Deadly Re-entry with Ferram

[fommil]

Hi all,

I installed Ferram (which is *awesome*) and my ship blew up on its first re-entry because I came in too fast. Now I make sure to slow down to an orbital speed of about 2000m/s and things seem OK. But I don't know what the magic is to decide what is/isn't a safe re-entry speed (one could argue that the experimenting is half the fun of the game). I understand that Ferram only models better aerodynamics, so I can only guess that faster re-entry is causing structural failure rather than too much heating.

But now I'm thinking about installing Deadly Re-entry too, but there is no real advice on **how** to do a re-entry with this mod turned on (except to have an AP of about 20km). What is this mod modelling? Is angle of re-entry the only thing that matters or does speed come into play as well?

I'm so excited by these mods: I've been playing for two major releases and I think I'm ready for the challenge of more realism :-)

[Ippo]

It's actually only about speed. A shallow angle of reentry makes sure you slow down in the higher layers of the atmosphere before you go to the lower ones: if you are slow enough, nothing prevents you from returning safely on a vertical trajectory... but that's not really practical.

Basically, just make sure you come down on a shallow path, or behind a heatshield, and you'll be fine (especially with FAR, that makes it a lot less deadly than in stock).

Be careful though: if you go UP too fast, you can burn on ascent. Not really common, but totally possible (and actually a real problem in RSS).

[fommil]

Cool! Thanks, so what kind of speeds are typically OK? Am I being too conservative with 1000-2000m/s (I guess I should work out what altitude that was at, probably about 100km)

[Superfluous J]

Coming in from Kerbin Orbit, be it LKO or Keostationary, I put my periapsis at 20km and I'm fine. Coming in from Mun I put my periapsis at 25km, and Minmus I put it at 30. I've never ever lost a ship, and I use Deadly ReEntry as well (which you implied in your title but I think you don't use it).

One very important thing, come in tail-first. If you have a rocket still attached to your command pod, it should be perfectly facing the prograde direction. Your navball should be facing retrograde. You can even turn off SAS (and you generally should). If you have fins on your rocket... don't. Make sure you don't have fins on your rocket during re-entry.

I've yet to come back from interplanetary but I suspect 30-35km would work for that, and maybe just slow me down enough to get into orbit to make another pass.

[Ippo]

Well, in my experience, ~2000 m/s is a good speed to hit the atmosphere (at ~40km) but ONLY behind heatshields. You might want to save some fuel to reduce the speed if you don't have heatshields. Note that heatshields are not required, in interstellar scott manley routinely lands spaceplanes without them: you just need to be VERY careful

[Carter]

With FAR you can also use your pod's torque to pitch up a little bit and actually generate lift. By doing this you can set a Pe like 20km, for instance, but prolong your time in the upper atmosphere. I've actually started climbing by a few m/s on a few reentries. You ycan also set a Pe of 45-50km and do successive aero-braking passes. I'd only ever do that if I was coming in from inter-planetary, any orbit with the Ap inside Kerbin SOI isn't that big of a deal.

[fommil]

Excellent, thanks for the hints! I've just made my first successful landing with both Ferram AND Deadly Re-Entry turned on. Two things came up:

1. I had lander legs on my pod, but they were blown off during re-entry when the heat got **really** high, then after the leg blew off the heat started to go down. I guess they are not covered by the heat shield, so without spending a lot of fuel to reduce speed in Kerbin re-entry, it's got to be a sea landing. Or am I missing something? It would certainly be good to be able to get through the atmosphere with lander legs intact.

2. the heat shield has a decoupler. Is there any reason for that? (I can only guess this was so that the hot heat shield doesn't radiate onto the lander once through the atmosphere). On Kerbin, what altitude is a good time to dispense with the heat shield and kick in the parachute? It doesn't really matter in stock, so I always just did it in upper atmosphere. I'm guessing about 10k feels right.

[Harry Rhodan]

Or am I missing something?

The capsule has a higher crash tolerance than the landing legs.

[Franklin]

Gotta keep in mind FAR attempts to make the atmosphere more realistic, and 2000 meters per second is almost 4500 miles per hour. Think about the effect of any amount of air pressure against anything but a needle-slick surface at 4500mph.

When you're starting out I'd recommend keeping the FAR panel open (button's up next to your fuel and contract buttons) and keep an eye on your Flight Status:

Green good, yellow bad. High Dyn Pressure might as well read 'You're probably gonna die'.

Drogue chutes are far more important in FAR, as you can't just bank on a dime, slam your belly against the wind and slow yourself like you can in stock. You'll disintegrate.

edit: As of FAR 0.13.2 you can change your speedometer readout from m/s to something more real-world applicable, which may help you visualize exactly how fast you're going when slamming into the atmosphere and banking:

0.13.2v------------------------------------  
Features:  
Aerodynamically-induced structural failures will now be applied.  Beware of high dynamic pressure
Added IAS and velocity in knots, mph and km/h to the airspeed settings

Edited September 16, 2014 by Franklin

[Franklin]

Playing with FAR for even an hour makes it very clear how badly KSP needs air breaks.

