1.0.4 Reentry

[wisnoskij]

I am having a hell of a time with the reentry in 1.0.4.

First off, I have never really understood drogue chutes, they are supposed to be for high speed, but no one has ever been clear on what even the general magnitude of the speed is. Secondly I have never used heat shields. I also am unsure of how the new radiators are supposed to work, presumably you would really really not want a radiator when reentering, since it would suck up the heat and transfer it to your ship.

So far I have only survived by having loads of chutes and deploying a few that were destroyed but slowed be down enough to not burn up.

I was also trying out realchutes, but it is really complicated.

Also, is there a way to delay deployment on detached parts. I am having a lot of problems with detached boosters smacking into the main ship or themselves even with loads of sepitrons (I think they are bobing back and forth).

[Snark]

Regarding chutes: There's a UI on the chute that indicates whether it's safe to deploy. Right-click on the chute. It will say "Unsafe", "Risky", or "Safe". Wait until it says "Safe".

Regular chutes will need to be under ~250ish m/s before they're safe to activate. Drogue chutes are about double that.

I generally don't have a problem with detached boosters smacking into the main ship, and I rarely use sepratrons (generally only use them for really huge monsters, like Eve landers). One thing that can help: when you're attaching a fuel tank (or SRB) to a radial decoupler, slide it down as low as it can go and still be attached to the decoupler. That is, you want the decoupler's attachment point to the radial-thing-being-decoupled to be as high as possible.

Doing it that way means that the separation force from the decoupler will be applied above the decoupled thing's center of mass, which will tend to make it rotate away from the central craft, which provides a nice natural separation. (I'll sometimes get a message that my radial boosters collided into each other after separation, but I've already discarded them so I don't care.)

Also, if your central rocket isn't already activated (i.e. if you're not asparagus), make sure that your central rocket is put together in the same stage as your radial decouplers. In other words, when you hit the space bar, you want your central ship's engine to ignite at the same time that your radial decouplers fire. Don't put it in two stages (i.e. you don't want "separate decouplers, pause, light engine"). Reason: you want that central ship accelerating hard away from the decoupled boosters, to minimize their chance of bumping into it.

[wisnoskij]

Regarding chutes: There's a UI on the chute that indicates whether it's safe to deploy. Right-click on the chute. It will say "Unsafe", "Risky", or "Safe". Wait until it says "Safe".

It that for stock or real, or both (does the material type effect it ability to withstand speed/heat)? Also, it is not just that I am unsure of when it is safe to deploy, but the ship will be destroyed before it is safe to deploy the chutes.

And it is not so much hitting the central stage and hitting themselves, I am really hung up and saving all stages of a rocket.

Also the change note indicated that the main chute had been changed to about 290, I think.

[AlexisBV]

I'd just like to add that I've not used heat shields (yet) either. I just gently aerobrake. Makes returns home a bit longer but simplifies design quite a bit. As for chutes, the unsafe/safe UI field is on stock. That being said, it can be a bit tricky trying to right-click on that while you're hurtling towards the ground

I've never used realchutes.

[imaspacestation]

If you aren't slowing down enough to deploy main chutes before you hit the ground, then you are coming in way too steep, thus way too fast. Try a more shallower approach on re-entry.

When all else fails, just slap on some airbrakes.

[Old Foxboy]

Did someone mention you can adjust the opening height of the chutes? 500m is too low in some cases, so better right click on the chute and set it to 1000m to have a safety margin.

[KSK]

If you aren't slowing down enough to deploy main chutes before you hit the ground, then you are coming in way too steep, thus way too fast. Try a more shallower approach on re-entry.

This. For capsule only re-entries, I find that setting my periapsis to 20-25km brings me in shallowly enough that I can deploy chutes at about 5,000m. Plenty of time. Not sure what a good periapsis would be for larger ships.

[Grumman]

Also, is there a way to delay deployment on detached parts. I am having a lot of problems with detached boosters smacking into the main ship or themselves even with loads of sepitrons (I think they are bobing back and forth).

When I have this problem, I just roll the ship a bit as I activate the decouplers - the added rotational velocity gets them moving away from the ship.

[Kurld]

You can also adjust the separation force and (I think) torque for the decouplers when you are in the VAB. Most stock forces seem WAY to much. So I typically set both to be very low for most cases. If your central rocket is under power at all the separated objects just kind of slide to retrograde.

