Mission Overview
    ================
 
      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 be
      performed 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 hydrogen
      production rate is high enough.