Re entry without heatshield - Stuck in Space?

[GoodDayMyFriend]

Hello Dear Forum Dwellers

I'm not all too happy about asking for help in my first post, but I really could use some advise on this.

http://i.imgur.com/MvuzqrP.png

Not sure if I can spoiler Images

After a small minmus science gathering mission, I now have to get the 3 brave kerbonauts back home. Unfortunately, I forgot to add a decoupler between the heatshield and the rest of the craft (usually I am that deviant to put the headshields in front, followed by a cone). I have the option to dock to my station, that has some return capabilities, however, I really don't feel like it. Even though I only put it up for situations like this. Instead, I want to try and bring it down without an active heatshield. It takes about 200ÃŽâ€v (out of 1800) to lower my kerbin periapsis, and then 800 for an orbit. So here are my questions:

Will my kerbals ever see their families again if I try?

What is the most efficient way to de orbit into a safe re entry?

Why can't I just let the parts blocking the heat shields burn up, without exploding myself?

Thats all. Have a nice 6 hours!

Edited July 29, 2015 by GoodDayMyFriend

[nigelvn]

Uhm, I don't use those data mods and don't know how to read them, but I can give some advise: Try to get into a 70 km x 70 km orbit then don't decouple and use the engines to burn retrograde whenever fire shows up, do this untill no fuel is left and then pray.

[Vanamonde]

Could you do a burn during re-entry to help slow the ship, and/or set a fairly high aerobraking altitude and make multiple passes?

[MaverickSawyer]

Could you do a burn during re-entry to help slow the ship, and/or set a fairly high aerobraking altitude and make multiple passes?

Yes. A series of moderate aerobraking passes would significantly reduce the final reentry velocity. And, sadly, most engines still make highly effective heat shields, so go in engine first.

Actually, can you post a picture of the vehicle as it is right now? It would help us determine what we have to work with.

EDIT: Upon closer inspection, it seems that our intrepid crew has over 1800 m/s of dV at their disposal. A propulsive capture is totally doable, so get into an orbit just above the atmosphere, then set your PeA to around 35-39 km. Ride the fire in, and use the engines to bleed off some of the worst of the speed before you have to use the air to do so. You'll wind up coming in a bit steep, but if you're doing so at only about 1200-1300 m/s, it's probably survivable. Just don't hit the chutes until you're below 450 m/s.

Edited July 28, 2015 by MaverickSawyer

[GoodDayMyFriend]

The node would bring me into 70km circular orbit. I am very doubtful that 700 dV would be enough, and aerobraking with this craft is probably not that effective. Still tempted to let everything in front the heatshield burn away

Isn't there a way to spoiler images?

[mrclucks]

You can play it safe and get a periapsis of 60km while burning retrograde the whole time you're in the atmosphere. After the first pass you should not have to orbit too many times before you slow down enough to properly reenter, and then just burn retrograde when you really start to flame up. While making the additional aerobrake passes, try to pass through the atmosphere with the most surface space facing retrograde so you can slow down quicker.

You could also go more risky and get a periapsis at 40-45km and burn retrograde once you reach 70km.

If you're facing retrograde and your engine and tank blow up, I believe that it shouldn't cause any more damage and you're ablator should start doing its job(can anyone verify?)

[Gaarst]

If you're playing with stock thermals and 100% heat, your shouldn't have any problem reentring, even at interplanetary speeds.

As it has been said before, a screenshot of the ship would help, but lower your Pe to 40-45 km and it should be fine; you may have to do multiple passes (if you don't want to, just set your Pe lower) but you shouldn't even need to burn retrograde to survive; unless your ship is a sort of spaceplane, then, reentry becomes a bit more delicate.

[CalculusWarrior]

You should have enough delta-v onboard to make a burn at a ~100 km or so Kerbin periapsis and circularize your orbit (as a Minmus transfer is ~950 m/s, returning should be the same). Then, it's just a matter of doing a standard Kerbin reentry; if you don't have any low-heat-tolerance parts aboard your vessel, you should make it to the surface fine, provided you point your engines forward and come in on a shallow trajectory.

[Snark]

It depends on how heavy your craft is, but I've found that returning from Minmus is pretty simple even without heat shields. And by "return", I mean just-reenter-and-land, without any fancy maneuvering such as making multiple aerobraking passes.

Just set your periapsis to something around ~35 km or so. When you enter atmosphere at 70 km, adjust your ship's attitude to the draggiest possible orientation (flying sideways, for most craft-- set to point "radial out" works nicely). Hold it there until you get low enough to start seeing reentry f/x (generally around 38 km), then rotate to point engine-first. You should do just fine.

