Spaceplane Reentry

[Geromey]

So, something occured: I`ve built a Space shuttle using stock parts because I dont really like mods that add lots of parts because these parts will then just fill up my parts list and once I uninstall them some tiny part

will **** my whole craft up.

- SO, I get to an altitude of 100KM to deploy a Sattelite.

- The Sattelite gets into orbit and I am happy.

- Then I try to get back into the atmosphere as shallow as I can so the reentry wont rip my Kerbals apart.

- During my decent I notice some parts getting too hot and I turn the craft so that they cool down. After that i came to me that I had airbrakes to slow be during reentry.

- Well... the airbrakes didn`t do much and I ended up overheating my main engine which then ripped all the other ones apart.

- Afer that I tried slowing my, now backwards facing craft down.

- G-Forces ripped the back (Where my Drag Chute was)  and my left wing apart.

- 3 Kerbals died that day.... And jeb survived by getting into his secret "If I **** this up" Pod and landed safely.

Conclusion: Any Ideas on how to cool down a Shuttle to prevent more of jebs crew from Dying?

 

[wumpus]

[warning: I don't make spaceplanes, but have used airbrakes to the point of feeling they are overpowered]

Are the airbrakes on?  How heavy is the craft and do you only have two of them?  How low is  your "shallow entry" (airbrakes should start to work above 40,000m)?  My most kerbal answer would be "more airbrakes", as I've found them overpowered in returning boosters space-x style.

Radiators near overheating parts might help, but understand that the radiators are heated by rentry as well and aren't all that effective.

I think that you really need to go in nose first.  Any spaceplane should create too much pressure going tail first (says someone who always sends boosters in tailfirst, with lots of radiators near the engine).  Pressure creates heat, not friction (although I have no clue how accurate stock aero is for this), but either will be a problem going tail first.

Drag chute ripped your plane apart: stick your drag chutes on the main body, just behind the center of mass.  The other answer would be struts,  and struts are bad for aero.   Limit struts in spaceplanes as much as possible.

 

[Kobymaru]

44 minutes ago, Geromey said:

- Then I try to get back into the atmosphere as shallow as I can so the reentry wont rip my Kerbals apart.

That's your problem right here. "As shallow as you can" basically translates to as hot as you can. This sounds counterintuitive, but it's true. The higher you are, the more "heat per slowdown" you get.

You have to find a sweet spot in the atmosphere, in my experience, put the periapsis on about 38 km.

The best and safest way to reenter is an angle of 90° AoA. Yes, that's 90°. Maintain that until you can't maintain it anymore, use RCS, reaction wheels, aero-surfaces and everything to maintain that as long as you can. When you get in the region of about 15-20 km, you can start "flying" instead of being a stone, but not before.

 

44 minutes ago, Geromey said:

- Well... the airbrakes didn`t do much and I ended up overheating my main engine which then ripped all the other ones apart.

Yes, that's not what airbrakes are for. That's what they were misused for in 1.0.4, but 1.0.5 fixed it. Airbrakes are for slowing down before landing, not killing off orbital velocities.

 

44 minutes ago, Geromey said:

- Afer that I tried slowing my, now backwards facing craft down.

That's a balance problem. Pump some fuel forward, to get the Center of Mass towards the Center of Pressure.

 

44 minutes ago, Geromey said:

- G-Forces ripped the back (Where my Drag Chute was)  and my left wing apart.

Conclusion: Any Ideas on how to cool down a Shuttle to prevent more of jebs crew from Dying?

What I said above, plus, I suggest using AtmosphereAutopilot which will limit your AoA and g-Forces when activated: 

 

I am having a wonderful time with safe and cuddly SSTO reentries with the 90° AoA trick and AtmosphereAutopilot and Trajectories. I'm considering of making a video of that.

[Geromey]

I have 4 Airbrakes and the craft is 68.5T.

My "shallow" decent: I burned retrograde at the exact opposite from KSC and my periapsis was around 30KM.

I did go nose first at 90 degrees. But after I turned the airbrakes on, instead of slowing me, they stalled my craft (Because I tried to pull up like space shuttles with shielding plates would)

When I then tried to turn back around to go nose first, G-forces Ripped me apart and my parachute was ripped off with the rest of the craft.

