Maneuver nodes for orbit insertion burn?

[Johnny Wishbone]

So, before anyone gets their neck in a knot about this, I'm not passing judgement. I find this interesting and I'm asking because I'm curious.

Lately, I've been watching a lot of KSP YouTube videos, both older ones and newer ones. One thing I keep seeing is people launching ships into a sub-orbital trajectory, coasting to apoapsis, and then doing an orbit insertion burn (aka circularization burn). That's pretty standard and not interesting. But what I do find curious and interesting is the number of people (especially very experienced players) that take the time to put up a maneuver node while coasting to apoapsis, and actually plan out their orbit insertion burn. I find this curious because, to me, its totally unnecessary. When you get near or at your apoapsis, just burn prograde until your periapsis gets high enough to put you in orbit or you get it to whatever height you want. There is no need for a maneuver node, yet I see players (even people like Scott Manley) do this time and time again. Why?

The best analogy I can come up with is getting into your car to go to your best friend's house and asking your sat-nav to give you directions and plot you a route there. You know how to get there; you don't need directions! Plotting a maneuver for something as simple as a prograde burn to raise your periapsis to a desired height seems very pointless to me and yet I see players do it all the time. So, I'm curious to know why? Is it really that much of a habit? Are people that dependent on maneuver nodes? The only time I use a maneuver node is to plot a transfer to another celestial body. Everything else, I use the navball and fly by eye. Its really not that hard once you understand the navball and the information it is presenting to you.

Again, I'm not trying to be judgemental. If this is something you do, that's fine with me. I'm just curious.

 

[ZeroG]

I do it with because I don't actually burn straight prograde, and I also want to estimate how long the burn will be. If it's supposed to take 40 seconds to circularize, I start the burn 20 seconds before apoapsis and point at the maneuver vector. Otherwise if you literally aim at prograde for your whole burn, you'll raise your apoapsis. If it's a high-acceleration ship or shallow trajectory I don't bother, but sometimes I use the node.

Edited June 22, 2017 by ZeroG

[Gaarst]

At least for me it's:

1. A habit.
2. Low TWR burns. It's not so much valid in stock, but when I circularise in RSS a 100 m/s burn can take several minutes, making a node is useful if you dont want to waste dV.
3. Precision. Having a node allows you to circularise in an (almost) perfectly circular orbit which is harder if you just eyeball it.
4. Rendez-vous. To dock quickly I raise my periapsis from below zero to an intersect with the target orbit in a single burn (and just warp until I meet my target before completing the Hohmann manoeuvre); again it's easier to do this accurately with a node than just eyeballing it.

[OrbitalBuzzsaw]

For me, with 6000+ hrs in the game, I did it once but I moved away from it.

[Starman4308]

I do it so I can let MechJeb (or a kOS script I wrote) handle the burn. Routine burns like circularization at apoapsis are utterly uninteresting to me, so I just let an autopilot handle that for me.

[memes in space]

1 hour ago, Johnny Wishbone said:

So, before anyone gets their neck in a knot about this, I'm not passing judgement. I find this interesting and I'm asking because I'm curious.

Lately, I've been watching a lot of KSP YouTube videos, both older ones and newer ones. One thing I keep seeing is people launching ships into a sub-orbital trajectory, coasting to apoapsis, and then doing an orbit insertion burn (aka circularization burn). That's pretty standard and not interesting. But what I do find curious and interesting is the number of people (especially very experienced players) that take the time to put up a maneuver node while coasting to apoapsis, and actually plan out their orbit insertion burn. I find this curious because, to me, its totally unnecessary. When you get near or at your apoapsis, just burn prograde until your periapsis gets high enough to put you in orbit or you get it to whatever height you want. There is no need for a maneuver node, yet I see players (even people like Scott Manley) do this time and time again. Why?

The best analogy I can come up with is getting into your car to go to your best friend's house and asking your sat-nav to give you directions and plot you a route there. You know how to get there; you don't need directions! Plotting a maneuver for something as simple as a prograde burn to raise your periapsis to a desired height seems very pointless to me and yet I see players do it all the time. So, I'm curious to know why? Is it really that much of a habit? Are people that dependent on maneuver nodes? The only time I use a maneuver node is to plot a transfer to another celestial body. Everything else, I use the navball and fly by eye. Its really not that hard once you understand the navball and the information it is presenting to you.

