PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "GIOEPA.TXT file is a digitized version of the instrumentation article appearing in ESA SP-1077 on pages 53-65, 1986" PUBLICATION_DATE = 1986-03-31 END_OBJECT END *****File GIOEPA.TXT \v Instrument Overview =================== \v \v The Giotto Energetic Particle Experiment ---------------------------------------- \v S. McKenna-Lawlor Experimental Physics Department, St. Patrick`s College, Maynooth, Ireland A. Thompson Cosmic Ray Section, Dublin Institute for Advanced Studies, Ireland D. O'Sullivan Cosmic Ray Section, Dublin Institute for Advanced Studies, Ireland E. Kirsch Max Planck Institut fur Aeronomie, Lindau, Germany D. Melrose Department of Theoretical Physics, University of Sydney, Australia K.-P. Wenzel ESA Space Science Department, ESTEC, Noordwijk, The Netherlands \v Abstract -------- \v The Energetic Particle Experiment (EPA) onboard Giotto will measure the energy distribution of electrons, protons and heavier nuclei with E >/= 20 keV during the cruise phase and in the cometary environment during Halley encounter. The detector system consists of three particle telescopes (T1, T2, T3), each incorporating two totally depleted silicon surface barrier layer detectors, and employing both active and passive background shielding. Coincidence logic provides eight different energy channels for T1 and four for each of T2 and T3. EPA has five real-time operating modes with high spatial (octosectoring) and temporal (0.5 s) resolution, as well as four storage modes which provide limited quadro-sectoring and 48 m temporal resolution. In-situ measurements will be made of the flux and spatial distribution of energetic electrons and cometary ions in the Halley environment. Particle acceleration due to magnetic- field-line reconnection processes will, if present, be detected. The occurrence of a solar-particle event during the encounter would provide special opportunities to study the comet/solar-wind interaction and the dust distribution around the comet, while the EPA would act as a reference for onboard instruments that are sensitive to particle radiation. Cruise-phase studies have already provided interplanetary particle flux levels since `switch-on' (22 August 1985) and flare-related particle enhancements were detected in September 1985. \v SCIENTIFIC OBJECTIVES ===================== \v \v 1. Introduction --------------- \v The Giotto mission carries a payload of ten experiments designed to deter- mine the detailed nature of the comet, image its nucleus and elucidate its interaction with the solar wind. The EPA experiment features a particle detector system which operates in the energy region >/= 20 keV and, in this regard, effectively extends the range of the plasma analysers on board Giotto to high energies. The main scientific objectives of EPA are described below. 1.1 Detection of energetic heavy ions of cometary origin Neutral atoms and molecules, sublimating from a cometary nucleus, expand out- wards unrestrained by any significant gravitational attraction at speeds of about 1 km/s. They are then photo-ionised by solar ultraviolet radiation on a characteristic time scale of 10**6 s, producing an ion distribution extending about 10**6 km around the comet. On ionisation, the newly created ions start cycloidal motion in the electric and magnetic fields of the solar wind, thereby gaining energy proportional to their mass (pick-up ions). For typical solar-wind velocities, the maximum energy gain is a few keV per atomic mass unit. Thus, for an ion in the water group (expected to be the predominant species), peak energies of some tens of keV are to be expected. The first in-situ measurements of cometary energetic ions were recently made by the International Cometary Explorer (ICE) during its encounter with Giacobini-Zinner (Wenzel, 1985). The Energetic Particle Anisotropy Spectrometer on ICE (which is a three-telescope solid-state detector system similar to EPA) detected energetic ions (E >/= 65 keV, if one assumes them to belong to the water group) for a period of about three days, corresponding to ~ 5 X 10**6 km, around the closest approach to Comet Giacobini-Zinner. The closest flyby distance was = 8000 km. These `pick-up ions' were strongly beamed and arrived from the solar direction, appearing in bursts of 10 to 30 min duration. The flux levels generally increased with decreasing distance from the comet (Wenzel et al., 1985). Observations made at high spatial (octosectoring) and temporal (0.5 s) resolution by EPA in the environment of Halley are thus particularly well suited to study the energetic ion population associated with this, especially active, comet. 