Looking for a method of construction for recessed engines

[Zamolxes77]

Started playing a mod, Kerbal Kommander, which is more of a KSP adventure game, in style of X3 or Elite dangerous. You basically take command of Jebediah (or other kerbal), in a junk ship and you make your fortunes by trading, mining, doing science, capturing roids. At beginning, you start with trading - you start only with 20,000 funds.

Anyway, in order to cut flying costs, aero-breaking becomes EXTREMELY important - you don't want to burn extra fuel, which you pay for (gets deducted from your profitssss), if you can help it. SO the ships have to be designed to aero-break, without the use of heat-shields (you don't have access to KSC to replace them), multiple times. While I'm a fairly experienced player who clocked over 1,000 hours in this game, I guess I'm in a crisis of imagination.

One method I used so far is engines 1st, ships with CoM towards the engines, so they will take the brunt of heating, sadly they can't take much, all are rated at 2000K (except nukes off course at 2900K, but they cost 10,000 kerbalbucks per engine). Another method I just thought of, is add shielded docking ports (2900K heat tolerance) on the front of the ship, but then the problem becomes of maintaining CoM forward, so the ship will naturally tend to turn nose in.

Is there a way to recess the engines, so they don't get caught in plasma trail, so I can still aero-break engines 1st, but brunt of the heating is takes by the hull, perhaps a Mk3 adapter?

Edited July 28, 2016 by Zamolxes77

[Pecan]

Possibly Infernal Robotics but radiators may be simpler.

[Zamolxes77]

I'm not trying to add a second mod that might conflict with this one, so robotics is out of the question. Didn't knew radiators help with dissipating re-entry heat, how many you actually need?

[Pecan]

Check the KSPedia in-game for details of how heating and radiators work.  "How many" depends a lot on your design.

[silent_prtoagonist]

I just started playing with Kommander as well, and I've been having similar thoughts about the importance of aerobraking. 

 

First thought: Use the 10m inflatable heat shield, which doesn't use ablator and is thus completely reusable. You'd just have to be careful to never accidentally jettison the thing. As an added bonus it lends itself to flying saucer designs, which are just cool. (This was always one of my favorite ships from Orbiter that used such a design http://www.orbithangar.com/searchid.php?ID=3629)  

 

Thought the second: Don't make such deep dives, staying relatively high and cool to protect the fragile parts, and make up for it by making your ship as draggy as possible/doing more braking passes. A good reentry vehicle has as much drag as possible (basically the opposite of a good aircraft, which is why the space shuttle flew like a brick) so that it sheds as much energy as possible in the upper atmosphere before the real heating begins. You could even give it some stubby wings/design it more like a spaceplane, which would allow you to fine tune your flight profile and ride that bleeding edge of just barely not exploding. 

Edited July 28, 2016 by silent_prtoagonist

[Corona688]

The problem with recessed engines is that engines don't work unless you point them at space.  Still, I've managed this in two different ways lately:

You have to look real close at the leftmost pic to see them, but there's a pair of ant engines behind the heat shield, angled 45 degrees forward so they can generate useful thrust while still being behind the heat shield.  You can see it firing in the middle one.  This works okay for my little return craft, since all it needs is enough dv to break orbit, but for anything big or serious, losing sin(45) percent of your thrust is unacceptable.

Second way:  Sideways spaceships.  These can work great in space though they can be tricky to balance.

As for aerobraking, I've had ENTIRE SPACE STATIONS pass through re-entry flames without a scratch -- because they were falling down sideways, in the position of maximum drag.  Lightweight things like empty tanks, science modules, etc falling sideways generate tons of drag.  Fast re entry might be better than slow re-entry, you get lots of heat either way but fast minimizes the time.  If you can make it do that, you have a chance.  Drag is still one of the harder to engineer things in this game of course.

