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The Dunatian, Playable Save File (Like a Scenario)

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selfish_meme

selfish_meme

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Will do.

I also wouldn't use the big 4, recruit some new Kerbals, I have some notes on what to name them to get the profession right, one other way is to play with leading and trailing spaces, they don't show up in the game but can change professions.

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JAFO

JAFO

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I also wouldn't use the big 4, recruit some new Kerbals, I have some notes on what to name them to get the profession right, one other way is to play with leading and trailing spaces, they don't show up in the game but can change professions.

That's ok.. I just used your earlier names:

Rick Kerman - Pilot

Mark Kermney - Engineer

Christopher Beck - Scientist

Beth Johanssen - Engineer

Alex Vogman - Scientist

Commander Lewis - Scientist

All except Mark Kermney are now aboard the Hermes.. Mark is twiddling his thumbs whilst awaiting assignment to the Ares 3 site.

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selfish_meme

selfish_meme

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That's ok.. I just used your earlier names:

Rick Kerman - Pilot

Mark Kermney - Engineer

Christopher Beck - Scientist

Beth Johanssen - Engineer

Alex Vogman - Scientist

Commander Lewis - Scientist

All except Mark Kermney are now aboard the Hermes.. Mark is twiddling his thumbs whilst awaiting assignment to the Ares 3 site.

Cool, I was just cleaning up the Delta II and Pathfinder. I felt a bit guilty, I had slapped the lander on the Delta II and called it a day. I found out later it did not work very well. She is a beauty now though 197 parts, should be 198 (I need to add a battery), and I have a Pathfinder on a Duna Intercept right now.

I also worked on the rovers and the Hab, I'll upload them tomorrow.

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JAFO

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Make sure you note the steps to reproduce the flyby so we can set it up in new savefiles.

Ok.. here we go. The write-up, and the save-file.

A Duna/Kerbin free return trajectory? Hmm, I've never plotted one myself but how hard can it be? You just have to find out the perfect time to reach Duna. There must be information here about this kind of maneuver.

- - - Updated - - -

OK looking into this the only examples of a Duna/Kerbin free return I can find involve simply performing a massive burn taking you close to a Duna encounter and out way past it back to Kerbin. That sounds like a crappy way of doing it. But it does the job, and if you do not perform an intercept burn you would simply return to Kerbin. It would be a long return though but this sounds like a simple way to do it.

Ok Majorjim, for you, and anyone else who may be curious about the what, how and why, here's some introductory notes before getting into the specific steps for this project.

To begin with, you'll need this: [WIN] Flyby Finder V0.82 [KSP1.04]

Unlike KSP TOT, it finds all flybys that match the user's specifications.. KSP TOT will only pick the one "best" flyby it can find.

Flyby Finder is Windows only, but it works fine running on Wine, so it can be used on Linux and Mac without any problems, if you have Wine installed. I haven't tried KSP TOT with Wine yet, but I think it'll work ok. Be aware that if it seems to not be working, it can take quite a while (as in, almost a minute!) to load and start running.

As good as Flyby Finder is, it doesn't provide one essential piece of information (nor does KSP TOT). And that's the Ejection Angle to Prograde/Retrograde. Maybe that can be calculated from the provided data, but I've no idea how, and besides, there's another tool that can tell us, when we give it the data provided by Flyby Finder.

Go to alexmoon's Launch Window Planner, and plug in the details of the planet you want the flyby for. Set the Transfer type to 'Ballistic', and click on the 'Show advanced settings' link. Set both the 'Earliest departure' and 'Latest departure' to the same day, as specified by Flyby Finder. Set 'Time of flight' to something that will cover all the bases, such as 0 to 1000 days. Click on the Plot it! button, and you will get a nice mini-display that should confirm the required delta-V as predicted by Flyby Finder, as well as the other details, including the all-important Ejection Angle.

If you're using a low-TWR craft like the Hermes, you'll also want to break up the many-minutes-long burn required, into smaller chunks, performed when the ship is close to periapsis. To calculate the burns and starting Ejection Angle, Red Iron Crown's Precomputed Low-TWR Interplanetary Transfer Burns are brilliant. As I needed to do a modified version of his transfer burns, to avoid running into the Mun's SOI, I extended his spreadsheet to get the Ejection Angle data I needed. Anyone who wants a copy can download it here.

Finally, you will probably want to have a few mods installed. At minimum, you'll want PreciseNode, because it takes some real fine-tuning to achieve flybys. Kerbal Alarm Clock is nice to have, if only to keep track of SOI-changes, so you can nursemaid your ship across them. MechJeb is very handy to have, for the simple reason that it makes for easy setting up of nodes for the multiple burns involved, and it is better at timing burns than any human. (And it isn't fooled by KSP's wildly inaccurate burn estimates.. it gets burn durations right.) If you think that's 'cheating', then consider this.. NASA "cheats" all the time. Their burns are computer controlled, because human reactions aren't quick or consistently reliable enough for accurate results. So you'll be in good company. If you install MechJeb, install MechJeb and Engineer For All as well. That way you don't need to add a part to your craft, all your craft will automatically have MJ or KER available. Speaking of KER, that's another helpful source of data. If you're following along with the rest of these steps, you'll also need HyperEdit to get the Hermes into orbit around Kerbin.

