Using the Oberth Effect | KSP (Not) Beginner's Guide

[@MikeAben]

Up Next: The Complete Science Lab Guide - kzbin.info/www/bejne/a32YooOhoLZjoas

[@danpettersson4671]

Instructive and fun, as always. Thank you for the information as well as for the entertainment. It really is one of the best descriptions I have ever seen on the subject. I usually just fiddle with the burns until it fits when I do this. Now I can have a method to my madness.

[@MikeAben]

Thanks. It certainly is a lot easier with the newer maneuver editing tools.

[@rtleitao78]

3000 hours of ksp. Decided to check it out again and had no idea about all those new tools. Cool stuff. I'll try it out.

[@p00bix]

Not quite that many hours, but same. There's so many new QoL features I barely know about

[@JohnWilliamNowak]

This is, incidentally, how ISRO reached Mars, by splitting the orbital insertion burn into multiple burns. The US doesn't do this because NASA has the Centaur cryogenic upper stage, which is a bit of a beast. IRL, multiple burns aren't quite free: each ignition increases the chance of a failure, which is simulated by the Kerbalism mod.

[@MikeAben]

Thanks, John. Would boil off be an issue too making you want to get the burn over and done with? With probes I typically stick on a chemical booster to deal with most of the ejection. It's just easier.

[@JohnWilliamNowak]

@@MikeAben Yes, hydrogen boiling off is an issue. The Trans-Lunar Insertion burn on the Apollo 3rd stage had to be performed fairly quickly or so much hydrogen would boil off they'd need to abort the flight. I believe modern stages are better insulated, but it's still a factor. Another factor is that Earth isn't a perfectly homogenous sphere. With each orbit, there's a bit of wobble which also complicates things.

[@JohnWilliamNowak]

@@MikeAben And I found some hard numbers on Wikipedia. en.wikipedia.org/wiki/Centaur_(rocket_stage) The first operational cryogenic upper stage was Centaur-Atlas which sent Surveyor to the moon. Centaur-Atlas had a 30 minute lifespan before the hydrogen boiled away. This has been increased considerably with Centaur III, but I don't know how much. Centaur V is under development and its endurance may be as much as 600 times that of Centaur III. There is no Centaur IV.

[@Savsgames]

good to see a tried and true method of planning oberths. I always just eyeball them.

[@dansiegel995]

Regarding burn precision, the more burns you have with this technique, the more precise you need to be. KOS or the human eyeball just can't cut it without lots of errors and corrections. I've just launched 4 of my 6 Nuke probes to Duna (2 huge science probes to get all the scansat, and 2 relay carriers with 3 relays and 1 lander each). I need to now send off my lander carrier (carrying 12 lander probes), and my land and return probe with the goo/ScienceJr stuff. Because I'm sending them 140 days ahead of the perfect window, my dV requirements are huge and the keyhole I have to hit it pretty darn small, even when I have the nuke engine set to 0.5% thrust for my correction burns. I think I'm gonna add RCS to these last two probes and use RCS for these < 1m/s correction burns. When travelling at 10000m/s, 1m/s can sometimes send you from the far left side of ike's orbit to the other far side of ike's in just a second or two while using the lowest thrust available on your engines. I few of those tiny RCS engines should do the trick...and I'll only burn them in prograde/retrograde using a maneuver node to plot the course. If you use anything other than retro/prograde on RCS for this, I fear the torque will make it worse than it was in the first place, even if you do have good reaction wheels. the nice thing with retro/prograde RCS is that your torque in those directions should be 0.000000x kNm/s^2...so small that hopefully the game just ignores it...lol.

[@stefelz]

Fantastic video to explain this rather complicated matter. Thank you so much for this, you totally improved my gameplay.

[@alartor]

As always, your tutorials are pure gold! Please keep 'em coming!

[@MikeAben]

Thanks

[@mishaerementchouk]

This is a neat trick with the false maneuver nodes to check for unwanted encounters. Thanks for the video. It’s a pleasure to watch. Your videos are probably the only ones that enforce several simple and formally known but routinely ignored ideas of orbital mechanics. Split burns, for instance, work because the maneuver node means that at this point in space and time the velocity must be this. How it’s achieved the ballistics don’t care because the mechanics is history independent.

[@MikeAben]

Thanks. Sorry for the late replay. KZbin sends member comments to a different place that I'm just finding now.

