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Mission Details

[Mission Flight Plan | Encounter with Comet Wild 2 | Data Collection | Drop Test | Earth Return]

Encounter Timeline

The encounter of the STARDUST spacecraft with Wild 2 spans a period 50 days before to 50 days after the actual fly-by of the comet. This is divided into five time periods during which various mission activities are planned.

  • Far Encounter: E-50 to E-1 days
  • Near Encounter: E-1 d to E-5 hr
  • Close Encounter: E-5 hr to E+5 hr
  • Closest Encounter: E-360 sec to E+360 sec
  • Post Encounter: E-0 d to E+50 days

Encounter Requirements

  • Collect Dust Particles
  • Images
    • Closest Encounter
      • Transmit Real Time One Image as Near as Possible to Nucleus
        • Image Size is 150x150 pixels
  • CIDA and DFMI - Store Science Data
  • Dynamics Science - Analyze Engineering and Doppler Data


  • Far Encounter
    OPNAV begins at E-50 days.
    • E-50 to E-30 Days
      • Two OPNAV opportunities per week
    • E-30 to E-10 Days
      • One OPNAV opportunity per day
    • E-10 to E-3 Day
      • Three OPNAV opportunities per day
    • E-3 Days to E-12 Hours
      • One OPNAV opportunity per hour.
  • Provide Sufficient Tracking Coverage to Support the Design of TCMs
  • OPNAV opportunity defined as: 25 windowed frames of various exposures except after E-3 days, where it is then reduced to 4 windowed frames.


  • Deploy the Aerogel Collector 9 Days Prior to Close Encounter
  • Perform a Roll About the X-Axis to Maintain Nav Camera Field of View (Pre and Post)
  • Command the Mirror to Maintain the Comet Nucleus Within the Nav Camera Field of View

Navigation Plan


Encounter Geometry


The spacecraft will encounter Wild 2 at 98.5 days past perihelion at 1.86 AU from the Sun when Wild 2 is far from its peak active period and relatively safe for a close flyby. The spacecraft will approach Wild 2 from slightly above its orbital plane.
Orbital Geometry at Closest Encounter, where RS is the orbital plane, R=radial direction, Sun to Wild 2, S=orthogonal to R along Wild 2 velocity direction.

Encounter Phase Sequence of Events

  • L+1691 to L+1841 (E-100 to E+50 Days)
    • Exiting Longest Solar Conjunction (~60 Days) at Start
    • 6 TCMs
    • Optical Navigation
    • One OPNAV opportunity per day
    • Deploy Aerogel Collector
    • CIDA Power During Entire Phase
    • DFMI Power for 30 minutes around closest approach
    • Encounter Training Excerises and Readiness Review
  • Sub-Phases
    • Pre-Far Encounter
      • NAVCAM calibration imaging: geometric and photometric
    • Far Encounter
      • E-50 to E-1 Days
    • Near Encounter
      • E-24 to E-5 Hours
    • Close Encounter
      • E-5 to E+5 Hours
    • Closest Encounter
      • E-4 to E+4 Minutes
    • Post Encounter
      • E+5 Hours to E+14 Day

Far Encounter


Far Encounter Details (E-50 to E-1 days)

  • Nominal Attitude +Z to Sun ±15° Deadband
  • Image Attitude Deadband is ±0.25°
  • Deploy Aerogel ~9 Days Before Encounter
  • HGA Communications
    • Downlink Allocation is 50% Images / 50% Other
      • 25% for Stored Engineering Telemetry and CIDA/DFMI Science Data
      • 25% for Real Time Engineering Telemetry
      • 50% for Images
    • Data Rate is 504 BPS (DSN 34 Meter Antenna)
    • At E-3 Days Use DSN 70 Meter Antenna (15,800 BPS)


  • Data
    • Images (Science, OPNAV)
      • 8 Bit/Pixel Images
      • Windowed and Compressed to Fit Bandwidth
    • CIDA Available for Data Collection

Far Encounter Subphase (E-50 d to E-1 d)
OPNAV will begin at about E-50 d when Wild 2 becomes detectable. The coma will be the focus of the imaging science during this period. Coma images acquired during this period will have resolutions of 32 to 1000 km per pixel. At E-1 d, the coma image begins to fill the FOV of the camera, and the focus of the imaging will be on the finer details.

