Space launch

{{main|Outer space#Boundary}}

File:SpaceShipOne Flight 15P photo Don Ramey Logan.jpg completed the first human private spaceflight in 2004, reaching an altitude of {{Convert|100.12|km|mi|abbr=on}}.{{citation |author=Coren |first=Michael |title=Private craft soars into space, history |date=July 14, 2004 |website=CNN.com |postscript=. |url=http://www.cnn.com/2004/TECH/space/06/21/suborbital.test/index.html?iref=newssearch |archive-url=https://web.archive.org/web/20150402190754/http://www.cnn.com/2004/TECH/space/06/21/suborbital.test/index.html?iref=newssearch |archive-date=April 2, 2015 |url-status=live}}|alt=A white rocketship with oddly-shaped wings at rest on a runway.]]

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 {{lang|fr|Fédération Aéronautique Internationale|italic=no}} has established the Kármán line at an altitude of {{convert|100|km|mi|abbr=on}} as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about {{Convert|100|km|mi|abbr=on}}, 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.{{citation |last=O'Leary |first=Beth Laura |title=Handbook of space engineering, archaeology, and heritage |date=2009 |editor1-last=Darrin |editor1-first=Ann Garrison |url=https://books.google.com/books?id=dTwIDun4MroC&pg=PA84 |series=Advances in engineering |publisher=CRC Press |isbn=978-1-4200-8431-3}}.{{rp|84}}{{citation | title = Where does space begin? | url = http://aerospaceengineering.aero/where-does-space-begin/ | website = Aerospace Engineering |access-date = 2015-11-10 | language = en-US |url-status=live | postscript=. | archive-url = https://web.archive.org/web/20151117034012/http://aerospaceengineering.aero/where-does-space-begin/ | archive-date = 2015-11-17}}
• Until 2021, the United States designated people who travel above an altitude of {{convert|50|mi|km|abbr=on}} as astronauts.{{citation |last1=Wong |first1=Wilson |title=Military space power: a guide to the issues |date=2010 |url=https://books.google.com/books?id=GFg5CqCojqQC&pg=PA16 |series=Contemporary military, strategic, and security issues |publisher=ABC-CLIO |isbn=978-0-313-35680-3 |last2=Fergusson |first2=James Gordon}}.{{rp|16}} 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".{{citation | postscript=. | title=FAA Commercial Space Astronaut Wings Program | publisher=Federal Aviation Administration | date=July 20, 2021

| url=https://www.faa.gov/documentLibrary/media/Order/FAA_Order_8800.2.pdf | access-date=2022-12-18 }}

• NASA's Space Shuttle used {{val|400000|u=ft|fmt=commas}}, or {{Convert|75.76|mi|km|sigfig=2}}, 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.{{citation | first1=John Ira | last1=Petty | date=February 13, 2003 | title=Entry | work=Human Spaceflight | publisher=NASA | url=http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/ | access-date=2011-12-16 | postscript=. | url-status=dead | archive-url=https://web.archive.org/web/20111027174930/http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/ | archive-date=October 27, 2011 }}

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 {{Convert|118|km|mi|sigfig=3|abbr=on}} 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 {{Convert|268|m/s|ft/s|abbr=on}}.{{citation | url=http://www.space.com/scienceastronomy/090409-edge-space.html | title=Edge of Space Found | date=April 9, 2009 | first1=Andrea | last1=Thompson | publisher=space.com | access-date=2009-06-19 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20090714002304/http://www.space.com/scienceastronomy/090409-edge-space.html | archive-date=July 14, 2009 }}{{citation | display-authors=1 | first1=L. | last1=Sangalli | first2=D. J. | last2=Knudsen | first3=M. F. | last3=Larsen | first4=T. | last4=Zhan | first5=R. F. | last5=Pfaff | first6=D. | last6=Rowland | date=2009 | title=Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere | journal=Journal of Geophysical Research | volume=114 | issue=A4 | pages=A04306 | doi=10.1029/2008JA013757 | bibcode=2009JGRA..114.4306S | postscript=. | doi-access=free }}

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.

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.

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

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.

