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On the trail of the Scramjet

Woomera in outback Australia
Woomera in outback Australia was the site of the world's first successful scramjet launch by Australian researchers.

Mention Woomera and you will receive many responses. It is place with a long and varied history. When Jonathan Swift wrote Gulliver's Travels, he located Lilliput in the middle of South Australia, just north of Pimba.

After World War II, everyone was testing rockets. But Britain - unlike the USA and the USSR - had no deserts, so they used outback Australia instead.

The area isn't really desert, just part of the arid zone of Australia, but it was near enough, and became a rocket range called Woomera.

The fictional Lilliput lies inside what is now the Woomera Exclusion Zone - a fitting placement given that most of the rockets launched there have been smallish.

The first Europeans here covered twenty miles on a good day. Between lunch and a rather early dinner, I drove what they would have traversed in a fortnight's seriously hard slog. As I hurtled towards Woomera to see a scramjet test I wondered what they would think if they could see how fast and light we travel now.

Scramjet

We are told scramjetliners may one day take us from Sydney to London (or sometimes New York to Tokyo) in two hours. Even if somebody built a scramjetliner, a ticket would cost millions of dollars, and the passengers would stay away because there would not even be time to open the second free bottle of champagne before the flight ended. On the other hand, there is a clear future for the scramjet as humanity moves into orbit and out into space.

Scramjets vs traditional rockets

A scramjet is an air-breathing Supersonic Combustion RAMjet. It is basically a very high speed scoop that gathers up air (oxygen), forcing it into a combustion chamber where the fuel (usually hydrogen) is burned, generating thrust that keeps the craft going. The only 'exhaust' is water. The trick is to get a scoop which has low enough drag so the scramjet generates a thrust greater than the drag caused by the scoop. This will always be a difficult balancing trick.

Launching of UQ`s HyShot rocket at Woomera Range
Launching of UQ`s HyShot rocket at Woomera Range, South Australia. (Courtesy: Chris Stacey, The University of Queensland.)

Traditionally, rockets carry energetic fuel and a ferocious oxidiser. Solid propellant boosters burn out in two or three minutes, after which they fall away, their duty done, having spewed out their toxic exhausts. Later stages of spacecraft use liquid fuels, often hydrogen and oxygen, with complex pumps and mazes of tiny holes that the gases pass through, mixing as they go. Even a simple rocket engine for liquid fuels will cost several million dollars.

Carrying an oxidiser lowers efficiency, because the oxidiser could be replaced by payload. One of the most efficient rocket fuels is hydrogen, but to burn one gram of hydrogen, you need eight grams of oxygen. You also need a second container to carry the oxygen. Most of the oxygen is waste - while some of the oxygen becomes reaction mass, scooped-up oxygen will do that just as well.

If the oxygen can be left out - or even drastically reduced in mass - and if the oxygen fuel pumps, metering and other gear can be left out or reduced, that makes a huge difference.

A jet engine compresses air with a fan before fuel is added and burned, providing thrust. But when you get to supersonic speeds the fans tend to overheat imposing a natural speed limit.

Future flying

The International 

            Space Station (ISS)
The International Space Station recorded by the STS-110 crew members on board the Space Shuttle Atlantis. (Courtesy: NASA)

If 22nd Century humans are routinely going into space, there are going to be pollution problems, because many of the fuels and oxidisers are noticeably unfriendly and toxic. By contrast, scramjets burn hydrogen to produce water.

The first generation of spacecraft, from Sputnik to Apollo, and even most of today's Mars missions, rely on straightforward single-use rockets, while second generation projects like the International Space Station rely on reusable vehicles like the Shuttle. Now comes the third generation: scramjet spacecraft that will do away with the need for onboard oxidiser.

The idealists say there is the potential here to increase lift efficiency a hundredfold - an ambitious estimate according to a NASA scientist - but it is a goal to aim at for the future.

Scramjet

Testing in a tunnel

The Hyshot leaves a spiral trail after launching
The HyShot leaves a spiral trail after its launch outside the tunnel.(Image: Peter Macinnis)

The real challenge with scramjets is to get them travelling very fast. The researchers have to test everything at once because all the components are untested components. Instead of risking failure after failure it seems better sense to test the components in a wind tunnel before putting them to the test in the field.

But a wind tunnel is too slow, so instead, the engineers at the University of Queensland (UQ) have been using the T4 shock tunnel in Brisbane.

A shock tunnel holds back hot helium as a piston hurtles into it, until the massive pressure bursts a piece of 3mm steel plate - called a 'diaphragm'. When it bursts a torrent of gas pours down the tunnel allowing testing of many of the design principles under high speed conditions.

