I want to emphasize point 4. Make sure both ships are normal/anti in orientation. I just couldn’t do it otherwise.
Matt_W
1885
It certainly makes it easier, and not just because it’s visually obvious. If you’re pointing normal, then as they orbit, both ships are only rotating around the axis of the docking port. And once you get them aligned, they share that rotation axis, so the relative rotation and motion will be slight.
If, on the other hand, you try to dock from a prograde/retrograde direction, the ships will be rotating around an axis perpendicular to the docking axis. Since LKO has about a 30 minute period, if it takes you 5 minutes to dock, the target ship will rotate 60° away from the docking axis in that time, meaning you have to constantly adjust your offset and rotation as you approach. It’s possible to dock this way (and sometimes you have to if you have a large station you can’t easily rotate), but you have to be fast and confident.
I am trying to dock in a polar orbit around the moon. I originally did this to gather science as it’s a science station, but now I think it was a big mistake as far as docking is concerned.
I’m constantly learning things in this game and this forum. This is so obvious, but yet it is not. Thanks guys.
@jpinard don’t give up.
.We choose to Dock … and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills,
Seriously docking opens up a whole new world of exploration.
@Matt_W @Fishbreath
If my station is in a polar orbit do I still want to be in this orientation?
Matt_W
1890
Yeah, normal/antinormal to your orbit. It will work the same regardless of what the planet below you is doing.
What is the minimum thrust to weight ratio you need to get from Kerbin Orbit to the Mun? I see that it’s best to have a TWR of ~10 for liftoff, but not sure about after that.
Matt_W
1892
You actually only need a TWR of about 2 to get to orbit. Higher than that and you accelerate fast enough that air drag becomes significant and eats up all your fuel. At a TWR of about 2, you speed up at about the same rate that the atmosphere thins as you ascend.
It takes about 850 m/s to get from LKO to a Mun intercept. Ideally you complete that burn in < 5 minutes so that the burn doesn’t take more than about 60° of the LKO orbit. To get 850 m/s in about 5 minutes you need an acceleration of 2.8 m/s/s, which means a Kerbin (and Earth) referenced TWR of about 0.3. (Kerbin TWR of 1 is just g, which is 10 m/s/s.)
Keep in mind that your TWR increases as you burn up your fuel because the thrust stays the same, but most of the mass of your rocket is fuel, so the weight goes down dramatically.
Trying to dock again and not doing well. When I’m trying to close from 1 km - 3 km what am I supposed to be using on the navball to do this? I am so disoriented and just can’t seem to close this last bit of distance cleanly. I am exactly 3 km under him in my orbit.
meeper
1894
I divide docking into three phases:
- Alignment: where you align orbits and get to within 3-5km (looks like you’ve nailed this)
- Intercept: when you’re within that 3-5km range and stop treating the docking interception as orbital maneuvers and start treating it as if both objects were floating in empty space. In other words, accelerate to a comfortable speed (10-20m/s is generally what I use) and keep your velocity indicator roughly aligned with your target on the navball. The further away you are, the more corrections you’ll need to make (pretending you are immune to orbital effects isn’t quite the same as actually being immune). Just keep your indicator aligned with your target.
- Terminal: you’re within a few hundred meters and can see your intended target (the docking port). This is the time when I adjust my trajectory to give me a clear run at the port, align my axis, and approach the target. Keep speeds in the sub-5m/s range here. The final docking connection should be made in the ~1m/s range.
For players new to docking, I always recommend they null out their velocities between each of those stages. It’s incredibly fuel inefficient, but I find it helps them reset their brains to shift between the different frames of reference necessary for docking.
Fozzle
1895
@jpinard You can actually get off of Kerbin with a TWR of 1.3, but as @Matt_W said closer to 2 is better. Also I don’t remember if this was shared before, so I’ll put it here. It’s my favorite rocket design delta v map. It’s a pretty good guideline on what you should be aiming for in delta v to get to various locations. This map assumes you are going during a decent transfer window. (It says KSP version 1.3 but it is still relevant in 1.7x)
Pod
1896
Have you watched any tutorial videos about this? Or there’s this on the KSP wiki. One you’re within 3km it’s all about just looking at the navbal; as you would when doing any other manoeuvrer, except you’re in ‘target’ mode.
