What is a Scramjet?

In today’s second chat in the Hypersonix series, we are talking about the key technology that will make our space launch systems reusable – the scramjet. 

So what is a Scramjet?

Well, a scramjet is an air-breathing engine, similar to the turbojet engine on a commercial aircraft. However unlike a turbojet, scramjets do not have rotating blades on the air intake.

Importantly, a scramjet can go a lot faster than a turbojet, without carrying oxygen like most rockets need to do.  A scramjet’s oxidiser comes free from the air!

Turbojets get too hot to go faster than Mach 3

Now, a turbojet engine sucks in air and generates ‘thrust’ (forward push) by burning fuel with the air which then shoots out the back, propelling the aircraft forward.

However, In order to take off, a turbojet needs rotating blades to compress the air, limiting it’s speed to about three times the speed of sound (Mach 3) since the blades get too hot to go any faster.

Fun fact: A Scramjet does not carry oxygen, nor does it use a compressor. It relies on the speed of the craft to generate shockwaves, thereby compressing the  incoming air and forcing it into the combustion chamber.

Scramjets are Hypersonic airbreathing engines

Speeding along faster than Mach 5 (hypersonic speed!), a scramjet doesn’t need any blades or other moving parts to produce thrust. 

The speed of the air “ramming” into the engine is enough to get the scramjet engine working, so it doesn’t have trouble with blades overheating. 

The “sc” in scramjet stands for “supersonic combustion”; as the air keeps moving faster than the speed of sound through the whole engine.  Figure 1 shows all the different parts that make up a scramjet.

Figure 1: A Scramjet Engine (NASA)

Scramjets can carry more than rockets, because they use less fuel

Travelling at its design speed, a scramjet is way more efficient than a rocket, because a rocket must carry oxygen as well as fuel.

Figure 2 shows NASA’s Space Shuttle blasting into orbit.  The massive orange tank that the Space Shuttle sits on contains 630,000 kilograms of liquid oxygen, as well as 106,000 kg of liquid hydrogen fuel.  

A scramjet needs fuel, but it doesn’t need to carry oxygen.  It gets all its oxygen from the air that it flies through.
Figure 2: NASA's space shuttle blasting into orbit.

Australian Scramjets

At Hypersonix we are developing the hydrogen fuelled ‘SPARTAN’ scramjet shown in Figure 3. 

It is designed to be the second stage of a satellite launch system, accelerating from Mach 5 to 10 and then releasing the final stage.

Our scramjet launch system only uses a rocket for the first and final part of the trip up to orbit, meaning we can carry more payload such as satellites and in the future, maybe even people!


‘Our scramjet launch system only uses a rocket for the first and final part of the trip up to orbit height, meaning we can carry more payload such as satellites and in the future, maybe even people!’

Another benefit of our scramjet system is that the exhaust from the hydrogen fuelled scramjet is just steam (superheated water), making our space access systems more environmentally sustainable.
Figure 3: A Scramjet powdered hypersonic plane designed by the University of Queensland's Centre for Hypersonics

At Hypersonix we are commercialising the world-leading scramjets developed by the University of Queensland, to make a re-usable launch system with revolutionary efficiency and unprecedented economy. 

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What does hypersonic mean?

Today’s first chat in our Hypersonix series answers the question, “What does Hypersonic mean?”
Well to start with, hypersonic means what you might expect: flying very, very fast!
To scientists, hypersonic means flying very fast within earth’s atmosphere, and to engineers it is the speed where they really need to worry about things getting very hot. A typical aluminium aircraft would collapse into a molten blob if it flew at hypersonic speeds.


Hypersonic flight is flight faster than Mach 5, or 5 times the speed of sound.

The speed of sound in air is known as Mach 1, and it is about 300 m/s in the upper atmosphere; or around 1000 km/hr.
Travel at speeds lower than Mach 1 is called subsonic. Most aircraft fly at subsonic speed, like the ones we all travel on when we go on vacation.
Supersonic aircraft fly at above the speed of sound and are less common. The most famous example is the British/French Concorde, which was a supersonic passenger aircraft that was able to cruise at Mach 2.2. 

A typical aluminium aircraft would collapse into a molten blob if it flew at hypersonic speeds.

Many modern fighter jets can also fly supersonic for short periods.

Hypersonic craft fly at speeds above Mach 5, or over 5000 km/hr, and within the atmosphere. This generates a lot of heat due to friction from the air.

So aircraft or spacecraft that fly hypersonic get very hot, and dealing with this heat is very important in how they are designed and built.

New materials to deal with heat
The NASA Space Shuttle flew at hypersonic speeds on its return to earth, and its thermal protection system had hundreds of ceramic tiles, many of which needed to be replaced after each flight.

The SPARTAN aircraft we are developing at Hypersonix will be made of high temperature composite materials that can glow white hot and still be used many times over.   

So when you think of hypersonic, think of heat. And yes, flying at hypersonic speed means flying very, very fast.

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