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How to get a circular orbit


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In my last thread I mentioned that I couldn't survive landing but that was solved. Now I have the prograde and retrograde markers but that makes a problem. Without a circular orbit I couldn't really do easier things. Before I think it is ok to have a 2000km apogee and a 71km perigee but then they said in the last thread that I need a circular orbit. So how to do that. Relying on the prograde marker would not work for me.

if u want to know about my orbital craft (w/ tourists) download it here

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To get suborbital, use a gravity turn:

  • When launching, make sure the rocket faces east.  That is, when you pitch using the S key, your rocket should turn towards the ocean.
  • When you reach ~75 m/s speed, pitch east 10 degrees and hold that.
  • When you hit an altitude of ~4000 meters, pitch another 10ish degrees east (you will be in the neighborhood of 20ish degrees at this point) and hold that.
  • When you hit an altitude of ~10000 meters, pitch east all the way to 45 degrees and hold that.
  • Pay attention to what your Ap is going to be; you may need to switch to map view or use a mod like KER or MJ.  When your Projected Ap hits ~71000 meters, kill the engine and coast.
  • Now the tricky part.  Pitch to somewhere between 70 and 90 degrees, and watch the time to hit Ap.  Again, you may need to use a mod (I use MJ).  When the time to hit Ap reaches 15 or so seconds, throttle up and keep throttling until the time to hit Ap hits 25 seconds.  You may need to alter your pitch up or down so as to both not hit Ap AND not go too far beyond 25 seconds.  Several bursts like this will get your Pe to about 71000 meters and keep your Ap at/just below 80000 meters.

Keep an eye on your TWR during all of this.  On the right of the navball is the force bar, right?  That goes up the more thrust you give.  Keep the pointer in that bar just over the first tick mark, and never over the second, any time you are thrusting.

This should help you circularize.  Obviously, once you get the orbit I mentioned above, you can do small thrusts at Ap to get the Pe closer.

I hope this helps!

Edited by Popestar
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50 minutes ago, Popestar said:

To get suborbital, use a gravity turn:

  • When launching, make sure the rocket faces east.  That is, when you pitch using the S key, your rocket should turn towards the ocean.
  • When you reach ~75 m/s speed, pitch east 10 degrees and hold that.
  • When you hit an altitude of ~4000 meters, pitch another 10ish degrees east (you will be in the neighborhood of 20ish degrees at this point) and hold that.
  • When you hit an altitude of ~10000 meters, pitch east all the way to 45 degrees and hold that.
  • Pay attention to what your Ap is going to be; you may need to switch to map view or use a mod like KER or MJ.  When your Projected Ap hits ~71000 meters, kill the engine and coast.
  • Now the tricky part.  Pitch to somewhere between 70 and 90 degrees, and watch the time to hit Ap.  Again, you may need to use a mod (I use MJ).  When the time to hit Ap reaches 15 or so seconds, throttle up and keep throttling until the time to hit Ap hits 25 seconds.  You may need to alter your pitch up or down so as to both not hit Ap AND not go too far beyond 25 seconds.  Several bursts like this will get your Pe to about 71000 meters and keep your Ap at/just below 80000 meters.

Keep an eye on your TWR during all of this.  On the right of the navball is the force bar, right?  That goes up the more thrust you give.  Keep the pointer in that bar just over the first tick mark, and never over the second, any time you are thrusting.

This should help you circularize.  Obviously, once you get the orbit I mentioned above, you can do small thrusts at Ap to get the Pe closer.

I hope this helps!

haven't tried yet, but it hopefully helps

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2 hours ago, Popestar said:

you may need to switch to map view

That was before KSP 1.7 though :) 

Anyway, just follow the basic steps as outlined by @Popestar, and you're good!

My personal preferred numbers vary a bit, but that doesn't change the general procedure at all.

As a final note, in my opinion circular orbits are a bit overrated, it's perfectly fine to end with an orbit of say 115x85 km instead of having a perfect 100x100 km orbit.

