SELENESafe Exploration for Lunar Environments: Navigation Experts |
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To determine the power needed to supply the TX/RX chain between the astronaut and the lunar lander, as well as between the astronaut and the RFID tags, it is necessary to breakdown the individual components of all the links. The breakdown of component quantity and peak power dissipation is shown in the table below. Additionally, the RF power needed to be supplied to the power amplifier to achieve a TX power of -5dB (300mW) is included in the diagram.
The power added efficiency of the T7023 Silicon-Germanium power amplifier is quoted to be 45%, an impressive value. By incorporating a feedback loop incorporating Adaptive Digital Pre-distortion to minimize non-linearity, boosting the overall efficiency. We assume that with this feedback loop we are able to achieve a total efficiency equivalent to the power added efficiency of the T7203 PA. Using this value, the power needing to be supplied to the PA is: The power which is dissipated by the amplifier and not transmitted is simply: Summing all of the dissipated powers together, it is found that the total peak power (assuming all components are operating at their peak) is ~ 6.1 Watts. Under the assumption that a typical lunar expedition will last no longer than six hours, and that the batteries used to supply the power must be recharged once reaching 10% capacity, we can determine the Watt-hours that need to be supplied: To achieve this capacity, we can simple Lithium Ion batteries connected in series. These batteries would be self-contained within the suit of the astronaut, and therefore shielded from any non-terrestrial environmental factors (temperature gradients, etc..). We have spec’ed our system to accommodate the small, inexpensive Canon MP-511 LI-ION Digital Camera Batteries. These batteries have the specifications as illustrated in the table below.
From this capacity, it is evident that our power needs can be achieved with four of these batteries connected in series (which will provide us with 48 Watt-hours). For increased safety margin, an additional four batteries will be included within every spacesuit as back-ups for unexpected failures. The lightweight and small size of these batteries allows makes this safety margin possible |