The CONTOUR spacecraft
JHU-APL PRESS KIT
Posted: June 28, 2002
CONTOUR has two operating modes. The cruising spacecraft spins steadily on its main axis and "hibernates" unattended for months at a time, with most systems turned off. For comet encounters and Earth swingbys CONTOUR is 3-axis stabilized and fully powered, its attitude fixed and its dust shield and instruments facing their target.
The Johns Hopkins University Applied Physics Laboratory designed and built the spacecraft, with instrument and component contributions from institutions and companies around the world. CONTOUR inherits much of its design and components from past or operating missions such as NEAR, TIMED, Cassini and Stardust, thus reducing costs and risks.
CONTOUR Remote Imager/Spectrograph
CRISP combines a narrow-angle optical imager with a near-infrared spectrometer. CRISP offers top pixel scales of about 4 meters - sharp enough to pick up surface details slightly larger than an automobile - and has 10 filters for visible color study of the nucleus. The spectrometer, covering wavelengths of 780 to 2,500 nanometers, has a spatial pixel scale about three times that of the imager.
Instead of facing forward, CRISP points out from the side of the spacecraft, so it remains protected by the dust shield. The camera's tracking mirror keeps the nucleus in the field-of-view and guides the spectrometer slit across the surface, building up an infrared compositional map. It obtains its sharpest images just seconds before and after closest approach.
CRISP is CONTOUR's "smartest" instrument. Scientists will load seven different imaging sequences in the camera's computer before each encounter; CRISP waits until the comet appears from behind the dust shield, then selects the appropriate sequence for the comet's location. CRISP's computer will also direct the spacecraft to "roll" if the comet isn't quite in its optimal field of view, and its mirror automatically tracks the nucleus for a full 30 degrees.
CONTOUR Forward Imager
Peeking through an opening in CONTOUR's dust shield, CFI locates and starts taking pictures of the target comet several days before the encounter. The navigation team uses these distant images to guide CONTOUR toward the nucleus, while the science team watches for phenomena in the coma.
As CONTOUR speeds closer to its target, CFI snaps color photos of the nucleus - capturing the movement of gas and dust jets in the inner coma - and images 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 looks at a mirror mounted on the side of a cube. After the mirror is peppered and pocked by particles, the cube rotates and supplies a "fresh" mirror for the next encounter.
Neutral Gas and Ion Mass Spectrometer
NGIMS measures 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 will 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 is a quadrupole mass spectrometer that employs two ion sources, each optimized for a specific set of measurements. Using both sources, NGIMS will rapidly switch between measurements of neutral gas and ambient ions in the coma as CONTOUR zips past the nucleus. NGIMS will 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
A copy of the Cometary and Interstellar Dust Analyzer instrument on the Stardust spacecraft, CIDA analyzes elemental and chemical composition of dust and ice grains in the comet's coma.
The instrument consists of an inlet, target, ion extractor, time-of-flight mass spectrometer and ion detector. Dust particles hit the target (a silver plate) and generate ions, which are detected by a time-offlight mass spectrometer. (Since heavier ions need more time to move through the instrument than lighter ones, the flight times of the ions can 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 will collect data continuously for several hours on either side of closest approach to the comet.
Spacecraft systems and components
CONTOUR uses its high-gain antenna to send data and receive commands when 3-axis stabilized; it uses a low-gain antenna when spinning in Earth orbit and between comet encounters and Earth flybys. In either mode, the spacecraft can receive commands and send data at the same time.
Command and Data Handling
For data, CONTOUR carries two solid-state recorders (one backup) capable of storing up to 5 gigabytes each. Data and telemetry can be downlinked at rates ranging from 11 bps to 85 kilobits per second, depending on CONTOUR's distance from Earth, whether the craft is spinning or 3-axis stabilized, and whether it's communicating through the high-gain or low-gain antennas.
Guidance and Control
CONTOUR has no internal reaction wheels. Operators fire the hydrazine thrusters to point, spin up, spin down or otherwise move the spacecraft. The processor in CONTOUR's primary digital camera (CRISP) also "talks" 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
The non-coherent Doppler system on CONTOUR, however, uses a transceiver in which the uplink and downlink frequencies are independent. The spacecraft uses a simpler transmitter/receiver combination with an on-board oscillator. The frequency of the uplink signal received from Earth is compared to the downlink frequency at the spacecraft, and the results are put into the spacecraft's telemetry. Before performing orbit determination, navigators on Earth use 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 requires an additional processing step relative to coherent transponding, its performance is just as accurate. It also enables simpler, more flexible hardware to be incorporated into highly integrated electronics modules such as those flown on CONTOUR.
Flight Data File
Vehicle: Delta 2 (7425-9.5)
Launch date: July 1, 2002
Launch time: 2:56:14 a.m. EDT (0656:14 GMT)
Launch site: SLC-17A, Cape Canaveral, Florida
Satellite broadcast: GE-2, Transponder 9, C-band
Launch timeline - Chart with times and descriptions of events to occur during the launch.
Launch windows - See the daily launch opportunities for CONTOUR.
Orbit trace - Maps showing the ground track for the launch.
Science goals - The science of CONTOUR aims at a closer look at comet diversity.
Delta 2 rocket - Overview of the Delta 2 7425-model rocket used in this launch.
SLC-17 - The launch complex where Delta rockets fly from Cape Canaveral.
Delta manufacturing - Map of where the parts for Delta 2 rockets are made.
Hardware flow - Illustration of how Delta 2s come together at the Cape.
Delta directory - See our coverage of preview Delta rocket flights.
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