[Kryxal]

Probably better than adjusting seperatron thrust is to adjust the fuel levels ... apply the force as fast as you can, but only as much as you need.

[mrclucks]

I've found that generally 1k kg per small inline parachutes and 2k kg per large inline parachutes is more than good.

If you're able to slow down to 8-10 m/s it should be good enough since the heat shield will break your fall, if not add a quick girder

[Snark]

Also the change note indicated that the main chute had been changed to about 290, I think.

Yeah, that's what they said. I trusted them and lost some parachutes that way.

My experience has been that if I just ignore the safe/unsafe marker and pop the chutes at close-to-290, then they get ripped off.

If I watch the safe/unsafe marker, I note that it seems to say "safe" at around 250 m/s for regular chutes. Popping the chute then always works.

So the release notes seem kinda misleading to me-- they don't reflect what I've observed in-game.

[almagnus1]

For deorbit into kerbin, I try to set my periapsis to 30k coming into Kerbin, and then hold off on chute deployment until I'm going about 250 m/s, which generally means I'm going slower than 250 m/s when the chutes actually deploy.

With a 30k periapsis, it allows you to put most of the deceleration onto your heat shield, while also slowing down a lot from 30k down to 20k and possible 10k, so you get to 250 while you've still got several km of altitude left, rather than being near the ground. If you design your reentry part of your craft right, you should be able to turn off SAS and it should take care of keeping itself pointed the right way, which is something that's very helpful with TAC-LS, as it allows you to conserve battery during re-entry, so you can use it when you land to stick the landing.

Hopefully that helps a bit.

[Sharpy]

I had some problems with the first stage of SRBs (with LF fuel tanks attached to top), and at that point the ship is far too heavy to roll it willy-nilly, so I attached to each four of the cheapest, simplest fins, angled 5 degrees away from the ship. Works like charm. In other cases I shut off the engine for a couple seconds to allow the stages to clear, before firing again.

As for the chutes, I usually activate them around 190m/s, when I'm some 800m above the ground. Sure I *could* activate them at some 6000m with 250m/s, but what then? Phys-warp x4 and go make myself a coffee? They need about 200m to slow down to their specific terminal speed anyway.

Edited July 2, 2015 by Sharpy

[tutike2000]

Drogues and regular chutes need to be in different stages.

1 drogue will probably be enough no matter what sort of craft you have - set its deployment height as high as possible, it should slow you down below 200m/s even if you have a monster of a lander.

Once at reasonable speed (250 or less), stage your regular chutes.

If your drogues can't survive your airspeed, you're coming in way too steep.

If you don't have drogues yes, you need to come in at a very shallow angle, or have leftover fuel to slow yourself down with.

---- Edit

Oh, now I notice that you're talking about chutes on your lifter. That gets a lot more complicated.

Either install StageRecovery to make your life easy, or tweak chute properties.

All chutes on the stage you drop need to be staged together, but deploy separately. Your drogues should deploy as soon as possible (min pressure, max height), and your regulars as low as possible (max pressure, min height).

Adjust until you can get it right, and don't stage your empty lifter if you're going too fast.

Edited July 2, 2015 by tutike2000

[Wemb]

Another thing to note is that saved ships and games done before the most recent updates have had problems with the small parachute - it takes about 700m vertically to slow a stock capsule down enough to land safely, but still deploys with 500m left - you should definitely check that.

Otherwise, I've found that from a low Kerbal orbit, a stock capsule can re-enter and land without a heat shield with out problems - what the heat-shield is really useful for is not to survive re-entry, so much as to add balast to a capsule and a science module, so it doesn't re-enter parachute first.

Also, if you're having problems hitting the ground a bit fast, add some legs, even if they collapse on hitting the ground, the rest of the capsule may well survive.

Wemb

[Faykin]

First, let's talk overheating.

Where is the heat coming from? How does it go away?

The heat is coming from friction (1). Friction is converting your speed into heat. Your craft is absorbing (2) the heat of that friction. In other words, the faster you are de-accelerating (3), the faster you accumulate heat

Your craft also radiates (4) heat. This heat radiation is based on the difference between the ambient temperature and the heat of your craft. In other words, the hotter you are, the faster you dump heat. Radiators increase that rate of transfer, but it's still a factor of temperature difference. As long as your radiators are hotter than the air around them, they will be dumping heat. Hint: Keep them out of the airstream, since the friction heats the air at the point of contact.

