Chapman Challenge

[Usonian]

I have some questions that are not strictly related to the Chapman Challenges, but this seems to be the forum thread for high-end discussions of TransX, IMFD and slingshot trajectories, so here goes...

I am working on a new Voyager addon. The spacecraft has sixteen 0.9 N thrusters, four working in the Z+ direction. So main thurst is only 3.6 Newtons. The thrusters have an Isp of 2109 and there is 103 kg of hydrazine fuel. There is a total Dv of 115 m/s. This is all that is available for course corrections after the initial ejection burn from LEO. I notice that the Chapman Probes have a total Dv in the 1200-1300 m/s range.

Question 1: Is it realistic to expect Orbiternuats to perform the Jupiter-Saturn-Uranus-Neptune slingshots with only 115 m/s for course corrections? Can the initial burn be that accurate using TransX and IMFD? If not, I will include multiple Spacecraft3 configurations: one with historically accurate performance, and one with "enhanced" performance similar to Chapman, and perhaps an "accurate but impatient" config with 115 m/s Dv but increased thrust so that burns are shorter and attitude control more responsive.

Question 2: I plan on including a launch scenario with TransX all set up. What would you say is the preferred version -- the one included with the Orbirter 2006 download (3.10), or the latest 3.13?

I have read this thread with great interest. I am too consumed with my own stuff right now to try the Chapman Probes, but I am looking forward to it! I also want to express my gratitude for Flytandem's tutorials and for this Chapman forum thread. Considering the power and flexibility of TransX and IMFD, it is amazing (well, scandalous, really) how marginal the documentation is that comes with those add-ons. It is a testament to your perseverance that you guys can accomplish so much with those important add-ons.

[tblaxland]

Quote:

Originally Posted by Usonian

 Question 1: Is it realistic to expect Orbiternuats to perform the Jupiter-Saturn-Uranus-Neptune slingshots with only 115 m/s for course corrections? Can the initial burn be that accurate using TransX and IMFD?

Well, I guess you have set us a challenge, haven't you? My suspicion, based on experience, is that 115m/s would not be sufficient but I haven't tried it yet. Never say never...

Quote:

Originally Posted by Usonian

 Question 2: I plan on including a launch scenario with TransX all set up. What would you say is the preferred version -- the one included with the Orbirter 2006 download (3.10), or the latest 3.13?

3.13, IMHO. It is not hard to find and is fairly widely used (3765 d'loads). Just put a link to it in your addon's description page on O-H.

[Usonian]

Quote:

Originally Posted by tblaxland

 Well, I guess you have set us a challenge, haven't you? My suspicion, based on experience, is that 115m/s would not be sufficient but I haven't tried it yet. Never say never....

Well, I can give some relief there. BrianJ just sent me a PM pointing out that my calculation was wrong! I wrote the post form work and mis-remembered the Voyager's mass. The correct Dv will be 281 m/s. A far cry better, but still tight.

Quote:

Originally Posted by tblaxland

 3.13, IMHO. It is not hard to find and is fairly widely used (3765 d'loads). Just put a link to it in your addon's description page on O-H.

Good idea. Seems that Voyager will appeal most to people who are really into TransX, and they are most likely to have the latest and greatest.

--added--

BTW, wasn't it a classy thing for BrianJ to discreetly point out my error in a PM? Nice guy, and a great addon developer.

[Usonian]

Quote:

Originally Posted by tblaxland

 3.13, IMHO. It is not hard to find and is fairly widely used (3765 d'loads). Just put a link to it in your addon's description page on O-H.

I am running into a snag with Transx 3.13. It does not want inherit a flight plan from a previous stage. All that that an "heir" vessel receives is the flight plan stages, but none of the data! (Kind of like inheriting a bank account holding only $1 -- not much of an inheritance.) This function works perfectly for me with 3.10 (I have not tried 3.11 or 3.12). It is an important function for the Voyager flight in that the Centaur stage is followed by a solid fuel Star 37 -- there is no time to recreate a flight plan after staging.

I caught on to this "inherit" function from Flytandem's earlier post (quoted below). He describes a possible bug in the process, with "Orbits to Incept" being dropped (or, I am guessing, reset to zero). This hasn't been a problem for Voyager, since Orbits to Incept is always set to zero anyway. I wonder which TransX version Flytendem is using?

Quote:

Originally Posted by flytandem

 I just flew the Chapman Ion 2 launched from Atlas V-422 and discovered something about TransX I had not known before. A previous post I made mentioned that it's a bummer that after separating from the launch vehicle, the Chapman probe needs to have the TransX plan reinstalled from scratch. Well it turns out that's not really true. But with a caveat. By going back to stage 1 and then back one more time there is a display to state where the plan is inherited from. Click the + to choose the Atlas or whatever craft had the plan you want and then click EXE. Voila the plan is brought into the Chapman.

But there is a problem that makes this not a wise thing to do. I suspect a bug that some day Steve may fix in a future version of TransX. Seems (I could be wrong) that the plan details are not full inherited. Some details are left behind. Any maneuver that's set up is left behind and also the orbits to icept is left behind. And the loss of orbits to icept may be causing a lockup of the sim when it advances to where this value is supposed to toggle down in value.