Orbital spaceflight

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Space Shuttle Discovery rockets to orbital velocity, seen here just after booster separation
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An orbital spaceflight (or orbital flight) is a

aerodynamic lift from the atmosphere to support itself.[1]: 84 [2]

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.[3]

Orbital launch

Orbital human spaceflight
Spacecraft First launch Last launch Launches
Vostok 1961 1963 6
Mercury 1962 1963 4
Voskhod 1964 1965 2
Gemini 1965 1966 10
Soyuz 1967 Ongoing 146
Apollo 1968 1975 15
Shuttle 1981 2011 134
Shenzhou
 2003 Ongoing 9
Crew Dragon 2020 Ongoing 11
Total - - 333

Orbital spaceflight from Earth has only been achieved by

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 39,000 ft (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

RBCC
powered spaceplanes. Gun launch has been proposed for cargo.

From 2015

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.[4]

Stability

The International Space Station during its construction in Earth orbit in 2001. It must be periodically re-boosted to maintain its orbit
Main article: Orbital decay

An object in orbit at an altitude of less than roughly 200 km is considered unstable due to

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.

Orbits

Main article: Geocentric orbit

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

According to orbital mechanics, an orbit lies in a particular, largely fixed plane around the Earth, which coincides with the center of the Earth, and may be inclined with respect to the equator. The relative motion of the spacecraft and the movement of the Earth's surface, as the Earth rotates on its axis, determine the position that the spacecraft appears in the sky from the ground, and which parts of the Earth are visible from the spacecraft.

It is possible to calculate a ground track that shows which part of the Earth a spacecraft is immediately above; this is useful for helping to visualise the orbit.

Orbital maneuver

Main article: Orbital maneuver
reaction control thrusters

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

Main article: Atmospheric entry

Returning spacecraft (including all potentially crewed craft) have to find a way of slowing down as much as possible while still in higher atmospheric layers and avoiding hitting the ground (

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[further explanation needed] heat upon re-entry.

Even if the orbiting objects are expendable, most[

example needed] are pushing toward controlled re-entries to minimize hazard to lives and property on the planet.[citation needed
]

History

  • 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 spaceflight by a woman to reach Earth orbit.
  • Crew Dragon Demo-2, launched by SpaceX and the United States on 30 May 2020, was the first successful human spaceflight by a private company to reach Earth orbit.

See also

References

  1. ISBN 978-1-4200-8431-3
    .
  2. ^ "Where does space begin? – Aerospace Engineering, Aviation News, Salary, Jobs and Museums". Aerospace Engineering, Aviation News, Salary, Jobs and Museums. Archived from the original on 17 November 2015. Retrieved 10 November 2015.
  3. ^ February 2020, Adam Mann 10 (10 February 2020). "What's the difference between orbital and suborbital spaceflight?". Space.com. Archived from the original on 16 June 2020. Retrieved 13 July 2020.{{cite web}}: CS1 maint: numeric names: authors list (link)
  4. Foreign Policy. Archived
    from the original on 10 December 2013. Retrieved 11 December 2013.
  5. ^ "Explorer 1 – NSSDC ID: 1958-001A". NASA. Archived from the original on 27 May 2019. Retrieved 21 August 2019.
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