Launch, In-Space and Entry Operations

1. Launch Logistics & Ground Operations

Launch Site Selection: Driven by Earth’s rotation (advantage at the equator for GTO), range safety (launching over oceans), and reachable orbital inclinations.
Integration Methods:
- Vertical: Vehicles like Ariane 5/6 are integrated upright. Requires massive Mobile Gantry structures but protects against horizontal structural loads.
- Horizontal: Used by Soyuz and SpaceX. More cost-effective but requires the spacecraft to be designed to handle loads in two orientations.
Cleanroom Standards: Spacecraft are integrated in ISO 8 (Class 100,000) or ISO 7 environments to prevent particulate and molecular contamination of sensitive optics and electronics.

A launch base should allow for:

The Criteria for choosing a site are:

Tsiolkovsky Rocket Equation: $Δ v = v_{e} \ln \frac{m_{0}}{m_{f}}$ . This governs how much velocity change a rocket can achieve based on its fuel mass and exhaust velocity.
Propellant Performance:
- Solid: Reliable and high thrust (boosters), but non-restartable and difficult to stop once ignited.
- Cryogenic ( $L O X / L H 2$ ): Highest efficiency (Specific Impulse $I_{s p} \approx 450 s$ ), but requires complex insulation to keep fluids at near absolute zero.
- Hypergolic: Ignites spontaneously upon contact. Used for in-space maneuvers and reaction control systems (RCS) due to high reliability.
Electric Propulsion: Uses Ion or Hall-Effect thrusters. High $I_{s p}$ but extremely low thrust; ideal for deep space or station-keeping, but cannot launch from Earth.

Staging Logic: To reach the orbital velocity of ~7.8 km/s, rockets must shed "dead mass" (empty tanks). Each stage is optimized for either high atmospheric pressure or vacuum conditions.
Gravity Turn: A maneuver where the rocket uses gravity to curve its trajectory from vertical to horizontal, minimizing "gravity losses" and aerodynamic stress ( $M a x Q$ ).
Launch Azimuth: The heading of the launch determines the orbital inclination. A launch due East ( $90^{\circ}$ azimuth) results in an inclination equal to the launch site's latitude.

Phasing Maneuvers: Catching a target (like the ISS) requires a lower, faster "phasing orbit." Raising the altitude slows the chaser down relative to the target.
Clohessy-Wiltshire Equations: Describe the relative motion between two objects in orbit.
Approach Geometry:
- V-Bar: Approach along the velocity vector.
- R-Bar: Approach along the radius vector (from Earth toward the target).

Hohmann Transfer: The most fuel-efficient way to move between two circular orbits using two impulsive burns.
Patched Conics: A method of simplifying complex gravity by breaking the flight into:
1. Departure (Earth's Sphere of Influence - SOI)
2. Heliocentric (Sun's gravity)
3. Arrival (Target planet's SOI)
Gravity Assist: Using a planet's orbital velocity to "slingshot" the spacecraft, increasing speed without using fuel.

Re-entry Heating: Spacecraft must dissipate kinetic energy as heat. Blunt-body shapes create a "bow shock" that keeps the hottest plasma away from the vehicle's skin.
Thermal Protection Systems (TPS):
- Ablative: Shields that char and flake away (e.g., Apollo, Dragon).
- Reusable Tiles: Ceramic tiles that radiate heat (e.g., Space Shuttle, Starship).
Landing Methods:
- Parachutes: Standard for capsules (Soyuz, Orion).
- Retro-propulsion: Essential for Mars (where the air is too thin for just parachutes) and for SpaceX first-stage recovery.

SpaceX Starship: A fully reusable system using the Raptor engine (Methane/Oxygen). Methane is chosen for its performance and the ability to be manufactured on Mars (Sabatier process).
NASA SLS: A heavy-lift expendable rocket designed for the Artemis lunar missions.