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How the hell do I return my SSTO to kerbin without any damage


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I made a neat little SSTO which can haul big sattelite into LKO but I can't deorbit onto kerbin without breaking things, if I aim prograde it just keeps going faster and my top wings burn up, tried adding airbrakes they burned as well, and when in dense air everything starts rotating, I can land safely for kerbals but i blow something up always (mostly engines) This is my SSTO, basic design and gets job done but that landing is pain in the ass, I tried moving fuel to the front because of empty cargobay but I Need more fuel or it is comlpetly useless EDIT: mass of satellite changes COM almost by nothing220200_screenshots_20170215191231_1.jpg

 

Conclusion  As I expected problem was in vessel I made second- differently designed (thanks for tips @AeroGav) SSTO better control overall tested it out with similiar cargo everything went as expected

 

Edited by Numerlor
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I don't really have experience with spaceplanes, but from what I can tell there aren't really many options for increasing their heat resistance. Many spaceplane builders I know simply use the cheats menu to turn off temperature destruction, though I'm not sure that's the answer you want to hear.

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well that is bad, this is my first real spaceplane and I don't like idea of cheating much, maybe I'll just keep crashing but keeping them alive at least I won't waste time on landing :D

Edited by Numerlor
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Contrary to common expectations, best reentry profile with Spaceplanes (as with Space Shuttle IRL) is to keep a very high Angle of Attack. 40° generally works fine, but in KSP even 90° AoA can be attempted. Presenting the largest surface to the airflow actually causes more drag, but while air density is still thin that is bearable, while airspeed gets greatly reduced; therefore when the spaceplane finally descends at altitudes where air density is high enough to be a factor, its speed is much lower. Drag is directly proportional to air density and to the square of airspeed, so reducing the latter while still high is very beneficial to reducing drag later, and with drag both the thermal and physics effects on parts.

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Re-entry is a hard thing I can say. But the idea of you reentering is all about velocity and your trajectory. For example: if you have steep trajectory (straight fall down) you will burn up, if your trajectory touches the atmosphere but not the surface you might end up with fried to death both kerbals and spaceplane. So try to leave not so much speed, but don’t bleed it of completely and you will re-enter normally with no horrible explosions and kerbal deaths

But if the problem is not in the trajectory ,try redesigning your space plane and  hide all the small pieces covered (they blow up first)Engines are not easy to hide but try fairings and stuff like that,you can even place the engines into the fuselage

Also if you can’t land normally just cover whole spaceplane in parachutes and job well done. Now you don’t even need to aim for KSC. But if you are a “cool pilot” and always attempt to land at KSC you should replace your wheels (they fail the most).

i hope it helped you a bit....

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My re-entry profile for Mk2 spaceplanes is this:

1.) Get into LKO.  Serious.  Dont' try re-entering directly from Mun, Minmus, and certainly not inter-planetary.  You want orbital velocity <2.5kms
2.) Retro-burn to place your PE at ~45km.  You want to bleed off most of your speed -above- this altitude.
3.) Orient prograde with the highest angle-of attack that your plane can do.
4.) Bleed of speed in the upper atmosphere.  Let the aerobraking drag your AP into the atmosphere.  You might even see your AP increase a few times depending on your AoA (skipping off the atmosphere).  PE will continue to decrease due to drag and loss of speed/energy.
5.) Patience.  It might take 3/4 of an orbit or more to re-enter (depending on drag profile).  This is -not- a precision method.  Eventually you will be going slow enough that you'll just kind of fall down into the thicker atmosphere where you can start flying like a plane again.

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I'm not a big spaceplane builder, but I've made a few.  I've never used the cheat menu for re-entry or general gameplay.  Of course this may be a consequence of not having made a large spaceplane in a while.  The bigger, the worse the ballistic co-efficient

What is your decent profile?  You may be going in too quickly.  I usually set my PE to about 35 km and that gets me through OK.  You may want to try keeping it up, and doing the high AoA trick to keep lift up.