Again, I'm not trying to be judgemental. If this is something you do, that's fine with me. I'm just curious.

 

No clue. I always just burn prograde. Maybe to get the circularization right? I never do, I only circularize good (I usually do a job that's good enough for basically anything, but not circular at all) when trying to do interplanetary maneuvers

Edited June 22, 2017 by memes in space

[LordFerret]

1 hour ago, Gaarst said:

At least for me it's:

1. A habit.
2. Low TWR burns. It's not so much valid in stock, but when I circularise in RSS a 100 m/s burn can take several minutes, making a node is useful if you dont want to waste dV.
3. Precision. Having a node allows you to circularise in an (almost) perfectly circular orbit which is harder if you just eyeball it.
4. Rendez-vous. To dock quickly I raise my periapsis from below zero to an intersect with the target orbit in a single burn (and just warp until I meet my target before completing the Hohmann manoeuvre); again it's easier to do this accurately with a node than just eyeballing it.

This ^

[Guest]

1. Low TWR burns, especially, as noted, in RSS/RO.

2. When using MechJeb because it's a simple click to add a circularization node followed by another click to execute it.

Otherwise there's really no need. If you don't like your orbit in stock KSP It's not like you have to waste a precious ignition from your engine and/or RCS fuel performing ullage.

[Greenfire32]

I only do it if my orbit needs to be inclined in some way. Otherwise, I feel the same.

I already know where I'm going, I don't need directions to get there.

[Foxster]

I'd never thought of doing that! Might give it a go...

Go given...Pointless. 

[Johnny Wishbone]

3 hours ago, ZeroG said:

I do it with because I don't actually burn straight prograde, and I also want to estimate how long the burn will be. If it's supposed to take 40 seconds to circularize, I start the burn 20 seconds before apoapsis and point at the maneuver vector. Otherwise if you literally aim at prograde for your whole burn, you'll raise your apoapsis. If it's a high-acceleration ship or shallow trajectory I don't bother, but sometimes I use the node.

This is true, and I get your point. For me, because I understand the navball, I know how to adjust my heading to compensate for any changes in my apoapsis during the burn (again, it isn't a very hard thing to do). I routinely get near perfect circular orbits (apsis within 100m of each other) by eye simply by reading the navball. For less experienced players, I understand this could be a tough thing to do, but I would expect more experienced players to be able to "freehand" it like I do. That said, your point is valid.

 

1 hour ago, regex said:

1. Low TWR burns, especially, as noted, in RSS/RO.

2. When using MechJeb because it's a simple click to add a circularization node followed by another click to execute it.

Otherwise there's really no need. If you don't like your orbit in stock KSP It's not like you have to waste a precious ignition from your engine and/or RCS fuel performing ullage.

Since I'm a stock player, I've never used MechJeb or played under the rules of RSS/RO. So these reasons would not have occurred to me. Thanks.

[Guest]

21 minutes ago, Johnny Wishbone said:

Since I'm a stock player, I've never used MechJeb or played under the rules of RSS/RO. So these reasons would not have occurred to me. Thanks.

Oh totally. I stopped doing it in stock a long time ago (incidentally after I started playing RSS/RO) because fine-tuning an orbit in stock is so cheap and easy. Often times it really doesn't even matter unless you're trying to set up for a rendezvous.

[NISSKEPCSIM]

I use maneuver nodes because, as @ZeroG said, I also like to estimate the time it will take to complete the orbital insertion. Also, almost all of my LKO craft launch straight into a rendezvous with this or that space station, so using a maneuver node to plan out where the orbits will intersect after the orbital insertion is pretty key to my strategy.

[Johnny Wishbone]

10 minutes ago, NISSKEPCSIM said:

I use maneuver nodes because, as @ZeroG said, I also like to estimate the time it will take to complete the orbital insertion. Also, almost all of my LKO craft launch straight into a rendezvous with this or that space station, so using a maneuver node to plan out where the orbits will intersect after the orbital insertion is pretty key to my strategy.

