Once you get to mach 5+ hypersonic speed, then a scramjet works and it is by far the most efficient type of engine for hypersonic speeds. A scramjet needs some other form of propulsion to get it to Mach 5. As a result, scramjets have become something of a well-studied technology in search of a practical application.
To reach these hypersonic speeds, Michael Smart, professor of hypersonics at the University of Queensland in Brisbane plans to combine an uncrewed scramjet with conventional rockets. He believes his Spartan launch system could radically reduce the costs of blasting satellites into orbit.
“All conventional satellite launch systems use different stages,” says Smart. “There’ll be a first stage rocket that normally gets up to Mach 5 or 6, you’ll have a second scramjet stage that goes two thirds of the way to space and you’ll have a final upper stage that takes the satellite into orbit.”
On the launchpad, Spartan will look and launch like a conventional rocket. Once it reaches hypersonic speeds, however, the first stage will drop away and the scramjet will unfurl its wings to blast the spacecraft into the upper atmosphere. When it runs out of air, the scramjet will separate and a small conventional rocket will carry the satellite into space.
As much of the Spartan system as possible is designed to be reusable. Both the scramjet and first stage rocket will fly themselves back to a runway landing – although the scramjet will undoubtedly look sleeker.
The scramjet will primarily be used to launch satellites, but it may also take tourists into space (Credit: University of Queensland)
There are about 1300 satellites orbiting in space, but the cost to launch a single satellite is astronomical.
Stage one of the system consists of an Austral Launch Vehicle (ALV), a reusable rocket booster that lifts the upper stages of the rocket to scramjet take-over speed of Mach five, before flying back to base using wings and propellers.
The second stage SPARTAN scramjet will fly like a plane up to Mach 10, releasing the final rocket/satellite that stays in space, before it too returns to base.
The combination of the ALV and SPARTAN allows 95 per cent of the system to be reusable.
ALV-0: Small scale (1:4), aircraft mode only, ultra low cost
ALV-1: Small scale (1:4), rocket and aircraft modes, alloy construction, HAVBUS avionics
ALV-2: Medium scale (1:2), full trajectory, liquid propulsion (LOX / Methane), capable of launching micro satellites (with upper stages) and hypersonic test vehicles
ALV-3: Commercial launch vehicle
“Once the rocket booster has finished its job we deploy wings and a small propeller and fly back to base,” says Smart, “It’s basically just a big tin can, it’s very light. It’d be like a small ugly aircraft.”
The only part of the launch system that will not survive the flight is the final third stage, which will burn up in the atmosphere after releasing its payload into orbit.
Over the past couple of years, Smart has been carrying out hypersonic tests with a rocket and a two-metre-long scramjet at Woomera – flying the aircraft at hypersonic speeds 400 kilometres across the desert. “It’s the best ever radio controlled plane,” admits Smart, although it’s way too fast to control with a joystick. “We pre-prepare all the flight software, press the button and off it goes.”
Although Smart’s goal is to get Australia back into the satellite launch business, hypersonic aircraft hold the promise of radically reducing flight times on Earth.
SOURCES- BBC News, Queensland University