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Contour

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Contour

Status: Operational 2002. First Launch: 2002-07-03. Last Launch: 2002-07-03. Number: 1 . Thrust: 26.77 kN (6,018 lbf). Gross mass: 970 kg (2,130 lb). Unfuelled mass: 497 kg (1,095 lb). Specific impulse: 293 s. Height: 1.80 m (5.90 ft).

CONTOUR was designed to provide the first detailed look at the differences between these primitive building blocks of the solar system, and answer questions about how comets act and evolve. Contour's flexible four-year mission plan included encounters with comets Encke, Nov.12, 2003, and Schwassmann-Wachmann 3, June 19, 2006.

CONTOUR was to examine each comet's nucleus, which scientists believe was a chunk of ice and rock, often just a few kilometers across and hidden from Earth-based telescopes beneath a dusty atmosphere and long tail.

SPACECRAFT
Dimensions: 8-sided main structure; 1.8 meters (6 feet) tall; 2.1 meters (7 feet) wide
Total Weight: 970 kilograms (2,138 pounds)

• Dry spacecraft and instruments: 387 kilograms (853 pounds)
  
• STAR-30 Solid Rocket Motor: 503 kilograms (1,109 pounds)
  
• Hydrazine fuel: 80 kilograms (176 pounds)

MISSION PROFILE
Launch Vehicle: Boeing Delta II Med-Lite (7425)
Launch Site: Cape Canaveral Air Force Station, Fla.
Launch Window: July 1-25, 2002 (6-second daily launch opportunities)
Spacecraft Separation: 63 minutes, 30 seconds after launch
First Acquisition of Signal: 85 minutes after launch (Goldstone DSN station, Calif.)
Injection into Sun-Orbiting Earth-Return Trajectory: Aug. 15, 2002
Comet Encounters: Nov. 12, 2003 (2P/Encke); June 19, 2006 (73P/Schwassmann-Wachmann 3)
Earth Swingby Maneuvers: Aug. 2003, Aug. 2004, Feb. 2005, Feb. 2006
Cost: $159 million

CONTOUR MANAGEMENT
Principal Investigator: Dr. Joseph Veverka, Cornell University, Ithaca, N.Y.
Project Management, Spacecraft Development and Mission Operations: The Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
Navigation and Deep Space Network (DSN) Support: NASA Jet Propulsion Laboratory, Pasadena, Calif.
Science Team: 18 co-investigators from universities, industry and government agencies in the U.S. and Europe

MISSION PROFILE

INDIRECT LAUNCH MODE - CONTOUR was the first mission to use the Indirect Launch Mode, a clever plan to put a spacecraft into an elliptical Earth orbit for several weeks before propelling it toward its destination. This method affords use of a smaller launch vehicle and a longer launch window and provided a valuable chance to monitor the spacecraft while it was close to home. After launch CONTOUR would stay in a highly elliptical Earth orbit, from as low as 200 kilometers out to nearly 115,000 kilometers. Each orbit took 42 hours; CONTOUR would make 26 trips around Earth before the injection maneuver.

On 15 August 2002, when it would be in just the right position for the maneuver injecting it into a Sun-orbiting, Earth-return trajectory. Performed with the STAR-30 solid rocket motor - the motor's only use - the 50-second maneuver would send CONTOUR speeding from Earth at nearly 13 kilometers per second. CONTOUR would be about 225 kilometers above the Indian Ocean when the maneuver began. Throughout its mission, CONTOUR looped around the Sun and back to Earth for several gravity "swings" toward the target comets. These maneuvers changed CONTOUR's orbit and made it possible for CONTOUR to reach more than one comet without a large amount of fuel. During the first Earth swingby, in August 2003, the team would also calibrate the spacecraft's instruments by photographing the moon and "tracking" the Earth. The mission included four Earth swingby maneuvers.

CONTOUR would make the following earth gravity swings:

• Aug. 15, 2003 - Closest Approach to Earth: 58,000 km
• Aug. 14, 2004 - Closest Approach to Earth: 40,180 km
• Feb. 10, 2005 - Closest Approach to Earth: 218,770 km
• Feb. 10, 2006 - Closest Approach to Earth: 30,000 km

CONTOUR would cruise between comet encounters and Earth swingbys in a spin-stabilized "hibernation" mode, designed to help the mission reduce spacecraft operations and Deep Space Network tracking costs. CONTOUR would hibernate for nearly 65 percent of its journey. During four separate cruise periods - ranging from 120 days to 300 days - mission operators would turn off CONTOUR's instruments and most subsystems; only the command receivers, thermostatically controlled heaters and critical core components stay on. The command systems automatically monitored spacecraft status and corrected potential faults. The mission operations team stood down while the science, mission design and navigation teams conducted low-level planning activities. Ground controllers woke the spacecraft by sending "active spin mode" commands 35 days before each Earth swingby. This gave them enough time to track the spacecraft, calibrate the instruments and prepare for the swingby maneuver.

