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.png) Artist concept ofDeep Space 1 firing its ion thrusters | |||||||||
| Mission type | Technology demonstrator | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Operator | NASA / JPL | ||||||||
| COSPAR ID | 1998-061A | ||||||||
| SATCATno. | 25508 | ||||||||
| Website | jpl.nasa.gov | ||||||||
| Mission duration | 3 years, 1 month and 24 days | ||||||||
| Spacecraft properties | |||||||||
| Manufacturer | Orbital Sciences | ||||||||
| Launch mass | 486 kg (1,071 lb)[1] | ||||||||
| Dry mass | 373 kg (822 lb)[1] | ||||||||
| Dimensions | 2.1 × 11.8 × 2.5 m (6.9 × 38.6 × 8.2 ft) | ||||||||
| Power | 2,500 watts[1] | ||||||||
| Start of mission | |||||||||
| Launch date | 24 October 1998, 12:08 (1998-10-24UTC12:08) UTC[2] | ||||||||
| Rocket | Delta II 7326[1] D-261 | ||||||||
| Launch site | Cape CanaveralSLC-17A[1] | ||||||||
| Contractor | Boeing | ||||||||
| End of mission | |||||||||
| Disposal | Decommissioned | ||||||||
| Deactivated | 18 December 2001, 20:00 (2001-12-18UTC21) UTC[2] | ||||||||
| Flyby of9969 Braille | |||||||||
| Closest approach | 29 July 1999, 04:46 UTC[2] | ||||||||
| Distance | 26 km (16 mi) | ||||||||
| Flyby of19P/Borrelly | |||||||||
| Closest approach | 22 September 2001, 22:29:33 UTC[2] | ||||||||
| Distance | 2,171 km (1,349 mi) | ||||||||
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 DS1 mission logo | |||||||||
Deep Space 1 (DS1) was aNASA technology demonstrationspacecraft which flew by anasteroid and acomet. It was part of theNew Millennium Program, dedicated to testing advanced technologies.
Launched on 24 October 1998, theDeep Space 1 spacecraft carried out a flyby of asteroid9969 Braille, which was its primary science target. The mission was extended twice to include an encounter with comet19P/Borrelly and further engineering testing. Problems during its initial stages and with its star tracker led to repeated changes in mission configuration. While the flyby of the asteroid was only a partial success, the encounter with the comet retrieved valuable information.
The Deep Space series was continued by theDeep Space 2 probes, which were launched in January 1999 piggybacked on theMars Polar Lander and were intended to strike the surface of Mars (though contact was lost and the mission failed).Deep Space 1 was the first NASA spacecraft to useion propulsion rather than the traditional chemical-powered rockets.[3]
The purpose ofDeep Space 1 was technology development and validation for future missions; 12 technologies were tested:[4]
The Autonav system, developed by NASA'sJet Propulsion Laboratory, takes images of known brightasteroids. 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 theNASA Deep Space Network (DSN), in effect an inverseGPS. 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.[5] The next spacecraft to use Autonav wasDeep 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 linearFresnel lenses made ofsilicone to concentrate sunlight onto solar cells.[6] ABLE Engineering developed the concentrator technology and built the solar array for DS1, with Entech Inc, who supplied the Fresnel optics, and the NASAGlenn 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 theGaAs 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.
Althoughion engines had been developed at NASA since the late 1950s, with the exception of theSERT missions in the 1960s, the technology had not been demonstrated in flight on United States spacecraft, though hundreds ofHall-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 theDeep Space 1 demonstration to show long-duration use of an ion thruster on a scientific mission.[7]
TheNASA Solar Technology Application Readiness (NSTAR)electrostatic ion thruster, developed at NASA Glenn, achieves aspecific 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 92millinewtons (0.33 ozf) thrust at maximal power (2,100 W on DS1), the craft achieved high speeds because ion engines thrust continuously for long periods.[7]
The next spacecraft to use NSTAR engines wasDawn, with three redundant units.[8]
Remote Agent (RAX), remote intelligent self-repair software developed at NASA'sAmes Research Center and the Jet Propulsion Laboratory, was the first artificial-intelligence control system to control a spacecraft without human supervision.[9] 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.[10] 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).[10] EUROPA was used as a ground-based planner for theMars Exploration Rovers. EUROPA II was used to support thePhoenix Mars lander and theMars Science Laboratory. Livingstone2 was flown as an experiment aboardEarth Observing-1 and on anF/A-18 Hornet at NASA'sDryden Flight Research Center.