1.2 Magnetic-field-line reconnection processes The similarity between the comet tail of Halley and the magnetotail of the Earth suggests that magnetic-field-line reconnection processes, similar to those occurring during substorms, can be expected (Vasyliunas, 1976). Furthermore, since the size of the comet tail (>/= 10**5 km) and the size of the Earth's magnetotail correspond closely and the dynamic action of the solar wind is the same, we can anticipate the production of particles of similar energies. As shown by Krimigis & Sarris (1979), reconnection processes in the Earth's magnetosphere lead to particle acceleration up to ~ 1 MeV. Such a high-energy component in the cometary particle distribution is detectable by EPA. Also, anisotropies in the distribution of such particles, when taken in conjunction with magnetic-field measurements onboard Giotto, could determine whether the magnetic field lines in the cometary tail are open or closed. 1.3 Measurements of solar particles during the encounter There is a significant probability (Richter, 1983) that an energetic proton event will be in progress at the time of Halley encounter. This expectation is based on solar-particle data observed by the Helios Plasma Experiment and aboard IMP-7/8 during the (previous) deepest minimum of solar activity ever observed, as well as on solar records covering the years 1963-65 contained in the Catalog of Solar Particle Events (for details see McKenna-Lawlor et al., 1983a). Solar-particle background measurements made by EPA can thus act as a reference for onboard components that are sensitive to particle radiation, such as channeltrons, channel plates and charge-coupled devices. It should be noted that Earth satellites or other spacecraft would not measure the relevant fluxes since these show strong variations with heliographic longitude. If a solar-particle event should indeed be in progress during the encounter, the comet/solar-wind interaction process would lead to a deformation of the interplanetary magnetic field and therefore to a deflection of low-energy solar particles (Ip, 198l; Schmidt & Wegmann, 1981). Sector measurements made by EPA's Telescope 2 and Telescope 3 (see Section 2.1) would identify such deflected particles and therefore provide remote sensing of the cometary bow shock and of the contact surface. Furthermore, on the basis of current estimated dust and gas production rates for Comet Halley, it is expected that the absorption of solar electrons with E> 30 keV and protons with E > 100 keV will set in at distances of /= 20 keV. Telescope 1 is oriented at 45deg to the spin axis of the spacecraft and looks backward with respect to Giotto's flight direction, whereas the other two telescopes are oriented at 135deg to the spin axis and view in the direction of the comet. EPA detects energetic ionizing particles by means of sets of solid state detectors so constructed that they effectively form telescopes pointing in distinct directions. All three telescopes have the same nominal geometric factor and similar discriminator thresholds in complementary channels. However, Telescope 2 is covered by an aluminised plastic foil which absorbs low-energy protons with E up to ~350 keV while permitting electrons with E >/= 20 keV to penetrate the foil. The count-rate differences of Telescope 3 and Telescope 2 thus allow ions and electrons to be distinguished, following the method developed by Anderson et al. (1978). 2.2 The detector system Each telescope uses two totally depleted, silicon surface barrier layer detectors (Table 1). The front detectors of Telescopes 1 and 3 are coated on one side with 20 micro g/cm**2 aluminium and on the other with 40 micro g/cm**2 of gold. The aluminium surface faces space. The front detector of Telescope 2 is coated with 60 micro g/cm**2 of aluminium and with an aluminised plastic foil to a total of 560 micro g/cm**2 to permit implementation of the Anderson method mentioned above. The half opening angle of each telescope is 15deg. \v ------------------------------------------------------------------------------- Table 1. Characteristics of silicon detector elements in each telescope Absorber Area used Thickness Thickness