This revised article was originally published in October of 1988 in "Space Flight," a monthly publication of the British Interplanetary Society, It contained predictions and ideas that still hold true. At that time the Department of Defense had undertaken development of the Evolved Expendable Launch Vehicle (EELV). Contracts were awarded to Boeing and Lockheed-Martin for development of the Delta IV and Atlas V, with versions of each for launching a range of payload weights. Goals of more reliable systems, simplified operations and a cost savings of 25% were published, To a large extent these goals were achieved, so the user community benefits. Whether there are cost savings is subject to question. There are indications that costs have escalated.
The several startups mentioned - Kistler, Kelley Aerospace, Beal Aerospace Technologies, Pioneer Rocketplane, Rotary Rocket and others have ceased operations, some going into bankruptcy. One company, not in business at the time, Space Exploration Technologies (SpaceX), under the leadership of Elon Musk has successfully produced rocket engines and launched its Falcon 9 model with two flights at this writing. This company offers flights at half or less than the cost of launching Atlas V or Delta IV. Although this is cause for optimism in this expensive business, in the aggregate, the cost of launching U.S. payloads will not be affected materially. There are not that many payloads and there exists a surplus of launch capability internationally. Payloads allocated to the more economical vehicle will increase the cost of Atlas V and Delta IV due to lowered production within the same cost structure. But no sane agency would make the mistake of placing all its launches with a single low cost producer.
So how does one achieve low launch costs across the board? And by that I mean really low. A 50,000 pound shipment by aircraft half-way around the world, passenger or freight, can be had for less than a half million dollars and still make a profit. Contrast that with 50,000 lbs to Earth orbit via space shuttle at nearly a billion dollars. The energy cost difference is trivial.
The solution lies in introducing a new terrestrial transport paradigm, which is transcontinental travel on ballistic arcs. Truth to tell, Earth is designed for ballistic travel. Why endure the rigors of flight for eighteen or more hours with engines running all the way when the same can be achieved in an hour with engines running for only a few minutes?
How to do this can be separated into two approaches that have undergone considerable study. The first method seeks high performance and runway takeoff and landing ability by taking on most of its oxygen during flight through the atmosphere and liquefying it for rocket propulsion after the craft has ascended above the atmosphere. An early study titled Aerospaceplane simply liquefied air, accepting the performance penalty that resulted from high nitrogen content. That study lost direction when Grumman's Alexander Kardovsky introduced an alternative approach employing supersonic ramjets (scramjets) and shortly after, funding, which amounted to about $5 million, was cut off.
The history of the next investigation, the National Aero Space Plane, or NASP provides an interesting window into how an ambitious program can get started, how it progresses, and in many cases how the results end up on the shelf with little or no hardware produced. A secret project called Copper Canyon was initiated in 1982 at the Defense Advanced Research Projects Agency (DARPA). At about the same time the British Government was funding Alan Bond's HOTOL concept, a single - stage-to-orbit (SSTO) air breathing launch vehicle. HOTOL funding was terminated in 1987. Subsequently Bond, in his company Reaction Engines Ltd. undertook new ideas on how to build an air-breathing engine. His Sabre engine is purported to yield higher performance than HOTOL. Bond's company presently promotes the SKYLON space launch vehicle, powered by the Sabre engine as a concept for a vehicle with orbital lift capability. It is designed for lifting freight and passengers to orbit, but could conceivably also fly intercontinental on ballistic arcs without the thermal problems encountered by hypersonic scramjet craft.
The U.S. program ran until 1985 under a contract awarded to Rockwell International. Other companies contributed to the study, which had the objective of reaching orbit with a single stage, applying air-breathing technology. The work was terminated early in 1986 when, in his State of the Union message, President Reagan called for development of "a new Orient Express that could, by the end of the decade, take off from Dulles Airport, accelerate to 25 times the speed of sound, attaining low Earth orbit or fly to Tokyo in two hours." This is the first time that something close to intercontinental ballistic travel was considered. The program was called NASP and was funded by both NASA and the Department of Defense. Though initially headed by Rockwell International, Rockwell and the other companies involved, including McDonnell- Douglas and General Dynamics eventually banded together to jointly tackle the formidable technical problems. General Dynamics and Marquadt worked on schemes for liquefying air and enriching it for rocket propulsion, needed to take the craft into orbit. The work continued until 1993 when the program was terminated due to budget and technical concerns.
In the ensuing years investigations concentrated on scramjet technology, first in a NASA program with the X-43A, a kayak sized craft designed to reach Mach 10. Three were built and tested. All were intended for just one flight. X-43 A was followed by an Air Force program called the X-51, aiming to demonstrate scramjet performance up to Mach 6. Five were built. The most recent flight was June 15, 2011, which ended prematurely.
In an integrated system like NASP it is difficult to distinguish what is engine and what is aircraft. The configuration is driven in a large part by the dual need to provide the lift requirements for the vehicle and air entry into the inlets over a broad range of speeds, altitudes and temperatures. In the end, such flight vehicles are little more than flying heat exchangers. In this age, when leaks in air conditioning systems in automobiles are not uncommon, the technology required for success may be hard come by.
But hypersonic travel via scramjet is not ballistic arc travel. Ballistic arc travel involves coasting over most of the flight path, actually entering space for a brief time (Lots of people will be space travellers). Scramjet powered hypersonic aircraft will likely only find military application.
The second method for ballistic transportation is under rocket power alone. Among various concepts that have been studied, the Lockheed-Martin VentureStar SSTO reusable launch vehicle stands out, mainly because of the considerable funding that went into studies - $922 million under contracts with NASA and $357 million spent by the contractor. This was to be a vertically launched craft that lands on a runway. The program initially called for development of a reduced size vehicle, the X-33, which was to operate as a sub-orbital demonstrator. In June of 1966 NASA awarded Lockheed-Martin a contract to develop the X-33, the work to be accomplished in Lockheed's Skunk Works in Palmdale, California. To strive for the light weight needed for an SSTO, research went into development of carbon composite propellant tanks for liquid oxygen and liquid hydrogen containment, which ran into considerable difficulty. Also , the choice of engine, the linear Aerospike, which historically has little more going for it than an attractive geometry, was a regrettable choice for propulsion. After five years of work the program was cancelled due to what were termed technical difficulties. Some research work was conducted in the ensuing years that showed success in constructing carbon composite tanks for both propellants.
Still, VentureStar stands as a concept that can accomplish both transport to orbit and ballistic arc intercontinental travel. The reality is that single-stage-to-orbit with the best available propellants, hydrogen and oxygen, is not feasible with current materials. We will have to wait for molecular scientists to come up with materials of construction several times stronger than what is currently available. Nevertheless, it seems useful to return to the concept, apply more conservative design, and concede that a little boost will be required to make it work.
This suggests a need for what might be called a stub booster, a high thrust, short run rocket that returns to its launch area. The million pound thrust engine that NASA intends to develop could serve for propulsion.
That in turn suggests how VentureStar can function both for orbital applications and international travel. Stub boosters could be located near air terminals at major destinations. It suggests also military applications where it is necessary to transport troops and materials much more rapidly than now possible.
Most importantly, there will be created a transport base that has a usage far beyond what any future orbital activity projects, which will result in dramatic reduction in cost not otherwise achievable.
by Edward Hujsak
www.reactionengines.co.uk
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