[@xionix4]

"We're going to hit the planet!" "No we're not." "I'm telling you, we're going to hit the planet!" "No, the computer said to do this an-- what was that?" "The atmosphere."

[@jmstudios457]

I also try to add up the orbital period of the pre-burns so that they end up at the transfer window. I launch 14-15 days before the window and use the skip orbit function to plan where I need to do my final burn, then drag it back till my orbital period hits 14-15 days, do the burn and then drag it back out and off we go.

[@LoopyAnh]

I havnt played KSP in 2 years, been waiting for KSP 2, hoping this summer, 1 thing I never really fully understood but recently finally looked into was the Oberth effect. Thanks for your video, it does explain it well and I enjoyed/learned stuff from the video.

[@authorified89]

Fantastic tutorials Mike, the best and easiest to grasp on KZbin. Even though I had a decent understanding of KSP, you took my gameplay to another level with your videos so thank you!

[@yo.aj6391]

Hi-5! I was trying figuring this out and bam! Mike comes out with the tutorial!

[@MikeAben]

The new maneuver tools really make this easy.

[@ljushastighet]

this video helped me get a jool encounter thank you

[@proxi_owo]

Splendid tutorial!

[@DavidBowring]

This was really interesting! Thanks so much for this and your other video’s too!

[@dansiegel995]

Mike, great video as always but a few comments/questions regarding my own experiments and the only 1 other low TWR video I've seen. 1. Wouldn't it be even more efficient to include normal/antinormal in your pre-burns? I believe if you take the ratio of prograde to normal/antinormal on your initial baseline burn, you can apply that ratio to determine how much normal/antinormal you pre-burns need. By using normal/antinormal in preburns, your final burn needs less normal/antinormal (the amount you need should I guess roughly be the same ratio from your first baseline burn). 2. Regarding ejection angles and using the Transfer Window mod- its hard to believe this all works considering your ejection angle should change, hence where you burn starts - when you spends WEEKS of time doing your burns (well, weeks of orbiting, same burn time roughly) - so, is it a math fact that every burn you should do be at the maneuver node location of your first baseline big burn? Or should you calculate roughly how much time you plan to spend orbitting around, use Transfer Window and plan a FUTURE burn based on your orbitting time, and start your pre-burns right away but at the location of where the ejection angle is in the future. Or is the answer somewhere in between, requiring Calculus instead of algebra which I don't think these mods can do. An example would be if using an ultra-low TWR using ion engines - what if I needed to do +10 pre-burns and I needed to spends MONTHS setting up the burn. Where exactly on the orbit do you do the burn? The periapsis every time, or do you need to adjust it everytime? 3. Is there any difference in efficiency in a-symmetrical burns? I realize why they were a-symmetrical in your example. If they weren't your 2nd pre-burn would have ejected you from the Kerbin's SOI. But what if you needed only 1500m/s of dV? You could do 3 burns of 500 m/s. Would that be more efficient that 2 burns of 250 m/s and 1 final burn of 1000m/s? 4. The problems with seeing the Mun/Minmus accidental encounters, would the patched conics number in settings affect this??

[@MikeAben]

All great questions. I started answering them but I'm at a wedding and a few wobblies in. This'll have to wait until tomorrow.

[@MikeAben]

Short answers. 1) Yes 2) Doesn't matter 3) Doesn't matter 4) Don't know

[@guyincognito1406]

Regarding #2 wouldn’t that just follow the general pro/retro at periapsis and inclination burns at apoapsis? The whole point I think is mainly you want to choose a location to burn where your speed is going to be at it’s highest.

[@dansiegel995]

@@guyincognito1406 you certainly wouldn't want to burn at AN/DN at each expanding orbit to fine tune your inclination. That would double the number of burns needed...although that wouldn't matter with ion engines. I believe if you keep the right ratio of normal/anti-normal compared to your baseline burn, you keep the same exact inclination throughout all of your incremental orbits..and because that normal/anti-normal is such a small fraction of the prograde, its nearly free dV.

