Launched on 24 October 1998, the Deep Space mission carried out a flyby of asteroid 9969 Braille, which was selected as the mission's science target. Its mission was extended twice to include an encounter with Comet 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 a partial success, the encounter with the comet retrieved valuable information. Three of twelve technologies on board had to work within a few minutes of separation from the carrier rocket for the mission to continue.
The Deep Space series was continued by the Deep Space 2 probes, which were launched in January 1999 on Mars Polar Lander and were intended to strike the surface of Mars. Deep Space 1 was the first NASA spacecraft to use ion-powered rocketry, in contrast to the traditional chemical-powered rockets.
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 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.
SCARLET concentrating solar arrayEdit
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. 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.
NSTAR ion engineEdit
- Main article: NASA Solar Technology Application Readiness
Template:Multiple image 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 92 millinewtons (0.331 ounce-force) thrust at maximal power (2100 W on DS1), the craft achieved high speeds because ion engines thrust continuously for long periods. The next spacecraft to use NSTAR engines was the Dawn spacecraft, with three redundant units.
Remote Agent (remote intelligent self-repair software) (RAX), developed at NASA Ames Research Center and JPL, 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). EUROPA was used as a ground-based planner for the Mars Exploration Rovers. EUROPA II was used to support the Phoenix Mars Lander and the Mars Science Laboratory. Livingstone2 was flown as an experiment onboard Earth Observing 1, and an F-18 at NASA Dryden Flight Research Center.
Another method for reducing DSN burdens is the Beacon Monitor experiment. During the long cruise periods of the mission, spacecraft operations are essentially suspended. Instead of data, the craft emits a carrier signal on a predetermined frequency. Without data decoding, the carrier can be detected by much simpler ground antennas and receivers. If the spacecraft detects an anomaly, it changes the carrier between four tones, based on urgency. Ground receivers then signal operators to divert DSN resources. This prevents skilled operators and expensive hardware from babysitting an unburdened mission operating nominally. A similar system is used on the New Horizons Pluto probe to keep costs down during its ten-year cruise from Jupiter to Pluto.
The Small Deep Space Transponder (SDST) is a compact and lightweight radio-communications system. Aside from using miniaturized components, the SDST is capable of communicating over the Ka 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.
Once at a target, DS1 senses the particle environment with the PEPE (Plasma Experiment for Planetary Exploration) instrument. It maps the objects with the MICAS (Miniature Integrated Camera And Spectrometer) imaging channel and discerns chemical composition with infrared and ultraviolet channels. All channels share a 10 cm telescope, which uses a silicon-carbide mirror.
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.
It was thought that the ion 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.
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 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.
The flyby of the asteroid 9969 Braille was only a partial success. Deep Space 1 was intended to perform the flyby at 56,000 km/h (Template:Convert/round mph) at only 240 m (Template:Convert/round 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 (Template:Convert/pround mi). This, plus Braille's lower albedo, 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. 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 Halley's Comet taken by the Giotto spacecraft. The PEPE instrument reported that the comet's fields were 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 of hydrazine 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.
Deep Space 1 succeeded in its primary and secondary objectives including flybys of the asteroid Braille and of Comet Borrelly, 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. However, on-board communications remain active in case the craft is needed in the future. It remains within the Solar System, orbiting the Sun.
A proposed alternative end-of-mission plan involved an encounter with the asteroid 1999 KK1 in August 2002. However, cost reasons meant this was not selected.
- the mass of the craft: 486.3 kg (1072 lb 2 oz) (with fuel)
- total cost: US$149.7 million
- development cost: US$94.8 million
- prime contractor: Spectrum Astro, later acquired by General Dynamics, and later sold to Orbital Sciences Corporation
- launch site: Cape Canaveral Air Station, Florida
- launch vehicle: Boeing Delta II model 7326
- maximum power: 2,500 W (of which 2,100 W powers the ion thrust engine)
- project manager: Dr. Marc Rayman
Before launch it was going to visit 76P/West-Kohoutek-Ikemura and 3352 McAuliffe. Because of the delayed launch, this was changed to 1992 KD (named 9969 Braille) and 107P/Wilson-Harrington, (4015 Wilson–Harrington). It achieved an impaired flyby of Braille and then aimed for 19P/Borrelly. 19P/Borrelly flyby was a success and then 1999 K1 was proposed a target, but not approved. During the mission high quality infrared spectra of Mars were also taken.
- ↑ "DS1 Technology Validation Reports". SCARLET Solar Array. Jet Propulsion Laboratory. 2001. http://nmp-techval-reports.jpl.nasa.gov/. Retrieved 2011-07-17.
- ↑ 2.0 2.1 Template:Cite journal
- ↑ http://dawn.jpl.nasa.gov/mission/spacecraft.asp
- ↑ Hamed Jafari (5 February 2007). "Remote Agent Executive for Deep Space 1". NASA. http://ti.arc.nasa.gov/tech/asr/planning-and-scheduling/remote-agent/. Retrieved 2009-04-22.
- ↑ Ron Garret (14 February 2012). "The Remote Agent Experiment: Debugging Code from 60 Million Miles Away". Google Tech Talks. http://www.youtube.com/watch?v=_gZK0tW8EhQ&feature=player_detailpage#t=2371s.
- ↑ Template:Cite video Slides
- ↑ Template:Cite journal
- ↑ 8.0 8.1 Template:Cite journal
- ↑ 9.0 9.1 Template:Cite journal
- ↑ E. Bell, II (5 August 2008). "Deep Space 1 (1998-061ADS1)". NSSDC Master Catalog. NASA - National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1998-061A. Retrieved 2009-04-22.
- ↑ 11.0 11.1 Comet Space Missions
- ↑ 12.0 12.1 Rayman & Varghese - THE DEEP SPACE 1 EXTENDED MISSION (2001)
- ↑ N. Shachtman - End of the Line for NASA Probe (2001) - W.I.R.E.D.
- Deep Space 1 website at the Jet Propulsion Laboratory (JPL)
- Deep Space 1 Mission Profile by NASA's Solar System Exploration
- Remote Agent homepage at NASA Ames Research Center's Intelligent Systems Division
- Deep Space 1 at Encyclopedia Astronautica
- Electric Propulsion at NASA JPL
- Dr Marc Rayman's mission log : Voyage of Deep Space 1 - final entry
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