UPDATE: I tried going in Nose first but then just burned up. Airbrakes didn`t slow me down and the Cockpit Overheated. 3 More Kerbals missing in Action

[Geromey]

Lovely answer! I haven`t used airbrakes for a long time. I used to put them on my landers to halpthem survive a really fast return (because I didn`t have enough Fuel to get me back into kerbin orbit)

And I tried going in extremely shallow because I honestly never landed a 68T Spaceplane and thought that, because it worked for Normal landers it would also work for a... well... 68T Spaceplane

I have to admit, it wasn`t my best design though so thats probably my biggest mistake

[Geromey]

I Landed... more or less successfully... KSC is only about six Kilometers away! Time to walk the Science home

I kind of tweaked the Design so now it enters the atmosphere smoothly....but once using the engines it flies like... a paper aircraft

[Fearless Son]

2 hours ago, Geromey said:

I have 4 Airbrakes and the craft is 68.5T.

My "shallow" decent: I burned retrograde at the exact opposite from KSC and my periapsis was around 30KM.

I did go nose first at 90 degrees. But after I turned the airbrakes on, instead of slowing me, they stalled my craft (Because I tried to pull up like space shuttles with shielding plates would)

When I then tried to turn back around to go nose first, G-forces Ripped me apart and my parachute was ripped off with the rest of the craft.

UPDATE: I tried going in Nose first but then just burned up. Airbrakes didn`t slow me down and the Cockpit Overheated. 3 More Kerbals missing in Action

What it sounds like is that you tried to turn too quickly at too high an atmospheric velocity.  It makes it real easy to lose control when you do that, and the shearing force of the air tends to rip things apart during even small changes in the direction of the force vectors when they are at high magnitude.  

I think that you are doing it mostly right, but it needs some adjustment.  By all means, aim for a periapsis around 35 KM, and come in with the ship's direction vector locked radial.  Make sure that all the less heat-resistant parts are on the top of the ship, as that will keep them in the lee of the air as it passes by the hull, and they will avoid overheating.  

[wumpus]

2 hours ago, Kobymaru said:

Yes, that's not what airbrakes are for. That's what they were misused for in 1.0.4, but 1.0.5 fixed it. Airbrakes are for slowing down before landing, not killing off orbital velocities.

Either there is something still broken in my installation, or they still seem open to abuse in 1.0.5.  At least, boosters with airbrakes tend to survive re-entry.

2 hours ago, Kobymaru said:

The best and safest way to reenter is an angle of 90° AoA. Yes, that's 90°. Maintain that until you can't maintain it anymore, use RCS, reaction wheels, aero-surfaces and everything to maintain that as long as you can. When you get in the region of about 15-20 km, you can start "flying" instead of being a stone, but not before.

Oddly enough, that's how the shuttle landed.  Are we going to get heat shields for spaceplane parts?

[Mikki]

@Geromey

Spaceplanes and shuttles should work fine in stockgame, all the above mentioned answers from our fellow Kerbonautic experts are also fine. My shuttle descend with Jeb in the cockpit is also fine errrm well... no its nuts. But Jeb survived. Thats all that matters.




And hello to the Forums!

[Chaos_Klaus]

I just read all the answers and I think someone else reading that might get confused so I want to clear things up again.

 

Drag goes with v² and heating goes with v³. That means going fast causes you a lot more heat that it causes drag. If you spend too much time at high speed in an atmosphere, you will heat up a lot! That also implies that you can do a reentry that is too shallow!! That is not that important on Kerbin, but many people overlook this when landing on Eve. They go too shallow and heat up slowly but steadily until they explode.

During your descent through the upper atmosphere, you want to create as much drag as possible, because you want to be quite slow before you hit the denser parts of the atmosphere. That means dropping into the atmosphere belly first. NOT nose first!! Nose first would give you the least amout of drag. You want lots of drag to slow down. 

Whether the craft wants to fly nose first or tail first is a question of aerodynamic stability. You need to design the orbiter so that it is stable without a payload and without fuel.

Flying belly first will also distribute the heat among many parts, which is good.

At some point you want to use the lifting properties of the shuttle to prevent dropping into the denser parts of the atmosphere too early. Just dip down the nose to maybe 40° AoA. You'll get both lift and drag out of that attitude.