[@MikeAben]

1) I actually didn't notice the normal component of the burn until I was editing. Yes, putting in a normal component into the early burns is likely a good idea. Here the ratio of prograde to normal was only about 10:1, so I suspect it wouldn't have made much of a difference. 2) I'm pretty sure this doesn't affect the ejection angle. The final burn is still at the same location in the orbit and at the same time (or close enough) that the ejection angle when you perform that burn wouldn't be much different as it would have been if you kept it a single burn. If doing this with Transfer Window Plannner, you would have to set the maneuver ahead of where TWP is telling you so that the burn will be at the right ejection angle 30 days from now. I got videos where I go over the math of this in an old let's play, but just put the amounts for the burn, pop ahead orbits until the time is about right, and then just move the node forward and back to dial in the encounter. 3) It doesn't matter if they're asymmetric. The key is to have as much of the burning as close to Kerbin as possible. 4) I'm not sure on that one, but my guess is no. I'm pretty sure the game won't show an encounter for a future orbit unless there's a maneuver on that orbit, but it's worth playing with to check.

[@PadreFriend]

These are great videos and an awesome series. Can you make a couple videos on planetary rovers?

[@MikeAben]

That's a common request, but I'm not sure what there is to talk about. Just think lander with wheels.

[@PadreFriend]

@@MikeAben I hadn't thought of it that way. Thanks!

[@ryba7846]

How about doing the 3rd burn just to get out of kerbins SOI and then do a 4th burn in sun orbit?

[@MikeAben]

It's better to do it all from LKO to take advantage of the velocity you already have, velocity you lose as you climb out of Kerbin's gravity well.

[@teacup8288]

Very helpful thanks

[@AnimatedStoriesWorldwide]

I'm not sure I understand the trade-off between, more maneuvers ("why not do 5-10 burns, theoretically?") VS having longer burns and fewer maneuvers, though more than 1 big one ("why not make one burn to the very edge of Kerbin's SOI and the other one to Jool?") Is it just because more maneuvers would be too tedious and only 2 burns be still too long and become inaccurate? (a bit confused but maybe I should RTFM on the Oberth effect first)

[@AnimatedStoriesWorldwide]

(Oh also, why place all 3 maneuvers before the first burn even took place if you are going to move them after each burn? Does the amount the move in between burn indicate something important?)

[@MikeAben]

The further you are from periapsis, the less efficient the burn. During a long burn, you spend a lot of time away from periapsis which is less efficient. Under the info tab of this video there's a link where I go over the math. Splitting into shorter burns has you spending more time close to periapsis, and so is more efficient. That said, you'll reach a point where the gains in efficiency are too small to warrant more burns.

[@AnimatedStoriesWorldwide]

@@MikeAben Ah thank you! Now I get the tradeoff!

[@guyincognito1406]

Think I put kerbol down last time because I was at this problem, had gotten a hang of the maneuver nodes but not how to split, which the falling into the planet was my exact problem. Is that maneuver button on the right new? I don’t recall that…

[@MikeAben]

It came in a few updates ago.

[@scottwilliams846]

My Mun's in a position where I can either get a gravity assist from it, or wait until my transfer window is closed. I'm going to try to get a gravity assist from it. But my current attempts to make maneuver nodes to get a slingshot off it make me leave Kerbin's SOI a little bit too early to get to Jool easily from the one maneuver. But waiting makes me too late, and getting an assist at the right time flings me into the sun or hinders me. I can try. Maybe leave Kerbin's SOI, then wait until the actual transfer window and then burn the 980? Maybe that will work?

[@donjonquavious4257]

Try setting a maneuver in muns SOI

[@scottwilliams846]

So what you're saying is that simply by discovering my Jool transfer window in my career mode game at 30 days from it, I'm too late to use it? Or do I have a few days' buffer where I can gather the science I need to and unlock the tech I need and I'll be fine?

[@MikeAben]

You can definitely make it work in much less time. Perhaps that second orbit won't be as large, but that isn't a big deal.

[@scottwilliams846]

@@MikeAben I also need to get some cash for the launch, so my next question is this: how long do I have to wait to go to Jool again if I miss it? But with my 79% reputation, I should be able to do the "aggressive negotiations and launch the most expensive thing I can afford and recover it for more money than it was worth" money exploit at least a couple times.

[@Alex-ff8si]

pov: you are an rss player who plays with stock parts, and doing my burn to jupiter in low earth orbit saved you 4000 dv

[@jonadair2588]

Hey Mike, great videos, thank you and keep them coming! I'm having a problem: when i add orbits to maneuver 1 (the second one we create), it moves up the projected line of the original burn. Any advice? Thank you sir

[@MikeAben]

A couple of questions. Is maneuver 1 (the one that's hopping ahead) at 0 m/s? And two, could you be hopping ahead of the original maneuver?