CONTOUR would get its first peek at the target comet several days before each encounter. The nucleus was still thousands of kilometers away - a mere speck against a background of stars - when the CONTOUR Forward Imager began taking pictures the navigation team would use to refine the spacecraft's path toward the comet. CONTOUR would transmit pictures and other encounter data just hours after closest approach.

TIMELINE FOR COMET ENCOUNTERS:

• 60 to 10 days before the encounter: The mission team determined the spacecraft's orbit and check out its systems and instruments.
• 10 days to 12 hours before: CONTOUR would take pictures and makes spectral observations of the coma. Optical navigation images - used to determine the craft's and comet's positions - were taken daily from up to 5 days before, then twice a day thereafter.
• 12 hours before to 12 hours after: CONTOUR was in full encounter mode; all instruments were turned on and filled the spacecraft's data recorders.
• 12 hours to 15 days after encounter: CONTOUR played back its data, sending it to the Mission Operations Center through the Deep Space Network. Five days after the encounter CONTOUR changed its trajectory with a short thruster firing, and the mission team determined the spacecraft's orbit.

• Encke - November 12, 2003 - Distance to sun - 1.08 AU; Distance to earth - 0.27 AU; Flybys speed 28.2 km/sec; Phase angle 12 degrees (The phase angle was the Sun-comet-CONTOUR angle. Zero degrees would mean the Sun was directly behind CONTOUR and the comet nucleus was fully lit; an angle of 180 degrees put the Sun behind the comet and the nucleus in full shadow (from CONTOUR's point of view). Low phase angles were best for viewing larger bodies; fine dust was brightest at high phase angles. )
• SW3 - June 19, 2006 - Distance to sun - 0.96 AU; Distance to earth - 0.32AU; Flybys speed 14.0 km/sec; Phase angle 101 degrees.
• Third target - CONTOUR's Earth-return trajectory made it possible to redirect the spacecraft toward a new comet. For instance, several additional targets were available after the SW3 encounter, including comets 6P/d'Arrest and 46P/Wirtanen. More importantly, CONTOUR's flexibility allowed it a rare opportunity to catch up with a bright, long-period comet that approached the Sun from the Oort Cloud, like Hale-Bopp in 1997. To find suitable candidates as early as possible, CONTOUR supported a worldwide "Comet Watch" program in which amateur and professional astronomers could search for candidate target comets approaching from the fringes of the solar system

• CONTOUR Remote Imager and Spectrograph (CRISP) - Mass: 26.7 kilograms (59 pounds). Power: 45 watts (average). Supplier: The Johns Hopkins University Applied Physics Laboratory, Laurel, Md. CRISP combined a narrow-angle optical imager with a near-infrared spectrometer. CRISP offered top pixel scales of about 4 meters - sharp enough to pick up surface details slightly larger than an automobile - and had 10 filters for visible color study of the nucleus. The spectrometer, covering wavelengths of 780 to 2,500 nanometers, had a spatial pixel scale about three times that of the imager. Instead of facing forward, CRISP pointed out from the side of the spacecraft, so it remained protected by the dust shield. The camera's tracking mirror kept the nucleus in the field-of-view and guided the spectrometer slit across the surface, building up an infrared compositional map. It obtained its sharpest images just seconds before and after closest approach. CRISP was CONTOUR's "smartest" instrument. Scientists would load seven different imaging sequences in the camera's computer before each encounter; CRISP waited until the comet appeared from behind the dust shield, then selected the appropriate sequence for the comet's location. CRISP's computer would also direct the spacecraft to "roll" if the comet wasn't quite in its optimal field of view, and its mirror automatically tracked the nucleus for a full 30 degrees.

