Final answer:
The question pertains to the engineering of spacecraft, especially those destined for distant parts of the solar system, which require high reliability, autonomy, and independent power sources to operate with a third attitude indicator.
Step-by-step explanation:
The subject of this question is engineering, specifically focused on spacecraft and the autonomous systems they require when exploring distant areas of our solar system. Space missions to outer planets like Saturn involve long flight times and communication delays due to the vast distances from Earth. Such challenges necessitate that spacecraft have high reliability and a high level of autonomy.
Independent power sources are crucial for these spacecraft, as reliance on solar energy is not feasible due to the diminished strength of the Sun's rays at such distances. Thus, missions like NASA's deep space voyages use plutonium-fueled nuclear power, while the European Space Agency's Rosetta had to rely on solar panels coupled with an automatic timer to hibernate and reactivate closer to the Sun.
Another example is the LightSail-1 mission, which aimed to demonstrate the feasibility of photon momentum travel using solar-powered Mylar sails. Regardless of the propulsion method, whether it is propellers or photon sails, an independent third attitude indicator is essential for spacecraft to navigate and maintain orientation without relying on direct control from Earth.