[@jonadair2588]

@@MikeAben thanks for your reply! the maneuver that's hopping ahead has no magnitude, it's 0 m/s. And when i add orbits, it still says "Maneuver 1", so that should indicate I'm not hopping ahead, right? Thank you so much Mike!

[@jonadair2588]

More data: the second maneuver we create is staying put now but it's odd b/c when i add orbits, the option to subtract orbits is darked out, and the 3rd maneuver we create doesn't "mess up" the first two maneuvers when i give it some magnitude (500 m/s), that is to say it doesn't change the position of the other two maneuvers (2 and 3, created 1st and 2nd). Am i doing something endemically wrong? Thank you so much, you are a ksp god.

[@jonadair2588]

Hah! I was not following the instructions: my maneuver 3 was not 30 days in the future. Now it's working. Thanks for your attention, Mike! You've really increased my skill level.

[@MikeAben]

@@jonadair2588 I'm not really sure then. I have seen strange behavior from maneuver nodes at times myself and have had to start over. Sorry if that doesn't really help.

[@sebdapleb1523]

can we get a tutorial for suicide burns? I was using kerbal engineering for this but it seems to have a problem with calculations; it always tells me to burn too early and I end up getting to 0 m/s way before 0 altitude I've been trying to solve this by throttling as I perform the landing burn but sometimes I end up crashing as a result and I know that there's got to be a better way.

[@MikeAben]

That's more of a math video than a tutorial. KE is likely making its calculation based on the current acceleration of the rocket, but max acceleration will increase due to mass loss from expended fuel.

[@alartor]

@@MikeAben If there is anything I love more than your tutorial videos... that's your math videos! ;D (and this is the perfect excuse for one of those; actually, it's one of the topics I'd love to sort out in KSP when I get the time, if not the top one, so... a tutorial or math video from you would certainly be xmas come early, hahah).

[@matttaylor2634]

Does anyone know if the manoeuvre tool (to head to Jool) he uses at the start is stock? I play on xbox if that makes a difference, i cant seem to find it.

[@MikeAben]

I can't speak to the consol version, but it is stock on the PC.

[@matttaylor2634]

@@MikeAben Ahh okay i'll have to do some digging. Thanks though your videos have taught me so much :)

[@tamasd8]

Which mod shows the "Start Burn in x" info at the bottom?

[@alartor]

No mod needed for that, that's stock KSP since quite a few versions (can't exactly say which one right now), though you might need to enable that option in the game settings (don't recall exactly which option from the top of my head).

[@tamasd8]

Thanks, I will look it up!

[@ImSPARK1]

I dont know but it feels cheat ? . Is it possible to do without oberth effect just in case ?

[@MikeAben]

Your comment makes me wonder whether you think I'm presenting some kind of game hack. It's real physics. I'm not reducing the dV cost below the cost on the maneuver. Just getting it as close to the maneuver dV number as possible. If you want to spend more fuel then what's shown on the node, go ahead.

[@webrevolution.]

I am a complete noob to this game still. I have like 20 hours, which are for sure waaaaaay less than you and than many of your viewers hours. But I noticed that when you show the long burn problem you are basically using the thrust at 100%, which is not what you're supposed to do cause in the nav ball, at its right you've set 50% as thrust for the computer to calculate when to start your burn. I think that if you'd switch that 50% to a 100% burn it will tell you to start the burn later and this would probably avoid the issue you're presenting. As I said I am new, so I might as well be wrong cause I do not have a lot of experience, but this is what I thought at first by watching your video carefully.

[@MikeAben]

The 50% sets the countdown to get you to start the burn early by half (50%) of the length of the burn. It doesn't have anything to do with thrust.

[@webrevolution.]

@@MikeAben oh well. Lol. Thank you for the tip then. Hahah.

[@AlwafiCharki]

@@MikeAben i didnt know that too thanks

[@MikeAben]

@@AlwafiCharki The game really doesn't explain things and depends on community spread.

[@AlwafiCharki]

@@MikeAben yeah they really need to focus on making the tutorial better even if KSP's community is unique