DETAILS
DETAILS
Pioneer 11 carries a payload of 12 scientific instruments having a mass of 30.4 kg and using 25 watts of power. The total spacecraft mass is 258 kg and the diameter of the high gain antenna reflector is 2.74 meters. It is powered by four radioisotope thermoelectric generators (RTG) located at the ends of two trusses extending from the body of the spacecraft. A long boom extending from the scientific instrument compartment supports the magnetometer sensor.
The spacecraft spin axis is parallel to the axis of the reflector. Several small thrusters using hydrazine are located at the edge of the reflector to make in-flight velocity adjustments, alter the spin rate and to keep the reflector pointed at the earth.
The data are transmitted to the earth by an 8 watt S-band transmitter at one of eight data rates (from 16 to 2048 bits per second).
Pioneer 11 made the second flyby of Jupiter. This was on December 3rd, 1974. On September 1, 1979, it became the first spacecraft to encounter Saturn.
The investigation objectives for the Pioneer 11 cruise data are:
NAME: GEIGER TUBE TELESCOPE (GTT)
TYPE: ENERGETIC PARTICLE DETECTOR
PI: JAVANALLEN
BUILD_DATE: 1973-04-06
MASS: 1.64 kg
HEIGHT: 0.145 mt
LENGTH: 0.171 mt
WIDTH: 0.145 mt
MANUFACTURER_NAME: THE UNIVERSITY OF IOWA
SERIAL_NUMBER: 0853-04
The GTT electronics system consists of two basic sections. The first is the power converter which regulates and filters the 28 Volt, 20kHz spacecraft power supply. The on-off command functions through a solid state switch by removing power from the driving circuitry.
Output voltages of +7.75, +5.00, -12.00, and +900 are supplied to the experiment. The 7.75 and 5.00 Volt lines are regulated to 1% and the 900 Volt lines are regulated with VR tubes.
The second section is the signal processor. This is used to condition the data from the seven detectors and consists of a MOS/TTL/transistor hybrid system containing MOS/TTL logic and transistorized discrete component interface circuits. The processor is completely redundant with the exception of the interface circuits. Upon command to the spacecraft, the signal processor can be switched from the main logic system to a standby redundant logic system. The function of the processor is to sequentially accumulate data on a frame basis from the seven detectors. Data are accumulated in a 24 bit register and then compressed quasi-logarithmically to 12 bits for transmission.
Six miniature Geiger-Müller (GM) tubes are used as basic detectors. Three of these (A, B, and C) are EON Corporation end-window type 6213 tubes. The three other tubes (D, E, and F) are EON Corporation type 5107 tubes. The six tubes were placed in a variety of physical arrangements. The seventh detector (G) is a thin (28 micron thick), single element solid state detector with a physical collimator. This detector was made by Nuclear Diodes, Inc.
Tubes A, C, and B are mounted in a single block. The central tube C is shielded omnidirectionally. Tubes A and B are similarly shielded except for thinner window unidirectional collimators in the +X direction. The individual counting rates of the three tubes are telemetered separately; also, double coincidences AB and triple coincidences ABC with a resolving time of 1 microsecond are formed and telemetered.
The second assembly comprises an omnidirectionally shielded triangular array of three 5107 tubes. The rate of D and the triple coincidence rate of the DEF are telemetered.
The third assembly uses the collimated solid state detector as input to a charge sensitive amplifier. This signal is delay-line clipped to 180 nanoseconds, amplified and then feed into a fixed level threshold discriminator. This threshold corresponds 0.61 MeV for protons. The output of the discriminator is then feed into an output circuit which shapes the pulse so that it is similar to that from the GM tubes; it is then treated in the same manner. Detector G looks in the +X direction.
The Z-axis of the instrument is parallel to the axis of rotation of the spacecraft. The +X axis points outward into free space from the rim of the instrument compartment of the spacecraft. The magnetometer and a portion of the magnetometer boom subtend a trivial fraction of the fields of view of the collimators of A, B, and G; otherwise, there is no physical obstruction within the fields of view.
The rotational axis (+Z) of the spacecraft is pointed continuously at the earth within an error of less than one degree and therefore lies approximately in the ecliptic plane. The spin period and sampling period are asynchronous; thus angular distributions of particle intensities as a function of roll angle in the equatorial plane of the spacecraft are assembled as a software operation by using attitude data supplied by the Ames Research Center. In our analysis the roll angle is measured from the ascending node of the spacecraft's equator on the ecliptic to the +X axis of the instrument at the midtime of the sample.
The instrument uses 12 bits in each 192-bit main science frame of the spacecraft's telemetry format. Quasilogarithmic data compression is used to maintain 1% accuracy at all possible counting rates. All outputs are digital. A complete cycle of the GTT data comprises eleven main science frames as follows: sync word, G, A, B, G, AB, ABC, C, D, ABC, and DEF.
