***** File SP1.DOC TABLES OF DUST PARTICLE SPATIAL AND MASS DISTRIBUTIONS IN COMET P/HALLEY FROM SP-1 EXPERIMENT ON BOARD VEGA 1 AND VEGA 2 SPACECRAFT Dust particle counter SP-1 The experiment is aimed to obtain the mass-spectrum of cometary dust particles and to estimate their mean density. The data thus obtained should permit acquiring the information about the dust component distribution around the nucleus, including the dust envelope fine structure. The experimental data analysis makes it possible to investigate the mechanisms of dust-particle ejection from the nucleus and the acceleration of particles in the presence of various factors. The instrument is used to record dust particles impacting the detector target and to estimate the charge in the detector output circuit. The laboratory experiments show that the total charge of plasma cloud ions generated by the particle impact with the target, is approximately proportional to the particle mass Q ~ A(V)m, where m is the particle mass, A is the velocity-dependent coefficient. For the particle velocity V ~ 80 km/s the coefficient A (extrapolated) is ~ 10**3 C/g. The SP-I instrument includes: a) open dust particle detector; b) screened dust particle detector; c) two identical signal amplifier/discriminator units, each connected with the output of its detector; d) digital data accumulation unit; e) power supply unit. Two identical detectors D1 and D2 consist of gold-covered target and a set of collectors placed above the target and oriented normally to it. The collectors are masked to protect them from direct impacts of particles. The mask and target are at a zero potential. The collector bias is + 30 V (even collectors) and - 30 V (odd collectors). Some of charged ions of the plasma cloud formed during the dust particle impact with the target are accumulated at the collector. The current pulses from the electrodes to which the positive potential is applied, are of negative polarity, those from the electrodes at the negative potential are of positive polarity. The micron film in front of one detector cuts off particles of small mass and density to permit estimating the mean density of particles in the vicinity of the mass spectrum center. The functional block diagram of the instrument is given in 'Venus-Halley Mission' (Balekanov 1985). The current pulses from D1 (D2) are converted by the diode converter DC and can be amplified by the three-cascade amplifier (AI). The converted signals enter the pulse-height selector PHS from DC outputs. The output signals from AI and its intermediate sections enter the other PHS inputs. The current pulses of positive polarity are amplified by the similar three-cascade amplifier A2 and enter the time gate (TG). The PHS samples pulses within the one-decade range. Each of the seven PHS outputs is assigned a specific channel. The PHS circuit uses a majority logic principle. A signal at the output of any channel locks all output signals from junior channels. Thus, there is only one signal at the PHS outputs whose amplitude corresponds to the senior (relative to others) channel. The PHS output signals enter the address encoder E and if they are accompanied by a TG output pulse a three-bit address code is generated for the storage-counter (SC). The table below shows the channels for given mass ranges. +-----------------+----------------------+----------------------+ | Channel number | Charge pulse amp, C | Mass Range, g | +-----------------+----------------------+----------------------+ | 1 | 10**-7 - 10**-8 | 10**-10 - 10**-11 | | 2 | 10**-8 - 10**-9 | 10**-11 - 10**-12 | | 3 | 10**-9 - 10**-10 | 10**-12 - 10**-13 | | 4 | 10**-10 - 10**-11 | 10**-13 - 10**-14 | | 5 | 10**-11 - 10**-12 | 10**-14 - 10**-15 | | 6 | 10**-12 - 10**-13 | 10**-15 - 10**-16 | | 7 | 10**-13 - 3x10**-14 | 10**-16 - 3x10**-17 | +-----------------+----------------------+----------------------+ The discriminator includes a calibration oscillator (CO) for the in-flight instrument calibration. In the calibration mode charge signals are generated, sent to the amplifier-discriminator inputs and enter the first and fifth channels, respectively. The storage-counter data are transmitted as a 224-bit message to the APV-N instrument via the data-exchange channels and they are included into the APV-N data message. The pulse accumulation time determined by the instrument interrogation cycle is 2.5 min in the tape-recording mode, and 2 s in the real-time data-transmission mode. The mass range of the instrument is determined by the mass-to-charge transformation coefficient, as well as by the efficiency of collectors and charge-pulse recording circuits. The efficiency of the instrument, that is, the recorded mass range, is determined from the calibration tests and model calculations. The SP-1 dust particle counter is developed by the Soviet specialists. Balebanov, V.M., Skuridin, G.A., Vorontsova, E.V., Bassolo, V.S.(eds.): 1985, Venus-Halley Mission, Louis-Jean, Gap Vaisberg et al. 1986, "Spatial Distributions of Low-Mass Dust Particles (m<10**-10 g) in Comet Halley Coma", ESA SP-250, p. 17. 2. OBSERVATIONS AND DESCRIPTION OF THE DATA TABLES The flyby trajectories of the Vega spacecraft in the cometocentric frame can be specified by the coordinates of the closest approach to the nucleus R0(R0x,R0y,R0z) and the components of the relative velocity V(Vx,Vy,Vz). The corresponding values for Vega1 and Vega2 were as follows: Vega 1: R0x = 7830 km; R0y = 2480 km; R0z = 3400 km; Vx = 28.64 km/s; Vy = -72.73 km/s; Vz =-12.95km/s; Vega 2: R0x = 7100 km; R0y = 2680 km; R0z = 2630 km; Vx = 30.53 km/s; Vy = -69.44 km/s; Vz =-11.88km/s; If the results of the dust flux measurements are referred to the time reckoned from the instant of closest approach, the corresponding distances to the cometary nucleus can be found as R=R0*sqrt(1 + (t/t0)**2), where the parameter t0 = R0/V. The SP-1 data for Vega1 spacecraft are formatted into table containing 1399 records. Each record consists of a time of measurement column (referred to closest approach, where 0 sec is 4:12:38 UT), and 2 columns of impact plasma sensor data (ch 2 and 4+6 combined). The data table for Vega2 is similar but the record contains 7 columns for all impact sensor plasma data. Total number of records is 2151.