[Added in 1.2pre build 1509] Suggestion: communication blackout during reentry

[Alshain]

I'm not sure this is a good idea.  In the real world we've found ways around this complication that KSP can not emulate.  So there is no way to make it go away later in your career when you would have developed the work around.

The Shuttle sent a signal up to a relay satellite through a hole in the plasma created by the design of the craft which was then sent back to mission control.  Understanding the phenomenon as we do now, we can design all re-entry vehicles to do that.  So it's only applicable to the early space program before we learned how to get around the issue.

Edited September 19, 2016 by Alshain

[Gaarst]

23 minutes ago, NathanKell said:

@Gaarst coefficient: 100. Shock temp: 1100 K. Static density: 0.000075 (60km Kerbin, 75km Earth)

That works fine on reentry for my testing but can lead to some blackouts even with no flames during ascent.

Obviously RSS/RO would increase the coefficient number quite a bit.

Wouldn't it be more accurate to calculate N_e as shown in the page Jovus linked with the Saha equation? And cut communications when the plasma frequency goes above a given threshold (dependent on Ne)?

I believe than even though pretty simplified it could be accurate enough for KSP's model. And since all the 3 threshold constants you suggested are the variables of the equation, it would essentially be the same, only with the resultant number only mattering in the end.

As the plasma frequency would be calculated, the only setting to be tweaked on the used end would be the frequency of the communications. Though that would mean setting it to an absurdly low value to have actual blackout during Kerbin entry.
Edit: then an upgrade to the communication system to avoid this could just be a simulating frequency increase.

 

Also, for blackout during ascent, I don't really see how this could be fixed as on Kerbin most of the orbital velocity is gained during the actual ascent phase, when inside the atmosphere. For Earth the speeds at which blackout may occur are reached above the atmosphere so it can't happen, but for Kerbin, I often reach orbital velocities while still below 60km (with a flat profile and reasonable TWR).

Edited September 19, 2016 by Gaarst

[The_Rocketeer]

26 minutes ago, Gaarst said:

don't really see how this could be fixed as on Kerbin most of the orbital velocity is gained during the actual ascent phase

Simple, adjust the static density criteria so it kicks in/cuts out at a lower altitude, say 45km instead of 60km. Means re-entry blackouts will be a little shorter, but should rule them out for most ascents.

Edited September 19, 2016 by The_Rocketeer

[Gaarst]

7 minutes ago, The_Rocketeer said:

Simple, adjust the static density criteria so it kicks in/cuts out at a lower altitude, say 45km instead of 60km. Means re-entry blackouts will be a little shorter, but should rule them out for most ascents.

Isn't 45-60km the altitude when reentry is the hottest? 45km is pretty low for plasma to kick in.

[The_Rocketeer]

Just now, Gaarst said:

Isn't 45-60km the altitude when reentry is the hottest? 45km is pretty low for plasma to kick in.

vOv maybe. If you want to get serious about it, what you need is the progression curves of all 3 trigger criteria during a normal ascent and normal re-entry to see what the optimal descent-only trigger values are.

But I'm happy with an abstract system. According to this page      blackouts end at speeds exceeding Kerbin orbital velocity anyway, so based on Kerbal physics they're probably just not an issue for the little green dudes.

[The_Rocketeer]

Ok, so MSpaint is not my field of expertise any more than the physics of orbital reentry, but I decided to stretch the image around a bit and adjust it to Kerbal scale:

Looks like a blackout kicking in at about 55km altitude and ending about 40km altitude is about right. But I have to add, KSP re-entry deceleration is usually way less linear than this graph suggests, so perhaps this isn't really a useful comparison.

Oh, yah, and I know the time scale is absurd for KSP, but well, I don't care.

Edited September 19, 2016 by The_Rocketeer

[Gaarst]

Doing some number crushing, results coming soon-ish.

[Gaarst]

So I took some data during a LKO reentry with a pod, and here is what I found: while the convective heat coefficient reaches a peak around 30km and agrees pretty much with the presence or not of reentry effects (between 51km and 21km) appearing when it crosses a given threshold, the plasma frequency reaches a max around 28km and flattens out from 20 to 15km, allowing a maximum blackout period from 35 to 20km.

NathanKell's criteria would mean a blackout period from 56 to 21km.

Edit: note that the deceleration starts around 35km and ends below 15km

Edited September 19, 2016 by Gaarst

[kcs123]

57 minutes ago, Gaarst said:

note that the deceleration starts around 35km and ends below 15km

In my re-entry profiles I notice considerable slowdown due to drag at 50km. 30-35 km is my usual Pe on re-entry, depending on craft weight and if I carry heating shield at all or not. 30-35 km is area with most of airbreaking. Down to 15 km it is slowdown below 1.5 mach, most of time even slower. In those area if you are going any faster, communication blackout is least of your problems.

[Gaarst]

2 minutes ago, kcs123 said:

In my re-entry profiles I notice considerable slowdown due to drag at 50km. 30-35 km is my usual Pe on re-entry, depending on craft weight and if I carry heating shield at all or not. 30-35 km is area with most of airbreaking. Down to 15 km it is slowdown below 1.5 mach, most of time even slower. In those area if you are going any faster, communication blackout is least of your problems.

