Deep Space 1 is a spacecraft launched on 24 October 1998 as part of NASA's New Millennium program. Its primary goal was the testing of technologies to lower the cost and risk of future missions.
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 impact the surface of Mars.
Among the technologies tested by DS1 were:
- an ion thruster, specifically the NSTAR electrostatic ion thruster
- 'Autonav,' an autonomous navigation system (which can also find imaging targets) which reduces ground intervention
- 'Remote Agent' (remote intelligent self-repair software)(RAX), written in Common Lisp
- SDST (Small, Deep-Space Transponder), a miniaturized radio system
- MICAS (Miniature Integrated Camera And Spectrometer), a smaller, lighter combination of prior instruments
- PEPE (Plasma Experiment for Planetary Exploration), again a combination of what would have been larger instruments
- SCARLET (Solar Concentrator Array of Refractive Linear Element Technologies), a lighter source with high power
- The Beacon Monitor experiment, where the spacecraft sends only a status signal during cruise, reducing cost
Deep Space 1 succeeded in its tasks and also achieved its secondary goals: flybys of the asteroid Braille and of Comet Borrelly, returning valuable science data and stunning pictures. Deep Space 1 was retired on December 18, 2001.
The NSTAR ion thruster, developed at NASA's Glenn Research Center
, achieves a specific impulse
of one to three thousand 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 of thrust at maximum power (about a third of an ounce-force), the craft achieved high speeds because ion engines thrust continuously for long periods. The engine fired for 678 total days, a record for such engines. The next spacecraft to use NSTAR engines is the Dawn Mission
, with three redundant units.
Powering the engine are the SCARLET (Solar Concentrator Array of Refractive Linear Element Technologies) solar arrays, also developed at NASA Glenn. These use linear Fresnel lenses
made of silicone
to concentrate sunlight onto solar cells. Combined with more efficient, dual-junction cells, the SCARLET arrays generate 2.5 kilowatts with less size and weight than conventional arrays.
The Autonav system, developed at NASA's JPL
, 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.
Remote Agent, 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. 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), and a model-based diagnostic system (Livingstone). EUROPA was used as a ground-based planner for the Mars Exploration Rovers
, and EUROPA II is being used to support the Phoenix Lander
and the upcoming Mars Science Laboratory
. Livingstone2 was flown 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 SDST (Small Deep-Space Transponder), as the name implies, is a compact 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
Other, secondary technologies are built in, at the component level, and in the spacecraft built by Spectrum Astro.
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 can cause the closely-spaced ion extraction grids to short. The contamination was eventually cleared, as the material was eroded by arcs, sublimed by outgassing, or simply allowed to drift out. This was achieved by repeatedly restarting the engine, 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 star fields to its internal charts. The mission was saved when the MICAS camera was reprogrammed to stand in for the star tracker. Although MICAS is more sensitive, its field-of-view is an order of magnitude smaller, creating a higher 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, mostly for problems with identifying objects that were not bright enough or were difficult to identify because of the interference of light. Objects within the field generated spurious reflections into the instrument.
The Remote Agent system was presented with three simulated failures on the spacecraft and correctly handled each event. The simulations were: 1) a failed electronics unit, which Remote Agent fixed by reactivating the unit; 2) a failed sensor providing false information, which Remote Agent recognized as unreliable and therefore correctly ignored; and 3) an attitude control thruster (a small engine for controlling the spacecraft's orientation as needed) stuck in the "off" position, which Remote Agent detected and compensated for by switching to a mode that did not depend on that thruster. Overall 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. No usable data was returned.
The flyby of Braille was only a partial success. Deep Space 1 was intended to perform the flyby at 56,000 km/h at only 240 meters 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. 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 DS1 spacecraft survived the comet passage intact. Once again, the sparse comet jets did not appear to point towards the spacecraft. The spacecraft eventually ran out of hydrazine fuel for its attitude control thrusters. Fortunately, the highly efficient ion thruster had a sufficient amount of propellant left to perform attitude control, in addition to its responsibility as main propulsion, thus allowing the mission to continue.
decided not to pursue a further extended mission after the Borrelly encounter, and on December 18
, Deep Space 1 was switched off and left to orbit the Sun.
- the mass of the craft: 486.3 kg (1072 lb 2 oz) (including fuel)
- total cost: $149.7 million
- development cost: $94.8 million
- prime contractor: Spectrum Astro
- launch site: Cape Canaveral Air Station, Florida
- launch vehicle: Boeing Delta II, a 7326-model
- maximum power: 2500 W (of which 2100 W powers the ion thrust engine)
- project manager: Dr. Marc Rayman