Landing on Duna w/o Drogue Chute

[arkie87]

I tried making a craft to land on duna. I put loads of regular parachutes (did not yet unlock drogue shoots in career mode) and small wings to help me steer and slow down. I've managed to get velocity below 300 m/s (i think as low as 240 m/s) but the parachute color in staging still didnt change from red, so when i deployed, the chutes broke.

(1) Is it possible to land on Duna (without retrograde burn) w/o drogue chutes? Or am i experiencing a bug/incorrect physics and i should download a mod (real chutes, for instance)?

(2) Does this make sense? The density is so low on Duna, could the atmosphere really break my chute off?

(3) Does it have something to do with being below Mach 1? Duna's temperature is much lower than Kerbin, so Mach 1 is much slower. Is that it?

What am i doing wrong?

To clarify: my problem isnt that the parachutes dont slow me down enough and i crash, but rather, i cant slow down enough to be able to deploy them without them being destroyed instantly. 

Edited December 1, 2015 by arkie87

[Starhawk]

1. I do not know.  My only Duna landing in 1.0.5 required a significant retrograde burn before I could deploy my chutes.  I was always able to slow enough to deploy normal chutes just using the atmosphere in previous versions.

I'm afraid I can't help with the other two question.  But I'm quite sure others will.

Happy landings!

[arkie87]

40 minutes ago, Starhawk said:

1. I do not know.  My only Duna landing in 1.0.5 required a significant retrograde burn before I could deploy my chutes.  I was always able to slow enough to deploy normal chutes just using the atmosphere in previous versions.

I'm afraid I can't help with the other two question.  But I'm quite sure others will.

Happy landings!

Thanks for the reply.

Same for me-- in past versions, i could deploy chutes whenever. 

Do you happen to remember how fast you were going before you could deploy chutes in 1.0.5? To what speed did you burn retrograde before you could deploy chutes?

[Starhawk]

3 minutes ago, arkie87 said:

Thanks for the reply.

Same for me-- in past versions, i could deploy chutes whenever. 

Do you happen to remember how fast you were going before you could deploy chutes in 1.0.5? To what speed did you burn retrograde before you could deploy chutes?

'Fraid not.  I was freaking out a bit at the time.  I just saw the staging icon change colour and slammed the spacebar.

Good luck, and...

Happy landings!

[Alshain]

The answer is no.  You need something to slow you down on Duna.  The atmosphere is thin so its terminal velocity is much faster.  You need drogues or engines or both, air brakes probably won't work well either (haven't tried).  Parachutes barely work, I still needed engines to get to safe drogue range.  It's just really thin atmosphere.

1) Not a bug, this is normal FWIW Mars is pretty close to the same, we can't parachute into Mars without engines.  In fact that's why the first probes crashed.

2) I'm not sure what drives the 'safe chute indicator'.  It's worth some tests for certain.  The atmosphere is thin so I wouldn't expect them to rip off once you get through heating.  I'm just not sure.  I have a lander on Duna now, I might quicksave and run some tests later today.

3) As I said, I'm not sure if it is a fixed 'speed' that drives that little red indicator.  If it is, I would say that is a bug because it should be more adaptive to the planet you are on.  I don't know that is how it behaves at all, I'm speculating.

Edited December 1, 2015 by Alshain

[arkie87]

17 minutes ago, Starhawk said:

'Fraid not.  I was freaking out a bit at the time.  I just saw the staging icon change colour and slammed the spacebar.

Good luck, and...

Happy landings!

Sounds like me when i attempted to land on Duna-- freaking out, Except i crashed and then f9'ed

3 minutes ago, Alshain said:

The answer is no.  You need something to slow you down on Duna.  The atmosphere is thin so its terminal velocity is much faster.  You need drogues or engines or both, air brakes probably won't work well either (haven't tried).  Parachutes barely work, I still needed engines to get to safe drogue range.  It's just really thin atmosphere.

Thanks for the reply.

