Before detailing how the Precision Doppler system described last week can be used to guide the critical Lunar Transfer operation, I want to discuss other systems enabled by the Phase Locked RF mode.

If the ground station, in the Phase Locked link, offsets its uplink, Reference signal by the same amount (but opposite direction) that the returned, Doppler shifted downlink signal is offset, then the spacecraft transmitter's frequency (halfway between the two signal frequencies seen at the ground station) can be precisely maintained. It can be as accurate as the ground station's best frequency reference. The low cost, low power and fraction of a gram transmitter in a small spacecraft can thus achieve “Part Per Billion (= ppb)” frequency accuracy. (Note that Relativistic effects – appearing as a “Quadratic Doppler Shift” - are ignored in this discussion.)

Since this accuracy corresponds to the Doppler Shift for 0.3 meter per second motion (about 1 foot per second), very close velocity measurements can be made by receiving stations not directly linked to the satellite. Good crystal oscillators have a stability better than this 1 ppb and can maintain this accuracy long term as a “GPS Disciplined” oscillator. Adding two Earth receiving Stations at substantial distances from the original ground station, will allow the spacecraft's three dimensional velocity vector to be measured to this resolution (about 0.003% of its orbital or escape velocity).

This does not produce the phenomenal Distance accuracy of the primary, Locked Loop, since the errors will accumulate with time, and can add tens of kilometers each day. But the 0.003% velocity vector accuracy is more than good enough to “Hit the Moon”.

Three descent “Ham Radio” setups, in appropriate places, could monitor – and provide feedback – for the critical “Lunar Transfer” orbital transition .

The ability to accurately achieve this transition is the difference between needing a $60 Million ++ (GTO+) launch system, and making do with a $10 Million (or less as Secondary Payload) launch to LEO. And that is not a trivial factor in business planning!