Right.. with that out the way, let's get down to the specific methodology/steps needed to set up the Kerbin-Duna-Kerbin free-return trajectory for The Dunatian.

  1. Create a new game-save, then exit the game without going any further.
  2. Open the save's persistence file with a text editor (not Notepad, it adds invisible characters to files, that may mess things up). Set UT = 11146000 - This is Year 2, Day 91, Hour 0, Minute 6. Doing this will save you having to time-warp 2 years and 91 days before launching Hermes, and will place Hermes about 10 minutes before our initial burn is due to commence. Save the file.
  3. Start KSP and load the game-save. Go to the VAB and load Hermes. Add the crew, then put the ship on the launchpad.
  4. Using HyperEdit, put Hermes in a 100x100km equatorial orbit around Kerbin.
  5. Once in orbit, ensure the throttle is at zero, and stage the engines. Do it now, because if you don't, you'll forget later!
  6. Open the Map view, and rotate the view so that you're looking directly down on Kerbin from above, and Hermes is at the 12 o'clock position.
  7. Quickly tap the . key once, then the , key once. This will stop the jittering, which will make it hard to create a manoeuvre node, otherwise.
  8. Click on Hermes orbit between the 7 and 8 o'clock positions, and create a manoeuvre node.
  9. If PreciseNode didn't automatically pop up, press the p key to bring it up.
  10. Temporarily set the prograde value to 4000. This ensures we will get an Ejection Angle display.
  11. Set the UT value to 11146823.6 - This should set the Ejection Angle to 133.3°. If not, use the 1, 0.1, 0.01 and +/- buttons to adjust UT until you get a solid 133.3° reading. (The reason for this value is that we need a final Ejection Angle of 136°, and from Red Iron Crown's spreadsheet, we know that we need to adjust this by 2.7°, to allow for the 19 hours and 14 minutes it will take to do our preliminary burns, before we are ready to do our final burn at 136°.) IT IS VERY IMPORTANT THAT THIS INITIAL ANGLE BE CORRECT. TAKE THE TIME TO GET IT RIGHT.
  12. Set the prograde value back to zero. Do not move or adjust the node in any way. The node is going to be the foundation of our periapsis for all subsequent burns, and it has to be in exactly the right position.
  13. Open the MechJeb Manoeuvre Node Editor. You can leave PreciseNode open if you want.
  14. Make sure that auto-warp is enabled, set the MJ prograde to 100m/s. Click the Update button.
  15. Click the Execute next node button and wait until MJ has completed the burn and cancelled the node. The orbit's apoapsis should now be 240km.
  16. Close the Manoeuvre Node Editor, and open the MechJeb Manoeuvre Planner.
  17. Select 'Create Node' -> 'Change Apoapsis' to 419km at 'Next Periapsis'. Click on the Create and execute button. Wait until MJ has performed the burn and cancelled the node.
  18. Repeat step 17, six more times, raising the apoapsis in turn to 658km, 987km, 1471km, 2250km, 3708km, and finally 7409km.
  19. Next comes the fun/tricky part.. the final burn. This burn is performed 66 minutes after the ideal window specified by Flyby Finder, because if we burned exactly at the launch window, we'll hit the Mun's SOI, and our altered course will smash us into Kerbin. The one hour delay allows us to sneak past the edge of the Mun's SOI without touching it. So we'll need to make some minor corrections to our course to take this delay into account.
  20. Close the MechJeb Manoeuvre Planner. Enter the following settings into PreciseNode. UT = 11216020. Prograde = 501.5. Normal = -10.3. Radial = 0.
  21. The Ejection Angle will be flickering, but it should average about 138°.
  22. Zoom out, and set Duna as your Target. If you're lucky, you should already see a pair of closest approach markers. Due to small variations in burn times, etc, most likely you're going to have to tweak things. You're aiming to get a closest approach in the vicinity of 60,000km.
  23. By means of the 1, 0.1, 0.01 and +/- buttons, carefully adjust the UT until you get a close approach. As soon as you have one, use the MS (Memory Save) button to record the settings. This way, if you mess up, you can get it back by using the MR (Memory Recall) button.
  24. Continue to tweak the closest approach lower and lower until you have it down around 60,000km, saving the settings each time you get an improvement. Sometimes, one click will make it a tiny bit worse, then another click will improve it even more, so don't stop increasing or decreasing the moment you see a change in the wrong direction.
  25. At the end of the burn, we're going to sneak that 60,000km down a bit lower, but for now, press AltF5 and create a named quicksave. If you mess the burn up, you'll want to be able to AltF9 to try again.
  26. Now that PreciseNode has set up the burn,use MechJeb's Manoeuvre Node Editor to execute it. This will be a long one, at 3 minutes and 9 seconds. However, we DON'T want MJ to execute the final few seconds of the burn, because it will mess things up, if you allow it.
  27. MJ will throttle the burn down when it gets to the last 2-3m/s. When it gets to about 1m/s remaining, click on the Cancel/Abort execution button, and cancel the node. The closest approach will probably show something in excess of 100,000km. We'll handle the fine-tuning ourselves.
  28. Hit t to enable the SAS in Stability Assist Mode. This will make sure the Hermes stays aligned on the burn axis.
  29. Press AltF5 and create a named quicksave. I suggest using the current closest approach distance as the name of the save.
  30. Keeping the mouse pointer over the close-approach markers, gently tap the Shift once, to barely fire the engines. When the approach reduces by about 10,000km, quickly hit the x key to kill the engines, and then make another named quicksave.
  31. Repeat steps 29 and 30 until you get the distance down to the low 50,000's. This is as close as it's safe to get. We need to stay out of Duna's SOI, or we'll get our course messed up big-time, but at the same time, we want to be as close as is possible to make rendezvous easier for the DAV. Duna's SOI begins at 47,922km. My personal best closest approach is 51,900km.
  32. When you're happy with the distance, make a quick-save, and set an SOI alarm with Kerbal Alarm Clock. Time-warp to the SOI change, and shepherd the Hermes across.. now save again.

