Landing a Spaceplane at KSC

[Mr. Me]

NKS has been designing a pair of small passenger SSTOs, but there is one problem: I don't know how to land near KSC. I always end up having to land in the desert to the west (like, desert temple west). Anyone have some tips to achieve a pinpoint landing?

[Tex_NL]

How to land at KSC? Practice, practice, practice.

Next time pay close attention WHERE you start your de-orbit burn and how low you you drop your Pe. Then land wherever you can.

Lets say you've landed a quarter of Kerbin ahead of KSC. Next time perform the EXACT same de-orbit burn. But ... do it a third of Kerbin later than the first. Now you'll land a lot closer to KSC.
Also pay close attention to where the orbital path intersects the surface. By increasing or decreasing your AoA you can extend or reduce your flightpath.

[AeroGav]

https://www.youtube.com/watch?v=_buA6LODPTw 

A space capsule has no lift, only drag, so it's trajectory follows the ballistic line pretty accurately.  However, it will always undershoot the blue line, and land a bit before where it indicates you are coming down.   Once you've started re-entry,  you're pretty  much a passenger.

A space plane makes lift as well as drag,  and if it has a good lift drag ratio can glide much further downrange than the blue line indicates.  You can control your plane's lift:drag ratio by adjusting the angle of attack - that is the difference between where the nose is pointed and the prograde marker.      At speeds above 200 m/s, lift:drag ratio is best with the nose about 5 degrees above the prograde.  

If you think you are undershooting the space centre, keep the nose close to this pitch angle for best "glide".     It can stretch a very long way like this.     I've retro burned to 40km before, and my plane passed below 50km just as the sun was coming up.   Holding the best glide angle,  we went all the way round the planet one more time, dropping below 25km at 1300 m/s just as the sun was coming up AGAIN.    So your initial retro burn PE   and aim point aren't as important as the body angle you maintain during entry. 

If you start overshooting,  pitch up to a higher angle of attack, lift increases, but drag rises more than lift, so the glide ratio gets worse.   You can also lower the landing gear (for some reason , rubber tyres never burn up), and open cargo bays to really dirty the plane up.

To summarise, my preferred technique for easy, accurate landings -

1.  retro burn when you're on the opposite side of Kerbin to the space centre, to a PE of 20Km or less.

2. stay in map mode during re-entry, so you can see what's happening to your trajectory. Keep the navball visible rather than hidden so you can also monitor your angle of attack.  If worried about thermals,  mechjeb HUD can keep it at the top of your screen for you.

3. stay pitched up fairly high until your PE drops to ground level.  It will then start to move west.  I'd say slightly in the ocean off the west coast of the space centre continent is a good aim point,  lower the nose to  a better gliding angle to stop it going any further west.

4. once you get below 25km / 1300m/s you are an airplane again, go back to normal view.  

Edited February 15, 2017 by AeroGav
added vid

[Aegolius13]

Yeah,  trial and error is really the only way to figure out where,  and how much,  to burn.   Every plane will be abit different.   You may want to try the "Trajectories" mod, but it's not ask that accurate for planes since it doesn't know your intended angle of attack on reentry.

Even after you've dialed in your burn,  you may need to adjust your flying to fine tune things.  If it looks like you're coming up short, decrease your angle of attack to reduce drag.   It's also helpful to keep a bit of LF in case you need to run engines.

Conversely, if you're going to overshoot, try to maximize drag.   Increase angle of attack,  deploy flaps or airbrakes,  extend landing gear, etc.  You can also do back and forth turns just to reduce speed.  If you do overshoot the runway,  you can also just turn your plane around and land in the other direction. 

[Tex_NL]

14 minutes ago, Aegolius13 said:

Even after you've dialed in your burn,  you may need to adjust your flying to fine tune things.  If it looks like you're coming up short, decrease your angle of attack to reduce drag.   It's also helpful to keep a bit of LF in case you need to run engines.

Conversely, if you're going to overshoot, try to maximize drag.   Increase angle of attack,  deploy flaps or airbrakes,  extend landing gear, etc.  You can also do back and forth turns just to reduce speed.  If you do overshoot the runway,  you can also just turn your plane around and land in the other direction.

Depending on the situation the exact opposite may be true. Increasing the AoA can increase the amount of lift prolonging the flight. Reducing the AoA reduces lift and causes you to drop faster to denser air. Hence more drag and a shorter flight.
As long as you still pretty high up experiment and see what happens. Then adjust your behaviour to get the desired result.

Quick-saving while still in orbit can give you a second chance. Don't hesitate to (ab)use it.

[A_name]

Use the Trajectories mod, it will show you a red 'X' marker where you are predicted to land. If you want to keep it stock, trial and error is the only real way. This is because your landing spot will be influenced by a bunch of factors including the shape and size of your orbit and that of your craft. For a LKO, I usually burn over the deserts west of the KSC continent and aim for my orbit to touch the ground east of KSC on the peninsula that looks like Korea.