• CONTOUR Forward Imager (CFI) - 9.7 kilograms (21 pounds). Power: 9 watts (average). Supplier: The Johns Hopkins University Applied Physics Laboratory. Peeking through an opening in CONTOUR's dust shield, CFI located and started taking pictures of the target comet several days before the encounter. The navigation team used these distant images to guide CONTOUR toward the nucleus, while the science team watched for phenomena in the coma. As CONTOUR sped closer to its target, CFI snapped color photos of the nucleus - capturing the movement of gas and dust jets in the inner coma - and imaged the coma in wavelengths sensitive to major species of ionized gas. Instead of pointing directly at the comet and into the stream of speeding dust, CFI's telescope looked at a mirror mounted on the side of a cube. After the mirror was peppered and pocked by particles, the cube rotated and supplied a "fresh" mirror for the next encounter.

• Neutral Gas and Ion Mass Spectrometer (NGIMS) - Mass: 13.5 kilograms (30 pounds). Power: 36 watts (average). Supplier: NASA Goddard Space Flight Center, Greenbelt, Md. NGIMS measured the abundance of and isotope ratios for many neutral gas and ion species in each comet's coma. Combined with CIDA's dust measurements, NGIMS data would yield key information on the elemental makeup of the nucleus and allow scientists to study the chemical differences between the comets. Tracing its heritage to the Ion and Neutral Mass Spectrometer on the Saturn-bound Cassini spacecraft, NGIMS was a quadrapole mass spectrometer that employed two ion sources, each optimized for a specific set of measurements. Using both sources, NGIMS would rapidly switch between measurements of neutral gas and ambient ions in the coma as CONTOUR zipped past the nucleus. NGIMS would measure the chemical and isotopic composition of neutral and ion species over a range of 1 to 294 atomic mass units.

• Comet Impact Dust Analyzer (CIDA) - Mass: 10.5 kilograms (23 pounds). Power: 10 watts (average). Supplier: von Hoerner & Sulger, GmbH, Schwetzingen, Germany. A copy of the Cometary and Interstellar Dust Analyzer instrument on the Stardust spacecraft, CIDA analyzed elemental and chemical composition of dust and ice grains in the comet's coma. The instrument consisted of an inlet, target, ion extractor, time-of-flight mass spectrometer and ion detector. Dust particles hit the target (a silver plate) and generated ions, which were detected by a time-of flight mass spectrometer. (Since heavier ions needed more time to move through the instrument than lighter ones, the flight times of the ions could be used to calculate their mass.) Detectable sizes range from 1 to several thousand atomic mass units, encompassing the elements and many compounds, including heavy organic molecules. Both CIDA and NGIMS would collect data continuously for several hours on either side of closest approach to the comet.

SPACECRAFT SYSTEMS AND COMPONENTS
Dust Shield - Comet dust particles were like speeding bullets to a spacecraft going 60,000 miles an hour, but CONTOUR had its own bulletproof vest: a 25-centimeter thick, layered shield of Nextel, a dense fabric like that found in firefighters' coats (among other uses). Much like the shield protecting the International Space Station, its separated layers of Nextel shatter incoming dust grains, and a Kevlar backstop absorbed remaining debris.
Electronics - CONTOUR used an APL-developed Integrated Electronics Module (IEM), a space- and weight-saving device that put a spacecraft's core avionics onto small circuit cards in a single box. CONTOUR's IEM contained 10 cards that comprised the command system, data collection and formatting system, data recorder, guidance and control processor, and X-band receiver and transmitter. CONTOUR also carried a backup IEM.

Power - CONTOUR drew power from a body-mounted, 9-panel gallium arsenide (GaAs) solar array. Maximum power depended on solar distance and angle; peak power at 1 astronomical unit (AU) was 670 watts. A 9 ampere-hour super nickel cadmium (NiCd) battery stored backup power in case the solar panels point too far off the Sun. The spacecraft was designed to operate out to 1.3 AU (195 million kilometers) from the Sun.

Propulsion - CONTOUR had a solid rocket motor and a blow-down hydrazine system. In its only use, the STAR-30 solid rocket motor provided the 1,922 meter-per-second change in velocity ("delta-v") CONTOUR needed to blast out of Earth's orbit and enter a heliocentric Earth-return trajectory on Aug. 15, 2002. The hydrazine system, used to maneuver the spacecraft for the remainder of the mission, included 16 thrusters placed in four modules of four thrusters each.

