Beginner's Guide to Cosmonautics

Space travel is a complicated profession. After all, rocket science has long become a common phrase for difficult to understand topics. Add on top of that the jargon built up over more than two centuries of spaceflight, and for the layperson a conversation between cosmonauts will just sound like stream of technobabble. If you don't want to be completely lost next time you travel through space, look no further: This article will explain the most important concepts and phrases.

Intro to Orbital Mechanics

Orbits

Getting into space is not that hard, in the grand scheme of things. The real issue is staying there. After all, you never escape gravity: Once you turn off your engines, you will be in free fall. The trick to not hitting the planet is, well, missing it. If you just move sideways fast enough, you'll keep falling past the planet. This is called an orbit.
When taking off, a rocket does not fly straight up, but gradually turns over to build horizontal speed until it eventually is fast enough to stay in orbit. This is doubly true for an SSTO spaceplane, which flies horizontally from the beginning and slowly climbs higher in the atmosphere while gaining horizontal speed.
An orbit can largely be described using three measurements: Apoapse, periapse and inclanation. Apoapse and periapse are the highest and lowest point respectively. Since the orbit is an ellipsis, with the central body at one of the focal points, this fully determines the shape of the orbit. The inclanation of the orbit, describes how the plane of the orbit is oriented in space. It is the angle between it and the equator of the central body.

Maneuvers

The path a spacecraft will take through space is determined by it's current altitude (i.e. the distance to the center of the celestial body it is orbiting) and its velocity. To maneuver in space, then, is to change your velocity in such a way, that the orbit will have the desired properties afterward. It is important to note that, if no further maneuver takes place afterwards, the spacecraft will always return to the point in which the maneuver took place.
Any maneuver can be broken down into three components, in which velocity is added or subtracted. A velocity change in the direction of motion changes the height of the orbit. Adding velocity will raise it and subtracting velocity will lower it. Adding velocity in the direction perpendicular to the plane of the orbit will tilt it, i.e. change the inclination. Adding velocity inward or outward will roughly speaking rotate the orbit in its plane, though it also is deformed in the process.
Every maneuver requires a certain "amount" of velocity change. Based on the usual mathematical notation, this is called the delta V of the maneuver. Which maneuvers a spacecraft can do, and equivalently which places it can get to, thus depends on how much it can change its velocity. For this reason, delta V is also used as a characteristic of rockets, where it depends on the dry mass, fuel capacity, engine efficiency and so on.

Directions

In space, where there is no clearly defined "up" and "down", the systems for describing directions work a little differently. There are in fact two different systems, used for different purposes. One is fixed with relation to the ship and used to describe locations in or near the craft. The other one is relative to the orbit and is used to describe maneuvers.

Everyday Equivalent	Relative to Craft	Relative to Orbit
Up	Dorsal	Radial out
Down	Ventral	Radial in
Forward	Forward	Prograde
Backward	Backward	Retrograde
Left	Port	Normal
Right	Starboard	Anti-normal

A spacecraft has six possible directions of movement, three each for translation and rotation. They have names taken from the phrases for the movement of water vessels.

Axis	Translation	Rotation
Forward/Backward	Surge	Roll
Dorsal/Ventral	Heave	Yaw
Starboard/Port	Sway	Pitch

Glossary

The following is a list of assorted cosmonautical terms and their meanings.

Burn	Firing the engines of a spacecraft. Also used to describe maneuvers, for example: "A 142 m/s retrograde burn".
CAPCOM	Short for capsule communications. In the early days of space travel this was the person in mission control responsible for talking to the cosmonauts. Nowadays it refers to the flight controllers coordinating docking at spacestations or takeoff and landing at spaceports, analogously to the tower in air travel.
EDL	Originally short for entry, descent and landing, i.e. the systems of a spacecraft facilitating a safe return to Earth. However, over the years it has instead come to be cosmonaut slang for shore leave, be it on a planet surface or in space.
EVA	Short for "extravehicular activity". Working outside of the vessel, when this requires a pressurized suit.
Hydrolox	Short for (liquid) hydrogen and liquid oxygen. The most common rocket fuel.
RCS	Short for reaction control system. The smaller thrusters used for rotational control and small lateral movements.
Rendezvous	The maneuvers necessary for two spacecraft to end up in the same location. This involves some counterintuitive physics: For example, if you want to catch up with another craft ahead in the orbit, you might intuitively want to accelerate toward it. This, however, would raise your orbit, therefore increasing the orbital period and causing you to fall behind. Instead, you need to decelerate to lower the orbit and catch up that way.

See Also