Research File 005
Rockets &
Aerospace Engineering
Controlled explosions climbing out of Earth's gravity well at 28,000 km/h. The engineering that makes it possible is beautiful, brutal, and mathematically exact.
Controlled explosions climbing out of Earth's gravity well at 28,000 km/h. The engineering that makes it possible is beautiful, brutal, and mathematically exact.
A rocket works by expelling mass at high velocity in one direction, producing thrust in the opposite direction. That's it. Every action has an equal and opposite reaction. The challenge is doing this with enough force, efficiency, and reliability to escape Earth's gravity.
A rocket engine mixes fuel and oxidiser in a combustion chamber, burns them to create hot expanding gas, and accelerates that gas through a nozzle to maximize exhaust velocity. The faster and heavier the exhaust, the more thrust — Newton's Third Law applied at enormous scale.
Liquid oxygen + refined kerosene. Falcon 9's Merlin engine uses this. High density (compact tanks), good performance, simpler to handle than hydrogen. LOX stored at −183°C. Exhaust velocity ~3.3 km/s. Most common in first stages.
Highest performance of any chemical propellant. Hydrogen must be stored at −253°C — just 20° above absolute zero. Extremely difficult to handle. Best specific impulse (~450s) — the theoretical ceiling of chemical propulsion.
SpaceX Raptor engine burns this. Cleaner than RP-1, easier than hydrogen. The critical advantage: methane can be produced on Mars from CO₂ and water (Sabatier process). Starship is designed to be refuelled on Mars for the return trip.
Pre-mixed fuel and oxidiser cast solid into the casing. Simple, storable, very high thrust at ignition. Cannot be throttled or shut down once lit. Used in Space Shuttle SRBs, military missiles, and solid upper stages.
An orbit is not "escaping gravity." It is falling toward Earth while moving horizontally so fast that you keep missing. At orbital velocity (~7.8 km/s), the curve of your trajectory exactly matches the curve of Earth's surface beneath you. You fall forever without hitting anything.
There is no fuel required to stay in orbit — just the initial velocity. An orbit is a state of freefall. Everything in the International Space Station floats not because there is no gravity — gravity is nearly as strong there as on the surface — but because everything is falling at the same rate.
The currency of spaceflight. Every manoeuvre costs Δv. Getting to LEO: ~9.4 km/s. Lunar orbit from LEO: ~3.2 km/s more. Mars from LEO: ~1.1 km/s more (with aerobraking). You spend Δv like money — run out and you're stuck.
Most fuel-efficient way to move between two circular orbits. Two burns: one to enter an elliptical transfer orbit, one to circularise at the new altitude. Used for almost all orbital manoeuvres from satellite repositioning to Mars missions.
Using a planet's gravity to gain velocity without propellant. Voyager used Jupiter and Saturn to reach interstellar space. New Horizons used Jupiter to reach Pluto in 9 years instead of 45. Essentially stealing momentum from a planet.
Engine efficiency — thrust per unit of propellant per second. Chemical rockets top out at ~450s. Ion engines reach ~10,000s. Nuclear thermal could reach ~1,000s. Higher Isp = more Δv from the same propellant mass.
A Falcon 9 costs ~$60M to build and only ~$200K to fuel. If you throw it away each time, launch costs stay high. If you can land and reuse it, cost per flight drops dramatically. SpaceX turned rockets from single-use fireworks into aircraft.