SpaceX CEO Elon Musk was a guest in Sunday's episode of The Simpsons, and a jab from Lisa, who says that "for a man who likes electric cars he sure burns a lot of rocket fuel," seems to have hit the right note, compelling real-life Musk to give the world a quick rocketry lesson on Twitter.
Yes, it's coming from a cartoon character, but it's an interesting remark -- Elon Musk is also CEO of electric car company Tesla, trying his hardest to prove that gas-guzzling cars are the stuff of the past. Yet, SpaceX's Falcon 9 rocket's nine engines burn tens of thousands of gallons of kerosene per launch.
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There's a good reason why SpaceX is not trying to build an electric rocket, however -- according to Musk, it simply cannot be used to reach Earth's orbit.
If u saw @TheSimpsons and wonder why @SpaceX doesn't use an electric rocket to reach orbit, it is cuz that is impossible— Elon Musk (@elonmusk) January 26, 2015
Reason is Newton's Third Law. In vacuum, there is nothing to "push" against. You must react against ejected mass.— Elon Musk (@elonmusk) January 26, 2015
In subsequent tweets, Musk also quickly explains why space elevators, ion thrusters and railgun-based propulsion are unrealistic options for space travel as well.
And pls don't ask me about space elevators until someone at least builds a carbon nanotube structure longer than a footbridge— Elon Musk (@elonmusk) January 26, 2015
Ion thrusters are great, but have extremely tiny force (photon thruster even less). Must have more thrust than weight or you don't go up.— Elon Musk (@elonmusk) January 26, 2015
Final one: anything launched by a railgun (if you could ever reach ~ Mach 27) would explode upon exiting the barrel in our dense atmosphere— Elon Musk (@elonmusk) January 26, 2015
There you have it, folks: Even if electric cars one day take over the automotive industry, when it comes to space travel, for now we're likely stuck with good old propellant-based rocket engines.
BONUS: Check out a clip featuring Elon Musk from the Sunday's The Simpsons episode, below.