Re entry target KSC?

[Elroy Jetson]

Guys,

 

I'm looking for some basic seat of the pants tips to narrow down my landing zone.  im really most interested in landings back on kerbin near KSC to maximize my refund on parts.  Is there an eyeball method or does this require sophisticated maneuver node stuff?

i have tried to estimate the atmosphere and deceleration to come close, but I usually don't even land on the correct continent.

[bewing]

The basic stock answer is that you need some level of aerodynamic control over your RV. You have to fly your way back down in something resembling an airplane/glider.

Secondary stock answer is to reduce your reentry speed with a strong retrograde burn. The slower you are going, the more accurately you can eyeball it. A variation on this theme is to retroburn a bit, come in high and fairly fast still pointed retrograde, and do a second retroburn to <250 m/s surface velocity while you are over KSC and pop some chutes.

Third answer is a variation on both methods. When you are ascending, you need low aerodynamic drag. When you are descending,  you need high drag. To change your drag configuration, you need deployable control surfaces. So you put some deployable control surfaces on your RV. Before you reenter, you set their authority to 150 (max). As you approach KSC, you deploy the control surfaces (in opposite directions is best). This creates huge drag, puts you in an uncontrollable tumble, and drops you out of the sky on top of KSC. (If you think you might be slowing down too much, you undeploy the control surfaces again.)

As I recall, you are playing on xbox? In that case, mods can't help you (but there is one).

 

Edited March 7, 2019 by bewing

[Elroy Jetson]

Ya, I'm on PS4 so no mods for me.

lets say I'm in a reasonable circular orbit about 95k or so with an average velocity that I would have from a local orbit, I don't remember what that is, 2300 or something like that?  If I have enough fuel to do a de orbit burn but not a lot extra, is there a best location to start the burn reference to my desired touch down?  

 

once in a while I get close...

[Rocket In My Pocket]

42 minutes ago, Elroy Jetson said:

Ya, I'm on PS4 so no mods for me.

lets say I'm in a reasonable circular orbit about 95k or so with an average velocity that I would have from a local orbit, I don't remember what that is, 2300 or something like that?  If I have enough fuel to do a de orbit burn but not a lot extra, is there a best location to start the burn reference to my desired touch down?  

 

once in a while I get close...

I usually just eyeball it.

Can heavily depend on the vehicle itself though, and your return profile amongst other things. Can you use the debug menu on console? I like to teleport my spaceplanes up and test them in a de-orbit a few times to get a feel for it.

I don't typically concern myself with landing ballistic return vehicles like those commonly found on rockets near the KSC as they aren't worth recovering anyways given so little of the original vehicle (and thus cost) is left by the time it returns from space. SSTO's and/or spaceplanes are a different story though as you stand to gain a lot by recovering them closer, my rule of thumb is starting the burn 1/4 to a 1/5 of the total planets circumference before the KSC; when it comes to anything with wings. Then I drop the Pe to 0 right on top of the KSC.  Atmo heating is fierce, but brief, and once you are done riding that out, you can start dialing in your approach to the KSC and refining it visually. (That it works for me and my designs is no guarantee it'll work for you and yours though. Lol.)

Edited March 7, 2019 by Rocket In My Pocket

[bewing]

You might want to do a search on the term "ballistic coefficient", and read a bit.

The point is that it depends completely on your craft.

A high mass, low drag craft will sail for many kilometers past your aim point. A low mass, high drag craft will fall out of the sky way before you expect it to.

So no, it's a lot trickier than just picking a burn reference. In any case, you pretty much always want to do your deorbit burn on exactly the opposite side of Kerbin from KSC, but the important part is picking the right Pe for your burn. A Pe of 30km to 35km is often a wise choice.

One trick you can sometimes do is just before reentry, you start your craft spinning. This can increase your drag a bit, and slow you down some. It's not a big effect, though.

Edited March 7, 2019 by bewing

[Curveball Anders]

I usually cheat by taking note of my pos and doing a quicksave before my re-entry burn.

Then I check the diff between my landing and my start, and how off I was.

Reload and redo the reentry burn at the calculated pos.

 

[Grogs]

4 hours ago, bewing said:

So no, it's a lot trickier than just picking a burn reference. In any case, you pretty much always want to do your deorbit burn on exactly the opposite side of Kerbin from KSC, but the important part is picking the right Pe for your burn. A Pe of 30km to 35km is often a wise choice.