Any maneuvering during reentry will cause you to slow down. The real space shuttle did S-turns during descent to shed off speed.

Edited February 16, 2016 by Chaos_Klaus

[Evanitis]

(oops, wrong thread..)

Edited February 16, 2016 by Evanitis

[Evanitis]

1 hour ago, Mikki said:

Jeb survived. Thats all that matters.

Well, your Shuttle has a nice, centered CoL that probably doesn't move much (or at all) between launch and re-entry. It also seems to have a nice wing-area/mass ratio. It looks easy to land. Though those silly looking round control surfaces seem to have a questionable efficiency.

^ this on the other hand is a very bad design. I have no clue why everyone keeps building shuttles like this. It's CoM is way too behind. The player tried to compensate it with placing all the wings to the back, but that leads to awful pitch controls, thus tipping over and breaking apart. I bet it could only land by the cheat menu.

Edited February 16, 2016 by Evanitis

[Kobymaru]

4 hours ago, wumpus said:

Oddly enough, that's how the shuttle landed.  Are we going to get heat shields for spaceplane parts?

Spaceplane parts *are* heatshields. Check out their max temp, it's ridiculously high

[Edax]

2 hours ago, Evanitis said:

 

^ this on the other hand is a very bad design. I have no clue why everyone keeps building shuttles like this. It's CoM is way too behind. The player tried to compensate it with placing all the wings to the back, but that leads to awful pitch controls, thus tipping over and breaking apart. I bet it could only land by the cheat menu.

Yeah!  What were they thinking putting the fuel tank in the back?  There's no way to pump the fuel forwards to keep the COM forward on reentry, bunch a noobs!

[Gargamel]

Another approach I use, I burn all my fuel retorgrade to start my reentry, usually about 1k dv.  This drops me down to a managable speed that won't overheat.  I'm going to have to try the higher AOA's approach too. 

[Aethon]

On 2/16/2016 at 0:43 PM, Chaos_Klaus said:

Flying belly first

Klaus is right.  I set a 35 km periapse one third of the way around Kerbin past the space center and use a cobra reentry style.  Not once have I had a heating issue.

 

 

 

 

Point the nose at the zenith and hold it there.

[Gojira1000]

As everyone has said - nose at 45-90 degrees and a Pe of about 35-38km and you should be happy. Unless you're really booting along, in which case take a few high-altitude aerobrake passes on your orbits (still with the nose at 90) to get your speed into, say, the 2400-2600m/s range before trying to de-orbit..

[Kamenjar]

Agree with Klaus and Aethon. With 100km deorbit you must be doing something wrong to have heating issues. I've re-entered with gazillion small and large (how's 300t+ wet mass sound?) and never had any issues re-entering from LKO.  I've always pretty much used Val's  method of re-entry (at https://kerbalx.com/Val/SSTO-C-9-Payroll-Mk1).

And since I mentioned Val and this is my first post even on the forums - using this opportunity to thank her/him for sharing crafts on kerbalx -- learned most of what I know about SSTOs from those

Some tips:

• You don't want to go in too shallow because your heat builds fast in upper atmosphere and you don't get much drag to slow you down there.
• I think that optimal aerobraking at LKO velocities happens at around 35km-20km area where you don't have too much air to explode you and not too little air so you can't brake. Another reason for "cobra" approach is to have both drag and lift push you up so you skid across that area as much as possible.
• You want to have reaction wheels to keep you pointed up. If you are over 100t or so, you want to add airbrakes probably, but should be able to keep a 20 degree angle up to some point when you just won't have enough oomph to keep you pointed up.
• If you are not using mods to show you your dry COM in VAB, or if you are using rocket engines, which will use fuel unevenly, it's safe to keep COM mostly forward during descent by shifting fuel forward. You can also check your current COM by zooming all the way in - wherever it zooms in to, it's the COM.

[suicidejunkie]

For my spaceplane, I put a pair of puff thrusters on the nose, so there's less need for control surfaces or fuel balancing.  A speedy 0 AoA descent below 40km to minimize heating, and then a quick pitch up to 60 and bleed the speed down to 1600m/s where the external shock temperature is safely below the part limits.

That would be the cobra descent plan.  I aim for 40km, hit 35km, and should probably go lower, but that's deep enough to work for me so its all good.