And that's it! (I bet when you asked me to note the steps needed, you didn't think it was gonna be this complicated! :D)

You can now time-warp to a few days/weeks before Duna closest approach, and use HyperEdit to place all the various assets on Duna.

The game-save (and associated quick-saves) in which I did all the above, can be downloaded here:

https://www.dropbox.com/s/hcs5j4gy6rbmf6z/The%20Dunatian.zip?dl=0

The save also includes the "fixed" Hermes craft, now properly balanced, a hitherto unused tank (the adapter behind the Hitchhiker Container) has had fuel added, and the essentially useless monoprop in the capsule has been removed to save a little weight.

Edited by JAFO
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JAFO

JAFO

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Selfish_Meme, what do you think of my rover?

Not that I was the one you're asking, but since I'm still awake and SM isn't... so, without having tried it, it looks very easy to tip over.. how's it handle?

Also, as per the book, they need to be able to tow each other.. and your rovers don't have any docking clamps.

- - - Updated - - -

It took longer than expected, but here it is:

http://i.imgur.com/RWt6ZQF.png

Hey, that looks great! :cool: Edited by JAFO
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selfish_meme

selfish_meme

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Selfish_Meme, what do you think of my rover?

I had a quick glance only, it seems to be OK, the part count is twice what the current rovers are and we know from testing that having multiple high part count vessels interacting on Duna is a surefire way to summon the Kraken. It needs docking ports front and back and be able to survive several rolls, plus have a self righting mechanism in case it gets stuck on it's side or roof. It needs to drain power but not so quickly you have to recharge every 5 minutes, this is while hooked up to the second rover and carrying the RTG, I found two of the large batteries, plus two RTG's for 4 driving wheels to be about perfect. The second rover should not be able to drive on it's own and contain enough solar panels to recharge. Then you need to do a drive, go get the RTG or a bit further and see what happens when it rolls and how often you roll.

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CommanderSpock

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I had a quick glance only, it seems to be OK, the part count is twice what the current rovers are and we know from testing that having multiple high part count vessels interacting on Duna is a surefire way to summon the Kraken. It needs docking ports front and back and be able to survive several rolls, plus have a self righting mechanism in case it gets stuck on it's side or roof. It needs to drain power but not so quickly you have to recharge every 5 minutes, this is while hooked up to the second rover and carrying the RTG, I found two of the large batteries, plus two RTG's for 4 driving wheels to be about perfect. The second rover should not be able to drive on it's own and contain enough solar panels to recharge. Then you need to do a drive, go get the RTG or a bit further and see what happens when it rolls and how often you roll.

I'll see if I can get it to meet your criteria.

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selfish_meme

selfish_meme

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It took longer than expected, but here it is:

http://i.imgur.com/RWt6ZQF.png

So, what should I do next?

I really like it, can you use sn actual mars landscape picture as the background, and a bit less global illumination so there are shadow. Also I want to don an ad for the rovers " the real Hero of the Dunatian"

- - - Updated - - -

I have the file, but I don't have the time to get the kerbals there, put them in the rovers, and go through all of that. Too much other stuff.

You can just use Hyperedit, it takes 2 seconds

- - - Updated - - -

Ok.. here we go. The write-up, and the save-file.

Ok Majorjim, for you, and anyone else who may be curious about the what, how and why, here's some introductory notes before getting into the specific steps for this project.

To begin with, you'll need this: [WIN] Flyby Finder V0.82 [KSP1.04]

Unlike KSP TOT, it finds all flybys that match the user's specifications.. KSP TOT will only pick the one "best" flyby it can find.

Flyby Finder is Windows only, but it works fine running on Wine, so it can be used on Linux and Mac without any problems, if you have Wine installed. I haven't tried KSP TOT with Wine yet, but I think it'll work ok. Be aware that if it seems to not be working, it can take quite a while (as in, almost a minute!) to load and start running.

As good as Flyby Finder is, it doesn't provide one essential piece of information (nor does KSP TOT). And that's the Ejection Angle to Prograde/Retrograde. Maybe that can be calculated from the provided data, but I've no idea how, and besides, there's another tool that can tell us, when we give it the data provided by Flyby Finder.

