The configuration, trajectories, and payloads of a spinning Earth-orbiting satellite designed by ESA for a post-perihelion flythrough (Giotto mission) of Comet Halley are described. Experiments approved for use on two identical three-axis stabilized Venera spacecraft destined to encounter the comet after releasing probes to Venus are listed as well as the instruments to be carried on Japan's Planet-A flyby mission. The main features launch windows are given for each spacecraft

Rahe, J.

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PLANS FOR COMET HALLEY
Jurgen Rahe
Laboratory for Astronomy and Solar Physics
NASA-Goddard Space Flight Center
Greenbelt, MD 20771
1. Introduction
When comet Halley is again near the Sun and Earth in 1985/86, we have the unique opportunity
to measure cometary properties in situ, through special Halley missions flying through the comet
at times of high activity. In Th~e following sections, characteristics of three already approved
missions will briefly be described. The main features of these missions are listed in Table 1
which is based on Friedman (1980) and Reinhard and Dale (1980).
Table 1
Characteristics for Comet Halley Missions
ESA (Giotto) Japan (Planet-A) USSR (Venera)
Launch date
Launch vehicle
Spacecraft mass
Spacecraft type
Communication rate
Encounter date
Encounter speed
Targetted miss distance
lo aiming accuracy
Nucleus position knowledge
Payload mass
July 1985
Ariane
750 kg
Spin
53 kbit/s
13 March 1986
68 km/s
103 km
90 km
500 km
53 kg
August 1985
Impr. Mu-3S
120 kg
Spin/despin
128 bit/s
9 March 1986
70 km/s
105 km
105 km
500 km
10 kg
December 1984
Proton
~ 1000 kg
Three-axis
10 kbit/s
8 March 1986
70-80 km/s
104 km
104 km
500 km
50 kg
2.< The Orbit of Comet Halley
; The comet's orbit was calculated by D. K. Yeomans (1981). This prediction is based on 885
observations, obtained in 1759, 1835-36, and 1909-11. He gives the following set of osculating
orbital elements:
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https://ntrs.nasa.gov/search.jsp?R=19820006151 2020-03-21T10:09:46+00:00Z
Epoch
T
8
e
0)
n
i
1986 Feb.
1986 Feb.
0.587096
0.967267
111P8534
5891531
162?2378
19
9.
AU
.0 (E.T
6613 (E T.)
Figure 1 shows the relative positions of comet Hal ley and the Earth in 1985-86. The comet will
pass perihelion on February 9, 1986, at heliocentric and geocentric distances of r = 0.59 AU and
d = 1.54 AU, respectively. The dates of the comet's closest approach to Earth before and after
perihelion passage are November 27, 1985 (r = 1.5 AU, d = 0.62 AU) and April 11, 1986 (r = 1.3 AU,
d = 0.42 AU), respectively. The comet will cross the ecliptic plane twice, first on November 9,
1985 (r = 1.8 AU, d = 0.9 AU), and again on March 11, 1986 (r = 0.85 AU, d = 1.0 AU).
RELATIVE POSITIONS OF COMET HALLEY AND EARTH 1985-86
210' 150°
120°
JUNE DEC
300'
330° 30°
r = PERIHELION Of COMET HALLEY
E, = POSITION OF EARTH AT PRE-PERIHELION CLOSE APPROACH OF COMET (NOV. 27, 1985)
Ej = POSITION OF EARTH AT POST-PERIHELION CLOSE APPROACH OF COMET (APR. 11, 1986)
O = POSITION OF EARTH AT PERIHELION OF COMET HALLEY (FEB. 9, 1986)
Figure 1. Schematic drawing of Earth and comet Halley's orbit in 1985-86.
Several space agencies have studied flyby or flythrough missions to Comet Hal ley in 1985/86.
A variety of different trajectories and plans is possible and has been discussed in the literature
(e.g., Farquhar and Wooden, 1977; Friedman, 1980). Launch energies for pre- and post-perihelion
encounters are low (C3 = 5 to 20 km2 s-2), and the flyby speeds are approximately 70 km s~l.
The requirement of minimum launch energy demands an encounter of the probe with the comet in the
ecliptic plane, to which Halley's orbit has an inclination of 162°. The launch energy necessary
for a pre-perihelion encounter (about November 9, 1985) is considerably higher than the one for a
post-perihelion encounter (about March 11, 1986). Since in addition, the comet's activity is
expected to be higher after perihelion than before, most attention is being given to a
post-perihelion encounter.
3. ESA's Giotto Mission
The European Space Agency (ESA) will fly a post-perihelion flythrough mission using a
spinning Earth-Orbiting Satellite (Fig 2.; this Figure as well as Figs. 3 and 4 are taken from ESA
Bulletin 24, 1980). It is called the "Giotto" mission. The science instruments have already been
selected "(Tee Table 2). The nominal launch date is July 10, 1985, encounter date is March 13,
278
Table 2
Giotto Payload with Mass Allocation
(as of March 1981)
Experiment Mass
(kg)
Power
(w)
Telemetry
Bps
I
Halley Multicolor camera
Mass and Energy Spectrometer System
10.2 10.5 20,000
for Analysis of the Gaseous Environment
Ion Mass Spectrometer
Particulate Impact Analyzer
Dust Impact Detection System
Plasma Analyzer
Positive Ion Cluster Composition Analyzer
Implanted Ion Analyzer
Halley Optical Probe Experiment
10.
8.
10.
2.
3.
0.
2.
1.
