Description

Pioneer 9 was the fourth in a series of solar-orbiting, spin-stabilized, and solar-cell and battery-powered satellites designed to obtain measurements of interplanetary phenomena from widely separated points in space on a continuing basis. The spacecraft carried experiments to study the positive ions and electrons in the solar wind, the interplanetary electron density (radio propagation experiment), solar and galactic cosmic rays, the interplanetary magnetic field, cosmic dust, and electric fields. Also, a new coding process was implemented for Pioneer 9.

Its main antenna was a high-gain directional one. The spacecraft was spin-stabilized at about 60 rpm, and the spin axis was perpendicular to the ecliptic plane and pointed toward the south ecliptic pole. By ground command, one of five bit rates, one of four data formats, and one of four operating modes could be selected. The five bit rates were 512, 256, 64, 16, and 8 bps. Three of the four data formats contained primarily scientific data and consisted of 32 seven-bit words per frame. One scientific data format was used at the two highest bit rates, another was used at the three lowest bit rates, and the third contained data from only the radio-propagation experiment. The fourth data format contained mainly engineering data. The four operating modes were real-time, telemetry-store, duty-cycle store, and memory readout. In the real-time mode, data were sampled and transmitted directly (without storage) as specified by the data format and bit rate selected. In the telemetry-store mode, data were stored and transmitted simultaneously in the format and at the bit rate selected. In the duty-cycle store mode, a single frame of scientific data was collected and stored at a rate of 512 bps. The time period between collection and storage of successive frames could be varied by ground command between 2 and 17 min to provide partial data coverage for periods of up to 19 h, as limited by the bit-storage capacity. In the memory readout mode, data were read out at whatever bit rate was appropriate to the satellite distance from the Earth.

Contact with Pioneer 9 by controllers was maintained until May 1983. Mission controllers made an unsuccessful attempt in 1987 to contact the spacecraft. The mission was declared inactive at that time.

Spacecraft and Subsytems

Instruments

Triaxial Magnetometer

A boom-mounted, triaxial fluxgate magnetometer was used to study the interplanetary magnetic field and its fluctuations. The sensors were orthogonally mounted with one axis parallel to the spacecraft spin axis. Upon command, a motor interchanged a sensor in the spin plane with the sensor along the spin axis, enabling inflight determination of zero levels. Every 24 hours, the instrument was commanded into a self-calibrate sequence, and this was often repeated after the sensors were flipped. The instrument, which had a dynamic range of plus or minus 200 nT with a resolution of plus or minus 0.2 nT, was capable of inflight demodulation of the signals received from the two sensors in the spin plane. Each magnetic field component was digitized into a 10-bit telemetry word. Nine magnetic field components, comprising three magnetic field vectors, were transmitted in each spacecraft telemetry frame.