Go to alexmoon's Launch Window Planner, and plug in the details of the planet you want the flyby for. Set the Transfer type to 'Ballistic', and click on the 'Show advanced settings' link. Set both the 'Earliest departure' and 'Latest departure' to the same day, as specified by Flyby Finder. Set 'Time of flight' to something that will cover all the bases, such as 0 to 1000 days. Click on the Plot it! button, and you will get a nice mini-display that should confirm the required delta-V as predicted by Flyby Finder, as well as the other details, including the all-important Ejection Angle.

If you're using a low-TWR craft like the Hermes, you'll also want to break up the many-minutes-long burn required, into smaller chunks, performed when the ship is close to periapsis. To calculate the burns and starting Ejection Angle, Red Iron Crown's Precomputed Low-TWR Interplanetary Transfer Burns are brilliant. As I needed to do a modified version of his transfer burns, to avoid running into the Mun's SOI, I extended his spreadsheet to get the Ejection Angle data I needed. Anyone who wants a copy can download it here.

Finally, you will probably want to have a few mods installed. At minimum, you'll want PreciseNode, because it takes some real fine-tuning to achieve flybys. Kerbal Alarm Clock is nice to have, if only to keep track of SOI-changes, so you can nursemaid your ship across them. MechJeb is very handy to have, for the simple reason that it makes for easy setting up of nodes for the multiple burns involved, and it is better at timing burns than any human. (And it isn't fooled by KSP's wildly inaccurate burn estimates.. it gets burn durations right.) If you think that's 'cheating', then consider this.. NASA "cheats" all the time. Their burns are computer controlled, because human reactions aren't quick or consistently reliable enough for accurate results. So you'll be in good company. If you install MechJeb, install MechJeb and Engineer For All as well. That way you don't need to add a part to your craft, all your craft will automatically have MJ or KER available. Speaking of KER, that's another helpful source of data. If you're following along with the rest of these steps, you'll also need HyperEdit to get the Hermes into orbit around Kerbin.

Right.. with that out the way, let's get down to the specific methodology/steps needed to set up the Kerbin-Duna-Kerbin free-return trajectory for The Dunatian.