 

Those nose thrusters also come in handy for the almost-tail-landing-->nope-its-a-belly-flop move to get it wheels-down on Minmus for refueling.  Also for popping the nose up to take off from Minmus.

Most of the mass is at the engine when empty, so during the flop move it pivots nicely with the nose having all the speed.  The thrusters then arrest that just before the gear touches down.

[Evanitis]

15 hours ago, suicidejunkie said:

A speedy 0 AoA descent below 40km to minimize heating, and then a quick pitch up to 60 and bleed the speed down to 1600m/s where the external shock temperature is safely below the part limits.

0 AoA above 40km? Sounds rad, but indeed I don't experience much slowing before that. Not much heating either when I'm coming in with nose pulled up to 90°. I generally use the thin atmo above 40km to fine-tune my landing approach. If the target area is too far, I pick a low initial AoA, while if I'm afraid to overshoot, I pull up early.

Love the idea of the nose-engine too. I doubt it's the best solution to balance the dry-CoM or to help in atmoless landings, but a totally viable and fun looking one.

[suicidejunkie]

Well, I do start out at 90 AoA at 70km, but the control surfaces can't really do anything in that regime and the cockpit gyro gives up pretty quick, so the rest of the trip down is pretty close to 0 AoA until it is time to slow down,

I don't worry too much about the target zone, as 200 LF will take you a long long ways using a whiplash when you get to start the flight at 20km & 1200m/s.  Having to turn around if you overshoot into booster bay is definitely expensive, so I tend to aim roughly for the east side of the desert and cruise over the mountains.

If I really do it wrong, there's plenty of land to set down on, and an automated KAA mining rover can always come by with a can of fuel to finish the trip.

[Evanitis]

20 minutes ago, suicidejunkie said:

the control surfaces can't really do anything in that regime and the cockpit gyro gives up pretty quick

That sounds like a design issue. If the CoL is slightly behind the CoM (as it should), you should be able to pitch as much as you want once in the atmo, even with torque from the pod turned off. Though if one doesn't pay attention at building the plane, the CoM shifts backwards as the fuel is spent. That leads to all sorts of funny instabilities on re-entry. Not being able to pull up the nose is one of the less catastrophic options.

33 minutes ago, suicidejunkie said:

I don't worry too much about the target zone, as 200 LF will take you a long long ways using a whiplash

Indeed, it's easy to pinpoint a landing if one has fuel remaining - it doesn't require any further trickery. Though I kinda' always land with fully dried tanks. If I have such luxury for landing, I fix it on the next iteration. Taking juice to orbit just to bring it down is pretty wasteful. I rather have more payload.

[suicidejunkie]

On 2/19/2016 at 1:11 PM, Evanitis said:

That sounds like a design issue. If the CoL is slightly behind the CoM (as it should), you should be able to pitch as much as you want once in the atmo, even with torque from the pod turned off. Though if one doesn't pay attention at building the plane, the CoM shifts backwards as the fuel is spent. That leads to all sorts of funny instabilities on re-entry. Not being able to pull up the nose is one of the less catastrophic options.

Indeed, it's easy to pinpoint a landing if one has fuel remaining - it doesn't require any further trickery. Though I kinda' always land with fully dried tanks. If I have such luxury for landing, I fix it on the next iteration. Taking juice to orbit just to bring it down is pretty wasteful. I rather have more payload.

This is probably getting a bit off topic, but you're probably right.

I've got a set of control fins for canards, so it has a lot of authority within about 20 degrees of prograde, but beyond that, it is perhaps overly stable

Fuel isn't an issue, since the orbital depot has 300 tons of it with Minmus tankers queued up.  In all fairness I should be landing with *full* tanks to make a profit on the trip!

[ForScience6686]

Since most space planes have the wings far rear, as you hit thicker air you'll be fighting the planes natural tendency to keep the draggy bits at the rear.  I try and keep my wings as far forward as possible to minimize this.  Think of levers and darts.  Also, steep re entry is a better option in my opinion.  High aoa all the way down to safe cruising speeds.  With planes you have the lift to use to your advantage and can transfer vertical speed into horizontal speed. Wings at 30 degrees to prograde seem to offer the best lift over drag and anything above should be used for reducing speed.