Realistic information gathering

[innovine]

The MFDs supply the exact orbital elements for my spacecraft, but this doesn't seem very realistic to me, especially when I'm not in Earth orbit (with the advantages of the gps system).

I know the Apollo astronauts took star sightings with a sextant, and had radar altimeters to verify the distance to the moon. I'm curious if anything like this has been implemented in Orbiter? (I'm not familiar with the NASSP and AMSO addons, yet).

What techniques might be used for spacecraft to perform navigation and guidance themselves, without relying on information processing sent up by ground stations? Do you think the Apollo techniques will still be used on manned missions to Jupiter and Saturn?

Any info around realistic gathering of guidance and navigation would be really welcome, historic, present-day or speculative processes, it's all welcome!

 

[Urwumpe]

Unless you install strong active radar into a spacecraft, ground based radar will remain important. It is simply more accurate, also a lot of orbit data is calculated from the Doppler Shift of the telemetry signals.

Star Sightings and landmark sightings are good, but pretty inaccurate unless you invest a lot of time into the process. Automated star sighting is more accurate there, but also taking more time and requires careful monitoring.

 

[innovine]

Can star tracking be used for more than determining attitude? It's not going to tell you your orbital elements I guess. Any suggestions for how these might be determined without ground support (say for a mission to the outer planets, or interstellar flight)?

 

[N_Molson]

The stars and the Sun are excellent sightings because they don't "move", relatively to the observer (in reality they do, but it is neglectible on the duration of a space mission). [slight correction : in the case of a Mars or NEO mission, the Sun isn't a fixed reference]

The orbital parameters of the planets and natural satellites of the Solar System are well-known, and very predictible (The ability to reproduce an eclipse in Orbiter is a proof of that).

So if you enter that data in a computer, and have an automatic system that tracks the planets and stars, it should be possible to get orbital elements. Probably less accurate than telemetry data, though, because mesurements errors are inevitable.

The idea is that as long you have a fixed tri-dimensional reference (the stars), you can calculate the relative position of other objects (if you have the right data in the computer).

A Mars mission would probably have to use such a navigation method. Telemetry updates each 15 minutes (the time required for the radio waves to make the trip) while in Mars orbit would not be practical (and Mars orbit implies a radio blackout 40% of the time).

Of course, you also have Inertial Navigation Systems that give accurate positioning data, according they are re-calibrated on a regular basis to avoid errors.

 

[innovine]

The orbital parameters of the planets and natural satellites of the Solar System are well-known, and very predictible (The ability to reproduce an eclipse in Orbiter is a proof of that).

Actually I've been doing a bit of reading about how Cassini navigates, and it's position/trajectory is much more accurately known than, say, Titan's orbit. Probably due to doppler effects in the telemetry and so on, but this means that when approaching for a flyby, Cassini is using radar ranging to fix Titans position.

I like all this navigation stuff. If I have the time, I will make an attempt to implement something for Orbiter eventually, perhaps a telescope/sextant for making angle measurements, and a radar altimeter. A little guidance computer for calculating would also be nice. I think it would be neat to have a display showing what it thinks my orbit is, which I need to occasionally refine by performing different observations.