Noble’s team proved that supersonic land travel doesn’t necessarily guarantee death, but the dangers are still daunting, as Noble explained to me on a visit to his team’s engineering center at the University of the West of England in Bristol. As a vehicle passes from transonic to supersonic speeds—around 700 mph to 750 mph—the vehicle itself may be traveling at Mach 1, but air flowing over it might be moving faster than the speed of sound. For a poorly designed car traveling that fast, the varying airflow can transmit catastrophically unbalanced forces because faster-moving air exerts less pressure than slower-moving air.
And then there’s the shock wave. At subsonic speeds, a moving body transmits sound waves ahead, forcing air molecules to make way for the object approaching. As it closes in on supersonic speeds, however, a jet car catches up to the sound waves, which collect and form a pressure wave at the front. That wave is, literally, the sound barrier. Breaking the sound barrier triggers an immediate change in air pressure, releasing the pressure from the shock wave and causing the deafening crack of a sonic boom. Somehow, the car must pass through this barrier without, as Noble puts it, being torn to bits “like it were put through an office shredder.”
Noble’s first Bloodhound SSC show car sits in a campus garage downstairs from the Bristol office. The full-scale fiberboard mock-up is just an exoskeleton, but at 42 feet, it’s so long that they’ve had to turn it diagonally to fit inside the garage. Alongside the model, in a cylindrical case the size of an economy car, sits Bloodhound’s main source of propulsion—a Eurojet EJ200 turbofan engine, best known for powering the delta-winged Eurofighter Typhoon jet, still in service with the British, German, Italian and Spanish air forces. A V12 racing engine similar to that of an Aston Martin sports car rests inside the mock-up’s belly. This V12, however, plays only an indirect role in providing forward motion. It’s a pump designed to funnel 2,100 pounds of hydrogen peroxide oxidizer from an aluminum tank located behind the cockpit into Bloodhound’s main weapon: the rocket. Inside the rocket, which will be mounted either above or below the jet engine (that’s still being debated), the oxidizer ignites a grainy synthetic rubber to generate 27,500 pounds of thrust. This solid-liquid hybrid rocket design is the safest bet, because unlike entirely solid-fuel rockets, it can be shut down easily: Turn off the oxidizer pump, and the candle goes out. In all, the twin power supplies of the Bloodhound SSC will provide as much power as 252 Aston Martin Vanquish S’s.
All this hardware—the sports-car-worthy engine being used as a fuel pump—makes it obvious why Noble believes it will take as much as $17 million to build a car that can reach 1,000 mph. Which is why he spends as much time hustling for sponsorship money as he does thinking about the technical aspects of the project. “Allied to that almost naive, anything-is-possible enthusiasm is a very shrewd business mind,” says David Tremayne, author of The Fastest Man on Earth, an account of Noble’s Thrust 2 record run. “Lots of people dream of doing these things, but besides having the ability to articulate that dream, Richard also has this understanding of how the business world works, and that is the true key. He’s like one of those wobbly balls with sand in the bottom. Push it over, and it just springs back upright.”single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.