by Jos Heyman, Columnist
The United States Air Force (USAF) had always considered space as a logical extension of the air space in which it has its operations and it sought to achieve this in several ways.
In the early days, this belief resulted in several projects that concerned the long range delivery of bombs, such as expressed through the Project Bomi (Bomber Missile) project that was commenced by the Bell Aircraft Co. for the USAF in 1951. This project was supervised by Dr. Walter Dornberger, one of the Peenemunde engineers. The design consisted of two rocket powered winged aircraft. The mothership constituted the first stage with a crew of two and would have had five rocket engines, which would fire for 130 seconds after lift-off. The first stage would then separate and return to base.
The second stage, or space plane, with a single crew member, was to have three rocket engines and would maintain a speed of 13,600 km/h. Initially, it was intended that, after dropping a bomb, the spaceplane would make a 180 degree turn and return to base. However, later it was considered more practical for the spaceplane to continue in orbit until closer to the landing site. Development did not proceed, but the ideas led to several programs that lead toward crewed spacecraft in the format of spaceplanes.
One of these ideas was a concept to transport troops and cargo quickly to the battlefield using basic Redstone missiles be fitted with a passenger/cargo pod. They would be sent on a ballistic trajectory before landing suspended from a parachute. Needless to say this idea never got much further than being an idea.
A more serious effort to develop a space plane was commenced on October 14 , 1957, a mere 10 days after the launch of Sputnik-1. On this day, the USAF issued preliminary directives for a manoeuvrable space plane. The project, with the military designation X-20, was an attempt to combine the best features of two approaches: high speed flight in space and the capability to return with airplane like control.
In March of 1958, eight aerospace companies submitted proposals. In June of that year, Boeing, as well as a Bell/Martin consortium, were awarded contracts for further studies into the project. By December 9 , 1959, it was obvious that the Bell/Martin proposals relied heavily on unproven technology and Boeing was awarded a development contract.
Known also as model 844 Dyna Soar, the proposed craft was a delta-winged glider. It was to be rocketed into space by a powerful booster and, once in orbit, the pilot would be able to fly to any point on the globe at speeds of more that 27,000 km/h. When the pilot completed his mission, he would fly his craft back into the atmosphere and land at an airfield of his choice.
The term Dyna Soar was derived from dynamic and soaring, meaning the vehicle was to use both centrifugal force and aerodynamic lift. Centrifugal force was to sustain the craft at orbital speeds when it would be flying just fast enough to off-set the pull of the Earths gravity. The aerodynamic lift would be afforded by the wings and would be used for flight in the atmosphere.
During re-entry, the craft would encounter severe surfaces heating. To resist the heat, ceramic materials were to be used in addition to high nickel alloy steel, molybdenum, and columbium. The heat resistant materials were to radiate the heat from the surfaces of the craft back into the atmosphere. Nevertheless, the surface of the Dyna Soar would be so scorched, it would have looked like an old fashioned wood stove. However, it would have been a simple task to prepare the craft for re-launch.
The design also incorporated many other unusual features, including a main landing gear which was to consist of landing skids with wire brushes mounted on the them and a nose gear designed to resemble a shallow kitchen pan. This unusual combination was dictated by the fact the high re-entry temperatures ruled out rubber tires and lubricated bearings, and subsequently, conventional brakes.
By 1961, the design was frozen and the Air Force formally ordered ten production vehicles. At that point of time, it was planned to fly seven scale models of the X-20 on top of Scout rockets into sub-orbital trajectories to test high speed flight as well as thermal protection. It was further envisioned that air drop tests would commence in 1963 using a B-52 mothership. These flights, which would be unmanned as well as manned, would take place over Edwards Air Force Base, in California.
In 1964 the first unmanned sub-orbital flight was to take place, with the first unmanned orbital flight to occur in late 1965. After two such flights, the first manned orbital flight was scheduled for early 1966, after which flights at three months intervals were planned. At that point in time, funds would be made available for a total of 12 flights. All orbital flights were to be launched by a modified Martin Titan launch vehicle.
But in mid-1961 the government, in the embodyment of the Secretary for Defense McNamara, began to question the project and delays crept into the program, leaving only the pure space flight aspect as viable. When it appeared that this was adequately being met by the other crewed space projects of the United States, eventually the entire Dyna Soar project was cancelled. By then, Boeing had built a full scale mock-up of the Dyna Soar and some material for production had been cut, although no construction had commenced. The Air Force had already selected a number of potential pilots for the projects initial phase and subsequent operational phase.