  1. Create a new game-save, then exit the game without going any further.
  2. Open the save's persistence file with a text editor (not Notepad, it adds invisible characters to files, that may mess things up). Set UT = 11146000 - This is Year 2, Day 91, Hour 0, Minute 6. Doing this will save you having to time-warp 2 years and 91 days before launching Hermes, and will place Hermes about 10 minutes before our initial burn is due to commence. Save the file.
  3. Start KSP and load the game-save. Go to the VAB and load Hermes. Add the crew, then put the ship on the launchpad.
  4. Using HyperEdit, put Hermes in a 100x100km equatorial orbit around Kerbin.
  5. Once in orbit, ensure the throttle is at zero, and stage the engines. Do it now, because if you don't, you'll forget later!
  6. Open the Map view, and rotate the view so that you're looking directly down on Kerbin from above, and Hermes is at the 12 o'clock position.
  7. Quickly tap the . key once, then the , key once. This will stop the jittering, which will make it hard to create a manoeuvre node, otherwise.
  8. Click on Hermes orbit between the 7 and 8 o'clock positions, and create a manoeuvre node.
  9. If PreciseNode didn't automatically pop up, press the p key to bring it up.
  10. Temporarily set the prograde value to 4000. This ensures we will get an Ejection Angle display.
  11. Set the UT value to 11146823.6 - This should set the Ejection Angle to 133.3°. If not, use the 1, 0.1, 0.01 and +/- buttons to adjust UT until you get a solid 133.3° reading. (The reason for this value is that we need a final Ejection Angle of 136°, and from Red Iron Crown's spreadsheet, we know that we need to adjust this by 2.7°, to allow for the 19 hours and 14 minutes it will take to do our preliminary burns, before we are ready to do our final burn at 136°.) IT IS VERY IMPORTANT THAT THIS INITIAL ANGLE BE CORRECT. TAKE THE TIME TO GET IT RIGHT.
  12. Set the prograde value back to zero. Do not move or adjust the node in any way. The node is going to be the foundation of our periapsis for all subsequent burns, and it has to be in exactly the right position.
  13. Open the MechJeb Manoeuvre Node Editor. You can leave PreciseNode open if you want.
  14. Make sure that auto-warp is enabled, set the MJ prograde to 100m/s. Click the Update button.
  15. Click the Execute next node button and wait until MJ has completed the burn and cancelled the node. The orbit's apoapsis should now be 240km.
  16. Close the Manoeuvre Node Editor, and open the MechJeb Manoeuvre Planner.
  17. Select 'Create Node' -> 'Change Apoapsis' to 419km at 'Next Periapsis'. Click on the Create and execute button. Wait until MJ has performed the burn and cancelled the node.
  18. Repeat step 17, six more times, raising the apoapsis in turn to 658km, 987km, 1471km, 2250km, 3708km, and finally 7409km.
  19. Next comes the fun/tricky part.. the final burn. This burn is performed 66 minutes after the ideal window specified by Flyby Finder, because if we burned exactly at the launch window, we'll hit the Mun's SOI, and our altered course will smash us into Kerbin. The one hour delay allows us to sneak past the edge of the Mun's SOI without touching it. So we'll need to make some minor corrections to our course to take this delay into account.
  20. Close the MechJeb Manoeuvre Planner. Enter the following settings into PreciseNode. UT = 11216020. Prograde = 501.5. Normal = -10.3. Radial = 0.
  21. The Ejection Angle will be flickering, but it should average about 138°.
  22. Zoom out, and set Duna as your Target. If you're lucky, you should already see a pair of closest approach markers. Due to small variations in burn times, etc, most likely you're going to have to tweak things. You're aiming to get a closest approach in the vicinity of 60,000km.
  23. By means of the 1, 0.1, 0.01 and +/- buttons, carefully adjust the UT until you get a close approach. As soon as you have one, use the MS (Memory Save) button to record the settings. This way, if you mess up, you can get it back by using the MR (Memory Recall) button.
  24. Continue to tweak the closest approach lower and lower until you have it down around 60,000km, saving the settings each time you get an improvement. Sometimes, one click will make it a tiny bit worse, then another click will improve it even more, so don't stop increasing or decreasing the moment you see a change in the wrong direction.
  25. At the end of the burn, we're going to sneak that 60,000km down a bit lower, but for now, press AltF5 and create a named quicksave. If you mess the burn up, you'll want to be able to AltF9 to try again.
  26. Now that PreciseNode has set up the burn,use MechJeb's Manoeuvre Node Editor to execute it. This will be a long one, at 3 minutes and 9 seconds. However, we DON'T want MJ to execute the final few seconds of the burn, because it will mess things up, if you allow it.
  27. MJ will throttle the burn down when it gets to the last 2-3m/s. When it gets to about 1m/s remaining, click on the Cancel/Abort execution button, and cancel the node. The closest approach will probably show something in excess of 100,000km. We'll handle the fine-tuning ourselves.
  28. Hit t to enable the SAS in Stability Assist Mode. This will make sure the Hermes stays aligned on the burn axis.
  29. Press AltF5 and create a named quicksave. I suggest using the current closest approach distance as the name of the save.
  30. Keeping the mouse pointer over the close-approach markers, gently tap the Shift once, to barely fire the engines. When the approach reduces by about 10,000km, quickly hit the x key to kill the engines, and then make another named quicksave.
  31. Repeat steps 29 and 30 until you get the distance down to the low 50,000's. This is as close as it's safe to get. We need to stay out of Duna's SOI, or we'll get our course messed up big-time, but at the same time, we want to be as close as is possible to make rendezvous easier for the DAV. Duna's SOI begins at 47,922km. My personal best closest approach is 51,900km.
  32. When you're happy with the distance, make a quick-save, and set an SOI alarm with Kerbal Alarm Clock. Time-warp to the SOI change, and shepherd the Hermes across.. now save again.

And that's it! (I bet when you asked me to note the steps needed, you didn't think it was gonna be this complicated! :D)

You can now time-warp to a few days/weeks before Duna closest approach, and use HyperEdit to place all the various assets on Duna.

The game-save (and associated quick-saves) in which I did all the above, can be downloaded here:

https://www.dropbox.com/s/hcs5j4gy6rbmf6z/The%20Dunatian.zip?dl=0

The save also includes the "fixed" Hermes craft, now properly balanced, a hitherto unused tank (the adapter behind the Hitchhiker Container) has had fuel added, and the essentially useless monoprop in the capsule has been removed to save a little weight.

OK I wanted some time to reply to this properly. I am so blown away by the amount of work gone into this, I already repped you so I can't again but this deserves it. I want to post this somewhere else so everyone can see it. This deserves so much more recognition than I can give it.

I am not even sure I CAN replicate those steps, or I should say I'm not sure I can devote the time to understanding how to replicate those steps. But I am glad it's possible. Again I wish I could rep you more.

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JAFO

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Thanks for the compliments, SM! (and for the rep, Commander Spock!)

For me, the fascinating thing about getting the flyby was that you actually get to see the Oberth Effect in operation. All the preliminary burns are 100m/s (+/- one or two tenths of a m/s). So they should all be identical in duration, right? With the Hermes, a 100m/s burn works out to 43 seconds. But as your speed at periapse starts to increase after the first few burns, thanks to the Oberth Effect, each 100m/s increase requires a shorter burn than the one before it. By the time you're at the penultimate 7409km burn, it only takes 38 seconds of thrust to add 100m/s. (KER's Flight Engineer is great for seeing this, it shows the precise duration of each burn when the node is set up.)

My rough estimation suggests that all told, the Oberth Effect saved me something in the range of 16-17 seconds of thrusting. in other words, that's 40m/s of thrust I got for "free", or, more to the point, I saved 40m/s of fuel. Not a lot, but hey, every little bit helps, and as my first free-return test showed, at the end of the trip, that might make the difference between life and death for the Hermes crew.

