New Guy struggling with making circular orbit? please help

[🍔 Mentally Tribbled 🍔]

Hi all, sorry for being a pain but i need a little help understanding this game here. So i got this a while back and honestly i forgot about it (yeah good start) but i thought i'd give it a go now. so I'm playing sandbox mode (this is after playing tutorial which honestly confused the heck out of me here :P) and built myself my first space craft which has 4 stages on it. the top stage is just a ferring section which houses the stations core in it (yeah i'm trying to build a station in orbit here, the second stage has two of those 800 litre fuel tanks on it and 1 reliant engine, the third stage is four engine boosters (each one made of two more of these 800 litre fuel tanks and a reliant engine) attached by the explosive strut decouplers and the fourth stage which is the liftoff stage is made up of 8 solid fuel thumper engines attached by the explosive decoupler struts.

Now i've tested this engine crazy design and some how it can actual get into orbit (yeah i successfully built something that didn't exploded into a million pieces on the launch pad), the 8 thumper stage gets me to 20,000m before the engines cut out at which point i jettison and use the second stage boosters to get my apoapsis upto about 80,000m. so far so good still have like half my fuel left and the third and final stage of full tank to go at this point.

Now this is were i'm starting to struggle a bit here and need a little help. I'm trying to make a circular orbit of about 80,000m on both apoapsis and periapsis, i've done some digging around and practically everyone is saying when you get to about 30 seconds before apo, fire yorur engines on prograde to get periapsis to appear on your orbit. so i do this, however everytime i do this the apo ends up going to something stupidly ridiculas like 200,000m and peri is still buried in the planet.

Can someone please explain to me what the heck i'm doing wrong here and how i can correct this, it's literally driving me insane here.

[edorward]

Before I answer your question in any detail, tell me what your trajectory looks like before you start your insertion burn. Is it high, steep, and tight, or low, wide, and almost an orbit already?

[Quenllian]

Funny :). Not sure if it makes any sense for me to explain too much here but yeah, burning at apoapsis is the most fuel efficient way. But there is no particular rule when to start. That depends on the angle of your trajectory and the thrust to weight ratio. If you see the apoapsis running away from you, you're going much too fast, so throttle down. But if your rocket goes straight past the apoapsis, that means you lack enough thrust. In that case, just aim somewhat radially out, toward the sky. In any case, keep the apoapsis near your vessel.

However, if you really wanna know how to get that right, I highly recommend watching some of Scott Manley's tutorials on Youtube. And there are also lots of awesome mods. BetterBurnTime for example would give you neat timings when and how long to burn for whatever you do.

[Chibbity]

1: Launch over ocean, slowly tilting nose down till you are at 45 degrees. This should be done in a relatively timely fashion. Continue to burn at 45 degreees until AP is 70k. Cut engines and coast till 30 seconds from AP.

2: At 30 seconds to AP, start burning parallel to the horizon. Ie. towards the horizontal white line on the navball. Keep your time till AP between 10 and 30 seconds for the duration of the burn. (You can check it in map view.) Nose up to increase time till AP, nose down to decrease. Imagine AP is a ball on your nose you are pushing ahead of you, don't let it get behind you. (KER mod helps a lot with this, I recommend it. If you are opposed to modding, doing it from the map view with the navball up is the best way.)

3: Cut engines at 70k PE. Congrats. Nice, circular orbit.

[flopp]

I keep hearing people saying "Use KER" and stuff, but its outdated mate. only works for 1.3, not 1.4.3

[Quenllian]

KER still works for 1.4 but someone also created a brand new fork recompiled for 1.4 here.[github.com]

[ThunderTurtle]

First, get into an orbit. Make sure the periapsis is above 70,000 km. If you want to circularize the orbit you have to raise the periapsis by burning prograde at the apoapsis until the apoapsis and periapsis start to move. When they move about half way around the orbit from where they started you should be in a pretty circular orbit. You have to do this step very gently. When they start moving, cut your engines and do gentle burns.

