Space launch

A space launch is the phase of a spaceflight mission during which a launch vehicle reaches space. The launch may be sub-orbital or the launch may continue until the vehicle reaches orbit. A space launch begins at a launch pad, which may be on land or at sea, or when the launch vehicle is released mid-air from an aircraft.

History

Rocket propulsion Although alternatives have been proposed for launches from Earth into space, the only means used to date has been rocket propulsion. Rockets using both liquid propellant and solid propellant have been used for space launch.

Spacecraft and crew Most space launches carry a spacecraft that does not include people. The payload may be a robotic spacecraft or a warhead. In contrast, human spaceflight missions are launched with astronaut crew or passengers on board.

Distributed launch

Issues with reaching space

Definition of outer space

There is no clear boundary between Earth's atmosphere and space, as the density of the atmosphere gradually decreases as the altitude increases. There are several standard boundary designations, namely:

The Fédération Aéronautique Internationale has established the Kármán line at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself. Until 2021, the United States designated people who travel above an altitude of 50 mi (80 km) as astronauts. Astronaut wings are now only awarded to spacecraft crew members that "demonstrated activities during flight that were essential to public safety, or contributed to human space flight safety". NASA's Space Shuttle used 400,000 ft, or 75.76 miles (120 km), as its re-entry altitude (termed the Entry Interface), which roughly marks the boundary where atmospheric drag becomes noticeable, thus beginning the process of switching from steering with thrusters to maneuvering with aerodynamic control surfaces. In 2009, scientists reported detailed measurements with a Supra-Thermal Ion Imager (an instrument that measures the direction and speed of ions), which allowed them to establish a boundary at 118 km (73.3 mi) above Earth. The boundary represents the midpoint of a gradual transition over tens of kilometers from the relatively gentle winds of the Earth's atmosphere to the more violent flows of charged particles in space, which can reach speeds well over 268 m/s (880 ft/s).

Energy By definition for spaceflight to occur, sufficient altitude is necessary. This implies a minimum gravitational potential energy 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 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, do not need to be considered. At much higher altitudes than many orbital ones maintained by satellites, altitude begins to become a larger factor and speed a lesser one. At lower altitudes, due to the high speed required to remain in orbit, air friction is an 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

Impact Space launches have shown among other things to increase aluminium concentration and pH-Levels around launch sites. That said proper regulation and measures can reduce and even increase environmental protection of launches. Furthermore, soot and debris from launches, particularly failed launches, have literally negatively impacted wide areas below. Leftover of launches are for example dumped in the ocean at places like the Pacific Ocean area called the spacecraft cemetery. Beside ecological environments, lands and their communities, particularly indigenous peoples, have been colonized to build the necessary infrastructure, disregarding them without reaching out for consultation or consent. Many rockets use fossil fuels, some launch systems use hydrogen, while some rocket manufacturers (i.e. ArianeGroup) are using different launch fuels (such as methane produced from biomass). Launches exhaust often water vapor, which is a potent greenhouse gas and at high altitudes not very common. Also methane it self, which is used as a fuel, is a potent greenhouse gas.

Carbon emissions As the number of rocket launches is expected to increase, the cumulative effect that launching into space has on Earth is expected to be significant and not to be underestimated. A single common Falcon 9 launch emits carbon dioxide into the mesosphere of about 26 km3. 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.

Sustained spaceflight

Suborbital launch

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