Flight Question TransX Question.

[RAF Blackace]

I have flown the Voyager mission once with success (Just), but wanted to try it again. But this time I am faced with a problem I just don't know the answer to, probably because I am still learning the intricacies of TransX.

The images are from the successful mission, they show me just before entering Jupiter's SOI and set up for what appears to be a perfect slingshot to Saturn. But despite being on the right apparent trajectory the approach to Saturn seems off for some reason?

The current mission I am on has an even worse off set to Saturn and even though I correct the slingshot trajectory to keep is as close to the plan as I can, when I leave Jupiter's SOI and the plan jumps to the cruise to Saturn the offset is so great it uses up nearly all the fuel to correct it. The error post sling of Jupiter appears to end up almost the same as the error pre sling Jupiter. Regardless of how accurate I stick to the plan.

Even this successful mission used nearly 40% of the available fuel to correct the trajectory to Saturn, leaving very little left for the rest of the trip. I managed to fly past Neptune with 0.05% fuel left so I only just made it.

My question is. What can I do to reduce the apparent trajectory error shown at stage 4, when I am still at stage 1?

 

[RAF Blackace]

I think I have worked out what is happening. Because TransX does not take into consideration all bodies, despite it thinking I am on a perfect slingshot trajectory, I am not. I need to add an offset to the Pe Ratio just after the final trajectory course manoeuvre.

By the way. All these final course correction manoeuvres are done just outside the SIO. I have found that despite the Pe ratio jumping around alarmingly within the SOI, the end result of the slingshot (and the Pe Ratio at actual periapsis) is always the same as you set up before entering it, so there is simply no point in wasting huge amounts of fuel trying to correct it when you are in the SOI.

I took a wild guess (honestly) at setting the slingshot to Pe Ratio = 1.025 for the Jupiter flyby.

Without this small correction, the offset to Saturn after the Jupiter slingshot was 8G and there is now way I can expend that amount of fuel at this stage.

After making this small change, the offset to Saturn after the Jupiter slingshot was only 9M, well into Saturns atmosphere and easily good enough. Now I know how to correct these apparent huge errors I should be able to complete the rest of the mission with ease.

Hope this helps others who have come across this before. It seems that sometimes you just need to take a guess and hope your close enough.

 

[RAF Blackace]

Here I have taken images showing what I mean.

In columns 1 and 2, it shows the slingshot if I have a supposed near perfect sling according to TransX. Row 1 shows before SOI and after the last course correction manoeuvre. No further burns were done after this point. Row 2 shows at Jupiter Periapsis, and Row 3 shows after leaving the SIO and after Transx has jumped to the cruise stage. As you can see, the Saturn error is huge, and is almost exactly the same error I saw since leaving Earth SOI.

In Columns 3 and 4 the only difference is that I did a small additional burn to raise the Pe Ratio to 1.025 before entering Jupiters SOI and whilst still in the Jupiter cruise stage. No further burns were done after this point. After the sling, you can now see that this has now corrected the error and the course correction burn for the Saturn cruise stage is well within the fuel tolerance.

 

[RAF Blackace]

I have continued the mission by also estimating this error correction for the Saturn flyby to Uranus. I am now on course for Uranus with still more than 60% fuel remaining. It really does make a massive difference to fuel expenditure. If only I knew of a better way of calculating it, or a way to get Transx to calculate it for me.

 

[boogabooga]

I recommend that you learn to use IMFD with/instead of TransX.

TransX is fine for delta glider/Arrow freighter type spacecraft, but if you are are on a delta-V budget, you are going to suffer. Perhaps I just don't know how to use TransX well.

IMFD has a powerful n-body trajectory map. It helps a lot in situations like yours, as it is much more accurate.

There will be naysayers that claim that TransX is the tool to use for slingshot trajectories as IMFD doesn't have multi-slingshot support. In my experience, IMFD's powerful map program more than makes up for this shortcoming.

The trick is to use the offsetting functionality of the course program together with the map. Since you can see a much more accurate prediction of your actual course, you can correct your course early via offsetting.

Protip: you can bring up extra IMFD maps in external MFDs. You are NOT limited to one map per plan. You can bring up separate maps for different stages of your flight. This allows you to set up a sling pass that you can tell with some confidence will get you to your NEXT target. Staying one step ahead in the map planning pretty much gives IMFD the capability of multiple slingshot planning. Only more accurate.

Which Voyager add-on are you using?

 

[RAF Blackace]

Thanks for that advice boogabooga.

I am using Voyager - The 32nd Anniversary Edition (P1)

I have had very little luck with IMFD and slingshots so I resort to TransX, but it is not that accurate as I have found.

Having said that. I am indeed beginning to learn that the map program in IMFD together with using the offset in the course program can predict the errors that TransX does not take into consideration due to the fact that it does not account for all the bodies affecting the spacecraft.