In simple terms, you can learn a great deal about how a scramjet behaves in a shock tunnel, but there remains the problem of linking this to reality. The proof really comes when you fly all of the bits.

If the tunnel is not realistic, all the money you tried to save by using the tunnel becomes money wasted. So the HyShot launch at Woomera was mainly about gathering real data to compare with shock tunnel data.

Scramjet

So how did the test go?

On July 30, 2002 the University of Queensland HyShot team culminated many years of work when they sent their second scramjet payload up into the atmosphere on the back of a Terrior Orion rocket in a test flight. They made history - it turned out to be the first successful launch of a scramjet in the world.

The staged Terrier Orion rocket and UQ payload
The staged Terrier Orion rocket and UQ payload on the launch pad at Woomera. (Courtesy: The University of Queensland.)

The dramatic TV footage of the Orion-Terrier rocket actually doesn't show the scramjet working - the rocket is simply there to get the scramjet up into the air and moving quickly. The two-stage rocket used aluminium powder and ammonium dichromate, solid fuel like a Lilliputian Titan 4, to send the payload right up into space, to 314 kilometres.

The timing of the launch had to fit around what else was out in orbit. At one stage they had to wait because the projected path of the rocket was within a few thousand metres of the orbit of an American satellite - too close to take any risks!

On the day, everything went to plan. The first stage rocket burned for six seconds, accelerating the craft to Mach 3.6, or 3.6 times the speed of sound. That ran up the sky, leaving a white trail behind that stopped halfway up the sky, and then the roar reached us, standing out on the plain, several kilometres away.

This was a 16-second silent pause while the slim second stage and the payload slipped free of the spent initial stage. The second stage sits on top of the first stage, and simple drag caused the first stage to fall behind.

The business end, the slimmer second stage and its payload, coasted upwards, losing speed from Mach 3.6 back down to Mach 3.2, stabilising any flutters from the first blast. It also pushed through the worst of the lower atmosphere before the second stage rocket kicked in, high in the sky, boosting it up to Mach 7.7.

The second rocket blast took it to 56 kilometres above the Earth, just 39 seconds after the scramjet took off. It then simply coasted to the top of the parabola. This is 'going ballistic' in the scientific form of the word.

When it levelled out it had been flying for just over four-and-a-half minutes. Gravity kicked in and it tilted and began to plunge back to the atmosphere. By the time the turn was completed, three minutes later, it was almost halfway down to the ground again.

We have scramjet!

Oh, what a feeling... members of the successful HyShot team
Oh, what a feeling... members of the successful HyShot team (from left) Judy Odam, Dr Ross Paull, Bert Paull, Dr Allan Paull, Dr Susan Anderson, Myles Frost, Suhee Won and Aggie Branczyk. (Courtesy: The University of Queensland.)

As the air thickened, the rocket and the passenger scramjet slowed to Mach 7.6, and more oxygen began to pass through the system.

At 35 km up in the air - about three times the height jetliners fly at - the scramjet kicked in, just as it disappeared over the horizon, as seen from the control block.

The payload was sending data back to receivers on Earth from 40 channels different channels including pressure readings, temperature readings, acceleration measurements and magnetometer readings.

The rocket flew as it should, and the scientists tracked it down range and retrieved the telemetry back from the other end to make sure that everything went to plan. The remote stations were in contact with the base by satellite phone, and so the remote stations knew where to point their equipment in order to find the craft as it hurtled towards them at Mach 7.6.

So from a first generation of toxic rockets to a generation of slightly less toxic reusable craft like the Shuttle, now we are turning to the third generation of space lift, in the form of a scramjet.

The scramjet flew for just six seconds, but then the first flight by the Wright Brothers only lasted 12 seconds, and Robert Goddard's first rocket flight in 1926 lasted just 2.5 seconds, so that would seem to place the scramjet in the middle of the duration span for historic space and flight exploits.

Certainly, as one of the University of Queensland people told me over dinner when I mentioned Jonathan Swift, the achievement was by no means Lilliputian.

History will be the judge, but I agree.

We have liftoff!

The world's first successful flight of a scramjet using supersonic combustion has been confirmed by the Australian team responsible. Read the lab's News in Science story to find out more.

Scramjet

Related Links

In Space - the ABC's gateway to the stars

The University of Queensland's HyShot news

NASA homepage

In the News

Keep informed of developments in scramjet technology and HyShot research from the University of Queensland team with The Lab's News in Science stories. This index is continually updated.

Bullet-shaped scramjet put to the test (23/03/2006)
A new scramjet engine, shaped like a bullet, will be tested in the Australian desert tomorrow by an international team of scientists that hopes it will be more efficient than previous designs.

Earlier Stories

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Published 17/10/2002
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