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Kerbin CommNet coverage on hard mode

Robin Patenall

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Having played with KSP on hard mode, I found it quite annoying that you don't get full CommNet coverage of Kerbin when you are in orbit unless you are very high. I kept losing control of vessels with only probe cores when I was launching or attempting to do a re-entry burns, so I thought that I'd create a map so I could see the altitude you need to have CommNet a signal when in hard mode (or when you've set the Occlusion Modifier to 1.0).

I ended up creating two, one for orbital heights (75km to 250km) and one for surface heights (10m to 60km). Each colour patch indicates where there is no CommNet signal at a given altitude.

The most interesting bit is that there is a large CommNet blackspot East of the KSC, just about the place that you might be attempting to circularise and it goes very high, this means that launching a vessel with just probe cores onboard really needs a relay satellite to be in place first. Looking at the map, it looks like an initial relay satellite might be best launched into a polar orbit giving you much more time (via North Station One) to circularise before you lose connection.

I've done a bit of testing and it does seem to match the reality of the game. Hopefully these will be helpful to people

Orbital Heights


Large (4096 x 2048) and Small (1024 x 512)

Surface Heights


Large (4096 x 2048) and Small (1024 x 512)



Edited by Robin Patenall
Fixed the size of the large downloads
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  • 1 month later...
41 minutes ago, Nazalassa said:

Did you use math, or approximated the heights?

It doesn't look like either is taking terrain height into account, but I don't think CommNet does either for occlusion purposes but goes solely by body radius and occlusion modifier.  But on the surface level map, I think terrain height would matter if we are talking landed/spashed vessels having  comms; that is landing on a peak a few km high might put you in comms LOS of a ground station while being at sea level one may not have comms at same distance from ground station

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Lots, and lots, of math, but I let my PC do it.

I wrote a python script the would check each Lat / Long / Altitude to see if that point had an unobstructed line of sight to any of the ground stations. There was some optimisation that would stop at the lowest height that had CommNet coverage as I believe (but didn't prove rigorously =) that if there is a connection at a given height then there is always a connection above that. It wasn't that efficient, but it never took that long to run and I worked with smaller map images while debugging before using the high resolution maps for release.

I found a list of the Lat / Log of the ground stations but had to get the altitude with the WayPoint Manager mod. I assume that they broadcast from terrain ground level (mostly as I know there are actual objects there) and this does appear to match up with the tests I made in game but I'm always open to be proved wrong. I had to make a reasonable assumptions about how KSP calculates CommNet occlusion (i.e. the occluding object is a sphere with radius = Planet Radius * Occlusion Modifier) but this matches what others have said in this forum and does appear to be correct.


DarthGently is right, CommNet appears to ignore terrain, I've seen active connections pass through mountains even when the Occlusion Modifier is 1.

The altitudes on the maps are above sea level and yes if land on high terrain you may get a signal where are you might not in the same position at sea level. In fact one of  my reasons for building the maps was my loss of signal just before landing in the waters East of the KSC near the Island airstrip. The KSC is about 70m above sea level and you don't need to go far to lose signal just before impact (important for powered landing)

The minimum height ALS for connection at the Island airfield is about 450-500m 

Edited by Robin Patenall
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