How do we test a Scramjet in the Laboratory?

T4 Shock tunnel

The pioneering Australian Space Scientist Professor Ray Stalker did something in the late 1960s that no-one had ever done before.  He found a way to create true hypersonic flow in the laboratory.  He invented the “free-piston shock tunnel”. 

The shock tunnel uses a heavy piston that speeds up to almost 1000 km/hr to burst a thick steel plate.  This creates a shock wave that travels down the shock tube to heat and compress the “test gas”, which is the air that we want to pass over and through our scramjet.  Once the shock wave has given its energy to the air, the air is accelerated through a hypersonic nozzle and ploughs into the test section at enormous speed, creating the conditions we need to test scramjets on the ground.

     Figure 1 - A schematic of a hypersonic wind tunnel

When a scramjet is flying in the atmosphere, it is moving at hypersonic speed through still air.  In the laboratory, the scramjet is stationary, while the air is moving at hypersonic speed.  As far as the scramjet is concerned, this is the same thing.  Its only the “relative” speed that matters.

Leaders in hypersonics
The University of Queensland in Brisbane is home to the most productive scramjet test facility in the world.  It’s a free-piston shock tunnel called “T4” that was designed by Professor Stalker.  T4 has been operating since 1989 and has performed over 12,000 hypersonic experiments!
Figure 2 shows a video of a scramjet test at the University of Queensland.  When you watch the video you will see that the tests are quite violent!   However, you will also notice that the experiment only last for a very short time.  In fact, a typical test time for a scramjet test in T4 is three milliseconds!  That is three-thousandths of a second.  It is much shorter than anything we as humans can experience!

A typical test time for a scramjet test in T4 is three milliseconds!  That is three-thousandths of a second 

   Video - T4 scramjet test at the University of Queensland

So how can we do a useful scramjet test in such a short time?  Well it’s the tremendous speed of the air that makes it all possible.  Some quick numbers tell the story.  In a typical experiment the air is moving at roughly 2000 m/s.  So if the experiment lasts for 3 milliseconds, then a hypersonic jet of air 6 meters long passes through the scramjet.  A typical model that is tested in T4 has a length of one meter, so the jet of hypersonic air created by T4 is 6 times longer than the model.  This is more than enough to do a scramjet test.

But how do we measure anything in such a short time?
Figure 3 shows an image of a scramjet model that has been opened up so we can see inside it In a typical experiment, hydrogen fuel is injected at the front of the scramjet and combustion occurs between the hydrogen and the oxygen in the air. In order to measure the effect of the combustion we need very specialised electronics that can respond quickly enough. In a typical experiment, we record data at 1 million samples per second.  Nowadays, with the amazing electronics that we use every day, this is not that difficult.

   Figure 3 - Scramjet engine in T4

To finish up I thought we would put a human face on all the technology.  Figure 4 shows PhD student Ryan Whitside and Research Fellow Wilson Chan who are doing experiments in T4.

Figure 4 – Hypersonic system researchers working at the University of Queensland

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Building the scramjet that works

In blog 2 we talked a little bit about how a scramjet can operate at hypersonic speed.

Today we will talk in more detail about some of the problems that we have solved to build a scramjet that works.

Here in Australia, we have led the world in hypersonic flight research over the last 20 years. Researchers at the University of Queensland developed the scramjet engines used for the SPARTAN. 

Over 100 people earned their doctorate (PhD) here while solving some of the challenges unique to scramjets. We have accumulated a vast body of knowledge and experience right here in Australia, overcoming difficult technological obstacles using hypersonic wind tunnels, some of the world’s fastest computers and most importantly some good Australian ingenuity.

Join us as we continue to lead the world in the hypersonics race.

Problem 1 - Ignition

Scramjets do not work below Mach 5.  But once that speed is reached, they are the most efficient engine we know of.

Figure 1 shows the components that make up a scramjet.  The inlet, or intake, collects the air as the vehicle travels along at hypersonic speed.  This generates shock waves, that compress the air so that it is hot enough to burn fuel.  Next the air enters the combustor, where fuel is injected. 

This is one of the most difficult parts of the engine, as the air remains supersonic throughout and is moving extremely fast through the engine.

   Figure 1: Cross section of a Scramjet (UQ)

For combustion to occur, the fuel must be able to mix with the oxygen in the air (air is made up roughly of 21% oxygen and 79% nitrogen), and then burn before the air passes out the back of the engine. 

