The discovery of observable electromagnetic radiation originating from beyond the Earth by Karl Jansky in the 1930s [1] has since resulted in the creation of an entire field of inquiry drawing inferences about the material of the universe based on analyzing observable electromagnetic radiation. However, the greatly increasing number of wireless devices is reducing the sensitivity of these radio observatories through pesky interfering signals in addition to raising the noise floor. One remaining solution to clean measurements is putting a radio telescope on the far side of the moon.
On the far side, an observatory samples the spectrum between 1 and 4 GHz with ADCs collecting data at 500Ksp/s with a quantization rate of 8 bits. Each sample is converted down to baseband for sampling through a series of downconverters mixing at incremental frequencies. To transfer the collected spectrum data from the moon, a communication link based on one geostationary satellite about the moon acting as a repeater can send data to the three rotating (relative to the moon) geostationary satellites about the Earth. The large spectrum being sampled yields a raw data rate of 48 Gbps which is made more manageable through QAM-1024, Turbocoding for lower allowable SNRs, and using CDMA to spread the 12288*2 small bites of the spectrum over a bandwidth of around 60 GHz. The long chip sequences required with so many channels yields a fairly high processing gain that enables communication from the moon to Earth with only 1 W. However, the moon's uplink is higher at 1000 W, because the repeater system is looking for power above the noise floor and nothing more. However, this implementation is not perfect. The vast number of discrete components makes for a potential service disaster waiting to happen. Furthermore, sampling re-interleaving and ordering may prove to be difficult to do on a continuous stream on the Earth side. Yet, the prospect of using such a low power makes for an attractive and affordable design.