I've seen claims on the forum that, being less efficient, a long final burn, such as my 3-min 9-second escape-velocity burn, totally wipes out any fuel saving gained earlier by the Oberth Effect. I think this is false logic, because at the end of the day, practically speaking, there's no way to really avoid a long escape burn. Especially as the Mun will inevitably get in the way, if you keep doing longer and longer 100m/s 'loops' until you reach escape velocity. So a long escape burn will have to happen at some point, regardless of any fuel saving made earlier. So as far as I'm concerned, I still managed to save 40m/s of fuel that I otherwise would not have had.

I am not even sure I CAN replicate those steps, or I should say I'm not sure I can devote the time to understanding how to replicate those steps. But I am glad it's possible.

Well, at least you can just make use of the file I sent you. The game-state of the save I linked to is, Hermes has just left Kerbin's SOI, So you have as much flexibility as possible with positioning/timing of everything else.

Now that I have a nice close approach, my next test will focus on the return to Kerbin. Unlike the first attempt, this time Hermes has as much delta-V as possible, and I want to see if it can successfully re-orbit Kerbin when it intercepts.

Once that's done, the real fun will begin, attempting a Hermes rendezvous with the DAV. I think figuring out the correct timing and course is going to be tricky..

Again, my thanks for starting this project.. it's forcing me to learn and stretch myself and my brain in new ways. I'm having so much fun I can't express it. :cool:

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selfish_meme

selfish_meme

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Thanks for the compliments, SM! (and for the rep, Commander Spock!)

For me, the fascinating thing about getting the flyby was that you actually get to see the Oberth Effect in operation. All the preliminary burns are 100m/s (+/- one or two tenths of a m/s). So they should all be identical in duration, right? With the Hermes, a 100m/s burn works out to 43 seconds. But as your speed at periapse starts to increase after the first few burns, thanks to the Oberth Effect, each 100m/s increase requires a shorter burn than the one before it. By the time you're at the penultimate 7409km burn, it only takes 38 seconds of thrust to add 100m/s. (KER's Flight Engineer is great for seeing this, it shows the precise duration of each burn when the node is set up.)

My rough estimation suggests that all told, the Oberth Effect saved me something in the range of 16-17 seconds of thrusting. in other words, that's 40m/s of thrust I got for "free", or, more to the point, I saved 40m/s of fuel. Not a lot, but hey, every little bit helps, and as my first free-return test showed, at the end of the trip, that might make the difference between life and death for the Hermes crew.

I've seen claims on the forum that, being less efficient, a long final burn, such as my 3-min 9-second escape-velocity burn, totally wipes out any fuel saving gained earlier by the Oberth Effect. I think this is false logic, because at the end of the day, practically speaking, there's no way to really avoid a long escape burn. Especially as the Mun will inevitably get in the way, if you keep doing longer and longer 100m/s 'loops' until you reach escape velocity. So a long escape burn will have to happen at some point, regardless of any fuel saving made earlier. So as far as I'm concerned, I still managed to save 40m/s of fuel that I otherwise would not have had.

Well, at least you can just make use of the file I sent you. The game-state of the save I linked to is, Hermes has just left Kerbin's SOI, So you have as much flexibility as possible with positioning/timing of everything else.

Now that I have a nice close approach, my next test will focus on the return to Kerbin. Unlike the first attempt, this time Hermes has as much delta-V as possible, and I want to see if it can successfully re-orbit Kerbin when it intercepts.

Once that's done, the real fun will begin, attempting a Hermes rendezvous with the DAV. I think figuring out the correct timing and course is going to be tricky..

Again, my thanks for starting this project.. it's forcing me to learn and stretch myself and my brain in new ways. I'm having so much fun I can't express it. :cool:

Apparently we might want a retrograde orbit, and to launch to the west to maximise the Landers dV and lessen the dV for the return.

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JAFO

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Apparently we might want a retrograde orbit, and to launch to the west to maximise the Landers dV and lessen the dV for the return.

I assume you're talking about a retrograde parking orbit around Duna.. as an entire retrograde Hermes mission would involve insane closing velocities on planetary approaches. Apart from which, I think you may be a little mixed up here.. Duna rotates west to east.. if a lander descends west to east, you subtract Duna's rotational velocity from that of the lander, to get the relative horizontal surface speed. If the lander descends east to west, you need to add Duna's rotational velocity to the lander's, to get the relative horizontal surface speed. It would take more dV to compensate, not less..

Apart from which, Duna's Sidereal rotational velocity is only 30.688 m/s anyway, so there's not much advantage to be gained even when you do work with Duna, rather than against it.

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selfish_meme

selfish_meme

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I assume you're talking about a retrograde parking orbit around Duna.. as an entire retrograde Hermes mission would involve insane closing velocities on planetary approaches. Apart from which, I think you may be a little mixed up here.. Duna rotates west to east.. if a lander descends west to east, you subtract Duna's rotational velocity from that of the lander, to get the relative horizontal surface speed. If the lander descends east to west, you need to add Duna's rotational velocity to the lander's, to get the relative horizontal surface speed. It would take more dV to compensate, not less..

Apart from which, Duna's Sidereal rotational velocity is only 30.688 m/s anyway, so there's not much advantage to be gained even when you do work with Duna, rather than against it.

