Spaceflight is used in space exploration, and also
in commercial activities like space tourism and satellite telecommunications.
Additional non-commercial uses of spaceflight include space observatories,
reconnaissance satellites and other earth observation satellites.
A spaceflight typically begins with a rocket launch,
which provides the initial thrust to overcome the force of gravity and propels
the spacecraft from the surface of the Earth. Once in space, the motion of a
spacecraft—both when unpropelled and when under propulsion—is covered by the
area of study called astrodynamics. Some spacecraft remain in space
indefinitely, some disintegrate during atmospheric reentry, and others reach a
planetary or lunar surface for landing or impact.
Types of spaceflight
The first human spaceflight was Vostok 1 on April
12, 1961, on which cosmonaut Yuri Gagarin of the USSR made one orbit around the
Earth. In official Soviet documents, there is no mention of the fact that
Gagarin parachuted the final seven miles. The international rules for
aviation records stated that "The pilot remains in his craft from launch
to landing". This rule, if applied, would have "disqualified"
Gagarins space-flight. Currently the only spacecraft regularly used for human spaceflight
are Russian Soyuz spacecraft and the U.S. Space Shuttle fleet. Each of those
space programs have used other spacecraft in the past. Recently, the Chinese
Shenzhou spacecraft has been used three times for human spaceflight, and
On a sub-orbital spaceflight the spacecraft reaches
space and then returns to the atmosphere after following a (primarily)
ballistic trajectory. This is usually because of insufficient specific orbital
energy, in which case a suborbital flight will last only a few minutes, but it
is also possible for an object with enough energy for an orbit to have a
trajectory that intersects the Earth's atmosphere, sometimes after many hours.
Pioneer 1 was NASA's first space probe intended to reach the Moon. A partial failure
caused it to instead follow a suborbital trajectory to an altitude of 113,854
kilometers (70,746 mi) before reentering the Earth's atmosphere 43 hours after
The most generally recognized boundary of space is
the Kármán line (actually a sphere) 100 km above sea level. (NASA alternatively
defines an astronaut as someone who has flown more than 50 miles or 80 km above
sea level.) It is not generally recognized by the public that the increase in
potential energy required to pass the Kármán line is only about 3% of the
orbital energy (potential plus kinetic energy) required by the lowest possible
earth orbit (a circular orbit just above the Kármán line.) In other words, it
is far easier to reach space than to stay there.
On May 17, 2004, Civilian Space eXploration Team
launched the GoFast Rocket on a suborbital flight, the first amateur
spaceflight. On June 21, 2004, SpaceShipOne was used for the first
privately-funded human spaceflight.
A minimal orbital spaceflight requires much higher
velocities than a minimal sub-orbital flight, and so it is technologically much
more challenging to achieve. To achieve orbital spaceflight, the tangential
velocity around the Earth is as important as altitude. In order to perform a
stable and lasting flight in space, the spacecraft must reach the minimal
orbital speed required for a closed orbit.
artist's imaginative impression of a vehicle entering a wormhole for
interstellar travel Interplanetary travel is travel between planets within a
single planetary system. In practice, the use of the term is confined to travel
between the planets of the Solar System. Interstellar spaceflight five
spacecraft are currently leaving the Solar System on escape trajectories. The
one farthest from the Sun is Voyager 1, which is more than 100 AU distant and
is moving at 3.6 AU per year. In comparison Proxima Centauri, the closest
star other than the Sun, is 267,000 AU distant. It will take Voyager 1 over
74,000 years to reach this distance. Vehicle designs using other techniques,
such as nuclear pulse propulsion are likely to be able to reach the nearest
star significantly faster.
Another possibility that could allow for human
interstellar spaceflight is to make use of time dilation, as this would make it
possible for passengers in a fast-moving vehicle to travel further into the
future while aging very little, in that their great speed slows down the rate
of passage of on-board time. However, attaining such high speeds would still
require the use of some new, advanced method of propulsion.
Intergalactic travel involves spaceflight between
galaxies, and is considered much more technologically demanding than even
interstellar travel and, by current engineering terms, is considered science