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Space launch is the earliest part of a
flight Flight or flying is the process by which an object moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space (i.e. spaceflight). This can be a ...
that reaches space. Space launch involves
liftoff Liftoff, lift-off, or lift off may refer to: Technology * Lift-off (microtechnology), a fabrication technique * Flame lift-off, a separation of flame from burner device * Takeoff, the first moment of flight of an aerospace vehicle * Reduction o ...
, when a rocket or other space launch vehicle leaves the ground, floating ship or midair aircraft at the start of a flight. Liftoff is of two main types:
rocket launch A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...
(the current conventional method), and
non-rocket spacelaunch Non-rocket spacelaunch refers to theoretical concepts for launch into space where much of the speed and altitude needed to achieve orbit is provided by a propulsion technique that is not subject to the limits of the rocket equation. Although al ...
(where other forms of propulsion are employed, including airbreathing jet engines or other kinds).


Issues with reaching space


Definition of outer space


Energy

Therefore, by definition for spaceflight to occur, sufficient altitude is necessary. This implies a minimum
gravitational potential energy Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (conver ...
needs to be overcome: for the Kármán line this is approximately 1 MJ/kg. W=mgh, m=1 kg, g=9.82 m/s2, h=105m. W=1*9.82*105≈106J/kg=1MJ/kg In practice, a higher energy than this is needed to be expended due to losses such as airdrag, propulsive efficiency, cycle efficiency of engines that are employed and
gravity drag In astrodynamics and rocketry, gravity loss is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field. In other words, it is the cost of having to hold the rocket up in a gravity field. Gravity lo ...
. In the past fifty years spaceflight has usually meant remaining in space for a period of time, rather than going up and immediately falling back to earth. This entails orbit, which is mostly a matter of velocity, not altitude, although that does not mean air friction and relevant altitudes in relation to that and orbit don't have to be taken into account. At much, much higher altitudes than many orbital ones maintained by satellites, altitude begins to become a larger and larger factor and speed a lesser one. At lower altitudes, due to the high speed required to remain in orbit, air friction is a very important consideration affecting satellites, much more than in the popular image of space. At even lower altitudes, balloons, with no forward velocity, can serve many of the roles satellites play.


G-forces

Many cargos, particularly humans have a limiting g-force that they can survive. For humans this is about 3-6 g. Some launchers such as gun launchers would give accelerations in the hundred or thousands of g and thus are completely unsuitable.


Reliability

Launchers vary with respect to their reliability for achieving the mission.


Safety

Safety is the probability of causing injury or loss of life. Unreliable launchers are not necessarily unsafe, whereas reliable launchers are usually, but not invariably safe. Apart from catastrophic failure of the launch vehicle itself other safety hazards include depressurisation, and the Van Allen radiation belts which preclude orbits which spend long periods within them.


Trajectory optimization


Carbon emissions

Many rockets use fossil fuels. A SpaceX Falcon Heavy rocket for instance burns through 400 metric tons of kerosene and emits more carbon dioxide in a few minutes than an average car would in more than two centuries. As the number of rocket launches is expected to increase heavily in the coming years, the effect that launching into orbit has on Earth is expected to get much worse. Some rocket manufacturers (i.e.
Orbex Orbital Express Launch Ltd., or Orbex, is a United Kingdom-based aerospace company that is developing a small commercial orbital rocket called Prime. Orbex is headquartered in Forres, Moray, in Scotland and has subsidiaries in Denmark and Germany ...
,
ArianeGroup ArianeGroup (formerly Airbus Safran Launchers) is an aerospace company based in France. A joint venture between Airbus and Safran, the company was founded in 2015 and is headquartered in Issy-les-Moulineaux. It consists of three core arms: aeros ...
) are using different launch fuels (such as bio-propane,methane produced from biomass).Can we get to space without damaging the Earth through huge carbon emissions
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Sustained spaceflight


Suborbital launch

Sub-orbital space flight is any space launch that reaches space without doing a full orbit around the planet, and requires a maximum speed of around 1 km/s just to reach space, and up to 7 km/s for longer distance such as an intercontinental space flight. An example of a sub-orbital flight would be a ballistic missile, or future tourist flight such as
Virgin Galactic Virgin Galactic is an American spaceflight company founded by Richard Branson and his British Virgin Group retains an 11.9% stake through Virgin Investments Limited. It is headquartered in California, and operates from New Mexico. The compan ...
, or an intercontinental transport flight like
SpaceLiner SpaceLiner is a concept for a suborbital, hypersonic, winged passenger supersonic transport, conceived at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, or DLR) in 2005. In its second role the SpaceLiner is intended as ...
. Any space launch without an orbit-optimization correction to achieve a stable orbit will result in a suborbital space flight, unless there is sufficient thrust to leave orbit completely. (See Space gun#Getting to orbit)


Orbital launch

In addition, if orbit is required, then a much greater amount of energy must be generated in order to give the craft some sideways speed. The speed that must be achieved depends on the altitude of the orbit – less speed is needed at high altitude. However, after allowing for the extra potential energy of being at higher altitudes, overall more energy is used reaching higher orbits than lower ones. The speed needed to maintain an orbit near the Earth's surface corresponds to a sideways speed of about 7.8 km/s (17,400 mph), an energy of about 30MJ/kg. This is several times the energy per kg of practical rocket propellant mixes. Gaining the kinetic energy is awkward as the airdrag tends to slow the spacecraft, so rocket-powered spacecraft generally fly a compromise trajectory that leaves the thickest part of the atmosphere very early on, and then fly on for example, a
Hohmann transfer orbit In astronautics, the Hohmann transfer orbit () is an orbital maneuver used to transfer a spacecraft between two orbits of different altitudes around a central body. Examples would be used for travel between low Earth orbit and the Moon, or ...
to reach the particular orbit that is required. This minimises the airdrag as well as minimising the time that the vehicle spends holding itself up. Airdrag is a significant issue with essentially all proposed and current launch systems, although usually less so than the difficulty of obtaining enough kinetic energy to simply reach orbit at all.


Escape velocity

If the Earth's gravity is to be overcome entirely then sufficient energy must be obtained by a spacecraft to exceed the depth of the gravity potential energy well. Once this has occurred, provided the energy is not lost in any non-conservative way, then the vehicle will leave the influence of the Earth. The depth of the potential well depends on the vehicle's position, and the energy depends on the vehicle's speed. If the kinetic energy exceeds the potential energy then escape occurs. At the Earth's surface this occurs at a speed of 11.2 km/s (25,000 mph), but in practice a much higher speed is needed due to airdrag.


Types of space launch


Rocket launch


Non-rocket launch


References


External links

* http://www.spacelaunchreport.com/ A periodic news digest of worldwide space launch activity.
LATEST SATELLITE LAUNCHES from http://www.n2yo.com/


is an online publication devoted to in-depth articles, commentary, and reviews regarding all aspects of space exploration. {{DEFAULTSORT:Space Launch Spaceflight concepts