imaginations have been titillated by the seemingly endless possibilities of space travel. There has never been a shortage of fantastic, though perhaps implausible, methods of spaceflight within this genre. What's more interesting, however, is the vast array of current prospects for the future of manned spaceflight that are kicking around in the science literature. To this end, actual science is as exciting, or more so, than the fantasies of sci-fi authors.
The fastest and tallest elevator in the world currently resides in the Taipei Financial Center 101 in Taipei, Taiwan. It reaches speeds of 60 kilometers per hour as it races passengers up the 508 meters of the building. Now imagine putting the Taipei elevator on steroids, increasing its size and speed by several orders of magnitude, and attaching it to a station in space. This seemingly far-fetched idea of a "space elevator" is just one of the possibilities that has some NASA scientists abuzz. First conceived of over 100 years ago by Russian scientist Knostantin Tsiolkovsky, the elevator concept gained considerable attention in the late 1970s after sci-fi author Arthur C. Clarke wrote his novel "Fountains of Paradise" which told of a quest to construct just such an elevator.
How the researchers envision this marvel working is as fascinating as the concept itself. The idea is to construct an enormous tower fifty kilometers tall to serve as the terrestrial station. Atop the tower would be a cable constructed of carbon nanotubes which would run thousands of kilometers into space and attach to a counter-balance, perhaps a space station or even an asteroid, that functions as a stabilizing point. Once the structure is assembled a means of shuttling passengers back and form is needed; here's where things get truly interesting. Scientists imagine using magnetically powered (Maglev) trains to zip people at thousands of kilometers an hour along the elevator into space.
Figure 6. Flight patch from STS-107. Image courtesty NASA.
Clarke believed in the design concept and felt that the future would make the space elevator a reality. Asked when he sees his concept coming to light he replied, "Probably about 50 years after everyone quits laughing." But Clarke is not alone in the quest for the space elevator; coalitions of scientists and science enthusiasts the world over are working out plans. Much of the impetus for research has been provided by NASA which awards large grants to promising designs through its Centennial Challenge Program.
NASA is not alone, though, in seeing a bright future for the space elevator; giant Otis Elevators Company is making impressive strides forward in elevator technologies. John Thackrah, vice president of engineering for the company thinks workable models might make the leap out of imagination soon: "Today we have the technology to create elevator systems for a five-mile-high tower," Thackrah said. "At the rate of our development efforts we could apply technology we are working on for today's existing market to the NASA concept within the next 10 years."
Perhaps the space elevator will be the next evolutionary step in manned space "flight." As the shuttles age, the STS program is what many consider to be the end of the line for safe flights. However, NASA should not simply drop out of the manned spaceflight arena; nor do they seem to be considering this path. Rather, through innovation and healthy competition NASA is fostering research into other avenues of space travel that could continue along the initial concepts of economy and reusability that the shuttle strived for. In any case, the future for spaceflight is an open field and many exciting and imaginative concepts will likely be seen in years to come.
References/Links
Launius, Roger D. After Columbia: The Space Shuttle Program and the Crisis in Space Access. Astropolitics, 2: 277322, 2004.
http://science.howstuffworks.com/space-shuttle3.htm http://history.nasa.gov/index.html