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Those top fins have half the max temperature of the side ones (in Kelvin); they're more suited to building airliners than re-entry. It's going to be extremely difficult to prevent them from burning up regardless of your re-entry profile. Try replacing them with duplicates of the side fins.

http://wiki.kerbalspaceprogram.com/wiki/FAT-455_Aeroplane_Tail_Fin - 1200 K (926° C)

http://wiki.kerbalspaceprogram.com/wiki/Big-S_Spaceplane_Tail_Fin - 2400 K (2126° C)

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Tried with 40° angle of attack (maybe I overdid while I was not looking) but I started turning, again. Worst thing Is I always forget to autosave in space and I don't want to make boring ascent over and over and over and over again, so I give up for today I'll try method @Shadowmage  suggested

Edited by Numerlor
Suggests or suggested? Who knows but suggested sounds better in this case
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1 hour ago, diomedea said:

best reentry profile with Spaceplanes (as with Space Shuttle IRL) is to keep a very high Angle of Attack. 40° generally works fine, but in KSP even 90° AoA can be attempted.

I often employ the radial out setting of SAS to keep the reentering spaceplane on maximum drag in the highest layers of the atmosphere. Just keep in mind: if your spaceplane in low fuel circumstances doesn't tend to point prograde by itself, you need to know to pitch down before the drag gets too high.

An additional tip, to help with the structural integrity: If you have the advanced settings on, a rightclick on parts will show setting 'Autostrut: Disabled'. Click on it to toggle to other options that will reinforce your craft. It may also help you need much less external struts, which would improve the aesthetic and the aerodynamics of your craft.

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10 minutes ago, swjr-swis said:

I often employ the radial out setting of SAS to keep the reentering spaceplane on maximum drag in the highest layers of the atmosphere. Just keep in mind: if your spaceplane in low fuel circumstances doesn't tend to point prograde by itself, you need to know to pitch down before the drag gets too high.

An additional tip, to help with the structural integrity: If you have the advanced settings on, a rightclick on parts will show setting 'Autostrut: Disabled'. Click on it to toggle to other options that will reinforce your craft. It may also help you need much less external struts, which would improve the aesthetic and the aerodynamics of your craft.

i like to do struts myself and from what I know and according to ksp wiki struts are physicsless part

Edited by Numerlor
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1 minute ago, Numerlor said:

i like to do struts myself and from what I know and according to ksp wiki strjuts are physicsless part

Physicsless parts still add mass and drag to your craft; from the link you cited:

Quote

The mass of the part and the drag experienced by it are added to the parent's part. The part itself has no mass but it still contributes to the vehicle's mass.

 

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36 minutes ago, HebaruSan said:

Those top fins have half the max temperature of the side ones (in Kelvin); they're more suited to building airliners than re-entry. It's going to be extremely difficult to prevent them from burning up regardless of your re-entry profile. Try replacing them with duplicates of the side fins.

http://wiki.kerbalspaceprogram.com/wiki/FAT-455_Aeroplane_Tail_Fin - 1200 K (926° C)

http://wiki.kerbalspaceprogram.com/wiki/Big-S_Spaceplane_Tail_Fin - 2400 K (2126° C)

I like building fins out of strakes, since they hold fuel.  But then again, the OP doesn't need much LF tankage as he doesn't have any nuke engines.   If he was concerned with that, he'd have chosen big S wings I'm sure.

20170115153518_1_zpsdp6pfeez.jpg

Re: Tumbling/stability 

Recommend he download RCS build aid, all his engines are at the back, I'm worried that CoM might move forward ahead of CoL after the cargo is gone and most of the fuel burns off.

The above ship has passenger cabins and mining gear at the front to balance the weight of the engines,  a straight cargo ship needs some engines further forward to balance it full & empty, like this

20170115201301_1_zpszqmzcd5x.jpg

I also recommend the OP swap to inline cockpit.   After the tail fins, the next most vulnerable part is that pointy cockpit , because parts at the front get most of the heat.  

As regards re-entry attitude, craft design is most of the story, there are downsides to every flight profile.    If heat is the primary concern, (rather than actually coming down near the space centre),  hold 20 degrees nose up the moment you drop below 70km, and lower the landing gear for extra drag.   You can also open the cargo bays for extra drag but in some designs that causes tumbling.    If things get desperate (ie. about to blow) you can start tumbling deliberately as it spreads the heat around.   But up to that point you're better off maintaining a high lift, high drag, but not stalled condition.  When you tumble, there is no lift and you develop a high rate of descent, so it's best not to start tumbling 70km up.

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18 minutes ago, AeroGav said:

I'm worried that CoM might move forward ahead of CoL after the cargo is gone and most of the fuel burns off.

I also recommend the OP swap to inline cockpit.   After the tail fins, the next most vulnerable part is that pointy cockpit , because parts at the front get most of the heat.  

