Orbital spaceflight

An orbital spaceflight (or orbital flight) is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) above 100 kilometers (62 mi); this is, by at least one convention, the boundary of space. To remain in orbit at this altitude requires an orbital speed of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires greater delta-v.

Due to atmospheric drag, the lowest altitude at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 150 kilometres (93 mi).

The expression "orbital spaceflight" is mostly used to distinguish from sub-orbital spaceflights, which are flights where the apogee of a spacecraft reaches space, but the perigee is too low.

Space Shuttle Discovery rockets to orbital velocity, seen here just after booster separation

Orbital launch

Orbital human spaceflight
Name Debut Launches
Vostok 1961 6
Mercury 1962 4
Voskhod 1964 2
Gemini 1965 10
Soyuz 1967 147
Apollo 1968 21
Shuttle 1981 135
Shenzhou 2003 6

Orbital spaceflight from Earth has only been achieved by launch vehicles that use rocket engines for propulsion. To reach orbit, the rocket must impart to the payload a delta-v of about 9.3–10 km/s. This figure is mainly (~7.8 km/s) for horizontal acceleration needed to reach orbital speed, but allows for atmospheric drag (approximately 300 m/s with the ballistic coefficient of a 20 m long dense fueled vehicle), gravity losses (depending on burn time and details of the trajectory and launch vehicle), and gaining altitude.

The main proven technique involves launching nearly vertically for a few kilometers while performing a gravity turn, and then progressively flattening the trajectory out at an altitude of 170+ km and accelerating on a horizontal trajectory (with the rocket angled upwards to fight gravity and maintain altitude) for a 5-8 minute burn until orbital velocity is achieved. Currently, 2-4 stages are needed to achieve the required delta-v. Most launches are by expendable launch systems.

The Pegasus rocket for small satellites instead launches from an aircraft at an altitude of 12 km.

There have been many proposed methods for achieving orbital spaceflight that have the potential of being much more affordable than rockets. Some of these ideas such as the space elevator, and rotovator, require new materials much stronger than any currently known. Other proposed ideas include ground accelerators such as launch loops, rocket assisted aircraft/spaceplanes such as Reaction Engines Skylon, scramjet powered spaceplanes, and RBCC powered spaceplanes. Gun launch has been proposed for cargo.

From 2015 SpaceX have demonstrated significant progress in their more incremental approach to reducing the cost of orbital spaceflight. Their potential for cost reduction comes mainly from pioneering propulsive landing with their reusable rocket booster stage as well as their Dragon capsule, but also includes reuse of the other components such as the payload fairings and the use of 3D printing of a superalloy to construct more efficient rocket engines, such as their SuperDraco. The initial stages of these improvements could reduce the cost of an orbital launch by an order of magnitude.[1]


ISS on 20 August 2001
The International Space Station during its construction in Earth orbit in 2001. It must be periodically re-boosted to maintain its orbit

An object in orbit at an altitude of less than roughly 200 km is considered unstable due to atmospheric drag. For a satellite to be in a stable orbit (i.e. sustainable for more than a few months), 350 km is a more standard altitude for low Earth orbit. For example, on 1 February 1958 the Explorer 1 satellite was launched into an orbit with a perigee of 358 kilometers (222 mi).[2] It remained in orbit for more than 12 years before its atmospheric reentry over the Pacific Ocean on 31 March 1970.

However, the exact behaviour of objects in orbit depends on altitude, their ballistic coefficient, and details of space weather which can affect the height of the upper atmosphere.


There are three main 'bands' of orbit around the Earth: low Earth orbit (LEO), medium Earth orbit (MEO) and geostationary orbit (GEO).

Due to orbital mechanics, orbits are in a particular, largely fixed plane around the Earth, which coincides with the center of the Earth, and may be tilted with respect to the equator. The Earth rotates about its axis within this orbit, and the relative motion of the spacecraft and the movement of the Earth's surface determines the position that the spacecraft appears in the sky from the ground, and which parts of the Earth are visible from the spacecraft.

By dropping a vertical down to the Earth's surface it is possible to calculate a ground track that shows which part of the Earth a spacecraft is immediately above, and this is useful for helping to visualise the orbit.

Orbital maneuver

Skylab 4 - command service module
Skylab mission docked to the Skylab space station

In spaceflight, an orbital maneuver is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth—for example those in orbits around the Sun—an orbital maneuver is called a deep-space maneuver (DSM).

