| MISSION_DESCRIPTION |
The mission overview was paraphrased from A'Hearn, et al. (2005)
[AHEARNETAL2005] with permission from the Deep Impact project.
Mission Overview
================
The goal of the Deep Impact mission is to understand the physical
and chemical properties of a comet as a function of depth below
the surface. To reach this goal, Deep Impact reproduced
the impact of a boulder onto a cometary nucleus at a speed
characteristic of collisions in the asteroid belt. The mission
delivered an Impactor spacecraft of approximately 360 kg
onto the nucleus of 9P/Tempel 1 at a relative speed of 10.2 km/s.
The kinetic energy of the Impactor, about 19 gigajoules,
produced a crater with a diameter between 100 and 250 meters
in about 200 seconds (A'Hearn, et al. (2005) [AHEARNETAL2005A],
Shultz and Ernst (2005) [SCHULTZ&ERNST2005], and
Richardson, et al. (2005) [RICHARDSONETAL2005]).
Initial results of the encounter are discussed by
A'Hearn, et al. (2005) [AHEARNETAL2005A], which estimated
an impact time of 4 July 2005 at about 05:44:36 UTC
(Earth-received time 05:52:02 UTC).
Deep Impact consisted of two spacecraft, launched together
on 12 January 2005, and flew together until one day before
impact on 4 July 4 2005. On July 3, the two spacecraft separated
while on a course to impact comet Tempel 1. The Impactor
immediately went into auto-navigation mode using an algorithm
that ensured that it would impact the comet in an illuminated area.
The Impactor observed the comet with a visible CCD (ITS)
until seconds before the impact. Shortly after separation,
the Flyby spacecraft performed a trajectory correction maneuver
to allow it to pass approximately 500 km below the nucleus,
as seen from the Sun. The Flyby spacecraft recorded the encounter
and the impact with the High Resolution telescope's visible CCD
(HRIV) and infrared imaging spectrometer (HRII) as well as with
the Medium Resolution telescope's visible CCD (MRI).
Deep Impact is the eighth mission in NASA's Discovery Program.
It was proposed and accepted as a partnership between the
University of Maryland, which manages the science and the
outreach, the Jet Propulsion Laboratory, which manages the
hardware development and flight operations, and Ball Aerospace
and Technologies Corporation, which provides the hardware.
The Science Data Center for the mission is located at Cornell
University. The center maintains all data for the mission,
including ground-calibrations, from all instruments accessible
All data are accessible over the Internet to every member of
the Deep Impact science team.
The mission, science objectives, instrumentation, and expected results
are described in a special edition of Space Science Reviews (SSR)
dedicated to the Deep Impact. See A'Hearn, et al. (2005)
[AHEARNETAL2005], Blume (2005) [BLUME2005], Mastrodemos, et al. (2005)
[MASTRODEMOSETAL2005], Hampton, et al. (2005) [HAMPTONETAL2005],
Klaasen, et al. (2005) [KLAASENETAL2005], Belton, et al. (2005)
[BELTONETAL2005], Lisse, et al. (2005) [LISSEETAL2005],
Sunshine, et al. (2005) [SUNSHINEETAL2005], Richardson, et al. (2005)
[RICHARDSONETAL2005], Schultz and Ernst (2005) [SCHULTZ&ERNST2005],
Thomas, et al. (2005) [THOMASETAL2005], and Yeomans, et al. (2005)
[YEOMANSETAL2005], and McFadden, et al. (2005) [MCFADDENETAL2005].
These SSR papers are included on the documentation volume of the
Deep Impact archive.
Plans for the world-wide Earth-based observing campaign for the
mission are described by Meech, et al. (2005) [MEECHETAL2005]
in the SSR edition. McFadden, et al. (2005) [MCFADDENETAL2005]
discuss the Education and Public Outreach component of Deep Impact.
Analysis of TV and flight calibration data and Deep Impact calibration
pipeline are discussed in Klaasen et al. (2006) [KLAASENETAL2006].
This Deep Impact calibration paper is included on the documentation
volume of the Deep Impact archive.
Mission Phases
==============
Information in this section is based on a publication about the
anticipated flight data by Klaasen, et al. (2005) [KLAASENETAL2005].
This section will be updated as flight data are archived into
the PDS.
Although several phases were defined for mission operations,
four general phases are defined for the archive of flight-related
data: thermal-vacuum ground calibrations (TV), 9P cruise, and
9P encounter, and 9P post-encounter cruise.
THERMAL-VACUUM GROUND CALIBRATIONS (TV1-TV5)
--------------------------------------------
Currently, data acquired during TV1 through TV4 are archived
in the PDS. The science team used these data for pre-flight,
calibration analysis. TV5 data is expected to be archived
in 2006.
TV# Instruments Tested Start Time Stop Time
--- -------------------- ---------- ----------
TV1 HRII 2002-06-27 2002-07-02
TV2 HRII, HRIV 2003-08-15 2002-09-03
TV3 ITS 2003-01-16 2003-01-30
TV4 HRII, HRIV, MRI 2003-02-23 2003-03-12
TV5 HRII, HRIV, MRI, ITS 2004-06-30 2004-07-01
9P CRUISE
---------
Mission Phase Start Time : 2005-01-12 (DOY 012)
Mission Phase Stop Time : 2005-04-30 (DOY 120, Impact-65 days)
The 9P cruise phase began at the lift-off of the launch vehicle.