So, to keep from exploding because of heat, you want to slow down your heat accumulation, by reducing your rate of de-acceleration.

How do you slow down slower, over a longer period of time? Shallow re-entry, where most of your speed is horizontal, rather than vertical. You want to go round and round Kerbin until you are going slowly, rather than plunging straight towards the center of the world.

Simple way of doing that is have your perapsis between 28k and 32k meters above the surface when you hit the atmosphere. Aim to miss Kerbin, not hit Kerbin.

Ok, so now we have your craft re-entering the atmosphere in such a way that it doesn't explode from heat, and has plenty of time to slow down.

You want to have enough parachutes so you are travelling under 7m/s when you touch down. I've found that means 1 kg of parachute for every 15 kg of craft, or 0.1 tons of chute (one radial chute) for every 1.5 tons of empty weight.

When do you deploy? When your speed is below 250 m/s. With the shallow re-entry profile, most of my craft get below 250 m/s by 6000m off the ground. Depends on how aerodynamic your craft is. If you need more drag, consider air brakes or landing struts - extending them will increase your drag. Deploy them after all the flaming graphics have stopped, to keep them from burning off.

tl:dr: 1 radial chute for every 1.5 tons of craft. Set your perapsis for 30km. Deploy your landing gear after the flames have died down. Deploy the chutes after your speed is below 250 m/s.

(1) And compression. Ignoring compression as it adds complexity without actually changing the answer

(2) Part of that heat goes to atmo, part to the craft. Simplified because it doesn't actually change anything

(3) And travelling, due to compression heat. Ignoring that component because.

(4) Radiation and conduction (I don't think convection is modeled). Simplified.

Edited July 2, 2015 by Faykin
annotations

[ExEvolution]

that's the full deploy height, and that is 500m above the ground, that height changes as the ground height changes. All adding extra height to the full deploy does is make it take longer to reach the ground once your parachute has slowed your decent to the terminal velocity of the craft with parachute drag.

Your craft should be reaching that velocity between 50 and 300 meters, if its not reaching it within that distance, you're probably not using enough parachutes to support the mass

- - - Updated - - -

First, let's talk overheating.

Where is the heat coming from? How does it go away?

The heat is coming from friction (1). Friction is converting your speed into heat. Your craft is absorbing (2) the heat of that friction. In other words, the faster you are de-accelerating (3), the faster you accumulate heat

Your craft also radiates (4) heat. This heat radiation is based on the difference between the ambient temperature and the heat of your craft. In other words, the hotter you are, the faster you dump heat. Radiators increase that rate of transfer, but it's still a factor of temperature difference. As long as your radiators are hotter than the air around them, they will be dumping heat. Hint: Keep them out of the airstream, since the friction heats the air at the point of contact.

So, to keep from exploding because of heat, you want to slow down your heat accumulation, by reducing your rate of de-acceleration.

How do you slow down slower, over a longer period of time? Shallow re-entry, where most of your speed is horizontal, rather than vertical. You want to go round and round Kerbin until you are going slowly, rather than plunging straight towards the center of the world.

Simple way of doing that is have your perapsis between 28k and 32k meters above the surface when you hit the atmosphere. Aim to miss Kerbin, not hit Kerbin.

Ok, so now we have your craft re-entering the atmosphere in such a way that it doesn't explode from heat, and has plenty of time to slow down.

You want to have enough parachutes so you are travelling under 7m/s when you touch down. I've found that means 1 kg of parachute for every 15 kg of craft, or 0.1 tons of chute (one radial chute) for every 1.5 tons of empty weight.

When do you deploy? When your speed is below 250 m/s. With the shallow re-entry profile, most of my craft get below 250 m/s by 6000m off the ground. Depends on how aerodynamic your craft is. If you need more drag, consider air brakes or landing struts - extending them will increase your drag. Deploy them after all the flaming graphics have stopped, to keep them from burning off.

tl:dr: 1 radial chute for every 1.5 tons of craft. Set your perapsis for 30km. Deploy your landing gear after the flames have died down. Deploy the chutes after your speed is below 250 m/s.

(1) And compression. Ignoring compression as it adds complexity without actually changing the answer

(2) Part of that heat goes to atmo, part to the craft. Simplified because it doesn't actually change anything

(3) And travelling, due to compression heat. Ignoring that component because.

(4) Radiation and conduction (I don't think convection is modeled). Simplified.