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1 hour ago, VoidSquid said:

That was before KSP 1.7 though :) 

Anyway, just follow the basic steps as outlined by @Popestar, and you're good!

My personal preferred numbers vary a bit, but that doesn't change the general procedure at all.

As a final note, in my opinion circular orbits are a bit overrated, it's perfectly fine to end with an orbit of say 115x85 km instead of having a perfect 100x100 km orbit.

well yeah but last time in the other thread someone say that having a very uncircular orbit (170x70km) would destroy some of my progress and stuff like that

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5 minutes ago, Anonymous49 said:

well yeah but last time in the other thread someone say that having a very uncircular orbit (170x70km) would destroy some of my progress and stuff like that

Let's say 170x71 km, Pe above the 70 km atmosphere border of Kerbin.

And why would that "destroy your progress"?

 

Edited by VoidSquid
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3 hours ago, Anonymous49 said:

So how to do that. Relying on the prograde marker would not work for me.

See to orbital mechanics. Circular orbit is circular if PE and AP are  same/similiar distance from origin. To achieve this You can burn at AP prograde to move Your PE "up" and when it is almost the same orbit is circular enough. And retrograde from PE to get AP down if You would have tighter circle.

Then You can play with inclination normal/antinormal (it would be important for mission) and there are some other points (often in quarter wher You have ascending/descending node) where pro/retro burn can efficient move Your PEargument.

On navbal You have markers in orbit mode (surface/orbit/target velocity diference) that are forward (prograde) backward (retrograde) in Your velocity frame, then normaln/antinormal in origin frame and radiat out/in in origin/orbit frame (it is more relevant to robit in eliptical orbit and in origin during landing). This is graspto explanation, not mechanical corect.

In surface mode they are slightly diferent (normaln/antinormal are invisible) and pro/retro are measured a bit diferent, and target mode change its orgin to be relative.

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4 hours ago, Anonymous49 said:

Relying on the prograde marker would not work for me

Naturally. Almost no craft is that perfectly attuned that it can do a perfect gravity turn after the initial pitch by just following prograde. Use SAS hold instead and do some manual steering as required. :) 

Edited by VoidSquid
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7 hours ago, Anonymous49 said:

someone say that having a very uncircular orbit (170x70km) would destroy some of my progress and stuff like that

 

There is some advantages  to be able to launch in a more circular orbit but is far from a disaster if your orbit is not perfect (specially while you are still learning how to do it). You just raised the orbit more than necessary, probably will have a slighter higher reentry velocity and if you are going somewhere else you may lose a bit of efficient in your transfer burn. 

Anyways, the procedure @Popestarexplained should work just fine. However the ideal gravity turn is something else:  get the initial tilt right and the craft will steer itself into orbit, no need to watch the throttle, just  a more powerful rocket  tilt more/earlier  while a less powerful will tilt less/later. The craft need to be aerodynamic stable  or at least stable enough to hold prograde with SAS (needs and advanced probecore or high leve pilot)

Now,  it requires quite a bit of practice/experience to pull it off with any kind of consistency.*  Definitely not something a new player should be too worried about. Instead learn how to make corrections when your turn is less than perfect:

  • If your apoapsis is not raising, pitch up (if that happens right after the launch,  consider instead to revert and start with less tilt)
  • If your apoapsis and time to apoapsis is increasing too quickly, pitch down(mostly early in the launch) or throttle down(mostly later on). 
  • If your apoapsis is increasing but your time to apoapsis is not, throttle up.

*Personally, I like to design my launch vehicles (both rockets and spaceplanes) to not require any steering input, but I'm unaware of anyone else that follow that design choice.

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The point around achieving a circular orbit (for a Kerbin orbital flight) is that its efficient, which means you don't need to take so much fuel, so the rocket can be smaller/cheaper etc. Its an ideal you should aim for. With the contracts not needing a specific inclination, it should be easy to do too. Its not so much that it will "destroy your progress" but that its a basic part of orbital maneouvring which if you can't do, you won't be able to learn more involved aspects such as going to the Mun (and returning), or landing on the Mun (with no atmosphere) etc. Or positioning satellites.

