Explorer 38 measured the intensity of celestial radio sources, particularly the Sun, as a function of time, direction and frequency. The spacecraft was gravity gradient oriented. The spacecraft weight was, and average power consumption was 25 W. It carried 2 long V-antennas, one facing toward the Earth and one facing away from the earth. A long dipole antenna was oriented tangentially with respect to the earth's surface. The spacecraft was also equipped with one 136 MHztelemetry turnstile. The onboard experiments consisted of four step-frequency Ryle-Vonberg radiometers operating from 0.45 MHz to 9.18 MHz, two multichannel total power radiometers operating from 0.2 MHz to 5.4 MHz, one step frequency V-antenna impedance probe operating from 0.24 MHz to 7.86 MHz, and one dipole antenna capacitance probe operating from 0.25 MHz to 2.2 MHz. Explorer 38 was designed for a 1-year minimum operating lifetime. The spacecraft tape recorder performance began to deteriorate after 2 months in orbit. In spite of several cases of instrument malfunction, good data were obtained on all three antenna systems. The small satellite observed for months the "radio sky" in frequencies between 0.2 MHz and 9.2 MHz, but it was subjected to the continuous radiointerference coming from our planet, both natural and artificial.
Instruments
Explorer 38 has 4 antennas deployed in orbit:
2 V-shaped antennas with each of the 4 branches being long and used by scientific experiments;
a cross-dipole turnstile antenna for the transmission of telemetry on a frequency of 137 MHz.
The scientific experiments are:
4 Ryle-Vonberg radiometers analyzing frequencies between 0.45 MHz and 9.18 MHz;
2 multi-channel radiometers analyzing frequencies between 0.2 and 5.4 MHz;
An impedance probe associated with 5 antennas analyzing frequencies between 0.24 MHz and 7.86 MHz;
A capacitive probe associated with the dipole antenna analyzing frequencies between 0.25 MHz and 2.2 MHz.
Results
The following results are reported in 1971:
Absolute spectrum and average cosmic noise up to the frequency 0.5 MHz.
Collection of radio data transmitted during type III solar radio bursts in the 0.2 MHz-5 MHz frequency band. These elements made it possible to obtain a first estimate of the solar coronaelectrondensity gradient, the solar wind speed and density inhomogeneities in the solar corona regions between 10 and 30 solar radiis. A second radio broadcast of hectometric frequency was observed.
An upper limit to the radio flux emitted by Jupiter's HFradio broadcasts was determined by the observations made during the Moon's occultations of the giant planet.
Radio emissions from the Earth of natural and human origin are both widespread and often very intense on the frequencies observed.