Lastly, counter-thrust during re-entry helps.  Every bit of speed you bleed off makes things cooler.  Slow thrust for a long time is very helpful.  Those ant engines in the first pic are firing the entire time from 50,000m to 5,000m and I never get thermometer pop-ups on that "lander".  RCS would be just as effective.  I'm not sure if the heat shield is still strictly necessary or not.

If you can get them, air-brakes are nice for adding lots of drag when and only when you need it, and moving your center of drag to where it needs to be to keep your craft balanced where you want it during re-entry.  You can also open bay doors and stuff to make drag.

Edited July 28, 2016 by Corona688

[Corona688]

Oh, and depending on how far you go, heat shields are still necessary for some things.  I'd never try a direct re-entry from anywhere but low kerbal orbit without one.  Indirect, stopping in LKO, is okay.

[radonek]

• Don't be needlessly scared by reentry effects. Flames start long before heat becomes real problem.
• Even ablatorless heatshield is useful, because of high temperature tolerance. So are radiators. Yes, they do little to increase you heat capacity, but can shield more fragile parts.
• If you can't increase your heat capacity, increase drag.
• Airbrakes are incredibly useful, as they can also help stabilize craft. And Un-Deploing them can be used to control drag in flight, very useful if you find you aimed PE deeper down then you want.
• Angle your ship a little bit, and rotate it slowly to give parts a second to cool.
• Fuel have heat capacity. If you have any and CoM allows for it, pump it to hot parts.

As for actual ship design, you can stick radial engines into overhanging heatshield with a little trick. Things is, point from which thrust is projected is offset a bit from where drag&heat is accounted. With a bit of experimenation, you can tune it to the point where engine is behind heatshield, but thrusting outside of it. Not sure if it applies for all engines, but I did this successfully with LV-N. Just attach radial engines over heatshield, place it on launchpad and fire for a while. Look if flight log says shield was damaged by engine, push it a bit lower, rinse, repeat…

OTOH I consider this kind of cheat, so here's another option - have radial engines behind deployable shield. Never tested that, but it should work.

[fourfa]

Two things: 

Heat shields with ablator turned down to zero have heat tolerance of 3300! I use these all the time just to save mass. I have definitely never needed the ablator inside the Kerbin SOI. If you have it on it'll get used up for sure, but try a normal ballistic re-entry from higher than Minmus with zero ablator; you won't overheat the shield. 

Two, this is super exploity- but engine exhaust will pass straight thru the 10m inflatable shield as if it wasn't there. Try it. 

[theJesuit]

Part of me wonders whether or not an engine inside an open ended cargo bay would work?

I have no idea as I've never tried! 

Peace.

[fourfa]

10 hours ago, Zamolxes77 said:

One method I used so far is engines 1st, ships with CoM towards the engines, so they will take the brunt of heating, sadly they can't take much, all are rated at 2000K (except nukes off course at 2900K, but they cost 10,000 kerbalbucks per engine)

You sure?  My KSP says 2500K

[sardia]

What does your ship look like? I don't get why your engine + fuel tank entering engine first isn't enough for low orbit maneuvers.

[Red Iron Crown]

Use the inflatable heatshield in the nose, put the engines on outriggers that don't reach further than the heatshield, in a "pull" configuration. Docking port in the middle for attaching payload behind. Everything is heatshielded, it's fully reusable, and having the engines up front makes it more stable during aerobraking. The downside is you can't burn retrograde while aerobraking.

[swjr-swis]

2 hours ago, fourfa said:

Two, this is super exploity- but engine exhaust will pass straight thru the 10m inflatable shield as if it wasn't there. Try it.

Visibly, yes. But the effective thrust will be decimated. Do a test with the exhaust going through the shield, and with the engines just sticking out so the exhaust is fully outside the shield... you'll see the difference.

[fourfa]

Erp.  Yep, of course you're right.  The problem was that if you look at the engine's right click menu, it shows a number for thrust that is not modified by occlusion at all.  