Just to make it clear, the heat is not coming from Friction, it is coming from compression of the air around the object and is known as the Isentropic Process. Compression heats, decompression cools

Edited July 2, 2015 by ExEvolution

[Wolf Baginski]

I'd just like to add that I've not used heat shields (yet) either. I just gently aerobrake. Makes returns home a bit longer but simplifies design quite a bit. As for chutes, the unsafe/safe UI field is on stock. That being said, it can be a bit tricky trying to right-click on that while you're hurtling towards the ground

I've never used realchutes.

The chutes can be in a stage of their own. Or two, drogues first and main chutes second, Or you can set them up with Action Groups. Staging is simple, just hit the space-bar.

Either way, you open multiple chutes at the same time, if you set it up that way.

Smart Parts http://kerbaldevteam.tumblr.com/post/79232581790/modding-mondays-smart-parts is worth a look for automating things.

[Reactordrone]

that's the full deploy height, and that is 500m above the ground, that height changes as the ground height changes. All adding extra height to the full deploy does is make it take longer to reach the ground once your parachute has slowed your decent to the terminal velocity of the craft with parachute drag.

Your craft should be reaching that velocity between 50 and 300 meters, if its not reaching it within that distance, you're probably not using enough parachutes to support the mass

- - - Updated - - -

There's a reason the chute deployment height was changed from 500m to 1000m. A Mk 1 pod with a Mk 16 chute will lose about 650m altitude while the parachute fully deploys.

[Mars Mullo]

For deorbit into kerbin, I try to set my periapsis to 30k coming into Kerbin, and then hold off on chute deployment until I'm going about 250 m/s, which generally means I'm going slower than 250 m/s when the chutes actually deploy.

With a 30k periapsis, it allows you to put most of the deceleration onto your heat shield, while also slowing down a lot from 30k down to 20k and possible 10k, so you get to 250 while you've still got several km of altitude left, rather than being near the ground. If you design your reentry part of your craft right, you should be able to turn off SAS and it should take care of keeping itself pointed the right way, which is something that's very helpful with TAC-LS, as it allows you to conserve battery during re-entry, so you can use it when you land to stick the landing.

Hopefully that helps a bit.

Well said... best post in this thread yet.

Another item I noticed. If you have Real Chutes you get two heat shields. 1 has only 100 ablative and is cheaper... but has a jettison able shield which can take alot of load off your chutes.

The stock heat shield (I think) is more expensive weighs more but has 200 ablative so can burn up longer. Which means you can actually take a shallower periapsis of about almost 40km ... burn longer.

As for drouge chutes .. can you open them at high altitude with little atmosphere and slow speed earlier before teh hot plasma speeds are even reached?

- - - Updated - - -

....

Otherwise, I've found that from a low Kerbal orbit, a stock capsule can re-enter and land without a heat shield with out problems - what the heat-shield is really useful for is not to survive re-entry, so much as to add balast to a capsule and a science module, so it doesn't re-enter parachute first.

......

Wemb

Just to clarify here.

We all know the Mk1 command pod has a heat shield built into it right? The others don't.

So bringing down a naked command pod of the other varieties without a heat shield is considered a death wish. I'm not saying it is impossible ... but with new heating mechanics is probably even less likley to survive without a heat shield attached.

[Wemb]

We all know the Mk1 command pod has a heat shield built into it right? The others don't.

Ah, no, we didn't all know that - thanks!

I am wondering what sort of insane re-entry you need to do in order to _need_ 200 units of ablation (ablator? asbestos? :-) - I've done re-entries back from the Mun at about 3,000 mps but which haven't used used up more than 4% of the shield yet.

Wemb

[Starhawk]

We all know the Mk1 command pod has a heat shield built into it right? The others don't.

Actually, no. The Mk1 command pod and the Mk1-2 command pod are designed to survive LKO reentry without heat shields.

Heat shields have an ablator resource which is consumed. The command pods have no such resource.

Happy landings!

[Pi_]

Forgive my off topic, but I've been away recently.

I see this thread title referring to v1.0.4 posted on June 30th. And on forum homepage Harvester announced v1.0.3 on June 22. So did Squad really put out a new update in just one week?

[Starhawk]

There was a save-breaking bug in 1.0.3 for some ships. 1.0.4 is a hotfix for that.

I'm still running 1.0.3 because the bug didn't affect any of my ships.

Happy landings!