Explorer 43

Not to be confused with Explorer 18, also known as IMP-1.

Explorer 43

Explorer 43 satellite in space
Names	IMP-I IMP-6 Interplanetary Monitoring Platform-6
Mission type	Space physics
Operator	NASA
COSPAR ID	1971-019A
SATCAT no.	05043
Mission duration	3.5 years (achieved)
Spacecraft properties
Spacecraft	Explorer XLIII
Spacecraft type	Interplanetary Monitoring Platform
Bus	IMP
Manufacturer	Goddard Space Flight Center
Launch mass	635 kg (1,400 lb)
Dimensions	135.64 cm (53.40 in) in diameter by 182.12 cm (71.70 in) high
Start of mission
Launch date	13 March 1971, 16:15:00 GMT
Rocket	Thor-Delta M6 (Thor 562 / Delta 083)
Launch site	Cape Canaveral, LC-17A
Contractor	Douglas Aircraft Company
Entered service	13 March 1971
End of mission
Decay date	2 October 1974
Orbital parameters
Reference system	Geocentric orbit
Regime	Highly elliptical orbit
Perigee altitude	242 km (150 mi)
Apogee altitude	196,574 km (122,145 mi)
Inclination	28.70°
Period	5626.00 minutes
Instruments
Instruments Electrostatic Fields Electrostatic Waves and Radio Noise (Project) Electrostatic Waves and Radio Noise -- GSFC Electrostatic Waves and Radio Noise -- Iowa Electrostatic Waves and Radio Noise -- Minnesota Interplanetary Long Wavelength Radio Astronomy Experiment -- Time Resolution Interplanetary Long-Wavelength Radio Astronomy Experiment -- Flux Resolution Low-Energy Protons and Electrons Measurement of Magnetic Fields Measurement of Solar Plasma Solar and Galactic Cosmic-Ray Studies Radio Astronomy Nuclear Composition of Cosmic and Solar Particle Radiations Study of Cosmic Ray, Solar, and Magnetospheric Electrons Measurement of Solar Plasma Medium-Energy Solar Protons and Electrons Solar Proton Monitoring Experiment
Explorer program

Explorer 43, also called as IMP-I and IMP-6, was a NASA satellite launched as part of Explorer program. Explorer 43 was launched on 13 March 1971 from Cape Canaveral Air Force Station (CCAFS) (restored to its old name of Cape Canaveral in 1974), with a Thor-Delta M6 launch vehicle. Explorer 43 was the sixth satellite of the Interplanetary Monitoring Platform.

Spacecraft and mission

Explorer 43 continued the study, begun by earlier IMPs, of the interplanetary and outer magnetospheric regions by measuring energetic particles, plasma, electric fields and magnetic fields. Its orbit took it to cislunar space during a period of decreasing solar activity.

A Radio astronomy experiment was also included in the spacecraft payload. The 16-sided spacecraft was 182.12 cm (71.70 in) high by 135.64 cm (53.40 in) in diameter. The spacecraft spin axis was normal to the ecliptic plane, and its spin rate was 5 rpm, with propulsion Star-17A. The initial apogee point lay near the Earth-Sun line. The solar-cell and chemical-battery powered spacecraft carried 2 transmitters. One continuously transmitted PCM encoder data at a 1600 bps information bit rate.

The second transmitter was used for transmission of Very low frequency (VLF) data and for ranging information. Three orthogonal pairs of dipole antennas were used for the electric fields experiments, and one of these pairs was also used for the Radio astronomy experiment. The members of the antenna pair along the spacecraft spin axis extended 2.9 m (9 ft 6 in), the members of the pair used in both the electric field and radio astronomy experiments extended 45.5 m (149 ft), and the members of the third pair were slightly unbalanced, extending 24.4 × 27.6 m (80 × 91 ft), respectively. All four elements perpendicular to the spin axis were to have extended 45.5 m (149 ft).

Experiments

Electrostatic Fields

Two dipole antennas were mounted orthogonally in the spin plane of the spacecraft while a third dipole antenna was mounted along the spacecraft spin axis. Antenna element lengths were -X, 27.6 m (91 ft); +X, 24.4 m (80 ft); -Y and +Y, 45.5 m (149 ft); -Z and +Z (spin axis), 2.9 m (9 ft 6 in). Electrometers measured the analog potential difference between the elements in each pair of antennas simultaneously every 5.12 s. The potential differences were sampled digitally through a 14-bit analog/digital converter every 0.64-seconds. The DC sensitivity was 100 microvolts per meter.

Electrostatic Waves and Radio Noise -- Project

This experiment, as originally defined by NASA Headquarters, has been separated at NSSDC into its Iowa (71-019A-03), Minnesota (71-019A-12), and GSFC (71-019A-16) components. Initial experiment performance was normal.

