| Department of Planetary Sciences
Lunar and Planetary Laboratory |
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Graduate Program |
Deep Impact Image Sequence Simulations:
Visualizing a Comet Impact & Flyby Mission
by James Richardson and H. Jay Melosh
Contents:
Objectives
As part of the Deep Impact
Discovery mission, the purpose of this project is to simulate the flyby
spacecraft's view of the target comet plus the expansion and behavior
of the impact ejecta plume emanating from that target comet. If all goes as
planned, in July of 2005, a small, 370 kg impactor will be intentionally
collided with comet Tempel 1 at a closing speed of 10.2 km/sec.
In the most likely scenario, this collision will produce a small impact crater
on the surface of the comet (probably a few hundred meters in diameter and
taking a few miniutes to form) and a corresponding ejecta plume which will be
observed by the flyby spacecraft for a period of about 14 minutes following the
impact.
These simulations will assist in the mission planning stages of the mission,
allowing us to develop an optimum image sequence for the very brief time in
which the flyby spacecraft will be able to image the comet, impact crater, and
ejecta plume at close range. Additionally, the ejecta
plume simulations will assist the science team in attempting to determine the mass
of Comet Tempel 1 by observing the behavior of the impact ejecta.
Comet Flyby & Impact Animations
Below are some sample flyby animations, based upon an ephemeris supplied by
Jennie Johannesen of JPL, and a "modified Borelly" comet model developed by
Nick Mastrodemos for the purpose of testing the targeting algorithyms.
These animations are done over a one hour period, from -30
minutes to +30 minutes of the time of impact. One animation shows the flyby from
the viewpoint of the medium resolution instrument, while the other shows the
flyby from the viewpoint of the high resolution instrument. Note that the
actual close-range image sequences for Deep Impact will only include the first
13 1/3 minutes beyond the time of impact, following which the spacecraft
will be placed into a "safe mode" as it passes through the plane of the
comet's orbit (where the majority of the cometary dust lies). The MPEG files
for these animations are below:
Flyby 1
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Flyby 2
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Simulated Image Sequences
Below are some sample simulated image sequences, for both the medium resolution
and high resolution cameras. These initial image sequences were devised by
Kenneth Klaasen of JPL. The sequences run from 1 hour before the time of
impact to 13 1/3 minutes (800 seconds) beyond the time of impact, after which
the spacecraft will be placed into a save orientation for passage through the
plane of the comet's orbit (and highest dust concentrations). These sequences
are available as either a compressed archive file (a GZIP'ed "tarball") or can
be accessed directly via a browser.
Each image represents the full field-of-view of the specified instrument,
scaled in pixel resolution to fit the given display window (indicated by the
View parameter).
A green box around some portion of the image indicates that only the outlined
portion of the CCD array will be stored and transmitted (with the indicated
Size and Field of view). Four images sizes will be possible: 1024x1024
(full-size), 512x512, 256x256, and 128x128. The pitch and yaw indications
are measured for the given instrument, referenced to the spacecraft-nucleus relative
velocity vector.
Flyby 1
Medium Resolution Instrument (MRI)
High Resolution Instrument (HRI)
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Flyby 2
Medium Resolution Instrument (MRI)
High Resolution Instrument (HRI)
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Three Shape Models for use in Image Sequence Simulations
Presented in this section are three possible polygon shape models for use in our image sequence simulations: (1) a simple triaxial ellipsoidal shape model, (2) an Eros-based shape model, and (3) the "modified Borelly" shape model developed by Nick Mastrodemos. All three of these models have been scaled to have an average principal axis radius of 3000 m (3 km), and have a spherical coordinate resolution of 2 degrees (16022 total vertices). The shapes are rendered here using 32040 triagular polygons and a standard Lambertian photometric function.
Triaxial Ellipsoid Shape Model [9.0 x 4.5 x 4.5 km]: (shown above as seen from the +x, +y, and +z axes) This model is mathematically derived. Below are the two files which make up the shape model: The first "vertices" file lists the x, y, z, r, theta, and phi (where theta = 0-2Pi, phi = 0-Pi) coordinates for each vertex in the shape model (in an indexed order), with meters and degrees as the given units. The second "facets" file lists the indices of the vertices used for each polygon (v1, v2, v3), followed by the x, y, z, theta, and phi normalized coordinates for the normal vector to the polygon (note that in the spherical case, r = 1 for all vectors and is not listed).
Eros Based Shape Model [10.9 x 3.2 x 3.9 km]: (shown above as seen from the +x, +y, and +z axes) This model is a scaled version of the publically available shape model for the asteroid Eros produced from NEAR mission laser altimeter measurements. Below are the two files which make up the shape model: The first "vertices" file lists the x, y, z, r, theta, and phi (where theta = 0-2Pi, phi = 0-Pi) coordinates for each vertex in the shape model (in an indexed order), with meters and degrees as the given units. The second "facets" file lists the indices of the vertices used for each polygon (v1, v2, v3), followed by the x, y, z, theta, and phi normalized coordinates for the normal vector to the polygon (note that in the spherical case, r = 1 for all vectors and is not listed).
Borelly Based Shape Model [11.1 x 3.8 x 3.3 km]: (shown above as seen from the +x, +y, and +z axes) This shape model is a modified and extrapolated version of comet Borelly, and has been adapted from vector data provided by Nick Mastrodemos (thanks Nick!). Below are the two files which make up the shape model: The first "vertices" file lists the x, y, z, r, theta, and phi (where theta = 0-2Pi, phi = 0-Pi) coordinates for each vertex in the shape model (in an indexed order), with meters and degrees as the given units. The second "facets" file lists the indices of the vertices used for each polygon (v1, v2, v3), followed by the x, y, z, theta, and phi normalized coordinates for the normal vector to the polygon (note that in the spherical case, r = 1 for all vectors and is not listed).
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Last Modified: August 27, 2002
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