{{excerpt|Trajectory optimization}}

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.{{cite web | last=Hollingham | first=Richard | title=When rockets go wrong – protecting the environment from catastrophe | website=BBC Home | date=2024-06-29 | url=https://www.bbc.com/future/article/20240627-the-environmental-cost-of-rocket-launches | access-date=2025-02-10}}

Furthermore soot snd debris from launches, particularly failed launches, have literally negatively impacted wide areas below.{{cite web | last=Wattles | first=Jackie | title=The most powerful rocket ever built exploded over a populated island. Residents are still dealing with the fallout | website=CNN | date=2025-01-30 | url=https://edition.cnn.com/2025/01/30/science/spacex-starship-explosion-debris-turks-caicos/index.html | access-date=2025-04-13}} 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.{{cite web | title=“Colonizing Our Community”: Elon Musk’s SpaceX Rocket Explodes in Texas as Feds OK New LNG Projects | website=Democracy Now! | date=2023-04-21 | url=https://www.democracynow.org/2023/4/21/spacex_gulf_coast | access-date=2025-02-10}}{{cite web | title=The Terrible Irony of Destroying Earth in Search of Plan(et) B: SpaceX’s Impacts to Boca Chica, Texas | website=Defenders of Wildlife | date=2024-10-17 | url=https://defenders.org/blog/2024/10/terrible-irony-of-destroying-earth-search-of-planet-b-spacexs-impacts-boca-chica-0?utm_source=chatgpt.com | access-date=2025-02-10}}{{cite web | title=French Guiana: the negative legacy of French colonialism | website=International Viewpoint | date=2018-08-21 | url=https://internationalviewpoint.org/spip.php?article5664 | access-date=2025-02-10}}

Many rockets use fossil fuels, some launch systems use hydrogen, while some rocket manufacturers (i.e. Orbex, ArianeGroup) are using different launch fuels (such as bio-propane; methane produced from biomass).{{cite web |title=Can we get to space without damaging the Earth through huge carbon emissions? |date=2020-01-30 |website=Los Angeles Times |archive-url=https://web.archive.org/web/20230722093000/https://www.latimes.com/business/story/2020-01-30/space-launch-carbon-emissions |archive-date=2023-07-22 |url-status=live |url=https://www.latimes.com/business/story/2020-01-30/space-launch-carbon-emissions}}

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.{{cite web | last=Pultarova | first=Tereza | title=How environmentally friendly is SpaceX's Starship? | website=Space.com | date=2024-03-21 | url=https://www.space.com/spacex-starship-rocket-launches-environmental-impact | access-date=2025-04-13}}

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 {{val|26|u=km3}}.{{cite journal | last=Kokkinakis | first=Ioannis W. | last2=Drikakis | first2=Dimitris | title=Atmospheric pollution from rockets | journal=Physics of Fluids | volume=34 | issue=5 | date=2022-05-01 | issn=1070-6631 | doi=10.1063/5.0090017 | url=https://pubs.aip.org/aip/pof/article-abstract/34/5/056107/2847501/Atmospheric-pollution-from-rockets?redirectedFrom=fulltext | access-date=2025-04-13 | page=| url-access=subscription }} 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.

{{Main|Suborbital spaceflight}}

Sub-orbital space flight is any space launch that reaches space without making a full orbit around the planet, and requires a maximum speed of around 1 km/s 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, or an intercontinental transport flight like SpaceLiner. 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).

{{Main|Orbital spaceflight}}

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 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.

{{Main|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.

{{excerpt|Rocket#Spaceflight}}

{{excerpt|Non-rocket spacelaunch|only=paragraphs}}

{{reflist}}

• {{usurped|1=[https://web.archive.org/web/20090517114303/http://www.spacelaunchreport.com/ Article title]}} A periodic news digest of worldwide space launch activity.
• [https://www.n2yo.com/satellites/?c=latest-launches LATEST SATELLITE LAUNCHES from http://www.n2yo.com/].
• [http://www.thespacereview.com/index.html The Space Review] is an online publication devoted to in-depth articles, commentary, and reviews regarding all aspects of space exploration.

{{Spaceflight}}

{{DEFAULTSORT:Space Launch}}

Category:Spaceflight concepts