Depletion Shape (cm**2) (micro m) (micro g/cm**2) Voltage (V) ------------------------------------------------------------------------------- T1 A 0.384 100 20 Al 30 Circular 40 Au B 1.35 200 20.5 Al 60 Circular 40.0 Au ------------------------------------------------------------------------------- T2 A 0.384 100 60 Al 30 Circular +500 foil 40 Au B 1.26 200 20 Al 60 Circular 40 Au ------------------------------------------------------------------------------- T3 A 0.384 100 20 Al 30 Circular 40 Au B 1.29 201 20.5 Al 60 Circular 40.0 Au ------------------------------------------------------------------------------- \v The active areas of the front and back detectors are 0.384 cm**2 and l .3 cm**2 respectively, as defined by the mechanical collimator. Thus, all channels that use the anticoincidence of the back detector are partly actively shielded. The instrument is also passively shielded from galactic and solar cosmic rays. The shielding penetration thresholds are >/= 130 MeV for particles with Z >/= 2, ~ 30 MeV for protons and ~ 2.0 MeV for electrons. The energy channels and the corresponding discriminator logic combinations of the three telescopes are listed in Table 2a. The low-energy threshold of ~ 20 keV for electrons is essentially determined by the detector noise. The geometric factor of each telescope for isotropic radiation is 8.1 X 10**-2 cm**2 sr for all channels except 6 and 8, which record penetrating galactic and solar cosmic rays. The geometric factor (Daly (1995)) can be derived by considering the detection area as a function of the input direction A(theta) to be integrated over all directions (theta, phi), where theta is the angle to the central axis of the collimation system, and phi is the azimuth angle about that axis. The system is symmetric about phi. The energy-loss diagram for the front and back detectors, as well as the discriminator thresholds for protons, are displayed in Figure 2 from McKenna-Lawlor et al. (1986). \v ELECTRONICS =========== \v 2.3 Analogue electronics and coincidence logic According to a simplified block diagram of the EPA instrument, the front and back detectors are fully depleted by the application of +30 V and +60 V, respectively. The detector signals are then amplified, following charge-to- voltage conversion, in a hybrid pulse amplifier with baseline restorer. The front detectors of Telescopes 1 and 3 are alternately switched after the charge-sensitive amplifier every 0.5 s (using a tunnel diode switch) to the same pulse amplifier and discriminator (A1 to A5) chain. After each 0.5 s switching, a dead time of 250 micro s is introduced to avoid false pulses. The front detector of Telescope 2 has a separate amplifier chain with four discriminators. The three back detectors of the three telescopes are connected in parallel to an amplifier chain with two discriminators, B1 and B2. The discriminator B1, switches at 80-85 keV and B2 at 950 keV energy loss. The output signals of the discriminators are normalised and then fed into the coincidence logic. The coincidence resolution time is 1.5 micro s. The resultant channels are given in Table 2a. 2.4 Digital electronics The digital electronics contain an 1802 microprocessor, which compresses 19 bit counts quasi-logarithmically to 8 bit words. The Giotto spacecraft has three different telemetry formats; F1 (46 kbit/s), F2 (46 kbit/s) and F3 (5 kbit/s). For all three formats, the bit rate of the EPA is 180 bit/s. When F1 and F2 have reduced bit rates of 23 kbit/s, however, the EPA has a reduced telemetry rate of 90 bit/s. \v ------------------------------------------------------------------------------- Table 2a. EPA channel specification and discriminator logic Telescope 1 Ch. 1. 29-46 keV FWHM p,e A1 A2 B1 Ch. 2. 44-77 keV FWHM p,e A2 A3 B1 Ch. 3. 78-215 keV FWHM p,e A3 B1 A4 Ch. 4. 0.217-3.5 MeV p, alpha A4 A5 B1 Ch. 5. 4.5-20.0 MeV p A4 A5 B2 Ch. 6. 20-50 MeV p A4 B1 B2 A5 Ch. 7. 3.5-12.5 MeV alpha A5 B1 Ch. 8. e > 18OkeV e A1 A4 B1 B2 p > 50MeV p Telescope 2 (with foil) Ch. 1. 20-30 keV e A1 A2 B1 Ch. 2. 30-60 keV e A2 A3 B1 Ch. 3. 60-150keV e A3 B1 A4 Ch. 4. 0.35-3.5 MeV p A4 B1 Telescope 3 (open) Ch. 1. 26-44 keV FWHM p,e A1 A2 B1 Ch. 2. 45-76 keV FWHM p,e A2 A3 B1 Ch. 3. 78-213 keV FWHM p,e A3 B1 A4 Ch. 4. 