[1.12.*] Deadly Reentry v7.9.0 The Barbie Edition, Aug 5th, 2021

[Kitspace]

Mass? That is becoming quite confusing. Does the capsule need to be lighter or heavier for the deceleration to be more slow and gentle?

[Kitspace]

And what about manned launch aborts late into the flight? Of course I have heard of that weird Soyuz ignition failure story where guys had to experience more than twenty gees and everybody was looking for them dead on the ground until it was found out that they were extremely lucky... What does the launch ascent path look like so it allows us to abort at any time by just cutting the engines and take the crew back down safely? I am sure that in the game on most launches most of the time in case of a late flight abort the entry angle will be much greater than survivable even for kerbals... No good...

[jrandom]

More massive means you won't slow down as much until you hit the thicker atmosphere, risking death by g-forces. Too light and you'll slow down quicker, but that means you'll spend more time in the upper atmosphere (because you won't be screaming down through it as fast), risking death by overheating.

Edit: Or if you're heavy but are coming in extremely shallow -- that risks overheating as well. The whole process is just *fraught* with danger!

Edited July 5, 2014 by jrandom

[jrandom]

And what about manned launch aborts late into the flight? Of course I have heard of that weird Soyuz ignition failure story where guys had to experience more than twenty gees and everybody was looking for them dead on the ground until it was found out that they were extremely lucky... What does the launch ascent path look like so it allows us to abort at any time by just cutting the engines and take the crew back down safely? I am sure that in the game on most launches most of the time in case of a late flight abort the entry angle will be much greater than survivable even for kerbals... No good...

I don't know what the launch abort limits are. I've put escape towers on my rockets in the past, but have only used them when the first stage misbhaves -- the one time I I aborted during the second stage, the escape tower added so much velocity that I wound up in a rather steep ballistic trajectory and exploded when re-entering the atmosphere.

[Starwaster]

Mass? That is becoming quite confusing. Does the capsule need to be lighter or heavier for the deceleration to be more slow and gentle?

One thing though, the mass issue isn't an issue if you're dealing with stock drag; drag will slow you down the same no matter how much mass you have.

[kalor]

Keep in mind that the appropriate reentry angle is going to be different depending on the height of your orbit, the size of your craft, and the mass of your craft. There's no simple "aim for here" rule that I'm aware of.

True... I've never really considered the size of the craft, but I've really found the AP to be more vital than the PE. I've had de-orbits take as long as a week on Kerbin (completely un-powered, after the unfortunate instance of not reading "This side up" on my retro boosters >.>) from very high orbits, to mostly direct descent, for lower ones (powered, of course).

As a general rule, I take it as slow as I have the time for. Gives more room for error, should I make one (and i do, often )

[jrandom]

I just realized I've been thinking of RSS re-entries which are a lot less forgiving.

[kalor]

There is that. in RSS I don't think I've ever gotten anything down in one piece, except for each individual piece of debris, that is...

[Starwaster]

There is that. in RSS I don't think I've ever gotten anything down in one piece, except for each individual piece of debris, that is...

Never? I pretty routinely bring my crew and equipment down in one piece, except for accidental suborbitals....

Spaceplanes are problematic in that my favorite design is hard to get on the runway in one piece because its swan neck design typically results in the crew smacking into the pavement. The rest of the plane then proceeds to a picture perfect landing (unmanned no less)

[Kitspace]

I personally do not use stock aerodynamics at all. As far as I know in real life escape towers are often the first or the second thing to separate from the launch vehicle as they are not used above fifteen to twenty kilometres so on some launch vehicles they are to blast off even before the first stage burnout. Even after that you can just separate the pod and parachute back down to safety. I am talking about those aborts late into the flight something like higher than eighty kilometres and faster that maybe a thousand metres per second. In real life everything happened suddenly at an absolutely unexpected point and no official abort command was ever given the engine just did not start when it should have and guys got back home alive even regarding that it was not the most pleasant experience. I am quite sure that with most Kerbal ascent paths something like this would result in a crash.

[sebi.zzr]

The DL for RSS heat shields don't work,can someone point me where can i find cfg-s.Ty

[NathanKell]

Kitspace: in addition to what jrandom said, a higher ballistic coefficient (mass divided by wetted area, i.e. surface area hit by oncoming air) means that when you do start decelerating rapidly upon hitting the lower atmosphere, while you won't suffer the heat for very long, the heating will be very severe, in contrast to the slower, more measured heating you would receive in the upper atmosphere with a lower BC. In other words, your shielding might not be able to keep up, you'd be heating up too fast.

That's in addition to the crushing G forces already mentioned, of course.

It's one of the problems of spaceflight (and, actually, one of the few good arguments for winged crew launch vehicles) that an abort mid-ascent will lead to a suborbital reentry, and suborbital reentries are super dangerous. Your best bet once you pass a certain point on your ascent will be an abort to orbit rather than an abort to reentry.

