Universal Space Networks, one of the Google Lunar Xprize's preferred partners maintains a network of communications systems. They have offered the use of their system for half the price of the normal going rate and therefore it has become the most efficient and economical option for the earth station. The frequency has been chosen to comply with their system and the gain values are provided in the system specifications. The link parameters table below describes all of the necessary parameters for the Earth to Moon link. The italicized parameters represent those which were calculated following the table.
| Link Parameters | ||
| Carrier Frequency | u: 2.050 GHz | d: 8.175 GHz |
| Bandwidth | u: 3.5 MHz | d: 3.5 MHz |
| Distance | 3.763*10^5 km | |
| Beamwidth | Narrow | |
| Required SNR | -130.5 dB | -130.5 dB |
| ES Antenna Gain | u: 78 dBW (EIRP) | d: 37.0dB/k |
| MS Antenna Gain | u: 32 dB |
d: 44 dB |
| Power | u: incl. in ES AG | d:1.7 dBW |
In order to optimize the performance of the link while simultaneously minimizing the amount of power transmitted and moon station dish size, a link budget for the downlink was first calculated using the equation below:
To simplify the calculation, the losses at the transmitter end and receiver end can be absorbed into the gain values. Since all of the antenna specifications are given in dB, the logarithmic form of the equation is used:
However, since the G/T value was provided rather than G, the link budget can be rewritten to the following:
Finally, the transmitter gain and power terms can be combined for the EIRP of the transmitter can be solved for:
Using the values from the above table, the EIRP necessary is 38.89dB
Rain attenuation must be taken into account, for this link. Using the equations described on the main communications page and the altitude and rain height averages for Hawaii, where the earth station is located, the rain attenuation is estimated to be about .8dB.
The adjusted EIRP must be 36.98 dBW.
In order to try and keep the size and costs of the moon station low, a collapsable reflector antenna with diameter of 2 meters has been chosen. Assuming an antenna efficiency of .8, the gain provided by this antenna for the downlink is 35.2dB.
Therefore, the power transmitted by the moon station must be 1.7 dB or 1.5 W
For the uplink, An S-band frequency is being used, Since the same antenna will be used on the moon station for both the uplink and the downlink, the gain for the lower frequency signal will be lower. Assuming .8 efficiency again, the antenna gain will be 26.16dB.
Working the link budget for the uplink returns a necessary EIRP of only 38.9 from the earth station. This value is far below what Universal Space networks offers, so the dish will in fact work for both links.
