Re: It's not "Rocket Science"
(you need storable fuel that still flows in the frigid temperatures of space and you need to get that fuel into the engine at 0g)
That's usually achieved by keeping the fuel tanks at a desired temperature, especially for hydrazine, which freezes at about 2C. The Voyagers, New Horizons, and Cassini are maintaining their hydrazine and electronics at approx. 20C. New Horizons, for example, put its hydrazine tank in the center of its structure and keeps it at 10 - 30C with waste heat from its electronics.
Of course, there are still risks of fuel freezing in an outlying pipe, which has happened. In 2014, a Russian Fregat upper stage failed because hydrazine froze in a pipe. That case was due to the line being too close to a super chilled helium line rather than the "frigid temperatures of space," but the means of addressing fuel freezing needn't be very low freezing point substances. (Fregat relocated the fuel and helium lines.)
Biting the hand that feeds IT
