What reference point(s) to astronauts use to navigate in space?

Question

On Earth, we don't need reference points, because we only travel in 2-dimensional space (left/right, and forward/backward). In outer space, however, not only do you throw in another dimension (up/down), but you also need a reference point to figure out which way is up, down, left, right, forward, and/or backward.

How do they figure this out? I know they use degrees as coordinates, but I'm wondering what their reference point is - the sun? And if they use the sun as a reference point, in 3-dimensional space, how would they know if it's above, below, in front of, or in back of them?
Do they just figure out where the Earth should be in relation to the sun, according to what the date/season is, and then base their coordinates for traveling everwhere else on that? What if they're nowhere near earth - how do you know which way is which?

Thanks guys for the answers. I've heard about using starmaps and such, but I've always wondered - what if those charted stars moved for some reason (asteriod collision / star death /etc) then wouldn't that mess up the navigation?

Answer 1

In earth orbit, to navigate to a particular point in space, the spacecraft(s) in question are two of the reference points. Radar is used to find distance between them. The third reference point is the earth, to find altitude and altitude difference.

During the Apollo flights to the moon the astronauts used a sextant type device to orient their spacecraft toward a particular direction, using stars of known position. Once the direction from the spacecraft to several stars was determined the direction the spacecraft was pointing was known. Then, if they determined they were off course or at the wrong velocity, they could re-orient the craft, fire their rockets, and get into the proper trajectory or velocity.

The direction they were moving was set by the rocket used to put them on the lunar trajectory. Rockets use an Inertial Guidance System. The IGS is a series of gyroscopes that are used to detect motion in three dimensions (the gyroscopes try to wobble, or precess when motion occurs in a particular direction, and when they do that devices to which they are attached put out an electrical signal). The IGS is wired to a computer programmed with a particular velocity and speed target and the rocket (with spacecraft attached) is guided toward that pre-programmed target. So, on launch the rocket is programmed to continue until the three gyroscopes detect that the target has been reached (that is, so much time X speed in some direction). In effect, the reference point is the launch pad.

Answer 2

Most of our current exploration is close enough to Earth to use it or the sun as the primary reference. The easiest reference is the communication signal. It has a direction and a frequency. Changes in the frequency and response time will indicate speed and distance. Often one channel is simply a reference signal for this purpose.

A second reference is needed to determine the spacecraft's attitude. NASA's Deep Space Array consists of radio installations spread around the world to provide trianglation points for a space craft to orient itself, using radio signals it is programmed to recognize.

Probes that go farther out are usually programmed also to find the sun, especially those which use solar power, of course. Beyond that, deep space probes are usually programmed with a rudimentary star map that can identify several bright stars by spectrum and relative location to each other.

Nothing we've sent out has gone far enough to significantly alter the appearance of the constellations. By that distant time, the on-board computers will need sophisticated 3D star maps.

Answer 3

Hmm.

All of your answerers have made a predictable but flawed assumption - that spacecraft navigate.

Actually this would entail them having to have far too many instruments. What actually happens is that they are observed from Earth, and this data is used to navigate for them.

The position and movement of Earth is well known, so this is not a problem.

See link below:

Answer 4

What you're saying is not 100 % true. If you are on earth in an aircraft, you're dealing with three dimensions.

The reference for space craft is arbitrary. If one is in low earth orbit, and earth based coordinate reference my be used. If the craft is in solar orbit, the sun would probably be used and if it were headed for another far out planet or an asteroid, the target may be the reference. It's whatever works for the mission and multiple references may be used for different parts of the same mission.

http://www.answers.com/topic/space-navigation-and-guidance

Answer 5

Good question, however I don’t think we are characters in cartoon movie that is restricted to travel only in two dimensional space. The universe and everything in it is three dimensional, height weight and depth. Astronomers believe the earth is at the center of the universe so the earth is the universal reference point. What scientists can’t figure out is the 4th dimension which some of them believes is special and some of them believes time is the 4th dimension.

Answer 6

I have watched many a shuttle mission (NASA-TV) and while I cant find specific information, I do believe they are using celestial navigation, because I have heard references to instrumentation that sounded like an automatic star tracker.

Answer 7

They use Many but the least you must have is four reference points the first three triangulate your position the Fourth one runs from that app ex out to you destination.basicly.but its all still just really really good guessing cause everything out their is moving hundreds of thousands of miles per hour in some direction.so that there destination point has nothing ther yet they just try to merge with it so they need to know where it will be in the time it takes them to get there.

Answer 8

They can used stars because they are at fixed positions or they could use radiowaves that can act sonar or echo sounding but only as a different wave in a vacuum.