Solar Plasma Detector

A truncated hemispherical electrostatic analyzer (120-deg total parallel-plate curvature) with three contiguous current collectors was used to study the directional intensity of the electrons and positive ions in the solar wind. Ions were detected in 30 logarithmically equispaced energy per unit charge (E/Q) steps from 150 to 15,000 V. There was an electron mode of operation in which electrons were measured in 14 logarithmically equispaced E/Q steps ranging from 12 to 1000 V. There was also a zero E/Q, or background, step. The three collectors measured particles incident from three different contiguous angular intervals relative to the spacecraft equatorial plane (same as the ecliptic plane). Two collectors measured flux from 10 to 85 deg on either side of the spacecraft equatorial plane, and the third measured flux in a 20-deg interval centered on the spacecraft equatorial plane. As the spacecraft was spinning, fluxes were measured in 23 possible 2-13/16-deg-wide azimuthal angular sectors. Seventeen of these sectors were contiguous and bracketed the solar direction. The remaining six sectors were widely spaced. The instrument had three modes of data collection: polar scan, azimuthal scan, and maximum flux. At the two highest bit rates (512 and 256 bps), the polar-scan mode was alternated with the azimuthal scan mode at each E/Q step. In the polar-scan mode, all three collectors were observed, and the peak flux obtained and the azimuthal direction (to 2-13/16 deg) of the observation were reported for each collector. In the azimuthal scan mode, the peak flux observed in the 23 azimuthal sectors was recorded for the central collector at each E/Q step. At the low bit rates (64, 16, and 8 bps), the maximum flux mode was used at each E/Q step followed by either (1) for ions, a polar scan and an azimuthal scan at that E/Q step where the peak flux measurement during the maximum flux mode was obtained, or (2) for electrons, a polar scan and an azimuthal scan at E/Q = 100 V. In the maximum flux mode, only the central collector was observed, the peak flux obtained, and the azimuthal direction (to 2-13/16 deg) of the observation reported. A complete set of measurements consisted of seven sets of ion measurements (at each E/Q step) and one set of electron measurements (at each E/Q step). At the high bit rates (512 and 256 bps) one set of ion measurements took 62 s and one set of electron measurements, 38 s. At the low bit rates (64, 16, and 8 bps), one set of ion measurements took 37 s and one set of electron measurements took 28 s. At 64 bps, a complete set of measurements (seven ions plus one electron) was taken and telemetered every 402.5 s. At 16 bps, it took 1610 s, and, at 8 bps, it took 3220 s.

Two-Frequency Beacon Receiver

Both 423.3-MHz and its 2/17 subharmonic 49.8-MHz signals were transmitted from a 4.6-m steerable parabolic antenna at Stanford University to the two-frequency radio receiver on the spacecraft. The high-frequency signal served as a reference signal, since its propagation time was not appreciably delayed. The low-frequency signal was delayed in proportion to the total electron content in the propagation path. On the spacecraft, a phase-locked receiver counted the beat frequency zero crossings of the received signals to obtain measurements of phase-path differences. Differential delay of the group velocity was also observed, and these values were telemetered to the ground station and used to calculate the total electron content. The ionospheric contribution (up to a selected altitude obtained from other experimental techniques) could be subtracted to produce data describing the interplanetary electron content of the solar wind and its variations. More detailed descriptions of the experiment can be found in J. Geophys. Res., v. 71, pp. 3325-3327, and in Radio Sci., v. 6, pp. 55-63.

Cosmic Dust Detector

This experiment was designed (1) to measure the cosmic-dust flux density in the solar system, (2) to determine the distribution of cosmic-dust concentrations in the earth's orbit, (3) to determine the gradient, flux density, and speed of particles in meteor streams, and (4) to perform an inflight control experiment on the reliability of the microphone as a cosmic-dust sensor. The experiment instrumentation was identical to that carried on Pioneer 8, consisting essentially of two thin-film-grid detectors (separated by a distance of 5 cm) that produced an electrical signal when the film was penetrated by a micrometeoroid. Each film had a sensitive area of 100 sq cm and was composed of 16 segments that provided both the direction and the time of flight needed for the meteoroid to traverse the 5-cm distance between the front-film and the rear-film sensor. The combined results of the Pioneer 8 and 9 cosmic-dust experiments lent strong support to the hypothesis that the bulk of meteoroid dust is of cometary origin.