Electrostatic Waves and Radio Noise -- GSFC

The AC electric field intensity in 12 narrow channels was measured from 0.1 to 100-Hz. The experiment had an optimum noise threshold of 10 microvolts per meter. Each channel was sampled once every 5.12-seconds at the high bit rate. The antennas used in the dc field experiment (71-019A-02) were also utilized in this experiment.

Electrostatic Waves and Radio Noise -- Iowa

Three orthogonal loop antennas and the three orthogonal (nearly balanced) dipoles gained simultaneous E and B field data in 16 logarithmically equispaced narrow channels from 20-Hz to 200-kHz. These detectors were also used in the dc electric field (71-019A-02) experiment. The spectral frequency resolution was about 30%. Each E-B channel was sampled every 5.12-seconds. A short back-up dipole antenna (about 1 m (3 ft 3 in) tip to tip) was also used to detect very short wavelength plasma phenomena. Analog B or E data from 0 to 30-kHz in three segments were also telemetered on the special purpose 4-watts analog channel. This experiment was designed to be used in conjunction with the low-energy proton and electron differential energy analyzer (LEPEDEA).

Electrostatic Waves and Radio Noise -- Minnesota

This experiment was designed to determine the polarization, direction of propagation, flux, and direction of the wave normal surface for plasma waves. The time-averaged correlation at one channel frequency from any combination of the six antenna elements could be simultaneously calculated by six onboard analog computers. There were 64 logarithmically equispaced frequency channels centered from 23-Hz to 200-kHz with a 15% bandwidth at 3-dB. Averaging time was 2.5-seconds at the high bit rate. The combinations of elements and the sequence of frequencies to be measured were controlled either by an onboard computer or from the ground.

Interplanetary Long Wavelength Radio Astronomy Experiment -- Time Resolution

This experiment was designed to study the radio spectra of the galaxy, the Sun, and Jupiter with relatively high time resolution. Two stepped-frequency radiometers, attached to a single 91 m (299 ft) dipole antenna (also used in the electric field experiments), stepped through the frequency range of 30-kHz to 2-MHz in 32 steps.

Interplanetary Long-Wavelength Radio Astronomy Experiment -- Flux Resolution

The objective of this experiment was to study the spectra of the galaxy, the sun, and Jupiter with high flux resolution (about 1%). A radiometer, operating in either a stepping mode (eight frequencies) or at a single frequency, was connected to a 91 m (299 ft) dipole antenna, which was also used in the electric field experiments. The frequency range covered was 0.05 to 3.5-MHz.

Low-Energy Protons and Electrons

This experiment was designed to conduct comprehensive observations of the differential energy spectra, angular distributions, spatial distributions and temporal variations of electrons and protons over the geocentric radial distance range from 1.03 to 30 Earth radii. Two arrays of curved-plate cylindrical electrostatic analyzers and continuous channel multipliers were used for this purpose. One analyzer, the LEPEDEA (low-energy proton and electron differential energy analyzer), was to measure the energy spectra and angular distribution of protons and electrons separately in the energy range 24 eV to 50 keV (16 energy intervals for protons and electrons separately). The other analyzer, the LEPEDEA (low energy proton differential energy analyzer) measured the energy spectra and angular distribution of protons in the energy range 1.7 to 550 eV (eight energy intervals). The analyzers were mounted perpendicular to the spacecraft spin axis. An EON type 213 Geiger–Müller counter, whose collimated field of view of 15° half angle was oriented approximately parallel to that of the LEPEDEA, was used to measure the intensity of electrons of energies greater than 45 keV and protons of energies greater than 500 keV and to provide background measurements for the LEPDEA. One continuous channel electron multiplier failed on 10 August 1974, so that no useful electron data were collected for the last 7 weeks of the spacecraft life. Otherwise, the experiment functioned normally over the spacecraft lifetime.

Measurement of Magnetic Fields

This experiment was designed to measure accurately the vector magnetic field in the interplanetary medium and in the Earth's magnetosphere, magnetotail, and magnetosheath. The detector was a boom-mounted triaxial fluxgate magnetometer with four ranges: ± 16, 48, 144, and 432 nT, respectively. Corresponding sensitivities were ± 0.06, 0.19, 0.56, and 1.69 nT, respectively. Automatic range selection capability was included. A flipping mechanism permitted inflight calibration of the three sensor zero levels. The vector sampling rate was 12.5 samples per second. The experiment functioned normally through the spacecraft life.

Atmospheric entry

The spacecraft reentered the Earth's atmosphere on 2 October 974, after a highly successful mission.