Watching Jonathons’ video presentation on micro depots for very small satellites even before servicing large satellites or manned vehicles, and reading a few articles on electric propulsion triggered a thought, or possibly just a memory of something suggested elsewhere. What if the micro depot had a laser or microwave mounted to not only fuel the vehicles but also to leverage the propellant capabilities.
An orbital laser for boosting just refueled cubesats would not have to be all that large to have an effect all out of proportion to its’ size. Say the kilogram cubesat just bought a half kilogram of hydrogen plus the beamed powers services sold separately for a prospecting mission to an NEO that required 5 km/sec of V to reach. The laser would need to add enough heat to get an Isp of about 1,200 out of the hydrogen aboard the cubesat. The exhaust would still be cooler than that of any normal chemical rocket engine. The orbit of the depot would allow it to follow the cubesat being boosted around half an orbit or more. A 2,000 second burn (lase?) would only require an average of a quarter gee of acceleration. Average thrust is in the 300-400 gram range. That puts the power beam requirements at well under a megawatt depending on assumptions.
By getting high Isp performance on board the cubesat with basically a tank and nozzle instead of the higher complexity and expense of an electric propulsion system with on board power, it should be possible to get the costs really low. A small depot/beam facility could send thousands of explorers and prospectors a year way out there for relatively small change in the cubesat propulsion costs. The high Isp also considerably reduces the costs of shipping propellant to orbit compared to chemical engines.
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