0.22-3.5 MeV p, alpha A4 A5 B1 ------------------------------------------------------------------------------- Note: Telescope 3 has the option of a further four channels corresponding to channels 5 to 8 of Telescope 1. This option is used in operating modes 3 and 7. \v \v ------------------------------------------------------------------------------- Table 2b. EPA channel threshold for heavy ions Telescope 1 Argon+ or Argon++ Ch. 1. 92-156 keV Measured with Ar+ Ch. 2. 127-221 keV Measured with Ar+ Ch. 3. 206-462 keV Measured with Ar++ Ch. 4. 0.46-3.5 MeV Measured with Ar++ Telescope 3 Argon++ Ch. 1. 90-162 keV Ch. 2. 132-220 keV Ch. 3. 200-438 keV Ch. 4. 0.44-3.5 MeV Telescope 3 H2O+ Ch. 1. 78-115 keV Ch. 2. 97-145 keV Ch. 3. 144-270 keV ------------------------------------------------------------------------------- \v During the cruise phase of Giotto, telemetry contact with the ground station is not continuously available. In order to fulfil the scientific objectives of the experiment, cruise-phase storage modes as well as real-time operation modes have been provided. In the storage modes, the integration time for particle fluxes is 48 min and the data are stored in a 64 kbit RAM experiment memory (storage capacity 13.6 days) for transmission to ground during spacecraft telemetry contact. Problems introduced by the Sun-sensitivity of the front detectors of Telescope 1 and Telescope 3 (as described above, Telescope 2 is covered by a foil), combined with the varying solar aspect angle during the cruise phase, are overcome by the availability of a variety of real-time and storage operation modes, which allow switching by multiplexer from light-disturbed to undisturbed telescopes at different times during the mission. During the encounter phase, the solar aspect angle will be 107.2deg and this allows us to operate all three telescopes simultaneously (see Section 6). \v ------------------------------------------------------------------------------- Table 3. Modes and telescope combinations Real-time modes Mode 1 T1 T2 T3 Mode 2 T1 T2 T3 Mode 3* T1 T2 T3 Mode 4 T1 T2 T3 Mode 5 T1 T2 T3 Storage modes Mode 6 T1 T2 T3 Mode 7* T1 T2 T3 Mode 8 T1 T2 T3 Mode 9 T1 T2 T3 Other modes Mode 10 Dump memory Mode 14 Fast memory test ------------------------------------------------------------------------------- * In Mode 3 and Mode 7, eight energy channels are realised for T3. \v 2.5 DC-DC converter The DC-DC converter is connected to the +26.9 V power line of the spacecraft and uses a synchronisation signal of 62.0 kHz. An oscillator stage generates a 62 kHz voltage, which is then transformed and rectified to several secondary voltages: +6 V for the analogue electronics; +5 V for the digital electronics; and +30 V and +60 V for the front and back detectors. The sum of the secondary currents is measured as a voltage drop across a resistor, amplified and read into a housekeeping channel to indicate the functional status of the instrument. \v OPERATIONAL MODES ================= \v 2.6 Telemetry commands, operation modes and the electrical interfacing A total of five real-time modes, four storage modes, one memory dump mode and one mode for a fast memory test have been implemented (Table 3). False commands lead automatically to mode 5, which is the encounter mode of the experiment. The telemetry commands are summarised in Table 4. \v ------------------------------------------------------------------------------- Table 4. Telemetry commands MSB LSB -------------------------------------- Command description Z885 0 to 7 8 9 10 11 12 13 14 15 ---------------------------------------------------------------- Select Mode x x x x x x Mode 1 Real time 0 0 0 0 0 1 Mode 2 Real time 0 0 0 0 1 0 Mode 3 Real time 0 0 0 0 1 1 Mode 4 Real time 0 0 0 1 0 0 Mode 5 Real time 0 0 0 1 0 1 Mode 6 Storage 0 0 0 1 1 0 Mode 7 Storage 0 0 0 1 1 1 Mode 8 Storage 0 0 1 0 0 0 Mode 9 Storage 0 0 1 0 0 1 ---------------------------------------------------------------- Mode 10 dump memory 0 0 1 0 1 0 ---------------------------------------------------------------- Mode 14 mem. test 0 0 1 1 1 0 ---------------------------------------------------------------- Microprocessor reset x Reset 1 No reset 0 ------------------------------------------------------------------------------- Note 1: Bits 0-7 are ignored by the EPA Note 2: Any bit pattern not specified above will switch the EPA experiment unit into mode 5. \v The digital data start generally with the header word of the EPA experiment. Then follow two bytes for the spin counter, one status byte and up to sixteen quasi-logarithmically compressed