Spacecraft Study Guide

📖 Core Concepts Spacecraft – Vehicle built to travel and operate in outer space (e.g., satellites, probes, crew capsules). Flight Categories – Sub‑orbital: reaches space (> 100 km) and returns without completing an orbit. Orbital: placed into a closed orbit around a body. Human vs. Robotic – Human missions carry crew; robotic missions operate autonomously or via remote control (space probes). Recoverable vs. Expendable – Recoverable spacecraft survive re‑entry and can be reused; expendable remain in space or are discarded after one use. Kármán Line – Internationally accepted boundary of space at 100 km altitude. Subsystems – Groups of hardware that perform a single function (e.g., Attitude Control, Propulsion, Power, Thermal). --- 📌 Must Remember First artificial satellite: Sputnik 1 – 4 Oct 1957. First crewed orbital flight: Vostok 1 – Yuri Gagarin, 1961. Geostationary orbit altitude: 35 900 km (satellite appears stationary). Major crewed nations (as of 2016): USSR/Russia, United States, China. Space Shuttle retirement reasons: high refurbishment cost, safety concerns, expensive expendable components. Starship goal: transport crew & cargo to Earth orbit, Moon, Mars; support up to 100 crew for interplanetary trips. --- 🔄 Key Processes Attitude Determination & Control Measure orientation (star trackers, sun sensors, gyros). Adjust using reaction wheels, thrusters, magnetic torquers. Guidance, Navigation & Control (GNC) Guidance: compute desired trajectory. Navigation: determine current position/velocity (e.g., GPS, ground tracking). Control: fire thrusters or engines to follow the trajectory. Gravity‑Assist (Voyager example) Fly close to a planet → spacecraft gains/loses speed relative to the Sun, changing its path without extra propellant. --- 🔍 Key Comparisons Sub‑orbital vs. Orbital Sub‑orbital: no closed orbit, short flight, returns quickly. Orbital: achieves sufficient horizontal velocity (7.8 km s⁻¹ for Low Earth Orbit). Communications Satellite (GEO) vs. LEO Constellation GEO: single satellite, stationary view, high latency (240 ms). LEO: many moving satellites, low latency, requires tracking antennas. Space Capsule vs. Spaceplane Capsule: blunt, non‑winged, relies on heat shield, typically reusable only partially. Spaceplane: winged, can glide to runway, fully reusable (e.g., Space Shuttle). --- ⚠️ Common Misunderstandings “Space begins at the Kármán line” – It is a convention; some agencies use 80 km or 50 mi. All reusable spacecraft are cheap – Reusability reduces launch cost only if refurbishment is inexpensive (Space Shuttle proved otherwise). Robotic = unmanned – Some uncrewed missions are piloted remotely; autonomy level varies. --- 🧠 Mental Models / Intuition “Orbit = balance” – Think of a satellite constantly falling toward Earth but moving forward fast enough to miss it; orbital speed is the “sweet spot” where gravity = centripetal force. “Spacecraft as a LEGO bus” – The bus (structural subsystem) holds payloads and subsystems (power, thermal, etc.) like LEGO bricks; swapping a brick changes function without redesigning the whole bus. --- 🚩 Exceptions & Edge Cases Re‑entry heat shield – Capsules survive re‑entry via blunt‑body physics; spaceplanes need both heat shields and aerodynamic control surfaces. Gravity‑assist windows – Rare planetary alignments (e.g., 1979–1982 for Voyager) are needed; not always available. Geostationary satellites over high latitudes – Appear low on the horizon, requiring larger ground antennas. --- 📍 When to Use Which Choose GEO vs. LEO for communications: Use GEO for continuous coverage of a fixed region (broadcast TV, weather). Use LEO constellations for low‑latency broadband (e.g., Starlink). Select spacecraft type based on mission: Capsule → simple re‑entry, high‑mass payload, limited maneuverability. Spaceplane → need runway landing, multiple missions per year, higher development cost. Pick propulsion type: Chemical rockets for rapid orbit insertion or de‑orbit burns. Electric (ion) propulsion for long‑duration, low‑thrust deep‑space missions. --- 👀 Patterns to Recognize “Orbit altitude → purpose” – GEO (35 900 km) → communications; LEO (200–2 000 km) → imaging, science, crew transport. “Mission cost drivers = reusability + refurbishment time” – Space Shuttle (high cost) vs. Starship (designed for rapid turnaround). “Subsystem naming = function” – Attitude → orientation; Thermal → temperature control; Power → generation & distribution. --- 🗂️ Exam Traps Confusing “sub‑orbital” with “sub‑orbital launch vehicle” – The vehicle may be orbital (e.g., a rocket) even if the flight is sub‑orbital; focus on the flight profile, not the launch vehicle type. Assuming all “spaceplanes” are reusable – The Buran flew once uncrewed; reusability is a design goal, not a guarantee. Mixing up “recoverable” and “reusable” – A recoverable capsule can be retrieved but may be discarded after one use; reusable implies multiple flights (e.g., SpaceX Dragon). Attributing the first crewed spacecraft to the United States – The first crewed orbital spacecraft was Soviet Vostok 1, not U.S. Freedom 7 (which was sub‑orbital). ---