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Old 12-16-2014, 10:58 AM   #1
Tutorial Publisher
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Default great-grand-tour

I've been away from Orbiter for nearly two years working RL tasks. I did drop into the forum a few times to see what was happening. Glad to see some activity here.

A couple days ago I fired it up and got to wondering about the idea of doing a combination of inner slings like Cassini but date it to go out for the voyager grand tour alignment. Maybe it's wondering about an alternate history where we focused more on unmanned probes instead of manned journey's to the moon in the 60's. Or perhaps it's just an exercise in TransX button pressing.

I found a couple of options, both free-coasting so no deep space maneuvers...

First is a 1972 start that goes Earth to Venus then Venus then Earth then out for the JSUN tour. It has a much lesser dV than the actual Voyager missions did. But a bit slower than Voyager arriving a full year later to Neptune.

I couldn't help but also wonder about adding Mars in there, so the full tour would only miss Mercury in our planet slinging list. It took a while but I found a path. It starts in 1969 and like the 1972 scenario, it has a light initial dV as compared to the actual voyager missions but unlike both actual Voyager and the 1972 scenario, this one has a substantially faster encounter speed to Jupiter and regardless of starting 7 years before Voyager (but still doing the last sling from Earth in 1976), it gets to Neptune 3 years before Voyager and leaves the solar system something like 25% faster. Encounter at Neptune was faster than 21 km/sec.

This 1969 Mars include scenario starts out with the usual retrograde eject from Earth to drop to Venus but must do 1.5 orbits before that initial sling at Venus. But after that it goes out for a close sling of Mars then back Venus all in the next orbit, then one orbit later it slings Earth, then out for an Ap beyond Jupiter to drop back at a fairly high encounter speed to Jupiter which gives it the extra speed for the rest of the tour.

Anyway I tossed the scenarios into a dropbox folder (link below). I am not sure what TransX version it uses but I did notice it has the Auto-Min adjustment which I haven't played with yet. I hope these scenarios open and show the stages for those who wish to look at it or fly it.


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Old 12-18-2014, 02:22 AM   #2
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About how long does it take to come up with such a plan in TransX?

I am wondering about the relative time commitment of using Trajectory Optimization Tool versus using TransX directly.
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Old 12-18-2014, 06:29 AM   #3
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The simple plan without Mars only took an hour or less. Maybe even 30 minutes. Can't remember.

Then I tried for close to two hours the first evening looking for the Mars include and eventually gave up. Then tried again the next morning and found the solution in about another hour or two. But it is a very narrow window. It doesn't take much change of the initial eject from Earth in either date or velocity to cause the Venus Mars Venus (that part is really like a free return) to fail. Plane changes were really messing things up. Mars was just so wimpy to be much help to redirecting back to Venus. It was shooting in the dark. I almost couldn't believe the find when it came. I was just as far from the solution 1 minute before I found it as I was 1 hour before I found it. Maybe I was just tired and not focused.

But the trick to some extent is being fairly fast at roughing out the transfer stages so that many attempts can be made in short time. No need to be precise at that point. Just get it close enough in a transfer so that the next stage is able to show up so that one can quickly rough out that stage etc. Then when it fails and just seems wrong, (and it does dozens of times) quickly go back and either tweak a slight change or perhaps a completely new idea like adding additional orbits for a transfer.

Remembering what one has tried helps to not waste time retrying failed ideas.

Some orbiteers enjoy programming, some like flying complex craft. I have more fun just pushing the stages around than I ever do flying.

BTW I did fly the Mars include grand tour. I ended up leaving the solar system at about 25 km/sec. The Neptune pass was in June 1987. And I went ahead and advanced to today's date and it showed I would be 161 AU from the sun now (December 2014).
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