I will trust you on this, I was just repeating something I saw on another thread. Is it still a flyby at the edge of the SOI of Duna?

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I will trust you on this, I was just repeating something I saw on another thread. Is it still a flyby at the edge of the SOI of Duna?

Also I was thinking that when the physical possibilty of it is proven, when you set up a new file, you can simply add the velocity using Hyperedit rather than doing all the pe kicks.

We have to add a counterbalanced DDV to Hermes yet as well, plus a non encumbered version for the pickup.

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Report on Hermes close-approach free-return trajectory testing - Round 1

Now that I have a nice close approach, my next test will focus on the return to Kerbin. Unlike the first attempt, this time Hermes has as much delta-V as possible, and I want to see if it can successfully re-orbit Kerbin when it intercepts.

Once that's done, the real fun will begin, attempting a Hermes rendezvous with the DAV. I think figuring out the correct timing and course is going to be tricky..

Once I began, I realised the above was not the correct approach. I should make any required course corrections for the Duna portion of the journey, before attempting to return to Kerbin. Otherwise, I wouldn't know if Hermes actually carried sufficient delta-V.

On reaching the flight's mid-point, I checked for the close-approach markers, and as expected, they were gone. Hermes would pass 900,000 km ahead of Duna. A little under 80m/s of prograde correctional burn would be necessary to get a suitable flyby, though this would naturally result in Hermes missing its' Kerbin encounter later. I was expecting this, as the same thing happened on my first attempt. Crossing orbits ahead of Duna was a nice bonus (my previous attempt passed behind Duna), as it would make things a little easier for the DAV to rendezvous. Experimenting with various approaches, I was able to get to within 2,500km of Duna's surface, along the way spending 9 hours in Duna's SOI. A nice side-effect of passing through Duna's SOI was that the gravitational pull nudged my trajectory back 50,000km closer to Kerbin's orbit, saving me a little fuel on my later correctional burn to rendezvous with Kerbin.

As a result of this testing, I was able to determine the factors that would be necessary for a successful rendezvous with the DAV. At the 2,500km periapse, my slowest surface speed relative to Duna was 2,900m/s. By the time I'd left Duna's SOI, that speed was in excess of 5,450m/s. Though I didn't think to check, when I entered Duna's SOI, my speed at that time would have been similar. So ideally, a DAV launch should be timed to encounter Hermes at periapse. Once we have some idea of the necessary flight time involved, this will simplify the setting of a KAC alarm for the DAV launch.

After departing Duna's SOI, I course-corrected for a Kerbin encounter, and set off in pursuit. On entering Kerbin's SOI, I set up a burn to bring my periapse down to around 100km. On setting up a circularisation burn, I discovered that I was approx. 800m/s short of what would be required. Deciding that a wildly eccentric orbit was better than none, I fired up the engines to see what would happen. The orbit closed with literally only 40m/s of delta-V remaining! My final orbit was 145km x 15,000, with dry tanks. Had I not been able to save 40m/s due to the Oberth Effect when departing Kerbin, I would have failed to gain a capture, and the crew would have been doomed to orbit the sun, somewhere out near Duna's orbit. Talk about cutting things close!

For my next experiment, I'm going to try a mid-course correction that will allow me to pass behind Duna, instead of in front. The delta-V penalty for the DAV should not be too severe, and I'm curious to see if it will prove to be more fuel-efficient for the Hermes. The main problem that I can see at this stage is that Duna's gravity will nudge my orbit 50,000km in the wrong direction if I make the same kind of close approach on the opposite side of Duna, than I did this time.

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I will trust you on this, I was just repeating something I saw on another thread.

I had a feeling you'd gotten the idea elsewhere.. Think of it this way.. you're in a lander above Duna. You're dropping towards the surface, and you have a proper west-east motion of 100m/s. Duna has a west-east motion of 30m/s. Your effective motion relative to Duna's surface is 70m/s. So if you cancel 70m/s of your sideways motion, relative to Duna, you are now stationary and falling straight down.

If, on the other hand, you have 100m/s of east-west motion, your effective motion relative to the surface, which is moving in the opposite direction to you, is now 130m/s. To become stationary relative to the surface, you now need to not only cancel your 100m/s of sideways motion, but you need to dial in 30m/s in the opposite direction.

When you launch off the surface of Duna, because you were previously in contact with the planet, you have 30m/s of west-east motion automatically added to your sideways vector when you lift off. If you also fly west-east, that 30m/s gets added to any sideways velocity you feed in from your engines. If, on the other hand, you took off east-west, your true sideways vector is 30m/s less than your relative surface velocity would suggest.

Is it still a flyby at the edge of the SOI of Duna?

No.. my fear of entering the SOI turned out to be unjustified. Because of the relative closing speeds involved, a few hours spent in Duna's SOI has only a relatively small effect on Hermes' trajectory. In fact, as my report above shows, if passing ahead of Duna, it can even have a positive effect on Hermes' course. This means we can get much closer to Duna, which I'm expecting (pending empirical testing) to make the DAV rendezvous easier.

Also I was thinking that when the physical possibilty of it is proven, when you set up a new file, you can simply add the velocity using Hyperedit rather than doing all the pe kicks.

