Launch window

Launch window is the interval at which a launch of a spacecraft is possible, so that the mission can be fulfilled. Failure to conduct the start within the startup window, it must be postponed until the next launch window.

The location and size of the startup window depend on the starting place of the energy reserves and the controllability of the available launcher and the actual mission profile.

If the mission only it is to bring a spacecraft into orbit, the launch can take place at almost any time. The launch window is then obtained from further limitations, such as the requirement that the launch should take place in daylight.

Overflight zone

A first limitation is derived usually by the permitted overflight zone. The exact location of the projected flight path on the ground depends on the basis of the earth's rotation from the starting time; the launch window opens or closes, therefore, when the web the edge of the allowable zone reaches or leaves. Restrictions may be (especially on the ground in the event of a crash ), the communication range of ground stations or ships for tracking, in special cases, for political reasons necessary for reasons of safety.

Manned space flights

For human spaceflight higher standards of safety, so that the launch window may need to be shortened. Among other things, the launch window is limited by the length of time strapped the crew before the start can spend in the spaceship. The flyover zone must be considerate of possible emergency landing then if necessary.

Rendezvous in orbit

In some cases, the aim of the mission to carry out a rendezvous with an already in -orbit spacecraft. This maneuver was first conducted in August 1962, when Vostok 4 was started so that the spaceship is initially started Vostok 3 approached to a few kilometers. Rendezvous done now several times a year with the International Space Station, which was flown by Space Shuttle, Soyuz spacecraft and Progress transporters or will.

The position of the start window is derived from the fact that a spacecraft in orbit, at intervals of approximately 24 hours every point on the earth flying, the latitude is less than the track inclination. Within the startup window there is a time with the least energy expended. Will not start at this time, more fuel is needed. The size of the startup window is then obtained from the energy reserves and the controllability of the launcher. The launch window for the Space Shuttle on its way to the ISS was both open for a few minutes, however, the start of the rendezvous missions in the Gemini program had to be done within a few seconds. At Gemini 11, the launch window was only open for 2 seconds.

Satellite groups

Special precision at the start is necessary if the satellite launched is part of a satellite group, and the required orbit must be synchronized with several other satellites. The launch window may shrink in these cases to within a few seconds. , Such as in the satellites of the A-Train

Moon flights

Since the moon's orbit is elliptical and inclined to the equatorial plane of the earth, the energy required for a flight to the moon during the month and from mission to mission is different. When the Apollo program have limitations regarding the choice of the landing site had to be taken into account ( äquatornah and not too close to the edge of the moon ), and that the sun was not yet very high in the landing site on the lunar horizon. This means that only a launch window per month, which was opened about three to four hours resulted.

Interplanetary probes

The energy required for a spacecraft to other planets is extremely dependent on the starting time. The cheapest option is the energy transfer to the Hohmann orbit. In this case, the launch window opens only once during the synodic orbital period of the target planet. This is when Mars over two years, for other planets less.

For missions to the outer planets, the position of Jupiter must be considered, which is usually used for a swing-by maneuver.

The length of the startup window is at a planetary mission several days to a few weeks depending on the power reserves of the launcher. Within this launch window, due to the Earth's rotation only at a specific time to start the day, so that opens the start screen for a long time once a day. The first launch attempt is usually set to a date a few days before the optimum time so that delays can be compensated by technical problems or the weather.

Organizational constraints

Limitations of non-technical nature may arise, so as not to allow them to persist over holidays or similar occasions a mission, thus saving labor costs. This category also includes the outspoken by NASA -fly zone over the year 1999/ 2000.

General

The term from the start window that opens and closes, became popular with the reporting of the moon flights in Apollo program. There was talk back then of the moon window.

Also for the landing of a spacecraft there is a similar period to which the braking rockets must be fired to go down in the foreseen area. But it speaks not of landing window.

Time Critical seen the launch window is a sub- concept of the time window.