This has to happen very quickly.  Say our scramjet combustor is 2 metres long, as is the case for our SPARTAN scramjet. 

At Mach 8 the air passes through the scramjet at approximately 2000 metres/second.  So that means that the fuel must mix and burn with the air in one thousandth of a second! 

This is not easy to accomplish. 

It is like trying to keep a match alight in a cyclone.

It's like trying to keep a match alight in a cyclone

Problem 2 - Changing conditions with changing speeds

For access-to-space, the scramjet must accelerate from Mach 5 to Mach 10.

However, creating more thrust than drag is not the hard part. 

As the speed increases at hypersonic speeds, conditions change substantially.  It must therefore be able to operate under a range of conditions as it accelerates.
Figure 2 shows a UQ designed scramjet engine that was tested in a hypersonic wind tunnel.  Its shape allows it to operate successfully over a large speed range.

Figure 2: Scramjet model tested in the hypersonic wind tunnels at UQ

The SPARTAN scramjet starts working at Mach 5 and increases speed to Mach 10, before releasing the upper stage to go up to space.  As it does this the angles of all the shock waves change, and so does the air velocity and temperature through the engine.  The SPARTAN scramjet is able to account for this and still generate thrust.

Now we want to use the results of the decades of hard work that have gone into developing Scramjets in Queensland.

With the inclusion of Scramjets, our launch system is much more efficient than the existing rocket-only launch systems that the rest of the world is using.

This offers huge immediate benefits and opens up exciting future possibilities.
It’s time to take SPARTAN into the real world and that is what we are doing at Hypersonix.

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Boomerang Booster Rockets

The rocket that returns to its launch site!

The idea of flying a “spaceship” many times over into space has grabbed the imagination of kids and adults alike for decades. 

The NASA Space Shuttle first flew in 1984 with the idea it would “shuttle” astronauts between earth and space on a weekly basis. 

But the reality of flying to space many times over proved to be more complicated and expensive than we had hoped.  A typical “shuttle” mission could cost up to $1 Billion US dollars.

So what is a better way to use at least part of a space launch system many times over?

Figure 1: Stages of a space launch system
All space launch systems are “staged”.   In a typical rocket shown in Figure 1, the first stage or “booster” lifts and accelerates the upper stages until its fuel runs out.  The second stage then fires, leaving the booster behind. 

It can then accelerate more quickly without the dead weight of the booster hanging around.  Once the second stage is out of fuel, the same thing happens again with the second stage now left behind.  The third stage then takes over. 

In the end it’s only the payload that ever attains the incredible velocity of 7.8 km/s needed to stay in orbit around the earth.  As explained by Vintagespace, “staging is just a clever way of getting rid of dead weight when you are doing something complicated like putting a payload into space”.

If we want to start to think about flying at least a part of our space launch system many times over there are two good reasons to start with the booster.  First of all, it is discarded first, so it attains the lowest velocity of all the stages; and secondly, it is the biggest and therefore most expensive piece of a space launch system. 

SpaceX have begun to reuse their 1st stage boosters.  We have all seen their spectacular landings on floating launch pads many of hundreds of kilometres “down-range” of the launch site.  These landings have been achieved by a very complex manoeuvre involving continued use of the rocket motor. 

But what about using the atmosphere of the earth for the slow down?  What about using wings to “fly” all the way back to the launch site?  This is what the Hypersonix “Boomerang” boosters are designed to do.
Figure 2: Spartan space launch systems with two Boomerang Boosters (UQ)

Figure 2 shows a computer generated image of the SPARTAN space launch system.  It uses two booster rockets to accelerate the 2nd stage to Mach 5 scramjet take-over speed. 

But look closely at the boosters. 

They each have a wing stowed along their backs, and tail fins at their base.  These are not used when the booster is doing its job of accelerating the upper stages on their way to space. 

These “aerodynamic” components are there to enable it to fly back to the launch site.  Just like a boomerang returns to the thrower if it is thrown in the right way.

Figure 3: The SPARTAN launch profile (UQ)
Figure 3 shows a schematic of the launch of a small satellite by SPARTAN.  Once the boosters have done their job, they each separate and start to fall back to earth. 

At this point their flight computer uses the tail fins to slow down and re-enter in a controlled way using the earth’s atmosphere.  It can’t use its wing just yet, as it’s going way too fast and they would simply break off. 