I think i worded it poorly. My problem isnt that the parachutes dont slow me down enough and i crash, but rather, that i cannot deploy them at all. My question is: is that realistic or is it a bug?

[Alshain]

Ok, I just ran some tests and in my opinion (unless there is something about aerodynamic stresses I do not understand) it is bugged or poorly designed.  Duna != Kerbin but the behavior of the parachutes is identical on Kerbin and Duna.  The indicator is correct, if it is red they WILL break, but the indicator goes red at the exact same surface speed as on Kerbin.  To me, this isn't correct.  Duna should be more forgiving on the parachutes because it doesn't have the same atmosphere.  Conversely Eve should be more punishing.

I think it's likely a simplistic badly thought out design that was done quickly.  The planet should be part of the equation and it isn't, it's a fixed speed.

Edited December 1, 2015 by Alshain

[OhioBob]

1 hour ago, Alshain said:

To me, this isn't correct.  Duna should be more forgiving on the parachutes because it doesn't have the same atmosphere.  Conversely Eve should be more punishing.

I think it's likely a simplistic badly thought out design that was done quickly.  The planet should be part of the equation and it isn't, it's a fixed speed.

I agree.  The safe deployment of parachutes should be based on drag force, not velocity.  Drag force is proportional to air density times velocity squared.  Duna air is about 1/8th the density of Kerbin air, therefore we should be able to deploy the parachutes on Duna at a velocity that is about 8^1/2 times the safe deploy velocity on Kerbin, which would be about 700 m/s.  This needs to be fixed.

Edited December 1, 2015 by OhioBob

[arkie87]

41 minutes ago, OhioBob said:

I agree.  The safe deployment of parachutes should be based on drag force, not velocity.  Drag force is proportional to air density times velocity squared.  Duna air is about 1/8th the density of Kerbin air, therefore we should be able to deploy the parachutes on Duna at a velocity that is about 8^1/2 times the safe deploy velocity on Kerbin, which would be about 700 m/s.  This needs to be fixed.

Thanks for the answers.

So Mach 1 has nothing to do with it, i presume (and Mach 1 is slower on Duna than on Kerbin because of temperature)?

The only thing that will destroy a chute is drag force (assuming temperature isnt a problem)? That means the parachute can be deployed in upper atmosphere safely, but they will break off once air density increases and drag force increases? This will cause problems as from a drag force perspective, parachutes can be deployed in upper atmosphere, so the parachute deploy indicator in staging wont be RED. On the other hand, since external temperature is too hot, perhaps they WILL be marked red and it wont cause problems for noobs...

How difficult would it be to write a mod that fixes this? Could module manager set a different critical velocity for each planet?

1 hour ago, Alshain said:

Ok, I just ran some tests and in my opinion (unless there is something about aerodynamic stresses I do not understand) it is bugged or poorly designed.  Duna != Kerbin but the behavior of the parachutes is identical on Kerbin and Duna.  The indicator is correct, if it is red they WILL break, but the indicator goes red at the exact same surface speed as on Kerbin.  To me, this isn't correct.  Duna should be more forgiving on the parachutes because it doesn't have the same atmosphere.  Conversely Eve should be more punishing.

I think it's likely a simplistic badly thought out design that was done quickly.  The planet should be part of the equation and it isn't, it's a fixed speed.

It seems like you are suggesting that KSP doesnt break parachutes if the force exceeds a certain threshold, but rather, just checks the speed and maybe altitude.

How difficult would it be to write a mod that breaks chutes if the force they WOULD impart is greater than a threshold value, instead of some other criteria?

Edited December 1, 2015 by arkie87

[Alshain]

I don't know for sure, but I have a feeling @stupid_chris RealChute mod probably has a much better behavior.  Maybe he can confirm that.

Edited December 1, 2015 by Alshain

[arkie87]

1 minute ago, Alshain said:

I don't know for sure, but I have a feeling @stupid_chris RealChute mod probably has a much better behavior.  Maybe he can confirm that.