Sure. But the point of this topic is the use of maneuver nodes specifically for the OIB. It just seems so pointless to me; a waste of time. But apparently there are some reasons why people use them for that specific purpose, and thats why I asked.

[Snark]

6 hours ago, ZeroG said:

I do it with because I don't actually burn straight prograde, and I also want to estimate how long the burn will be. If it's supposed to take 40 seconds to circularize, I start the burn 20 seconds before apoapsis and point at the maneuver vector. Otherwise if you literally aim at prograde for your whole burn, you'll raise your apoapsis.

^ This.

6 hours ago, Gaarst said:

1. A habit.

^ Also this.  I'm very much a creature of habit, such that the "path of least resistance" for me, on tasks I do repetitively, is to always do them exactly the same way every time, even if that way may not actually be literally the least effort in particular cases.  Why?  Because if I deviate from my routine, then I have to think about it, and the mental effort of deviating from and disrupting my routine exceeds the (to me) small benefit of trying to optimize particular instances, unless it's an extreme case.

I launch a lot of rockets, so I've got my routine down pat and I prefer not to deviate from it.

 

Aside from the above reasons, I've got a few more:

Perfect circularity.  I'm OCD about wanting to hit a perfectly circular orbit.  Yes, it's irrational.  There's absolutely zero practical reason for this, it's just one of those things, like wanting to hit a high score in a video game.  Having a maneuver node lets me fine-tune this really well, and I'm scrupulous about getting the maneuver-node indicator down to 0.0 (not 0.1) m/s on the "remaining burn" display.

Launch location not on the equator.  Sometimes I play with a mod, like Galileo's Planet Pack, where KSC isn't located on the equator.  Often I like to put my orbital infrastructure (space stations, refueling depots, etc.) in perfectly equatorial orbits.  So, when I launch, my initial Ap generally isn't on the equator yet, but it's a significant part of the way there.  So when I do my circularization burn, I like to include a bit of normal component to the prograde burn, so that I reduce my orbital inclination from the equator while circularizing, which in turn means less dV needed later to get a perfectly coplanar orbit.  It's a lot easier to do that sort of thing with a maneuver node.

Handy countdown to Ap.  There's the initial boost phase off the pad, then a minute or two of coasting until I get to Ap.  Just how much time I may have until Ap will vary, depending on various factors:  TWR, altitude of target orbit, how well I nailed the gravity turn.  Often, I like to use that little "breathing space" while I'm coasting to Ap in order to do various little housekeeping chores:  taking science measurements (if it's early career), deploying solar panels and antennas, deactivating engine gimbal, maybe a quick EVA, various other things.  I like to know "how much time do I have until I need to burn at Ap", while I'm in flight view (not the map screen).  Having the maneuver node gives me a handy countdown indicator right there.

Direct launch-to-intercept.  When I'm launching a craft to rendezvous with an orbiting target (LKO kerbal rescue contracts, for example), I like to launch directly to intercept.  That is, I don't launch to a lower (or higher) circular orbit and then wait a few orbits until they line up before setting a rendezvous.  Rather, I timewarp while sitting on the launchpad until the target is in the right spot, then I launch to rendezvous with it directly, i.e. my circularization burn finishes with me parked right next to the target.  That's kinda hard to do without maneuver nodes (in this case, I generally use a maneuver node for a small burn significantly earlier than Ap, so that I can get the rendezvous distance down to something small, like under a kilometer).

 

[tater]

If I am setting up a rendezvous, then I do, otherwise I tend not to bother.

[swjr-swis]

More reasons I've noticed for myself:

• When doing forum challenges, creating and screencapturing the circularization maneuver nodes is part of the/my documentation of challenge attempts.
• How much is the circularization going to be, in time or dV, if you follow 'my' ascent profile? It's a handy bit of information to be able give when putting a craft up for download. Since I don't use mods I can't rely on KER or MJ to show that, making a maneuver node is the quick stock alternative.

Edited June 22, 2017 by swjr-swis
more reasons

[KerikBalm]

I do it for a burn time calculation - particularly while playing a 3x rescale of kerbin (but only a 1.25x rescale of the atmosphere). The dV requirements are much higher, and as a result my TWR is often much lower to achieve the higher dV needed, so it can be handy for calculating burn time and comparing to time to apoapsis

Edited June 22, 2017 by KerikBalm

[ansaman]

I CAN manually circularize my orbit. It takes a bit of doing by tweaking the amount of thrust so the time to apoapsis remains constant until the apoapsis and periapsis are roughly equal. I think it is easier to deal with calculations with a circular obit and it LOOKS nicer.

