Universe Today

Upcoming commercial space flights are no longer only about rich, adventure-seeking space tourists. Researchers hope to capitalize on the prospect of quick, low-cost and frequent access to the micro-gravity environment of sub-orbital space. "We’ve got these great vehicles coming online and most of the discussion about them so far have centered on the tourism market," said Erika Wagner, member of SARG – the Suborbital Applications Researcher Group. "As researchers we felt this was a fantastic opportunity to do both science and education, as well."
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An international company announced plans to launch a commercial space venture using spacecraft designed for a once classified Russian space program. Excalibur Almaz Limited plans to offer week-long orbital space flights beginning as early as 2013 with updated 1970's era Reusable Return Vehicles, designed for flying to the USSR's top-secret Almaz space station. Excalibur Alamaz's press release said they would be "taking a big leap beyond the sub-orbital flight market targeted by most other private space companies."
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Hypersonic is a type of supersonic flight; airborne and at a speed above Mach 5. This is isn't a concrete definition because any speed faster than the speed of sound is considered supersonic – meaning literally "above sound". In the end, the definition more has to do with the limits of aeronautical technology than an actual natural limit.

So what limit defines hypersonic? For a time after the breaking of the sound barrier in the 1950's, there were limits on how fast and how long an aircraft could travel at supersonic speeds without suffering the effects of drag and strain on the aircraft's structure. Most supersonic aircraft topped out at speeds of around Mach 3; three times the speed of sound. Only vehicles like the US space shuttle exceed these speeds, and only upon reentry.

A possible solution emerged with the advent of an air breathing jet engine called the ramjet. The ramjet functions by using the forward motion of the aircraft to compress and force air through itself. Along with a faster and more efficient fuel injector this allowed the jet engine to burn the fuel and air mixture in the combustion chamber at higher speeds creating a significantly greater amount of thrust. This innovation made it possible for aircraft to reach a top speed of Mach 5; however, the same problem came up that limited previous jet aircraft. After a certain speed even ramjet engines could not take in air fast enough making it impossible to go any faster. The ramjet worked by using the shock wave created when breaking the sound barrier to slow down air to a speed that it could be funneled into the engine's intake for compression in the combustion chamber. The shock wave disappears at speeds higher than Mach 5, so the ramjet faces the same issues of drag and structure failure. Accordingly, a lower limit for hypersonic flight was created.

The scramjet solved this problem in quite a simple way. The engine was not not designed to slow air down at all, but rather was adapted to take in air at supersonic speeds. (This meant fewer moving parts in the engine and a single scoop intake optimally placed on the craft). The craft's design also had to change. NASA successfully tested its own hypersonic design;a very thin wedge, a concept much different than the airplane designs most people are familiar with. These design changes opened a new realm of speed for aircraft with the possibility of a hypersonic craft that can reach speeds as high Mach 30 – the speed of the Earth's rotation.

Though the concept has proven viable in testing, it will be a while until passenger ready hypersonic aircraft are regularly used by the US Air Force and NASA, but the consequences for spaceflight are extraordinary. A reliable hypersonic aircraft will most likely replace the shuttle as a cheaper alternative for suborbital flight. As matter of fact, the estimates are that such a craft could save NASA as much as $9,000 dollars per pound (.45kg) of payload. This reduction of cost would make commercial spaceflight a more realistic possibility.

If you enjoyed reading this article there are several others you can enjoy on Universe Today. First you can expand you knowledge about hypersonic jet engines with this article on Scramjets. You can also read about a British design company designing a commercial hypersonic aircraft.

There also other interesting articles about hypersonic flight on the internet. There is a great site that centennialofflight.gov that has a very detailed article on the history of hypersonic flight. There is also an interesting blog about hypersonic flight on CNN.com

You can also listen to Astronomy Cast episode 101 Advanced Propulsion Systems.

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