Voyager: How Did They Navigate Unknown Worlds?

Something struck me as confusing, and I'm sure it's just that I don't have enough information yet.

The Voyager mission found MANY surprises in the planets they studied.
In fact, it seems they were wrong about more than they were right about, not to mention all they found out that they simply did not consider before.

What is confusing to me is that they planned this intricate and precise trajectory employing gravity assist while knowing so little about the planets, including geological makeup. Hell, they STILL don't know how deep the clouds are on Jupiter and know nothing at all about the central mass (if there even IS one).

Lacking all this information, how did they know how far and fast the planets would "sling" the Voyagers?
The measurements had to be extremely precise to get it right, where did they get the numbers?
How did they know how much gravitational force Saturn would exert on the crafts?
How did they avoid debris and moons that were so far that they did not even know they existed at the time?
With all fuel burned up early in the voyage, how did they change the trajectory mid-course like they did to pass over the north pole of Neptune?

The Voyager Enigma

All very good questions.

However, I doubt you will receive many satisfactory answers...

You do not need detailed geological information to compute celestial mechanics. The orbital data and total mass gives all you need. This information has been well known for generations.

one_raven said:

Something struck me as confusing, and I'm sure it's just that I don't have enough information yet.

The Voyager mission found MANY surprises in the planets they studied.
In fact, it seems they were wrong about more than they were right about, not to mention all they found out that they simply did not consider before.

What is confusing to me is that they planned this intricate and precise trajectory employing gravity assist while knowing so little about the planets, including geological makeup. Hell, they STILL don't know how deep the clouds are on Jupiter and know nothing at all about the central mass (if there even IS one).

Lacking all this information, how did they know how far and fast the planets would "sling" the Voyagers?
The measurements had to be extremely precise to get it right, where did they get the numbers?
How did they know how much gravitational force Saturn would exert on the crafts?

By observing how Saturn effected the satellites we already knew it had. This told us Saturn's mass. (which is all we needed to know)

How did they avoid debris and moons that were so far that they did not even know they existed at the time?

Even with the yet undiscovered moons, Saturn's neighborhood is not very crowded. The chances of hitting anything significant, while not zero, were extremely small.

With all fuel burned up early in the voyage, how did they change the trajectory mid-course like they did to pass over the north pole of Neptune?

I would have to say that they hadn't used up all their fuel and they had some reserve to make small course adjustments.

On the course change issue, see the following press release.

http://www.jpl.nasa.gov/releases/80s/release_1986_1085.html

Note that Voyager had thrusters and fuel to allow it to make course corrections.

Thanks for all the information.
It all makes sense now.

Nommos Prime (Dogon) said:

All very good questions.

However, I doubt you will receive many satisfactory answers...

Oh shut up. Like you really know anythink. All the answers were great ones. Go back to your conspiracy theories.

There were some surprises that *could* have made a difference. For example, the rings of Jupiter. Like all planetary rings, they are composed of small particles; if anyone of these had collided with Voyager (or the earlier Pioneers, or Galileo, ...) some damage would have been done, possibly fatal (to the spacecraft ) damage. These rings weren't discovered until Voyager 1 took some deep pictures (I don't recall whether this was before it reached the Jovian system or as it was leaving); Voyager 2 was reprogrammed to do more detailed investigation (and planetary rings became a much more active topic, with all kinds of discoveries subsequently, for Saturn, Uranus, and Neptune).

Fortunately, the Voyagers didn't go anywhere near the Jovian rings (we already knew that the radiation environment that close in would have been fatal to the spacecraft ). However, there was once a plan to send a craft (one of the Voyagers?) through the Cassini division in the Saturn ring system - the thought was it was truly a clear gap. Fortunately, this is not how the trip ended up, because the Voyagers showed that the Cassini division isn't empty at all!

The Voyagers' trajectories enabled us to make much more accurate estimates of the masses (and orbits) of the planetary moons which they passed near; the closer they passed, the more accurate the estimates. Conversely, before the fly-bys, inaccuracies in the estimates meant the possibility of collision; it was partly for this reason that the only extremely close flyby (of Triton) was the last one done; it mattered much less by then if there was a collision! (similar story for Voyager 1 and Titan).