#d2f@DDATHD21.BITNET (#D2F) (11/12/85)
Ralf Eberhardt
Technische Hochschule Darmstadt
Hochschulrechenzentrum/Beratung AB
Petersenstrasse 30
6100 Darmstadt
WEST GERMANY
(#d2f%ddathd21.BITNET@wiscvm.wisc.EDU)
SINCE THERE HAVE BEEN QUESTIONS ABOUT ESA'S HALLEY MISSION IN THIS
DIGEST LATELY, HERE IS SOME INFORMATION OUT OF THE "ESA BULLETIN"
(ISS. MAY 84) :
Terminal Navigation for Giotto - the benefits of international Co-
operation (R.E.Muench,Orbit Attitude Division,ESOC,Darmstadt,Germany)
... Giotto is a spin-stabilised spacecraft with a despun high-gain
antenna, pointed continuosly towards the Earth during the cruise and
encounter phases. The spacecraft, which weighs 950 kg at launch, is
equipped with the following instruments for navigational purposes:
- V-slit Sun sensors
- Infrared pencil-beam Earth sensors (for the geostationary transfer
orbit only)
- Star mapper (for the cruise phase only)
- Hydrazine thrusters for attitude and orbit manoeuvres
- Solid-propellant motor for the perigee kick.
... The encounter (with Halley) is planned for a fixed arrival time on
13/14 March 1986, based on ground station availability, and with a
nominal target point several hundred kilometres sunward of the comet
nucleus. For navigational purposes, this aiming point will be defined
in the Giotto target plane, which contains the spacecraft position at
comet encounter, the plane normally being parallel to the spacecraft's
velocity relative to the comet.
For navigational purposes,the scientific instruments onboard can be
classified into three groups. The first group consists of those experi-
ments that could expect their optimal return by impacting the comet nu-
cleus. They are a plasma analyser (electron), a neutral mass-spectro-
meter, a magnetometer, and an optical probe.
The second group requires an optimal flyby at a distance of no more than
500 km on either side of the nucleus with respect to the Sun (impact
would be suitable, though less desirable). This group comprises an
ion mass-spectrometer, a dust impact detector, a dust mass-spectrometer,
an instrument for measuring energetic particles, and a plasma analyser
(fast ion).
The last group contains only one experiment, a multicolour camera. Its
optimal flyby distance is 1000 km on the sunward side of the comet, de-
termined by the flyby velocity (movement of camera mirror) and the size
of the comet's inner coma.
Apart from checkout and several rehearsals, the instruments will only
be switched on during the last four hours before encounter. At encoun-
ter, with a relative velocity between comet and spacecraft of 68 km/s
the disturbances caused by the cometary dust may influence the space-
craft's stability, so that the communications downlink could be lost.
(...)
Under the patronage of the Inter-Agency Consultative Group (IACG),
international cooperation in all areas concerned with comet Halley
is being explored and developed. Here the Japanese Planet-A and
and MS-T5 missions, the Soviet Vega mission and NASA's ICE (formerly
ISEE-3) mission to comet Giacobini-Zinner will try to optimize the
overall scientific return by attempting a collaboration that should
both improve the returns of the individual missions and maximize the
overall scientific return from the missions as a whole. Of particular
interest for Giotto navigation is the earlier flyby of the two Vega
spacecraft.
OUT OF THE SAME 'ESA BULLETIN' COMES THE FOLLOWING TABLE OF KEY
MISSIONS TO HALLEY'S COMET:
AGENCY PROJECT LAUNCH FLYBY-DATE FLYBY-DISTANCE
---------------------------------------------------------------------
ESA GIOTTO JULY 85 13 MARCH 86 500 KM
INTERCOSMOS VEGA-1 DECEMBER 84 6 MARCH 86 10000 KM
VEGA-2 DECEMBER 84 9 MARCH 86 3000 - 10000 KM
ISAS MS-T5 JANUARY 85 MARCH 86 0.1 AU
PLANET-A AUGUST 85 8 MARCH 86 100000 KM
NASA ICE (*)DECEMBER 83 28 MARCH 86 0.21 AU
----------------------------------------------------------------------
(*) Lunar swingby manoeuvre to inject ICE (formerly ISEE-3) into a
heliocentric trajectory to comet Giacobini-Zinner (flyby on
11 September 85, 15000 km on the sunward side)
SINCE ALL THIS INFORMATION IS FROM MAY 1984, I DON'T KNOW IF IT'S
STILL ALL VALID, BUT I TRUST IN ITS RELIABILITY.
--- Ralf Eberhardt