Need help on major problem I got with large shuttles re-entry to Kerbin

[SalehRam]

Hi,

I was able to build a large shuttle that I used to deliver a satellite and get my Kermas from my first station... the problem is, I got the shuttle stuck in space :D:D

My issue is with the re-entry...

1. I am not sure if it is normal and expected to consume ALL the fuel on the shuttle between getting out of the atmosphere and establish an orbit course around, then do rendezvous with a target... I end up almost 0 on fuel.
   
2. Being "very" low on fuel, so even if I got enough, the existing thrusters won't be able to push the shuttle to KSC if I end up far from it.
   
3. The semi-complex design of the shuttle make it super heavy for maneuvers and to fly it for long time.
   
4. I don't know yet how to make a re-entry and land on the KSC as well.
   
5. When attempt to re-enter Kerbin, the shuttle ends up falling at high speed and uncontrollable... I have read some about shuttles and how can we control them in Kerbin atmosphere, but I could not do it...
   

I have attached the shuttle I built, and I'm not sure if something is wrong with it or not... it is a bit tricky to handle it during launch and before getting rid of the large fuel tank... but it worked for me so far.

https://drive.google.com/file/d/0B4vxG7-rvmD2Ti0yMmplWDhJSW8/view?usp=sharing

Thanks for the tips and help!

Edited February 26, 2015 by SalehRam

[Empiro]

Well it sounds like you're off to a good start if you're in space.

I am not sure if it is normal and expected to consume ALL the fuel on the shuttle between getting out of the atmosphere and establish an orbit course around, then do rendezvous with a target... I end up almost 0 on fuel.

Being close to out of fuel is pretty normal. It doesn't take much fuel to make small changes while in low Kerbin orbit, and it only takes 50-100 m/s to de-orbit yourself. If you're totally out of fuel, then it sounds like you need to either bring more or figure out if you can have a more efficient ascent profile.

Being "very" low on fuel, so even if I got enough, the existing thrusters won't be able to push the shuttle to KSC if I end up far from it.

That's also normal. Real shuttles glide back and land without using fuel. It means that you'll need to use trial and error to figure out when to do your deorbit burn, however.

3. The semi-complex design of the shuttle make it super heavy for maneuvers and to fly it for long time.

4. I don't know yet how to make a re-entry and land on the KSC as well.

5. When attempt to re-enter Kerbin, the shuttle ends up falling at high speed and uncontrollable... I have read some about shuttles and how can we control them in Kerbin atmosphere, but I could not do it...

I haven't taken a look at your shuttle -- I don't have access to the game at the moment, so some screenshots would help. However, the general advice would be to make sure that the center of mass when empty is ahead of your center of lift, and to make sure you have enough control surfaces and lifting surfaces. In stock KSP, that just means adding plenty of wings and elevators. It might be too late if your shuttle is already in space though, which is why it's a good idea to do atmospheric tests ahead of time.

[capi3101]

In answer to #4 - a reasonably reliable method I use is one suggested in DocMoriarty's KSP Space Plane Construction and Operation Guide:

1. Set a marker out at KSC. Preferably, this is a set of flags set put on either side of the runway lengthwise (i.e. one on the ocean-side end of the runway, and one on the other side) - you can use the flag to check your alignment on the KSC Runway. Additional markers at 1, 5, 10 and 20 kilometers out on the landward end of the runway can be placed as well; this would give you a rudimentary ILS. If you've got a mod like NavUtilities, you just need a single mark for KSC itself. A powered probe core on the Launchpad will do just fine.

2. You want to put a maneuver node on the far side of Kerbin exactly opposite from KSC. You'll want to position it so that your craft will reach the node within one minute; for each additional minute of lead time, you'll need to add a lead angle of one degree.

3. Set the maneuver node to put your periapsis over KSC at an altitude of 44,000 meters. If you're at a higher orbit than 100x100, set the periapsis lower and vice versa (DocMoriarty suggests 45,500 for a 72x72 orbit, for example). Burn as indicated.