Another method for reducing DSN burdens is theBeacon Monitor experiment. During the long cruise periods of the mission, spacecraft operations are essentially suspended. Instead of data, Deep Space 1 transmitted acarrier signal on a predetermined frequency. Without data decoding, the carrier could be detected by much simpler ground antennas and receivers. If DS1 detected an anomaly, it changed the carrier between four tones, based on urgency. Ground receivers then signal operators to divert DSN resources. This prevented skilled operators and expensive hardware from babysitting an unburdened mission operating nominally. A similar system was used on theNew Horizons Pluto probe to keep costs down during its ten-year cruise from Jupiter to Pluto.
TheSmall Deep Space Transponder (SDST) is a compact and lightweight radio-communications system. Aside from using miniaturized components, the SDST is capable of communicating over theKa band. Because this band is higher in frequency than bands currently in use by deep-space missions, the same amount of data can be sent by smaller equipment in space and on the ground. Conversely, existing DSN antennas can split time among more missions. At the time of launch, the DSN had a small number of Ka receivers installed on an experimental basis; Ka operations and missions are increasing.
The SDST has since been used onmany other space missions such as theMars Science Laboratory (the Mars roverCuriosity).[11]
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 atime-of-flight mass spectrometer.
The MICAS (Miniature Integrated Camera AndSpectrometer) instrument combined visible light imaging with infrared and ultraviolet spectroscopy to determine chemical composition. All channels share a 10 cm (3.9 in) telescope, which uses asilicon 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 comet76P/West–Kohoutek–Ikemura and asteroid3352 McAuliffe.[12] Because of the delayed launch, the targets were changed to asteroid9969 Braille (at the time called 1992 KD) and comet19P/Borrelly, with comet107P/Wilson–Harrington being added following the early success of the mission.[13] It achieved an impaired flyby of Braille and, due to problems with the star tracker, abandoned targeting Wilson–Harrington in order to maintain its flyby of comet19P/Borrelly, which was successful.[13] An August 2002 flyby of asteroid1999 KK1 as another extended mission was considered, but ultimately was not advanced on the basis that the scientific justification was not sufficiently strong when considering risk and cost.[14][15] During the mission, high quality infrared spectra ofMars were also taken.[13][16]
The ion propulsion engine initially failed after 4.5 minutes of operation. However, it was later restored to action and performed excellently. Early in the mission, material ejected during launch vehicle separation caused the closely spaced ion extraction grids to short-circuit. The contamination was eventually cleared, as the material was eroded by electrical arcing, sublimed by outgassing, or simply allowed to drift out. This was achieved by repeatedly restarting the engine in an engine repair mode, arcing across trapped material.[17]
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 thestar 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.[13]
Without a working star tracker, ion thrusting was temporarily suspended. The loss of thrust time forced the cancellation of a flyby past comet107P/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.
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.[18]
The flyby of the asteroid9969 Braille was only a partial success.Deep Space 1 was intended to perform the flyby at 56,000 km/h (35,000 mph) at only 240 m (790 ft) from the asteroid. Due to technical difficulties, including a software crash shortly before approach, the craft instead passed Braille at a distance of 26 km (16 mi). This, plus Braille's loweralbedo, meant that the asteroid was not bright enough for the Autonav to focus the camera in the right direction, and the picture shoot was delayed by almost an hour.[13] The resulting pictures were disappointingly indistinct.
However, the flyby of Comet Borrelly was a great success and returned extremely detailed images of the comet's surface. Such images were of higher resolution than the only previous pictures of a comet --Halley's Comet, taken by theGiotto spacecraft. The PEPE instrument reported that the comet's solar wind interaction was offset from the nucleus. This is believed to be due to emission of jets, which were not distributed evenly across the comet's surface.
Despite having no debris shields, the spacecraft survived the comet passage intact. Once again, the sparse comet jets did not appear to point towards the spacecraft.Deep Space 1 then entered its second extended mission phase, focused on retesting the spacecraft's hardware technologies. The focus of this mission phase was on the ion engine systems. The spacecraft eventually ran out ofhydrazine fuel for its attitude control thrusters. The highly efficient ion thruster had a sufficient amount of propellant left to perform attitude control in addition to main propulsion, thus allowing the mission to continue.[18]
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.[13][16]
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.[18] It remains within the Solar System, in orbit around the Sun.[2]
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