[Whisky Tango Foxtrot]

If I circularize with a manoeuvre node I can get into orbit with one burn rather than burning a bit, waiting to catch up to my new AP, burning a bit more, etc. The downside is that atmospheric drag can throw the node off so I can only place one after I've already left the atmosphere. Since I usually launch into an extremely low atmosphere-skimming orbit (since my launch vehicles tend to be designed solely to get their payload into orbit with as little wasted dV as possible so that my orbital tugs then rendezvous and take the payload to its final destination) that doesn't give me much time.

[Moach]

there's a simple method by which I normally heave just about every kinda crazy doom-beast spacecraft into orbit by the seat of my pants mostly.... no mechjeb or nodes required

 

thought it helps to have something like NanoGauges, or some other form of keeping an eye on your ApA and PeA without having to alternate back and forth from the map (which I find a bit unsettling, as it throws off my sense of orientation for a few moments that I'd rather not compromise)

 

the most basic form of this "maneuver" (only Indiana Jones would have the cheek to call it a "procedure") is something which I had explained in a VERY early tutorial video, in the primordial days of KSP, back in a Time Before The Mün

this is how it's done, without ANY instruments and without using the map view (which didn't exist back then), look:

 

you no longer need to do this THAT much by the seat of your pants - but the principles are all the same

 

it takes some 2250 m/s to orbit kerbin at about 100km - this is my ideal orbit, since it's low enough to make the most of the oberth effect* on the way out to anywhere else

*extending your ApA works most efficiently from a burn performed at as low a periapsis as you can get without hitting something denser than space

feel free to quote me on my "explanation" of the oberth effect - just don't try it at home... or anywhere else where you have a ceiling...

 

on Kerbin at least, in most cases, the first 1000 m/s onto orbit are really just a matter of pointing the nose at your velocity vector and working the throttle (assuming you care for such cozy comforts as "throttle control") so that you don't shoot straight up and waste all your fuel vertically and/or run too shallow as to turn yourself into an unplanned hypersonic test aircraft... when this works correctly, it is almost indistinguishable from a maneuver called a "gravity turn" 

the video above gives you some more or less well-defined values to keep in mind during ascent - you can easily tell if your high or low by remembering a few "checkpoints" of altitude, speed and nose elevation angle along your ride up to space

nowadays, I use NanoGauges just to be sure - it's one of my all time favourite mods, for it provides all the information you need without being unkerbalistically precise about it... so you can still fumble your way into space but without the hassle of alternating to/from the map view all the time

 

with or without mods - the trick is, watch your vertical speed, altitude and orbital velocity as you scare away the planet with your mighty rocket - you want all those things to converge on their "planned" values at exactly the same time as you cut your engines... obviously, that never really happens - but close enough is all you need (you can always improve your performance with a well told story afterwards)

if you do this just right - you will have MECO (Main Engine Cut Off) at the precise moment when your orbit becomes circular - this can be verified by checking that you have near-zero vertical velocity, and at that same time, your altitude is somewhere in between an ApA and a PeA that you find satisfactory enough to call an orbit

 

nevertheless, even though I shoot for 100km, I usually end up at least a bit higher some 90% of the time -- seems the (stock) atmosphere on Kerbin makes for a vertical launcher "comfort-zone" around 120~150km... it's curiously much harder to set up shop lower than that, and you often end up wasting oodles of fuel to kill the vertical speed needed to clear the atmosphere - I find the precision required to pull off a circular orbit below 100km without a secondary burn and/or fuel waste sits just astride the fine line that separates skill from luck

 

so don't sweat it - between 100 and 150km is a very good orbit to start with, and if everything goes well, you'll only need to fire up the engines again when you're burning off on the way to your fate destination

