6 ms·
I didn’t realize krypton was a fuel source. I thought Elon put in an easter egg, only to be disappointed by my ignorance.
by elamje 7y ago
I didn’t realize krypton was a fuel source. I thought Elon put in an easter egg, only to be disappointed by my ignorance.
- SECProto 7y agoIt's not a fuel, it's a propellent (simply put, solar electric is used to accelerate the Krypton out the end of the thrusters)
- wtallis 7y agoThe krypton isn't being used as a chemical reactant, and in fact being largely chemically inert is a benefit for ion thrusters. I suspect they're using krypton instead of xenon due to the latter being more expensive, even though the higher atomic mass of xenon would be beneficial.
- Tuna-Fish 7y agoLower atomic mass gives better Isp, although for power-limited situation you usually want to maximize thrust instead. In the pre-flight press conference the topic of krypton thrusters came up, and at first he made a superman joke, but then said the real answer was the lower cost of krypton.
- isolli 7y agoWhat does "Isp" stand for?
- KAMSPioneer 7y agoProbably meant specific impulse. https://en.wikipedia.org/wiki/Specific_impulse https://en.wikipedia.org/wiki/Specific_impulse
- ProblemFactory 7y agoIt stands for Specific Impulse, which is a measure of fuel economy for rocket engines.
- dotancohen 7y agoSpecific impulse. It is a convoluted method of measuring the exhaust velocity, and thus the efficiency, of a reaction engine.
- skykooler 7y agoLower atomic mass gives better Isp for chemical rockets, for which the exhaust velocity is proportional to the temperature of the exhaust divided by the square root of the atomic mass of the exhaust product. However, these satellites are using ion propulsion. In ion engines, the exhaust velocity is constant, so a higher atomic mass allows each atom / molecule to carry more energy. This makes higher mass fuels like Xenon better for ion engines. (Radon would be better still but the radioactivity poses problems for various systems.)
- mikeash 7y agoWhy is the exhaust velocity constant? I would naively expect the engine to impart roughy equal energy into each atom, so that lighter atoms would be faster. But I know little of the specifics of ion engines.
- Tuna-Fish 7y agoThrust power = Isp * thrust. For the same amount of input power, increasing molecular size raises thrust and reduces Isp.
- baq 7y agoKrypton is reaction mass. Sir Isaac Newton is the deadliest son-of-a-bitch in space.