Aerospace Glossary
Technical aerospace terminology explained clearly for educated readers. No jargon-filled definitions—just clear, accessible explanations.
A
Aphelion
The point in an orbit where an object is farthest from the Sun. For example, Earth reaches aphelion around early July each year, when it is approximately 152 million kilometers from the Sun. This is the opposite of perihelion. The term comes from the Greek words "apo" (away from) and "helios" (sun).
Related terms:
C
Cislunar
The region of space between Earth and the Moon, including lunar orbit. Artemis missions will establish infrastructure in cislunar space.
Cryogenic Propellant
Rocket fuels stored at extremely low temperatures, such as liquid hydrogen (-253°C) or liquid oxygen (-183°C). They provide high performance but pose storage challenges.
D
Delta-v
The change in velocity required for a spacecraft to perform a maneuver. Higher delta-v requirements demand more propellant, making it a critical factor in mission planning.
F
Fairing
The protective nose cone of a rocket that shields payloads from aerodynamic forces during ascent through the atmosphere. It separates and falls away once in space.
H
Hohmann Transfer
An orbital maneuver using two engine impulses to transfer between orbits. It is the most fuel-efficient way to move between circular orbits of different altitudes.
L
Lagrange Point
Positions in space where the gravitational forces of two large bodies (like Earth and Sun) balance, allowing spacecraft to maintain stable positions with minimal fuel.
Low Earth Orbit
An orbit around Earth with an altitude between 160 and 2,000 km. LEO is where the ISS operates and where most human spaceflight occurs.
M
Methalox
A rocket propellant combination of liquid methane (CH₄) and liquid oxygen (LOX). Chosen for its performance, storability, and potential for in-situ production on Mars.
P
Payload Capacity
The maximum mass a launch vehicle can deliver to a specific orbit. Capacity decreases significantly for higher energy orbits like geostationary or lunar trajectories.
Perihelion
The point in an orbit where an object is closest to the Sun. For example, Earth reaches perihelion around early January each year, when it is approximately 147 million kilometers from the Sun. This is the opposite of aphelion. The term comes from the Greek words "peri" (near) and "helios" (sun).
Related terms:
S
Specific Impulse
A measure of rocket engine efficiency, representing the thrust produced per unit of propellant consumed. Higher Isp means better fuel efficiency.