A collection of research projects of the National Aeronautics and Space Administration (NASA) designed to improve space transportation beyond technologies existing at the beginning of the twenty-first century.
During the early days of space exploration, many of the top rocket designers in NASA thought that the best way to fly into space was with a self-contained spacecraft, reusable in much the same way that an aircraft is reusable after each flight. However, the technology to develop such a reusable spacecraft did not exist in the 1960’s. In order to compete with the Soviet Union to develop a crewed space program, NASA decided to adapt existing missile technology as boosters for crewed spacecraft. Thus, the early Mercury and Gemini Programs used Redstone, Atlas, and Titan missiles as boosters. The difficulty with these boosters was that they had a tendency to fail in flight. Special care, therefore, was given to the individual boosters used in the crewed space program. The Saturn rockets, developed for the Apollo Program, were designed from the beginning as boosters for crewed spaceflight. The Saturn rockets, however, were essentially very large versions of the type of rocket used on earlier flights. Though not a single Saturn rocket ever failed catastrophically in flight, it was not considered to be much safer than earlier rockets. The designs of the Saturn rockets were an upgrade of existing technologies. Upgrading existing technologies was a way of achieving a lunar vehicle in the shortest time possible, with a goal of beating the Soviet Union to the Moon. Though mishaps occurred during the Apollo missions, none resulted in loss of life while in flight due to rocket failure.
In addition to the safety issues surrounding early rocket designs, another difficulty was that the spacecraft and rockets could be used only one time. A great deal of effort and expense went into the construction of the rockets, but they were used for only a few seconds to launch the spacecraft from the Earth. The spacecraft itself was a small capsule that was designed to be used for only one flight. With each space mission requiring its own rocket booster and spacecraft, space travel proved to be extremely expensive. As early as the 1970’s, before the Apollo missions had even finished, NASA was investigating the possibility of a new spacecraft that would be safer and cheaper to operate. Such a spacecraft would be reusable numerous times. Due to budget considerations, the resulting spacecraft, the space shuttle, was a compromise solution. Only part of the spacecraft was reusable. Furthermore, the space shuttle was launched into space using modifications to existing technologies used to launch some uncrewed spacecraft. The space shuttle ultimately proved to be not nearly as reliable and safe as had been hoped. Following the solid rocket failure and the resulting explosion that destroyed the space shuttle Challenger on January 28, 1986, NASA implemented new stringent safety measures that added to the cost of space shuttle missions. Even with these new safety measures, it was recognized that there remained a significant chance for additional catastrophic launch vehicle failures that could result in loss of the spacecraft and crew.
One of the goals of the space shuttle program had been to provide an inexpensive and safe transportation system into low-Earth orbit (LEO) in order to promote and assist future space activities, such as launching and repairing satellites or constructing and servicing LEO space stations. The space shuttle has achieved a tremendous success record, and has made important strides toward opening LEO to greater development. However, by the late 1980’s, NASA had come to realize that the space shuttle was far too expensive and unreliable for the needs of the foreseeable future. Ideas began to emerge for a replacement to the space shuttle as the primary workhorse of the crewed space program.
The early work on a replacement for the space shuttle tended to be unfocused and was conducted by different departments and divisions within NASA. The National Space Transportation Policy of 1994 finally formalized the goal to develop new space transportation systems. This policy statement divided the responsibility of developing new space transportation systems into two categories: new reliable, expendable launch vehicles and new reusable launch vehicles. Research toward developing new expendable launch vehicles was to be done by the Department of Defense. Research on the development of a second-generation reusable launch vehicle was to be NASA’s responsibility. Soon afterward, NASA organized the Advanced Space Transportation Program (ASTP) to oversee the development of new reusable spacecraft. The ASTP is headquartered at the Marshall Space Flight Center in Huntsville, Alabama. Research related to the ASTP, however, is conducted at nearly all NASA centers and in many university and aerospace industry laboratories.
The primary goals of the ASTP are to reduce the costs of launching payloads into LEO from more than $10,000 per pound in the year 2000 to about $1,000 per pound by approximately the year 2010, and as little as about $100 per pound by 2025. The ultimate goal is to reduce payload launch costs to only about $10 per pound by 2040. Such inexpensive launch technology would permit a great expansion of space-related activities by both government agencies and private enterprises. In addition to reducing costs, the ASTP seeks to increase safety. Upgrades and improvements to the space shuttle are expected to increase safety margins by a factor of ten by the year 2010, when new space transportation systems may become available. Within twenty-five years, NASA hopes to make space travel one hundred times safer, and within forty years, to make space travel nearly one thousand times safer. In order to achieve the increased cost-effectiveness and safety, NASA cannot simply rely on improvements to the space shuttle. New technologies and spacecraft must be developed. This was the responsibility of the ASTP.
The National Space Transportation Policy of 1996 reinforced the policy statements of 1994. The ASTP was enlarged and expanded and became the Integrated Space Transportation Plan (ISTP). The ISTP goals and timetables were the same as the ASTP’s for reducing costs and increasing safety for space travel. The first steps toward those goals were to upgrade and improve the space shuttle fleet, NASA’s first generation of reusable launch vehicles. The ISTP would also upgrade technologies to develop a new reusable vehicle to service the International Space Station (ISS). This new vehicle is to be a second-generation reusable launch vehicle operating similarly to the space shuttle, but much more efficient and advanced. The second-generation vehicle is expected to achieve the cost and safety goals for 2010. To achieve the remaining goals, however, requires the development of entirely new technologies and systems, not just revisions and upgrades of existing technologies and systems. Thus, the ASTP was incorporated within the ISTP to develop the third- and fourth-generation reusable launch vehicles needed for the future.
