Courtesy of NASA's National Space Science Data Center
Launch Date/Time: 1998-10-24 at 12:08:00 UTC
On-orbit dry mass: 373.7 kg
Nominal Power Output: 2500 W
Mars-crossing near-Earth asteroid 9969 Braille (formerly known as 1992 KD) in July, 1999 and will fly by comet Borrelly in September 2001. As part of the technology demonstrations, the probe carries the Miniature Integrated Camera-Spectrometer (MICAS), an instrument combining two visible imaging channels with UV and IR spectrometers. MICAS is used to study the chemical composition, geomorphology, size, spin-state, and atmosphere of the target objects. It also carries the Plasma Experiment for Planetary Exploration (PEPE), an ion and electron spectrometer which measures the solar wind during cruise, the interaction of the solar wind with target bodies during encounters, and the composition of the cometary coma.
The Deep Space 1 spacecraft is built on an octagonal aluminum frame bus which is 1.1 x 1.1 x 1.5 m in size. With instruments and systems attached, the spacecraft measures 2.5 m high, 2.1 m deep, and 1.7 m wide. The launch mass of the spacecraft is about 486.3 kg, which includes 31.1 kg of hydrazine and 81.5 kg of xenon gas. The probe is powered by batteries and two solar panel "wings" attached to the sides of the frame which span roughly 11.75 m when deployed. The solar panels, designated SCARLET II (Solar Concentrator Arrays with Refractive Linear Element Technology) constitute one of the technology tests on the spacecraft. A cylindrical lens concentrates sunlight on a strip of GaInP2/GaAs/Ge photovoltaic cells and acts to protect the cells. Each solar array consists of four 160 cm x 113 cm panels. The array will furnish 2500 W at 100 volts at the beginning of the mission, and less as the spacecraft moves further from the Sun and as the solar cells age. Communications are via a high-gain antenna, three low-gain antennas, and a Ka-band antenna, all mounted on top of the spacecraft except one low gain antenna mounted on the bottom.
Propulsion is provided by a xenon ion engine mounted in the propulsion unit on the bottom of the frame. The 30 cm diameter engine consists of an ionization chamber into which xenon gas is injected. Electrons are emitted by a cathode traverse discharge tube and collide with the xenon gas, stripping off electrons and creating positive ions. The ions are 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 are collected and injected into the ion beam to neutralize the electric charge. Of the 81.5 kg of xenon, approximately 17 kg were consumed during the primary mission.
Other technologies which will be tested on this mission include 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 are integrated into a load bearing element).
Deep Space 1 was launched from Pad 17-A at the Cape Canaveral Air Station at 12:08 UT (8:08 a.m. EDT), 24 October 1998, the first launch under NASA's Med-Lite booster program, on a Delta 7326-9.5 (a Delta II Lite launch vehicle with three strap-on solid-rocket boosters and a Star 37FM third stage). 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 is not known. All critical spacecraft systems were performing well.
DS1 flew by the near-Earth asteroid 9969 Braille at 04:46 UT (12:46 a.m. EDT) on 29 July 1999 at a distance of about 26 km at approximately 15.5 km/sec relative velocity. A software problem caused the spacecraft to go into a safing mode at approximately 12:00 UT on 28 July, but the problem was solved an the spacecraft returned to normal operations at 18:00 UT. Up to six minor trajectory correction maneuvers were scheduled in the 48 hours prior to the flyby. The spacecraft made its final pre-encounter transmission about 7 hours before closest approach, after which it turned its high-gain antenna away from Earth to point the MICAS camera/spectrometer camera towards the asteroid. The spacecraft had a target-tracking problem and the MICAS instrument was not pointed towards the asteroid as it approached, so no images or spectra were obtained. MICAS turned off about 25 seconds before closest approach at a distance of about 350 km and measurements were taken with the PEPE plasma instrument. The spacecraft then turned after the encounter to obtain images and spectra of the opposite side of the asteroid as it receded from view, but due to the target-tracking problem only two black and white images and a dozen spectra were obtained. The images were taken at 915 and 932 seconds after closest approach from 14,000 km and the spectra were taken about 3 minutes later. The data were transmitted back to Earth over the next few days. The diameter of Braille is estimated at 2.2 km at its longest and 1 km at its shortest. The spectra showed it to be similar to the asteroid Vesta.
The primary mission lasted until 18 September 1999, the spacecraft is now in an extended mission. By the end of 1999 approximately 22 kg of xenon had been used by the ion engine to impart a total delta V of 1300 m/s to the spacecraft. The original plan was to fly by the dormant comet Wilson-Harrington in January 2001 and comet Borrelly in September 2001. The star tracker failed on 11 November 1999 and a new extended mission to fly by comet Borrely (using techniques developed to operate the spacecraft without the star tracker) in September 2001 is now planned. All new technologies on board DS1 were successfully tested during the primary mission.
Deep Space 1 has a total mission cost of $152.3 million comprised of $94.8 million for development, $43.5 million for launch, $10.3 million for operations, and $3.7 million for science.