Do you jettison heat shields?

[MR L A]

I know adding "jettison heat shield" to staging is an option, though I find myself using it extremely rarely. Sometimes I use it for a rover, though I always find myself slightly annoyed that it doesn't jettison (automatically) just as the parachutes open fully... so it does that thing where it sits at the bottom of your craft despite not actually being attached to it =/

Does anyone regularly use the option? If so, why?

Edited July 14, 2018 by MR L A

[RealKerbal3x]

I do, not sure why. For realism I guess.

Also, I jettison it before the chutes open fully, then wiggle my capsule about a bit so it flies off.

[Urus28]

Depends of the mission actually. For a return on Kerbin I don't jettison heat schield, for other planets I will jettison.

[MR L A]

1 minute ago, RealKerbal3x said:

I do, not sure why. For realism I guess.

Also, I jettison it before the chutes open fully, then wiggle my capsule about a bit so it flies off.

Yeah, I end up doing that... though it spoils the "realism" a bit for me 

2 minutes ago, Urus28 said:

Depends of the mission actually. For a return on Kerbin I don't jettison heat schield, for other planets I will jettison.

Yeah, thinking about it, I do jettison for Duna if I'm using chutes just to cut the weight down a bit. Deffo not on Eve though otherwise a parachute descent takes even longer

[RealKerbal3x]

Just now, MR L A said:

Yeah, I end up doing that... though it spoils the "realism" a bit for me 

Fun fact: The Apollo capsule's heat shield was built into the spacecraft, so it wasn't jettisoned. The ability to jettison the heat shield is useful for landing rovers though.

[The Aziz]

For Kerbin returns - never, it's always few kerbollars more for recovery, anywhere else when it's not needed (basically, Duna and Eve, never encountered Laythe atmo so) I drop it, it's few kilograms less.

[MR L A]

Just now, RealKerbal3x said:

Fun fact: The Apollo capsule's heat shield was built into the spacecraft, so it wasn't jettisoned. The ability to jettison the heat shield is useful for landing rovers though.

I think it's built in for quite a few capsules... afaik the Dragon capsule has one built in - I seem to remember someone saying something about the difficulty of having landing legs that could extend through the shield without compromising its functionality. Not sure about Mercury and Gemini... anyone?

2 minutes ago, The Aziz said:

Eve [...] I drop it, it's few kilograms less.

Do you really want a few kilograms less when gently floating through Eve's atmosphere? 

[The Aziz]

38 minutes ago, MR L A said:

 gently floating through Eve's atmosphere? 

Yeah...

I mean, I've managed to land on Eve in one piece once so far (with no plans for return) so there's not a problem, but for Duna every useless piece of junk is just dead weight when I want to go back to space. I leave the lander to fall back and crash once I dock with my mothership so it's not that I need it again.

[Zeiss Ikon]

Can't say for certain on Gemini, but the Mercury heat shield was built to jettison.  This caused some drama during John Glenn's flight -- after launch, while running down a checklist, he turned the heat shield jettison switch (a rotary knob) the "wrong" way to be sure it was off -- and it turned a few degrees, apparently due to a defective stop in the switch itself.  This caused the "jettison" light to come on at the telemetry board in Mission Control, and resulted in Glenn being told to keep the retro pack attached to the spacecraft through reentry, instead of cutting its straps and letting it fly away after it had done its job -- the hope was that the retro pack's straps would  help keep the heat shield in place.

Glenn wasn't told why this procedure change was made, however, and during reentry he noticed something flopping outside the capsule window (most likely one of the retro pack straps, burned free at one end).  Once the capsule could be examined, it was determined that when the heat shield release switch was turned the wrong way, it would make contact on the status light, but not on the actual jettison system, but NASA had no way to know that while Glenn was in orbit.  As a result, Glenn's capsule was the only one from which the heat shield was recovered after flight.