While I agree that's most efficient in terms of delta-V, it makes it a lot harder for a precision landing IMO. If I have the fuel (and by this point in the mission I know if I do), I'll usually make my de-orbit burn ~ 30 degrees before reaching KSP, and then have the intersect point with the surface be ~ 2x the distance to the island past KSC.

4 hours ago, Curveball Anders said:

I usually cheat by taking note of my pos and doing a quicksave before my re-entry burn.

Then I check the diff between my landing and my start, and how off I was.

Reload and redo the reentry burn at the calculated pos.

 

And then I do this. De-orbit burn, save, re-enter. Then reload and burn a bit more if I'm long. Or burn (anti)normal if I'm missing left/right.

 

A couple of other things:

- Don't pre-deploy your chutes (i.e., have them on the same stage as the final stack separator). That way you can deploy them early if it looks like you're going to overshoot, and wait a bit if you're not.

- Make sure you're in an equatorial orbit since KSC is right on the equator. I usually do this by setting the Mun as my target and making sure the ascending/descending nodes are at 0.0 degrees.

[Gargamel]

On 3/7/2019 at 12:56 PM, Curveball Anders said:

I usually cheat by taking note of my pos and doing a quicksave before my re-entry burn.

Then I check the diff between my landing and my start, and how off I was.

Reload and redo the reentry burn at the calculated pos.

 

This is where I usually start from.  I'll do a couple re-entries as test with various space craft, and then figure out then best approach that covers most of them

Usually, it works out that I start burning over the last part of the Desert continent, and then wait till the orbit line reaches just a bit beyond the string of islands East of KSC.  So roughly a 300 dV burn, give or take a hundred.   That usually get's me fairly close.

But when I've gotten my program down to using the same class of vessel for most trips, I'll have their re-entry profile pretty well figured out.   The issue becomes nailing it the same way every time.    To this end, I'll make a plane that has buoys it can drop while in flight.   I'll fly due East from the KSC and then drop the two buoys at the edges of where I want the orbit line to be when I re-enter.   That way, on the map view, I'll have a "gate" that I put the orbit line into and I'm usually within 10km of the KSC every time, usually much closer.   This method has landed me on various buildings a number of times. 

But the key is to do the same thing every time.   Have the same identical re-entry sequence planned for every vessel.  Some here have said don't deploy your chutes early, well I do.   It doesn't matter, as long as you setup your plan to do the same thing every time.  That way it is repeatable, and easily adaptable to new craft.

3000th post.  yay!

Edited March 8, 2019 by Gargamel
typos

[TheFlyingKerman]

Combining with the tricks above. If the craft has some wing, and the wing has AoA, it would tend to generate lift and land beyond the projected impact point. Otherwise it tends to land short due to drag. One can manipulated this difference the get a controlled landing. Give this a trial for example

https://kerbalx.com/TheFlyingKerman/Simple-reusable-lifter-S-2B

 

[Tyko]

If you're just in low Kerbin orbit my trick is to do my de-orbit burn right over that giant crater about a 3rd of the way West around the planet. Drop your PE to about 35km when you're right over that and it'll put you close to the KSC.

Edited March 11, 2019 by Tyko

[Cheif Operations Director]

If your going for a medium to steep re-entry angle aim for the islands 30 km from the KSC coast. Planting a flag thief is useful. If you come in at high enough speed you should land within 30 km of that island and if your orbiting West to east them within 15km of the space center. You can make a maneuver node and plan by just holding down retrograde until it is on the islands and you should have a pretty precise landing zone. The shallower your de-orbit angled the farther west you will land (assuming your going west to east) 

[Aeroboi]

On 3/7/2019 at 6:36 PM, bewing said:

*snip*

The point is that it depends completely on your craft.

A high mass, low drag craft will sail for many kilometers past your aim point. A low mass, high drag craft will fall out of the sky way before you expect it to.

