| MISSION_DESCRIPTION |
The text below is summarized from
the the New Millennium Project Technology Validation Reports for
Deep Space 1 with permission of the web site NASA Responsible
official, C.W. Minning.
Mission Overview
================
The primary goal of the DS1 mission was to validate advanced, high
risk technologies that are important for future space and Earth
science programs. Secondary goals were scientific in nature, and
included obtaining images, spectra and particles and fields
measurements of a near-Earth asteroid and a comet.
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.
DS1 flew by the near-Earth asteroid 9969 Braille (1999 K2) 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 and
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, after which
the spacecraft entered an extended mission phase. Early in this
phase, the commercial star tracker failed, leaving the craft
unable to point its main antenna toward Earth or operate its ion
propulsion system. A two-phase approach allowed recovery of the
mission. First, ground crews devised a new method of pointing the
high-gain antenna at the Earth, so the radio signal received at
the Deep Space Network could be used as an indicator of the
spacecraft attitude. Second, new software was developed to allow
the science camera to perform the duties of the star tracker,
allowing the spacecraft to return to three-axis operation and
continue its mission.
DS1 flew by Comet 19P/Borrelly at 22:30 UT on 22 September 2001 (8
days after the comet's perihelion). The flyby occurred at a
distance of 2171 km with approximately 16.58 km/sec relative
velocity. At the time, 19P/Borrelly was 1.36 AU from the sun and
1.48 AU from the Earth. Three different types of science data
were obtained during the encounter: The miniature integrated
camera and spectrometer (MICAS) obtained both optical (0.5 to 1.0
microns) images, and spectra from 1.3 to 2.6 microns, and the
Plasma Experiment for Planetary Exploration (PEPE) obtained
measurements of the ion and electron energy and ion mass to charge
ratios. The images obtained near closest approach represent the
highest resolution images of a comet's nucleus to date.
Mission Phases
==============
DS1 Mission Timeline
Launch (Cape Canaveral, Florida): 24 Oct 1998
Instrument verification completed: 13 Jul 1999
Asteroid Braille (1992 K2) encounter: 28 Jul 1999
End of primary mission: 18 Sep 1999
Coast period (MICAS observes Mars): 20 Oct 1999
Star tracker failure: 11 Nov 1999
Comet Borrelly encounter: 22 Sep 2001
Deep Space 1 retired: 18 Dec 2001
Launch:
Following launch, several days were spent conducting an evaluation
of the spacecraft, verifying its health and preparing it for
mission operations. Dedicated technology experiments began
within a week of launch. Of course, some technologies were used
as part of regular spacecraft operations, in particular the solar
array, transponder, and AuotNav, but those and all other
technologies also were subjected to in depth characterization
tests. Radiometric determination of the trajectory was combined
with results of the IPS tests to generate and optimize an updated
low-thrust trajectory that was transmitted to the spacecraft.
After verification of its functional capability, AutoNav was tuned
in flight, particularly to account for discrepancies between the
predicted and the actual MICAS images. As the mission
progressed, more reliance was placed on AutoNav, with conventional
navigation used to validate its performance. After ten days of
thrusting, the spacecraft was turned to thrust along the vector
(subject to a variety of constraints) for reaching the encounter
targets for the primary and extended mission.
Cruise 1:
In February 1999, a completely new software load of 4.1 MB was
installed. This new software enabled the testing of four of the
previously excluded technologies (the software package remote
agent was not in this load), upgraded AutoNav (to accommodate
scattered light in the MICAS images), fixed bugs identified after
launch and improved spacecraft operability. To accommodate the
remote agent experiments in May, the flight software was patched
and remote agent software was uploaded. In June, following the
remote agent experiment, the flight software was replaced again.
This last load contained new operational enhancements and upgrades
to a number of systems, including AutoNav upgrades for enhanced
image processing and functions needed to execute encounters.