Oh, and I generally do jettison heat shields, and I do it as soon as the parachutes pre-deploy (doesn't bother me to have it stick to the command pod until final deployment) -- just that little bit less stress on the parachute system, a fraction of a m/s lower descent velocity.  I'm probably subconsciously thinking that, in a multi-parachute system, it might make a big difference if one parachute fails to deploy or tears off from aero loads.

Edited July 14, 2018 by Zeiss Ikon

[Atkara]

For the most part, it depends on the type of payload, it's impact tolerance and the planet it's coming down to. If either of these 3 requires a heat shield jettison, I'll do it.

[ARS]

Nope, I don't jettison heatshield, since it's still worth some funds when recovered. Even if it isn't possible to get any benefit, it still provides some protection on landing due to being smashed first

[The Aziz]

55 minutes ago, ARS said:

Nope, I don't jettison heatshield, since it's still worth some funds when recovered. Even if it isn't possible to get any benefit, it still provides some protection on landing due to being smashed first

Yeah, landing legs are overrated

[ARS]

27 minutes ago, The Aziz said:

Yeah, landing legs are overrated

Or should I say, Explosive finale

 

[The Aziz]

11 minutes ago, ARS said:

Or should I say, Explosive finale

Coming in with a bang?

[Rocket In My Pocket]

For returning from anywhere in Kerbin's SOI?

No, I don't jettison the heatshield; because I typically don't even bring one.

That said, even if I did; I doubt I would, as I often forget this is even a feature entirely lol.

Edited July 14, 2018 by Rocket In My Pocket

[MR L A]

3 hours ago, Zeiss Ikon said:

Can't say for certain on Gemini, but the Mercury heat shield was built to jettison.  This caused some drama during John Glenn's flight -- after launch, while running down a checklist, he turned the heat shield jettison switch (a rotary knob) the "wrong" way to be sure it was off -- and it turned a few degrees, apparently due to a defective stop in the switch itself.  This caused the "jettison" light to come on at the telemetry board in Mission Control, and resulted in Glenn being told to keep the retro pack attached to the spacecraft through reentry, instead of cutting its straps and letting it fly away after it had done its job -- the hope was that the retro pack's straps would  help keep the heat shield in place.

Glenn wasn't told why this procedure change was made, however, and during reentry he noticed something flopping outside the capsule window (most likely one of the retro pack straps, burned free at one end).  Once the capsule could be examined, it was determined that when the heat shield release switch was turned the wrong way, it would make contact on the status light, but not on the actual jettison system, but NASA had no way to know that while Glenn was in orbit.  As a result, Glenn's capsule was the only one from which the heat shield was recovered after flight.

Oh, and I generally do jettison heat shields, and I do it as soon as the parachutes pre-deploy (doesn't bother me to have it stick to the command pod until final deployment) -- just that little bit less stress on the parachute system, a fraction of a m/s lower descent velocity.  I'm probably subconsciously thinking that, in a multi-parachute system, it might make a big difference if one parachute fails to deploy or tears off from aero loads.

I think I'd heard this story before, but thanks for reiterating it! I love this one a lot

[FinalFan]

I have only done it once so far, on a high-gravity orbit and return challenge (out of concern for the weight).  But I think I would on any vessel where I was concerned about the delta-V and didn't need it anymore.  (I'm on my first game and have yet to enter the SOI of any planet other than Kerbin.) 

[MR L A]

1 hour ago, FinalFan said:

I have only done it once so far, on a high-gravity orbit and return challenge (out of concern for the weight).  But I think I would on any vessel where I was concerned about the delta-V and didn't need it anymore.  (I'm on my first game and have yet to enter the SOI of any planet other than Kerbin.) 