 

and don't bother too much with a perfect circular orbit either - unless you're setting up a satellite or some such, anything less than 20km between your ApA and PeA is generally fine, as long as the latter isn't running through any stretches of atmosphere/terrain, so don't waste your fuel trying to be perfect...
(|ApA-PeA|<10km is pretty damn nice, and <5km is just showing off)

also at this point I often just ditch any awkwardly sized near-empty stages I might still have that make orienting the ship difficult, the little dV saved by emptying out a clunky hulk of leftover fumes most often doesn't compensate running out of RCS juice later on (or the dV lost by hauling up extra gas for steering the hulk)

 

anyways - that's my method... I rarely ever use orbit entry burns on the way up from kerbin - I got lots of practice with that planet in the days when there was really nowhere else to go...

for other bodies, I usually do use nodes almost every time - not just because I haven't memorized any such checkpoints to do it "Kerbin style", but mostly because, without atmospheres (which most destinations don't have) you can very safely hurl yourself suborbital, let go all the controls, and calmly adjust a node at some convenient point along your ballistic trajectory without ending up like a cinder block inside a tumble dryer

 

Edited June 24, 2017 by Moach

[magnemoe]

On 22.6.2017 at 2:40 PM, Gaarst said:

At least for me it's:

1. A habit.
2. Low TWR burns. It's not so much valid in stock, but when I circularise in RSS a 100 m/s burn can take several minutes, making a node is useful if you dont want to waste dV.
3. Precision. Having a node allows you to circularise in an (almost) perfectly circular orbit which is harder if you just eyeball it.
4. Rendez-vous. To dock quickly I raise my periapsis from below zero to an intersect with the target orbit in a single burn (and just warp until I meet my target before completing the Hohmann manoeuvre); again it's easier to do this accurately with a node than just eyeballing it.

Yes, my standard for intercept is to aim a bit in front of target, then plan the circulation burn so I get an intercept. High orbit or no atmosphere and I aim behind, this way I don't raise pe to circulate until rendezvous after one orbit. 

Only launches I don't mark an circulation node is very low twr ones where I have to burn both to keep Ap up in front while lifting Pe. 

[WanderingKid]

On ‎6‎/‎22‎/‎2017 at 10:23 AM, Johnny Wishbone said:

Sure. But the point of this topic is the use of maneuver nodes specifically for the OIB. It just seems so pointless to me; a waste of time. But apparently there are some reasons why people use them for that specific purpose, and thats why I asked.

I'm killing time during the glide anyway, why not setup a maneuver node and make it easy to warp to it?  Mostly it's a habit for me with KAC and simple circularization.  It's not a matter of ability, it's a matter of laziness.  I find it easier to hit a maneuver node than to bother caring about eyeballing the NavBall.

Can I?  Sure.  Do I want to bother?  Nope.

[wumpus]

3 hours ago, WanderingKid said:

I'm killing time during the glide anyway, why not setup a maneuver node and make it easy to warp to it?  Mostly it's a habit for me with KAC and simple circularization.  It's not a matter of ability, it's a matter of laziness.  I find it easier to hit a maneuver node than to bother caring about eyeballing the NavBall.

Can I?  Sure.  Do I want to bother?  Nope.

A lot of this depends on how high you want your orbit to be.  If you are skimming the edge of the atmosphere (for more Oberth), you really won't be able to "warp to" (or use the physicsless warp) until after you've circularized.

As someone who uses a lot of low-TWR designs for circularization, I probably *should* use a maneuver node.  But I'll stick to KE and easily readable "time to AP" and AP/PE readings.

Anyone know the efficiency of burning 1/2 burn length before AP vs. burning for constant time to AP?  I know plenty of my designs would crash if I used a naive maneuver node (some of them barely coast at all), but I'd wonder about efficiency for less crazy launches.

[Rocket In My Pocket]

Agreed.

I've never had an issue getting perfectly circular orbits manually. Maybe it just stems from impatience? Lol. As soon as Ap hits 70k I time warp till I'm about 30-45 seconds out from it, then I get oriented and do my burn.

That said; I've got no issue with those that make maneuver nodes, I used to when I was learning and I can see how it would just become a habit after a while. Personally my computer isn't the best and swapping back and forth between map view and flight view while in atmo can be tedious and awkward so I got away from doing it.

Edited June 24, 2017 by Rocket In My Pocket