How to heat-proof ships?

[quasarrgames]

I have a large interplanetary mothership, the kind you can't really just attach a bunch of heatshields to. Whenever i try to put it down in the atmosphere, the nose and engines and cockpit burn up. I was wondering if anyone had any suggestions on the best ways to heat-proof ships.

Here's what i've figured so far:

-aerobrakes are only good if you can slow down quickly. In the upper atmo, they're mostly useless.

-Radiators are basically stylish finnicky heatshields that don't always work.

-some parts will only overheat when they're facing in the same direction as the "wind". Nukes don't burn as quickly when they brake sideways, but when facing straight retrograde they can burn away in seconds.

-wings work well for drag and control too

-clipping can result in overheating and death for no reason sometimes

-

 

Anything else?

Edited March 1, 2016 by quasarrgames

[FancyMouse]

There's also the question of which atmosphere. Duna is probably not going to cause any problem, while Eve it's probably impossible unless you protect everything behind heatshields.

Also, relative velocity should be reduced as much as possible, especially with Laythe where you should enter at a correct angle for capture.

I actually can't find any one of your points that I totally agree with, but without more info probably I can't confidently deny either.

[Snark]

A screenshot would help.

What atmosphere, and what sort of encounter velocity are we talking about?

[quasarrgames]

We're talking from duna to kerbin, so not that demanding. I'd like to do it in more LESS  than 29 passes though. If it can dip to 40km and come out unscathed, i'd be happy. I'm planning to do it by covering my nukes and just facing straight retrograde. This strategy worked in the past for me quite well.

Another thing i like to do is attach wings to all my boosters and just pancake into the atmosphere.

Edited March 1, 2016 by quasarrgames

[Streetwind]

When you say "typical interplanetary mothership", my inner eye instantly conjures up an image of a long, thin stalk of assorted trusses and tanks. Not sure that your vessel actually does look like that, but it's what I imagine.

The problem with such a craft is the so-called ballistic coefficient, which is a fancy term for "amount of mass behind a certain cross-section profile". Because the ship is thin, it has a small cross-section, but because it is long and fitted with nukes and designed to tug other spacecraft around, it is also heavy. This results in a high ballistic coefficient, which is pretty much the antithesis of "heat-proof" because it forces you to go much deeper into the atmosphere before you experience any sort of meaningful slowing effect. In other words, the mere act of constructing a ship in this way is the source of its troubles. You will probably not be able to heat-proof such a craft to your liking, at least until 1.1 rolls around and gives you that delicious 10 meter inflatable heatshield that RoverDude made. It will greatly increase a vessel's cross-section without adding much mass, thus lowering the ballistic coefficient and letting you aerobrake that much better and safer for it. Of course, the fact that it is also a heatshield in addition to its giant size helps as well

(Again, not sure if that is your problem, but it is *a* problem that motherships often have.)

[Plusck]

Well, Streetwind's post got me thinking and, specificall, about fairings.

If you have the time to send it to Duna, you could create your own "inflatable" heatshield. It involves a Klaw backed by a fairing drawn out to its largest and flattest extent. Getting up from Kerbin would be a nightmare, but if you put one on each end of your mothership, aerodynamic forces should balance out and ensure that the heavier end of the ship (i.e. the engines) ends up pointing mostly downwards.

I frankly have no idea if that would ever work, but I've seen videos of people using fairings as heatshields in earlier versions of KSP so unless that has changed greatly, it should at the very least help. Even if it's sacrificial, it might be enough to allow the rest of the ship to survive.

[Snark]

13 hours ago, quasarrgames said:

We're talking from duna to kerbin, so not that demanding. I'd like to do it in more than 29 passes though. If it can dip to 40km and come out unscathed, i'd be happy. I'm planning to do it by covering my nukes and just facing straight retrograde. This strategy worked in the past for me quite well.

Really need to see a screenshot, plus an indicator of total ship mass.  It really matters, there's no way to generalize without some feeling of what we're dealing with.

Not sure what you mean about wanting to do it in "more than 29 passes".  You want to do a whole lot of braking passes?  I'm confused.

Coming in from interplanetary, I find there's not a lot of use in trying to do a lot of aerobraking passes:  the first pass is by far the harshest one (in terms of dumping dV), bigger than all the others combined, so if you can do that one, you might as well just aerobrake straight to the desired altitude.