[Taki117]

Well, in my experience, ~2000 m/s is a good speed to hit the atmosphere (at ~40km) but ONLY behind heatshields. You might want to save some fuel to reduce the speed if you don't have heatshields. Note that heatshields are not required, in interstellar scott manley routinely lands spaceplanes without them: you just need to be VERY careful

Spaceplanes do have heat shielding, they just don't use Abaltive shielding. They instead have reflective shielding which instead of absorbing the heat into a material that boils away (And takes some heat with it) it reflects that heat away from whatever it's protecting. (Think Shuttle Tiles vs Apollo Heat Shield)

[fommil]

The capsule has a higher crash tolerance than the landing legs.

Not when it has a science experiment underneath :-P

Edited September 16, 2014 by fommil

[Wanderfound]

First up, the Deadly Reentry mod is nowhere near as lethal as its rep implies. Ferram's aerodynamic failures are a much bigger threat.

Second: circularise first. Don't try to go directly from Minmus to KSC. You can still use aerobraking to circularise, but you need to stay out of the lower atmosphere until you've pulled it back down out of the hypersonic range.

When I'm being sensible, I try to stay above 30,000m until I'm at Mach 5, and above 20,000m until I'm at Mach 2.

When I'm not being sensible:

&

&

Canards work quite well as coal-mine canaries.

[Superfluous J]

without spending a lot of fuel to reduce speed in Kerbin re-entry, it's got to be a sea landing

Not at all. You need the fuel to slow yourself down whether you hit water OR land, but you don't need that much. If your chutes slow you down to say 10-15m/s you just need to burn right at the last few seconds to slow down to 5-6m/s.

Not when it has a science experiment underneath :-P

If you're bringing a science experiment home in anything with a Kerbal in it, you're running an unnecessary risk. Well before re-entry your Kerbal should get out, right click that expeirment, and take the data from it so if the experiment goes kablooey, the science remains in the pod in (relative) safety.

[StarkRG]

Coming in from Kerbin Orbit, be it LKO or Keostationary, I put my periapsis at 20km and I'm fine. Coming in from Mun I put my periapsis at 25km, and Minmus I put it at 30. I've never ever lost a ship, and I use Deadly ReEntry as well (which you implied in your title but I think you don't use it).

One very important thing, come in tail-first. If you have a rocket still attached to your command pod, it should be perfectly facing the prograde direction. Your navball should be facing retrograde. You can even turn off SAS (and you generally should). If you have fins on your rocket... don't. Make sure you don't have fins on your rocket during re-entry.

I've yet to come back from interplanetary but I suspect 30-35km would work for that, and maybe just slow me down enough to get into orbit to make another pass.

Hmm, see I tend to go lower the higher my entry speed. My thinking behind this is that if I'm too high I won't slow down in time and I'll end up having to go around again (and depending on how I've rationed my life support and electricity supplies that might end up killing my kerbals). More velocity means more that needs to bleed off in order to return. FAR/NEAR atmospheres are pretty damn thin down to around 20km. Dropping down from Minmus I tend to dip to somewhere around 28km-30km.

I haven't returned from interplanetary speeds yet, but I figure one pass at around 35km-40km for capture should put me on the ground during the second pass.

Second: circularise first. Don't try to go directly from Minmus to KSC.

Nonsense. I've returned direct from Minmus easy. Takes a little getting used to, I'll grant you, but it's not as difficult as it first seems. I found 35 requires another go around while 25 kills you, I think 28 might be the sweet spot. Granted I tend to do this thanks to using TAC life support and reducing the amount of stuff I bring along to a minimum. I tend to not bring my solar panels back with me unless I can help it which means if I need another go around I'll likely run out of power before I get back, this might mean my kerbals die from lack of electricity or, more likely, it'll mean I can't orient my capsule properly.

If you're bringing a science experiment home in anything with a Kerbal in it, you're running an unnecessary risk. Well before re-entry your Kerbal should get out, right click that expeirment, and take the data from it so if the experiment goes kablooey, the science remains in the pod in (relative) safety.

It's a risk, but in career every little bit of money you can return counts (depending on how hard up you are), and some of those experiments aren't cheap.

[Superfluous J]

It's a risk, but in career every little bit of money you can return counts (depending on how hard up you are), and some of those experiments aren't cheap.

If you must bring the experiment home, eliminate all risk by taking the science anyway. That way, if the experiment survives you get the money, but if the experiment explodes you still get the science.

