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Earth to Orbit. Launching a payload to Earth orbit requires its acceleration to 26 times the speed of sound (Mach 26). Hence, a lot of propellant -- about 10 tons per passenger -- is consumed. Worse, even the Space Shuttle jettisons much of its hardware which greatly boosts the already high cost. More cost-effective launching options have been proposed, but few are being developed, and those slowly without the generous funding of yesteryear. (A summary on past and proposed Earth-to-orbit space vehicles is available from spacefuture.com.)
Soyuz. First launched in 1963, the Soyuz is a two-stage rocket that can deliver a payload of over 15,000 pounds (5,600 kg) into Low-Earth Orbit (LEO) at a 51.6 degree inclination. It is the primary launcher used for manned Russian space flights but also launches nearly half of all Russian space missions (manned and unmanned) as it is also used to deploy low-altitude reconnaissance satellites. On October 31, 2000, a Soyuz rocket was launched from the Baikonur Cosmodrome in Kazakstan with the first three-man crew of the International Space Station (see photo).
Proton. This medium-lift rocket was first introduced in 1965 as the first Russian launcher not based on a ballistic missile prototype. It has been used in both three- and four-stage versions, where the three-stage rocket was used for many support missions of the Mir Space Station while the four-stage version primarily launches geostationary satellites. The first stage of the Proton incorporates 6 strap-on boosters that provide over two million pounds (746,000 kg) of thrust. As 3-stage Proton rockets can lift over 44,000 pounds (16,400 kg) into LEO, it is being used for the largest components of the International Space Station that are launched by the Russian Space Agency.
Partially Reusable Launch Vehicle (RLV)
The Space Shuttle launches with rockets but soon jettisons them, eventually gliding back to land without propulsive power. Although each of the three Shuttle Orbiters remaining in operation -- Discovery, Atlantis, and Endeavour -- is designed to fly at least 100 missions, they have flown only a combined total of 100 by October 2000. Excluding the prototype Enterprise used for testing, the first operational Orbiter was Columbia, which was delivered to NASA's Kennedy Space Center (Florida) in March 1979 but was destroyed on re-entry on February 1, 2003. The fifth operational Orbiter Challenger was destroyed in an explosion soon after launch in January 1986. As a result, Endeavour was built as a replacement for Challenger and delivered in May 1991. No decision to replace the Columbia had been made as of February 27, 2003.
The Shuttle consists of three major components: the Orbiter which houses the crew and cargo; a large external tank that supplies liquid fuel holds fuel for the Orbiter's main engines; and two solid rocket boosters that provide most of the Shuttle's lift during the first two minutes of a Shuttle's launch. The Orbiter is intended to returns intact, and the two solid rocket boosters are recovered from the sea for re-use after jettisoning from a height of about 28 miles (45 km). However, the external fuel tank is left to burn up in the atmosphere after each launch, after being jettisoned at near orbital velocity from about 70 miles (133 km) up.
Each Shuttle can lift 63,500 pounds (28,803 kg) of cargo and passengers into orbit. The orbiters can achieve a maximum speed of over 17,300 mph (almost 27,880 kph). Their orbits range from 115 to 400 statute miles (185 to 643 km) from the Earth's surface. See NASA's "Shuttle basics" page for more statistics.
The goal of the cancelled RLV program was to design each succeeding generation of RLVs to be 10 times less expensive and 10 times safer than the previous generation. Three generations of RLVs will be developed to succeed the Space Shuttle over a 40-year period. See Nasa's chart comparing the desired characteristics of each generation.
The wedge shaped X-33 was being developed cooperatively by NASA and Lockheed Martin Skunk Works. It was to be a half-scale prototype of a Single-Stage-to-Orbit (SSTO) Reusable Launch Vehicle (RLV) with two linear aerospike engines that would fly at 15 times the speed of sound and replace the Space Shuttle. On 3/1/2001, however, market competition for intended commercial applications from lower cost Russian, Chinese, and European rockets, as well as a fuel tank design setback and cost-overruns, led NASA to cancel the project despite good engine tests and near completion (90 percent) of the hull. Efforts by the U.S. Air Force is to takeover X-33 funding for meeting its near-term space deployment needs were blocked repeatedly.
Third-Generation RLV : maglev-assisted launch vehicles.
The weight of rocket fuel is a big problem in launching spacecraft. While it takes a lot of fuel to lift a vessel off the ground, the fuel loaded on also has to be lifted. Hence, if electrical power through a maglev-assisted launch can substitute for some of the fuel needed, the spacecraft would be a lot lighter and cheaper to launch since the electrical power used would cost much less than the rocket propellant used today.
NASA / Aerospace
Another image with more details.
Maglev-assisted launch of a
3rd-generation RLV would use
magnetic fields on a long track to
lift up and accelerate a spacecraft to
600 mph (965 kph) until it takes off
like an airplane and switches on
rocket engines to fly into space.
Currently, NASA has a test track at its Marshall Space Flight Center that is 50 feet (15 meters) long, about 2 feet (0.6 meters) wide and about 1.5 feet (0.5 meter) high, that sits on concrete pedestals. Each 5-foot-long (1.5 meter) section of the track weighs about 500 pounds (230 kg) because of the weight of the iron used in its motor, and the track is also covered with non-magnetic stainless steel. A larger 400-foot (122 meter) track is planned to demonstrate show that the maglev system is controllable at higher speeds and to assess if energy can be saved by only powering small sections of the track at a time.
Fourth-Generation RLV : beam-assisted launch vehicles.