words of science data. The data frame consists of twenty 8 bit words. An onboard 16 bit register is used as a spin counter and allows us to identify the 48 min intervals of our storage data. During the cruise phase, this counter shows an overflow approximately every three days (2**16 X 4 s). After each data dump, a real-time mode is switched on for a few minutes and this allows a proper time correlation of the stored data to be established (since then the spin counter and the OCOE time are read simul- taneously). The most important timing signals are the Sun reference pulse, which is received every 4.0 s, the spin segment clock, and the 48 min signal. Table 5 describes the overall electrical interface between the spacecraft and the EPA instrument. \v ------------------------------------------------------------------------------- Table 5. Interface summary Parameter Signal type --------------------------------------------------- Power Experiment main bus voltage Thermistor Spacecraft powered Telemetry data Serial digital Science Serial digital Housekeeping Analogue Single ended Housekeeping --------------------------------------------------- Command Memory load address Memory load clock Memory load data --------------------------------------------------- Timing signals Sun reference pulse Spin segment clock (2**14 bit/spin) Spacecraft time (48 min low/high) Telemetry mode status (2 bit) --------------------------------------------------- Special signals Converter synchronisation ------------------------------------------------------------------------------- \v \v SOFTWARE ======== \v 2.7 Onboard software The data-handling by the onboard software is spin synchronised. The spin period of 4 s is divided into four quadrants with the numbers 0,1,2,3. Each quadrant is subdivided into an odd and even sector. Thus, the real-time modes 1,2,3 and 4 have eight sectors/spin (that is 0.5 s for each sector) for each energy channel. Mode 5 has four sectors per spin. It counts in all three telescopes, alternating between T1 and (T2+T3) for the odd and even sectors, respectively. When a reduced telemetry rate (90 bit/s) is used during real-time measurements, only the data quadrants 0 and 2 will be transmitted. Due to the internal data- handling process, the real-time data are delayed by 2 s (half-spin) before their transmission to the ground station. For storage modes 6 and 7, only quadro-sectoring of one energy channel was possible. Mode 8 counts omni- directionally in Telescopes 2 and 3, while mode 9 counts omni-directionally in all three telescopes. The output of the coincidence channels is sampled in 8 bit counters which are read eight times per second by the 1802 microprocessor. Thus, average count rates up to 2040 s**-1 in each channel can be handled without a counter overflow. The counts are integrated and stored temporarily in the 64 kbit RAM by the microprocessor using 19 bit frames (storage capacity 524287 per channel). At the end of the measuring interval the stored count rates are quasi-logarithmically compressed to 8 bit words, which are then either transmitted to the ground station when real-time modes are used, or stored in the 64 kbit RAM when a storage mode is operating. A 19 bit frame shows an overflow during a 48 min interval when an average count rate >/= 182 s**-1 is detected in the relevant channel. The onboard 64 kbit RAM allows storage of 65535/(20 X 8) intervals which corresponds to approximately 13.6 days. The time to read out the memory is 65535/180 s ~6 min (extending to ~12 min when only a reduced telemetry rate of 90 bit/s is available). New telemetry commands are executed by the EPA instrument after reception of the next Sun reference pulse. \v PLATFORM MOUNTING ================= \v \v 3. Mechanical Design -------------------- \v The six electronic boards are mounted in a 140 X 60 X 95 mm**3 aluminium box. The three telescopes are mounted on a separate aluminium platform. A gold- coated GFK flange (0.2 mm thick) connects the box to the telescope platform. It was necessary to connect the electronic box and the telescope platform to secondary ground and to isolate the four feet of the box from the spacecraft experiment platform using Vespel washers to obviate electrical interference. To protect the charge-sensitive amplifiers from disturbances by high-frequency magnetic fields (0.5-2 MHz region) produced by the spacecraft telemetry system, the whole experiment was