Navigation

How will navigation be accomplished in space well beyond Earth?

This subject area will probably be under a state of transition for some time as humankind expands outward across the solar systema and eventually beyond. A navigational grid is part of the system and it will need to have a “zero” orientation similar to the Greenwich meridian in the modern system of time keeping. At first, this zero position will most likely be the current position of Earth in its orbit around the sun, meaning the grid will rotate around the Sun with the Earth always maintaining a zero spoke in the grid and all the other bodies will move on the grid. However, as exploration expands across the system, navigational beacons will be set to aid in navigation and other alternatives to the Earth zero meridian will become possible.

In order to be useful, most navigation system will want to present the users position as “home” and show all other bodies relative to its native home. But all navigation systems will need a common framework to communicate with each other. Whatever the zero meridian ends up being, the whole thing will be transparent to users who will see most of their perspective from their native home position.

Eventually it seems likely that there will be an extensive grid of navigational beacons making it fairly trivial to calculate your present location anywhere in the system. An interesting consequence of using a virtual home position is that the concept of the year (or some similar time frame) will become a variable and relative positions of one location to another will change over time unless their orbits are perfectly synchronized. Your proximity to various other bodies will come in constantly changing combinations and time frames. Planning a family get-together on a holiday date will become much more complex.

Once a craft goes beyond the limits of the Solar System, the Sun becomes the basic anchor point and perhaps rotational vectors will depend on some galactic scale grid.

An excellent Scientific American article explains how it’s done today:
How do space probes navigate large distances with such accuracy and how do the mission controllers know when they’ve reached their target? – [sciam.com]

The accurate navigation of space probes depends on four factors: First is the measurement system for determining the position and speed of a probe. Second is the location from which the measurements are taken. Third is an accurate model of the solar system, and fourth, models of the motion of a probe.

First

For all U.S. interplanetary probes, the antennas of the Deep Space Network (DSN) act as the measurement system. These antennas transmit radio signals to a probe, which receives these signals and, with a slight frequency shift, returns them to the ground station.

Second

Calculation of the trajectory of a space probe requires the use of an inertial coordinate system as well, wherein a grid is laid over the solar system and fixed relative to the star background. For interplanetary missions, an inertial coordinate system with an origin at the center of mass of the solar system is used.

Third

The third component of interplanetary navigation is an accurate model of the solar system. Gravity is the most important force acting on a spacecraft. Determining these gravitational forces requires accurate knowledge of the locations of all of the major bodies, such as the sun and all the planets, over the course of time. This information is provided by the planetary ephemeris, which has been in continuous development since the beginning of the interplanetary space program.

Note – “ephemeris” is a list of position values in astronomy.

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