Near Encounter


  • Navigation Images are 8 Bits/Pixel (Windowed and Uncompressed)
  • Attitude Deadband is ±0.25° (Imaging and communications)
  • Continuous Communications Using HGA and DSN 70 Meter Antenna
  • Telemetry Data Rate is 15,800 BPS
  • Close Encounter Block Loaded at E-24 Hours
  • CIDA Available for Data Collection
  • Final Uplink Contains TCM and Updated Close Encounter Timing
  • After TCM, ACS is in Encounter Mode (±0.3°, 1lb Thrusters Enabled)

Near Encounter Subphase (E-1 d to E-5 hr)
STARDUST enters the terminal navigation phase with increased OPNAV activities. Continuous communication with Earth (70-m stations) will be established. At E-3 d the OPNAV picture rate will be increased to one per hour. All data acquired since the previous TCM (E-2 d) will be processed on the ground as each image is received for image location extraction, orbit determination, and the final TCM computation. We expect to obtain finer details of the coma when we image Wild 2 during this period. The Wild 2 nucleus will still be a pinpoint until the end of this phase when it begins to occupy about a pixel. Images of Wild 2 with resolutions ranging from 6.5 to 32 km per pixel will be obtained during this period.

Close Encounter


Close Encounter Details

  • Data Rate is 15,800 BPS (DSN 70 Meter Antenna)
  • Science
    • Images
      • Images are Hardware Compressed (8 Bits/Pixel)
      • Flexible Number of Image Sets Prior to Centroiding
        • Window
        • S/W Compress
      • All Images Prior to Centroiding Are Downlinked, Not Stored On-Board
    • CIDA and DFMI Data is Stored and Downlinked as Bandwidth is Available
    • Dust Collection Happens
  • Centroiding Starts at E-30 Minutes
    • Image Every 10 Seconds
    • Flight Software Calculates Projected Mirror Position and Commands
    • New Mirror Profile at E-10 Minutes
    • Centroiding Ends at E+8 Minutes


Close Encounter Subphase (E-5 hr to E+5 hr)
This is the core science period of the mission. At E-5 hr the spacecraft will begin to enter the coma (100,000 km from Wild 2) and the nucleus will start to emerge as an extended body in the camera FOV. All comet science will be on with exception of the DFMI at -15 minutes. Continuous tracking of the spacecraft with the 70-m station is planned until the end of this mission subphase. Dust collection will have been enabled with the deployment of the dust collector at E-9 days. The spacecraft dust shield and the collector array will orient perpendicular to the dust stream (spacecraft-comet relative velocity) to protect the spacecraft from the dust hazard while maximizing the collection area. CIDA will provide information on comet particle composition during the fly-through. Data from up to 10,000 CIDA events will be compressed and stored on board. The data volume allocated is about 200 Mbits. Imaging and real-time transmission of data will be made from E-5 hr to E-6 min. At E-6 min, a final black and white picture surrounding the nucleus will be sent in real time. Any images taken after E-6 min will be stored on board. Figure 8 shows details of mission activities occurring from E-6 min to E+6 min. Due to the uncertainty in delivery, the image of the nucleus may spill out of the FOV of the camera beginning at about E-2 min. Although the scanning mirror can compensate for down-track and in-plane errors, only banking the spacecraft (by providing the second axis to the mirror) can correct out-of-plane errors. Because of this, temporary loss of high-gain lock to Earth during the ±6 min of the encounter is expected. The medium gain antenna will take over the critical communications function during this time.

Figure 8. Timeline During Closest Encounter, E-6 min to E+6 min

Closest Encounter


  • Images Are 8 Bits/Pixel
  • 72 Images Stored In Memory
  • No Images Taken During Roll
  • CIDA and DFMI Data is Stored


Post Encounter


  • Stow Aerogel Collector
  • Transmit Science Data
    • Image Data
      • 600 MBits of Image Data
      • Approximately 30 Hours at 15,800 BPS using HGA
    • CIDA Data
      • 100 MBits of Data
    • DFMI Data
      • 16 MBits of Data

Post-Encounter Subphase (E+5 hr to E+50 d)
Post-encounter spacecraft health check, reconstruction of flyby conditions and downlink of recorded data will constitute the activities of this mission phase. DSN tracking similar to cruise-phase mode will resume.



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[Mission Flight Plan | Encounter with Comet Wild 2 | Data Collection | Drop Test | Earth Return]
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