Your magic ascent path that always allows "cut the engines and the crew will be fine" may well not exist for some (most) LVs.

sebi.zzr: link fixed.

[Kitspace]

So there are points in the ascent paths in real life where if anything bad and unexpected happens the crew dies and nothing can be done about it to save the crew?

[RedAV8R]

So there are points in the ascent paths in real life where if anything bad and unexpected happens the crew dies and nothing can be done about it to save the crew?

Yep. Some decent reading here and HERE. For the most part, every one of these is untested, with the exception of the one Shuttle Abort to Orbit. These were planned and trained for, and some were quite difficult and dangerous to accomplish.

Edited July 7, 2014 by RedAV8R

[Felsmak]

I don't know whether this has been said before or not, but I just made an interesting discovery about heat shields. It seems like (accidentally) clipping the shield into the capsule as demonstrated below does strange things to physics, and I've been doing some testing in the game to confirm this.

A normal capsule will lose its speed rather quickly upon entering the atmosphere and then land safely on the ground. A clipped capsule, on the other hand, will barely lose any speed at all. The heat shield evaporates as normal, but the capsule will either reach the lowest parts of the atmosphere at orbital speeds, or return to space and repeat the process until the shield gives up and kills everyone.

Possible bug, maybe?

[Starwaster]

I don't know whether this has been said before or not, but I just made an interesting discovery about heat shields. It seems like (accidentally) clipping the shield into the capsule as demonstrated below does strange things to physics, and I've been doing some testing in the game to confirm this.

A normal capsule will lose its speed rather quickly upon entering the atmosphere and then land safely on the ground. A clipped capsule, on the other hand, will barely lose any speed at all. The heat shield evaporates as normal, but the capsule will either reach the lowest parts of the atmosphere at orbital speeds, or return to space and repeat the process until the shield gives up and kills everyone.

http://i.imgur.com/7RxXa7d.png http://i.imgur.com/2Lgieqq.jpg

Possible bug, maybe?

A bug definitely but not a Deadly Reentry bug. DREC does not affect aerodynamics at all.

[NathanKell]

Not a bug per se, just a weird consequence of how FAR handles drag. FAR applies drag to "open nodes," i.e. attach nodes with nothing attached, as a way of detecting flat areas. This is why adding nosecones in FAR makes you less draggy; you're closing the open node. This is also why setting node size correctly is incredibly important, as otherwise the drag will be incorrect.

However, the key thing about this is that FAR also varies what it applies based on whether the node is "pointing" forwards or backwards, i.e. above or below the part's CoM. If it's forwards, it gets a ton of drag; if backwards, only a bit (and some stability increase). Think about the difference between a rocket with a flat nose and streamlined tail, and a streamlined nose and flat tail.

The point here is that when you attach a heatshield by the wrong node, FAR thinks the open node is pointed away from the oncoming air on reentry, and therefore it doesn't add much drag at all.

[Felsmak]

Oh, I see! Thanks for the info.

[dlrk]

This seems to be causing an issue with the dtobi's new inflatable heatshield. Is there a way to add a new, properly sized, open node that enlarges when the shield is inflated?

[John FX]

Just wanted to say that I got into DRE through BTSM and now, even not playing BTSM I have DRE installed (I like making cute heatshielded return capsules)

good mod. I can see this and FAR being stock some day. (must download FAR)

[dlrk]

I'm sorry if I missed it somewhere, but is there a guide to adding heatshields to parts in the CFG?

[NathanKell]

There's no compiled guide. Basically you just add a shield module, tweak the values to taste, and add AblativeShielding if the shield is more than purely reflective. Check out DeadlyReentry.cfg, which does the module adding, for examples.

[dlrk]

What do the values refer to, and what is a reflective versus ablative shield? Are any RL heat shields reflective?

[NathanKell]

There are in general three types of heat shields:

Heat sinks

Reflective

Ablative

Now, most combine those. But still.

Heat sinks soak up the heat and then radiate it slowly over time. This was the first type of heat shield used.

Reflective just means that it "reflects" away some of the heat; not all the heat of the air impact needs to be soaked or dissipated through ablation. Any heat shield worth its salt will be at least *somewhat* reflective!

Ablative shields contain a coating of ablative material that boils away under the impact of the air (heating), thus dissipating heat.

Sink-type is hard to model in DRE. The closest would be to give a very high max temperature to the part, and decent reflectivity. The others are, obviously, easier.

I've added some notes to the bottom of the readme. Check it out here.

https://github.com/NathanKell/DeadlyReentry/blob/master/Readme_DREC.txt#L88

[dlrk]

Got it thanks! Can you elaborate a little more on the direction vector?