K_a-Band Link Budget Analysis for Deep Space Communications

The emerging demand for increased data rates between Earth, the lunar gateway, Mars, and various other deep space probes will stretch existing deep space network (DSN) antennas beyond capacity. The DSN antennas distributed across Canberra, Madrid, and Goldstone are capable of tracking the Mars Reconnaissance Orbiter (MRO) travelling tens of millions of kilometers from Earth, and life extension efforts continue to support such critical space infrastructure. However, these legacy systems still suffer failures and outages that have resulted in delays in data communication and this situation continues to be a significant challenge. This explains the current interest in this area. Thus it is timely that we present a fresh tutorial on a link budget to Mars, elucidating use of the latest ITU-R model recommendations for propagation through the Earth’s atmosphere. To facilitate communication to Mars, we target a downlink frequency in the K<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> band (31.8–32.3 GHz) as it allows for increased data transmission rate, increased effective isotropic radiated power (EIRP) and reduced antenna size. In this tutorial paper, we therefore focus on a link budget in the K<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> band and take into account all major sources of attenuation including free space path loss (FSPL), rain, fog, and system noise temperature (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sys</sub>), which are critical for ensuring a positive link margin. As a case study, the presented link budget uses parameters for actual MRO communications and the Canberra DSN antenna assuming communication from the Mars Reconnaissance Orbiter (MRO) to the Canberra DSN-DSS-35. For point of comparison, we compare this with the case of Lunar to Earth communications.