INSTRUMENT_HOST_DESC |
Instrument Host Overview
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Planet-A and MS-T5 are identical except for their
scientific payloads. The main spacecraft body is a
cylinder, 140 cm in diameter and 70 cm high. The
spinning spacecraft is about 250 cm high, from the
top of the high- gain antenna dish to the bottom of
the medium-gain antenna. Its outer wall is covered
by solar cells which produce 100 W of power under
optimum conditions.
An equipment platform mounted to a central thrust
tube carries most of the subsystems, including the
mechanically despun, high-gain antenna, two
hydrazine fuel tanks, the thrusters, and the
experiment sensors . A star scanner and a nutation
damper are attached to the thrust tube. Planet-A
and MS-TS weigh 139.5 kg and 138.1 kg,
respectively, including lO kg of hydrazine
propellant in each case. Both spacecraft are
spin-stabilized, with the facility to change the
spin rate . The spin axes of both spacecraft will
be kept perpendicular to the ecliptic plane. The
spin-rate of Planet-A will be changed quite
frequently. It must be reduced, for example, to
0.2 rpm during the UVI imaging operating using an
onboard momentum wheel, while during communication
periods and during solar-wind measurements a
spin-rate of 6.3 rpm is preferable. The
spacecraft/Earth geometry and the data-rate
requirements preclude the use of a single antenna
for the duration of the mission. The antenna
subsystem therefore consists of a high-gain
antenna, a medium-gain antenna as a backup, and a
low-gain antenna for near-Earth operation. The
despun high-gain antenna has an offset- parabolic
reflector with a diameter of 80 cm and a gain of
21.5 dB in uplink and 22.5 dB in downlink
transmission. The communications subsystem
operates in 5-band using a 5 W transmitter.
Planet-A has two data formats: Format-1 provides
Ultra-Violet Imager (UVI) data. Format-2
Solar-Wind Experiment (ESP) data (Table below).
The data rates of both spacecraft are 2048 bit/s
(without coding) in 'high bit rate' and 64 bit/s
(with convolutional coding) in 'low bit rate' mode.
The bit rate used will depend on the communication
distance.
The ground station for the mission has been built
at Usuda, about 170 km northwest of Tokyo. The
station's 64 m diameter dish antenna has a gain of
approximately 63 dB. A 64 bit/s communication link
(convolutionally encoded PCM) is expected to be
possible from 1.1 AU, which will be the comet-Earth
distance during the Planet-A encounter.
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Table. The Planet-A scientific payload
Experiment Mass Power Data rate (bit/s) Principal Investigator
(kg) (W) Format 1/2
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H 1568/0 E. Kaneda, Geophys. Res. lab.,
UVI 7.5 8.9 L 98/0 Faculty of Science, Univ. of
Tokyo
H 0/1408 T. Mukai, Res. Div. Planetary
ESP 4.7 4.9 L 0/88 Science, ISAS, Tokyo
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Format UVI and UVI check H = High bit rate
ESP L = law bit rate
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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.
'Encounters with Comet Halley, The first results', Nature, Volume 321, No.
6067, 15 May 1986.
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