Counts from each detector channel are accumulated for a period of time in seconds equal to 192/b, where b is the telemetry rate in bits per second for the entire spacecraft (b=16, 32, 64, 128, 512, 1024, or 2048, as selected by ground command).
The GTT experiment utilizes two commands. A power ON/OFF command and a function command for Main/Standby processor selection.
UNIVERSITY OF IOWA GEIGER TUBE TELESCOPE ENERGY RANGES AND
GEOMETRIC FACTORS OF PIONEER 11 DETECTORS
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EFFECTIVE
INVERSE
OMNIDIRECTIONAL 1
GEOMETRIC _______
EFFECTIVE ENERGY FACTOR 4*pi*Q
DETECTOR RANGE, MEV (1/Q),cm**-2 TYPE (cm*cm*sr)**-1
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ELECTRONS
A-C 0.0421 23 O ...
D E>31 63 O ...
AB E>21 6910 D 550
ABC E>21 6910 D 550
DEF E>31 3150 O ...
PROTONS
A-C 0.6180 8.2 O ...
D E>80 23 O ...
AB E>130 2463 D 196
ABC E>130 2463 D 196
DEF E>150 11500 O ...
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TYPE D=DIRECTIONAL O=OMNIDIRECTIONAL
The electrical power for the spacecraft is provided by four Type SNAP 19 radioisotope thermal generators (RTG's) of the Atomic Energy Commission. There are also several much weaker radioisotpe heater units (RHU's) for spot heating. The heating of these systems is provided by a mixture of plutonium isotopes; principally plutonium 238. Gamma and X-rays from the decay of some of the isotopes, produce a time varying background in the singles rates of the GM tubes. These background rates can be calculated using the following formulae.
R(A)=1.137*RR
R(B)=0.905*RR
R(C)=0.958*RR
R(D)=0.254*RR
RR=1.103E-02*[2*f(t)+0.9*f(t+0.832)]
+5.53E-03*[3*g(t)+g(t+0.832)] counts/second
where f(t)=23.792*EXP(-0.3623*t)+12.120*EXP(-0.0094*t)
-35.912*EXP(-0.2432*t)
g(t)=EXP(-0.0081*t)
and t is measured in years with t=0 on March 15, 1971.
Detector G is a thin solid state detector and is insensitive to this radiation and hence requires no correction. Detector G also has a small Am-241 alpha particle source at the edge of its viewing cone to provide an inflight calibration. This source gives a background counting rate of 0.06 counts per second.
The multiple GM detector rates and the solid state detector rate require no correction as a function of temperature. The singles rates of the GM tubes require a slight temperature correction. This temperature correction is of the form, A'=A(T)*X(T) for detectors A, B, and C, and for detector D, the form is D'=D(T)*Y(T), where
X(T)=1.0+0.0003694*(75.0-T) and Y(T)=1.0-0.0006514*(75.0-T).
The temperatures in degrees F as a function of time for Pioneer 11 are given in the following table.
PIONEER 11 TEMPERATURES
YEAR PERIOD (DOY) TEMPERATURE PERIOD TEMPERATURE
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1973 96 77.8 97 67.0
98 64.8 99 65.8
100 67.0 101-119 69.9
120-125 67.0 126-131 64.8
132-148 58.1 149-153 55.9
154-205 50.1 206-226 46.6
227-272 50.1 273-312 48.4
313-317 43.7 318-365 46.6
1974 1- 28 46.6 29-290 44.7
291-365 42.9
1975 1-101 42.9 102-139 35.8
140-365 42.9
1976 1-167 42.9 168-366 41.1
1977 1- 24 41.1 25-302 39.29
303-365 37.52
1978 1-252 37.52 253-365 35.77
1979 1-149 35.77 150-365 34.03
1980 1-155 34.03 156-172 32.30
173-188 34.03 189-366 32.30
1981 1-216 32.30 217-365 30.58
1982 1-120 30.58 121-365 28.88
1983 1- 48 28.88 49-332 27.20
333-365 25.52
1984 1- 60 25.52 61 23.86
62 22.22 63-184 20.59
185-276 18.98 277-366 17.38
1985 1- 35 17.38 36-116 15.80
117-205 14.22 206-365 12.66
1986 1- 63 11.11 64- 70 9.55
71-139 8.00 140-310 6.43
311-365 4.86
1987 1- 31 4.86 32-189 3.22
190-304 1.63 305-365 -0.03
1988 1- 87 -0.03 88-231 -3.54
232-366 -5.33
1989 1- 7 -5.33 8-150 -7.12
151-292 -8.91 293-365 -10.70
1990 1- 70 -10.70 71-212 -12.49
213-355 -14.28 356-365 -16.07
1991 1-133 -16.07 134-275 -17.86
276-365 -19.65
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