Mission Overview
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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.