I find IMFD much more accurate than TransX, but it is almost useless for slingshots. It would however help enormously in telling me how much I need to burn for to correct the errors in TransX.

Without using IMFD, and by guessing the offsets I managed to complete the Voyager 2 mission (which I only just managed to complete previously with 0.5% fuel remaining) with just under 50% fuel remaining (see image). I am certain that using the offset and map programs of IMFD alongside the TransX slingshot plan would improve fuel efficiency even more.

This is a really interesting mission for me, and is probably one of the hardest to accomplish in Orbiter along with the Dawn mission (which I managed but it nearly blew my brains apart).

Love this program. A big thank you to Scott Conklin for this mission, and also to BrianJ for all of his wonderful missions.

 

[RAF Blackace]

If anyone wants to try this mission. There is a missmatch between the launch tower position (Pad 41) and the Titan. I had to edit the file to get the launcher back into its launch tower. Probably because the titan launch tower and this mission were written at different times and the Canaveral scene changed somewhat with the introduction of the Hi-Res textures.

Also the launch sends you off with a Rinc of more than 13 degrees and not the <1 degree it claims to in the text. No idea why that is but manual intervention during the launch phase can correct this quite easily.

---------- Post added at 02:48 AM ---------- Previous post was at 02:43 AM ----------

I hate the Delta gliders with a passion. Simply because their engines are far too powerful and their fuel is far too efficient. Totally unrealistic. I did use realistic settings for the Delta Glider and was quite happy to find just how difficult even achieving orbit was.

I prefer realistic settings whenever I can use them. What is the point of a simulator if your not really simulating real rocket engines?

---------- Post added at 02:55 AM ---------- Previous post was at 02:48 AM ----------

I recommend that you learn to use IMFD with/instead of TransX.

TransX is fine for delta glider/Arrow freighter type spacecraft, but if you are are on a delta-V budget, you are going to suffer. Perhaps I just don't know how to use TransX well.

IMFD has a powerful n-body trajectory map. It helps a lot in situations like yours, as it is much more accurate.

There will be naysayers that claim that TransX is the tool to use for slingshot trajectories as IMFD doesn't have multi-slingshot support. In my experience, IMFD's powerful map program more than makes up for this shortcoming.

The trick is to use the offsetting functionality of the course program together with the map. Since you can see a much more accurate prediction of your actual course, you can correct your course early via offsetting.

Protip: you can bring up extra IMFD maps in external MFDs. You are NOT limited to one map per plan. You can bring up separate maps for different stages of your flight. This allows you to set up a sling pass that you can tell with some confidence will get you to your NEXT target. Staying one step ahead in the map planning pretty much gives IMFD the capability of multiple slingshot planning. Only more accurate.

Which Voyager add-on are you using?

Just a question on this, when using the map program in IMFD, the course shown is truncated because it can only plot a certain amount of the course. This is why I cant use it when plotting a slingshot from Jupiter to Saturn for instance. Is there a way of extending its capabilities to display more than I usually see now?

 

[RAF Blackace]

I let the simulation run after the Neptune flyby and my voyager 2 probe today is currently 121AU away from the Sun, which is interesting because the real Voyager 2 is only 106AU away.

And all this by using only about 130 Delta-V from the available 250 Delta-V. Try doing that with a Delta Glider!

Sail on sweet bird.

 

[RAF Blackace]

Here are the complete mission scenarios from this mission for anyone interested. Every course correction, every planet fly by, and every one of them commented.

You do of course need this..

[ame="http://www.orbithangar.com/searchid.php?ID=4073"]Voyager - The 32nd Anniversary Edition (P1)[/ame]

And the Pad 41 addon which you can get from..

[ame="http://www.orbithangar.com/searchid.php?ID=1233"]Launch Complex 40 and 41[/ame]

But you will have to edit the file to get the pad lined up with the launcher as I previously said. I can help you with that if you want.

 

[boogabooga]

Just a question on this, when using the map program in IMFD, the course shown is truncated because it can only plot a certain amount of the course. This is why I cant use it when plotting a slingshot from Jupiter to Saturn for instance. Is there a way of extending its capabilities to display more than I usually see now?

Yes, there is way. Turn on "adaptive". I think you also have to turn down the accuracy a little, too.

 

[RAF Blackace]

Yes, there is way. Turn on "adaptive". I think you also have to turn down the accuracy a little, too.

Thanks, due to this simple yet effective advice I can now fly the mission without using the TransX manoeuvre mode. Although I do find it impossible to get the accuracy that TransX gives, it does indeed fill in the missing gaps in TransX's accuracy close in to a planet with the map.

Thanks for the tip, its taken me a very long time to get to know how to do this properly.