Sign in to follow this  
Nerfherde

A rant about KSP

Recommended Posts

Since i see a lot of players having problems with docking I thought about creating a topic about what helped me with it, but ill try asking here doing it here first.

Ill keep rendezvous part out as it's a theory problem and it can be solved by learning how orbits and maneuver nodes work.

But for the docking itself, when the ships are a hundred meters apart. Even Scott Manley mentioned he needs to push the IKJL buttons sometimes just to check in which direction the craft will go before committing to a maneuver. I had that problem too before i tried switching I and K controls.

It really made a ton of difference, now by watching the craft from behind IKJL are 100% intuitive J/L : left/right I/K : up/down translation. After a moment of using this system i could rotate camera around and still press correct buttons without even thinking of it. It made it much easier to dock as i could concentrate on other docking aspects, and sometimes just use Nav ball to see where the ship was going and make corrections, and camera was set from the most cinematic angle for screenshots. (Something that was completely out of the question on default controls).

There is another part that points that the default control mode is incorrect. If you use Mk-1 cocpit from IVA view the will actually translate downwards. Similarly if you have a velocity vector forwards on Navball, JL will go naturally left-right but IK will go down-up which is reverse.

In RL planes we use a control set that's set in "top down" position, stick movement (rotation of its base) corresponds to rotation of the aircraft. If we look at the controls from the back, it looks like top and down are reversed. (i think the idea of reversing controls is from this effect). But it's intuitive to use (especially when using joysick or flying an actual plane).

For RCS translation in RL people usually use a small stick that is in line with the front-back of the craft, this makes pressing UP or moving the stick UP and going UP intuitive, KSP has it reversed where pressing UP moves ship down. (I'm not 100% sure how it is actually done on space shuttle but i think i saw it used that way somewhere).

So i have a question, does anybody here tried reversing default IK ? Or is maybe the KSP control method is copied from the way its used on ISS or Space shuttle? (That would still not disqualify my method as in KSP our main camera and reference points are outside behind the ship, something that is not possible in RL).

Share this post


Link to post
Share on other sites
Okay, let's do docking:

Step 1: Put yourself in an elliptical orbit with your apoapsis touching your target's orbit.

Step 2: At ascending/descending node, correct your inclination to your target.

Step 3: Wait (and time accelerate) until you and your target pass close by at that intercept. You actually want your target to be just behind you in your orbit.

Step 4: Burn at your apoapsis until you and your target have a very close intercept, 1km or less is good but you can work with more.

What? Why on earth would you do it this way? It's much easier to get yourself into a circular orbit at the same altitude and ahead of your target and then burn prograde until you get an intercept. This way you can get an intercept after one orbit.

Share this post


Link to post
Share on other sites
What? Why on earth would you do it this way? It's much easier to get yourself into a circular orbit at the same altitude and ahead of your target and then burn prograde until you get an intercept. This way you can get an intercept after one orbit.

It uses far more fuel to burn prograde to catch up with your target than it does to put yourself in a transfer orbit.

Share this post


Link to post
Share on other sites
It uses far more fuel to burn prograde to catch up with your target than it does to put yourself in a transfer orbit.

We're talking LKO right? "Far" more fuel it torturing the term to breaking point. Yes it uses more, but not enough to worry about. 20-30m/s of dV typically and it saves a LOT of faff and is easier to master. Since we're talking to someone who's struggling with it the easier strategy is imho the more relevant, maybe once they're better at it they can try transfer orbits.

Personally speaking I don't know why anyone would bother with transfer orbits for LKO for the sake of saving 30m/s of dV.

Share this post


Link to post
Share on other sites
We're talking LKO right? "Far" more fuel it torturing the term to breaking point. Yes it uses more, but not enough to worry about. 20-30m/s of dV typically and it saves a LOT of faff and is easier to master. Since we're talking to someone who's struggling with it the easier strategy is imho the more relevant, maybe once they're better at it they can try transfer orbits.