[Wanderfound]

Nonsense. I've returned direct from Minmus easy. Takes a little getting used to, I'll grant you, but it's not as difficult as it first seems. I found 35 requires another go around while 25 kills you, I think 28 might be the sweet spot. Granted I tend to do this thanks to using TAC life support and reducing the amount of stuff I bring along to a minimum. I tend to not bring my solar panels back with me unless I can help it which means if I need another go around I'll likely run out of power before I get back, this might mean my kerbals die from lack of electricity or, more likely, it'll mean I can't orient my capsule properly.

Can it be done? Certainly. Should it be recommended as an approach to someone who's already having problems? Probably not.

[StarkRG]

Can it be done? Certainly. Should it be recommended as an approach to someone who's already having problems? Probably not.

Sure, but at the same time, the best way to learn how and eventually get used to it is to fail often. Avoiding it isn't going to make things easier.

[Thahat]

also, when making an SSTO or something with wings this mod combo, think nasa style, keep your nose pointed diagonally up in the direction of travel (its the downward speed that kills you, not the forward one, the downward one compresses air creating a crapton of heat) because then you can change your forward momentum into upward momentum and gravity will remove the upwards one over time, in other words, same altitude, slowing down. and then when you get under 600M/s or something you can fly it like a normal plane

[J.Random]

Just keep your Pe at 30km+. Your ablative heatshield will be able to keep you safe from overheating even if you try lower Pe, but if you try to brake too fast, you'll kill your kerbals with G-forces. It's safer to brake slower and skip out of the atmosphere for another pass (again, heat isn't really the problem).

[rentaspoon]

Glad I'm not the only one struggling, I've made lots of successful landings but none with wings.

I need to learn because I'm going for a no parachute no revert career once I finish this one

[Alshain]

I've been considering DRE as well but my big problem is how do you possibly do all that dancing around in the atmosphere to prevent overheating and then still hit the runway without an hour long flight after de-orbit. I've tried doing some of the suggestions here without DRE, just to practice speed management first and I'd always come in too fast or I go up and down again to reduce speed and end up on the wrong side of the planet.

Edited September 18, 2014 by Alshain

[Wanderfound]

I've been considering DRE as well but my big problem is how do you possibly do all that dancing around in the atmosphere to prevent overheating and then still hit the runway without an hour long flight after de-orbit. I've tried doing some of the suggestions here without DRE, just to practice speed management first and I'd always come in too fast or I go up and down again to reduce speed and end up on the wrong side of the planet.

Keys for me:

* Don't overdo the "pitch up on reentry" stuff. Yeah, sure, you bleed off speed faster while doing that, but you can only get away with it in the upper atmosphere where there's sod-all drag anyway. It's usually quicker to dive to 30,000m, keep your angle of attack close to 0°, and toast your plane as close as you dare to burning up. Keep descending as fast as you can get away with. A sacrificial battery or something near the nose acting as a coalmine canary may help you learn the limits.

* Circularise first. It's a lot easier coming in at Mach 7 than Mach 12.

* Open your intakes as soon as you hit air.

* Think about using spoilers and flaps to enhance drag. Make sure you balance 'em right if you do, though; involuntary pitching at hypersonic speed is not a long term survival strategy.

* S-turns. Not yawing, but a proper 90° bank and a very delicate pitch-up. Just keep an eye on your sink rate while doing it; not a lot of vertical lift when you're standing on a wingtip.

* Get your aero design smooth enough that your plane can cruise with 3x or 4x physics acceleration, in both descent and level flight. Just remember to turn it back down to 1x before you touch the controls, and keep an eye on things while cruising. Return to 1x and restabilise if the plane starts to oscillate.

I've lost plenty of planes to Ferram on reentry, but I've never lost one to overheating. I have melted off quite a few sets of canards, though.

You can get away with a surprising amount of high-G high-temp high-speed daftness at relatively low altitudes, but it is a matter of riding the limits.

Edited September 18, 2014 by Wanderfound

[Alshain]

Keys for me:

Everything you listed (except the first one) is exactly what I do. but I can't get speed down fast enough that way to avoid what I'm sure would burn up the craft. S curves don't work that high, I can use them near the runway just fine but at that speed @30k my wings will shear off.

[Wanderfound]

Everything you listed (except the first one) is exactly what I do. but I can't get speed down fast enough that way to avoid what I'm sure would burn up the craft. S curves don't work that high, I can use them near the runway just fine but at that speed @30k my wings will shear off.

Have a look at the altitude, sink rate, speed, angle of attack and G-meter. This is a plane that only has two struts per wing.

You let the lift of the wings do the turning for you; there's barely any pitching involved at all. Watch the G meter as you do it, and back off the instant it gets too high. And, as always with planes: curves, not angles. No sudden moves.

(note: 12G not actually recommended, I was having fun. A constant 4G or so is plenty.)

Edited September 18, 2014 by Wanderfound