Aerobraking is a
spaceflightSpaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications...
maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low...
at the low point of the orbit (periapsis). The resulting
dragIn fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid . Drag forces act in a direction opposite to the oncoming flow velocity...
slows the
spacecraftA spacecraft is a craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters space then returns to the Earth. For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body. Spacecraft used for human spaceflight carry people on board as...
. Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, and it requires less fuel than does the direct use of a
rocket engineA rocket engine or simply "rocket" is a jet engine[Rocket Propulsion Elements; 7th edition- chapter 1] that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
.
When an interplanetary vehicle arrives at its destination, it must change its
velocityIn physics, velocity is the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI system, it is measured in meters per second: or ms-1. The scalar absolute value of velocity is speed...
to remain in the vicinity of that body.
Aerobraking is a
spaceflightSpaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications...
maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low...
at the low point of the orbit (periapsis). The resulting
dragIn fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid . Drag forces act in a direction opposite to the oncoming flow velocity...
slows the
spacecraftA spacecraft is a craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters space then returns to the Earth. For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body. Spacecraft used for human spaceflight carry people on board as...
. Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, and it requires less fuel than does the direct use of a
rocket engineA rocket engine or simply "rocket" is a jet engine[Rocket Propulsion Elements; 7th edition- chapter 1] that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
.
Method
When an interplanetary vehicle arrives at its destination, it must change its
velocityIn physics, velocity is the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI system, it is measured in meters per second: or ms-1. The scalar absolute value of velocity is speed...
to remain in the vicinity of that body. When a low, near-
circular orbitthumb|200px|Two bodies with a slight difference in mass orbiting around a common [[barycenter]] with circular orbits.In astrodynamics or celestial mechanics a circular orbit is an elliptic orbit with the eccentricity equal to 0...
around a body with substantial gravity (as is required for many scientific studies) is needed, the total required velocity changes can be on the order of several kilometers per second. If done by direct propulsion, the
rocket equationThe Tsiolkovsky rocket equation, or ideal rocket equation, is a mathematical equation that relates the delta-v with the effective exhaust velocity and the initial and end mass of a rocket....
dictates that a large fraction of the spacecraft mass must be fuel. This in turn means the spacecraft is limited to a relatively small science payload and/or the use of a very large and expensive launcher. Provided the target body has an atmosphere, aerobraking can be used to reduce fuel requirements. The use of a relatively small burn allows the spacecraft to be captured into a very elongated
elliptic orbitIn astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity greater than 0 and less than 1. In a gravitational two-body problem with the eccentricity in this range both bodies follow similar elliptic orbits with the same orbital period around their common...
. Aerobraking is then used to circularize the orbit. If the atmosphere is thick enough, a single pass through it can be sufficient to slow a spacecraft as needed. However, to reduce the effect of
frictionFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties:...
al heating, and because the unpredictability turbulence effects, atmospheric composition, and temperature make it difficult to accurately predict the decrease in speed that will result from any one pass through the atmosphere, aerobraking is typically done with many orbital passes through a higher altitude, and therefore thinner, region of the atmosphere. When aerobraking is done in this way, there is sufficient time after each pass to measure the change in velocity and make any necessary corrections for the next pass. Achieving the final orbit using this method takes a long time (e.g., over six
monthThe month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately 29.53 days...
s when arriving at
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
), and may require several hundred passes through the atmosphere of the planet or moon. After the last aerobraking pass, the spacecraft must be given more
kinetic energyThe kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its...
via rocket engines in order to raise the periapsis above the atmosphere--unless, of course, the intent is to land the spacecraft.
The kinetic energy dissipated by aerobraking is converted to
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
, meaning that a spacecraft using the technique needs to be capable of dissipating said heat. The spacecraft must also have sufficient surface area and structural strength to produce and survive the required drag, but the temperatures and pressures associated with aerobraking are not as severe as those of
reentryAtmospheric reentry refers to the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space, in the case of Earth from an altitude above the "edge of space." This article primarily addresses the process of controlled reentry of vehicles which are intended...
or
aerocaptureAerocapture is a technique used to reduce velocity of a spacecraft, arriving at a celestial body with a hyperbolic trajectory, in order to bring it in an orbit with an eccentricity of less than 1. It uses the drag created by the atmosphere of the celestial body to decelerate. Only one pass in the...