Telecommunications - CONTOUR's transceiver-based X-band communications system included an 18-inch directional high-gain dish antenna, two low-gain antennas and one pancake-beam antenna. The worldwide stations of NASA's Deep Space Network provided contact with the spacecraft after launch. CONTOUR used its high-gain antenna to send data and receive commands when 3-axis stabilized; it used a low-gain antenna when spinning in Earth orbit and between comet encounters and Earth flybys. In either mode, the spacecraft could receive commands and send data at the same time.

Command and Data Handling - CONTOUR's radiation-hardened, high-performance 32-bit Mongoose V processor received "time tagged" commands from the ground about a week (or sooner) before a scheduled maneuver or operation. Commands were normally uploaded at rates of 500 bits per second (bps), though the system could support rates of 7.8 and 125 bps. For data, CONTOUR carried two solid-state recorders (one backup) capable of storing up to 5 gigabytes each. Data and telemetry could be downlinked at rates ranging from 11 bps to 85 kilobits per second, depending on CONTOUR's distance from Earth, whether the craft was spinning or 3-axis stabilized, and whether it's communicating through the high-gain or low-gain antennas.

Guidance and Control - CONTOUR's guidance and control system included an Earth-Sun sensor, an advanced stellar compass (star tracker) and a gyroscope. When CONTOUR was 3-axis stabilized, its Mongoose V flight computer processed location and position information from the sensors to carry out specific Sun-, Earth- or comet-pointing instructions from mission operators. Ephemeris data on the positions of Earth, the Sun and the target comets was uploaded regularly into CONTOUR's flight computer. CONTOUR had no internal reaction wheels. Operators fired the hydrazine thrusters to point, spin up, spin down or otherwise move the spacecraft. The processor in CONTOUR's primary digital camera (CRISP) also "talked" directly to the flight computer during comet encounters, directing the craft to roll (if necessary) to keep the nucleus centered in the camera's tracking mirror.

Non-coherent Doppler Tracking - Deep space missions traditionally used transponders for both communication and navigation. A transponder was a "coherent" system in which the downlink frequency was based on the frequency of the uplink signal from Earth. With such a system, navigators could compare the received downlink frequency to the known transmitted uplink frequency and determine the velocity of the spacecraft (relative to Earth) from the Doppler effect. The non-coherent Doppler system on CONTOUR, however, used a transceiver in which the uplink and downlink frequencies were independent. The spacecraft used a simpler transmitter/receiver combination with an on-board oscillator. The frequency of the uplink signal received from Earth was compared to the downlink frequency at the spacecraft, and the results were put into the spacecraft's telemetry. Before performing orbit determination, navigators on Earth used this telemetered information to convert the downlinked Doppler record into what it would have been had it come from a coherent transponder. While this technique required an additional processing step relative to coherent transponding, its performance was just as accurate. It also enabled simpler, more flexible hardware to be incorporated into highly integrated electronics modules such as those flown on CONTOUR.

Characteristics

Spacecraft delta v: 1,900 m/s (6,200 ft/sec). Electric System: 0.67 average kW.

NASA NSSDC Master Catalog Description

The Comet Nucleus Tour (CONTOUR) spacecraft is presumed lost after numerous attempts at contact. The spacecraft was scheduled to ignite its STAR 30 solid rocket engine on 15 August 2003 at 08:49 UT (4:49 a.m. EDT). This firing was to take CONTOUR out of Earth orbit and put it on a heliocentric trajectory. However, following the scheduled firing time, no further contact was made with the craft. Telescopic surveys were made under the assumption that the firing took place on schedule, and three objects were identified near the expected position of CONTOUR, leading investigators to believe that the firing took place and that these objects were parts of the spacecraft and rocket engine. An investigation board concluded that the most likely cause of the mishap was structural failure of the spacecraft due to plume heating during the solid-rocket motor burn. Alternate possible but less likely causes determined were catastrophic failure of the solid rocket motor, collision with space debris, and loss of dynamic control of the spacecraft.

The Comet Nucleus Tour (CONTOUR) Discovery class mission had as its primary objective close fly-bys of two comet nuclei with the possibility of a fly-by of a third known comet or an as-yet-undiscovered comet. The two comets to be visited were Encke and Schwassmann-Wachmann-3, and the third target was d'Arrest. It was hoped that a new comet would be discovered that would be in the inner solar system between 2006 and 2008, in which case the spacecraft trajectory would have been changed if possible to rendezvous with the new comet. Scientific objectives included imaging the nuclei at resolutions of 4 m, performing spectral mapping of the nuclei at resolutions of 100-200 m, and obtaining detailed compositional data on gas and dust in the near-nucleus environment, with the goal of improving our knowledge of the characteristics of comet nuclei.