There is another advantage in circularising the orbit before a landing, which is it will minimise the speed to lose before that landing. Yes you can go for a landing from 40000x71 orbit if you like (and might need to later!) but beware of the energy you'll have dropping from an Ap of 40000km rather than an Ap of 71km.

ETA Another advantage is that it lets you choose your landing site much more - you have the entire circumference to choose from, so you can choose something flat, in daylight.

But no, orbits around Kerbin for tourist contracts don't NEED to be perfectly circular.

 

10 hours ago, Popestar said:

To get suborbital, use a gravity turn:

  • When launching, make sure the rocket faces east.  That is, when you pitch using the S key, your rocket should turn towards the ocean.
  • When you reach ~75 m/s speed, pitch east 10 degrees and hold that.
  • When you hit an altitude of ~4000 meters, pitch another 10ish degrees east (you will be in the neighborhood of 20ish degrees at this point) and hold that.
  • When you hit an altitude of ~10000 meters, pitch east all the way to 45 degrees and hold that.
  • Pay attention to what your Ap is going to be; you may need to switch to map view or use a mod like KER or MJ.  When your Projected Ap hits ~71000 meters, kill the engine and coast.
  • Now the tricky part.  Pitch to somewhere between 70 and 90 degrees, and watch the time to hit Ap.  Again, you may need to use a mod (I use MJ).  When the time to hit Ap reaches 15 or so seconds, throttle up and keep throttling until the time to hit Ap hits 25 seconds.  You may need to alter your pitch up or down so as to both not hit Ap AND not go too far beyond 25 seconds.  Several bursts like this will get your Pe to about 71000 meters and keep your Ap at/just below 80000 meters.

Keep an eye on your TWR during all of this.  On the right of the navball is the force bar, right?  That goes up the more thrust you give.  Keep the pointer in that bar just over the first tick mark, and never over the second, any time you are thrusting.

This should help you circularize.  Obviously, once you get the orbit I mentioned above, you can do small thrusts at Ap to get the Pe closer.

I hope this helps!

The above is a good guide.

I'll add - probably for later on when you get more refined at it - step 5 I aim for about 68km; the reason being, step 6 inevitably involves burning before you reach Ap, and this raises the Ap a bit. Putting it another way, burning just before Ap raises the Pe a lot, and the Ap a bit.

Edited by paul_c
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I believe OP was advised to try for circular orbits because he/she was losing craft to excessive re-entry forces. In which case the benefit of a circular orbit would be to reduce the speed of re-entry by not driving the apoapsis higher than necessary in the first place before trying to re-enter. In other words, you fall less hard if you're not falling from as high. 

A while back I made a guide to getting to orbit. It might help. It might not. :D At any rate, here it is. 

 

 

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I don't think "circular" is the actual point here, but having an orbit with not-so-much-kinetic-energy. In other words: an eccentric orbit of say 80x200 km has a lower kinetic energy than circular 500x500 km orbit. Whatever kinetic energy a given orbit has, that energy (minus the energy to go for a suborbital Pe) has to be killed somehow to be able to land, usually by atmospheric friction. And naturally, the higher Pe and Ap are, the more kinetic energy that orbit has.

Hence, going for an orbit with a reasonable low Ap and Pe (both above 70km, for Kerbin) is the way to go.

Edited by VoidSquid
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13 hours ago, VoidSquid said:

Naturally. Almost no craft is that perfectly attuned that it can do a perfect gravity turn after the initial pitch by just following prograde.

I disagree. Any reasonably designed rocket will have a completely natural tendency to follow a standard gravity turn, requiring minimal input. You really only need to pay attention to two variables.

