S.1 Spacecraft Propulsion Systems Chapter 1: Introduction to ...

Impulse bits
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Impulse bit is the smallest change in momentum required to allow for e.g. fine attitude
and orbit control of a spacecraft.
Storable propellants
Storable Propellants are liquid (or gaseous) at ambient temperature and can be stored for
long periods in sealed tanks, e.g. monopropellant hydrazine (see chapter S1B8C3).
In contrast, cryogenic propellants, which are liquefied gases at low temperature, such as
liquid oxygen (-147 °C) or liquid hydrogen (-253 °C) are difficult to be used for long space
flight missions.
Note: at present only storable propellants are used for space flight missions.