Deorbit and re-entry

Returning spacecraft (including all potentially manned craft) have to find a way of slowing down as much as possible while still in higher atmospheric layers and avoid hitting the ground (lithobraking) or burning up. For many orbital space flights, initial deceleration is provided by the retrofiring of the craft's rocket engines, perturbing the orbit (by lowering perigee down into the atmosphere) onto a suborbital trajectory. Many spacecraft in low-Earth orbit (e.g., nanosatellites or spacecraft that have run out of station keeping fuel or are otherwise non-functional) solve the problem of deceleration from orbital speeds through using atmospheric drag (aerobraking) to provide initial deceleration. In all cases, once initial deceleration has lowered the orbital perigee into the mesosphere, all spacecraft lose most of the remaining speed, and therefore kinetic energy, through the atmospheric drag effect of aerobraking.

Intentional aerobraking is achieved by orienting the returning space craft so as to present the heat shields forward toward the atmosphere to protect against the high temperatures generated by atmospheric compression and friction caused by passing through the atmosphere at hypersonic speeds. The thermal energy is dissipated mainly by compression heating the air in a shockwave ahead of the vehicle using a blunt heat shield shape, with the aim of minimising the heat entering the vehicle.

Sub-orbital space flights, being at a much lower speed, do not generate anywhere near as much heat upon re-entry.

Even if the orbiting objects are expendable, most space authorities are pushing toward controlled re-entries to minimize hazard to lives and property on the planet.


  • Sputnik 1 was the first human-made object to achieve orbital spaceflight. It was launched on 4 October 1957 by the Soviet Union.
  • Vostok 1, launched by the Soviet Union on 12 April 1961, carrying Yuri Gagarin, was the first successful human spaceflight to reach Earth orbit.
  • Vostok 6, launched by the Soviet Union on 16 June 1963, carrying Valentina Tereshkova, was the first successful woman carrying out a spaceflight to reach Earth orbit.

See also


  1. ^ Belfiore, Michael (December 9, 2013). "The Rocketeer". Foreign Policy. Retrieved December 11, 2013.
  2. ^ "Explorer 1 - NSSDC ID: 1958-001A". NASA.
Air launch to orbit

Air launch to orbit is the method of launching rockets at altitude from a conventional horizontal-takeoff

aircraft, to carry satellites to low Earth orbit. It is a follow-on development of air launches of experimental aircraft that began in the late 1940s. This method, when employed for orbital payload insertion, presents significant advantages over conventional vertical rocket launches, particularly because of the reduced mass, thrust and cost of the rocket.

Air launching is also being developed for sub-orbital spaceflight. In 2004 the Ansari X Prize $10 Million purse was won by a team led by Burt Rutan's Scaled Composites, launching the SpaceShipOne from the purpose-built White Knight carrier aircraft.

America's Space Prize

America's Space Prize was a US$50 million space competition in orbital spaceflight established and funded in 2004 by hotel entrepreneur Robert Bigelow. The prize would have been awarded to the first US-based privately funded team to design and build a reusable manned capsule capable of flying 5 astronauts to a Bigelow Aerospace inflatable space module. The criteria also required the capsule be recovered and flown again in 60 days. The prize expired January 10, 2010, without a winner or any test flights attempted. The teams were required to have been based in the United States.

Amir Ansari

Amir Ansari (Persian: امیر انصاری‎) is an American Chief Technology Officer and Co-Founder of Prodea Systems.

Along with his sister-in-law Anousheh Ansari, he made a multimillion-dollar contribution to the Ansari X Prize foundation on May 5, 2004, the 43rd anniversary of Alan Shepard's sub-orbital spaceflight. The X Prize was officially renamed the Ansari X Prize in honour of their donation.

Born in 1970 in Tehran, Iran, Ansari immigrated to the United States before the Iranian Revolution. He received his Bachelor of Science degree in electrical engineering and computer science at George Mason University. Amir, along with his brother Hamid and sister-in-law Anousheh Ansari, founded Telecom Technologies, Inc. (TTI) in 1993, and served as the company's CTO. TTI was acquired by Sonus Networks, Inc. in January 2001.Prodea has announced the formation of a partnership with Space Adventures, Ltd. and the Federal Space Agency of the Russian Federation (FSA) to create a fleet of suborbital spaceflight vehicles for global commercial use.

British Interplanetary Society

The British Interplanetary Society (BIS), founded in Liverpool in 1933 by Philip E. Cleator, is the oldest space advocacy organisation in the world. Its aim is exclusively to support and promote astronautics and space exploration.

Exos Aerospace

Exos Aerospace Systems & Technologies is a aerospace manufacturer and developer of reusable launch systems intended to support unmanned orbital spaceflight launches, and is based in Caddo Mills, Texas.

Kosmos (rocket family)

The Kosmos (also spelled Cosmos, Russian: Ко́смос) rockets were a series of Soviet and subsequently Russian rockets, derived from the R-12 and R-14 missiles, the best known of which is the Kosmos-3M, which has made over 440 launches. The Kosmos family contained a number of rockets, both carrier rockets and sounding rockets, for orbital and sub-orbital spaceflight respectively. The first variant, the Kosmos-2I, first flew on 27 October 1961. Over 700 Kosmos rockets have been launched overall.