. Simulations of the
Mars Reconnaissance OrbiterNASA's Mars Reconnaissance Orbiter is a multipurpose spacecraft designed to conduct reconnaissance and exploration of Mars from orbit....
aerobraking use a
forceIn physics, a force is any agent that causes a change in the motion of a free body, or that causes stress in a fixed body. It can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a...
limit of 0.35 N per square meter with a spacecraft cross section of about 37 m², and a maximum expected
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
as 340 °F (170 °C). The force, of roughly 0.2 N (0.04 lbf) per square meter, that was exerted on the
Mars ObserverMars Observer was an unmanned spacecraft designed to study the geoscience and climate of Mars. The first of the proposed Observer series of planetary missions, it was launched by NASA on September 25, 1992. Three days before Mars Observer was scheduled to enter the orbit of Mars, contact with the...
, during aerobraking is comparable to the force of a 40 mph (60 km/h) wind on a human hand at sea level on Earth.
Related methods
AerocaptureAerocapture is a technique used to reduce velocity of a spacecraft, arriving at a celestial body with a hyperbolic trajectory, in order to bring it in an orbit with an eccentricity of less than 1. It uses the drag created by the atmosphere of the celestial body to decelerate. Only one pass in the...
is a related but more extreme method in which no initial orbit-injection burn is performed. Instead, the spacecraft plunges deeply into the atmosphere without an initial insertion burn, and emerges from this single pass in the atmosphere with an apoapsis near that of the desired orbit. Several small correction burns are then used to raise the periapsis and perform final adjustments. This method was originally planned for the Mars Odyssey orbiter, but the significant design impacts proved too costly.
Another related technique is that of
aerogravity assistAn aerogravity assist, or AGA, is a spacecraft maneuver designed to change velocity when arriving at a body with an atmosphere. A pure gravity assist uses only the gravity of a body to change the direction of the spacecraft trajectory. The change in direction is limited by the mass of the body,...
, in which the spacecraft flies through the upper atmosphere and utilises
aerodynamic liftA fluid flowing past the surface of a body exerts a force on it. Lift is defined to be the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the fluid-dynamic force parallel to the flow...
instead of drag at the point of closest approach. If correctly oriented, this can increase the deflection angle above that of a pure gravity assist, resulting in a larger
delta-vIn astrodynamics, the term delta-v, literally "change in velocity" , has a specific meaning: it is a scalar which takes units of speed that measures the amount of "effort" needed to carry out an orbital maneuver, i.e., to change from one trajectory to another.Where is the instantaneous thrust is...
.
Spacecraft missions
Although the theory of aerobraking is well developed, utilising the technique is difficult because a very detailed knowledge of the character of the target planet's atmosphere is needed in order to plan the maneuver correctly. Currently, the deceleration is monitored during each maneuver and plans are modified accordingly. Since no spacecraft can yet aerobrake safely on its own, this requires constant attention from both human controllers and the
Deep Space NetworkThe Deep Space Network, or DSN, is an international network of large antennas and communication facilities that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected...
. This is particularly true near the end of the process, when the drag passes are relatively close together (only about 2 hours apart for Mars).
On 19 March 1991, aerobraking was demonstrated by the
HitenThe Hiten spacecraft , built by the Institute of Space and Astronautical Science of Japan, was launched on January 24, 1990. It was Japan's first lunar probe, the first robotic lunar probe since the Soviet Union's Luna 24 in 1976, and the first lunar probe launched by a country other than Soviet...
spacecraft. This was the first aerobraking maneuver by a deep space probe.
HitenThe Hiten spacecraft , built by the Institute of Space and Astronautical Science of Japan, was launched on January 24, 1990. It was Japan's first lunar probe, the first robotic lunar probe since the Soviet Union's Luna 24 in 1976, and the first lunar probe launched by a country other than Soviet...
(a.k.a. MUSES-A) was launched by the
Institute of Space and Astronautical Sciencewas a Japanese national research organization of astrophysics using rockets, astronomical satellites and interplanetary probes.In 2003, three national aerospace organizations including ISAS were merged to form Japan Aerospace Exploration Agency...
