Mission Overview
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Planet-A and MS-T5 were launched separately by M-3SII launchers. The M-3SII launcher is a new three-stage solid-propellant rocket with - a solid kick-stage motor attached. Both spacecraft were injected directly into a heliocentric comet transfer trajectory. Immediately after launch,each spacecraft was tracked for about 8 h per day.
They were be despun from 120 rpm, to about 30 rpm, using the thruster subsystem. The spacecraft's attitude was initially automatically adjusted such that its spin axis was perpendicular to the Sun-spacecraft line. During the subsequent ground contact, the spin rate was further reduced to 6.3 rpm and the spin axis reoriented to be perpendicular to the ecliptic plane. After the first 4-5 d of ranging and accurate orbit determination, a mid-course correction manoeuvre was carried out. During the interplanetary cruise, attitude maintenance operations will have to beperformed at 1Od intervals.

Both spacecraft will make their closest approach to Halley near the time of the comet's post-perihelion crossing of the ecliptic plane. The Planet-A spacecraft will be targeted to pass Halley's nucleus on the sunward side at a distance of 150000 km on 8 March 1986. Solar-wind measurements will be carried out continuously on Planet-A during the cruise, except during the periods of UVI imaging, and this spacecraft will be in contact with the ground station for 7-8 h per day. In this period, during which the spacecraft will be spinning at 6.3 rpm, its bubble memory will be read out, solar-wind measurements made, and commands received from the ground. During the remaining 15 h per day the spacecraft will be spinning at 0.2 rpm and taking images. It takes 5 - 10 min to spin-down and 30 min to spin-up the spacecraft. During the 15 h, six images can be taken, spaced in time, to fill the 1 Mbit bubble memory. At large distances from the Earth, data can be transmitted from the spacecraft at a rate of 64 bit/s. In this mode,each memory read-out will require about 4 h.

Imaging is planned to start in early November 1985, when Halley crosses the ecliptic plane at a heliocentric distance of 0.85 AU. An attempt will be made to find the comet with the camera as soon as possible, despite the large distance from the spacecraft. Imaging will continue at least until mid-April 1986, when the hydrogen corona will no longer be detectable. Halley will then be at a heliocentric distance of 1.39 AU and at the same time will be reaching its closest distance to Earth of 0.42 AU. During Planet-A's journey to Halley, an attempt may also be made to image the corona of Giacobini-Zinner if this comet's hydrogenproduction rate is high enough.