Personally speaking I don't know why anyone would bother with transfer orbits for LKO for the sake of saving 30m/s of dV.

I would dispute that it's even easier to do it that way. With the transfer orbit method you set up 2 burns with the maneouvre node system, then you're effectively done. If you do the catching up maneouvre then not only does it waste fuel but you also tend to approach your target more quickly rather than simply arriving in the correct orbit which can potentially make it more difficult.

Anyway, I found docking hard at first but my system works for me and now I find it trivial, which is really where I get the impression the OP wants to get to.

Share this post


Link to post
Share on other sites
It uses far more fuel to burn prograde to catch up with your target than it does to put yourself in a transfer orbit.

I suppose it depends on where the target vessel is; if it's on the opposite side of the planet, then I'll put myself in a 175 x 175 km orbit, then wait until a maneuver node shows a close encounter.

For all you MechJeb haters out there, this is actually a trick I learned from that infamous autopilot, but now I've given up using it for most activities.

Share this post


Link to post
Share on other sites
If you do watch a video again pay close attention to the navball. You can learn most of docking from staring at that little ball. The navball indicators will tell you 95% of what you need to know to dock. Seeing how translation affects the lineup of your prograde and target indicators was huge to finally being able to dock.

I do think that the docking cam mod would be a neat addition to the stock game, they gave us the tools to get the job done conceptually on the navball.

This is important information for people trying to dock. I have only got 6-8 dockings under my belt, but I can do it, and I spend almost all my time staring closely at the navball markers, ignoring the camera view. Also docking can take me 30-60 minutes if I miss or hit too fast and need to come around and try again, so you have to expect that it takes a while of super slow creeping two ships together.

Something that helped me a lot is this:

- you want the 'direction of motion' indicator to line up with the 'target direction' indicator.

- use the 'direction the ship is pointing' indicator to move the 'direction of motion' indicator around.

- forward RCS (the h key) will attract the 'direction of motion' indicator.

- reverse RCS (the n key) will repel the 'direction of motion' indicator.

- alternately attract and repel the 'direction of motion' indicator as needed to keep it lined up AND keep your speed under control.

- Be ready to spend 10-30 minutes staring at those indicators, corralling the 'direction of motion' indicator with your heading indicator.

The hardest part for me is switching to the target ship to rotate the port to face the other ship. Whenever I change back, the first ship has gotten all out of alignment and needs fixing to give yourself time for that. Also, the target ship will continue drifting out of alignment as well after you rotate it, so that needs to be handled too.

Share this post


Link to post
Share on other sites

Sadly the root problem here likely is that orbital mechanics just aren't for everyone.

My advice is to go back to the basics and learn to understand the basic underlying physics of why things behave the way they do when orbiting. You don't need to understand all the math behind it, but you need to be able to comprehend the basic concepts.. Because when you don't, this game is going to be insanely hard.. Especially when trying to do something like matching orbits and docking.

Share this post


Link to post
Share on other sites
I would dispute that it's even easier to do it that way. With the transfer orbit method you set up 2 burns with the maneouvre node system, then you're effectively done. If you do the catching up maneouvre then not only does it waste fuel but you also tend to approach your target more quickly rather than simply arriving in the correct orbit which can potentially make it more difficult.

Anyway, I found docking hard at first but my system works for me and now I find it trivial, which is really where I get the impression the OP wants to get to.

Well the fact that you need to use the maneuver node system indicates a more complex maneuver (I just turn prograde, burn and watch the intercept indicators) and if you got your tansfer orbit cock on and got an intercept at your periapsis you'll have to burn to raise your periapsis, a mirror image of the burn I do to lower my apoapsis, so I don't see your point about approaching your target more quickly.

I use my system for the simple reason - it's fast. The last ship I sent to Jool was 260 tonnes all in and carried 6 probes, 2 lander/rovers. It took 14 launches and 13 docks to fully prep the ship. I don't want to be messing about with maneuver nodes BEFORE I even break orbit ;)

Share this post


Link to post
Share on other sites

My two cents as I've had to go through a lot of learning to get to docking. As you can see in my badges I'm a beginner, too.

