Builders of a private spaceship are ironing out control problems with their craft uncovered during drop testing at a Mojave, California desert test site.

Engineers at Scaled Composites have been wrestling with issues of airflow over tail control surfaces of their SpaceShipOne suborbital vehicle. A fourth high-altitude drop test of the craft on October 17 has assessed several modifications to the tail section.

SpaceShipOne is the first piloted winged aircraft with outboard horizontal tails. Fully understanding the craft's handling properties through the atmosphere is crucial.

During a glide to Earth after flying to the edge of space, the vehicle's tail section flips up to a "feathered" position -- moved to a 65-degree angle to the main body. This critical positioning of the hinged tail section slows the craft to allow a safe and sound glide down to the airstrip.

The craft is being readied for winging its way to the edge of space, a competitive shot at winning the $10 million X Prize. Numbers of rocket teams around the world are vying for the X Prize purse by designing and building various types of suborbital, passenger-carrying spaceships.

Noted aircraft builder, Burt Rutan, is leader of the SpaceShipOne venture, along with a cadre of specialists at Scaled Composites, based at Mojave, California.

A step-by-step ground and air test program has been scripted. That test series now includes four SpaceShipOne high-altitude drops currently listed by Scaled Composites: August 7, August 27, September 23, and October 17, 2003.

Still to come are in-the-air ignitions of SpaceShipOne's hybrid rocket motor. SpaceDev of Poway, California was picked by Scaled Composites in mid-September as the vendor of choice to supply key hardware for the propulsion system.

To attack SpaceShipOne's handling concerns, a bit of high-speed road rage was used.

Putting high-tech computational fluid dynamics (CFD) analysis of their design aside, SpaceShipOne handlers decided to "road test" the craft's boom-tail.

Using a bit of creative Ford driving (CFD), a modified Ford-250 pickup truck tested various changes to SpaceShipOne's tail section. Putting pedal to the metal, the truck accelerated to high speeds to carry out full-scale "wind tunnel" evaluation of the tail assembly. These tests enabled Scaled Composite experts to study several modifications to SpaceShipOne's tail section meant to counter aerodynamic problems uncovered in the prior drop test last September.

Several days of ground testing validated aerodynamic fixes meant to solve the tail stall problem. The fixes were first flown on the October 17 drop test of SpaceShipOne. After release from the White Knight carrier plane at 46,200 feet, pilot Mike Melvill checked out the vehicle's handling qualities.

The Scaled Composite team reported "considerable improvement" of SpaceShipOne's flying attributes, with no vehicle pitch up noted. Real time video from the craft to mission control was used to study aerodynamic improvements to the craft's tail section.

Other test objectives during the fourth drop test included evaluating SpaceShipOne's hybrid rocket motor controller, with Melvill checking out the "Arm," "Fire," and safing switches as well as the oxidizer dump valve. A set of planned maneuvers of the vehicle included full rudder pedal sideslips in the air and more aggressive nose pointing while in the feathered configuration.