Orbit maneuvers

In space travel and celestial mechanics or space flight mechanics, an orbit maneuver is a process with which an artificial earth satellite or an interplanetary missile is brought to a different orbit by igniting a recoil motor for a limited time .

The subject of path maneuvers is always a metered change in speed (acceleration, braking) in amount and / or direction. Major changes require a rocket motor that can be switched off (with liquid fuel or possibly with ion propulsion ); nozzles for compressed gas are sufficient for minor changes.

Since, in addition to the dosage of the recoil (backwards or forwards), its exact direction is also decisive, the missile must be stabilized in space (gravitational, magnetic or gyroscopic stabilization ). These instruments can also be supplemented or checked by suitable sensors such as star sensors .

The purpose of an orbit maneuver can be:

• for earth satellites or for artificial satellites around the moon or other planets:
  • the enlargement of the orbit axis (altitude) or orbit time (through acceleration)
  • the reduction of the orbit axis, flight altitude or orbital time (by braking)
  • the achievement of a certain orbit shape (e.g. circular orbit , rendezvous maneuver , sun-synchronous orbit)
  • the change in the path plane (due to lateral acceleration)
  • a small course correction (mostly with gas jets);
• for lunar probes or interplanetary space probes  :
  • the enlargement or reduction of the path axis (see above)
  • the control of a transition path to another celestial body
  • swiveling into an orbit around it (see also lunar satellite ) or leaving such an orbit for onward flight or return
  • the initiation of a landing maneuver
  • the control of a swing-by on a celestial body ( gravitational maneuver to increase or decrease the orbital energy)
  • Course corrections to fine-tune the trajectory or timing.

historical development

In the first years of space travel, the technology of orbit maneuvers was not yet developed, so the orbits reached depended solely on how accurately the rocket launch could be controlled. The deviations of the burning time or the burning speed from the target value were typically a few per thousand, the directional errors a few tenths of a degree. In the case of the first lunar probes , these errors caused z. B. from a planned " hard landing " on the earth's satellite became a flyby at a distance of tens of thousands of kilometers.

Later, the transition to the moon or Mars / Venus was followed by a so-called park orbit around the earth. After a precise orbit measurement , the required acceleration could be dosed much more precisely than directly with a longer burning time of the top rocket stage .

The flight of today's space probes can be controlled a hundred to a thousand times more precisely than at that time, but this requires a complex sequence of several orbit maneuvers. The first time such a series of maneuvers was used was during the flight of the Mercury probe Mariner 10 between November 1972 and March 1975:

• Exact determination of the path of the park path
• Shot in a transition orbit to the planet Venus
• Orbital maneuvers for an accurate swing-by at Venus, which reduced the orbital energy by 60% ( required to reach planets near the Sun )
• fine modification of the orbit axis (distance from the sun )
• last course corrections near Mercury for the first flyby
• Timing of the sun's orbit in order to get close to it again after two orbits of Mercury (2 × 88 days)
• Orbit corrections for a third approach at a lower altitude.

The flights of the Voyager probes to Jupiter and the outer gas planets were even more complicated , with special approximations to some of Jupiter's moons being carried out.

The newer comet probes and the Pluto probe New Horizons were also controlled in such a targeted manner that gravity assist maneuvers and fly-bys of other celestial bodies were possible.

See also

• Interplanetary navigation

literature

• Richard Heinrich Giese : Space Research Volume I, Chapter IV Application of Space Flight Mechanics . BI university paperback 107 / 107a, Bibliogr.Inst., Mannheim 1966
• August W. Quick: Components of space travel. Control and regulation in space technology . Springer Paperback, 2013
• Manfred Baur: Planets and space travel - expedition into space . Tessloff-Verlag 2001