Watch every tutorial on docking multiple times while practicing. Sports players often watch videos. Studies show that watching can be nearly as beneficial as practicing because the mind will go through the motions. Kind of like when the brain fires the same synapses for moving as when just thinking about it.

I like to have engines that point both directions especially for heavy loads. Make the prograde engines activate with the 1 group and deactivate with the 2 group. Likewise, make retrograde engines deactivate with the 1 group and activate with the 2 group. Avoid the toggle option as this can bug out. This saves me a lot of hassle of spinning my craft around. Not necessary, but huge help with big pay loads like space station parts.

My most useful advice and one that hung me up, is make sure your RCS is balanced. I had a real problem getting my tanker to dock until I finally scrapped the lifter and redesigned my RCS paying more attention to center of mass. I then used a mod to put it in orbit and made sure translation (I J K L) didn't cause any rotational drift. This helped so much. If you want tips on RCS balance I might be able to help you out.

Edited by Limited Infinity

Share this post


Link to post
Share on other sites
I suppose it depends on where the target vessel is; if it's on the opposite side of the planet, then I'll put myself in a 175 x 175 km orbit, then wait until a maneuver node shows a close encounter.

For all you MechJeb haters out there, this is actually a trick I learned from that infamous autopilot, but now I've given up using it for most activities.

Must admit, I use Mechjeb extensively here. Primarily for the orbital information and rendezvous module, as well as the SAS functions. I'm fond of BIG ships and holding a button down for over a minute till the thing turns 180 degrees isn't stimulating gameplay.

My advice to anyone is get Mechjeb 1.9.8, use the data and things WILL become clearer. The data provided by the base game is FAR from complete at the moment.

Share this post


Link to post
Share on other sites

Soooo i got me 2 stations in nice perfect orbits around kerbin. About 200k and enough fuel to get to the mun if I want. So far so good. Now what? I tried Reading the very nice instructions here, but to no avail.

Share this post


Link to post
Share on other sites
Soooo i got me 2 stations in nice perfect orbits around kerbin. About 200k and enough fuel to get to the mun if I want. So far so good. Now what? I tried Reading the very nice instructions here, but to no avail.

post a pic of the map view, someone will talk you in.

Share this post


Link to post
Share on other sites

My most useful advice and one that hung me up, is make sure your RCS is balanced. I had a real problem getting my tanker to dock until I finally scrapped the lifter and redesigned my RCS paying more attention to center of mass. I then used a mod to put it in orbit and made sure translation (I J K L) didn't cause any rotational drift. This helped so much. If you want tips on RCS balance I might be able to help you out.

You don't need mods to test RCS balancing. Just launch it to put it on the pad/runway, then alt-f12 to open the debug menu and click 'hack gravity' then test away. This is really about the only time I use the debug menu at all.. Testing for thrust balancing. If the devs ever add a 'center of thrust' marker for RCS, I wouldn't even have to do this.

Share this post


Link to post
Share on other sites
Or is maybe the KSP control method is copied from the way its used on ISS or Space shuttle? (That would still not disqualify my method as in KSP our main camera and reference points are outside behind the ship, something that is not possible in RL).

Actually, I think the translation keys (as well as the rotation keys, for that matter) are mapped the way they are because that's how it's done in most flight simulator games, where the keyboard directions correspond to the joystick directions. The "up" key is the same as pushing the joystick forward, which pitches the nose down, while pulling back on the joystick / pushing the "down" key brings the nose up. I've never had problems with the default scheme, but that might be because I used to play a ton of Red Baron as a kid.

Share this post


Link to post
Share on other sites

Hehe, actually, about RCS i remember seeing a video of how the real Life rcs worked in the Gemini program. Aligned them accordingly and it works. Im trying to find a good Place to upload pics to now...

