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Little Kerbonaut!

How do I Land at KSC

Question

So I built a Falcon Nine with a reusable booster and I want to find out hoe to land the booster back the KSC. But I don’t know how to do it does anyone else know how?

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It's really hard to do in the stock game. To be able to land your booster, you may need something like the FMRS mod.

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Are you turning the rocket around then thrusting back ward or are you getting all the way into orbit? I'm assuming suborbital here, so I dunno try this.. Take note of your surface velocity on the launch pad (rotational speed of surface of kerbin), launch, then once at booster turn-around point, pause the game and add your current surface velocity while in space to kerbins' surface velocity and retroboost to that total velocity? I dunno if that would work as I haven't done it myself, but I am curious to know if it'd work :P 

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I've got lazy and use the Trajectories mod these days.  However, with a bit of trial and error you can get the right trajectory back to KSC by retro burning almost the other side of Kerbin.

The technique is ideally from a perfect 80x80 equatorial orbit (line yourself up the the Mun as target is easiest) ideally with less than 200dV so you have a good TWR for later.   A lower apoapsis will mean you reenter sooner after the burn, meaning more atmospheric drag, so your periapsis will need to be higher.  I find it easiest to disable 3/4 of my engines so I don't have too much uncontrollable TWR at this point and the suicide burn later - remember you've burn most of your fuel on ascent.

  1. Set a manoeuvre node over certain continental features on the other side of Kerbin from KSC.   You need a retro burn to bring your periapsis down to maybe 30km over a spot on the next continent past KSC. (This depends on your vessel's weight and drag.  eg A heavier vessel with more fuel on board may need a lower periapsis.) Save at this point, so you can return and repeat with any necessary tweaks.
  2. As you re-enter, stay pointed retro all the way, your periapsis will move away from you as air resistance slows you and alters your orbit.  It will eventually disappear below the surface further round Kerbin.   Your trajectory will keep getting gradually steeper, more so as you hit thicker atmosphere.
  3. When you're below 1000m/s you know a landing is imminent and it's best to switch to landscape radar altitude (rather than sea level altitude).  It may be useful to save at this point in case your targeting is good, but the suicide burn goes wrong.  If only SpaceX had this facility for real life!
  4. With nerves of steel, wait until around 2000m, at 200-300m/s, for your suicide burn. (Highly dependent on your TWR - I usually have disabled most engines and still have a high TWR.)
  5. Deploy landing gear (if you have any), stay retro until your speed is ~5m/s, throttle down and hit radial out in case you've overcooked it.  There's no shame in landing with 50m/s of dV after having slowly descended the last 50m, way better than leaving a new crater!  Beware of using up all your dV with a long slow burn, though.  Make a note of what throttle setting gives you the fastest deceleration within a manageable time period for landing, it may be useful to adjust your engines' thrust limiters accordingly, or enable/disable some on larger vessels.

Expect to be way off on your first attempt, but you can crudely refine this by adjusting the periapsis height of your re-entry burn node and repeating the process from your save in step 1.  Less altitude will bring your landing closer west, more will push it further east.  Try 500m increments first if you're 10's of kms off.  Tuning of the landing point can be achieved either by subtle adjustments to periapsis, or by moving your burn node and hence periapsis east or west.  Finally, airbrakes or a small burn gives you some good control of landing site.  I found airbrakes have most effect in this respect between about 1500-300m/s so use sparingly.

I've yet to find an effective way to affect north-south alignment once in atmosphere other than using aerodynamics.  It's so much easier to steer a spaceplane in this respect, so small winglets or fins can be helpful if you're bothered about that aspect.

I hope that helps, happy landings!

 

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Posted (edited)

Go into/start in high orbit, like maybe 200km.   Then use a manuever note to calculate a very steep entry near the KSC, ideally as close to 90 degrees with respect the surface as you can get.  Since your entry is steep, you don't lose much lateral position due to drag.  The height required depends on how powerful your retrograde burn is.

You might also need to burn retrograde during descent to prevent the craft from burning up.

Edit: So I can see specifically say Falcon 9, probably you wouldn't have enough fuel for my approach. 

Edited by SJC_Hacker

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3 hours ago, SJC_Hacker said:

You might also need to burn retrograde during descent to prevent the craft from burning up.

Very much yes. :confused:

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I use FMRS for the "go-back-in-time" aspect, and KER to see where I'm going to land.  It puts a giant bullseye on the ground where it expects you to land.  Not quite as accurate as Trajectories, but if all you're doing is a boostback to the KSC, it's close enough.

I know the thread title is old, but if you click on the first link for the github fork, it has an updated version.

 

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Yes, as @bewing says, it's extremely tricky to safely land a first stage from a suborbital trajectory within atmosphere while getting your upper stages to orbit.  You have to have so much TWR on your second stage that you can significantly boost its apoapsis quickly before you're out of physics range to switch back to the first stage.

Fortunately, KSP scales are such that a Falcon-9 like booster can easily be an SSTO, release it's payload and go back to KSC.

I've been tempted to try FMRS but always found ways to SSTO anything I wanted to recover, which in my experience is a whole lot easier.

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What I have been doing is separating my booster and quickly plotting a maneuver with the second stage and getting it into orbit then trying to landing I haven’t had any successful attempts of landing it so I don’t know if it completely works yet.

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28 minutes ago, Little Kerbonaut! said:

What I have been doing is separating my booster and quickly plotting a maneuver with the second stage and getting it into orbit then trying to landing I haven’t had any successful attempts of landing it so I don’t know if it completely works yet.

Sounds like you've got the process down. What kind of trouble are you having with the booster landing?

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Umm not blowing up half of the engines on reentry and slowing down the booster enough.

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2 hours ago, Little Kerbonaut! said:

Umm not blowing up half of the engines on reentry and slowing down the booster enough.

Stick on some airbrakes.  If the booster blows up, add more.  If the airbrakes are overheating, retract them for about 3 seconds.

I did a whole bunch of booster recoveries in this thread, if you want some examples of successful booster returns.

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I have four aerobrakes on it and I deploy them when I enter the atmosphere but it doesn’t always work.

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I find multiple Vectors on an engine plate seems to be the best way to do it, I never have any problem with overheating whereas every other engine configuration I've tried tends to explode.

Unless you use FMRS,l doing a SpaceX style return means you need to have good timing to boost the upper stage, switched back to the first stage and land it, then switch back to the second stage to circularise.  Personally I prefer to build a VTOL SSTO, and either bring it down on the next orbit, or dock a returning module to it for it to bring back down.

I do something a bit closer to Blue Origin, with small wings to help the glide on re-rentry, and with Trajectories and kOS I can put them down on the runway reliably but getting them to land on the pad is a lot harder.

 

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I use four aerobrakes and some fins on the bottom of the craft to help slow down on landing.

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