Like the later MOL program, the Dyna Soar project was not directly connected with the lunar effort which dominated the United States thinking in those days. It is further doubtful whether the project had any significant direct impact on the Space Shuttle project. Nevertheless, had the project been completed, it would have provided the United States with an alternative means to space and, as such, the cancellation of the Dyna Soar program must be considered an unfortunate occurrence.
When NASA developed the Mercury manned spaceflight project, the USAF showed great interest in potential applications of this spacecraft for military purposes. One of those possibilities studies involved the use of a Mercury capsule with a small, one crew space laboratory with a 280 cubic feet interior space. Access from the Mercury spacecraft to this miniature space station was to be through an inflatable tunnel.
In a similar way as the USAF was interested in Mercury development, they also displayed an interest in a crewed Earth orbital facility based on NASAs Gemini spacecraft. Blue Gemini was the name given to an Air Force proposal to continue Gemini flights after Gemini-12 for Air Force research purposes and the development of a satellite inspector. The program envisaged seven flights, which were to land with a paraglider wing and skids, rather than in the sea. But in 1963, Congress refused to fund Blue Gemini and the proposal lapsed.
The Manned Orbiting Laboratory (MOL) program was commenced in 1963 as an alternative to the Dyna Soar project. The objective of this program was to demonstrate the functioning of a crew performing military functions in space. This knowledge was deemed essential before any specifications of an operational nature could be drawn up and, as such, the program was more scientific and engineering in nature than directly of a military nature.
It was anticipated that during a series of 30 day duration flights, a range of scientific, technical, and biological experiments could be conducted while a number of EVAs would evaluate the ability of an astronaut to work outside the spacecraft.
Given the go-ahead on August 15, 1965, MOL was to comprise of the Gemini B, a Gemini spacecraft with the original Service Module removed and an access hatch cut through the heat shield, and a new, non-recoverable, Laboratory Module which could accommodate the two crew members during their mission. The latter would have an aft section with living quarters and a forward section for the mission experiments. The dimensions of the Laboratory Module, which was to be built by Douglas, have been quoted as 3.05m in diameter and 12.8m in length. The weight was 9100 kg.
The program envisioned seven flights, the first two of which would be automated, with the remaining flights being crewed and taking place at six months intervals. The MOL was to use the Titan IIIM version of the Titan IIIC launch vehicle, which was to be fitted with two larger solid fuelled strap-on boosters. All flights were to be launched from Vandenberg AFB in California, into a polar orbit, which would ensure that any sensitive instrumentation would not fall over foreign territory should a mission fail.
Commencing in November of 1965, 17 military astronauts were selected for the program. By 1964, 12 primary and 18 secondary experiments had been selected for the MOL project.
However, from the start. the MOL project was bedevilled by the twin problems of development delays and a perception that the project was a duplication of NASAs plans for the Apollo Applications Program and the Manned Orbital Research Laboratory (MORL). The latter was a study of the feasibility of adapting a Saturn 1B stage into an orbiting laboratory and eventually materialized as Skylab.
On November 3, 1966, the one and only MOL research flight was launched using the Gemini that had been recovered from the unmanned Gemini-2 mission. The flight was not identified as MOL but rather by the designation of one of its three payloads: OV4. The 9661 kg Orbiting Vehicle (OV)4 3 was a boiler plate model of the Manned Orbiting Laboratory to which the reconditioned Gemini-2 spacecraft was attached. The objective of the flight was to test the launch vehicle configuration as well as to qualify the MOL heat shield. By 1969 the first launch date had slipped to 1972 and the MOL project was eventually cancelled on 10 June 1969.
The Space Shuttle, in its initial plans, offered the military a means to gain quick access to space for pure military purposes and a series of military flights were planned of which most were to be launched from a separate launch facility at Vandenberg Air Force Base, in California.
A first flight from the Vandenberg launch site was scheduled for March 20, 1986, and was to be flown by the orbiter Discovery as the STS-62A mission. However, less than two months earlier, the demise of the orbiter Challenger on January 28, 1986, had suspended all flights of the Space Shuttle. Before that, two Space Shuttle flights (STS-51C and STS-51J) had been two dedicated military flights conducted from the Kennedy Space Center.
In the wake of the Challenger disaster, a comprehensive review of the Space Shuttle program saw the use of the launch vehicle for scientific purposes only. It was, in principle, no longer to be used as a launch vehicle for commercial satellites or military application flights. Also, all flights from Vandenberg, for which at least another seven had been planned for the 1986 to 1988 time frame, were cancelled.
