**Astronautics** (alternatively also cosmonautics) is the theory and practice of navigation beyond Earth's atmosphere.

The term *astronautics* (originally *astronautique* in French) was coined in the 1920s by J.H.Rosny, president of the Goncourt academy, in analogy with aeronautics. Because there is a degree of technical overlap between the two fields, the term aerospace is often used to describe both at once. In 1930, Robert Esnault-Pelterie publishes the first book on the new research field.

As with aeronautics, the restrictions of mass, temperatures, and external forces require that applications in space survive extreme conditions: high-grade vacuum, the radiation bombardment of interplanetary space and the magnetic belts of low Earth orbit. Space launch vehicles must withstand titanic forces, while satellites can experience huge variations in temperature in very brief periods. Extreme constraints on mass cause astronautical engineers to face the constant need to save mass in the design in order to maximize the actual payload that reaches orbit.

The early history of astronautics is theoretical: the fundamental mathematics of space travel was established by Isaac Newton in his 1687 treatise Philosophiae Naturalis Principia Mathematica. Other mathematicians, such as Swiss Leonhard Euler and Franco-Italian Joseph Louis Lagrange also made essential contributions in the 18th and 19th centuries. In spite of this, astronautics did not become a practical discipline until the mid-20th century. On the other hand, the question of spaceflight puzzled the literary imaginations of such figures as Jules Verne and H. G. Wells. At the beginning of the 20th century, Russian cosmist Konstantin Tsiolkovsky derived the famous rocket equation, the governing equation for a rocket-based propulsion, enabling computation of the final velocity of a rocket from the mass of spacecraft (
m
1
), combined mass of propellant and spacecraft (
m
0
) and exhaust velocity of the propellant (
v
e
).

Δ
v
=
v
e
ln
m
0
m
1
In fact this equation was derived earlier by William Moore, a British mathematician who worked at the Royal Military Academy at Woolwich. For more information on the mathematical basis of space travel, see Orbital mechanics.

By the early 1920s, American Robert Goddard was developing liquid-propellant rockets, which would in a few brief decades become a critical component in the designs of such famous rockets as the V-2 and Saturn V.

Although many regard astronautics itself as a rather specialized subject, engineers and scientists working in this area must be knowledgeable in many distinct fields.

Astrodynamics: the study of orbital motion. Those specializing in this field examine topics such as spacecraft trajectories, ballistics and celestial mechanics.
Spacecraft propulsion: how spacecraft change orbits, and how they are launched. Most spacecraft have some variety of rocket engine, and thus most research efforts focus on some variety of rocket propulsion, such as chemical, nuclear or electric.
Spacecraft design: a specialized form of systems engineering that centers on combining all the necessary subsystems for a particular launch vehicle or satellite.
Controls: keeping a satellite or rocket in its desired orbit (as in spacecraft navigation) and orientation (as in attitude control).
Space environment: although more a sub-discipline of physics rather than astronautics, the effects of space weather and other environmental issues constitute an increasingly important field of study for spacecraft designers.
Aeronautics and aerospace
Mechanical engineering
Physics