Lunar satellite

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A lunar satellite is a space probe or satellite that acts as an orbiter and is placed in orbit around the Earth's moon .

Reaching a lunar orbit is a very demanding task in space travel , which requires a high level of control technology right from the start . But even more complex is the braking maneuver required around the moon to reduce the probe's excess speed.

Requirements for reaching the lunar environment

In order to fly close to the moon , the burn-out speed of the top rocket stage must be kept to an accuracy of about one per thousand. B. eliminate the energetically favorable solid rocket . The direction of the "shot" must also be kept to a few hundredths of a degree (i.e. the direction of flight of the probe when transitioning from earth orbit to moon flight) and the launch window must be hit within a few seconds (because of the variable angular positions in the earth-moon system ).

Although probes were supposed to land hard on the moon in the first years of space travel , the USSR and the USA only succeeded in doing so after four failed attempts each.

See also: Chronology of the moon missions .

Because at the beginning the control of rocket launches was still too imprecise, so that - quite apart from false starts - instead of the "direct shot" it was mostly a flyby at a distance of 6,000 to 60,000 km. Therefore, in the 1960s, the first thing to do was to bring the probe to a park orbit around the earth. Only after precise orbit measurement of this trajectory was the required (positive) speed correction as well as time and duration of the orbit maneuver for the transition path to the moon calculated . This had to be coordinated so that the probe arrived at the same point on the lunar orbit at which the moon reached it even after the required flight time.

Orbit maneuvers to swivel into the lunar orbit

To swing into a lunar orbit, the next critical moment is the braking or orbit maneuver. This maneuver must also be exactly right in terms of time, direction and change in speed.

A probe flying from the earth to the moon must reach approximately the second cosmic speed of 11.2 km / s after take-off , i.e. H. the escape speed required to leave the earth's gravity field . It corresponds to 140.7% of the orbit speed - i.e. H. the speed in the parking lane is to be increased by about 40% or almost 4000 meters per second, which must be done at an angle of about 90 ° across the moon.

When the probe then reaches the weightless point between the earth and the moon (due to time constraints, this must not be too slow), it begins “to fall towards the moon” and would “fall around” it unchecked or hit it at about 2000 m / s .

The excess speed ( kinetic energy ) is reduced by braking rockets, which have to ignite exactly in the direction of the orbit movement. If you brake just right, the probe swings into lunar orbit. This takes place in the orbit plane , which results from the mutual position of the earth and moon when the rocket launches, from its direction ( geographical latitude / azimuth ) and the time that has passed since then.

Scientific and technical targets of lunar orbiters

Lunar satellites are of outstanding importance for selenography (e.g. the Lunar Orbiters and Clementine ) and selenodesia (e.g. Lunar Prospector ). In addition, lunar satellites offer the advantage of observing the earth's magnetic field from a relatively constant distance (e.g. IMP-E ). Radio astronomical experiments (e.g. RAE-B and Luna-19) in a lunar orbit are also advantageous , since no interfering radio waves are received from the earth, especially on the remote side. In the lunar orbit, several relay satellites can be used to communicate with objects on the back of the moon.

Possible confusion

The term lunar satellite could also be misunderstood as a technical term for a natural satellite of the moon . However, such a satellite does not exist because its orbit would not be stable.

See also


  • Hans Reichardt: Artificial earth satellites. Akad.-Verl., Berlin 1959
  • Rainer M. Wallisfurth: Russia's way to the moon. Econ, Düsseldorf 1964

Individual evidence

  1. ^ The second earth moon, special case 1: moon around the moon ( Memento from March 4, 2016 in the Internet Archive ), article on the website of the Wilhelm Foerster Observatory eV