It genuinely excites me that you've not left Kerbin's SOI yet. I wish I could relive the moment I finally explored elsewhere in the Kerbol system, that and the first time I docked  Literally one of the most exciting/relieving moments of my life which is probably why I've stuck with KSP for so long

[FinalFan]

1 minute ago, MR L A said:

It genuinely excites me that you've not left Kerbin's SOI yet. I wish I could relive the moment I finally explored elsewhere in the Kerbol system, that and the first time I docked  Literally one of the most exciting/relieving moments of my life which is probably why I've stuck with KSP for so long

You'll notice that I haven't entered any foreign planetary SOIs.  I've sent out a couple of asteroid missions where I didn't wait for them to come to me.  (No contract, but exciting!  It's the first time I've made serious decisions on a mission with trading off time and delta-V.  I sent a giant refueling station-miner to a C-type and then to an E-type (currently en route, to then return it to Kerbin), but the C-type didn't have as much fuel as I expected.)  I'm waiting for a Duna transfer window right now.  I'm spending my time before then sending Duna mission prototypes on shakedown cruises around Kerbin sytem.  My first one had fuel cells but no oxidizer (until I launched a retrofit). 

[Superfluous J]

I tend to do it after full chute deployment if my speed is over 7m/s with it on, but it'll be less with it off. And I've usually decided this before the mission starts, and set it up for it in staging.

But truthfully I frequently don't even bring one.

[Gargamel]

1 hour ago, 5thHorseman said:

I tend to do it after full chute deployment if my speed is over 7m/s with it on, but it'll be less with it off.

Yup, a "oh that's a little fast" scenario.  Once I've worked out the details of that particular ship, it either stays on, or is automatically jettisoned.  I have a ship that it was easier to jettison extra fuel rather than the heatshield.   Of course, that may be a little inefficient given the various costs of fuel vs HS. 

Now for the inflatables, yeah, they have to be jettisoned, as they get in the way for landing usually.

Or if the craft in question is designed to launch to orbit again, I'll try to jettison the shield after the chutes fully open, but still high enough that it should drift far enough away if it doesn't explode on impact.   Don't want to 'twist an ankle' landing on it. 

[Dirt The Space Dirt Fox]

I actually think, though perhaps it's been a while so hard to be sure, that I might even prefer to keep my heat shield on if I'm coming down just a little too fast for comfort, because slamming the heat shield into the ground enough to destroy it was enough to save my capsule by breaking the fall. However in that case I'd recommend attaching it so it had the shroud (Or another part, but the idea is saving on mass) which gives a little space between your heat shield and capsule to ensure the capsule doesn't slam the ground at the same time as the shield due to clipping. Your mileage may definitely vary.

[klesh]

I wont vote because my answer would be “sometimes”, which is neither yes (always), no (never), nor rarely.  

I’ll do it should I need to shed some mass while under parachute descent to ensure a safe touchdown speed at the end of a flight. 

[FinalFan]

1 hour ago, klesh said:

I wont vote because my answer would be “sometimes”, which is neither yes (always), no (never), nor rarely.  

I’ll do it should I need to shed some mass while under parachute descent to ensure a safe touchdown speed at the end of a flight. 

What would you say the percentage is of jettisoned heat shields out of all the missions you fly with heat shields?

[Freds]

Depends on the mission and the vehicle. 

This is my guideline to heat shields.

Being heat shields always the bottom part of a non-return probe, is just natural its use as 'landing legs' (why install landing legs if one can just crash the heatshield and, sometimes, watch an explosion?? )

For returnable landers, i use as above, but the lander has landing legs. Heat shields are dropped during ascention staging.

For Curiosity style rover landing, heatshield ejection is mandatory.

For aerobreaking , ejection is mandatory when there is no other aerobreaking planned.

For spaceplanes and SSTOs, there is a no-heatshield policy.

For landerplanes (landerplane is a 'spaceplanes' designed just to land, without return - nice for carry bigrovers or permament research bases), heatshield is usefull as a safety measure during initial stages of reentry - just remember to pack a bunch of solid rocket separators on its detach. My landerplanes also ejects the engines and glides to the intended land point. The remaining fuel are used for energy generation.