Launch window
Encyclopedia
Launch window is a term used in spaceflight
to describe a time period in which a particular launch vehicle (rocket
, Space Shuttle
, etc.) must be launched. If the rocket does not launch within the "window", it has to wait for the next window.
For trips into largely arbitrary Earth orbits, almost any time will do. But if the spacecraft
intends to rendezvous
with a space station (such as the International Space Station
) or another vehicle already in an orbit, the launch must be carefully timed to occur around the times that the target vehicle's orbital plane
intersects the launch site.
For launches above low Earth orbit
(LEO), the actual launch time can be somewhat flexible if a parking orbit
is used, because the inclination and time the spacecraft initially spends in the parking orbit can be varied. See the launch window used by the Mars Global Surveyor
spacecraft to the planet Mars at http://mars.jpl.nasa.gov/mgs/overvu/delta/window/window.html.
To go to another planet using the simple low-energy Hohmann transfer orbit
, if eccentricity of orbits is not a factor, launch windows are periodic according to the synodic period; for example, in the case of Mars
the period is 2.135 years, i.e. 780 days. In more complex cases, including the use of gravitational slingshot
s, launch windows are irregular. Sometimes rare opportunities arise such as when Voyager 2 took advantage of 175 year planetary alignment (launch window) to visit Jupiter, Saturn, Uranus and Neptune. When such an opportunity is missed, another target may be selected. For example, the Rosetta
mission of ESA
was originally intended for comet 46P/Wirtanen
, but a launcher problem delayed it and a new target had to be selected (comet 67P/Churyumov-Gerasimenko
).
Launch windows are often calculated from porkchop plot
s that show the delta-v
needed to achieve the mission, plotted against the launch time.
The term 'launch window' is often used metaphorically, particularly in economics
, to describe the launch of a product, the 'window' describing a key opportunity for the product to be released. For example, a film
may be scheduled for release in the summer - a popular time for films- but if there is a problem in development, it might miss that launch window and make less of a profit.
missions to the International Space Station
are restricted by beta angle
cutout. Beta angle (
) is defined as the angle between the orbit plane and the vector from the Sun. Due to the relationship between an orbiting object's beta angle (in this case, the ISS) and the percent of its orbit that is spent in sunlight, solar power generation and thermal control are affected by that beta angle. Shuttle launches to the ISS were normally only attempted when the ISS is in an orbit with a beta angle of less than 60 degrees.
Spaceflight
Spaceflight is the act of travelling into or through outer space. Spaceflight can occur with spacecraft which may, or may not, have humans on board. Examples of human spaceflight include the Russian Soyuz program, the U.S. Space shuttle program, as well as the ongoing International Space Station...
to describe a time period in which a particular launch vehicle (rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
, Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
, etc.) must be launched. If the rocket does not launch within the "window", it has to wait for the next window.
For trips into largely arbitrary Earth orbits, almost any time will do. But if the spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
intends to rendezvous
Space rendezvous
A space rendezvous is an orbital maneuver during which two spacecraft, one of which is often a space station, arrive at the same orbit and approach to a very close distance . Rendezvous requires a precise match of the orbital velocities of the two spacecraft, allowing them to remain at a constant...
with a space station (such as the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
) or another vehicle already in an orbit, the launch must be carefully timed to occur around the times that the target vehicle's orbital plane
Orbital plane (astronomy)
All of the planets, comets, and asteroids in the solar system are in orbit around the Sun. All of those orbits line up with each other making a semi-flat disk called the orbital plane. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded...
intersects the launch site.
For launches above low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
(LEO), the actual launch time can be somewhat flexible if a parking orbit
Parking orbit
A parking orbit is a temporary orbit used during the launch of a satellite or other space probe. A launch vehicle boosts into the parking orbit, then coasts for a while, then fires again to enter the final desired trajectory...
is used, because the inclination and time the spacecraft initially spends in the parking orbit can be varied. See the launch window used by the Mars Global Surveyor
Mars Global Surveyor
The 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 2...
spacecraft to the planet Mars at http://mars.jpl.nasa.gov/mgs/overvu/delta/window/window.html.
To go to another planet using the simple low-energy Hohmann transfer orbit
Hohmann transfer orbit
In orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits, typically both in the same plane....
, if eccentricity of orbits is not a factor, launch windows are periodic according to the synodic period; for example, in the case of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
the period is 2.135 years, i.e. 780 days. In more complex cases, including the use of gravitational slingshot
Gravitational slingshot
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
s, launch windows are irregular. Sometimes rare opportunities arise such as when Voyager 2 took advantage of 175 year planetary alignment (launch window) to visit Jupiter, Saturn, Uranus and Neptune. When such an opportunity is missed, another target may be selected. For example, the Rosetta
Rosetta (spacecraft)
Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by...
mission of ESA
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
was originally intended for comet 46P/Wirtanen
46P/Wirtanen
46P/Wirtanen is a small short-periodic comet with a current orbital period of 5.4 years. It was the original target for close investigation by the Rosetta spacecraft, planned by the European Space Agency. It belongs to the Jupiter family of comets, all of which have aphelia between 5 and 6 AU. Its...
, but a launcher problem delayed it and a new target had to be selected (comet 67P/Churyumov-Gerasimenko
67P/Churyumov-Gerasimenko
Comet Churyumov–Gerasimenko, officially designated 67P/Churyumov–Gerasimenko, is a comet with a current orbital period of 6.6 years. It is the destination of the European Space Agency's Rosetta spacecraft mission, launched on March 2, 2004....
).
Launch windows are often calculated from porkchop plot
Porkchop plot
Porkchop plot is a chart that shows contours of equal characteristic energy against combinations of launch date and arrival date for a particular interplanetary flight....
s that show the delta-v
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
needed to achieve the mission, plotted against the launch time.
The term 'launch window' is often used metaphorically, particularly in economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...
, to describe the launch of a product, the 'window' describing a key opportunity for the product to be released. For example, a film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
may be scheduled for release in the summer - a popular time for films- but if there is a problem in development, it might miss that launch window and make less of a profit.
Specific issues
Space ShuttleSpace Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
missions to the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
are restricted by beta angle
Beta angle
The beta angle is a value that is used most notably in spaceflight. The beta angle determines the percentage of time an object such as a spacecraft in low Earth orbit spends in direct sunlight, absorbing solar energy. Beta angle is defined as the angle between the orbit plane and the vector from...
cutout. Beta angle (
) is defined as the angle between the orbit plane and the vector from the Sun. Due to the relationship between an orbiting object's beta angle (in this case, the ISS) and the percent of its orbit that is spent in sunlight, solar power generation and thermal control are affected by that beta angle. Shuttle launches to the ISS were normally only attempted when the ISS is in an orbit with a beta angle of less than 60 degrees.See also
- Collision avoidanceCollision avoidanceIn spaceflight, collision avoidance is the process of preventing a spacecraft from colliding with any other vehicle or object.-Launch Windows:Collision avoidance, or COLA is a concern during spaceflight launch windows...
- Delta-v budgetDelta-v budgetIn the astrodynamics and aerospace industry, a delta-v budget is the estimated delta-v requirements for the various propulsive tasks and orbital maneuvers over one or more phases of a space mission.Sample delta-v budget will enumerate various classes of maneuvers, delta-v per maneuver, number of...
- Interplanetary travelInterplanetary travelInterplanetary spaceflight or interplanetary travel is travel between planets within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System....
- Oberth effectOberth effectIn astronautics, the Oberth effect is where the use of a rocket engine when travelling at high speed generates much more useful energy than one at low speed...