Experimental rocket fuses helicopter, rocket

Can a bizarre spacecraft that is powered by a rotating rocket engine and that lands like a helicopter transform space travel? In March, an American company will be a step closer to finding out, when a prototype of the Roton craft starts putting these concepts to the test.

Known as the atmospheric test vehicle (ATV), the prototype will be used to test the craft's unique landing system-four helicopter blades, each 7 metres long, intended to slow the Roton's descent. If the tests are successful, the
first Roton could blast into orbit as early as next year. It should slash the cost of getting satellites into space, says Gary Hudson of the Rotary Rocket Company in Redwood City, California.

The secret lies in its outlandish design (see "Rocket revolutionary", New Scientist, 1 August 1998, p 24). Its conical body is built from lightweight graphite composites instead of aluminium. Hudson has also eliminated the need for the heavy turbopumps that feed fuel to conventional rocket engines by making the whole engine spin. Ninety-six com-bustion chambers are mounted around the edge of a disc 7 metres wide. Spinning at 720 revolutions per minute, the disc throws fuel and oxygen outwards into the chambers from storage tanks in the craft's body. And to make the craft
truly reusable, the Roton is supposed to land gently beneath whirling rotor blades-which is where the ATV comes in.

Over the next year the ATV will make about 10 manned flights at Mojave in California to test the rotors and landing systems. Although it lacks the spinning rocket engine needed to get it into orbit, the ATV will still be able take off under its own power, thanks to the small rocket thrusters on the tips
of its rotors (see Diagram). In real missions, the thrusters will be used just before the Roton reaches the ground. The extra lift they generate should allow the spacecraft to land without being damaged.

In the upcoming tests, however, the thrusters will also lift the ATV off the ground. With each rocket producing 350 pounds of thrust, the rotors will spin fast enough for the Roton to climb off the launch pad like a helicopter. "The rockets will provide about 5 to 10 minutes of power," says
Hudson. "In fact, it's the largest tip-powered helicopter ever built."

After its ability to hover has been tested, the ATV will be flown to an altitude of about 2000 metres. Then the thrusters will be switched off, but as the craft descends, the airflow will keep the rotors spinning, providing enough lift to slow its descent. Just before it reaches the ground, the pilot will adjust the angle of the rotor blades to maximise lift and slow the craft's descent to about 1 metre per second. The tip thrusters will be fired at this stage too, says Hudson, allowing the Roton to hover for a few seconds before
touching down gently.

Over the next 18 months, the Rotary Rocket Company plans to build three more Rotons: an unpowered version for training, and two complete craft for orbital missions in 2000.