ALFA: a constellation mission for low frequency radioastronomy

The ALFA mission is proposed to be the first astronomical observatory to make high-resolution radio images in the vast region of the electromagnetic spectrum below Earth's ionospheric cutoff between 30 kHz and 30 MHz. The ALFA imaging interferometer consists of 16 identical small satellites with dipole antennas and low frequency radio receivers, distributed in a spherical array 100 km in diameter, yielding images with thousands of times the resolution previously available in this frequency range. The array will be placed in a nearly circular distant retrograde orbit about the Earth, with a typical range of 10/sup 6/ km. Each satellite communicates directly with a small (11 m.), low-cost antenna at each DSN site, providing parallel data paths and continuous coverage. As a result, the array is resilient to individual satellite failures; observing by the rest of the array will be unaffected.