Andrews Space is to build a small spacecraft to demonstrate propulsion and power technologies and orbital mechanics for NASA's space exploration programme. The SmallTug is a step towards larger cargo craft able to move supplies in cislunar space at lower cost than conventional spacecraft.

Small Seattle-based Andrews has received an initial 12-month, $2.7 million contract to design the SmallTug. During the 36-month, $16 million second phase, it plans to build and launch the 100kg (220lb) spacecraft for a one-year mission to the L1 lunar LaGrange point and back. The SmallTug will demonstrate electric propulsion, stretched-lens solar arrays and N-body orbital trajectories.

Propelled by a low-thrust, solar-electric Hall thruster, it will draw power from ultra-light refractive solar concentrator arrays – technology first demonstrated in 1998 on NASA's Deep Space 1 probe. N-body orbital mechanics involve extremely low delta-V trajectories between planetary bodies and their LaGrange points, which require less fuel than conventional trajectories.

Launched into low-Earth orbit (LEO) as a secondary payload on an evolved expendable launch vehicle, the SmallTug will demonstrate a cyclic trajectory to L1 and back representative of a routine cargo-type operation. "The delta-V savings are quite significant – 40-70% – which significantly reduces the launch mass to LEO," says Eric Wetzel, principal investigator.

With the lightweight stretched-lens solar arrays producing about 500W of power and the Hall thruster giving just "100s of Watts" of thrust, the spacecraft will take about two-thirds of its year-long journey to get to L1 and one-third to get back, says Wetzel. An operational craft would be moving so slowly at both ends that it would be possible to load and unload cargo without stopping, he says.

*Aerojet is to develop a 600kW electric propulsion system for future cargo vehicles for Moon and Mars missions, under a four-year, $32.4 million NASA contract. Using four 150kW Hall thrusters, the unit will be 30 times more powerful than current thrusters and require one-third less xenon propellant.


Source: Flight International