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

[Gaarst]

Now that we have communications (or soon) to add a little realism to magically controlled probes, it could be a good thing to add communications blackout during the "hot" phase of reentry.

As a spacecraft reenters atmosphere, the shock heating creates a layer of plasma around the craft. As plasma is essentially a fully ionised gas, it is charged, and generates an EM field which messes up all radio communications towards or from the craft.

It might add a little difficulty and challenge to atmospheric entries of unmanned crafts (for manned craft you just wouldn't be able to transmit science during this phase).

Edited September 20, 2016 by Gaarst

[pandaman]

That seems like it shouldn't be too difficult to implement, maybe link it to the 'flames' so you have an already existing visual clue? (But what do I know I'm not a programmer).

[Waxing_Kibbous]

KSP players- looking for ways to make their favorite game harder everyday

[nascarlaser1]

this would need to have a toggle, for people who either do not want, or have no practice with this kind of difficulty.

[pandaman]

4 minutes ago, nascarlaser1 said:

this would need to have a toggle, for people who either do not want, or have no practice with this kind of difficulty.

Absolutely, that's pretty much a given for any new difficulty features.

[Hodari]

Sounds like a good idea for realism to me.  As far as actual gameplay goes, I'm not sure it would really have a huge impact since a well designed re-entry craft should naturally hold retrograde on its own anyway and a lot of probes won't be intended to return at all in the first place.  It would at least force players to make sure they DO design any returning probes properly though.

[pandaman]

As @Hodari said it probably wouldn't have much impact gameplay wise, but If it is fairly easy to do it would be a great 'realism' tweak.

It may be as simple as something like .." IF flames are visible THEN comms don't work", but it probably isn't that easy.

[Jonfliesgoats]

This is a fantastic idea!  It should be pretty easy to implement too. 

[Rath]

It should need pretty big flames though.  I dont want to be going only 600m/s in a plane and suddenly get comms blackout.

[NathanKell]

Question: Should antennas in the shadow of the shockwave also be knocked out? I.e. is it a question of how much plasma is around the antenna itself, or how big the bow shock is?

 

I.e. consider the big ol' inflatable shield, and a pod with an antenna on it. Should you still have comms?

[NathanKell]

Also: based on convective coefficient (sqrt(rho) * vel^3) or Q (rho * vel^2) ?

[Laie]

I guess the blackout will be over by the time you need to deploy chutes, but will it also start late enough so that aerodynamics will keep the craft pointed into the wind?

Blackout is a nice idea, but if I need a programming interface to cope with the effects, I'd like to postpone the proposal until a stock programming interface exists.

[pandaman]

2 hours ago, Laie said:

I guess the blackout will be over by the time you need to deploy chutes, but will it also start late enough so that aerodynamics will keep the craft pointed into the wind?

Blackout is a nice idea, but if I need a programming interface to cope with the effects, I'd like to postpone the proposal until a stock programming interface exists.

The 'Deploy When Safe' option for parachutes should hopefully deal with that concern.

 

3 hours ago, NathanKell said:

Question: Should antennas in the shadow of the shockwave also be knocked out? I.e. is it a question of how much plasma is around the antenna itself, or how big the bow shock is?

I.e. consider the big ol' inflatable shield, and a pod with an antenna on it. Should you still have comms?

Good question...

My own 'gut feeling' here is that, from a gameplay perspective, it's probably not going to have a huge impact as it will only be in effect for a relatively short time so, at it's most basic once the 'plasma' reaches a certain threshold then comms for the vessel could just cut out for the duration.  This would I guess be the simplest way to represent the effect, and you wouldn't need to worry about calculating  the extent of the 'shadow'.

However, if say a relay station in orbit was able to connect to the vessel from outside the 'shadow' (in the same basic way that you avoid planetary occlusion) then I guess in theory you could get around the loss of comms issue like that.  I don't know if that would actually work well enough to be practical IRL, and even then to simulate it in game may require a lot of extra calculations for very little overall gain, but that's your call, you understand that side of it far better than I do.

3 hours ago, NathanKell said:

Also: based on convective coefficient (sqrt(rho) * vel^3) or Q (rho * vel^2) ?

I'm not a mathematician, but I guess that means the faster you go, the hotter you get, the bigger the plasma is and therefore the larger it's 'shadow' is, and the greater the affected 'volume' behind it.

What I think this boils down to is whether the extra complexity of the calculations to represent the 'shadow' effect would give enough benefit to be sensible and worthwhile for the game.

[magnemoe]

Main issue at least in 1.13 is that hold retrograde eat power as mad so it works far better to just use sas and do manual input, one small battery+ pod power is far to little. 

[Waxing_Kibbous]

47 minutes ago, magnemoe said:

Main issue at least in 1.13 is that hold retrograde eat power as mad so it works far better to just use sas and do manual input, one small battery+ pod power is far to little. 

A lot of work has been done on the SAS in 1.2, from my experience so far the excessive power use on reentry has been fixed.