It seems to me that his mod only affects parts his mod adds; It doesnt change behavior of stock parts,correct?

So my ship currently orbitting duna is screwed, right?

[OhioBob]

41 minutes ago, arkie87 said:

That means the parachute can be deployed in upper atmosphere safely, but they will break off once air density increases and drag force increases?

The drag force on the parachute peaks sharply when it first deploys.  This is because the deployment of the chute results in a sudden change in the vehicle's drag area and drag coefficient, and a rapid lowering of vehicle's terminal velocity.  There is a sudden increase in the drag force until the vehicle reestablishes terminal velocity.  If the parachute is going to rip off, this is the time.  If the chute survives the initial deployment, you should be good thereafter.  As the vehicle descends under the parachute, it will steadily slow down as the air thickens, maintaining terminal velocity.  The drag force on the parachute should remain approximately steady.

[Alshain]

7 minutes ago, arkie87 said:

It seems to me that his mod only affects parts his mod adds; It doesnt change behavior of stock parts,correct?

So my ship currently orbitting duna is screwed, right?

Not correct.  It applies to stock parts as well.  However, you I don't think you can configure the chutes outside the VAB/SPH.

Edited December 1, 2015 by Alshain

[stupid_chris]

You could by editing the persistence file, but it would require knowing exactly what you're doing as else you might screw up, well, everything. I don't think stock can be fixed outright due to how heating is handled internally.

[cantab]

If chutes are breaking when deployed below 300 m/s on Duna that does seem like a bug. Landing on Duna with only main chutes should be possible with a craft generating enough drag for its mass before chute deployment. Airbrakes are an excellent way to do that, or a winged re-entry vehicle could work, or just something very light such as most probes.

[arkie87]

1 hour ago, OhioBob said:

The drag force on the parachute peaks sharply when it first deploys.  This is because the deployment of the chute results in a sudden change in the vehicle's drag area and drag coefficient, and a rapid lowering of vehicle's terminal velocity.  There is a sudden increase in the drag force until the vehicle reestablishes terminal velocity.  If the parachute is going to rip off, this is the time.  If the chute survives the initial deployment, you should be good thereafter.  As the vehicle descends under the parachute, it will steadily slow down as the air thickens, maintaining terminal velocity.  The drag force on the parachute should remain approximately steady.

Dont quite understand why you are saying all this. What i said was that if KSP uses ONLY drag as a means to determine whether the parachute will survive, it will tell you that you can deploy it at 60 km @ 8 km/s since density and resulting drag force is so low. That will subsequently cause problems when you get lower and the parachute catches fire and burns up.

20 minutes ago, cantab said:

If chutes are breaking when deployed below 300 m/s on Duna that does seem like a bug. Landing on Duna with only main chutes should be possible with a craft generating enough drag for its mass before chute deployment. Airbrakes are an excellent way to do that, or a winged re-entry vehicle could work, or just something very light such as most probes.

Yeah, my vehicle is quite heavy. Its a lander with Bob on board and a full tank of gas. I think ill have to burn retrograde until i can deploy chutes.

[OhioBob]

4 hours ago, arkie87 said:

Dont quite understand why you are saying all this.

Because you wrote:

"The only thing that will destroy a chute is drag force (assuming temperature isnt a problem)? That means the parachute can be deployed in upper atmosphere safely, but they will break off once air density increases and drag force increases?"

which looked to me like you were asking if the increasing air density would increase the drag force and rip the parachutes off.  If that wasn't a question, then why the question marks?

 

Quote

What i said was that if KSP uses ONLY drag as a means to determine whether the parachute will survive, it will tell you that you can deploy it at 60 km @ 8 km/s since density and resulting drag force is so low.

You'll never be able to deploy a parachute at such an extreme altitude as 60 km.  Parachutes have a minimum semi-deploy pressure, which is tweakable.  The minimum pressure setting is 0.04 atmosphere for main chutes and 0.02 atmosphere for drogue chutes, which are also the default settings.  On Kerbin these pressures occur at altitudes of 17,590 m and 21,204 m.  On Duna these pressures occur much lower, at 4,448 m and 9,266 m respectively.