Matt_W
1898
And if you’re using the Docking Port Alignment Indicator mod–which you should because the stock navball doesn’t give you all the info you need to dock–this is a rough, brief, but effective guide for using that:
https://forum.kerbalspaceprogram.com/index.php?/topic/40423-16x-docking-port-alignment-indicator-version-683-updated-030319/&do=findComment&comment=619937
The stock navball doesn’t provide an indicator that shows when your vessel is oriented parallel to the docking axis. You have to estimate this visually, which can be surprisingly hard to do. DPAI provides this as well as other helpful indications for docking.
A couple of real-life things to consider. I know these sound like dumb mistakes but trust me I’ve made them, sometimes twice.
-
Make sure docking ports are installed correctly. When I first start I thought there would be a male and female connector. That’s not right, the two males connect. Shouldn’t be a problem unless you a change the default orientation.
-
Have your view either on the chase or locked view. It is much easier to zoom and see what the problem is.
3 .Make sure the area around the ports is clear of potential obstructions. I put spotlights over my docking ports. (Even had Red, Green, Blue and White color lights at times). Unfortunately, I put the lights too close and the docking port on my lander hit the spollight. Just yesterday. I had surface mount antenna protrude over the docking port.
-
If you get with 5 meters there is magnet attraction to the ports so they will pull the ships together.
If you find that get with a 2 or so meters but it is still not docking try using the WASD to change the orientation. I’ve had to use those keys on more than 2/3 of my successful docking.
-
If you read the comments on Scott’s docking tutorial you’ll see there are a lot of frustrated dockers in KSP. (Also plenty of astronauts and cosmonauts were similarly frustrated in real life before they developed docking assistance tools).
Matt_W
1900
Make sure you’re within a couple of km, then:
- Set the other vessel as your target.
- Point your vessel heading at the retrograde indicator. (
). In target mode, the pro/retrograde markers indicate the direction of your velocity relative to the target. I.e., the prograde marker shows the direction you’d be moving if you fixed the other vessel in space and measured your motion in that fixed frame.
- Now you want to cancel out your target relative velocity. Burn until your velocity indicator on the navball shows zero. This will mean that you are not moving relative to the target.
- Point your vessel heading at the target prograde (
). The target should now be stationary and directly in front of your vessel.
- Burn until you have about 20 m/s of closing speed. Right after you start your burn, the target prograde ( ), prograde marker (
), and your vessel’s heading (
) should all be on top of each other. This indicates that you are pointing at the target and moving toward it.
- As you get closer, the orbits of the two vessels will curve their paths relative to each other, so you may have to repeat steps 2-5 a couple of times.
- Once you’re within 100m or so, set the target docking port as your target and your docking port as “control from here”, then follow Scott’s docking procedure, using RCS to translate around.
It’s been a while since I played, but my recollection is that the most helpful steps for docking are making sure that the docking ports are set as your target/control locations (so you can use the navball for alignment), and using the hotkeys for RCS thruster translational control. I want to say it’s ‘IJKL’ in conjunction with ‘U’ and ‘H’ for forward/back.
When you’re in docking mode can you use WASD plus U and H? or does that do something else? Even though I have small hands I need to do forward/back with a separate hand than the cardinal directions.
I finally have time today so I’m excited to redesign my refueler (which was a nightmare to control) along with trying to dock again. Biggest problem with refueler was accurate RCS because it is a little on the big and heavy side. If anyone wants to critique this monster:
Top section powered by 4 Nuke engines. One it’s about to dock it will stage separate and use RCS and/or mini thrusters to close in:
Drop off tanks powered by 4 SRBS’, 4 tanks with Mainsails, the center stage is powered by 5 Mastadon engines. It is surprisingly stable getting into Kerbin orbit. Getting to the Mun is a pain since the Nuke engines have such terrible TWR and I’m trying to send a rather large supply of fuel:
Big problem is apparently the one advanced inline stabilizer can barely rotate the craft in space without RCS. So I of course run out of RCS fuel. Those things that stick out? I thought it would be good to have the ports be further out from the craft so it’s easier to see/dock and instead of just having tubes I could have RCS tanks as the support beams:
Full thing on launch pad:
I use Stage Recovery hence all the parachutes.
