A full worked 3U CubeSat mission design case study — sun-synchronous orbit selection, a five-subsystem mass budget, worked solar-array power sizing, ADCS pointing accuracy tied to ground sample distance, and a UHF communications link budget carried through to a link margin in dB.
The project brief: a 3U CubeSat (4.0 kg maximum wet mass) built for Earth imaging on a nominal one-year mission life, with every subsystem sized against a hard mass ceiling and a power ceiling set by whatever a body-mounted solar array on a 30 cm-long bus can actually generate. Deliberately framed as this program's smallest-margin real project, it is a first-order mission design worked the way a CubeSat systems engineer actually works one, where every budget has to close on paper because there is no opportunity to fix an undersized subsystem once the spacecraft is on orbit.
This module walks the whole design the way a real mission architect would: a worked sun-synchronous orbit rationale, a five-subsystem mass budget summing to the 4.0 kg limit with real margin, an orbit-average power calculation carried through to solar-panel area, a pointing-accuracy requirement derived directly from the imaging payload's ground sample distance, and a UHF link budget closed against worst-case low-elevation pass geometry. The full worked numbers, complete bill of materials, and finished design reasoning are part of the unlocked module below.