Mercury 2

Mercury 2 may refer to:

Mercury-Redstone 2, a sub-orbital spaceflight launched January 31, 1961, carrying Ham, a chimpanzee

Mercury-Atlas 2, an unmanned test flight of the Atlas rocket and Mercury spacecraft, launched February 21, 1961

Mercury(II), the element mercury in the +2 oxidation state

Blackburn Mercury II, an early airplane

Bristol Mercury II, an aero-engine

Mercury 3

Mercury 3 could refer to:

Mercury-Redstone 3, The first American manned (sub-orbital) spaceflight, made by astronaut Alan Shepard.

Mercury-Atlas 3, an unmanned test flight of the Atlas rocket and Mercury spacecraft.

Blackburn Mercury III, an early airplane

Bristol Mercury III, an aero-engine

Mercury 4

Mercury 4 could refer to:

Mercury-Redstone 4, a.k.a. Liberty Bell 7, a manned sub-orbital spaceflight made by astronaut Gus Grissom.

Mercury-Atlas 4, an unmanned orbital test flight of the Atlas rocket and Mercury spacecraft.

Mercury4, an Australian boy band.

Mercury(IV), the element mercury in the +4 oxidation state

Bristol Mercury IV, an aero-engine


V. M. Myasishchev Experimental Design Bureau (Экспери­мен­тальный Машин­ост­роительный Завод им. В. М. Мясищева) or OKB-23, founded in 1951 by Vladimir Myasishchev) was one of the chief Soviet aerospace design bureaus until its dissolution in 1960. Vladimir Myasishchev went on to head TsAGI. In 1967, Myasishchev left TsAGI and recreated his bureau, which still exists to this day. The bureau prefix was "M." As of 2003, its workforce is estimated at approx­imately one thousand. Myasishchev and NPO Molniya intend to use the V-MT or M-55 as launch vehicle for sub-orbital spaceflight.In July 2014, the merger of Myasishchev and Ilyushin to create a single modern production complex was announced by the Board of Directors of OAO Il.

Orbital Vehicle (disambiguation)

Orbit Vehicle, Orbital Vehicle, Orbiting Vehicle, Orbiter Vehicle, or variation, may refer to:

Spacecraft which attain orbit

A vehicle capable of orbital spaceflight

Orbiter space probesSpace Shuttle, the NASA vehicles designated "OV" (for 'Orbiter Vehicle')

Orbiter Vehicle Designation, for the NASA STS Space Shuttle program

ISRO Orbital Vehicle, the proposed Indian government manned orbital spacecraft

Orbiting Vehicle (OV), the SATAR series of USAF experimental satellites

San Diego Space Society

The San Diego Space Society (SD Space) is a chapter of the National Space Society based in San Diego and founded in 2008.The group's goal is to raise awareness of the benefits of space exploration and San Diego's role in space development by promoting space education in local schools and events such as the San Diego Science Festival.SD Space organized the first SpaceUp, an unconference about space, at the San Diego Air & Space Museum in 2010. The 2-day event was covered by Spacevidcast and attended by representatives from NASA, Google Lunar X Prize, Masten Space Systems, and Quicklaunch.SD Space operates the Space Travelers Emporium, a combination of retail store, library, and clubhouse in South Park, San Diego. The Emporium plans to sell tickets for sub-orbital spaceflight through companies such as Virgin Galactic. To coincide with the 41st anniversary of the Apollo 11 launch, the Emporium screened Moon Beat, a documentary film by director Kevin Stirling told from the perspective of journalists who covered the U.S. Space Program at the time of the moon landing.

Scaled Composites White Knight

The Scaled Composites Model 318 White Knight (now also called White Knight One) is a jet-powered carrier aircraft that was used to launch its companion SpaceShipOne, an experimental spaceplane. The White Knight and SpaceShipOne were designed by Burt Rutan and manufactured by Scaled Composites, a private company founded by Rutan in 1982. On three separate flights in 2004, White Knight conducted SpaceShipOne into flight, and SpaceShipOne then performed a sub-orbital spaceflight, becoming the first private craft to reach space.

The White Knight is notable as an example of a mother ship which carried a parasite aircraft into flight, releasing the latter which would then execute a high-altitude flight, or a sub-orbital spaceflight. This flight profile is shared with The High and Mighty One and Balls 8, two modified B-52s which carried the North American X-15 into flight. It is also shared with White Knight Two, a descendent which carries SpaceShipTwo into flight as part of the Virgin Galactic fleet.

Following the SpaceShipOne flights, the White Knight was contracted for drop tests of the Boeing X-37 spaceplane, from June 2005 until April 2006. The White Knight was retired from service in 2014, and is in the inventory of the Flying Heritage Collection.