[magnemoe]

Just now, Waxing_Kibbous said:

A lot of work has been done on the SAS in 1.2, from my experience so far the excessive power use on reentry has been fixed.

nice, and yes it should be possible, mechjeb don't use more than normal sas functionality. 
Think the problem with the 1.13 stock is that it use far to much torque and over correcting, then have to correct again and so on. Build an tiny probe using octo2, the tiny reaction wheel oscar fuel tank and ant and you see that it vibrates just with sas. 

[The_Rocketeer]

7 hours ago, NathanKell said:

I.e. consider the big ol' inflatable shield, and a pod with an antenna on it. Should you still have comms?

I think no.

The ion interference disrupts the signal, not the equipment's ability to broadcast or recieve.

From Wikipedia: Communications Blackout - Spacecraft Reentry

Quote

reentry blackouts, are caused by an envelope of ionized air around the craft, created by the heat from the compression of the atmosphere by the craft. The ionized air interferes with radio signals

(italic/underline mine)

In the case of a heatshield, it still creates the ion envelope (just it's bigger), so signals would still be blocked.

Edit:

These two passages make really interesting and relevant reading also, particularly the 2nd one (same source as above).
 

Quote

Communications blackouts for re-entry are not solely confined to entry into Earth's atmosphere. They apply to entry into any atmosphere where such ionization occurs around a craft. The Mars Pathfinder endured a 30-second communications blackout as it entered Mars' atmosphere, for example. The Huygens probe endured a communications blackout as it entered the atmosphere of Titan.^[1]

Until the creation of the Tracking and Data Relay Satellite System (TDRSS), the Space Shuttle endured a 30-minute blackout. The TDRSS allowed the Shuttle to communicate by relay with a Tracking and Data Relay Satellite during re-entry, through a "hole" in the ionized air envelope at the tail end of the craft, created by the Shuttle's shape.

Perhaps there's an argument here for direct signals to ground being blocked, but signals via relay satellites getting thru - that would seem most realistic. On the other hand, it would only really work for craft big enough to create the 'hole', so perhaps @NathanKell it should only work for size 2 heatshields and larger?

Edited September 19, 2016 by The_Rocketeer

[Jovus]

7 hours ago, NathanKell said:

Question: Should antennas in the shadow of the shockwave also be knocked out? I.e. is it a question of how much plasma is around the antenna itself, or how big the bow shock is?

 

I.e. consider the big ol' inflatable shield, and a pod with an antenna on it. Should you still have comms?

In real life it definitely depends on the shape of the craft and the placement of the antennae; for example, the Shuttle ceased experiencing comms blackout during reentry after the deployment of the Tracking and Data Relay Satellite System because the sat was able to contact it from behind based on the Shuttle's shape leaving a hole in the envelope.

However, for the game, I'd probably just assume the envelope covers the entire craft. It's part of managing expectations; while it may not be the most realistic, it's easy to communicate to the player and for the player and game to agree on the effect. Or, split the difference: assume the bow shock covers the front 270 degrees of the spacecraft, and if a sat's in the right position, communication can still happen. (Where 'front' is defined by the velocity vector, not spacecraft orientation.)

7 hours ago, NathanKell said:

Also: based on convective coefficient (sqrt(rho) * vel^3) or Q (rho * vel^2) ?

 

Eyeballing it, I'd go with the former, based on gut feeling, this thread on the Orbiter forums, and the formula roughly half-way down this (rather simplistic) web-page.

If it gets to be actually important, I can trawl through scientific journals to see if I can find an answer, but it's not my specialty.

Or we could just assume Kerbals have figured out the trick to communicating through the bow shock. (Or, my favorite option, make that a late-tier upgrade.)

[The_Rocketeer]

@Jovus we're speaking the same language

[Jovus]

@The Rocketeer I'm really tempted to reply with a Pulp Fiction reference, but it wouldn't be appropriate for the forum.

(In a good way.)

[kcs123]

8 hours ago, NathanKell said:

Also: based on convective coefficient (sqrt(rho) * vel^3) or Q (rho * vel^2) ?

convective coefficient (sqrt(rho) * vel^3)

Although, plasma ion cloud is also related to high dynamic presure, for game purpose it should be enough to use convective coefficient.
You can have high Q in dense atmosphere and much lower velocity that does not create plasma ion cloud. It would be hard to balance game properly based on Q. Convective coefficient is much more suitable for such purpose.

[NathanKell]

For next pre, optional difficulty setting (defaults off).

Blackout will occur if all of these are true:

Convective coefficient > threshold A

shock temperature > threshold B

static density > threshold C

 

A-C are configurable in Physics.cfg.

[Jovus]

@NathanKell I can't like a post twice.

[Gaarst]

6 minutes ago, NathanKell said:

For next pre, optional difficulty setting (defaults off).

Blackout will occur if all of these are true:

Convective coefficient > threshold A

shock temperature > threshold B

static density > threshold C

 

A-C are configurable in Physics.cfg.

Thank you for this!

Do you have default values for ABC or will they have to be set manually? (I don't mind taking some time to tweak them to achieve a good result)

Edit: also will the whole craft be occluded? As The_Rocketeer quoted, the space shuttle had a small opening in the plasma layer at the back. Since I guess this would require a more advanced model I suppose all the comms will be cut for the next pre.

Edited September 19, 2016 by Gaarst

[NathanKell]

@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.