With any reasonably designed rocket, the standard launch-into-easily-repeatable-gravity-turns procedure is:

  • set SAS to hold
  • stage to launch
  • wait until X
  • nudge the nose Y degrees East
  • switch SAS to prograde
  • take your hands off the stick/keys and just stage if and when required, until Ap reaches a few km over your desired orbit altitude
  • coast
  • circularize (manually or with a node)

X = Either a specific speed or altitude, whichever seems more convenient for you. I usually go by speed, and find the right moment to be often somewhere between 80-120 m/s, depending on the flight characteristics of the rocket. Finding the sweet spot takes a bit of trial and error, but usually within that range you still make orbit, just not as efficient. Correcting for a less than perfect launch is simple: if it's too shallow, wait longer; if too steep, wait less.

Y = I usually nudge no more than 5 degrees. Much more than this tends to cause unwanted deviations in the flight path that will require additional corrections later.

If you want to turn the above almost perfectly repeatable, use launch clamps and pre-incline your rocket 5 degrees east. That way you literally only need to figure out X  (the exact moment when you need to switch SAS to prograde), and never even need to perform any steering inputs at all.

I would posit that getting used to performing launches as described here will not only allow you to repeatably achieve near-circular orbits, but also make it a routine thing that will allow you to get most launches with new rockets right in just one or two (test) launches.

 

6 hours ago, Spricigo said:

*Personally, I like to design my launch vehicles (both rockets and spaceplanes) to not require any steering input, but I'm unaware of anyone else that follow that design choice.

Ahem.

 

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11 minutes ago, swjr-swis said:

I disagree

And I disagree to that ;) 

When I built a new rocket (doesn't happen that often nowadays, I have a good variety of crafts), I usually come close to a good "auto-gravity-turn" design, just by experience. Might need a few iterations (tweaks, in particular thrust percentage for the different stages), but even the initial build is not that far of.

But I've been playing KSP for some 4000+ hours. A beginner just doesn't have the experience, naturally (check out any KSP beginner stream at Twitch). Hence my words "Almost no craft is that perfectly attuned that it can do a perfect gravity turn after the initial pitch by just following prograde"

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9 minutes ago, VoidSquid said:

But I've been playing KSP for some 4000+ hours. A beginner just doesn't have the experience, naturally (check out any KSP beginner stream at Twitch). Hence my words "Almost no craft is that perfectly attuned that it can do a perfect gravity turn after the initial pitch by just following prograde"

With all due respect: it doesn't require 4000 hours, nor does it need to be perfectly attuned. I did mention 'reasonably designed', yes? There's tutorials up the wazoo explaining what a good rocket looks like. KSP's simulation offers very wide margins of error (so wide, that people routinely put contraptions into orbit that by all rights shouldn't be able to even lift off). Besides, OP is past the point of basic rocket design already.

A gravity turn is the easiest possible way of launching a rocket into orbit, because it allows the rocket to follow a natural course, requiring only minimal input at the start. Think of it this way: most kids learn pretty quickly to throw a ball into a basket. The entire path of the ball is determined right at the start of it - how hard you throw, and at what angle. If you missed, adjust those two parameters and try again. Cutting down to basics, a real gravity turn only requires you to observe when you nudged and how hard, and from the path followed after that, you can easily tell which one you need to correct and how.

This helps a new player to learn to put things in orbit much faster for two reasons: without the stressy need to continuously steer (and then correct, and then correct some more, and then -wait stage first!- then correct again, oh dear why is it not steering where I tell it to OH I FORGOT TO STAGE AGAIN!!!) the player actually has time and opportunity to observe what the rocket is doing all by itself, and what made a difference in which way. Additionally, manual steering is highly inaccurate in KSP, and tends to introduce random path deviations, which just complicate things further.

Teaching newbies (or leaving them in the belief) that flying a rocket into orbit is some kind of arduous manual technique that requires thousands of hours to follow a specific path is a disservice, when they could instead be watching and learning while sipping a cup of their preferred beverage, calmly observing just the one or two actually important variables that will help them make a successful launch.

