Time Of Day Affects Launches

[Moesly_Armlis]

Does The Atmosphere Affect Launches depending on time?

The same vessel came down with a parachute at 6.8 m/s and at night it was 7.6 m/s

There was mention of the temperature and air pressure changing at night time.

The question is about launches.

Do launches at different times (morning, midday, evening, midnight) differ in delta V requirements for orbit?

[monophonic]

In theory the changes in pressure should have an effect as they change the drag forces on the craft.

In practice I think differences in craft construction as well as piloting cause so much bigger variability that the above effect is completely irrelevant.

[viktor19]

Does The Atmosphere Affect Launches depending on time?

The same vessel came down with a parachute at 6.8 m/s and at night it was 7.6 m/s

There was mention of the temperature and air pressure changing at night time.

The question is about launches.

Do launches at different times (morning, midday, evening, midnight) differ in delta V requirements for orbit?

Probably yes, because the air is denser during the day because of lack of Kerbol's direct heating. I agree with monophonic, your piloting is never exactly the same, so that has much bigger impact on your dV requirements

[Lukaszenko]

How would piloting affect a vessel coming down by parachute?

[BudgetHedgehog]

How would piloting affect a vessel coming down by parachute?

It doesn't, those are two separate things. The air density difference has a much bigger effect when parachuting because you're not piloting the craft, you're removing quite a large variable.

The original question was 'given that air density affects parachutes, does it also affect ascent?' - the answer is yes, of course, but during ascent, your piloting has a much bigger effect on ÃŽâ€V requirements than air density.

[Red Iron Crown]

Nighttime air is cooler and denser. That means very slightly more drag and very slightly greater efficiency for air-breathing engines. The effects are very, very minimal, hard to notice especially if you are flying manually.

[gmpd2000]

Nighttime air is cooler and denser. That means very slightly more drag and very slightly greater efficiency for air-breathing engines. The effects are very, very minimal, hard to notice especially if you are flying manually.

I wonder how much will it affect efficiency to a plane when flying over the south pole and in winter (polar night).

Or will it be too cold?

And let's say low altitude, to enjoy those -80°C winds!

(in real life, I mean)

Edited July 10, 2015 by gmpd2000

[Grumman]

I wonder how much will it affect efficiency to a plane when flying over the south pole and in winter (polar night).

There is no summer or winter on Kerbin - its orbital plane and rotational plane are aligned.

[cantab]

With the stock solar system there's no axial tilt, so the day and night are each 3 hours no matter where you are and what day it is.

[John FX]

If the air is more dense then the Isp of your (non jet) engines will be lower.

[RocketPilot573]

Well this is something I haven't thought about. Amazing how far in depth the devs made the aero and thermal systems.

[gmpd2000]

There is no summer or winter on Kerbin - its orbital plane and rotational plane are aligned.

With the stock solar system there's no axial tilt, so the day and night are each 3 hours no matter where you are and what day it is.

Meant in real life, sorry!

[moronwrocket]

Were the two vessels landing at the same altitude above sea level? I know I sometimes forget I have my altitude set to "above ground" and need to plan extra chutes when landing at high locations.

[J.Random]

If the air is denser at night then why did OP's night parachute landing was faster? #PinkElephantInTheRoom

[Moesly_Armlis]

Thanks for all the replies.

If the air is colder and denser at night. Then I thought it should have had a slower decent.

Not sure why it came down faster. It was a gentle touchdown at daytime and a crash at night. I was landing on a FL-T100 fuel tnak. The difference was 0.8 m/s

Looks Like this needs some testing.

Does anyone know of the mod that records the data?

Edited July 11, 2015 by MoeslyArmlis

[Skalou]

Does anyone know of the mod that records the data?

hi, i think i lnow what you want:

AeroGUI to read the real external temperature.

Graphotron if you want to record some parameters from sciences sensors.

i used this to know the Speed of sound in 1.0

your experiment is interesting me, maybe more by curiosity than efficicency of launch:

when is the hotter/colder air temperature? what are the variations of min/Max at differents altitudes?

for rocket, is it better to start in hot air? how much gain?

for spaceplane, is it better to start in cold? more drag but better lift and engine thrust?

any change for reentry?

so i will follow you

[Moesly_Armlis]

Thanks Skalou for directing me to Graphtron

These are preliminary data and analysis of the decent.

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The temperature seems to be the only difference.

Although the LV-T100 did survive at night this time. The was tested four times and only once did the fuel tank survive impact.

Mid-Day Testing

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Mid-Night Testing

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[PB666]

Nighttime air is cooler and denser. That means very slightly more drag and very slightly greater efficiency for air-breathing engines. The effects are very, very minimal, hard to notice especially if you are flying manually.

PV = nRT

Temperature is in Kelvin. Typical RL daytime/nighttime variation is 10'C (more in deserts less so in tropical forests and during polar winters) so that represents a 3.7% difference in density. Pressure is a surrogate for density

Fdrag = k * d * V^2

equilibrium velocity at SL 9.8m/s = k * d * V^2 if situation 1 is 7 m/s then 9.8 = 49 * d * k otherwise d* k = 9.8/49 = .2

Thus if d then drops by 3.7% the d * k = 0.1926 (last two digits trivial) 9.8 / .1926 = 50.88 = 7.13333

Therefore at 7 m/s the mean difference of a 10'C rise is approximately +/- 0.13 m/s therefore temperature should not explain the change unless D/N Temperature variation is considerably more extreme that earth. On earth daytime equilibrium velocity could be lower due to updrafts that occur over freshly plowed fields in mountainous region the down drafts on shaded sides and updrafts on heated slopes can be considerable.

I don't know if the OP look at the fuel remaining in his tanks the capsule also has monopropellant, and other devices such as decouplers may have not be deployed completely. Another cause for differences is the landing altitude, vessels that land at higher altitude are landing in less dense air.

The atmospheric height in KSP is 5 km represents a 2.6 fold drop in pressure.

For launches, throttle changes at 2500 altimeter have the greatest impact on DV, this is because ships are generally accelerating until this altimeter, which means drag has not equilibrated. Once (drag + gravity) = thrust a four fold increase in thrust only doubles the speed. It is very easy to see changes in DV with small changes in velocity.

Edited July 12, 2015 by PB666

[samstarman5]

Honestly had no idea these mechanics were in this game. So much for my paying attention in class.

Definitely is something to remember for when I begin my jet-assist rocketry arm of my space program.