I swear I did a test exactly like this at some point, and the thing was invisible to occlusion.  Maybe it was a pre-release build when the shield was brand new, and gained real colliders after that.  Anyway sorry for the bunk info!

[KerikBalm]

Stick them in a cargobay, and use the ramp?

 

I had something else in mind when I made these... but... it should work. In the above case, its a rover with 4x rapiers that can attach inside the cargobay on an otherwise suborbital mk3 design, and allow it to SSTO on laythe.

I also made a 4x LV-N module for it to allow it to get ot laythe (In which case, to get ot kerbin orbit, it used external rapiers that were decoupled upon reaching kerbin orbit, and then landed back at KSC).

Anyway, throw your engines in a mk3 cargobay, and have a ramp at the end.

2700K temperature resistance

[Zamolxes77]

11 hours ago, fourfa said:

You sure?  My KSP says 2500K

No I'm not sure lol, I believe you are correct and is around 2500K. I gotta try what you suggested with the heat shield with no ablator, that sounds like a neat idea. My current design uses an actual fairing on the back end, seems to work pretty well.

19 hours ago, silent_prtoagonist said:

You could even give it some stubby wings/design it more like a spaceplane, which would allow you to fine tune your flight profile and ride that bleeding edge of just barely not exploding. 

I thought about adding some wings to improve my drag coefficient.

1 hour ago, KerikBalm said:

Stick them in a cargobay, and use the ramp?

2700K temperature resistance

Neat idea !

<update> Damn my new ship I posted works even worse, I swear aerodynamic model seems to swing from one instance of the game to the next. Yesterday it worked fine, now it doesn't. i wonder if there's some horrendous bugs with the mod.

<further update>

I have tried the inflatable heat shield on nose, problem is, once inflated you can't deflate it (at least in this mod, never used it in stock), so when accelerating, having a mushroom on the nose proved to be ... extremely shaky at best. I replaced the fairing in picture with a heat shield, with zero ablator, added some wings A and wing D, plus I sneak 4 radiators in the wings, 2 on each side. Worked like a charm, I dipped at 37km Pe on 1st pass, when coming back from Minmus and Apo dropped to 6,000 km in one go. Everything stayed cool, except that reaction wheel i have under the docking port, I might have to move it somewhere else.

Btw, if you playing Kerbal Kommander, apparently you can BUY ablator as any other commodity at the space station !

Edited July 29, 2016 by Zamolxes77

[Jetski]

I use on every ship a shielded docking port on the front, and sometimes an open service bay aft to act as fins. Bigger version has 4 lvns in a cargo ramp, and 4 wings aft set sideways for max drag.   The little type E wings have very good drag, light in vacuum, and insane heat tolerance. just close the ramp and go for it!  Minmus to a 30k aerobrake, lots of temp gauges showing but no parts burning, 2 passes to LKO. No need to steer or anything

Edited July 31, 2016 by Jetski

[Zamolxes77]

41 minutes ago, Jetski said:

I use on every ship a shielded docking port on the front, and sometimes an open service bay aft to act as fins. Bigger version has 4 lvns in a cargo ramp, and 4 wings aft set sideways for max drag.   The little type E wings have very good drag, light in vacuum, and insane heat tolerance. just close the ramp and go for it!  Minmus to a 30k aerobrake, lots of temp gauges showing but no parts burning, 2 passes to LKO. No need to steer or anything

That's very nice, I never managed to aero- break that low coming from Minmus, something would explode. I'm at the point I can afford LV-N's in my KK game, so my cargo ship will get a redesign around new propulsion.

[Jetski]

My first ship, carries 3k cargo and aerobrakes to 32500m from Minmus Station.  keep locked prograde, but service bay drag acts as fins and keeps you generally pointed the right way

 

My LVN beauty, carries 7500 cargo, and can close bays and ramp for very hot aerobraking, I've gone as low as 27500 with this, the wings are super draggy and have very high heat tolerance.

2 passes and I'm back near Kerbin Station orbit.