Do stock fairings block/help with heat?

[archnem]

Hey all:

I'm about to send my first probes to Eve in 1.0.x, and I'm a bit worried about aerobraking at the end, since my probe is full of science-y doodads that might get eaten. Specifically, I'm wondering if using the stock fairings would do any good protecting the probe? Do they block or at least absorb heat or are they only good for aero?

Edited May 17, 2015 by archnem

[AaronLS]

They will protect the items inside from being heated directly, but the fairing will heat up and transfer heat slowly to the next item it is directly connected to. Sometimes this is a problem for things that have a much lower heat tolerance of 1200 degrees. On those occasions I've attached a small girder as the first item to then mount everything else to. But usually it is not a problem. Especially since heat transfer happens much more slowly and spreads out among connected parts, so it's unlikely that any single internal part will accumulate enough heat to be a risk.

A very sharp fairing reduces drag alot more than a blunt fairing, and I suspect this is related to how much heat is produced. So make your fairings sharp like this to reduce drag and hopefully also reduce heat generation:

http://i.imgur.com/vouXq09.jpg

[Baythan]

The biggest issue I have seen with using fairing and aerobraking is that they have so little drag that you might not slow down appreciably. A few of my tests of their heat resistance ended with surface impact on Kerbin at extreme speeds due to a significant lack of drag.

I'm waiting for the Trajectories mod to be finished so I can do more tests with aerobraking in less time(can get predictions without having to quicksave and reload over and over).

Edited May 17, 2015 by Baythan

[Geschosskopf]

Hey all:

I'm about to send my first probes to Eve in 1.0.x, and I'm a bit worried about aerobraking at the end, since my probe is full of science-y doodads that might get eaten. Specifically, I'm wondering if using the stock fairings would do any good protecting the probe? Do they block or at least absorb heat or are they only good for aero?

As far as I can tell, reentry heating only happens to parts exposed to the airstream. Thus, fairings both keep the parts inside from producing drag (assuming that now works as intended) and protect them from reentry heat. As AaronLS says, however, the fairing itself will heat up to some extent. This usually isn't a problem, though, because they were designed for this.

The thing about aerocapture/aerobraking, though, is that you don't have to do it all at once. All you need to do on the 1st pass is just capture into a closed orbit, which can be highly elliptical. You can then bring your Ap down more to where you want it on subsequent passes. If you do it this way, then you don't have to dig as deeply into the atmosphere on any given pass, so you spend less time in the air and the air you're in is thinner. Thus, no worries about heat.

As Baythan says, though, ALWAYS quicksave prior to making any aerobraking pass. If you don't like the results, quickload, tweak your Pe up or down a little as needed, and try again. And I, also, can't wait for an updated Trajectories mod to save a lot of this hassle

[Murph]

I can confirm that fairings do work very well to keep heat off the payload. I've just done a launch of a tiny-size probe on a small size launcher which got a bit too fast and horizontal too soon, to the point where the fairing popped up an overheat bar that filled past 50% by orbit, and the fairing itself started glowing red (the object itself, not the hover temperature gauge). On arriving in orbit, I turned on the temp overlay, and the fairing and lower stage were bright yellow. On jettisoning the fairing, the probe inside it was deep red (the coldest visual from that overlay), only the decoupler attached to the fairing base, and the probe's engine had started to get hot (via conduction), and they were colder than the lower stage, fairing base, and fairing.

Conduction was getting the heat in, but very slowly, despite the shell glowing red without any debug overlays enabled. Fairing was char grilled and extra crispy, lower stage was toasty but not well done as it was partially shielded by the fairing (it was slightly wider diameter, to accommodate radial parts on the probe). Payload was fairly cool other than decoupler and engine.

I don't have exact speeds to offer, but probably 2000m/s-ish @ 30,000m on Kerbin ascent which was mostly horizontal from about 20,000m, so a long sustained period of heating. I strongly suspect that the fairing and other bits would probably melt if you tried 3000m/s deep into a thick atmosphere. They are not a substitute for a proper ablative heat shield if you're going to go for a crazy ultra-fast aerobraking entry, but they will give a lot of protection to more vulnerable components inside them.

They work very well, pretty much as they should work, but they have their limits.

[archnem]

Awesome. Now how do I change this thread to "Answered"?

[DerpyFish]

Awesome. Now how do I change this thread to "Answered"?

Go to your thread and click the Edit Postbutton on your post. The editor will appear, offering you several options. Click the Go Advanced button to be taken to a editor page, with the options you need to change the thread's prefix. When switched to answerd click the save button. http://forum.kerbalspaceprogram.com/threads/85063-How-to-change-Unanswered-to-Answered