Solution to aerobraking huge ships.

[blakemw]

The numbers I found experimentally for Heat Shields is that for normal usage you only need ablator for aerobraking velocities of over 5500m/s. If playing sensibly it's quite hard to be going this fast when hitting any body other than Jool, and if you're being sensible you'd just get a gravity assist from Tylo. When returning from Moho or Jool to Kerbin, craft tend to be going almost this fast so having ablator can be good security but shouldn't be essential.

But if using mods then it's possible that ablator is more important. But mods can allow recharging ablator, most trivially is to use hyperedit to cheat more ablator in, but I seem to recall there are 1 or 2 mods that actually have a proper way to recharge ablator.

Edited April 3, 2018 by blakemw

[Pthigrivi]

1 hour ago, Rocket In My Pocket said:

There is no stock way to transfer ablator that I know of.

Personally in your shoes, I would make a modular set up with a docking port between the ship and the heatshield, then swap out a fresh one when ever you are refitting. Obviously you may need some kind of infrastructure for it, like an "orbital forklift" at your station. Or just a rack where you keep the spares, and then you nose the ship up to the new one after discarding the used?

Oh I did that once,

If you point yourself retrograde the sepratrons send the mounting gantry into back into the atmosphere. Which was fun, but as Blake points out in the end I found even a heat shield with with all its ablator burned off does just fine over and over again from Minmus (or most anywhere else).

Edited April 3, 2018 by Pthigrivi

[Rocket In My Pocket]

38 minutes ago, Pthigrivi said:

Oh I did that once

Absolutely love it.

[FleshJeb]

This was my solution for a refueling tanker that needs to aerobrake. I wanted to experiment with the "slippery" form rather than the blunt one.
It consists of a "dumb" (no probe core) fuel tank that mates to my mothership drive section. It's even capable of doing minor plane changes in atmo by spinning longitudinally. That's probably the Vall TWR with a full load (although it would typically have less oxidizer).

Note that the side docking ports are cheated on by allowing them to surface attach with Editor Extensions.

 

[magnemoe]

3 hours ago, Snark said:

Actually, I liked 'em on that ship.  When they're all running, the exhaust plumes (with the slight outward flare) looked pretty cool, like a fountain.

Nope, ablator can't be transferred.  It's why I like using the inflatable heat shield, since it doesn't have any ablator so it's 100% reusable.

It's worth noting that even the ablative heat shields actually do a pretty good job even without any ablator.  They're reasonably well insulated (don't transfer heat rapidly), and have a really high temperature tolerance (natch).  Yes, they work better with ablator, and if you're trying to bleed off multiple km/s of speed after a high-energy interplanetary transfer, then sure, you'll want ablator.  But for a Mun/Minmus milk run, or even a Duna/Kerbin shuttle?  I expect they'd be just fine even without the ablator.

This, add that the reusable ships tend to be large so the 10m shield is no huge cost and often needed as its large, you could use docking ports so you can drop the old and add an new then used up but never used them for anything who need multiple aerobrakes. 
As ship is reusable and use ISRU fuel its no reason to go small outside that smaller ships are easier to handle.  

[magnemoe]

4 hours ago, blakemw said:

The numbers I found experimentally for Heat Shields is that for normal usage you only need ablator for aerobraking velocities of over 5500m/s. If playing sensibly it's quite hard to be going this fast when hitting any body other than Jool, and if you're being sensible you'd just get a gravity assist from Tylo. When returning from Moho or Jool to Kerbin, craft tend to be going almost this fast so having ablator can be good security but shouldn't be essential.

But if using mods then it's possible that ablator is more important. But mods can allow recharging ablator, most trivially is to use hyperedit to cheat more ablator in, but I seem to recall there are 1 or 2 mods that actually have a proper way to recharge ablator.

Think it depend a bit on the weight of your ship, tankers tend to drop down to 35 km on an minmus return with an high speed trajectory who do the return in 4 days. 
Passenger ships going faster still don't need more than 45 as they are lighter, both uses the 10m shield and drag plate. 
 

[Pthigrivi]

Maybe its the scale that Im working at but I haven't really needed the 10m shield for anything but interplanetary braking. Right now Im running 2 reusable 6-crew personnel busses and a 10k LF tanker. Both can get by on the 3.75m shield. 

And man while Im asking for things squad will never make stock Mech Jeb's aerobrake predictions are the only way to live.

[MaverickSawyer]

On 3/7/2018 at 8:09 AM, Temeter said:

On my last eve-mission, I put one of the inflatable heatshield at the front of my craft, one at the top, and that made my ship spin so fast that no part over got hot enough to explode

Oh, you're one of THOSE players.  

[Atlas2342]

12 minutes ago, MaverickSawyer said:

Oh, you're one of THOSE players.  

Some people like to live dangerously.

[Archgeek]

On 4/3/2018 at 8:21 AM, Snark said:

I dunno, seems to me that except for streamlined atmospheric-flight ships, pretty much all spacecraft are ugly, ungainly concatenations of hardware.  It's part of their charm, at least to me. 

What I can't abide is stupid looking, but "ugly"?  Gimme.

Anyway, here's an example of fore-and-aft heat shields that I put together a year or two ago.  It's a ship that's built around the largest-size 5m tank from SpaceY:

 

On 4/3/2018 at 8:52 AM, Pthigrivi said:

*Winces* 
Haha jk thats not bad. I feel like the splayed out engines would irk me though?

Here is a place where opinions differ.  Looking upon that machine, I see a thing of great beauty.  Also, I wouldn't be so worried about that thrust angle.  Cosine losses only really get icky around 25 degrees, this looks to be maybe 15, which gives a loss of barely over 3.4%

[Snark]

31 minutes ago, Archgeek said:

Also, I wouldn't be so worried about that thrust angle.  Cosine losses only really get icky around 25 degrees, this looks to be maybe 15, which gives a loss of barely over 3.4%

^ This.  I don't have the .craft file handy (this was many careers ago, and it's been a long while), but I'm a calculator jockey and cosine losses bug me, so yeah, I made sure they stayed in line.  I'm pretty sure the splay angle is under 15 degrees-- I think it may have been 10.  So yeah, cosine losses are fairly negligible.

[Pthigrivi]

6 hours ago, Archgeek said:

 

Here is a place where opinions differ.  Looking upon that machine, I see a thing of great beauty.  Also, I wouldn't be so worried about that thrust angle.  Cosine losses only really get icky around 25 degrees, this looks to be maybe 15, which gives a loss of barely over 3.4%

I was mostly joking about the aesthetics. She's a fine beast. Good to know about the cos losses though, Im sure Im overly resistant to splayed engines.