Автономная навигация и солнечные технологии в космических миссиях NASA

NASA spacecraft launched in 1998

The Autonav system, developed by NASA's Jet Propulsion Laboratory, takes images of known bright asteroids. The asteroids in the inner Solar System move in relation to other bodies at a noticeable, predictable speed. Thus a spacecraft can determine its relative position by tracking such asteroids across the star background, which appears fixed over such timescales. Two or more asteroids let the spacecraft triangulate its position; two or more positions in time let the spacecraft determine its trajectory. Existing spacecraft are tracked by their interactions with the transmitters of the NASA Deep Space Network (DSN), in effect an inverse GPS. However, DSN tracking requires many skilled operators, and the DSN is overburdened by its use as a communications network. The use of Autonav reduces mission cost and DSN demands. The Autonav system can also be used in reverse, tracking the position of bodies relative to the spacecraft. This is used to acquire targets for the scientific instruments. The spacecraft is programmed with the target's coarse location. After initial acquisition, Autonav keeps the subject in frame, even commandeering the spacecraft's attitude control. The next spacecraft to use Autonav was Deep Impact.

Primary power for the mission was produced by a new solar array technology, the Solar Concentrator Array with Refractive Linear Element Technology (SCARLET), which uses linear Fresnel lenses made of silicone to concentrate sunlight onto solar cells. ABLE Engineering developed the concentrator technology and built the solar array for DS1, with Entech Inc, who supplied the Fresnel optics, and the NASA Glenn Research Center. The activity was sponsored by the Ballistic Missile Defense Organization, developed originally for the SSI Conestoga 1620 payload, METEOR. The concentrating lens technology was combined with dual junction solar cells, which had considerably better performance than the GaAs solar cells that were the state of the art at the time of the mission launch. The SCARLET arrays generated 2.5 kilowatts at 1 AU, with less size and weight than conventional arrays.

Although ion engines had been developed at NASA since the late 1950s, with the exception of the SERT missions in the 1960s, the technology had not been demonstrated in flight on United States spacecraft, though hundreds of Hall effect engines had been used on Soviet and Russian spacecraft. This lack of a performance history in space meant that despite the potential savings in propellant mass, the technology was considered too experimental to be used for high cost missions. Furthermore, unforeseen side effects of ion propulsion might in some way interfere with typical scientific experiments, such as fields and particle measurements. Therefore, it was a primary mission of the Deep Space 1 demonstration to show long duration use of an ion thruster on a scientific mission. The NASA Solar Technology Application Readiness (NSTAR) electrostatic ion thruster, developed at NASA Glenn, achieves a specific impulse of 1000–3000 seconds. This is an order of magnitude higher than traditional space propulsion methods, resulting in a mass savings of approximately half. This leads to much cheaper launch vehicles. Although the engine produces just thrust at maximal power (2,100 W on DS1), the craft achieved high speeds because ion engines thrust continuously for long periods.

Remote Agent (RAX), remote intelligent self repair software developed at NASA's Ames Research Center and the Jet Propulsion Laboratory, was the first artificial intelligence control system to control a spacecraft without human supervision. Remote Agent successfully demonstrated the ability to plan onboard activities and correctly diagnose and respond to simulated faults in spacecraft components through its built in REPL environment. Autonomous control will enable future spacecraft to operate at greater distances from Earth and to carry out more sophisticated science gathering activities in deep space. Components of the Remote Agent software have been used to support other NASA missions. Major components of Remote Agent were a robust planner (EUROPA), a plan execution system (EXEC) and a model based diagnostic system (Livingstone).

Once at a target, DS1 senses the particle environment with the PEPE (Plasma Experiment for Planetary Exploration) instrument. This instrument measured the flux of ions and electrons as a function of their energy and direction. The composition of the ions was determined by using a time of flight mass spectrometer.

The MICAS (Miniature Integrated Camera And Spectrometer) instrument combined visible light imaging with infrared and ultraviolet spectroscopy to determine chemical composition. All channels share a telescope, which uses a silicon carbide mirror. Both PEPE and MICAS were similar in capabilities to larger instruments or suites of instruments on other spacecraft. They were designed to be smaller and require lower power than those used on previous missions.

Prior to launch, Deep Space 1 was intended to visit comet 76P/West–Kohoutek–Ikemura and asteroid 3352 McAuliffe. Because of the delayed launch, the targets were changed to asteroid 9969 Braille (at the time called 1992 KD) and comet 19P/Borrelly, with comet 107P/Wilson–Harrington being added following the early success of the mission. During the mission, high quality infrared spectra of Mars were also taken. It was thought that the ion engine exhaust might interfere with other spacecraft systems, such as radio communications or the science instruments. The PEPE detectors had a secondary function to monitor such effects from the engine. No interference was found although the flux of ions from the thruster prevented PEPE from observing ions below approximately 20 eV. Another failure was the loss of the star tracker. The star tracker determines spacecraft orientation by comparing the star field to its internal charts. The mission was saved when the MICAS camera was reprogrammed to substitute for the star tracker. Although MICAS is more sensitive, its field of view is an order of magnitude smaller, creating a greater information processing burden. Ironically, the star tracker was an off the shelf component, expected to be highly reliable. Without a working star tracker, ion thrusting was temporarily suspended. The loss of thrust time forced the cancellation of a flyby past comet 107P/Wilson–Harrington. The Autonav system required occasional manual corrections. Most problems were in identifying objects that were too dim, or were difficult to identify because of brighter objects causing diffraction spikes and reflections in the camera, causing Autonav to misidentify targets. The Remote Agent system was presented with three simulated failures on the spacecraft and correctly handled each event. a failed electronics unit, which Remote Agent fixed by reactivating the unit. a failed sensor providing false information, which Remote Agent recognized as unreliable and therefore correctly ignored. an attitude control thruster (a small engine for controlling the spacecraft's orientation) stuck in the "off" position, which Remote Agent detected and compensated for by switching to a mode that did not rely on that thruster. Overall this constituted a successful demonstration of fully autonomous planning, diagnosis, and recovery. The MICAS instrument was a design success, but the ultraviolet channel failed due to an electrical fault. Later in the mission, after the star tracker failure, MICAS assumed this duty as well. This caused continual interruptions in its scientific use during the remaining mission, including the Comet Borrelly encounter. During late October and early November 1999, during the spacecraft's post Braille encounter coast phase, Deep Space 1 observed Mars with its MICAS instrument. Although this was a very distant flyby, the instrument did succeed in taking multiple infrared spectra of the planet.

Deep Space 1 succeeded in its primary and secondary objectives, returning valuable science data and images. DS1's ion engines were shut down on 18 December 2001 at approximately 20:00:00 UTC, signaling the end of the mission. On board communications were set to remain in active mode in case the craft should be needed in the future. However, attempts to resume contact in March 2002 were unsuccessful. It remains within the Solar System, in orbit around the Sun.