However, once the booster has slowed right down to around 150 km/hr, the wing can be swung out.  There is also a propeller motor hidden in the nose, which is also deployed. 

So now the boomerang boosters have turned into small aircraft, which can simply fly back to the launch site and land right next to where they were launched.

Fun fact: We get the biggest bang for our buck by reusing the first stage of the rocket, as this is the heaviest component which attains the lowest velocity through the flight.

Figure 4: Boomerang booster flying under its own propeller power (Photo by Juan Llobet Gomez)

 In 2015 the University of Queensland, along with some Brisbane start-up companies, flew a scaled version of the Boomerang booster (Figure 4).

These tests, and further flights in 2017 proved that the Boomerang booster can fly once its wing and propeller are deployed.

World First: Re-entry Test
What we now want to do at Hypersonix is a world first re-entry of the boomerang booster from 30 km altitude.

And we want the public at large to be a part of it through a crowd funding campaign.  Our goal is to do this flight in 2019.

Who wants to come along with us and be a part of space history?

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Throw-away Rockets – There must be a better way

In today’s third chat in the Hypersonix series, we are talking about reusable space launch vehicles – one of the features of our launch system.

Throw-away Rockets

The 1960’s was a tremendous decade for space exploration, thanks to the famous challenge set by President Kennedy. 

The challenge, “to send an astronaut to the moon, and return him safely to earth before the decade is out”, was a critical event in human history.  In response to this challenge, America forged ahead with the Apollo Program.

Figure 1: Apollo rocket on the launch pad
On the launch pad these enormous rockets creaked and groaned, as they contained tens of thousands of kilograms of liquid oxygen at -200 degrees Celsius. 

Once the rockets fired up, hot gases at over 3000 degrees Celsius spewed out, pushing the astronauts into space, and then to the moon.

After that, only about 1% of what was launched came back.  This was the command module that protected the astronauts during re-entry. 

So these were throw-away rockets!

Imagine you bought a new sports car, say a Porsche.  You pick it up from the show room all shiny and new.  Next day you and your best friend drive it to the beach. 

The drive is very exciting, and you get there safely and in record time.  When the day is over you drive the car into the ocean and throw away the keys!

What a waste!
Fun fact: The Apollo rocket carried so much oxygen and fuel, that only 1% of the total mass returned from space after the mission had finished.

It's time we left the 60's behind..

In 2018, we can face-talk with friends almost anywhere in the world.  We can holiday in far-flung places.  And we have decoded the human genome.  But most space launchers are still throwing rockets away like we are in the swinging 60’s with Austin Powers. 

The supposedly “cutting edge” activity of going to space has made few advances since the 60s.  However, thanks to a growing number of innovative aerospace companies, things are at last changing. 

In 2016 SpaceX safely landed one of their Falcon 9 booster rockets on a floating platform in the Atlantic Ocean.  In 2017 SpaceX not only retrieved one of their boosters, but re-flew it.

The space launch industry has now entered a time of great change. 

At Hypersonix we want to lead this change in the Australian small satellite launch industry, while continuing to develop the huge potential of scramjet technology.

Figure 2: Falcon 9 booster landed on a floating platform (SpaceX)
There is another way to get to space
Figure 3: SPARTAN small satellite launch system
In Australia, we are very interested in being able to put our own small satellites into orbit.  Remote sensing; bushfire monitoring; Outback Internet; there are all sorts of jobs that small satellites can do. 

Some of these satellites are not much bigger than an iphone, called CubeSats. 

We have been developing our hypersonic launch system to do just this.   It’s small; about the same size as a Boeing 737 you would catch between Sydney and Melbourne.

It uses scramjets, and we call it SPARTAN!  It’s a hypersonic aircraft and it is boosted up to speed by rockets.  Remember from last week’s chat [link], a scramjet only works at hypersonic speed, so it needs help to get to Mach 5.

Our rockets, however, are not throw away ones like in Apollo.  They will deploy wings and fly back to the launch pad to be used many times over. We call them our Hypersonix “Boomerang” boosters.
Figure 4: Hypersonix boomering booster


After being accelerated to Mach 5 by our Boomerang Boosters, the scramjet engines turn on. 

They push SPARTAN to the edge of space, releasing the satellite which is then taken up to its final orbit by a small rocket.  The SPARTAN then turns around and also flies back to base.

Now, this is the future of space travel!  

Flying to space, and coming back again.

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