Several proposed space-based X-ray observatories apply TES-based micro-calorimeters as energy-dispersive imaging detector. The number of independently readout pixels is an important figure of merit for the scientific yield of such instruments. Design studies have shown that the power consumption of the SQUID readout is one of the driving design parameters which limits the maximum number of pixels which can be accommodated. Different multiplexing schemes, each with different properties and multiplexing factors have been proposed and demonstrated for the readout of the TES-based detectors. In an effort to estimate how the different readout multiplexing schemes differ in scalability for future space-based applications, we have made a comparison of the reported power consumption of the main multiplexing schemes currently under consideration for different space-based telescopes, i.e. time-domain multiplexing, frequency-domain multiplexing, and microwave SQUID multiplexing. It was found that, despite the different architectures and multiplexing factors, the power consumption per pixel at cryogenic temperatures is rather similar. We will analyze the origin of this phenomenon, and discuss directions of development to further improve on this number.