This phase includes checkout of the HRII, HRIV, and MRI instruments
in the first 2-3 days after launch. Science calibrations began
shortly after checkout, then were performed approximately once
every month. The best sets of science calibrations were
acquired during the April, May, and June calibrations and
the post-impact calibration in July. Calibration targets
include the Moon, Earth, stars, nebulae, and galactic clusters.
Comet 9P/Tempel 1 was not imaged for scientific purposes during
this phase. Details of the cruise calibrations are available
in the Deep Impact Calibration paper by Klaasen et al. (2006)
[KLAASENETAL2006].
9P ENCOUNTER
------------
Mission Phase Start Time : 2005-05-01 (DOY 178, Impact-64 days)
Mission Phase Stop Time : 2005-07-13 (DOY 194, Impact+9 days)
Scientific data acquisition began during this phase. On the
approach of Tempel/1, the objectives were to determine
the size of the nucleus, map the albedo, color and spectral
variations of the surface, determine the rotational state of
the nucleus, and monitor the activity of the nucleus. Other
objectives included identifying large-scale structure in the
coma, mapping the evolution of the inner coma over a full
rotation period, and searching for satellites to constrain
the mass of the nucleus (none were found). During approach,
the HRII, HRIV, and MRI instruments acquired data at decreasing
sampling frequencies, and science calibrations were performed
in early May and June.
During approach, the solar phase angle of the nucleus
increased by about 0.5 degree/day, beginning at 28 degrees and
reaching 60 degrees at Impact minus 7 days. About 3 days from
impact the HRIV instrument spatially resolved the nucleus.
The HRII and MRI instruments did not resolve the nucleus until
the day before impact. Due to pointing errors, the HRII
instrument was not imaging the comet until June 20.
About 24 hours before the scheduled impact, the Flyby released
the Impactor at a distance of about 864,000 km from the comet.
The Impactor ITS instrument began acquiring and transmitting
data over an S-band link to the Flyby. The frequency of data
sampling increased as impact approached and the resolution
improved. About 18 hours before impact, a small set of
calibration data (darks and internal stimulator frames) were
acquired for each instrument. The pixel scales of the four
instruments as a function of time before impact were:
Pixel Scale (meters/pixel)
Time ITS HRIV MRI HRII
------- ----- ----- ----- -----
I-20 hr 7200 1480 7350 ~7000
I-1 hr 363 90 453 440
I-2 s 0.1 17 86 86
The last ITS image was taken about 05:44:31 UT with an estimated
pixel scale of 0.26 meters/pixel.
During the impact, the instruments on the Flyby recorded
the development of the crater and start of the ejecta flow.
As impact processes continued, HRII, HRIV, and MRI recorded
data at decreasing sampling rates. At Impact+760 seconds,
the Flyby went into shield mode (SM) to protect the instruments
from dust impacts during closest approach of Tempel 1. Shield
mode continued through I+40 minutes. During the impact event,
pixel scales of the instruments were:
Pixel Scale (meters/pixel)
Time HRIV MRI HRII
------- ------ ------ ------
I-3 s 17 86 86
I+1 s 17 85 86
I+24 s 17 84 83
I+24 s 17 84 83
I+470 s 7 38 39
SM 1.4 7 7
The Flyby remained in shield mode for about 22 minutes, through
closest approach and until the dust-impact hazard zone has been
passed. While in this mode, the spacecraft performed an attitude
maneuver to point its instruments back toward the nucleus. The
HRIV instrument continued to image the impact site for another
12 hours. The MRIV and HRII instruments continued to monitor
the comet for 60 hours, until 6 July 18:00 UT. During this
phase, the pixel scales of the instruments were:
Pixel Scale (meters/pixel)
Time HRIV MRI HRII
-------- ------ ------ ------
SM+31 m 36 ~181 ~190
SM+2 hr 145 725 744
SM+12 hr 871 4354 4370
SM+24 hr n/a 8709 8725
SM+36 hr n/a 13063 13080
SM+48 hr n/a 17418 17435
SM+60 hr n/a 21772 21790
During lookback, the Flyby began transmitting data stored in
buffer memory back to Earth. However, near the end of Tempel 1
imaging, the buffers on one of the processors were not cleared,
so some data were lost. The last science calibration started
about two days after impact and continued until 13 July,
thus concluding the scientific activities of the mission.
9P POST-ENCOUNTER CRUISE
------------------------
Mission Phase Start Time : 2005-05-14 (DOY 194, Impact+9 days)
Mission Phase Stop Time : 2009
Since the Flyby spacecraft and its instruments survived the
encounter with Tempel 1, a trajectory correction maneuver
was performed on July 20, to put the spacecraft into an orbit
for Earth return in late 2007 which favors an extended mission.
On August 9, 2005, the Flyby was put into sleep mode.
On February 10, 2006, an aliveness test was performed on the
spacecraft. The results of the wake-up and pointing activities
indicated it was healthy for an extended mission.
The SPICE SP-kernel providing the trajectory the Flyby
spacecraft extends to 2009. The SP-kernel providing the
ephemeris of Tempel 1 extends through 2050.
Mission Data
============
The following data acquired are being archived at the PDS:
- TV imaging (HRII, HRIV, MRI, ITS)
- Raw science imaging from flight (HRII, HRIV, MRI, ITS)
- Reduced science imaging from flight (HRII, HRIV, MRI, ITS),
initially in physical units of radiance (uncleaned); cleaned,
radiance and I-over-F sets are planned for 2006
- Raw navigation imaging from flight (MRI, ITS)
- Telemetry (5-Hz) from the Attitude Control and Determination
System (ADCS)
- Radio science data from flight
- SPICE data
- Select data from the Earth-based observing campaign
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