A number of military flights were still conducted from the Kennedy Space Center between 1988 and 1992, but the use of the Space Shuttle as a ready access to space vehicle, had lapsed.
Space Shuttle Flights
Expendable launch vehicles
With the loss of the Space Shuttle as a ready launch vehicle for military as well as civilian payloads, military space users again turned their attention to the use of expendable launch vehicles. But the usual time it takes take to get a Delta or Atlas launch vehicle ready for launch was considered too long for some military applications and the search for a quick response launch vehicle that could place payloads in orbit within a few days of a launch request remained a priority for the U.S. military.
Four current launch vehicles are perhaps best capable to meet the U.S. Air Forces requirement for quick response vehicles.
In 1990, Orbital Sciences Corp. and Hercules Aerospace introduced the Pegasus winged launch vehicle as an inexpensive way of launching small payloads. The vehicle is propelled by three solid fuelled stages and is air-launched by a Tristar launch aircraft, thereby avoiding the usual first stage. The initial flights were air-launched from a B-52.
The basic Pegasus, which also has the military designation ASB-11A, had a small, delta-shaped wing with a span of 6.70m attached to its first stage and the entire vehicle had a length of 15.50m. The payload bay had a length of 1.83m and a diameter of 1.22m. It had the capability to place a 375 kg payload into low orbit. The first flight of the Pegasus was on April 5, 1990 and up to June 7, 2002, there were nine flights.
The current version is the Pegasus XL, an improved version with increased propellant and a length of 17.60m. It has a capability to place a 443 kg payload into low orbit. The first flight of the Pegasus XL was on June 27, 1994 and the launch vehicle remains in use.
Orbital Sciences also developed the Taurus series of launch vehicles by matching the three stages of the Pegasus vehicle (less the wings) with a new upper stage. The first flight was on March 13, 1994, and to date there have only been eight flights, of which two, including the latest flight on February 24, 2009, were a failure. The Taurus rocket has a proven gestation time of just a few weeks, thanks to the simple launch site thats devoid of a large gantry or other major infrastructure need.
The use of redundant Minuteman II missiles as space launch vehicles has been the subject of a number of proposals. Only one of these proposals resulted into an actual launch vehicle when Orbital Sciences combined the modified first and second stages of the Minuteman II missile with the Pegasus upper stages and avionics. Named the Minotaur 1, it offered the combination a launch capability of 640 kg into a low orbit. The first launch was on January 27, 2000, and to date only six flights have occurred.
Developed by Space Exploration Technologies (SpaceX), the Falcon series of launch vehicles will provide a low cost launching facility through the use of standardized engines, which are clustered to achieve a desired launch vehicle. Its objective is to provide low cost launch vehicles and it is intended that the first stage be re-usable after a return to Earth via parachute and into a water landing. The launch vehicle makes use of existing materials and components, but the liquid fuelled Merlin and Kestrel rocket motors are newly developed. The first flight was on September 28, 2008.
Future launch vehicle developments include the Hybrid Launch Vehicle (HLV) proposals by Northrop Grumman, Lockheed Martin and Andrews Space that envisage a launch vehicle consisting of a reusable airplane as the first stage with expendable upper stages. The first stage would use a rocket engine for boosting the payload up to an altitude of 45 km where the upper stage would separate and send the payload into orbit. For the return to the launch site (or any other site for that matter), the first stage would use jet engines. The HLV would include medium-lift and heavy lift configurations.
The use of C-17 military transport aircraft as a vehicle for air launches has been tested in the joint USAF-Defense Advanced Research Projects Agency QuickReach program to evaluate the air launch techniques for a low-cost, rapid-reaction small satellite launcher. On September 29, 2005, a dummy rocket was successfully released from the cargo bay of a C-17. At an altitude of about 10 km, the dummy rocket was pulled away from the cargo bay by means of gravity. On June 14 and July 26, 2006, further tests were conducted, again using a dummy rocket. The operational QuickReach will have a length of 20m and a diameter of 2.50m.
It is clear for any of these launch vehicles to be used as a quick launch vehicle, with a limited preparation time, a range of requirements still need to be met. In particular, the hardware (i.e., rocket and spacecraft) required for a quick response launch requires time to manufacture and, unless a stockpile of launch vehicles and spacecraft are established, a quick response space vehicle will remain elusive.
About the author
Jos Heyman is the Managing Director of Tiros Space Information, a Western Australian consultancy specializing in the dissemination of information on the scientific exploration and commercial application of space for use by educational as well as commercial organisations. An accountant by profession, Jos is the editor of the TSI News Bulletin.