DS1 was immensely successful, the mission being extended several times.
Deep Space 1 (DS1) was the first of a series of technology demonstration probes developed by NASA's New Millennium Program. Although it was planned for the spacecraft to flyby asteroid and cometary targets, its primary mission was to prove innovative new technologies for future spacecraft. Among the technology demonstration equipment were the Miniature Integrated Camera-Spectrometer (MICAS), an instrument combining two visible imaging channels with UV and IR spectrometers. MICAS was used to study the chemical composition, geomorphology, size, spin-state, and atmosphere of the target objects. It also carried the Plasma Experiment for Planetary Exploration (PEPE), an ion and electron spectrometer which would measure the solar wind during cruise, the interaction of the solar wind with target bodies during encounters, and the composition of the cometary coma. DS1 was immensely successful, the mission being extended several times.
Spacecraft and Subsystems
The Deep Space 1 spacecraft was built on an octagonal aluminum frame, 1.5 m high, 1.1 m deep, and 1.1 m wide. Total dimensions with antennae deployed were 2.5 m high, 2.1 m deep, and 1.7 m wide. The probe was powered by batteries and two solar panel "wings" attached to the sides of the frame which spanned 11.75 m when deployed. The solar panels, designated SCARLET II (Solar Concentrator Arrays with Refractive Linear Element Technology) constituted one of the technology tests on the spacecraft. A cylindrical lens concentrated sunlight on a strip of GaInP2/GaAs/Ge photovoltaic cells and acted to protect the cells. Each solar array consisted of 4 160 cm x 113 cm panels. The array furnished 2500 W at 100 volts at the beginning of the mission, and less as the spacecraft moved further from the Sun and the solar cells aged. Communications were via a high gain antenna, two low gain antennae, and a Ka band antenna, all mounted on top of the spacecraft, and a third low gain antenna mounted on the service boom.
Propulsion was provided by a xenon ion engine mounted in the propulsion unit on the bottom of the frame. Total propellant aboard included 81.5 kg of xenon and 31.1 kg of hydrazine for the reaction control system. Of the 81.5 kg of xenon, 73.4 kg was expended by the end of the hyperextended mission in December 2001. The 30 cm diameter engine consisted of an ionization chamber into which xenon gas was injected. Electrons were emitted by a cathode traverse discharge tube and collided with the xenon gas, stripping off electrons and creating positive ions. The ions were accelerated through a 1280 volt grid at to 31.5 km/sec and ejected from the spacecraft as an ion beam, producing 0.09 Newtons (0.02 pounds) of thrust at maximum power (2300 W) and 0.02 N at the minimum operational power of 500 W. The excess electrons were collected and injected into the ion beam to neutralize the electric charge.
Deep Space 1 was the only mission ever to rely on ion propulsion as the primary propulsion. It operated the ion engine for 16,265 hours, far longer than any other mission (using any kind of propulsion) had operated its propulsion system.
Other technologies tested on this mission included a solar concentrator array, autonomous navigation plus two other autonomy experiments, small transponder, Ka-band solid state power amplifier, and experiments in low power electronics, power switching, and multifunctional structures (in which electronics, cabling, and thermal control were integrated into a load bearing element).
Deep Space 1 was successfully launched from pad 17-A at the Cape Canaveral Air Station at 12:08 UT (8:08 a.m. EDT), the first launch under NASA's Med-Lite booster program, on a Delta 7326-9.5 with three strap-on solid propellant rockets. At 13:01 UT the third stage burn put DS1 into its solar orbit trajectory. DS1 separated from the Delta II about 550 km above the Indian Ocean.
Telemetry was received by the NASA Deep Space Network 1 hour, 37 minutes after launch, a 13-minute delay from the expected time. The reason for the delay was radiation (from the Van Allen belts) causing false locks in the star tracker, thus delaying the spacecraft in acquiring its initial attitude after separation.
DS1 was originally scheduled to fly by the asteroid 3352 McAuliffe in 1999 and comet P/West-Kohoutek-Ikemura and the planet Mars in the year 2000 but because of a launch delay these targets were no longer possible. At launch the primary mission was planned to last until 18 September 1999, with the possibility of an extended mission to fly by the comet Borrelly in September 2001. DS1 was to fly by the near-Earth asteroid 1992 KD on 28 July 1999 at a distance of 5 to 10 km.
While the spacecraft accomplished a planetary-class mission, the asteroid encounter was not a required part of the mission. The point was to fly an operational mission in deep space to test advanced, high-risk technologies. The asteroid encounter was only a bonus in the primary mission. The NASA success criteria for the mission did not even include an asteroid encounter. The extended mission had a comet as a target, and DS1 returned the highest quality comet science data ever.
Spectrum Astro manufactured only a portion of the spacecraft. Unlike system contractors, which deliver a completed spacecraft, Spectrum Astro was a partner with JPL. Spectrum did part of the spacecraft and JPL did part, including telecom, reaction control, ion propulsion, software, advanced technologies, integration, and test.
The comet encounters were never a part of the primary mission at all. At launch, the concept was that if the primary mission were successful, and if the technologies worked, an extended mission would be proposed to encounter comet Borrelly. It was not until several months after launch that the extended mission concept was modified to include comet Wilson-Harrington. In the event, the primary mission exceeded its success criteria, and NASA approved the extended mission in August 1999. Then the spacecraft's sole star tracker failed in November 1999 during the extended mission. A 7-month rescue effort succeeded in recovering the capability to operate the spacecraft without the star tracker, but the rescue precluded encountering both comets. The original extended mission target of comet Borrelly was retained as the more scientifically compelling of the 2 comets.
