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GPS BLOCK IIR SATELLITES WILL PROVIDE SAME POWER PERFORMANCE AT THE FACE OF THE EARTH AS THE CURRENT BLOCK II/IIA SATELLITES

The GPS JPO would like to address any concerns that GPS signal power on the face of the earth from the new Block IIR satellites will be any different compared to the current constellation of Block II/IIA satellites. The Block IIR satellites will perform at the current Block II/IIA satellite power levels. All GPS receivers currently in use and in future design can expect the same level of performance from the signal power level provided from either a Block II/IIA or Block IIR satellite.

Actual GPS received signal level power measurements are made at a US Air Force tracking station located in California. Satellite signal level power at the face of the earth is commonly compared in terms of link margin. The link margin measures how much stronger the received signal is compared to the specified value. The actual measured link margin at the specified edge of earth (EOE) for the L1 signal is typically 3.5 dB averaged across the constellation of 24 Block II/IIA satellites. Based on actual factory test data from the first two Block IIR satellites, we predict a 3.5 dB link margin - the same as the actual power measurements from the Block II/IIA satellites now on orbit.

Power levels are predicted within a range of variation and at the start of satellite life. Naturally, on a satellite by satellite basis, there is still some very minor variation the in power level produced by each individual satellite and in measuring that variation, since these are very small levels. Test data from the first two Block IIR satellites indicate they are in the bounds of expected deviation at the beginning of satellite “life.” Thus, they are expected to perform at the same level as the current Block II/IIA satellites. Once satellite “life” starts with the satellite on-orbit, power levels at the face of the earth will decrease slightly with age of the satellite due many space environmental factors such as degradation of the solar panels. In addition, power levels at the face of the earth are also affected by conditions beyond satellite design parameters, as atmospheric and environmental conditions. The link margin provides a “reserve” capability to accommodate this gradual performance degradation and unusual atmospheric deterioration of the signal and still meet the specified signal strength on the earth.

The new Block IIR GPS satellite will provide users at or near the face of the earth the same level of expected performance as the current constellation of Block II/IIA satellites. The GPS JPO wishes to reconfirm our commitment to providing the GPS service as a national and international utility.