Oh, and if you do in fact have a heat shield, and simply happen to have some stuff attached below it that you don't mind losing (like an engine) ... feel free to slam into atmosphere pretty hard. If the engines and what-not explode, they don't hurt the craft, and ultimately you'll end up with the heat shield facing forward.

[Geschosskopf]

Hello Dear Forum Dwellers

I'm not all too happy about asking for help in my first post, but I really could use some advise on this.

Welcome aboard.

After a small minmus science gathering mission, I now have to get the 3 brave kerbonauts back home. Unfortunately, I forgot to add a decoupler between the heatshield and the rest of the craft...

Then no problem with reentry. The rest of the rocket will act as the heat shield. Especially if you set your Pe at Kerbin at about 37km and make 3 or 4 orbits doing this to lower your Ap down to within a few hundred km, after which you can reenter quite safely.

What may be a problem, though, is the landing. If you've got all the extra mass of the rocket stuck on the capsule, parachutes designed for the capsule only might not be enough to slow you down to a safe touch-down speed. HOWEVER, even then, probably the lower parts will explode and this will give a sort of retro-thrust on the capsule so it will probably survive anyway. Best thing, quicksave before you try it and then do something else if it doesn't work. Might have to use that station after all.

[GoodDayMyFriend]

Thanks for the help everyone! It indeed turned out to be just fine. Things did heat up into the red, and I slowed down dangerously late but the mission was a complete success after all!

^{​}

If the engines and what-not explode, they don't hurt the craft, and ultimately you'll end up with the heat shield facing forward.

If you're facing retrograde and your engine and tank blow up, I believe that it shouldn't cause any more damage and you're ablator should start doing its job(can anyone verify?)

Every time I tried that everything exploded. To me it seemed like the overheated parts caused to flip everything around. But it all happens very quickly so I'm not sure. Does anyone know a little more about that?

[Streetwind]

For the sake of completeness:

Going into a 70x70 orbit and then putting a periapsis of 35km is not the coolest and most gentle entry. Your vertical speed will be extremely low, especially in the beginning, meaning you spend a long, long time inside the atmosphere at orbital speeds. This is the "Mars atmosphere dilemma": not enough air to slow you, more than enough air to cook you alive. And yes, this is modeled in KSP now. If you turn on the thermal debug display and observe the skin temperature of your parts exposed to the airstream, you'll notice them very quickly spiking upwards as soon as you enter the atmosphere.

Getting a higher vertical speed will, ironically, result in less g-forces and shorter exposure to atmospheric heating. Additionally, you will much sooner encounter the thick parts of the atmosphere, where cold stratospheric air will actually help cool your craft. This is precisely why people find that they can do a direct reentry from Minmus without a heat shield! Because your orbit is so eccentric, the angle at which you enter the atmosphere is much steeper, you blitz through the hot but useless upper reaches of the atmosphere and very quickly get to the useful middle regions where you actually start bleeding off speed. But at the same time, the surface of the planet curves away from your vector of reentry, automatically working to make the angle shallower and keeping you in that middle range longer than you think you would be, letting you slow down safely and gradually without burning up.

If you want to observe this happening, I recommend the Trajectories mod. Unfortunately, since stock KSP's atmospheric calculation code is not publicly available, Trajectories doesn't work with it in 1.0+. But it does work with Ferram Aerospace Research. It's a slightly different atmosphere model, but it's close enough to stock KSP in this regard. You'll find that, counterintuitively, having a higher apoapsis can oftentimes result in a much gentler reentry path. Trajectories shows your maximum expected G-load while predicting your reentry trajectory; I've never been below 4 G on a return from low Kerbin orbit, but I've been as low as 3.3 G on a direct reentry from the Mun. (Disclaimer: I play with doubled planet sizes, so your G-loads my vary.) You can then try the same situations with stock aerodynamics and find a similar result.

Do note that yes, in some respects a high apoapsis is still dangerous. Your parts will blow up if they reach the maximum temp on either skin or internals. Long, slow reentries from low Kerbin orbit tend to overload your internal temperature limits (this especially happens to spaceplanes); quick, fast reentries from high apoapses tend to overload your skin temperature limits (this is what happens to ships trying to aerobrake at Jool and exploding in a split second, because Jool's atmosphere is set up wrong). If you have sensitive equipment on board, then a direct Munar reentry will absolutely fry them. However, rocket engines, service bays and pods in particular have such high heat tolerances that they will not fall prey to skin heating at the speeds you encounter anywhere in the Kerbin system. So if you have one of these parts at the bottom of your craft (where it will occlude the more vulnerable parts further up), you will generally be safe on a high apoapsis reentry.

Edited July 29, 2015 by Streetwind

[GoodDayMyFriend]

Nice post. Sadly it looks like the explosion mystery won't be resolved for now.

[Friend Bear]

Point your engine down..Have it take all the heat.