Spacecraft and Subsystems

The CONTOUR spacecraft has a total fueled mass of 775 kg, including a Star 30 SRM booster with a mass of 377 kg and 70 kg of hydrazine fuel. Power is provided by a body-mounted solar array designed for operation at distances between 0.75 and 1.5 AU from the Sun. It is three-axis stabilized for encounters and spin-stabilized during cruise mode between encounters. Communications are through a fixed 0.45 m diameter high-gain antenna which will support data rates greater than 100 kbit/sec at encounters. Data and images are stored on two 3.3 Gbit solid-state recorders with a capacity of 600 images. The spacecraft is equipped with four primary science instruments, the Contour Remote Imager/Spectrograph (CRISP), the Contour Aft Imager (CAI), the Dust Analyzer (CIDA), and the Neutral Gas Ion Mass Spectrometer (NGIMS).

Mission Profile

CONTOUR launched on a Delta 7425 (a Delta II Lite launch vehicle with four strap-on solid-rocket boosters and a Star 30 third stage) on 3 July 2002 at 6:47:41 UT (2:47:41 a.m. EDT) into a high-apogee Earth orbit with a period of 5.5 days from Cape Canaveral Air Force Station. Following a series of phasing orbits, the Star 30 solid rocket motor was to have been used to perform an injection maneuver on 15 August 2002 to eject CONTOUR from Earth orbit and put it in a heliocentric trajectory. After the scheduled firing time, contact was lost and has not been regained. It is assumed the firing was at least partially completed. The firing would have put CONTOUR in the proper trajectory for an Earth fly-by in August 2003 followed by an encounter with comet Encke on 12 November 2003 at a distance of 100 to 160 km and a fly-by speed of 28.2 km/sec, 1.07 AU from the Sun and 0.27 AU from Earth. Three more Earth fly-bys were to follow, in August 2004, February 2005, and February 2006. On 18 June 2006 CONTOUR would encounter comet Schwassmann-Wachmann-3 at 14 km/sec, 0.95 AU from the Sun and 0.33 AU from Earth. Two more Earth fly-bys were scheduled in February of 2007 and 2008, and a fly-by of comet d'Arrest was possible on 16 August 2008 at a relative velocity of 11.8 km/sec, 1.35 AU from the Sun and 0.36 AU from Earth. All fly-bys had a planned closest encounter distance of about 100 km and would have occurred near the period of maximum activity for each comet. After the comet Encke encounter, CONTOUR could have been retargeted towards a new comet if one was discovered with the desired characteristics (e.g. active, brighter than absolute magnitude 10, perihelion within 1.5 AU).

Photo Gallery

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Contour Credit: Manufacturer Image

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• Contour - . Payload: Discovery 6. Mass: 1,005 kg (2,215 lb). Nation: USA. Agency: Cornell, NASA. Manufacturer: APL. Program: Discovery series. Class: Comet. Type: Comet probe. Spacecraft: Contour. USAF Sat Cat: 27457 . COSPAR: 2002-034A. Apogee: 108,614 km (67,489 mi). Perigee: 212 km (131 mi). Inclination: 30.60 deg. Period: 2,486.10 min.

  Launch delayed from July 1st. The latest NASA Discovery mission was successfully launched on Jul 3. The CONTOUR (Comet Nucleus Tour) probe, built and operated by the Johns Hopkins University's Applied Physics Laboratory (APL), began its five year mission to explore three comets, using repeated encounters with the earth to modify its orbit in order to reach each target. The first burn of the second stage completed at 0659 UTC putting the spacecraft in a 185 x 197 km x 29.7 deg parking orbit. At 0746 UTC the second stage restarted for a short 4s burn to 185 x 309 km x 29.7 deg, and then separated once the PAM-D (ATK Star 48B) solid third stage was spun up. The 1.5 minute burn of the third stage motor at 0748 UTC put it and CONTOUR in a 90 x 106689 km x 30.5 deg phasing orbit. By July 8 CONTOUR's orbit was 214 x 106686 km x 29.8 deg. CONTOUR stayed in this phasing orbit until August 15, when it was injected into solar orbit using its internal ATK Star 30 solid motor. Flyby of the first target, comet 2P/Encke, was scheduled for Nov 2003.

• Contour Injection Maneuver To Leave Earth's Orbit - . Nation: USA. Spacecraft: Contour.