Share this post


Link to post
Share on other sites
Seems to me like it might be an attitude issue.

Lol, when I first saw this I thought you meant attitude as in the direction a ship is pointing, rather than behavior. God, I am a giant nerd.

Anyway, I've done docking quite a lot with my stations. When you get within visual range of the target, it's not worth fiddling with maneuver nodes at that point, and you would do better to try and align your prograde and target position markers on your navball. Be sure to kill horizontal speed early, to take into account the time it takes to decelerate.

Share this post


Link to post
Share on other sites

ThatBum: i first read ALTITUDE problem, so you are not alone :) The problem is I have never even got within Visual range :(

Share this post


Link to post
Share on other sites

But for the docking itself, when the ships are a hundred meters apart. Even Scott Manley mentioned he needs to push the IKJL buttons sometimes just to check in which direction the craft will go before committing to a maneuver. I had that problem too before i tried switching I and K controls.

It really made a ton of difference, now by watching the craft from behind IKJL are 100% intuitive J/L : left/right I/K : up/down translation. After a moment of using this system i could rotate camera around and still press correct buttons without even thinking of it. It made it much easier to dock as i could concentrate on other docking aspects, and sometimes just use Nav ball to see where the ship was going and make corrections, and camera was set from the most cinematic angle for screenshots. (Something that was completely out of the question on default controls).

This is where the CHASE mode for the camera comes in really useful. As your ship rotates, so does the camera (so the ship stays fixed on the screen and everything else seems to be rotating instead). This means that IJKL will always move your ship in a consistent direction relative to your screen. Once I discovered CHASE camera mode, it made my docking attempts at least 10 times easier.

Share this post


Link to post
Share on other sites

Okay. Well, you probably know by now, the point is to get the two orange arrows in the map view to line up with each other. Or the two purple arrows, which is the encounter after the orange arrows. The top arrow pointing down is where you will intersect the target's orbit, and the bottom arrow pointing up is where the target will actually be at that time. You also need to get one of the green sideways arrows, the ascending/descending nodes, in contact with the orange arrows. If you don't their altitudes relative to the planet will be the same at the encounter, but their altitudes relative to each other will be different because their inclination isn't the same. Just experiment with the maneuver nodes and try and get is as close as you can, using the guidance computer isn't going to hurt anything.

Another important point is knowing when to launch. If you launch when your target is on the opposite side of the planet, you'll need to spend a long time in a lower or higher transfer orbit to catch up to the station, or let the station catch up to you. It varies with different rockets and ascent profiles, but I find a good time to launch is when the target is just coming up over the horizon relative to the ship waiting on the launchpad.

Share this post


Link to post
Share on other sites

Thanks, alot for your help everyone. But I have to sleep will try everything you posted tomorrow, especially ThatBums advice :)

Share this post


Link to post
Share on other sites

1) Get your first craft into a roughly circular orbit, shoot for 100km to start. Orient it (using your navigation ball) pointing towards the 360/0 line on your navball, centered on the ball's horizon (line between the blue and brown)--that's horizontal to the plane of the earth, pointed towards the north pole. Now you're flying sideways. Hit T. And leave it alone until you come back with another ship.

2) Launch your second craft. During launch, pay attention to whether your target will be west of you (behind you) or east of you (ahead)--this assumes you take off and do your gravity turn to 90 degrees (east).

2a) is it behind you? Make your apoapsis higher by ~5000 m. Your speed will be slower the higher off the surface you are, so your target craft will catch up to you.

2b) is it ahead of you? Make your apoapsis lower by ~5000 m. Your speed will be faster at lower altitudes, so you will catch up to it.

