A study program was initiated at the Goddard Space Flight Center in 1962 to survey the astronomical observations most readily and profitably performed by an orbiting radio observatory, to analyze the antenna configurations most appropriate for such a mission and to develop the radiometers and other supporting instrumentation required for a radio astronomy satellite. This study has culminated in the conceptual design of a spacecraft intended solely for radio astronomical observations at

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... hs beyond the ionospheric cut-off. By utilizing long (250 m) antenna elements with a terminating resistance placed an odd number of quarter-wavelengths from the end, a V-antenna can be formed having a beamwidth less than 30° and an 18 db front-to-back ratio over a band of frequencies near 5 MHz. Proper combinations of four such long elements in a double-V or X configuration, furthermore can be made to yield some gain over a, dipole for observations as low as 0.3 MHz. A step-frequency, Ryle-Vonberg radiometer which employs an all solid-state-component comparison noise source has been developed to perform over a 70 db dynamic range with a relative accuracy of ± 0.5 db. A simple, precise instrument to measure both the resistive and reactive components of antenna impedance has also been developed for satellite use. Observations with this system from a gravity-gradient stabilized spacecraft in a 6000 km orbit would afford significant contributions to galactic studies, solar physics, and planetary astronomy by extending radio observations to frequencies in the range 0 3 to 10 MHz.