NASA Solar Technology Application Readiness

The NASA Solar Technology Application Readiness (NSTAR) is a type of spacecraft ion thruster called electrostatic ion thruster.^[1][2] It is a highly efficient low-thrust spacecraft propulsion running on electrical power generated by solar arrays. It uses high-voltage electrodes (including two fine grids) to accelerate ions with electrostatic forces.

The Deep Space 1 and Dawn used the NSTAR, a solar-powered electrostatic ion propulsion engine

Development and performance

Diagram of a generic gridded electrostatic ion thruster

The purpose of NSTAR program was to develop a xenon-fueled ion propulsion system for deep space missions.^[3] The NSTAR electrostatic ion thruster was developed at NASA's Glenn Research Center and manufactured by Hughes, and Spectrum Astro, Inc. in the early 1990s. The feed system development was a collaborative effort between JPL and Moog Inc.^[1]

The ions are accelerated through two fine grids with roughly a 1300 V difference between them for 2.3 kW operation,^[4][5] with a thrust of 20-92 mN, a specific impulse of 19000-30500 N·s/kg (1950-3100 s) and a total impulse capability of 2.65 x10⁶ Ns on DS1.^[5]

In 1996, the prototype engine endured 8000 hours of continuous operation in a vacuum chamber that simulates conditions of outer space. The results of the prototyping were used to define the design of flight hardware that was built for Deep Space 1 probe. One of the challenges was developing a compact and light weight power processing unit^[6] that converts power from the solar arrays into the voltages needed by the engine.^[3]

Performance

The engine achieves a specific impulse of up to three thousand seconds. This is an order of magnitude higher than traditional space propulsion methods, resulting in a mass savings of approximately half. Although the engine produces just 92 millinewtons (0.331 ounce-force) thrust at maximum power (2,100W on DS1 mission), the craft achieved high speed because ion engines thrust continuously for long periods of time.^[7] "The 30-cm ion thruster operates over a 0.5 kW to 2.3 kW input power range providing thrust from 19 mN to 92 mN. The specific impulse ranges from 1900 s at 0.5 kW to 3100 s at 2.3 kW."^[1]

Applications

Deep Space

The NSTAR ion thruster was first used on the Deep Space 1 (DS1) spacecraft, launched on 24 October 1998.^[8] The Deep Space mission carried out a flyby of asteroid 9969 Braille and Comet Borrelly. Deep Space 1 had 178 pounds (81 kilograms) of xenon propellant, with a total impulse capability of 2.65 x10⁶ Ns^[5] and was capable of increasing the speed of DS1 by 7900 miles per hour (12,700 kilometers per hour, 3.58 km/s) over the course of the mission.^[3] It used 2.3 kW of electrical power and was the primary propulsion for the probe.^[4]

Dawn

The second interplanetary mission using NSTAR engine was the Dawn spacecraft, launched in 2007 with three redundant units^[9] with a 30 cm diameter each.^[6][10] Dawn is the first NASA exploratory mission to use ion propulsion to enter and leave more than one orbit.^[11] Dawn carried 425 kg (937 lb) of on-board xenon propellant, and was able to perform a velocity change of 25,700 mph (11.49 km/s) over the mission.

Proposed uses

As of 2009^[update] NASA engineers state that NSTAR engines, in the 5-kilowatt and 0.04 pound-thrust range, are candidates for propelling spacecraft to Europa, Pluto, and other small bodies in deep space.^[1]

See also

• Electrically powered spacecraft propulsion
• NEXT (ion thruster) – Space propulsion system, a gridded electrostatic ion thruster
• Advanced Electric Propulsion System – Spacecraft propulsion system by NASA. 50kW Hall-effect thrusters, now for Lunar Gateway