Also, if you want to instead lower the apoapsis, you can burn retrograde at the periapsis and circularize from there.

[Dragon O' Chaos]

Check these out, they will help.

https://wiki.kerbalspaceprogram.com/wiki/Tutorial:_How_to_Get_into_Orbit
https://www.youtube.com/watch?v=_q_8TO4Ag0E

[MechBFP]

Originally posted by RunKittenzRComing:

I keep hearing people saying "Use KER" and stuff, but its outdated mate. only works for 1.3, not 1.4.3

Wrong.
https://github.com/jrbudda/KerbalEngineer/releases

[Trixi]

well, when you made your flight suborbital (ap ~ 79km) stop acclerating. Then let time pass to get short before you ap, point your rocket prograde (the direction you are flying) and burn until the pe and ap are about the same. if the ap/pe points are starting to wiggle in map view, you are pretty close to your circular orbit. the pe/ap points should be a quarter orbit ahead/back of you at those time.

[Purplefairy22]

Here's what i do.

SCENARIO:- (Stock Kerbal X-1) launched 90 degrees east
push my apoapsis above 70,000m.

to keep my apoapsis at that height i actually point the nose of my ship up or down respective of the horizon (Blue or green side on Navball). prograde is the heading of your ship, not the horizon.

The dividing line between the blue(sky) and ground(green? or brown?) [Sorry i am colour blind but from here on i'll use blue and green]
is 0 degrees. (thats the horizon directly in front of you)

{In these shots my heading is actually the horizon}
If i point my ship left (blue side of prograde marker my Apoapsis will rise.
if i point my ship right (green side) of prograde my Apoasis will drop.

e.g
https://steamcommunity.com/sharedfiles/filedetails/?id=1416391920 3 minutes in, my velocity is 1933m/s my apoapsis is 75,000 ish and i'm raising it by burning towards the sky at 5-10 degrees

https://steamcommunity.com/sharedfiles/filedetails/?id=1416391979 time now is 4:17. My apoapsis is still 75,000m my velocity is now 2153m/s (my fuels dropped quite a bit) but now i'm pointing the nose down to maintain 75,000 while building speed to increase my periapsis.

Essentially i'm manually adding a bit of Radial in and/or out (Towards or away from Kerbin) to Twist my orbit ahead or behind me while keeping the same heading and inclination. Sometimes i may pitch up or down (Left or right on navball) as much as 25 degrees
if i put the ship marker below my prograde vector i'd be going anti-normal which would push my orbit towards the south pole. and above would push it towrds the north pole

Knowing how the navball works means to can correct tilts and wobbles of unstable ships or poor launches while you gain orbital speed

Prograde/Retrograde is the X-Axis - Left to right
Normal/Anti-Normal is the Y Axis - Top to bottom
Radial in/Radial Out is the Z Axis - Forwards and backwards.

Hopefully this helps

[Gojak_v3]

Sounds like yer not using maneuver nodes and are just trying to wing it. I highly suggest since yer in sandbox just use a maneuver node as it will be a lot easier. You can use it to plan out a fairly circular orbit like you want.

As for what went wrong with what you did; I'm guessing yer ascent was too steep. So when you did yer burn on yer prograde you were still adding a lot of vertical altitude to yer trajectory. Just a tip (again don't know exactly what you did) you want to be a lot more horizontal. By about 40,000 meters you want to pitch yer rocket over so that the prograde is just barely above the horizon. If you do it like this, by the time you want to do yer orbital burn very little of it will go into increasing yer vertical altitude, and instead the majority of it going into making orbit.

But yeah, I'm guessing yer ascent was too steep. You want yer prograde to be a lot closer to the horizon.