The thrusting for the primary mission was accomplished in two
major periods. The brief hiatus in the thrust arc was inserted to
allow days for activation and initial testing of PEPE in the
absence of the IPS plasma, and experiments incompatible with the
IPS thrust attitude. The second thrust segment ended on April 27,
1999.
Braille Encounter:
All the technology testing was completed by July 1999. Following
the end of the testing, on July 29, 1999, the DS1 spacecraft
encountered (9969) 1992 KD at 15.5 km/s. As a result, the closest
approach to Braille was 28.3 +/- km rather than the planned 15 km.
The asteroid is believed to be elongated with a mean radius of
roughly 2 km and is the smallest solar system body targeted by
DS1. During the final days of the spacecraft's approach to the
body, AutoNav did lock onto the asteroid but the accuracy was not
high.
Cruise 2:
Following the encounter with Braille, DS1 had months of thrusting
until the primary mission ended on Sept 18, 1999. When DS1 was
launched, the plan for the primary mission incorporated a plan for
an extended mission taking the spacecraft to comet Borrelly. The
extension was approved by NASA in August 1999. Most of the
extended mission would be devoted to IPS thrusting. On Oct 20
1999, a coast period began which lasted through mid-December 1999
during which calibrations of all MICAS channels were conducted.
On November 11, 1999, after all the Mars infrared spectra were
taken, the spacecraft's stellar reference unit (SRU) stopped
reporting attitude data to the spacecraft computer. On June 21,
2000, the IPS thrusting was restarted under routine operations.
Borrelly Encounter:
Following its primary mission, DS1 embarked on an extended mission
devoted to comet science. In November 1999, the spacecraft had
suffered the loss if its stellar reference unit (SRU), its source
of 3-axis attitude knowledge. This was considered to be
catastrophic, but the operations team completed an ambitious two-
phase, 7-month recovery that included the development of new
software and new methods for operating the spacecraft.
One feature of the recovery was to use the visible CCD camera in
the miniature integrated camera/spectrometer (MICAS), one of the
technologies tested during the primary mission, as an attitude
sensor. The problem of navigating to the vicinity of the comet was
different from that of reaching a typical planetary encounter,
because the uncertainty in the comet's ephemeris dominated
navigation errors. From 25 August to 10 hours before the closest
approach to September 22, DS1 conducted 11 imaging sessions
spanning ranges to the comet of 40.3 x 10^6 km to 6 x 10^5 km.
On approach to Borrelly, DS1 viewed the comet near the south
ecliptic pole. The spacecraft's approach of 2171 km was at
22:29:33 UTC on 22 September 2001, with v(inf) = 16.58 km/s. The
encounter took place 1.36 AU from the Sun, 8 days after
perihelion.
Science data were acquired with 3 instrument suites. All were
body- fixed, so pointing required spacecraft maneuvers. MICAS'
1024 x 1024 CCD with 13-micro-rad pixels collected images in the
range of 0.5 to 1.0 micrometer. MICAS also obtained spectra from
1.3 to 2.6 micrometers with a sampling interval of 7 nm. Ion and
electron energy and angle spectra and ion mass/charge measurements
were made with an instrument included on the flight, the plasma
experiment for planetary exploration (PEPE). Over its 2.8pi sr
field of view, PEPE was sensitive between 8 eV and 32 keV, with a
resolution of 5% (energy and mass/charge). Magnetic field and
plasma wave measurements were made with sensors that had been
carried as an assessment of the IPS. These IPS diagnostic sensors
(IDS) measured the effects of the IPS on the spacecraft and space
environment during the primary mission and were reprogrammed in
flight to collect cometary science data.
Cruise 3 (HYPEREXTENDED MISSION):
The return of the data from Borrelly concluded DS1's two-year
extended mission. The spacecraft was undamaged by the encounter
and continued operating after the extended mission.
DS1's hyperextended mission included testing eight of the
technologies onboard, with a focus on the IPS. On 18 December
2001, following the last IPS test and the dumping of some final
data, a command was sent to place the spacecraft in one of its
safe states, now with the downlink off. This last command product
was the 9905th of the mission.
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