Energy It is equal to the energy expended (or work done) in applying a force of one newton through a distance of one metre. However energy is also expressed in many other units not part of the SI, such as ergs, calories, British Thermal Units, kilowatt-hours and kilocalories, which require a conversion factor when expressed in SI units. The SI unit of energy rate (energy per unit time) is the watt, which is a joule per second. Thus, one joule is one watt-second, and 3600 joules equal one watt-hour. The CGS energy unit is the erg and the imperial and US
Orbital replacement unit (HST) of fasteners). HST servicing mission 3A (SM3A) replaced (or added) 15 ORUs, e.g. it replaced the DF-224 computer with the "Advanced Computer". The electrical system of the International Space Station also has such subsystems that provide power generation, power distribution and energy storage. Orbital replacement unit (HST) An orbital replacement unit or orbital replaceable unit is a modular component of spacecraft that can be replaced upon failure either by robot or by extravehicular activity. The Hubble Space Telescope (HST) was designed with 70 such parts, including scientific instruments and limited-life items such as batteries. On HST some parts were designed