Length of "night" during geostationary orbits around Kerbin

[dubdubak]

So I started playing with RemoteTech2 and to begin my coverage network, I launched a satellite into a stationary orbit roughly 2868km above KSC. One thing I did not take into consideration was the electrical draw of the antennas and I find my satellite losing power during the "night," or rather when Kerbol is eclipsed/occulted by Kerbin... I was wondering if anyone might have an idea on calculating the duration of darkness so I can pack adequate batteries for the next satellite.

Or perhaps I should just establish my comm network at different altitude...

Any input is appreciated! Thanks!

Edited February 20, 2015 by dubdubak

[strongest_2hu]

According to the wiki, Kerbin's radius is 600 km and a stationary orbit is at 1.009 km/s. You should be able to solve this, at an orbit as high as that your answer will be close enough.

[WuphonsReach]

There's a few calculators around:

http://www.prism.gatech.edu/~bnichols8/projects/kspdarkness/main.shtml

http://wiki.kerbalspaceprogram.com/wiki/Orbit_darkness_time

I use a customized copy of the KSP Battery Calculator spreadsheet (on Google):

Original:

https://docs.google.com/spreadsheets/d/1yHS2LJJ6RAqb6gXNHwoaa8R9ZIqNtbe4ikbQ4e1dcUA/edit#gid=0

My customized version:

https://docs.google.com/spreadsheets/d/1L0W8LGDL2rFZe5PIshQUzu1pD1g7ZYfFNcKGoeHGEpw/edit?usp=sharing

[dubdubak]

Perfect! Thanks!

I just went with a rough estimate based off time warping and came up with about 20 minutes of orbit darkness time for a keosynchronous orbit. Ill have to see how close I was now!

[Scarecrow88]

Given that a Kerbin 'day' is 6 hours, the simple answer without giving it any thought is that night time will account for 3 hours of this. However, as a point on the ground moves into darkness, a satellite several hundred kilometres above that point will still be in full sunlight. Likewise at dawn, the satellite will enter daylight some time before the point on the ground below it does so.

To calculate how much time is spent in darkness you need to know how much of the orbit circumference falls in the shadow cast by Kerbin, the width of which will be equal to Kerbin's diameter. The speed of your satellite can then be used to work out how long it will spend in this shadow area.

[WuphonsReach]

I just went with a rough estimate based off time warping and came up with about 20 minutes of orbit darkness time for a keosynchronous orbit. Ill have to see how close I was now!

Pretty close actually. Dark period for 2869 altitude orbit around Kerbin is a maximum of 1195 seconds (19.92 minutes).

I tend to do a lot of part welding with UbioZur where I combine a probe core, reaction wheel and batteries. So my probe core usually ends up as something with at least 2400 battery capacity and usually 4-8k capacity. Batteries in stock KSP are very light for what they offer.

A satellite at KEO and 4000 battery capacity can support up to 3.35 energy/second. The Comm-16 only draws 0.13 and the Comm-32 and directional antennas draw 0.75-0.93 per second. That means I can easily run (1) Comm-16 plus (3) directionals without having power issues.

...

2869km orbits...

Moho - 36 minutes of darkness

Eve - 16 minutes

Kerbin - 20 minutes

Mun - 46 minutes (but you never orbit out that far, plan on 38 minutes)

Minmus - 81 minutes (but you never orbit out that far, plan on 68 minutes)

Duna - 35 minutes

Dres - 55 minutes

So worst-case is roughly 68 minutes of darkness for the inner bodies. And only if you are orbiting at 2000+ km altitude around Minmus. That means for a power draw of 2.93/s you need about 12000 battery capacity to survive for 68 minutes. The same satellite around Dres at 2869km would require 9600 battery capacity.

[KerikBalm]

circumference = 2*pi* radius

The satelite will go that distance in 6 hours...

This will give you the orbital velocity at geosynchronous orbit if you know the radius (although I guess you arelady know how fast your probe orbits)

Assuming a point light source infinitely far away (such that light rays are parallel)... Kerbin is casting a shadow 1200km wide.

If your probe travels 1 km/sec (close enough), it passes through that shadow in about 1,200 seconds (it would be slightly longer at 1 km/sec because the path through the shadow is slightly curved)

Anyway 1,200 seconds ... 60 seconds per minute = 20 minutes.

Just take 2x the bodies radius divided by your orbital velocity to calculate the length of the shadow for "high" orbits, and half your orbital period for "low" orbits.

[*Aqua*]

There's another good site: http://ryohpops.github.io/kspRemoteTechPlanner/

It calculates night time and battery capacity needed.

[thadisjones]

Always remember that when you put batteries on a keostationary probe, and do the math so you have just enough power to carry over the nights...

…the one time you NEED that remote to be operational, the Mun will be blocking the sun and your battery will be dead.