How to protect Radial parts from heat on re-entry? (Images included)

[TomDRV]

I've built this general manned spacecraft (inspired by SpaceX's Dragon) to do general manned transport and landings. It's designed to be 100% reusable. However, during re-entry some of the radials, namely the engines, overheat, how do I protect these? There are no heat shields for them.

Does mounting them further up make a difference? 

thanks

 

P.S Why won't my friend's rover budge? 

Edited July 14, 2016 by TomDRV

[Snark]

11 minutes ago, TomDRV said:

I've built this general manned spacecraft (inspired by SpaceX's Dragon) to do general manned transport and landings. It's designed to be 100% reusable. However, during re-entry some of the radials, namely the engines, overheat, how do I protect these? There are no heat shields for them.

Does mounting them further up make a difference?

Something that sticks out a lot, and has a lot of surface area sticking out, is going to catch a lot of heat.  It's one of the reasons I tend to avoid radially-attached engines.  (Some people like Thuds.  Personally, I never use them.  Drag, not-so-great Isp, reentry issues like you're experiencing.)

Mounting them up high probably won't make a lot of difference.

One thing you can do:  tumble.  Have your ship tumbling and spinning rapidly as it reenters.  Not only will that boost your drag and help you decelerate more, but it helps by rotating them out of the "line of fire" repeatedly, and may be able to keep 'em from burning off.

15 minutes ago, TomDRV said:

P.S Why won't my friend's rover budge?

Hard to tell for sure from that screenshot-- can't see how the wheels are attached.  Are they right-side up?  They have to be.  (Yes, it doesn't make physical sense, it's a wheel, it "ought" to work in any orientation.  But it doesn't.)

How you can tell:  From the wheel's attachment point (i.e. where it connects to the rover), there's a short, slanted "boom" that goes to the actual wheel itself.  Here's the question:  Which direction is that boom pointing, on the rover?  Does it slope downwards from the body of the rover?  If so, the wheel is right-side up and is supposed to work.  On the other hand, if it slopes horizontally (i.e. the slant is pointing fore or aft, rather than downwards-towards-the-ground), then the wheel is on sideways and won't work, because the "rollable surface" isn't pointed at the ground.

[Jarin]

The menu says "Wheel blocked: yes" which implies they've been clipped and are intersecting something. The current state of wheels is less than optimal, and clipping them, while it can make for good looking rovers, generally just doesn't work and results in blocked wheels.

[bewing]

Snark gave the right answer on the ship. Tumble it -- you won't even need the heatshield anymore, and you can put something productive on the bottom.

On the rover, Jarin is correct. However, it may not be the wheels that were clipped. That RCS block was definitely clipped into the wheels -- and the battery is too close. Both those things will stop the wheel from working.

[Foxster]

You can do it by using the larger heat shield and having just the bell housing of the engines exposed through imagined holes in the heat shield...

Make sure any other radial parts are within the "heat shadow" of the heat shield too, placing them on the angled part of the capsule if necessary.  

Edited July 15, 2016 by Foxster

[klesh]

Foxster has a good look going there.

[TomDRV]

Thank you guys, great help. I'm not too sure about that oversize heat shield though

[magnemoe]

7 hours ago, TomDRV said:

Thank you guys, great help. I'm not too sure about that oversize heat shield though

Wonder if you could clip the engines inside the fuel tank so their bells stick out of a 2.5m shield

[Spaceception]

Put a decoupler under the capsule, then put the larger heatshield on, that way you can have radial parts, and you won't die on reentry, win/win!

[TheDestroyer111]

Hmm... You must be reentering at insane speeds for even a temperature gauge to appear on the thud engines, let alone having them explode. On 120% reentry heating setting, I couldn't get the temperature gauges to appear at 2000m/s for the thud engine.

[Jarin]

I've never had any success with the "tumble" re-entry. I always just get things all over the ship insta-heating and exploding at the hottest part of re-entry, seemingly no matter how I set my PE. Any more specific advice?

[Norcalplanner]

It's also a viable idea to put some twitch engines up on the capsule itself, where they are fully occluded from reentry heating. My Bluebird crew transporter uses this design - I'll post a photo once I'm at my computer.

[kBob]

@JarinI don't like tumbling for the same reason everything tends to go bam!  But slight movements can help, just tap one of the movement keys-- just a slight movement can cause a heating part to briefly cool.  Best if you have SAS set on retrograde hold, then tap a key let SAS move the ship back and tab again and so on until temp gauges stop showing up; otherwise you can rock the vessel if you don't have retrograde hold.  The only problem with this is if your reentry vessel is unstable.  I usually put a heat shield with most of the ablator removed as the shield effect helps and a little weight on the bottom helps with stability, but you already have that covered.  Given how far out those stick in the OP (if you are using a similar design) it might actually take a couple of key taps to get them moved enough to briefly cool so play around a bit see to see if you can get this to work...hopefully there is something that will do the trick without going into a tumble.

Edited July 16, 2016 by kBob

[bewing]

OK, the best way to tumble is 90 degrees from prograde all the time that you are spinning. So your spin should go through normal, radial, anti-normal, and anti-radial. Once you have it spinning like that, add a little roll to it. And get it spinning like that before you hit the atmosphere. I am still in the "high Pe" camp. Over 59km. And don't think you can do a direct reentry from the Mun or something with a thermally fragile ship. Expect to do however many aerobraking passes it takes to get your Ap down to something survivable before you do you final reentry.

[Norcalplanner]

Here's an album of my Bluebird craft in its 6.4x variant.  This is just about the only use I have for the Twitch engine.

 

[dire]

For the rover, looking at the wheels from the top down, the left side (I think? Or it might be the right side) need to have their motors in reverse mode. The rear wheels need to have their steering in reverse mode (but the left has a reverse motor and the right has a normal motor). Don't put your wheels on in pairs; you have to mount each of them individually for the motor/steering settings to work.

And as @bewing said, if your wheels are clipped they will break. And don't let a kerbal on EVA anywhere near your wheels; if you let Jeb touch them they are likely to kill him and the rover both.