Prototype Lightcraft. A laser-launched "lightcraft" could rise on pulses of expanding, superheated air detonated into plasma as it is blasted by a high-energy laser beam focused on its parabolic-mirror-designed bottom. The air below the vessel is heated to temperatures of 10,000 to 30,000 degrees °K (about 18,000 to 54,000 °F) and explodes, providing thrust but leaving no chemical exhaust. Slots in the lightcraft's skirt push new colder, denser air into the engine as the vessel rises, to be detonated by another beamed pulse that pushes it higher. To maintain stability, the lightcraft is sent spinning on a spindle with a jet of nitrogen gas at about 6,000 revolutions per minute before launch.
In 1997, a six-inch (15-cm) diameter model was successfully tested in brief flights at the U.S. Army's High Energy Laser Systems Test Facility (HELSTF) near Los Cruces, New Mexico (toward the southern end of the White Sands Missile Range (Leonard David, New Scientist, 1/10/98.) The power source was the U.S. Army's Pulsed Laser Vulnerability Test System (PLVTS), a 10-kilowatt carbon dioxide laser that is used to test the vulnerability of military systems to laser attacks. To get the lightcraft flying, PLVTS produced 20 infrared pulses a second (Andy Walton, CNN Interactive). Each test only runs for about 100 laser pulses (or 5 seconds) because a metal band around the combustion chamber overheats and breaks. Hence, a cooling system is planned in continuing tests.
Sponsored by the U.S. Air Force Research Laboratory and NASA's Marshall Space Flight Center, future tests will involve lightcraft built with exotic materials such as composites or high-temperature-resistant ceramics. The plan is to launch a 2.2 pound (1 kg) satellite into orbit within five years. Over the next three years, the U.S. Air Force and NASA plan to use equipment already in the HELSTF inventory to assemble a 100-kilowatt laser, 10 times more powerful than the PLVTS -- which is already the most powerful laser of its kind in the United States.
An orbital launch will require a megawatt laser, 10 times more powerful than even the new Air Force-NASA laser that is planned, as such a lightcraft will have to travel five to six times the speed of sound. An orbital lightcraft will also have to carry fuel on board, most likely in the form of liquid hydrogen, for use when the vessel rises too high to use air as fuel. Of course, adding fuel will increase the vehicle's weight which then necessitates the use of a more powerful laser.
Advanced Lightcraft. Resembling a flying saucer, a 4th-generation RLV also could rely on beamed microwaves for propulsion. An advanced lightcraft under design at Renssalaer Polytechnic Institute would convert microwaves into electricity to power magnetohydrodynamic engines that would heat air (breaking air molecules into a plasma) and a magnetohydrodynamic fanjet would provides the lifting force. Only a small amount of propellant would be required for circularization, attitude control and deorbit. One prototype being considered may be made with a large helium-filled balloon that focuses microwaves beamed from the ground or space, which would power ion engines ringing the balloon to electrify air that pushes the vessel upwards.
A space elevator would reduce Earth-to-orbit transport costs from about US$ 10,000 per pound (US$ 22,000 kg) today to a few dollars (per lb or kg). Konstantin Tsiolkovsky first suggested the construction of a "celestial castle" in geosynchonous orbit that would be attached to a tower like the Eiffel Tower in 1895. Although technical discussions of the space elevator concept continued through 1975, it did not engender wide public awareness until renowned science-fiction writer, Arthur C. Clarke, used the concept in his 1978 novel, Fountains of Paradise. In 1999, a NASA conference determined that such a structure might become feasible by the end of the 21st Century (press release of September 7, 2000). David Smitherman of the Advanced Projects Office at NASA’s Marshall Space Flight Center has compiled a report titled, "Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium," based on the findings of the 1999 conference.
A space elevator is essentially a long cable extending from Earth's surface to space with its center of mass at geostationary Earth Orbit, 22,366 miles (35,786 km) above. As a result, the entire structure orbits the Earth in synchrony with the Earth’s rotation and so maintains a stationary position over its base attachment at an equatorial site, where such a tall structure is also less likely to experience tyhe high winds of tornadoes and hurricanes. Special vehicles and pipes and wires traveling along the cable would transport people, freight, gases, and power between Earth and space. Current proposals require a base tower about 30 miles (50 km) tall for tethering the cable tethered to the top. To keep the cable from falling back to Earth, it would be attached to a large counterbalancing mass beyond geostationary orbit, such as a re-positioned asteroid. Four to six elevator tracks, extending up the sides of the tower and cable structure to platforms at different levels, would allow electromagnetic vehicles to travel at high speed -- reaching thousands of miles (or km) per hour. Carbon nanotubes up to 100 times stronger than steel may be used for the space-segment of the space elevator structure. (For more information, go to NASA's Space Elevator Concept site.)
Propelled by magnets without moving parts,
electromagnetic vehicles would float above
space elevator tracks, so that high speeds
would be attained without the wear and tear
experienced with wheeled vehicles.
Orbital Transfer through Tethers : Tether systems for spacecraft, orbital stations, and planetary bases.
The new International Space Station and other future orbital stations and spacecraft may one day maintain their orbits without using rockets if they attach a propulsive tether system for propellant-free propulsion. NASA is developing the Propulsive Small Expendable Deployer System (ProSEDS) under the Future-X space technology development program to demonstrate feasibility of the propulsive tether concept. In essence, ProSeds will deploy a tether that applies the same principle powering electric motors -- sending a current through a wire loop to create an electrical circuit within a magnetic field. In space, one part of the circuit would be a long tether attached to an orbiting spacecraft, where the return path of the circuit is supplied by the electrically charged gas in the ionosphere and where the magnetic field is supplied by Earth itself. When properly controlled, the tether generates forces that can be applied as a brake or as a booster for an orbiting spacecraft or station.
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