Ballistic capture is a low energy method for a

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

to achieve an

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

around a distant planet or moon with no fuel required to go into orbit. In the ideal case, the transfer is

ballistic Ballistics may refer to: Science * Ballistics, the science that deals with the motion, behavior, and effects of projectiles ** Forensic ballistics, the science of analyzing firearm usage in crimes ** Internal ballistics, the study of the proc ...

(requiring zero

Delta-v Delta-''v'' (more known as "change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as ...

) after launch. In the traditional alternative to ballistic capture, spacecraft would use a

Hohmann transfer orbit In astronautics, the Hohmann transfer orbit () is an orbital maneuver used to transfer a spacecraft between two orbits of different altitudes around a central body. Examples would be used for travel between low Earth orbit and the Moon, or ano ...

, which requires the spacecraft to burn fuel in order to slow down at the target. A requirement for the spacecraft to carry fuel adds to its cost and complexity. To achieve ballistic capture the spacecraft is placed on a flight path ahead of the target's orbital path. The spacecraft then falls into the desired orbit, requiring only minor orbit corrections which may only need low power

ion thrusters An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity. An ion thruster ionizes a neutral gas by extracting some electrons out of a ...

. The first paper on using ballistic capture for transfer designed for spacecraft was written in 1987. The mathematical theory that describes ballistic capture is called

Weak Stability Boundary Weak stability boundary (WSB), including Low-energy transfer, is a concept introduced by Edward Belbruno in 1987. The concept explained how a spacecraft could change orbits using very little fuel. Weak stability boundary is defined for the thre ...

theory. Ballistic capture was first used by the Japanese spacecraft

Hiten Hiten may refer to: * Hiten (name), Indian given name * Hiten (spacecraft), Japanese lunar probe *Tennin , which may include , , and the specifically female version, the , are a divine kind of spiritual beings found in Japanese Buddhism, the ...

in 1991 as a method to get to the Moon. This was designed by

Edward Belbruno Edward Belbruno (born August 2, 1951, as a U.S. Citizen in Heidelberg, Germany) is an artist, mathematician and scientist whose interests are in celestial mechanics, dynamical systems, dynamical astronomy, and aerospace engineering. His artistic ...

and J. Miller. The ballistic capture transfer that performed this is an exterior ballistic capture transfer since it goes beyond the Earth-Moon distance. An interior ballistic capture transfer stays within the Earth-Moon distance. This was described in 1987 and was first used by the ESA SMART-1 spacecraft in 2004.

Advantages

Ballistic capture is predicted to be: * safer, as there is no time critical

orbit insertion Orbit insertion is the spaceflight operation of adjusting a spacecraft’s momentum, in particular to allow for entry into a stable orbit around a planet, moon, or other celestial body. This maneuver involves either deceleration from a speed in exc ...

burn, * launchable at almost any time, rather than having to wait for a narrow

launch window In the context of spaceflight, launch period is the collection of days and launch window is the time period on a given day during which a particular rocket must be launched in order to reach its intended target. If the rocket is not launched wit ...

, * more fuel efficient for some missions.

Low-energy transfer

Trajectories that use ballistic capture are also known as a

Low energy transfer A low-energy transfer, or low-energy trajectory, is a route in space that allows spacecraft to change orbits using significantly less fuel than traditional transfers. These routes work in the Earth–Moon system and also in other systems, such as ...

(LET). More precisely, the terminology ballistic capture transfer (BCT) is used. They are low energy because they use no delta-V for capture. However, a low energy transfer need not be a ballistic capture transfer. The term ballistic lunar transfer (BLT) is also sometimes used. The region about a target body where ballistic capture occurs is called a weak stability boundary. The term weak stability boundary transfer is also used, or for short, WSB transfer. In 2014, ballistic capture transfer was proposed as an alternate low energy transfer for future Mars missions. It can be performed anytime, not only once per 26 months as in other maneuvers and does not involve dangerous and expensive (fuel cost) braking. But it takes up to one year, instead of nine months for a Hohmann transfer.

Missions using ballistic capture

The following missions have used ballistic capture transfers, (EBCT – Exterior ballistic capture transfer, IBCT – Interior ballistic capture transfer):

Advantages

Low-energy transfer

Missions using ballistic capture

See also

References

Further reading