Mission Information
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MISSION_NAME |
INTERNATIONAL COMETARY EXPLORER
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MISSION_ALIAS |
INTERNATIONAL SUN-EARTH EXPLOR
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MISSION_START_DATE |
1983-12-22T12:00:00.000Z
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MISSION_STOP_DATE |
N/A (ONGOING)
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MISSION_DESCRIPTION |
Mission Overview
================
The effective launch of ICE took place on 22
December 1983. As the spacecraft distance from
Earth increased, tracking and data acquisition
involved the NASA Deep Space Network (DSN). The
necessity for this involvement is apparent if one
considers that the ISEE-3 radio system was designed
to transmit from the halo orbit at a geocentric
distance of 0.01 AU, whereas the distance to the
spacecraft at cometary encounter will be 0.47 AU.
A major effort required for the ICE mission was the
outfitting of antennas in the DSN to operate at the
ICE frequencies. Current plans are to utilize the
64 m DSN (Goldstone, Madrid, Canberra) and the 300
m dish at Arecibo as the prime station. The
anticipated data rate at encounter will be 1024
bit/s, although 512 bit/s may be used at other
times. The acceptable performance is based on a
bit error rate of 10**-4. There will be additional
coverage by the 64 m station at Usuda, Japan.
Operations outside the month centered on the
encounter date of 11 September 1985 are basically
cruise-science measurements, which will be
discussed in the next section. The ICE spacecraft
will be approaching the aim point on the main
plasma tail axis 10000 km from the nucleus. Some
idea of the spatial scales associated with key
instruments and their sampling times is given below
for the expected data rate of 1024 bit/s.
Instrument Sampling period(s) Spatial resolution (km)
_______________________________________________________________
Magnetometer 1/3 7
Plasma Waves
16 channel E 1 21
8 channel E,B 16 330
Plasma Electrons
2-d distribution 24 500
Energetic Protons 32 660
Radio Waves 56 1200
Plasma Ions 1200 25000
For the sampling period indicated, the 'spatial
resolution' is the distance travelled at the
relative encounter speed of 20.7 km/s. These
dimensions should be compared with the estimated
distance between bow-shock crossings of about 175
000 km and a measured main tail diameter of 5000
km. Expressed in terms of time, we expect the
spacecraft to be inside the bow shock for about 2 h
20 min and in the main plasma tail for about 4 min.
The magnetometer will produce many measurements
during the encounter period and we use it to
illustrate possible scientific product. Current
models of comets do not indicate a major
amplification of the cometary magnetic field over
the solar-wind value. However, major changes in
field-line direction are expected. Well away from
the comet the magnetic field should, on average,
show the Archimedian spiral angle of 135deg or
315deg to the radial appropriate for normal
solar-wind flow. Interior to the bow shock we
expect a different, possibly somewhat chaotic,
orientation tending to the ordered two-lobed
configuration along the axis of the plasma tail.
If the neutral sheet is encountered, a magnetic
reversal should be recorded. The model-dependent
nature of this description must be stressed. For
example, the bow shock may or may not exist. We
should know after 11 September 1985, and the model
will be tested in this and in other respects.
Obviously, we need data from as many different
experiments as possible to complete our model
testing. To enhance the science return from the
encounter, a Guest Investigator Program has been
established by NASA.
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MISSION_OBJECTIVES_SUMMARY |
Mission Objectives Overview
===========================
The third International Sun-Earth Explorer (ISEE-3)
was launched on 12 August 1978 as one element of a
three-spacecraft mission that began in 1977. The
original purpose was to study the solar-wind
interaction with the Earth's magnetosphere. The
spacecraft was maintained in a `halo orbit' about
the libration point, L1, where it monitored the
solar-wind input. It completed four years of
uninterrupted operation at that location. Several
opportunities to use ISEE-3 in an extended mission
phase were available. Among the most attractive
scientifically were exploration of the distant
geotail and an intercept of periodic Comet
Giacobini-Zinner. Either or both of these options
were available. The comet option was constrained
to an intercept of Giacobini-Zinner in September
1985; specifically, an intercept of Comet Halley
was not possible. In order to explore the comet
option, a subcommittee of the ISEE Science Working
Team (SWT) was formed at the request of the ISEE-3
Project Scientist, T. von Rosenvinge, and chaired
by E. Smith. The subcommittee and the SWT as a
whole found the option to be of considerable
scientific interest, and a report entitled
`Intercept of Giacobini-Zinner by ISEE' was issued
in June 1982, and revised in May 1983. An ad hoc
subcommittee of the Space Science Board recommended
that NASA proceed with both the geotail option and
the comet intercept. After an in-house review and
a review of the readiness of the spacecraft to
perform the intercept by the Goddard Space Flight
Center, NASA approved the intercept with Comet
Giacobini-Zinner. The maneuvers necessary to
achieve the trajectory that would send the
spacecraft into the distant geomagnetic tail and to
an intercept of Comet Giacobini-Zinner are not
simple. They are the brainchild of R. Farquhar,
Flight Director for the Project. Basically, five
gravitational encounters with the Moon were
required to change the spacecraft's orbit. The
last encounter was on 22 December 1983 when the
spacecraft made a close swingby passing only 120 km
above the lunar surface. This manoeuvre
effectively 'launched' the spacecraft from the
Earth-Moon system. At the same time, the
spacecraft was renamed the International Cometary
Explorer (ICE) to correspond to its new mission.
|
REFERENCE_DESCRIPTION |
Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', European
Space Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986.
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