3) Circularize your orbit. If you are not using nodes, use nodes. Learn how to use the three axes. Don't be afraid--a node doesn't lock you into anything and you can **** it up and delete it and start over. experiment, see what burning in different directions will do to your orbit. Nodes give you a blue tick mark on your navball--orient to follow it, then engage your engines to consume the delta-v that it's calculated you need in that direction. Use nodes to make concentric circles--inside your target to catch up, or outside your target it to let it catch you. Again, the circles should be 5000 m apart roughly.

some notes about nodes: yellow is prograde (faster) and retrograde (slower)--it has the effect of making your orbit larger or smaller. Blue moves you towards the planet or away; it has the effect of shifting your orbit left or right, so you can correct for lopsided orbits (unequal apo/peri). Purple corrects for orbits that are not equitorial--it matches the planes of each orbit so they're parallel. That's important.

4) Set your target craft to be your target. now click on the speed on the navball until it says "target": if you've done things right, then this number should be getting smaller, it is your speed relative to your target. Now your orbits are probably not on the same plane--look at it from the side and see if they line up. If so, great, go to the next step, but it's probably lopsided. But there is a point where they cross, and when you look at it top-down there should be a dashed line between the orbits at that point (called ascending or descending node). Place a maneuver node there and adjust the purple vector so you match planes. Orient towards blue tick, wait till you hit the node, and burn till your orbits are in the same plane.

5) Now we wait and plan--NO ENGINES YET. watch the purple tick marks as you complete each orbit; they show how close your craft are. They should be getting closer by about 30-80 km per orbit. Wait until the purple node says you'll pass your target on the next orbit. Now **** gets real. Your practice with nodes is about to pay off. Start placing nodes around your orbit and go prograde (yellow open) if you're catching up, or retrograde (hatched yellow) if its catching up--you want to adjust your orbit to touch your target's, ideally at a ascending/descending node. Then mess with the other vectors (blue and purple and yellow) to get the predicted distance (purple tick marks) to be 1 km or less apart. It is possible with less, but SO MUCH EASIER the closer you are. If you can't get it close, erase the node and try somewhere else. For the time being, ignore what your resulting orbit will be, you just want an intersect--just makes sure you don't put your periapsis at 10km or something to accidentally de-orbit. Once you've set your nav coordinates, orient your ship towards blue on the navball, wait for the timer to hit zero, and burn, but not all the way --now here's the clutch part: with about 10 m/s left, cut the engines and delete your node. You're still pointed in the right direction anyhow. Now barely turn on your engines and keep track of how close your closest approach will be. keep tapping the engines until your closest approach stops getting smaller. Often times you can get closer than you thought. but if you miscalculated you will still be as close as you can.

6) Close the gap--complete the orbit and wait for your closest approach. MAKE SURE YOUR NAVBALL STILL SAYS 'TARGET'. once you're within 2000 m or so, reorient your ship: were you at a lower orbit and catching up now? you need MOAR SPEED--orient towards prograde (open yellow navball icon) and burn until your relative speed is zero. Were you at a higher orbit? You need to slow down; burn prograde (hatched yellow navball icon) until relative speed is zero. At this point you can use RCS to get really good and zero'ed. Check your orbits. They should magically be pretty damned close. You're halfway there!

An important note in these final stages (again, make sure your navball is set to "target"): NOW yellow prograde/retrograde are speed relative to your target--it's the axis of your motion. Purple prograde/retrograde are the direction towards/away from your target. These are critical to get straight if you're going to close to within 50 meters.

7) Find the purple prograde marker on the navball--this will point you towards your target. is your nose pointed at your target? Good. What's the distance? Divide that number by 100, and burn towards the target at this speed (if you are 1000 m apart, burn at 10 m/s). That way you'll hit the target in 100s, whereever you are. Flip ~180 around towards the yellow retrograde marker--you want to close distance, but stop ALL relative motion at every step, reorient towards your target, burn at 1/100 the distance (speed = distance/100), flip 180 degrees while you're closing and point towards yellow retrograde, stop, rinse, repeat until you're within 50 meters.

