 Explorer 38 satellite | |
| Names | RAE-A RAE-1 Radio Astronomy Explorer-1 |
|---|---|
| Mission type | Radio astronomy |
| Operator | NASA |
| COSPAR ID | 1968-055A |
| SATCATno. | 03307 |
| Mission duration | 1 year (achieved) 57 years, 7 months and 15 days (in orbit) |
| Spacecraft properties | |
| Spacecraft | Explorer XXXVIII |
| Spacecraft type | Radio Astronomy Explorer |
| Bus | RAE |
| Manufacturer | Goddard Space Flight Center |
| Launch mass | 602 kg (1,327 lb) |
| Power | 25watts |
| Start of mission | |
| Launch date | 4 July 1968, 17:26:50GMT[1] |
| Rocket | Thor-Delta J (Thor 476 / Delta 057) |
| Launch site | Vandenberg,SLC-2E |
| Contractor | Douglas Aircraft Company |
| Entered service | 4 July 1968 |
| End of mission | |
| Disposal | Decommissioned |
| Last contact | 4 July 1969 |
| Orbital parameters | |
| Reference system | Geocentric orbit[2] |
| Regime | Medium Earth orbit |
| Perigee altitude | 5,851 km (3,636 mi) |
| Apogee altitude | 5,861 km (3,642 mi) |
| Inclination | 120.60° |
| Period | 224.40 minutes |
| Instruments | |
| Capacitance Probe Impedance Probe Planar Electron Trap Radio Bursts Receivers Step Frequency Radiometers | |
Explorer 38 (also called asRadio Astronomy Explorer A,RAE-A andRAE-1) was the firstNASA satellite to studyRadio astronomy. Explorer 38 was launched as part of theExplorer program, being the first of the 2 RAE satellites. Explorer 38 was launched on 4 July 1968 fromVandenberg Air Force Base,California, with aDelta Jlaunch vehicle.[3]
Explorer 38 spacecraft measured the intensity of celestial radio sources, particularly theSun, as a function oftime,direction andfrequency (0.2 to 20-MHz). The spacecraft wasgravity-gradient stabilized. The spacecraft weight was 602 kg (1,327 lb) and average power consumption was 25watts. It carried two 230 m (750 ft) long V-antennas, one facing toward theEarth and one facing away from the Earth. A 37 m (121 ft) long dipole antenna was oriented tangentially with respect to theEarth's surface.[3]
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 to 9.18-MHz, two multichannel total powerradiometers operating from 0.2 to 5.4-MHz, one step frequency V-antenna impedance probe operating from 0.24 to 7.86-MHz, and one dipoleantenna capacitance probe operating from 0.25 to 2.2-MHz. Explorer 38 was designed for a 12 months minimum operating lifetime.[3]
The spacecrafttape 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 and 9.2-MHz, but it was subjected to the continuous radiointerference coming from the Earth, both natural (aurorae,thunderstorms) and artificial.[3]
Explorer 38 has 4 antennas deployed in orbit:[4]
The scientific experiments are:
Determine reactive and resistive components of antenna impedance as a function of localelectron density,electron temperature,magnetic field, and vehicle potential. The impedance measurements was made at 10 frequencies (0.25 to 8-MHz).[5]
Determine reactive and resistive components of antenna impedance as a function of local electron density, electron temperature, magnetic field, and vehicle potential. The impedance measurements was made at ten frequencies (0.25 to 8-MHz).[6]
There were two planar electron traps mounted on opposite sides of the spacecraft. The trap consisted of a collector, positively biased in order to repel incoming ions and to reducephotoemission of electrons from the collector. A sawtooth voltage was applied to a grid, and the resulting current to the collector was telemetered. Electron density was obtained by analysis of the grid voltage-collector current profile. The electron density representing the ambient value was that obtained from the probe facing the direction of satellite motion. The spacecraft attitude for this purpose was determined either from the electron density or from the solar and magnetic sensors on the spacecraft. The data were tape recorded and telemetered once each orbit. These sensors operated nominally since launch and were providing electron density mapping data at spacecraft altitude.[7]
Thirty-two channel step frequencyradiometers were connected to the lower 230 m (750 ft)-long antenna and to the 37 m (121 ft)-long dipole via high-impedance preamplifiers. The burst radiometer on the dipole was stepped rapidly through 32 discrete frequencies between 0.2 and 5.4-MHz to generate dynamic spectra. The radiometers measured the amplitude, rate of change of frequency, and decay time of solar burst and other rapidly varying noise in the 0.2 to 5.4-MHz band. Operating in two sensitivity modes, these receivers could measure signals up to 50dB above the cosmic background level. The 32 channels were cycled every 7.7-seconds. The chief advantages of the burst radiometers were high time resolution and relatively few components for high reliability. The radiometer was a simple total-power receiver consisting of an input balun, a power divider, and several parallel tuned-radio-frequency strips. After about 18 months of operation, one of the preamplifiers on the lower V burst radiometer failed, reducing the sensitivity and changing the antenna pattern for that radiometer.[8]
This experiment used four Ryle-Vonberg radiometers connected to the three spacecraft antennas to provide high accuracy and long-term stability necessary for the sky mapping over many months of operation. One was connected to the 37 m (121 ft) dipole, one to the lower 230 m (750 ft) V-antenna, and two to the upper V-antenna. The Ryle-Vonberg radiometers used on the V-antennas were connected via balun transformers that provided an approximate match to the antenna impedance. Each radiometer was successively tuned to nine different frequencies in the band 0.48 to 9.18-MHz. Precise, automatic, and continuous calibration was inherent in this type of design. The intensities of celestial radio sources were measured by this experiment. The "fine" output channel of the Ryle-Vonberg radiometers failed after 3 to 9 months of operation. The Ryle-Vonberg "coarse" output channels provided good data without interruption, however.[9]
The following results are reported in 1971:
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