[🍔 Mentally Tribbled 🍔]

Wow, first off thanks to everyone helping me to understand this. seeing these comments tells me I have a lot to still learn about orbital manevours and such so thanks everyone. I'm seeing a lot of people trying to understnad what the heck i'm doing here that's screwing up my orbits and i'm sorry i've re-read what i posted and it's clear i've missed a few important details here. hopeful this will help clear it up. before i launch the first thing i do is turn sas on. then i start launch full burn (the solid boosters). at 5,000m i turn rcs on and set sas to prograde. I've tried to do manual turning to east direction at 10,000 without sas just using rcs but the flight becomes unstable. so i've been using sas to hold prograde tracjectory till orbit. like i said in previous comment i burn till solid run dry (usually about 20,000m) then dump them and coast upto my apo. 30 seconds before apo intercept i fire second stage (reliant booster tanks) while still holding sas locked on prograde to help boost my apoasis upto about the 80,000m mark. once my apo is reading 80,000 i kill the engines and coast. at this point i have about half fuel left in my booster tanks and the final stage single reliant for orbital insertation. Again i wait for the 30 second before intercept at apo before firing the remaining fuel in my booster tanks to increase my orbit path which at this point is increase by half the planet at this point. still hold prograde on sas at this point. i dump the boosters and use the final insertation booster to try to get full orbital but i seem to fall short. i usually end up with 3 quarters orbital path with pe still hidding the planet but my apo staying at about 100,000m. So i'm making some progress just having the little trouble with the last bits. Again thanks to all i really appreciate the help. I hope this helps to better explain what the heck i'm doing wrong?

[edorward]

I strongly recommend you download Kerbal Engineer. It's a simple mod that basically everyone uses for additional information about your craft and trajectory. The additional HUDs help you fly and the VAB info will help you design better craft.

It sounds like you are flying the profile generally correctly, but you simply don't have enough dV to achieve orbit. Try switching out your top engine for a Terrier instead of a Reliant. Terriers are lighter and more efficient in a vacuum than Reliants. That one change might be enough.

Incidentally, I get the feeling you aren't really using RCS. Do you actually have RCS thrusters on your craft? They aren't necessary on simple craft that aren't docking anywhere. The built-in reaction wheels in your pod should be enough to control a small craft. Adding fins with control flaps (deluxe deltas, for instance) will help in the low atmosphere.

[🍔 Mentally Tribbled 🍔]

I'll try switching the final reliant to a terrier, haven't tried that one to be honest. in answer to your second question yes i have 8 of the nozzled rcs thrusters on the final stage section of the rocket and i do use them. straight after i dump the solids i turn rcs on with sas to hold the course and they keeping me on course. honestly i tried without the rcs once and lets just say that went horribly wrong seeing how it blow straight through kerbal command :P. so yeah i defo make sure to have rcs on these things. I do use fins as well, the solids have the basic fins and the reliants have another set of fins on them, (i honestly can't remember the name of them but the look like shuttle fins without the black strips on them). I learned really quickly that these are defo life savers on rockets and small crafts.

[RoofCat]

Reliants are great launch engines. Period. They aren't really meant for anything else. Putting Reliant in second stage is kind of mistake. They can go all the way to orbit due to quite high early lifting capabilities and low own mass so they can lift a lot of fuel, but orbit isn't really their natural habitat. Also the missing gimbal is just bad for landers and lower Isp than Terrier has makes you haul more fuel than needed.

You could use Reliants PLUS SRB for start. With more tanks. So SRB help while those fuel tanks are still full and heavy and are dropped after. Best with some tanks on top of them, which were emptied by Reliant during SRB burn. Just make sure crosfeed is on. So you save on tank decouplers and have less dry (empty tank) mass hanging later on when the SRB are gone.

Otherwise you have great launch engine onboard which isn't used at launch. That's illogical. Why make it "payload" and not use all the power you have? Drop tanks instead to make it even better.



I actually did what you describe (Reliant on Thumper) myself once creating very low science Mun lander for my hard career where you land on Mun with your third launch already (4th goes to Minmus, 5th lands on Duna, 6th Ike, 7th Dres, 8th Pol and so on).
But that is not a great way to build ships. I was just going to extreme due to low part limits (30) and science (75) so early on.

Also KSP has integrated Training missions which should teach you basic stuff about flight.