0
2
0
5
6)4
')
0
9
9
11.4
2.8
5.5
1.0
4,184
3,200
6,000
2,000
2,200
368/1,368
CARDIOID
2982
TAR MAPPER \REAR BUMPER SHIELD
Figure 2. The Giotto spacecraft.
279
Launch
10/7
Earth at Halley encounter (post-PH
9/6
Figure 3. Left: Trajectory for Giotto for launch on July 10, 1985, and post-perihelion encounter
on March 13, 1986. Right: Geometry of encounter. The spacecraft trajectory is only
schematically illustrated.
Figure 4. Model of cometary coma and spacecraft trajectory (schematic)
280
1986; encounter speed is 68 km s"1. To protect the spacecraft against the dust particles
emitted by the comet and striking the spacecraft with a relative velocity of 68 km s~', a
special bumper shield will be installed, consisting of a thin (1 mm) front and a somewhat thicker
re'ar sheet that are about 25 cm apart. Since the survival of the spacecraft cannot be guaranteed,
all scientific data will be transmitted in real time. The encounter geometry is illustrated in
Figure 3. Giotto will be launched by an Ariane-2 in tandem configuration during a 15-day nominal
launch in July 1985. It is estimated that an encounter distance of less than 500 km from the
comet's nucleus can be achieved with a 50 percent probability.
i The major spacecraft features are (Reinhard and Dale, 1980): a 1.5 m dish antenna, inclined
and despun; a dual-sheet bumper shield; a solid-propel!ant injection motor; an active attitude and
orbit control system using hydrazine; and a power budget and thermal concept that guarantees 4 h
of active scientific data taking. The design of Giotto is similar to that of existing GEOS
spacecraft. It is spin-stabilized (15 rpm) and will have a total mass of 750 kg at launch and of
430 kg at the time of encounter. The scientific payload will have a total mass of 53 kg.
The spacecraft will enter the H-corona, cross the shock front and contact surface, image the
nucleus, and measure the dust, neutral and ionized particles (Fig. 4). The scientific instruments
will run on power from solar-charged batteries, with a maximum operating period of about 4 hours.
4. Planet-A Mission
After more than 10 years of studies of the Earth's upper atmosphere from sounding rockets, the
first Japanese scientific satellite "Ohsumi" was successfully launched in 1970. "Planet-A" will
be the first spacecraft to study solar system objects besides the Earth. It is planned that the
spacecraft will make measurements of the solar plasma and Venus during its cruise in
interplanetary space and then approach comet Halley on March 9, 1986. The launch is scheduled for
August 1985. The main instruments are listed in Table 3. They are a magnetometer, plasma
analyzer, plasma wave instrument, ultraviolet spectrometer, and ultraviolet imaging instrument.
The encounter speed will be about 70 km/sec, the spacecraft will pass the comet in a distance of
about 100,000 km.
Table 3
Scientific Instruments of Planet-A
1. Magnetometer
2. Plasma Analyzer
3. Plasma Wave Instrument
4. Vacuum Ultraviolet Imaging Instrument
5. Vacuum Ultraviolet Spectrometer
6. Wave Propagation Experiment
5. Venera-Halley Mission
The Soviet mission will use two identical three-axis stabilized spacecraft that are similar to
the Venera 11 and 12 missions. They will be launched in December 1984 and arrive at Venus in June
1985. The encounter distance with Venus is 30,000 km. Each spacecraft will release one probe to
Venus and will then continue to fly to Halley where they will arrive on March 8, 1986. The first
spacecraft will have an encounter distance with Halley of 10,000 km; the second spacecraft might
go as close as 4,000 km, if the first one survives the dust hazard. The spacecraft will have a
fixed antenna pointing to the earth, so that it cannot efficiently be protected against impacting
dust particles. Already approved experiments are listed in the upper part of the table. Each
spacecraft will carry a payload of about 50 kg.
281
Table 4.
Venera-Halley Mission Experiments
1. Approved experiments
a. Camera, narrow field and wide field )
I On Platform
b. UV and visible spectrophotometer J
c. IR spectrometer
d. Dust mass spectrometer
e. Dust counter
f. Plasma ion analyzer
g. Plasma waves analyzer (0.1 - 200 hz)
h. Plasma waves analyzer (100 - 30,000 hz)
i. Magnetometer
2. Complementary list (to be decided in June 1981)
a. H/D ratio by hydrogen cell
b. Neutral mass spectrometer
c. Cometary ions analyzer
d. Solar oscillations
e. Photopolarimeter
f. VLBI transmitter
6. Conclusions
The characteristics of the different missions discussed will undoubtedly be modified, and the
list of the science instrumentation listed in Tables 2, 3 and 4 might also be changed. But all
missions will certainly provide the most important science return during the coming apparition.
Acknowledgements
It is a pleasure to thank Drs. W. I. Axford, J. P. Blamont, L. F. Burlaga, L. D. Friedman and
R. Reinhard for helpful comments.
282
References
Farquhar, R. and Wooden, L. 1977, Opportunities for Ballistic Missions to Hal ley's Comet. NASA
TND 8453.
Friedman, L. D. 1980, Proc. XXXI Congress, Internat. Astronaut. Fed., Tokyo, Japan, in press.
Planet-A Project. 1979, Proc. of Working Group, Inst. of Space and Aeronaut. Sci., Univ. of Tokyo.
Reinhard, T. and Dale, D. 1980, ESA Bull. 24-, 6.
Yeomans, D. K. 1981, The Comet Hal ley Handbook, JPL 400-91, 1/81.
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