[arkie87]

16 minutes ago, OhioBob said:

Because you wrote:

"The only thing that will destroy a chute is drag force (assuming temperature isnt a problem)? That means the parachute can be deployed in upper atmosphere safely, but they will break off once air density increases and drag force increases?"

which looked to me like you were asking if the increasing air density would increase the drag force and rip the parachutes off.  If that wasn't a question, then why the question marks?

It was a question but your post didnt answer/address it. Increasing air density WILL increase drag if the parachutes are deployed before drag is significant, which is the assumption that is stated in the question (so thats why i didnt understand your answer).

[OhioBob]

3 minutes ago, arkie87 said:

It was a question but your post didnt answer/address it. Increasing air density WILL increase drag if the parachutes are deployed before drag is significant, which is the assumption that is stated in the question (so thats why i didnt understand your answer).

I don't think the parachutes can be deployed before drag is significant because of the minimum pressure setting.

[arkie87]

1 minute ago, OhioBob said:

I don't think the parachutes can be deployed before drag is significant because of the minimum pressure setting.

Is that setting not tweakable?

[Claw]

Chute indicators aren't programmed on a fixed speed. I believe they were originally programmed on dynamic pressure and/or thermo considerations. I'm not sure if that's the case for 1.0.5 (might be just thermo now), but I do know for certain that it's not intentionally a "fixed groundspeed." If that's happening, it's either a coincidence or a bug. I can confirm that I've successfully deployed parachutes with red indicators, so it might be an issue in the calculations (the indicator calculations are separate from the actual physics calcs).

Duna itself is harder to land on now. I'm not sure how much of that shift was intentional and how much was fallout due to high atmospheric changes.

Also, the Soviets were the first to hit the surface of Mars, and it was attributed to a descent computer failure (not a parachute failure). Several probes have used drogue chutes without initial retro firings, but landing big stuff on the surface of Mars by parachute alone isn't practical.

Edited December 2, 2015 by Claw

[Alshain]

Definitely not the case now Claw, I'm hitting it a about 260m/s while the indicator is red and they break.  That's about the same for Kerbin, just barely over the threshold of safe.  If it were to be realistic, there should be a rather significant difference, and I'm just not seeing it.  If there is a difference it's in single digits m/s which is barely any at all.

Edited December 2, 2015 by Alshain

[AeroGav]

 

Agree with what is said about parachutes,  but this is proof it is possible to land an aircraft on Duna in 1.05.   It does have a lot of wing though, on Kerbin it lands below 40 m/s, and 3 vernier engines thrusting downwards to help me flare without risk of tailstrike.  I'd began the transfer orbit the night before the 1.05 patch arrived, and was forced to land on Duna with a vehicle designed under 1.04.

Sounds like OP is very close to successful parachute deployment speed, at any rate.

[arkie87]

5 hours ago, AeroGav said:

 

Agree with what is said about parachutes,  but this is proof it is possible to land an aircraft on Duna in 1.05.   It does have a lot of wing though, on Kerbin it lands below 40 m/s, and 3 vernier engines thrusting downwards to help me flare without risk of tailstrike.  I'd began the transfer orbit the night before the 1.05 patch arrived, and was forced to land on Duna with a vehicle designed under 1.04.

Sounds like OP is very close to successful parachute deployment speed, at any rate.

I landed safely with retroburn. I think indicator finally turned green at around 200 m/s. Still not sure why this speed is LESS than on Kerbin? Seems to me like it should be larger than on Kerbin if drag/stagnation pressure is to blame. 

[Bluegillbronco2]

With a normal parachute and a VERY light probe you can get away with no retro burn to land. But you need a retro burn to slow down to a safe speed for the parachute. As long as the craft is light then a couple of drogues will slow you down below 50m/s witch is not that bad.

Edited December 2, 2015 by Bluegillbronco2
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