Explorer 38 (also called as Radio Astronomy Explorer A, RAE-A and RAE-1) was the first NASA satellite to study Radio astronomy. Explorer 38 was launched as part of the Explorer program, being the first of the 2 RAE-satellites. Explorer 38 was launched on 4 July 1968 from Vandenberg Air Force Base, California, with a Delta J launch vehicle.[3]
![]() Explorer 38 satellite | |
Names | RAE-A RAE-1 Radio Astronomy Explorer-1 |
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Mission type | Radio astronomy |
Operator | NASA |
COSPAR ID | 1968-055A ![]() |
SATCAT no. | 03307 |
Mission duration | 12 months (planned) |
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 | 25 watts |
Start of mission | |
Launch date | 4 July 1968, 17:26:50 GMT[1] |
Rocket | Thor-Delta J (Thor 476 / Delta 057) |
Launch site | Vandenberg, SLC-2E |
Contractor | Douglas Aircraft Company |
Entered service | 4 July 1968 |
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 program ← Explorer 37 |
Explorer 38 spacecraft measured the intensity of celestial radio sources, particularly the Sun, as a function of time, direction and frequency (0.2 to 20-MHz). The spacecraft was gravity-gradient stabilized. The spacecraft weight was 602 kg (1,327 lb), and average power consumption was 25 watts. It carried two 230 m (750 ft) long V-antennas, one facing toward the Earth and one facing away from the Earth. A 37 m (121 ft) long dipole antenna was oriented tangentially with respect to the Earth's surface.[3]
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 to 9.18-MHz, two multichannel total power radiometers 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 dipole antenna capacitance probe operating from 0.25 to 2.2-MHz. Explorer 38 was designed for a 12 months minimum operating lifetime.[3]
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 and 9.2-MHz, but it was subjected to the continuous radio interference coming from our planet, 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 local electron 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 reduce photoemission 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 frequency radiometers 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 50 dB 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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Explorers Program | |||
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List of Explorers Program missions | |||
Missions | ![]() | ||
Proposals |
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← 1967 · Orbital launches in 1968 · 1969 → | |
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Surveyor 7 | Explorer 36 | Kosmos 199 | OPS 1965 | OPS 5028 | Kosmos 200 | Apollo 5 | OPS 2243 · OPS 6236 | Kosmos 201 | E-6LS No.112 | Kosmos 202 | Kosmos 203 | OPS 7034 | Zond 4 | OGO-5 | Kosmos 204 | Kosmos 205 | Explorer 37 | DS-U1-Ya No.1 | OPS 5057 | Kosmos 206 | OPS 4849 · OPS 7076 | Kosmos 207 | Kosmos 208 | Kosmos 209 | Kosmos 210 | Apollo 6 | OV1-13 · OV1-14 | Luna 14 | Kosmos 211 | Kosmos 212 | Kosmos 213 | OPS 5165 | Kosmos 214 | Kosmos 215 | Kosmos 216 | Molniya-1 No.10 | 7K-L1 No.7L | Kosmos 217 | Kosmos 218 | Kosmos 219 | OPS 1419 | Kosmos 220 | ESRO-2B | Nimbus B · SECOR 10 | OPS 7869 | Kosmos 221 | Kosmos 222 | Kosmos 223 | Kosmos 224 | Sfera No.12L | OPS 5138 | Kosmos 225 | Kosmos 226 | IDCSP 20 · IDCSP 21 · IDCSP 22 · IDCSP 23 · IDCSP 24 · IDCSP 25 · IDCSP 26 · IDCSP 27 | Strela-2 No.3 | Kosmos 227 | OPS 5343 · OPS 5259 | Kosmos 228 | Kosmos 229 | Explorer 38 | Kosmos 230 | Molniya-1 No.13 | Kosmos 231 | OV1-15 · OV1-16 | Kosmos 232 | Kosmos 233 | Kosmos 234 | OPS 2222 | OPS 5187 | OPS 5955 | Explorer 39 · Explorer 40 | Kosmos 235 | ATS-4 | ESSA-7 | Orbiscal 1 · OV5-8 · Gridsphere 1 · Gridsphere 2 · Gridsphere B · Gridsphere R · LCS-3 · LIDOS · SECOR 11 · SECOR 12 · Radcat · P68-1 | Kosmos 236 | Kosmos 237 | Kosmos 238 | Kosmos 239 | OPS 5247 | Kosmos 240 | Zond 5 | Kosmos 241 | OPS 0165 · OPS 8595 | Intelsat III F-1 | Kosmos 242 | Kosmos 243 | LES-6 · OV2-5 · ERS-21 · ERS-28 | Kosmos 244 | Kosmos 245 | ESRO-1A | Molniya-1 No.14 | OPS 0964 | Kosmos 246 | Kosmos 247 | Apollo 7 | Kosmos 248 | Kosmos 249 | OPS 4078 | Soyuz 2 | Soyuz 3 | Kosmos 250 | Kosmos 251 | Kosmos 252 | OPS 1315 | OPS 5296 | Pioneer 9 · ERS-31 | Zond 6 | Kosmos 253 | Proton 4 | Kosmos 254 | Kosmos 255 | STV-1 | Kosmos 256 | Kosmos 257 | OPS 6518 | HEOS-1 | OAO-2 | Kosmos 258 | OPS 4740 · OPS 7684 | Kosmos 259 | ESSA-8 | Kosmos 260 | Intelsat III F-2 | Kosmos 261 | Apollo 8 | Kosmos 262 | |
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in underline. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets. |