Stock interplanetary transfers, how do you do it?

[Rocket Farmer]

Hi.

I play totally stock. It's not that I consider mechjeb users kids with training wheels, it's I would consider it training wheels if I used it for me.

Anyways I now have Eeloo and Moho intercepts and returns under my stock belt and figured I would share what I have learned and learn what others do.

To figure an intercept I start with Alex moon's calculator which gives a departure window. From there on the appointed day I use the node finder by picking a spot and then progressing it up to about where Alex's calculator says I should be burning.

Then I select my node finder and move it around my current path (selecting the center of it and dragging it around kerbal) till I get a peraposis close to my target planet's path.

I then pan over to the planet I want and ensure that my vertical angle on the node finder is correct to cross the planet's path with my own.

At this point I select the planet I am aiming for and target it. Then I go back and Move the pro grade / retro grade on my node finder until the little tags show up to show how far apart my ship and the planet will be in the future at the intercept point.

From there it's just a matter of playing with the prograde/retrograde as well as the 90/180 degree markers to push the two tags together until I get an intercept (ie push your orbit out with prograde and then in with the 180 degree burn several times). If it is really off you might even have to increase your vertical axis (goig out of the plane of the planets) to get the desired intercept.

After that I check my final DV and confirm its similar to Alex's calculator's calculated amount and burn for my target. No mechjeb needed and I am typically within 5% of optimal.

What do you other stock navigators do?

[Mr Shifty]

Here's the funny thing: MechJeb does nothing to help with this. I wrote a tutorial with basically the same steps a few weeks ago:

http://forum.kerbalspaceprogram.com/showthread.php/33547-Tutorial-Non-Hohmann-Interplanetary-Transfers

[Johnno]

Well when I played pure stock I wasn't even aware of the online calculators. I did my first interplanetary trips without any calculator or mod. Not having used mechjeb I'm not sure how automated and/or informative it is, but seeing as just using the online calculator makes your life so easy I feel it's no different than mechjeb unless you let mechjeb automate the flying entirely.

Simply put, I'd equate using the online calculator just as using a mod, no difference. Once you can calculate that stuff by hand, and actually do so for the fun of it, I'll tip my hat to you.

Nowadays I use the online calculator for rough numbers and then play it by feel while overengineering everything to have a bit of extra dV where needed by experience.

[Rocket Farmer]

Walked up hill in the snow to and from shool eh Johno?

Yes te online calculators are nice. I can do it without them (and did with my first probes) but they are a nice resource to backstop my calculations. Thank-you for adding your "input."

To mr. Shifty

I wish I had seen your post before as it looks very handy. Specifically I will incorporate the check to make sure you are burning prograde/retrograde to kerbal at your ejection point.

One item. I didn't see you using the target system? For me it has been very handy at figuring out the last little bit to get the intercept perfect.

My only issue is that typically as I lighten up during long burns my twc increases meaning if I split the time evenly on either side of my node I actually push more after the node than before as I am pushing faster at the end. I compensate by gestimating the difference And then correcting after the burn.

[Scarecrow88]

Then I select my node finder and move it around my current path (selecting the center of it and dragging it around kerbal) till I get a peraposis close to my target planet's path.

What do you other stock navigators do?

I usually push the apoapsis out to make an intercept. Struggling to imagine how you would do it by pushing the periapsis out.

[Rocket Farmer]

I suppose technically it can be either depending where you are going. Recently I have doing Moho intercepts so your best intercept is at your periapsis as it is at the lowest point of the gravity well.

However if you are pushing to outlying planets (Duna, eeloo, dres, etc) you are correct in that I would be pushing out my apoapsis.

[strongest_2hu]

The stock method of doing easy interplanetary intercepts without any math or guesswork:

1. Burn out of Kerbin SOI as gently as possible. From LKO this takes about 930 delta-V and has you exit at about 40 m/s if I remember correctly. Make sure if you are going to an outer planet from Kerbin you exit progade (relative to Kerbin's orbital path) and if you're going in you exit retrograde.

2. Now you're in an orbit nearly identical to Kerbin's. Set your target and time warp to the AN/DN, then match inclinations.

3. Make a maneuver node and give it enough delta-V that the maneuver orbit lies tangent to the target orbit. Move it around your current orbit until you get an encounter or near encounter, then adjust delta-V and node location until you get an encounter you're happy with.