One of the ASTP’s areas of research is in new rocket systems designed to operate with more efficient engines or using new propellants. Another consideration is the possibility of using radically new types of propulsion, such as nuclear or solar power. Further considerations include using external propulsion, in which the rocket is pushed into space by some force outside it, such as magnetically levitated craft, beamed energy systems, or tethers. In addition to researching new propulsion systems, the ASTP also is investigating new spacecraft designs capable of higher-speed atmospheric flight, and self-diagnostic systems capable of detecting failures before they occur. Most ASTP projects are still in the planning stages, and a majority may well never be constructed as new ideas emerge. Because the technologies envisioned with the ASTP do not yet exist, it is difficult to say exactly what form they will take.
New rocket designs range from more efficient uses of existing technology to radical new technologies. An example of an engine based on existing technology is the Fastrac engine, designed with a small number of readily available existing parts. The engine is reliable and inexpensive to build; it may ultimately cost as little as 10 percent of the construction costs of current rocket engines. A new rocket engine technology is the pulse detonation rocket engine. This engine operates in pulses rather than continuously, as with most rocket engines. Propellant is injected into the reaction chamber and detonated with a spark plug, creating a short burst of thrust. Such an engine can be made to be very powerful and efficient.
In addition to new designs for rocket engines, ASTP researches new propellants. Currently, launch boosters require separate fuel and oxidizers. A monopropellant, a propellant that is self-oxidizing, would require less storage space in a rocket and fewer propellant tanks, thus saving rocket weight and permitting heavier payloads to be lifted for the same cost.
Another strategy being considered for more cost-effective rockets is an air-breathing rocket. Current rockets carry both fuel and oxidizer as propellant. If a rocket could take oxygen from the atmosphere as it flies, in much the same way that a jet engine does, then there would be no need to carry oxidizers and the savings in weight could be used to carry additional payload. Such an engine could conceivably permit a spacecraft to take off and land in a manner similar to that of a commercial jet aircraft, and may be completely reusable, reducing spacecraft cost.
In order to utilize some of the new propulsion technologies, new airframe designs are needed to permit hypersonic flight many times the speed of sound. Furthermore, lighter-weight yet strong airframes would permit heavier payloads to be carried, reducing the per-pound cost of launches. Spacecraft design goals include improvements to permit a single spacecraft to operate for up to one thousand missions, a tenfold increase beyond the operational lifetime of the space shuttle. Furthermore, spacecraft servicing is expected to be simplified, so that a spacecraft may be serviced, much like a transoceanic airliner, between missions by only a few dozen personnel in less than a day. These innovations could reduce the cost of putting a payload into LEO to only a few hundred dollars per pound within two decades. To facilitate quick and effective maintenance, an integrated vehicle health management system is envisioned. In such a system, all parts of the spacecraft would have sensors that would be linked to a central computer that would monitor vehicle health and performance. The goal of an integrated vehicle health management system would be to detect weaknesses and defective parts before they become problems. This would make maintenance both easier and much less expensive.
In order to achieve the goals of the ASTP, entirely new propulsion systems may be required. Areas of research include both active and passive propulsion. Passive propulsion systems include magnetically levitated vehicles that would accelerate up to 600 miles per hour prior to takeoff along a magnetic track in much the same way as a magnetically levitated train. This initial velocity would mean that less rocket propulsion would be needed to achieve orbit. Focused-beam energy systems, such as high-powered lasers or microwave transmitters, could also be used to push objects into space. In such a system, fuel would not be needed and the spacecraft could be designed to carry primarily a payload.
Many payloads need to be deployed beyond LEO. Once in space, miles-long tethers can be deployed to utilize the Earth’s magnetic field to change spacecraft orbits without the need of rockets. A tether system was tested with limited success from the space shuttle in 1996. Away from Earth, solar electric ion propulsion may be used for uncrewed interplanetary trips. Solar cells can create electricity from sunlight, and this electricity can be used to accelerate ions from the engine to propel a spacecraft. NASA tested such an ion-propelled spacecraft, called Deep Space 1, in 1998. Other proposals include the use of nuclear reactors to power spacecraft. The nuclear reactor could be used to power an ion engine. If a suitable fusion reactor could be developed, then it may even be possible for a spacecraft to scoop hydrogen atoms from space as it travels to use as nuclear fuel, thus minimizing the need to carry vast amounts of hydrogen with it.
It is hoped that the ASTP will yield new technologies such as these or even ones not yet considered. These new technologies will gradually displace the current generation of chemical-powered rockets used for space travel, thus yielding a safer and more cost-effective space transportation system.
McCurdy, Howard E. Space and the American Imagination. Washington, D.C.: Smithsonian Institution Press, 1997. A history of space exploration containing some speculation as to future space needs for LEO travel. Marshall Space Flight Center. Advanced Space Transportation Program: Paving the Highway to Space. Huntsville, Ala.: Author, 1999. A fact sheet summarizing the areas of research in the ASTP. National Aeronautics and Space Administration. Introduction to NASA’s Integrated Space Transportation Plan and Space Launch Initiative. Washington, D.C.: Government Printing Office, 2001. A thorough synopsis of the ISTP, including the ASTP. Office of Aero-Space Technology. Advanced Space Transportation Program R&T Base Program Plan. Washington, D.C.: Government Printing Office, 1999. Extensive description of the organization and areas of study of the ASTP.
National Aeronautics and Space Administration
Reusable Launch Vehicles (RLVs) are part of NASA’s Advanced Space Transportation Program, intended to lower the cost and efficiency of the United States’ space program.