Technology demonstrations included the Miniature Integrated Camera-Spectrometer (MICAS) and the Plasma Experiment for Planetary Exploration (PEPE). DS1's payload consisted of 12 advanced technologies, 2 of which happened to be these instruments. Their purpose was not to make scientific measurements at the encounters, as the encounters were not part of the primary mission requirements. Their purpose in being included on the flight was, as with the other 10 technologies, to "demonstrate the in-space flight operations and quantify the performance" (quote from the success criteria). Both MICAS and PEPE were ambitious new designs for science instruments, with each integrating what normally would be 3 or 4 separate units into one, thus consuming much less power and less mass. DS1 was designed to determine whether and how well these new instruments could work.
Each also performed another function for another advanced technology: MICAS provided the visible images used by the autonomous optical navigation system, and PEPE aided in characterizing the effect of the ion propulsion system on the space environment. The science data at the asteroid were a bonus from their inclusion in the flight. Now in the extended mission, which was quite distinct from the primary and hyperextended mission, the focus was indeed to use these instruments (plus others onboard) to collect science data.
The rescue following the loss of the star tracker was one of the most remarkable rescues in deep space exploration. The star tracker had caused occasional brief problems during the primary mission. (The unit was not one of the new technologies; it was a commercial, off-the-shelf device.) On November 1999, during the extended mission, it stopped operating, depriving the spacecraft of its 3-axis attitude knowledge. As DS1 was the lowest cost interplanetary mission NASA had ever conducted (as measured in same-year dollars, including launch vehicle and mission operations), there was only limited redundancy, and the star tracker did not had a back up. This was such a significant failure that termination of the extended mission was given serious consideration, particularly given that the primary mission had already exceeded its success criteria. Indeed, before launch, the loss of the star tracker was considered catastrophic.
Without the star tracker, the spacecraft was capable only of pointing one axis toward the Sun and slowly spinning around that axis. Nevertheless, the operations team devised a method to point the high-gain antenna (HGA) to Earth using the downlink radio signal measured at the Deep Space Network as an indicator of spacecraft attitude. This was significantly complicated by the spacecraft being 1.7 AU away at the time. Once the HGA was pointed to Earth (first attempted and accomplished on January 14, 2000), a thorough diagnosis of the star tracker could be conducted. It was not recoverable.
Attention then turned to new ways to fly the mission. Over the next 4 months, new operational procedures were devised and new software was developed to use the camera as an attitude sensor in place of the star tracker. This was complicated by the camera having < 1% of the star tracker's field of view, a brighter limiting magnitude, an output rate 100 times slower, and an output format of image files as opposed to the star tracker's quaternions. In 4 months, the new software was designed, developed, tested, and integrated. In the beginning of June 2000, the entire flight software was replaced (this was, in itself, a delicate and complex operation, as the spacecraft did not have a redundant computer). The new system worked right away, restoring the spacecraft's 3-axis attitude knowledge and control. The ion propulsion system was reactivated, and thrusting to reach comet Borrelly resumed on June 28, one week ahead of the ambitious schedule that had been set in January. During the subsequent 18 months of operation, the system worked extremely well, allowing the spacecraft to reach comet Borrelly with few problems.
The spacecraft was not designed for a comet encounter. As just two examples of this, it did not have shielding from the cometary environment, and the attitude control system was not built to track a moving target at finite distance (that is, a target with angular acceleration). As a result of the rescue from the star tracker loss, the camera had to be used both for attitude reference and for science data acquisition at the comet. The rescue consumed more hydrazine (used principally for attitude control) than normal operations would have, and conserving the hydrazine was one of the highest priorities. Expending the hydrazine before the encounter was one of the highest risks. (The spacecraft did not have reaction wheels, so the mission would end within ~ 3 hours of exhausting the hydrazine.) Still, the encounter proceeded flawlessly, exceeding the science measurement goals. Visible images (the first ever to allow geology to be studied on a comet's nucleus) and infrared spectra were collected with MICAS, ion and electron energy and angle spectra and ion composition data were collected with PEPE, and plasma wave and magnetic field measurements were made with the IPS (ion propulsion system) diagnostics sensors (IDS). The IDS was included on the flight as part of the testing of the IPS. The suite of sensors, designed to assess the effect of the IPS on the spacecraft and space environment, was reprogrammed in flight to collect data at the comet.
The encounter was on September 22, 2001. Following the return of data from the comet, the DS1 Extended Mission was complete. Then the DS1 Hyperextended Mission began. It turned attention back to technology testing, taking advantage of the mission's unexpectedly long life. All 9 hardware technologies were exercised, some for the first time in over 2 years, to investigate the effects of aging, radiation, etc. The focus of the hyperextended mission was on the IPS, exploring modes that were too risky or otherwise inappropriate for earlier in the flight. All tests were completed successfully.
On December 18, 2001, with no further technology objectives and no further science objectives, and the hydrazine very low indeed, the spacecraft was commanded into a storage configuration, with the transmitter off but the receiver left on.
Gross mass: 486 kg (1,072 lb).
Unfuelled mass: 374 kg (824 lb).
Height: 2.50 m (8.20 ft).
Thrust: 0.0980 N (0.0220 lbf).
First Launch: 1998.10.24.
Number: 1 .