Cosmic-Ray Anisotropy

This experiment consisted of a CsI scintillator and three solid-state telescopes. The CsI scintillator was collimated by an anticoincidence plastic scintillator and had a conical aperture with a 38.2-deg half-angle. The scintillator look direction was centered in the ecliptic plane. Three solid-state detectors were oriented in a fan arrangement with respect to a fourth solid-state detector, such that each of the first three detectors formed a telescope with the fourth detector. Each of the three telescopes thus formed had an acceptance cone of 23-deg half-angle. The mean viewing directions of the telescopes were in the ecliptic plane and 48 deg above and below that plane, respectively. Two concurrent modes of counting were employed. In the first mode, counts were accumulated in eight separate 45-deg intervals during the spacecraft spin, while, in the second, spin-integrated counts were acquired. In the first mode, the scintillator separately measured particles with energies in the ranges 7.4 to 21.5 MeV/nucleon and 19.7 to 63.0 MeV/nucleon (no species discrimination) while each solid-state telescope separately measured protons in the energy ranges 3.3 to 3.6 MeV and 3.6 to 6.7 MeV. In the second mode, the scintillator separately measured particles in six contiguous energy intervals between 4.5 and 40 MeV/nucleon (interval lower limits at 4.5, 7.0, 9.6, 13, 21, and 28 MeV/nucleon), while each of the solid-state telescopes separately measured protons in the energy ranges 1 to 8, 1 to 5, 1 to 3, and 4 to 6 MeV, and alpha particles in the energy range 4 to 8 MeV. During each 224-bit main telemetry frame, two first-mode 9-bit accumulators and one second-mode 9-bit accumulator were read out. Inflight calibration of the scintillator and of some of the electronics was performed daily. See Bukata et al, IEEE Trans. Nuc. Sci., NS-17, pp. 18-24, 1970, for a more detailed experiment description.

Cosmic-Ray Gradient

This experiment utilized a telescope comprised of five solid-state sensors, a Cerenkov detector, and an anticoincidence shield. The telescope axis was perpendicular to the spacecraft spin axis. As determined by two coincidence modes and electronic discrimination of sensor output pulses, particles measured were (1) electrons in three contiguous energy intervals between 0.31 and 5.1 MeV, (2) protons in five contiguous energy intervals between 2.2 and 42 MeV, and (3) alpha particles in contiguous energy intervals between 5.8 and 42 MeV/nucleon. A third coincidence mode measured the sum of counts due to electrons above 0.6 MeV and nuclei above 14 MeV/nucleon. A fourth coincidence mode measured the sum of nuclei above 42 MeV/nucleon and electrons above 5.1 MeV. Spacecraft spin-integrated directional fluxes were measured in the various modes. Accumulation times and readout intervals were dependent on the telemetry bit rate and were typically in tens of seconds. In all cases, they were longer than the spacecraft spin period.

Electric Field Detector

Electrostatic and electromagnetic plasma waves were measured in the solar wind near 1 AU using an unbalanced electric dipole antenna. The 423-MHz Stanford University antenna, which served as the sensor, was capacitively coupled to three telemetry channels. Channel 1 was a 15% bandpass filter centered at 400 Hz, and channel 2 was a 15% bandpass filter centered at 30 kHz. These channels were each sampled 64 times per telemetry sequence. Channel 3 was a broadband 100-Hz to 100-kHz channel. The broadband channel was fed into a count-rate meter that measured the number of positive-going pulses per unit time having amplitudes large enough to cross the present trigger level. The trigger level was varied through eight steps, eight times per telemetry sequence. The trigger levels, together with the count rate at each level, gave a measure of the broadband power spectrum. Due to ambient conditions, these data usually represented the power at about 100 Hz. The telemetry sequence was repeated over time intervals from 7 min 28 s to 472 min 52 s.

Celestial Mechanics

The objectives of this investigation were (1) to obtain primary determinations of the masses of the earth and moon and the distance between the earth and sun, (2) to use the tracking data from the whole series of Pioneer probes in a program designed to improve the ephemeris of the earth, and (3) to investigate the possibility of a test of general relativistic mechanics using the Pioneer orbits and data. The instrumentation was a two-way S-band Doppler tracking mechanism, using high-gain antennas with disk-like patterns in a plane perpendicular to the spin axis of the spacecraft. When the spin axis was perpendicular to the ecliptic, radio signals from the antenna continuously illuminated the earth. Data were transmitted continuously and were received at ground-based Deep Space Network stations with 26.5-m diameter antennas, and at the 64-m antenna in California.

Launch-Orbit Information

Launch Information

Launch Date: 1968-11-08
Launch Vehicle: Delta
Launch Site: Cape Canaveral, United States
Mass: 147.0 kg

Summary