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2 minutes ago, swjr-swis said:

Teaching newbies (or leaving them in the belief) that flying a rocket into orbit is some kind of arduous manual technique that requires thousands of hours to follow a specific path is a disservice

With all due respect, I never said that. What I did say though is that for beginners, they more often than not simply don't have the experience (and patience) to build a rocket which does a gravity turn (almost) by itself.

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Thanks, I got a circular orbit. Most thanks to @Popestarfor telling me how to get a circular orbit. I got 79178m apogee and 78706m perigee.

Alternatively, big thanks to @VoidSquidfor telling me that I don't need a fully circular orbit.

Thanks to @paul_c for telling me that a circular orbit saves the most amount of fuel.

Thanks to @vv3k70rfor teaching me orbital mechanics 

 

P.S. There may be more, I haven't read every single comment.

 

Finished in 9:02am 13/1/2021

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3 hours ago, swjr-swis said:

Ahem.

Hi-five

1 hour ago, swjr-swis said:

Teaching newbies (or leaving them in the belief) that flying a rocket into orbit is some kind of arduous manual technique that requires thousands of hours to follow a specific path is a disservice, when they could instead be watching and learning while sipping a cup of their preferred beverage, calmly observing just the one or two actually important variables that will help them make a successful launch.

Couldn't agree more. But I think @VoidSquid is trying to address a different point that is also valid, the perspective of a brand new player (let's face it,  not a vivid memory for us anymore)

Yes, the veteran told you is a simple procedure, that you only need to pay attention to a couple of things while the craft fly itself into orbit. But you have no idea what information you should be getting from those things or if the values you are getting are still close enough to the values the veteran suggested. Are you still doing it correct? Maybe you should "do something" instead of watching the rocket fail. The veteran told you that you shouldn't, just keep calm and observe those few important things but the veteran is not piloting that craft, so you will do something. You will panic. :rolleyes:

 Tell me, that is not something that happened to you at some point? Maybe not in KSP, but at anything you were inexperienced at the time. It certainly happened to me... more than I like to admit. :blush:

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4 hours ago, Spricigo said:

Are you still doing it correct? Maybe you should "do something" instead of watching the rocket fail.

Exactly. It is very important when to start manouver (if You follow only markers without manouver markers) in term of seconds to node (let say PE, AP, descend/ascend) or even how and where on trajectory manipulate Your path. Higher TWR make in easier because velocity would change almost at given point without affecting other values. Longer burn against not manouver marker rotate whole reference a bit.

There are at least such cases (without manouver markers):

-for exact orbit use short single burn in PE/AP, after You get corect inclination;

-for exact orbit burn in ascending/descending node pro or retro to move Your PEargument;

-for fast landing insertion burn just after catching up gravity well to get You PE down;

-for cheap landing insertion circularize in PE, then in new PE, then select landing spot by inclination when You are slow (cheaper), then land suicide burn;

-for controling gravity assist choose You direction (let say normal/anti) and turn to stability assist to keep this vector without adjusting reference frame when You changing velocity;

-for ascend/descend start burning slowly on normal/antinormal a bit before node and if You at the node stop burning;

-for ascend/descend roll Your node on low value by burning slowly;

-for catching up PE argument burn slowly before the PE/AP to roll node in given seconds value before You controling Your thrust;

-for precise manouvers tweak You engine thrust (it will scale main throtle);

-for catching up docking or asteroid if target prograde burn on oposite side of target (in target mode) to move prograde marker on target marker to match; if retro bur ofset to retro to match retro with target/antitarget (depend on control default/reverse);

-for landing with atmosphere (specialy with dense atmosphere) move You AP a bit over atmosphere and PE a bit inside and use it for deceleration - it could take almost one orbit to fall;

-for landing without atmosphere decelerate retrograde and if You are about pass target burn horizontaly in retrograde direction to lose You forward vector;

-for pinpoint landing without dense atmosphere try to fall verticaly on target, change to docking mode and radial out, and control Your vessel sideways using main throtle (there be only Z/X working in docking mode, shift is assigned for RCS/verniers) to controll descend speed or even hower;

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