Space Adventures

Space Adventures, Ltd. is a Virginia, USA-based space tourism company founded in 1998 by Eric C. Anderson. As of 2010, offerings include zero-gravity atmospheric flights, orbital spaceflights (with the option to participate in a spacewalk), and other spaceflight-related experiences including cosmonaut training, spacewalk training, and launch tours. Plans announced thus far include sub-orbital and lunar spaceflights. As of October 2009, seven clients have participated in the orbital spaceflight program with Space Adventures, including one person who took two separate trips to space.


Spaceflight (also written space flight) is ballistic flight into or through outer space. Spaceflight can occur with spacecraft with or without humans on board. Examples of human spaceflight include the U.S. Apollo Moon landing and Space Shuttle programs and the Russian Soyuz program, as well as the ongoing International Space Station. Examples of unmanned spaceflight include space probes that leave Earth orbit, as well as satellites in orbit around Earth, such as communications satellites. These operate either by telerobotic control or are fully autonomous.

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.


A starship, starcraft or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems, as opposed to an aerospace-vehicle designed for orbital spaceflight or interplanetary travel.

The term is mostly found in science fiction, because such craft is not known to have ever been constructed. Reference to a "star-ship" appears as early as 1882 in Oahspe: A New Bible (1882).Whilst the Voyager and Pioneer probes have travelled into local interstellar space, the purpose of these unmanned craft was specifically interplanetary and they are not predicted to reach another star system (although Voyager 1 will travel to within 1.7 light years of Gliese 445 in approximately 40,000 years). Several preliminary designs for starships have been undertaken through exploratory engineering, using feasibility studies with modern technology or technology thought likely to be available in the near future.

In April 2016, scientists announced Breakthrough Starshot, a Breakthrough Initiatives program, to develop a proof-of-concept fleet of small centimeter-sized light sail spacecraft, named StarChip, capable of making the journey to Alpha Centauri, the nearest extrasolar star system, at speeds of 20% and 15% of the speed of light, taking between 20 and 30 years to reach the star system, respectively, and about 4 years to notify Earth of a successful arrival.

On November 8, 2018, Elon Musk announced that SpaceX was renaming the Big Falcon Rocket, a fully reusable launch vehicle and spacecraft system, to Starship.

Sub-orbital spaceflight

A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital revolution.

For example, the path of an object launched from Earth that reaches the Kármán line (at 100 km (62 mi) above sea level), and then falls back to Earth, is considered a sub-orbital spaceflight. Some sub-orbital flights have been undertaken to test spacecraft and launch vehicles later intended for orbital spaceflight. Other vehicles are specifically designed only for sub-orbital flight; examples include manned vehicles, such as the X-15 and SpaceShipOne, and unmanned ones, such as ICBMs and sounding rockets.

Flights which attain sufficient velocity to go into low Earth orbit, and then de-orbit before completing their first full orbit, are not considered sub-orbital. Examples of this include Yuri Gagarin's Vostok 1, and flights of the Fractional Orbital Bombardment System.

Usually a rocket is used, but experimental sub-orbital spaceflight has also been achieved with a space gun.

VSS Unity PF04

VSS Unity PF04 was a sub-orbital spaceflight of the SpaceShipTwo-class VSS Unity which took place on 13 December 2018, piloted by Mark P. Stucky and co-piloted by Frederick W. "CJ" Sturckow. Reaching an apogee of 82.7 km (51.4 mi), the flight satisfied the United States definition of spaceflight (50 mi (80.47 km)), but fell short of the Kármán line (100 km (62.14 mi)), the internationally accepted standard. The flight was operated by Virgin Galactic, a private company led by Richard Branson which intends to conduct space tourism flights in the future. VSS Unity PF04 was a success for the organization, following the 2014 VSS Enterprise crash. It was the first crewed spaceflight from U.S. soil since the Space Shuttle mission STS-135 in 2011.

X-15 Flight 91

X-15 Flight 91 was a 1963 American manned mission, and the second and final flight in the program to achieve sub-orbital spaceflight—a flight over 100 km in altitude—which was previously achieved during Flight 90 a month earlier. It was the highest flight of the X-15 program. It was the first flight of a reused spacecraft, as plane number three flew the previous sub-orbital flight on July 19. This mission was piloted by Joseph A. Walker on August 22, 1963, with the air-launch occurring from a modified Boeing B-52 Stratofortress support plane over Smith Ranch Dry Lake, Nevada, United States. Walker piloted the X-15 to an altitude of 107.96 km and remained weightless for approximately five minutes. The altitude was the highest manned flight by a spaceplane to that time and remained the record until the 1981 flight of Space Shuttle Columbia. Walker landed the X-15 about 12 minutes after it was launched, at Rogers Dry Lake, Edwards Airforce Base, in California. This was Walker's final X-15 flight.

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