Additionally, if you're using a spaceplane, you have the advantage that you can significantly alter your landing spot by maneuvering in the air during descent. So keep switching to map view to see how your trajectory is behaving and adjust accordingly. As others mention, increasing your AoA (that is, pitching up or down, or sideways while banking) creates drag and slows you down. If you're overshooting, increase your AoA and if you're undershooting point more prograde to reduce drag. In the upper atmosphere it's all about drag. But as you hit the light blue part of the atmosphere meter, you'll start generating lift, so flexibility increases. Here you can make significant trajectory changes by maneuvering like a plane as needed.

 

5 hours ago, Aegolius13 said:

If you do overshoot the runway,  you can also just turn your plane around and land in the other direction. 

Or you can land on the island runway!

Edited February 16, 2017 by A_name

[Mr. Me]

Thank you for your answers. I will try the Trajectories mod when I get home tomorrow. @A_name, do you have a link?

[A_name]

3 hours ago, AeroGav said:

A space capsule has no lift, only drag, so it's trajectory follows the ballistic line pretty accurately.  However, it will always undershoot the blue line, and land a bit before where it indicates you are coming down.   Once you've started re-entry,  you're pretty  much a passenger.

@AeroGav Obviously you know what you're talking about, but I wanted to point out that's not entirely accurate. The later versions of KSP give body lift to capsules, and while the cross range capabilities of a capsule are nowhere near those of a spaceplane, you still have some margin for maneuvering, especially if you do your maneuvers while still in the higher atmo.

6 minutes ago, Mr. Me said:

Thank you for your answers. I will try the Trajectories mod when I get home tomorrow. @A_name, do you have a link?

 

[ajburges]

3 hours ago, Aegolius13 said:

Yeah,  trial and error is really the only way to figure out where,  and how much,  to burn.   Every plane will be abit different.   You may want to try the "Trajectories" mod, but it's not ask that accurate for planes since it doesn't know your intended angle of attack on reentry.

Even after you've dialed in your burn,  you may need to adjust your flying to fine tune things.  If it looks like you're coming up short, decrease your angle of attack to reduce drag.   It's also helpful to keep a bit of LF in case you need to run engines.

Conversely, if you're going to overshoot, try to maximize drag.   Increase angle of attack,  deploy flaps or airbrakes,  extend landing gear, etc.  You can also do back and forth turns just to reduce speed.  If you do overshoot the runway,  you can also just turn your plane around and land in the other direction. 

Actually, trajectories is pretty good prediction these days. You just need to program and follow your flight path. I use horizonal AoA for entry and high atmo to plan burn. By the time you hit low atmo you have lower cross-range anyway.

[foamyesque]

One thing I've found useful is to maintain a consistent deorbit pattern -- 100km -> 45km, in my case -- from a known point on Kerbin, with certain speed and altitude markers as I cross various landmarks (either side of the ocean, then the mountains to the west of KSC). Since I also tend to build all my planes to have fairly similar flight characteristics, I can see whether I'm above or below my targets and adjust AoA and heading accordingly.

[Mr. Me]

Thank you for your answers. Thanks to the trajectories mod, the Freebird was able to land at KSC and will go on sale at NKS soon.

[ForScience6686]

I recommend setting beacon at the runway.  Then burn to bring my trajectory into the ocean at about the islands.  Where you burn depends on your craft, but I usually do it at the continent to the west just before crossing over the ocean before the peninsula (if that made sense).  Hold a high aoa in the way in, and adjust pitch to control trajectory.  The key is to get below 1400 m/s at 35km.  From there you, glide to the runway.  If you're coming in shallow, adjust for maximum glide, if too high, roll over and pull back to decrease speed and altitude.  Watch the map view, at maximum glide your ap will begin to catch back up to you.  Use your beacon to control descent, I keep my prograde almost on top of the target marker, usually slightly below.

 

I build all my space planes for this reentry, it is the most effective and fastest at getting me to the runway.  I have a couple designs that can do this from a 600km orbit.  

[Whisky Tango Foxtrot]

I have two SSTOs that I use regularly; one for passengers and one for cargo. Each plane always follows the same mission profile, with the passenger one going straight to my space station (at 250km elevation) and my cargo ship skimming the atmosphere in LKO, with both craft always staying in an equatorial orbit. Therefore, to make reentry easier, I used the KerbNet to mark the place where the two craft should do their retro-burn to lower their periapsis to 40km. It took a few tries to get the positions right, but once I got them it made things a lot easier. My exact position when I finish reentry still tends to vary a bit depending on what AoAs I used coming down and how much fuel/cargo I'm carrying, but they usually get me close enough that I can compensate for any errors by adjusting my glide angle or briefly re-activating my jets.

Edited February 18, 2017 by Whisky Tango Foxtrot