[radonek]

Few things from top of my head:

• if ship is aerodynamicaly stable it helps to put it in slow rotation
• if you go for shalow,  slow speed shedding, go with high AoA. Even a wingless craft have significant body-lift on high speeds.
• or go straight down as fast as possible. your craft have some thermal capacity which could be thought of as a resource. you obviously need to slow down very fast, before that resource is depleted, ergo you need a thick atmosphere. You also transfer heat out more efficiently then in thin stratospehere. this needs a sturdy vehicle since apart from hight thermal stress you also undergo extreme G forces.
   

[Snark]

57 minutes ago, radonek said:

or go straight down as fast as possible. your craft have some thermal capacity which could be thought of as a resource. you obviously need to slow down very fast, before that resource is depleted, ergo you need a thick atmosphere. You also transfer heat out more efficiently then in thin stratospehere. this needs a sturdy vehicle since apart from hight thermal stress you also undergo extreme G forces.

There's a problem with this.  The real danger is not G forces, but rather a "feature" that's built into the game's reentry logic that if you get too deep in the atmosphere while you're still going too fast, you go boom.  Instantly.  Regardless of heatshields.  Unless you have a very light ship with a whole lot of surface area, you're almost guaranteed to hit this unsurvivable "wall" if you just "go straight down as fast as possible".

This means that a given ship design has a certain limit to how steeply it can descend into atmosphere, regardless of its heat shielding, aero stability, and resistance to g-force.

It means that you're walking a fine line when you are coming back at interplanetary speeds.  For a given ship traveling at a given speed,

• There's a "maximum effective altitude" that you must be below, because if you're above that, you don't get enough braking and you go flying into space.
• There's a "minimum survivable altitude", that you must be above, because if you're below that, you explode.

The problem is that for certain combinations of ship speed and ship design, it's an impossible situation.  You can end up with a scenario where the maximum effective altitude is actually below the minimum survivable altitude, meaning that it's physically impossible both to get captured and to survive.

Therefore, the design goal is to come up with a ship that doesn't end up in that scenario.  However, there are a lot of different ways to accomplish them, and which of them are practical and/or effective totally depends on the specifics of ship design.  Therefore, we really need the OP to post a screenshot of the ship, along with what its mass is, before it's possible to offer any really practical suggestions.

[Wemb]

On 01/03/2016 at 8:21 AM, Streetwind said:

 

The problem with such a craft is the so-called ballistic coefficient, which is a fancy term for "amount of mass behind a certain cross-section profile". Because the ship is thin, it has a small cross-section, but because it is long and fitted with nukes and designed to tug other spacecraft around, it is also heavy. This results in a high ballistic coefficient, which is pretty much the antithesis of "heat-proof" because it forces you to go much deeper into the atmosphere before you experience any sort of meaningful slowing effect. In other words, the mere act of constructing a ship in this way is the source of its troubles. You will probably not be able to heat-proof such a craft to your liking, at least until 1.1 rolls around and gives you that delicious 10 meter inflatable heatshield that RoverDude made. It will greatly increase a vessel's cross-section without adding much mass, thus lowering the ballistic coefficient and letting you aerobrake that much better and safer for it. Of course, the fact that it is also a heatshield in addition to its giant size helps as well

 

As an aside, would attempting to re-enter such a craft (long, thin) sideways help much with this?  You'd increase the cross sectionand decrease the mass per unit area - the downside, of course, being more parts are being exposed to heat?  I ask as presummably this is how most SSTOs deorbit without burning up - by coming into the atmosphere by presenting the wings to the atmosphere.

Wemb

[bonyetty]

Small antenna on the front of nose cones can work to protect nose cones from heating and what's behind them in some circumstances. 

[Streetwind]

56 minutes ago, Wemb said:

As an aside, would attempting to re-enter such a craft (long, thin) sideways help much with this?  You'd increase the cross sectionand decrease the mass per unit area - the downside, of course, being more parts are being exposed to heat?  I ask as presummably this is how most SSTOs deorbit without burning up - by coming into the atmosphere by presenting the wings to the atmosphere.

Wemb

Yeah, pretty much. The thing with spaceplanes though is that they are rigid front to back, whereas some motherships are better compared to a well cooked noodle. Additionally, non-retractable solar panels and parts like science instruments with very low heat tolerances might be an issue.

[Snark]

1 hour ago, Wemb said:

As an aside, would attempting to re-enter such a craft (long, thin) sideways help much with this?  You'd increase the cross sectionand decrease the mass per unit area - the downside, of course, being more parts are being exposed to heat?  I ask as presummably this is how most SSTOs deorbit without burning up - by coming into the atmosphere by presenting the wings to the atmosphere

 

9 minutes ago, Streetwind said:

Yeah, pretty much. The thing with spaceplanes though is that they are rigid front to back, whereas some motherships are better compared to a well cooked noodle. Additionally, non-retractable solar panels and parts like science instruments with very low heat tolerances might be an issue.