enclosed in a Faraday cage of copper-coated aluminium, isolated from the main experiment platform by 2 mm thick glass-fibre washers. For the same reason, the telescope platform was covered by a protective shield. The semiconductor detectors themselves are laterally shielded by ~4 mm of aluminium. A view of the instrument complete with shield and Faraday cage and its location on the spacecraft are shown in Figure 5 and 6 in McKenna-Lawlor et al. (1986). \v SENSIVITY DESCRIPTION ===================== \v \v 4. Thermal Design ----------------- \v The aim of the thermal design is to keep the detector elements within the temperature range -10degC to 0degC during the cruise and encounter phases of the mission in order to minimise thermal noise (the spacecraft will pass maximum hot phase, solar constant ~ 2600 W/m^2, around day 180 of the mission). The telescope platform surface (~ 120 cm**2) is coated with conductive white paint (PGB-T) which has an absorption/emission ratio of alpha/epsilon = 0.3 and provides radiation cooling during approximately three quarters of the spin period. The temperature of the telescope platform is monitored by a thermistor, which is mounted near Telescopes 2 and 3. The EPA instrument has an internal energy dissipation of 0.7 W. It was therefore necessary to reduce the heat conduction between the box and the telescope platform as far as possible while still ensuring mechanical stability. The gold-coated GFK flange (mentioned above) connecting the box with the telescope platform has a wall thickness of 0.2 mm. Its gold coating (2 X 10**-4 mm thickness) was necessary to provide electrical shielding of the cables between the detectors and the charge-sensitive amplifiers. This flange has a heat conduction of ~ 0.02 W/K. \v CALIBRATION =========== \v \v 5. Pre-flight Calibration ------------------------- \v The Max-Planck accelerators at Lindau were used to calibrate Channels 1 to 4 of Telescopes 1, 2 and 3. In McKenna-Lawlor et al. (1986), the figures 7a-d show examples of the calibration curves for electrons, protons, H2O+ and Ar++ ions. Table 2b lists the derived energy thresholds for heavy ions. Channels 5 to 8 could not be calibrated using the Lindau accelerators and the energy thresholds will be derived from existing information concerning the energy loss of protons and alpha particles in similar silicon detectors. Due to accelerator constraints, the electron channels of Telescopes 2 and 3 were calibrated only with electrons in the range 10-30 keV. Figure 7a (left side) shows the count rates observed in Channels 1 to 3 of Telescope 3; Figure 7a (right side) shows a comparison between counts obtained with the foil- covered Telescope 2 (Channels 1 and 2) and Telescope 3 (Channels 1, 2 and 3). \v 6. Preliminary In-Flight Performance ------------------------------------- \v The `switch-on' of the EPA took place at ESOC on 22 August 1985 and the instru- ment was then tested in all its modes and found to be fully operational. At this time interplanetary conditions were particularly quiet (private communication from World Data Center A) and the particularly low noise counts observed in all three telescopes (which equalled the best bench performance of the instrument) could thus be taken to represent the background levels for the experiment. During the period between 10 October and 16 October 1985 (spanning the first rehearsal) mode 5 (encounter mode) was tested during the switch-on of other onboard instruments with a view to detecting any possible associated interference with the count rates. Nothing unusual was recorded. By mid-October the solar aspect angle had reached ~ 107deg, similar to that which will prevail during the encounter, and T3 was brought into a region of possible disturbance by light impinging on its outer detector (T2, which is oriented at the same angle as T3, is covered with a foil and is not affected). The count rate in Channel 1 of T3 did indeed increase in the sunward sector during this period, but no saturation effects were observed. Thus we can assume that mode 5 operation, which uses all three telescopes, will not be disturbed significantly by sunlight during the encounter. An anomalously high count in the corresponding sector of the lowest energy channel of T1 (which looks backwards with respect to the flight direction) during the same period could be attributed to light reflected from the spacecraft structure. By October 1985, the