I can completely relate this. On top of this wing incidence helps even further in this regard. It lowers the drag co-efficient of the vessel while it sinks through the atmosphere. When coupling a craft with several degrees of wing incidence while holding prograde is a usable idea. Through this way you can burn 1/2 away from the ksc with a periapsis of let's say i.e. 50km (could be 30 aswell)

If the spaceplane is aerodynamic while having mk1, mk2, mk3 fuselage parts, heat resistant parts, wings and landing gear and everything else in a cargo bay it can maintain close to orbital velocity nearing the ksc while dipping down to ~30km altitude. In that case you can pitch up when nearing the ksc to do a massive aerobrake (many g's involved)

I have a couple of such spaceplane that do this and it's a way to dead stick your aproach to the ksc easily.

If using a capsule it is trickier. It's best to dip down low by creating a longer retrograde burn then a typical lowest one. The consequence for this is that you have to do your burn somewhat earlier compared to the least efficient one which is a burn just enough to get into the atmosphere. You can install reaction wheels so you can pitch a few degrees. Heatshield have a lot of drag and a pitch angle can create a skipping effect to either elongate or shorten your aproach.

Use quiksave first so you can try again if your first attempt fails.

Remember that many people in the youtube videos re-capture their attempts to get the successful aproach.

Or they couple it with the trajectories mod, mechjeb or other instruments while having the UI shut down (F2)

[Cheif Operations Director]

8 minutes ago, Aeroboi said:

I can completely relate this. On top of this wing incidence helps even further in this regard. It lowers the drag co-efficient of the vessel while it sinks through the atmosphere. When coupling a craft with several degrees of wing incidence while holding prograde is a usable idea. Through this way you can burn 1/2 away from the ksc with a periapsis of let's say i.e. 50km (could be 30 aswell)

If the spaceplane is aerodynamic while having mk1, mk2, mk3 fuselage parts, heat resistant parts, wings and landing gear and everything else in a cargo bay it can maintain close to orbital velocity nearing the ksc while dipping down to ~30km altitude. In that case you can pitch up when nearing the ksc to do a massive aerobrake (many g's involved)

I have a couple of such spaceplane that do this and it's a way to dead stick your aproach to the ksc easily.

If using a capsule it is trickier. It's best to dip down low by creating a longer retrograde burn then a typical lowest one. The consequence for this is that you have to do your burn somewhat earlier compared to the least efficient one which is a burn just enough to get into the atmosphere. You can install reaction wheels so you can pitch a few degrees. Heatshield have a lot of drag and a pitch angle can create a skipping effect to either elongate or shorten your aproach.

Use quiksave first so you can try again if your first attempt fails.

Remember that many people in the youtube videos re-capture their attempts to get the successful aproach.

Or they couple it with the trajectories mod, mechjeb or other instruments while having the UI shut down (F2)

The problem is that the aerodynamic nosecose will blow up if you are not careful I have flipped many a shuttle while trying to prevent overheating. As soon as that nose cone breaks the game is up. Aerodynamics are ruined then  the cockpit will explode

Edited March 9, 2019 by Cheif Operations Director

[Superfluous J]

This one works on pretty much any world with air. Including Kerbin of course.

1. Quicksave.
2. Do your deorbit burn over a landmark that you can find later (I like the morning terminator)
3. Let your craft deorbit in a repeatable way. "Aim retrograde" if possible to eliminate any nonreproducible drag variances.
4. Note where it is in relation to where you burned.
5. Quickload.
6. Do your deorbit burn the distance you observed in step 4, behind your desired target. It goes without saying (but I'm saying it anyway) you need as close to exactly the same Pe as you did in step 2.
7. Profit!

Edited March 9, 2019 by 5thHorseman

[Scarecrow]

For a basic seat of the pants from a low orbit, I will do my de-orbit burn when I am over the continent just to the west of the KSC continent, at the part where I am just about to head over the ocean between the two.  I look to have my initial touch down point roughly double the distance from the KSC as the KSC is from the Island runway.  For a light ship this usually drops me back to the ground between the KSC and the mountains to the west of the centre.  A heavier craft will land a bit closer.  If you push the initial touchdown point a little further away, you can overshoot KSC for a watery splash down.

[Jaime]

Try the trajectories mod It's been a lifesaver for me (and my Kerbals )

[Dafni]

12 minutes ago, Jaime said:

Try the trajectories mod It's been a lifesaver for me (and my Kerbals )

OP said he's on console, no mods for him.

For the PC folks, and for completeness sake, Kerbal Engineer Redux now has an impact marker too.