NASA and US industry are developing reusable launch vehicle technologies with an eye toward cutting costs and reestablishing US dominance in the field. The Air Force, however, has begun to envision RLV applications that go beyond pure space launch.
In May 1996, officials at Air Force Space Command and Air Force Materiel Command created a military spaceplane integrated concept team to capitalize on the NASA-led effort to produce an RLV demonstrator, the X-33. "The [AFSPC and AFMC] commanders asked us to look at what mission areas might be satisfied by this technology, at the timing, and then to establish a roadmap," said Brig. Gen. Herbert M. Ward, AFSPC director of Requirements, in a January interview. The team is not locked into one mission area--such as space operations, which covers satellite launch. Instead they envision applications across all space missions. Hence the use of the broader term "spaceplane."
The USAF team, which includes NASA and Air Combat Command personnel, developed a concept of operations last summer. It envisions aircraft-like operations with rapid turnaround time; operations to, through, and from space; multimission capability; and worldwide operations from continental US basing.
Over the past several months, AFSPC officials pulled together basic data about the history, critical technologies, and possible missions in a briefing called "Military Spaceplanes: The Future."
One key question for the team concerns whether a spaceplane could help US space forces conduct their tasks more efficiently and cheaper than they do today. The civil-commercial RLV effort is geared toward providing lower-cost, reliable, and fast-turnaround space transportation. That satisfies only one aspect of the US military space missions: launch.
The ability to perform space control--that is, ensuring safe passage of US satellites on orbit and denying an enemy the ability to use its satellites against the US or its allies--does not exist today. Nor does the US possess any capability to apply force from space, other than with an ICBM, whose trajectory would take it through space before it plunged back to strike a target on Earth.
For that reason, the Air Force's team members are also looking at the potential of military spaceplanes to provide space control and force application from space, as well as to provide force enhancement, such as space surveillance, reconnaissance, warning, and communications.
A military spaceplane might take military payloads into orbit, deorbit payloads, or perform on-orbit maintenance. It might release a satellite in space, then come back into suborbit and fly around the globe once or twice to conduct communications support or bomb-damage assessment. It could take advantage of the high ground of space and, with operations closely resembling a conventional airplane's, fly over any region of the globe with impunity.
General Ward emphasized that he is not predisposed to a particular RLV concept. He said that no decisions had been made concerning whether the spaceplane should be manned or unmanned, employ vertical or horizontal takeoff, or be single-stage or multistage to orbit.
Early successes in NASA's current RLV effort, which since its inception has included participation by engineers from USAF's Phillips Lab at Kirtland AFB, N. M., spurred officials to formalize the operational concept team to ensure that they would be in a position to use those technologies when they matured. When that might be is another question that concerns the team members.
The concept team will try to answer these questions when it reports this spring. It will also try to determine what kind of investments to make in research and development or prototyping to develop that capability for the Defense Department. "One of our responsibilities is to go back to our commanders with the roadmap that says if this technology is mature then we can do the next step and these are the kinds of funds required," stated General Ward.
Not Really Déjà Vu
The spaceplane concept is not really new. In fact, the general idea has been around for more than 50 years. In 1944, two German scientists, Eugen Sanger and Irene Bredt, set down their prewar and postwar work into a concept for a hypersonic rocket-powered aircraft that could be boosted into orbit, then glide back to Earth--creating the term "boost glider." NASA officials credit the Sanger-Bredt work with directly influencing the shape of the first US spaceplane, the X-15, conceived in 1954. From it, USAF's Dyna-Soar X-20A, and the follow-on lifting bodies, the US developed technologies that led to the space shuttle.
However, today, the Air Force, NASA, and industry maintain that the technology for turning the original concept into reality now exists or is very close at hand.
Both the Air Force and the Navy collaborated with NASA on the X-15 program, which produced three vehicles for hypersonic aerodynamic research. In all, 199 flights took place from 1959 through 1968 in which the X-15s reached Mach 6.7 and an altitude of 354,200 feet.
The lifting bodies, such as the lightweight M2-F1 and heavyweight M2-F2, HL-10, and X-24A and B, were wingless vehicles designed to fly back to Earth from space and land like airplanes. Versions of these lifting bodies, both powered and unpowered, flew successfully from 1963 to 1975.
Probably the most recent US research effort was the high-profile USAF-NASA National Aerospace Plane (NASP), or X-30. Established at Wright-Patterson AFB, Ohio, in 1986, the NASP program heralded some of the same concepts now set forth by the spaceplane concept team. However, budget cuts forced the program's demise in 1994.
AFSPC officials point out that timing and technology separate NASP from the current spaceplane concept. The technology is more mature now than it was 10 years ago. They said the key also is to ensure that the system is affordable, as well as useful.
The US is not the only country interested in spaceplanes. Britain has developed several spaceplane concepts, some of which date to the 1950s. Japan began research into spaceplane technology in 1987. The European Space Agency had similar thoughts in mind when it designed its Hermes manned spaceplane.
NASA officials are so confident of RLV technology that they have already begun to discuss follow-ons to the X-33.
NASA began a three-pronged RLV program in 1994. The research effort includes technology demonstrations with the DC-XA, X-34, and X-33--each designed to demonstrate various technologies that could lead to a commercial RLV.
NASA and McDonnell Douglas upgraded the DC-X, a subsonic rocket flown eight times by Phillips Lab from 1993 to 1995. The DC-XA, Clipper Graham, made four successful flights demonstrating its vertical landing capability. However, testing ended July 31, 1996, when the vehicle toppled and exploded after its fourth flight.
The rocket tipped over, according to an incident investigation released January 7, because "a brake line on the helium pneumatic system for landing gear number two was not connected." NASA officials believe the four DC-XA test flights will aid RLV research but do not plan to build a follow-on DC-XB.
The second element of the RLV program features the X-34, a single-engine rocket with short wings and a small tail surface capable of flying at Mach 8 and an altitude of 250,000 feet. Orbital Sciences Corp. is developing the X-34, which will be carried aloft aboard OSC's L-1011 aircraft. It is scheduled to fly in 1998.
The final element is the larger, more powerful X-33 test vehicle, which will reach Mach 15 and altitudes of up to 50 miles. It will be half the size of but demonstrate all the technologies needed for a full-scale RLV. NASA selected Lockheed Martin to build the X-33, based on its lifting-body concept called VentureStar. It has a new aerospike engine and will launch vertically but land like an airplane. The first test flight for the X-33 single-stage-to-orbit vehicle is set for March 1999.
NASA officials stated last year that they are already working on technology beyond the X-33. They are looking at air-boosted rocket engines, currently under study, as well as the possibility for small two-stage vehicles. Unofficially dubbed "X-37," the effort would probably include two to four variants rather than one, as with X-34 and X-33. The only criteria, they said, is that they be reusable.
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