8) Remember your target ship in step 1, and how you oriented it to point at the north pole? You're going to do the opposite with your chase ship now--point towards the 180 degree mark on the horizon line on your navball. your ships should now be parallel and pointed in opposite directions. What this does--even though your orbits are the same now, your orientation as you complete an orbit changes. If you find you're drifting apart, this is usually why. but if you're oriented north/south, your orbits are parallel, and any change in direction is matched by your target. MAGIC.

9) Hit "v" until it says "chase cam mode". Look from the back end of your ship. Tap the "I, J,K,L" keys, see which direction your RCS ports thrust. Often times this is not intuitive--"J" may thrust you left, right, up or down, just keep it straight. It's always OK to tap it to remind yourself.

A note about RCS: You want your RCS ports ONLY AT 90 DEGREE ANGLES. A rule of thumb is "1 set of 4 for every 10 tons of craft". Try to balance them along the ship's center of mass. Using the I,J,K,L keys shouldn't push you off axis, but if it does, that's why you re-oriented towards 180 degrees--you can use the ASWD keys to keep pointing in that direction. Also, when you're building the thing in the VAB, looking out the door of the VAB is "south"--placing RCS ports along the cardinal directions using this as a reference point (0/90/180/270; N/E/S/W) will make a big difference using the IJKL keys, as only one pair should fire at any time. Your goal is to deal in only one vector (one direction out of the three in 3 dimensions) at any one time.

10) This is the money shot. More than ever you must think in 3 dimensions now. Correct your distance to target ONE VECTOR AT A TIME. First, use H and N to get the get the ships--still parallel--separated by a hair when looked at from the side. Now look from one side, then another, see which direction (vector) you're furthest from your target, and tap IJKL to see which pair of RCS keys will thrust you in that direction towards your target. Tap WASD to keep pointed towards 180 degrees--if your ship is small (less than 20 tons) and well balanced, you can keep ASAS on, otherwise you won't be able to see the RCS directions and you'll burn through monoprop like whoa, so you'll have to keep pointed south manually. Once you get close, stop. Try not to go more than 0.2-0.3 m/s--you've got to stop. Now repeat this ONE VECTOR AT A TIME until you are damned close. Pay attention to your H-N vector, and try to keep the ports close.

11) Keep shifting your focus from top to side to side and seeing which direction you're off, and then back to stern and hit the right IJKL RCS key to close that gap. Sometimes you can adjust the view to look along the axis of your target ship so you can gauge what "stationary" and "matched" and "parallel" are. Once your ports are matched and STATIONARY, tap H, get a bit of thrust, MAKE SURE ASAS IS OFF, and enjoy the fruits of your hard won fight.

Best of luck!

Share this post


Link to post
Share on other sites
What? Why on earth would you do it this way? It's much easier to get yourself into a circular orbit at the same altitude and ahead of your target and then burn prograde until you get an intercept. This way you can get an intercept after one orbit.

And you'd still find yourself in an elliptical orbit waiting for your target to catch up with you. Except in your example the intercept point is periapsis rather than apoapsis. In either case you're using an elliptical orbit to match orbital position at the contact point between yours and your targets orbits.

Step 3.5 in Fractal UK's example should have been to use a maneuver node at the contact point on your final orbit to fine tune your elipse for the closest intercept.

Step 5 would be to Circularize your orbit once your intercept happens then approach to dock.

As for doing it in 1 orbit, that depends on how much DV you want to use.

Share this post


Link to post
Share on other sites
And you'd still find yourself in an elliptical orbit waiting for your target to catch up with you. Except in your example the intercept point is periapsis rather than apoapsis. In either case you're using an elliptical orbit to match orbital position at the contact point between yours and your targets orbits.

To use a car analogy; that's like saying reversing round a corner is the same as going forwards around it. You're still going round a corner.

The key difference being the way I'm describing is EASIER as it doesn't involve buggering about with maneuver nodes, just point and thrust, which to my mind makes a damn sight more sense when you're talking to someone who can't arrange their own intercept.

A transfer orbit is definitely more efficient, but that comes with its own price.

Share this post


Link to post
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this