With this method I usually wind up in the situation where I'm subsonic (generally below 400 m/s) within 100 klicks of KSC. Done right you can glide right in; I've never accomplished that...

Bear in mind - this procedure works for the souposphere (i.e. stock aero). If you use NEAR or FAR, you'll need to make a series of tight turns as you approach to bleed off speed - otherwise you're going to wind up going WAY too fast, and won't be able to do much besides wave as you overshoot the runway...

I'll have to take another look at your shuttle to see what its flight characteristics are late in its flight. Depending on the design, your CoM could be shifting behind the CoL when you make your final burn for orbit, in which case a safe recovery is going to be highly problematic. The RCS Build Aid mod would be able to tell you if that's what's going on (it will show you your "dry center of mass", and let you know how much/in what direction the CoM shifts as you burn fuel); you could try that out with the orbiter in the SPH to see if that's what's going on.

[SalehRam]

Awesome tips guys, thanks a lot!

I'm going to do some test runs with a remote controlled shuttle and see how can I make this work...

Also thanks a lot for the re-entry method, which I'm sure will help a lot.

I'll post here with screenshots after I do the test runs, and will put the updated shuttle if I ever needed to modify it.

[SalehRam]

Ok, so I changed the shuttle, I was able to make it to orbit around 250km and now I am trying to get the best position to de-orbit and enter kerbin straight to KSC...

Here is the new shuttle I came up with:

https://drive.google.com/file/d/0B4vxG7-rvmD2SEdOOS1tRngweVU/view?usp=sharing

[theend3r]

Ok, so I changed the shuttle, I was able to make it to orbit around 250km and now I am trying to get the best position to de-orbit and enter kerbin straight to KSC...

Here is the new shuttle I came up with:

https://drive.google.com/file/d/0B4vxG7-rvmD2SEdOOS1tRngweVU/view?usp=sharing

It's a good practice to accompany craft files with pictures or post only pictures. I'm interested in other people's designs but usually not in downloading and testing them.

[SalehRam]

Here are screenshots for the shuttle

https://drive.google.com/folderview?id=0B4vxG7-rvmD2fmZNd1VybHJxUUFXYlF3Y3NudldQeEFTYzBIblItM0hiNWR0bXd3SWJuM2s&usp=sharing

[theend3r]

Here are screenshots for the shuttle

https://drive.google.com/folderview?id=0B4vxG7-rvmD2fmZNd1VybHJxUUFXYlF3Y3NudldQeEFTYzBIblItM0hiNWR0bXd3SWJuM2s&usp=sharing

Nice. The separatrons and RCS ports are a bit overkill though.

[SalehRam]

Nice. The separatrons and RCS ports are a bit overkill though.

I create action groups to enable and disable RCS ports as I see fit, and for the separatrons, that's the best combination I was able to come up with in order to prevent the parts from crashing into the shuttle while they separate...

Though I am still trying to find out the right alt to set my PE node on slow de-orbit maneuver, and so far I was able to narrow it down to 35km+/- for an orbit alt of 250km... the issue is, where do I position the PE node, is it right above KSC or ahead of it, as I get a different result every time for a reason I don't know...

[theend3r]

I create action groups to enable and disable RCS ports as I see fit, and for the separatrons, that's the best combination I was able to come up with in order to prevent the parts from crashing into the shuttle while they separate...

Though I am still trying to find out the right alt to set my PE node on slow de-orbit maneuver, and so far I was able to narrow it down to 35km+/- for an orbit alt of 250km... the issue is, where do I position the PE node, is it right above KSC or ahead of it, as I get a different result every time for a reason I don't know...

If you're not completely against modding the get the Trajectories mod. It will show you an approximate reentry trajectory. Still, it's better to complete your slow down some distance before KSP. I usually end my reentry just above KSP and have to do a turn to land.