detector platform of the EPA was at + 13degC, or 5degC less than the experiment platform of the spacecraft (due to the cooling action of the instrument's radiation plate), but still in excess of our specified temperature limits of -10degC to 0degC. This condition was accompanied by an increase in the noise counts in each of the three telescopes by a factor of ~ 2 (excluding the cosmic-ray component). In mid-September the EPA detected the first solar particle events in the cruise phase. These were associated with an increase of up to two orders of magnitude in the count rates. Channel 6 (which is off-scale) counts increased by a factor of about 10. The events were associated with a sequence of at least four minor flares (Table 6) reported by World Data Center A. \v ------------------------------------------------------------------------------- Table 6. Flares reported by World Data Center A in September 1985 Date Duration Remarks ------------------------------------------------------------------------------- 12 September 1985 1735-1740 UT Class C1 Behind limb 13 September 1985 0735-0745 UT Class C1 S14, E81 Region 4694 14 September 1985 0742-0819 UT Class B3.3 Region unknown 15 September 1985 0733-0757 UT Class C1 optical S11, E53 Region 4694 Class C4.3 ------------------------------------------------------------------------------- \v \v 7. Conclusion ------------- \v The EPA instrument has been successfully tested in all nine operational modes and has been collecting cruise-phase data for eight weeks (since `switch-on' on 22 August 1985) at the time of writing. Preliminary results indicate that the objectives of the experiment, listed in Section 1, can be realised, given the excellent performance of the instrument, and it is expected that variations of this lightweight and versatile particle detector system will be eminently suited for future deep-space missions to cometary and planetary targets. In view of the exciting results obtained with the ICE (formerly ISEE-3) particle detector experiment during Giacobini-Zinner Encounter (Wenzel et al., 1985), it is anticipated that particle measurements made by the EPA in the environment of Comet Halley will yield particularly interesting data. Further- more, it is expected that Comet Halley will be detected by the EPA several days in advance of Halley encounter. Acknowledgements The provision of financial support by the Irish National Board for Science and Technology (NBST) is gratefully acknowledged. References Anderson K A, Lin R P, Potter D W & Heetderks H D 1978, An experiment to measure interplanetary and solar electrons, IEEE Trans., GE-16, 153-156. Daly, P W 1995, Private Communication. Ip W-H 1981, Dynamics and chemistry of cometary comae: a pre-Giotto view, in Scientific and Experimental Aspects of the Giotto Mission, ESA SP-169, 79-91. Krimigis S M & Sarris E T 1979, Energetic particle bursts in the Earth's magnetotail, in Dynamics of the Magnetosphere (Ed. S.-I. Akasofu), p. 599, D. Reidel, Hingham, Mass. McKenna-Lawlor S, Thompson A, O'Sullivan D, Kirsch E, Melrose D B & Wenzel K-P 1983a, The detection of energetic cometary and solar particles by the EPONA instrument on the Giotto Mission, Adv. Space Res., 2, 193-201. McKenna-Lawlor S. Thompson A, O'Sullivan D, Kirsch E, Wenzel K-P & Melrose D 1983b, EPONA, an energetic particle detector system for the Giotto Mission to Halley's Comet, Proc. 18th Int. Cosmic-Ray Conf. (Bangalore), 9, 363-366. Mitchell D C & Roelof E C 1980, Thermal iron ions in high speed solar wind streams: detection by the IMP 7/8 energetic particle experiments, Geophys. Res. Lett., 7, 661-664. Richter A K 1983, Private Communication. Schmidt H V & Wegmann R 1981, Plasma flow and magnetic fields in comets, in Scientific and Experimental Aspects of the Giotto Mission, ESA SP-169, 3-7. Vasyliunas V M 1976, An overview of magnetospheric dynamics, in Magnetospheric Particles and Fields (Ed. B.M. McCormac), 99-110, D. Reidel, Hingham, Mass. Wenzel K-P, Sanderson T R, Hynds R J & Cowley S W H 1985, Observations of energetic ions from Comet Giacobini-Zinner, EOS Trans., in press. Wenzel K-P 1985, The ICE Spacecraft's Encounter with Comet Giacobini-Zinner; A first visit to a comet, ESA Bulletin No. 44, November 1985. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "MCKENNAETAL1986" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "DALY1995" END_OBJECT = INSTRUMENT_REFERENCE END_OBJECT = INSTRUMENT END