(ISAS) of Japan. Hiten flew by the Earth at an altitude of 125.5 km over the Pacific at 11.0 km/s. Atmospheric drag lowered the velocity by 1.712 m/s and the apogee altitude by 8665 km. Another aerobraking maneuver was conducted on 30 March.
In May 1993, Aerobraking was used during the extended
VenusianVenus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6...
mission of the Magellan spacecraft. It was used to circularize the orbit of the spacecraft in order to increase the precision of the measurement of the gravity field. The entire gravity field was mapped from the circular orbit during a 243 day cycle of the extended mission. During the termination phase of the mission, a
"windmill experiment", in which atmospheric drag was used to deorbit the Magellan spacecraft, was performed.
In 1997, the
Mars Global SurveyorThe Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on , the...
(MGS) orbiter was the first spacecraft to use aerobraking as the main planned technique of orbit adjustment. The MGS used the data gathered from the Magellan mission to Venus to plan its aerobraking technique. The spacecraft used its solar panels as "
wingA wing is a surface used to produce lift for flight through the air or another gaseous or fluid medium. The wing shape is usually an airfoil. The word originally referred only to the foremost limbs of birds, but has been extended to include the wings of insects , bats, pterosaurs, and aircraft.A...
s" to control its passage through the tenuous upper atmosphere of Mars and lower the apoapsis of its orbit over the course of many months. Unfortunately, a structural failure shortly after launch severely damaged one of the MGS's solar panels and necessitated a higher aerobraking altitude (and hence one third the force) than
originally planned, significantly extending the time required to attain the desired orbit. More recently, aerobraking was used by the Mars Odyssey and
Mars Reconnaissance OrbiterNASA's Mars Reconnaissance Orbiter is a multipurpose spacecraft designed to conduct reconnaissance and exploration of Mars from orbit....
spacecraft, in both cases without incident.
Aerobraking in fiction
In
Robert A. HeinleinRobert Anson Heinlein was an American science fiction writer. Often called "the dean of science fiction writers", he was one of the most popular, influential, and controversial authors of the genre. He set a high standard for science and engineering plausibility and helped to raise the genre's...
's fictional 1948 novel
Space CadetSpace Cadet is a 1948 science fiction novel by Robert A. Heinlein about Matt Dodson, who joins the Space Patrol to help preserve peace in the Solar System. The story translates the standard military academy story into outer space: a boy from Iowa goes to officer school, sees action and adventure,...
, aerobraking is used to save fuel while slowing the spacecraft
Aes Triplex for an unplanned extended mission and landing on Venus, during a transit from the Asteroid Belt to Earth.
In the movie
2010: The Year We Make Contact, the
Leonov uses aerobraking in Jupiter's atmosphere to rendezvous with the
Discovery.
In the
fourth episode"Darkness" is the fourth episode of military science fiction television series Stargate Universe, and is the first part of a two part story. The episode originally aired on October 16, 2009 on Syfy in the United States, followed by being aired in the United Kingdom and Ireland on October 20...
of
Stargate UniverseStargate Universe is a Canadian and American military science fiction television series and part of MGM's Stargate franchise. The series, created by Brad Wright and Robert C. Cooper which premiered with the first two parts of a three-part episode, "Air" on Syfy on October 2, 2009...
, the
AncientThe Ancients are a humanoid race in the fictional Stargate universe. They are called "Ancients" in the Milky Way, but are also known as Lanteans or Ancestors in the Pegasus galaxy and as the Alterans in their home galaxy, and they sometimes call themselves Anqueetas in their language...
ship
Destiny suffers an almost complete loss of power and must use aerobraking to change course. The episode ends in a cliffhanger with
Destiny headed directly toward a sun.
See also
- lithobraking
Lithobraking is a technique of descent by an unmanned space vehicle to the surface of a body by which the vehicle is slowed by impact with the body's surface....
- Atmospheric reentry
Atmospheric reentry refers to the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space, in the case of Earth from an altitude above the "edge of space." This article primarily addresses the process of controlled reentry of vehicles which are intended...
- aerocapture
Aerocapture is a technique used to reduce velocity of a spacecraft, arriving at a celestial body with a hyperbolic trajectory, in order to bring it in an orbit with an eccentricity of less than 1. It uses the drag created by the atmosphere of the celestial body to decelerate. Only one pass in the...