Thanks for the suggestion.. I'll give that a shot at some point. It would certainly help with the extremely tight fuel budget. We could handwavium it away by suggesting that the Taiyang Shen resupply mission included some additional propellant mass.

We have to add a counterbalanced DDV to Hermes yet as well, plus a non encumbered version for the pickup.

Hmmm.. I'd always assumed that the MDV was sent on ahead to Mars just like with the MAV and supplies.. not that it was ferried by the Hermes.

Ares 4’s MAV spent eleven months getting to Mars. It left before us and got here around the same time we did. As expected, Martinez landed it beautifully. It was one of the last things we did before piling into our MDV and heading to the surface.

I imagined that, after (or before) remote-landing the Ares 4 MAV, Hermes rendezvoused with the Ares 3 MDV in orbit, the crew transferred, and then descended to the surface. However, the book doesn't actually say if Hermes ferried any other vessels or not. Though now that I check, there is a kind of implication that the Hermes carries the MDV, in the way they were discussing stripping down the Ares 4 MDV for a rescue mission, at one point. If so, the MDV would have been mounted on the forward airlock, rather than one of the two airlocks located just abaft of the rotating crew quarters.

Fortunately, that's more of a logistics problem for you, than for me.. I only have to deal with the Hermes' rescue trajectory, not the initial mission flight.. :wink::sticktongue::D

Edited by JAFO
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selfish_meme

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I had a feeling you'd gotten the idea elsewhere.. Think of it this way.. you're in a lander above Duna. You're dropping towards the surface, and you have a proper west-east motion of 100m/s. Duna has a west-east motion of 30m/s. Your effective motion relative to Duna's surface is 70m/s. So if you cancel 70m/s of your sideways motion, relative to Duna, you are now stationary and falling straight down.

If, on the other hand, you have 100m/s of east-west motion, your effective motion relative to the surface, which is moving in the opposite direction to you, is now 130m/s. To become stationary relative to the surface, you now need to not only cancel your 100m/s of sideways motion, but you need to dial in 30m/s in the opposite direction.

When you launch off the surface of Duna, because you were previously in contact with the planet, you have 30m/s of west-east motion automatically added to your sideways vector when you lift off. If you also fly west-east, that 30m/s gets added to any sideways velocity you feed in from your engines. If, on the other hand, you took off east-west, your true sideways vector is 30m/s less than your relative surface velocity would suggest.

No.. my fear of entering the SOI turned out to be unjustified. Because of the relative closing speeds involved, a few hours spent in Duna's SOI has only a relatively small effect on Hermes' trajectory. In fact, as my report above shows, if passing ahead of Duna, it can even have a positive effect on Hermes' course. This means we can get much closer to Duna, which I'm expecting (pending empirical testing) to make the DAV rendezvous easier.

Thanks for the suggestion.. I'll give that a shot at some point. It would certainly help with the extremely tight fuel budget. We could handwavium it away by suggesting that the Taiyang Shen resupply mission included some additional propellant mass.

Hmmm.. I'd always assumed that the MDV was sent on ahead to Mars just like with the MAV and supplies.. not that it was ferried by the Hermes.

I imagined that, after (or before) remote-landing the Ares 4 MAV, Hermes rendezvoused with the Ares 3 MDV in orbit, the crew transferred, and then descended to the surface. However, the book doesn't actually say if Hermes ferried any of the other vessels or not. Though now that I check, there is a kind of implication that the Hermes carries the MDV, in the way they discussing stripping down the Ares 4 MDV for a rescue mission, at one point. If so, the MDV would have been mounted on the forward airlock, rather than one of the two airlocks located just abaft of the rotating crew quarters.

Fortunately, that's more of a logistics problem for you, than for me.. I only have to deal with the Hermes' rescue trajectory, not the initial mission flight.. :wink::sticktongue::D

(good thing, too.. because the present Hermes doesn't have anywhere near enough delta-V to get to Duna, enter a parking orbit, leave orbit again and return to Kerbin.. not by a long shot)

Well some good news the DAV still has 3000m/s of dV after reaching 100km orbit

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I have been doing some craft testing and fixing, the rovers are good, very good, tested on Duna and picked up the RTG no worries, no flips so far, I could if I wanted to but I would have to work at it, best thing is no skidding. Tested landing and ascending in the MAV, which is an SSTO, the second stage is completely superfluous, if we need some extra dV we could just ditch the second stage engine and decoupler. Also if you fill the landing stage that has enough TWR and dV to get you a pretty good head start, the MAV could probably come back to Kerbin on it's own easily. The Delta II and Pathfinder are...good, it's fiendishly difficult to pilot the SRB booster on the probe and get it just right, but thats what you get for authenticity. I am trying to add more resources on the probe to make injection easier but every bit of weight I add to the nose affects the balance of the whole craft giving it a horrible rotation. Not sure what to do with that one.

Oh I also tested the Ares V and cargo delivery which went without a hitch, impressed a friend no end.

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Better picture of Pathfinder on it's way to Duna

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Entering Duna's atmosphere ready to ditch fairing and deploy chutes

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