4. Time warp to the node and burn. Execute mid-course corrections as necessary.

[Razor235]

I really just eyeball it. If (for instance) a Duna window is open, I put a node on the (in an eastern equatorial orbit) nighttime side of Kerbin, and play with the gizmos until I get a decent non ÃŽâ€v-intensive transfer.

[Mr Shifty]

One item. I didn't see you using the target system? For me it has been very handy at figuring out the last little bit to get the intercept perfect.

Good point. I'll have to add that in if I ever update the tutorial. I wrote that after I'd been playing for about 3 days so wasn't down with all the helpful features.

[ScottyDoesKnow]

The stock method of doing easy interplanetary intercepts without any math or guesswork:

1. Burn out of Kerbin SOI as gently as possible. From LKO this takes about 930 delta-V and has you exit at about 40 m/s if I remember correctly. Make sure if you are going to an outer planet from Kerbin you exit progade (relative to Kerbin's orbital path) and if you're going in you exit retrograde.

2. Now you're in an orbit nearly identical to Kerbin's. Set your target and time warp to the AN/DN, then match inclinations.

3. Make a maneuver node and give it enough delta-V that the maneuver orbit lies tangent to the target orbit. Move it around your current orbit until you get an encounter or near encounter, then adjust delta-V and node location until you get an encounter you're happy with.

4. Time warp to the node and burn. Execute mid-course corrections as necessary.

This is what I've always done. Recently (as in yesterday) I've started doing slingshots around the moon for step 1.

[KerbMav]

SNIP

"Is this the least fuel intensive way to travel around?" I first wanted to write, because it seemed so overly complicated.

Then I googled and found this: http://www.racetomars.ca/mars/ed-module/human_mission/images/flight_path.jpg

So I will just be quiet and accept that I havent done much in this game yet to argue.

[Geschosskopf]

Thanks muchos, guys! Very informative and seemingly fairly easy to understand, although I'm sure my understanding will be shot full of holes when I actually try this .

[EndOfTheEarth]

The stock method of doing easy interplanetary intercepts without any math or guesswork:

1. Burn out of Kerbin SOI as gently as possible. From LKO this takes about 930 delta-V and has you exit at about 40 m/s if I remember correctly. Make sure if you are going to an outer planet from Kerbin you exit progade (relative to Kerbin's orbital path) and if you're going in you exit retrograde.

2. Now you're in an orbit nearly identical to Kerbin's. Set your target and time warp to the AN/DN, then match inclinations.

3. Make a maneuver node and give it enough delta-V that the maneuver orbit lies tangent to the target orbit. Move it around your current orbit until you get an encounter or near encounter, then adjust delta-V and node location until you get an encounter you're happy with.

4. Time warp to the node and burn. Execute mid-course corrections as necessary.

I do this most of the time, but I usually check first to see if Kerbin is in one of the sweet spots where I can just burn straight for a planet without having to get out of the SOI. Helped me with my manned Ike mission.

[Mr Shifty]

"Is this the least fuel intensive way to travel around?"

Short answer: no. It has the advantage of being easy to eyeball without any aids, but it's very inefficient.

Example:

- For a Kerbin to Eve transfer, the escape-then-transfer method requires about 920 m/s to get from 100km LKO to the edge of Kerbin's SOI, then another 750 m/s to transfer to Eve's orbit, for a total of about 1670 m/s, not including your capture burn into Eve's orbit (probably you can just aerobrake to save most of that), nor any correction burns.

- A direct Hohmann burn from 100km to Eve intercept costs about 1020 m/s, a savings of about 650 m/s. This is the fabled Oberth effect at work. Tangential burns are more effective when you're travelling faster. In fact, it costs only 100 m/s more at LKO to get to Eve than it does to escape Kerbin's SOI.

[John FX]

Short answer: no. It has the advantage of being easy to eyeball without any aids, but it's very inefficient.

Example:

- For a Kerbin to Eve transfer, the escape-then-transfer method requires about 920 m/s to get from 100km LKO to the edge of Kerbin's SOI, then another 750 m/s to transfer to Eve's orbit, for a total of about 1670 m/s, not including your capture burn into Eve's orbit (probably you can just aerobrake to save most of that), nor any correction burns.

- A direct Hohmann burn from 100km to Eve intercept costs about 1020 m/s, a savings of about 650 m/s. This is the fabled Oberth effect at work. Tangential burns are more effective when you're travelling faster. In fact, it costs only 100 m/s more at LKO to get to Eve than it does to escape Kerbin's SOI.

I guess the long answer is noooooooooooo!