Single Mk1 pod, no heatshield, peri at 10km and got no problem.

[Dman979]

If I understand correctly, this will be implemented in a pre-version.

Does it make sense to turn this on by default, and give it some values, and see how players react? That might give a more representative sample than your calculations.

Also, I am fully in favor of this idea. For final implementation, though, it should default to "Off."

[The_Rocketeer]

14 minutes ago, kcs123 said:

30-35 km is my usual Pe on re-entry

Slow-cooker re-entry, u get a little heat for a long time.

12 minutes ago, Gaarst said:

peri at 10km and got no problem

Flame-grill re-entry, u get a lot of heat for a little time.

I think the main difference is how and when you trade-off acceleration due to gravity against deceleration due to aero-friction. A high periapsis means u spread that gravity-acceleration over a longer time, so u end up slowing with less shock, but u have to sustain elevated temperatures for longer. Low periapsis means you don't need to worry about overheating as long as you have enough shock-shielding, but IRL you could end up killing your crew with G-forces. Based on the graph I linked, it looks like the shuttle re-entry followed @kcs123's approach - you can see it in the curve inversion on the altitude line - vertical speed levels off (I guess close to original periapsis altitude) and then increases again once the speed has fallen. @Gaarst's re-entry is similar to the left half of the graph, but he experiences the braking drag at lower altitude, so his vertical speed curve doesn't invert - he experiences maximum vertical deceleration closer to the ground, and vertical speed doesn't increase after that.

Edited September 19, 2016 by The_Rocketeer

[Gaarst]

@NathanKell Thank you very much for adding this in build 1509! Thing is even though I found the values to tweak in the Physics.cfg, I can't find the option to enable it in game. Am I blind, or did someone forget something?

[NathanKell]

@Gaarst Settings->Difficulty->Advanced

[Matuchkin]

I think it is better if communications gets cut even while a manned mission is reentering. I like to perceive that my ships are controlled by autopilot systems instead of the kerbals themselves.

[Gaarst]

29 minutes ago, NathanKell said:

@Gaarst Settings->Difficulty->Advanced

Works like a charm! Thank you!

[Jarin]

2 hours ago, NathanKell said:

@Gaarst Settings->Difficulty->Advanced

Can't launch 1.2 to check - is there any way to modify this in an existing career? Like @Alshain mentioned, once you get higher in the tech tree, you might want to assume your engineers have found workarounds and disable it.

Edited September 20, 2016 by Jarin

[Pthigrivi]

Edit: Ahh I see, nm. 

Edited September 20, 2016 by Pthigrivi

[Superfluous J]

15 minutes ago, Jarin said:

Can't launch 1.2 to check - is there any way to modify this in an existing career? Like @Alshain mentioned, once you get higher in the tech tree, you might want to assume your engineers have found workarounds and disable it.

It'll be in the CommNetParams section of your persistent.sfs file. Here's what mine looks like now that I've updated to 1509:

		CommNetParams
		{
			requireSignalForControl = False
			reentryBlackout = False
			rangeModifier = 1
			DSNModifier = 1
			occlusionMultiplierVac = 0.9
			occlusionMultiplierAtm = 0.75
			enableGroundStations = True
		}

Seems obvious what to change

Edited September 20, 2016 by 5thHorseman

[Jarin]

Just now, 5thHorseman said:

It'll be in the CommNetParams section. Here's what mine looks like now that I've updated to 1509:

		CommNetParams
		{
			requireSignalForControl = False
			reentryBlackout = False
			rangeModifier = 1
			DSNModifier = 1
			occlusionMultiplierVac = 0.9
			occlusionMultiplierAtm = 0.75
			enableGroundStations = True
		}

Seems obvious what to change

I meant in options, but that works too. I can get my hands a bit dirty if needed. Thanks  

[Superfluous J]

Just now, Jarin said:

I meant in options, but that works too. I can get my hands a bit dirty if needed. Thanks  

Yeah I don't see it in the options. Maybe in the alt-f12 menu?

...

No I poked around and don't see it. It may be there and I missed it but it's not obvious enough for me to consider it easier than editing the sfs file

[Jarin]

Yeah, for a once-per-savegame thing, I can fire up textpad.

[NathanKell]

I mentioned Settings because it's in ingame options. It's not a newgame-only setting.

[Superfluous J]

5 minutes ago, NathanKell said:

I mentioned Settings because it's in ingame options. It's not a newgame-only setting.

Oh my Jool. You just blew my mind.

I went back into the game to get screen grabs to show that the setting is not there, and neither is an "advanced" button, and realized that the header to the Settings Menu that reads "Difficulty Options: Custom" is not a header at all, but a BUTTON.

Clicking that gets a window with an Advanced button, and within there is the Reentry Blackout radio button.

I swear this is the same feeling you get when you're looking at that image of a chalice and suddenly see two faces.

[Jovus]

I would really, really like it if there were some kind of mid-late tier antenna upgrade that allowed you to ignore this, to simulate the real advancements in antenna tech we have (on paper) now.

Or at least if this only covers the front 270 degrees of the craft, so I can set up a sat network to avoid this on bodies where it really matters to me.

(Even if neither of these is included, it's still an awesome feature.)