Cargo doesn't change CoM Much as I said before, but I forgot to check fuel so I'll do that , and My concern isn't heat, I just want to land nicely and not damage any part doing that or at least go into flight instead of turning like if you pressed S, D and Q at the same time, only things that sometimes burn up are those tail fins but those aren't my main concern now because I have bigger problems than turning

BTW What resolution are you playing on? or did you just pump up the scale of GUI?

Edited by Numerlor
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23 minutes ago, Numerlor said:

 

BTW What resolution are you playing on? or did you just pump up the scale of GUI?

If you lose your tail fins your craft won't have any yaw stability, and yawing leads to the wings on one side getting more air than the other hence rolling etc.

I've only got a weaksauce 720p monitor but i did increase the size of the GUI to max in game options.  Firstly because I like watching my Kerbal's expressions and second the Bandicam watermark makes it hard to see the altimeter in my game videos unless it's huge.

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11 minutes ago, AeroGav said:

If you lose your tail fins your craft won't have any yaw stability, and yawing leads to the wings on one side getting more air than the other hence rolling etc.

While that is true, I don't have stability on any of 3 axes so yaw doesn't do as much

Edited by Numerlor
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First thing: as mentioned, you are exposing 1200 skin tolerance parts to the shockwave. That makes it hard to preserve them. If you are flying an efficient profile on RAPIERs or Whiplashes, they shouldn't even make orbit!

Second thing: it's not widely recirculated, but space planes do not do well with compromise reentries. Skimming at 45 km is the most hazardous entry because you maximise time going fast in low drag high temp regions. This allows the heat the skin takes to soak into the body and destroy stuff. Some designs can handle the compromise solution and gain some  flight efficency, but it is the most demanding rentry thermally.

There are two common safer re-entry profiles: spend some orbits above 55 km to bleed energy in the cool region or set Pe ASL and race to the cooler regions in a cobra manuver. I only have experience flying the second. The race down works well because the thermal profile you see in it is very similar to an efficent SSTO spaceplane launch. It does cost more dV to initiate though.

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12 hours ago, Spheniscine said:

Many spaceplane builders I know simply use the cheats menu to turn off temperature destruction, though I'm not sure that's the answer you want to hear.

I want to be rude and say "get gud nub" to this line of thinking, but we were all there once, and this forum is great for getting through that rough patch.

I like to design spaceplanes so their CoM doesn't shift at all regardless of fuel usage and payload (RCS Build Aid is the essential tool for this), tuck the CoL close behind the CoM, and make sure the craft has lots of reaction wheel (and lastly, hide all low-temp parts in cargo or service bays).  This allows re-entry with SAS set to radial-out (ie 90 degree angle of attack), maximum area exposed to drag, and stop-on-a-dime re-entry profile.  With a couple practice runs, all my ships drop to ~1000 m/s over the mountains west of KSC at around 25-30km.  Drop the nose, dive toward the grass, do a hard pull-out (watch out for tourist G-limits!) to dump speed, and float down onto runway 09.

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5 hours ago, ajburges said:

Second thing: it's not widely recirculated, but space planes do not do well with compromise reentries. Skimming at 45 km is the most hazardous entry because you maximise time going fast in low drag high temp regions. This allows the heat the skin takes to soak into the body and destroy stuff. Some designs can handle the compromise solution and gain some  flight efficency, but it is the most demanding rentry thermally.

There are two common safer re-entry profiles: spend some orbits above 55 km to bleed energy in the cool region or set Pe ASL and race to the cooler regions in a cobra manuver. I only have experience flying the second. The race down works well because the thermal profile you see in it is very similar to an efficent SSTO spaceplane launch. It does cost more dV to initiate though.

Spending time high makes reentries take forever, and IME the sharp drops tend to cause aerodynamic loading issues. 45km is my usual target for spaceplanes because with my usual AoA and wing loads, it's over reasonably quickly and a test-flight to 100km x 100km followed by an immediate deorbit burn to landing will almost always put me over a gigantic continent to test the landing on. :D

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IMO, I prefer the steep descent.  I set my trajectory to enter the ocean near the islands, hold a high aoa and hold on.  You can use your aoa to adjust your descent to make the runway.  This method needs a high drag profile to be able to slow down in time, but I never encounter issues in my builds.  It will also require a lot of fuel for deorbit.  However, I can always hit the runway for recovery.  If you're coming in too high, remember you can always roll over and pull back to point the nose down, this way drag is still a factor while the lift from the wings well decrease your altitude faster.  Basically, if you can get below 1400m/ s @35km, you'll be safe.

I even have some designs that can deorbit directly to the runway from 600km orbit.  

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