Navigating Space

[Allan]

At one point in time in my life I was a sailor. I have a fair knowledge and understanding of Logitude and Latitude, magnetic north, and compass degrees. With a little brush up I could probably navigate fairly well based on the residual knowledge of my Navy days.

All things considered, I don't see how any of what I understand about oceanic navigation correlates to space. A course compass (pictured) really doesn't much apply when your 360 degree is not limited to whats just around you.

I understand that you can navigate space if you have a light source to direct yourself toward. Sure you have to consider curvature, but that can be compensated for to hit your mark. But what if your destination does not emit, reflect, or absorb light? Is there a device like a course compass for space?

If you were in space looking out at space and you wanted to say "look over there" for something you knew would arrive, how could you go about percisely giving the area to monitor without having to stand there and point until the thing comes into view?

 

[jedidia]

I'd say there's two sides to "navigating in space". one is course planning, which is absolutely different than at seas, because there's completely different mechanics at work. That's the part Orbiter simulates.

The other part is calculating current position, heading and speed, which is pretty much a like to what they did at sea in times of old... triangulating the position by different stars at different times. Just that you have to take three dimensions into account, which makes the trigonometry a bit more complicated, and you'll need other star charts, but that's about it.
This is, incidentally, the part Orbiter doesn't simulate. Not as long as noone writes an addon that allows it. Current MFDs all take these values for granted, while in real life calculating them would be a critical part of the actual navigation.

 

[Lucy]

Last I checked, NASSP 7 includes the optics on board the old Apollo craft, but there's not currently a way I've seen of actually using them to navigate. However you can get Orbiter to label the right stars so they're easy to pick out. The part that's missing is a way to extract data from this and input it into the calculator.

 

[jedidia]

I think there was a "sextant MFD" for 2006, but I'm not sure what it does...

 

[T.Neo]

Indeed, the Apollo crews carried a sextant, and determining position and trajectory in space depends a lot on sun, star and planet tracking.

I've never heard of compasses being used in spaceflight and such a thing would be useless in interplanetary space, but gyroscopes are often used to determine orientation.

 

[Andy44]

Some info on astrogation here, but it doesn't go into detail about how to do it.

Basically, astrogation is a step-by-step process:

1. Attitude determination using either star sensors or sun and planet sensors.

2. Orbit determination using either ranging equipment from ground antennae or using instruments to take ranges from nearby bodies. Multiple sightings and comparison to background stars can, with processing, output a position and velocity, aka orbit state vector. Look in a scenario file; you will see each vessel's state vector at the start of the scenario.

3. Orbit propagation, which predicts the future positions and velocities of the ship. Orbiter does this in realtime to simulate spaceflight; in real life you propagate several days, weeks, or months into the future in a few minutes.

4. Maneuver planning, using the propagation from step 3 and the attitude from step 1. By knowing where your vehicle will be and how fast it will be going at key points, such as closest approach to the moon, you can plan maneuvers, such as a lunar orbit insertion. This is what we use TransX for in the sim. By knowing the attitude, we can determine which direction to thrust.

After a maneuver, the cycle starts over again. Even if you have planned several maneuvers in a row, you need to get a fresh attitude and orbit state after every maneuver to correct for errors. Also, an orbit propagation gets stale after time, so you need to get new states every so often, even when just coasting. This is the spacebourne equivalent of a navigation "fix" at sea or in the air.

 

[NukeET]

I think there was a "sextant MFD" for 2006, but I'm not sure what it does...

Check out this thread.

http://www.orbiter-forum.com/showthread.php?t=9065&highlight=Coelliptic