Explorer 38


Explorer 38
Explorer 38.jpg
Image of Explorer 38.
Mission typeRadioastronomy
COSPAR ID1968-055A[1]
SATCAT no.3307[2]
Spacecraft properties
ManufacturerGoddard Space Flight Center
Launch mass602 kg (1,327 lb)
Start of mission
Launch date4 July 1968, 17:26:50 (1968-07-04UTC17:26:50Z) UTC[3]
RocketDelta-J 476/D57
Launch siteVandenberg SLC-2E
Orbital parameters
Reference systemGeocentric
RegimeMedium Earth
Semi-major axis12,221.0 kilometers (7,593.8 mi)
Perigee altitude5,832.8 kilometers (3,624.3 mi)
Apogee altitude5,867.8 kilometers (3,646.1 mi)
Period224.1 minutes
Argument of perigee191.2321°
Mean anomaly77.9937°
Mean motion6.425801071
Epoch3 July 2018[2]

Explorer 38 (also called as Radio Astronomy Explorer A, RAE-A and RAE-1) was the first satellite to study radioastronomy. Explorer 38 was launched as part of the Explorers program, being the first of the 2 satellites RAE. Explorer 38 was launched on 4 July 1968 from Vandenberg Air Force Base, California, United States, with a Delta J rocket.


Explorer 38 measured the intensity of celestial radio sources, particularly the Sun, as a function of time, direction and frequency (0.2 MHz to 20 MHz). The spacecraft was gravity gradient oriented. The spacecraft weight was 602 kilograms (1,327 lb), and average power consumption was 25 W. It carried 2 750 feet (230 m) long V-antennas, one facing toward the Earth and one facing away from the earth. A 120 feet (37 m) long dipole antenna was oriented tangentially with respect to the earth's surface.

The spacecraft was also equipped with one 136 MHz telemetry 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 radio interference coming from our planet, both natural (aurorae, thunderstorms) and artificial.


Explorer 38 has 4 antennas deployed in orbit:[4]

  • 2 V-shaped antennas with each of the 4 branches being 751 feet (229 m) long and used by scientific experiments;
  • a 37 metres (121 ft) electric dipole antenna 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.[4]


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 corona electron density 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 HF radio 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 (40 dB higher than the cosmic background) on the frequencies observed (0.2 MHz to 9.2 MHz).[4]

See also


  1. ^ "RAE-A". NSSDCA. NASA Goddard Space Flight Center. Retrieved 17 June 2018. This article incorporates text from this source, which is in the public domain.
  2. ^ a b "Explorer 38 (RAE-A)". n2yo.com. Retrieved 2018-07-03.
  3. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 17 June 2018.
  4. ^ a b c "The spectrum of the extra-galactic background radiation at low radio frequencies" (PDF). NASA. J.K. Alexander, L.W. Brown and T.A. Clark. Retrieved July 3, 2018.

External links

  • Real Time Satellite Tracking and Predictions: Explorer 38 (RAE-A). n2yo.com
  • Data Displays of Radio Astronomy Explorer 1 (PDF)