@Wemb: yes, that can be an option in some cases-- mainly if the speeds involved are pretty low, i.e. you're already in a fairly low orbit and want to ease it lower.  However, at interplanetary speeds, it tends not to work-- anything that's not a heatshield has a tendency to get quickly fried.  Need some guidance from the OP about what sort of speed range he's talking about.  If he's aerobraking at Kerbin and is only going 2500 m/s or so, it could work.  But if he's coming back from interplanetary travel and is going 4000 m/s or more, there's no way it would work, it'll just go kablooie very quickly after hitting atmosphere no matter what way it's oriented, unless he's got heat shielding.

So, below 2500 probably okay, above 3500 almost certainly not okay.  In between, the actual limit is totally dependent on the ship design & total mass, so it's hard to say more precisely than that unless the OP can post a screenshot and give an indication of the speeds and masses involved.

Also +1 to Streetwind's comments.

[Kamenjar]

My minmus tanker is 250T and aerobrakes using big-s elevons. I have a dozen of elevons "Extend" in an action group to act as big heat-resistant aerobrakes. Front is aerodynamic with 1.5m to 2.5m adapters (1 straight and 2 slanted) with all three having a shielded docking port. I go in straight prograde in order to get a predictable capture. You will get better results if you go in "cobra", like spaceplanes. When I dip to 26km or so from Minmus, the whole ship is on fire with every component having a temp bar in red and skin temp reaches 2500K, but I end up aerocapturing to 90km apo / 25km peri in a single pass. I also have 4 smallest radiators on the rear. Not sure how much they help. The most heat-sensitive part on the ship is a pair of retractable 1x6 panels that go on the sides (2000K).

Now with interplanetary speeds it's a whole different beast depending on your velocity when entering kerbin's SOI, but you can hopefully make use of some ideas from this design. Or use it mostly as-is, if you velocity when entering SOI is minimal or, if you can slow down to minmus orbit equivalent.

Edited March 3, 2016 by Kamenjar

[moogoob]

Are you trying to aerocapture the whole ship? Do you have any fuel left to slow down first? I take tons more than I need for that reason. Why not include a (detachable, heat-shielded) pod that the science and kerbals hop into to complete re-entry while the mothership just does a flyby and zooms off into inter-planetary space. Or burns up, your choice. Have you considered slingshotting off of the Mun to reduce your velocity somewhat?

That's what comes to mind if I were returning from an interplanetary mission.

Edited March 4, 2016 by moogoob

[Daeridanii]

So, a few answers, I hope:

• Radiators aren't good heat shields, but they're good at rejecting heat from specific parts. Not a good bet for reentry, better if you're dealing with part-specific (ISRU) or overall (Sun-diving) heat.
• Best aero-protection for motherships are fairing used as heat shields (Think of attaching a UFO to the front of the ship). Not stylish, but quite protective, used correctly.
• Don't dip so low, if you're overheating. Atmospheric pressure does contribute quite a bit to heating.
• Finally, consider gravity assists, and plain old thrusting. SRBs will slow you down quite a bit if you want, and overall, this might be the best solution if nothing else works.

This is all I could think of, so I hope that it works.

[Kerbal101]

From my observation, given the small diameter orbit and periapsis touching at 30k - it depends on two ship-specific factors:

A-how much lifting surfaces your ship possesses (fins, wings, aerobreaks etc)

B-how much density it has (tanks full of fuel are worst, empty tanks are best)

That is, landing a full can of fuel without overheat is much harder than an empty one with wings.

 

If A is high and B is low, then your ship can glide against winds incoming at prograde ("cobra") and both gradially drop speed for free as well as produce anti-radial effect ("glide", in contrast to "sink").

If A is low and B is high, then your ship will behave like brick. There will be not enough anti-radial lift (against body) and the mass will push it into radial vector (towards Kerbin). Arm it with engines, point nose between retrograde and anti-radial and fire when you notice overheating to start. Exact m/s and altitude depends on mass of ship.. I'd say, no more than 1900m/s below ~35k (less than 1700 m/s might turn out dangerous or inefficient; descending angle will become sharp). Then perform either powered descend by following retrograde vector and optionally lots of parachutes (1 chute per 4 tonne) and optionally airbrakes. Drogue chutes will also help reduce landing speed, saving on fuel.

 

Also, I found out that for large heavy ships, rotation also gives pseudo retrograde-burn effect. That means, the steeper landing angle and faster meeting with Kerbin at higher speed. For large ships this might turn out disadvantageous.

Edited March 6, 2016 by Kerbal101