Stock game communications range

[eatU4myT]

Please tell me where I am going wrong in my thinking here! 

In the opening days of a career, I have enough rocketry tech to launch a simple probe that can reach Eve.  However, I need to wait until I research RA-2 antenna (or something of equivalent power) in order to be able to communicate with it when it gets there, to transmit science back and make it worth sending it in the first place.

So, I wait until I have researched RA-2's, stick a couple of them on and off we go.  I arrive at Eve some time later, and oh dear, I don't have line of sight to KSC (Kerbin facing the wrong way etc.)  What to do?  A relay!  If I put something in a nice high polar orbit of Kerbin, I will get line of sight.  But to give me enough power for the relay to connect to my probe, it would need to have around 30 to 40 RA-2's!? (depending on exactly how far away Eve is from kerbin when I arrive).  That's right isn't it - the relay needs enough power to reach the probe, regardless of the power of the DSN?

What am I missing?  Do we just accept temporary blackouts, and hope we don't need to make a correction or caputre burn at just the wrong moment?  I guess I can deal with having to take science readings and then wait until signal is restred to transmit them, but waiting 3 hours to perform a burn seems not good.  Do I just assume I will have improved the tech of my antennas at Kerbin in the time it takes for the probe to reach Eve?  Its a fair assumption that I will have, but it doesn't seem like the answer real life space agencies accepted when sending probes to Venus in the early days!  Did they just accept some downtime?

Thanks

[PrvDancer85]

If u dont want the restrictions with commnet, then just turn it off. I'm sorry i dont get what your question is but here are some informations regarding commnet and antenna ranges

Edited September 24, 2018 by PrvDancer85

[eatU4myT]

Its difficult, becuase I do want to bother, I just think I'm missing something.

I guess maybe what my question really is (other than perhaps "have I got something wrong in my rough calculations") is "what were radio communications like with the Mariner 2 spacecraft...?!"

Thanks

[Aeroboi]

@eatU4myT

38 minutes ago, eatU4myT said:

But to give me enough power for the relay to connect to my probe, it would need to have around 30 to 40 RA-2's!? (depending on exactly how far away Eve is from kerbin when I arrive).  That's right isn't it - the relay needs enough power to reach the probe, regardless of the power of the DSN?

That's not true. You can't stack antennas of a certain rating to magically extend their range. You only need a minimum of 2 x RA-2 antennas on the relay satellite. 3 if that relay satellite has to connect with other relay satellites around Kerbin which I would advice. So that's one to connect to the KSC, another to connect with another relay satellite around Kerbin and another one to connect with your deep space Evian probe. The probe then also requires a RA-2 or better antenna to connect with the relay satellite (obvious statement)

As for your particular scenario, If you do a normal hohmann transfer orbit Eve is always on the same side of the Sun as Kerbin would be by the time you get there. So the RA-2 will suffice. And when you then get there you do your mission lasting a couple of hours so you wont need any connection thereafter.

Connection range of a antenna is pronounced in Gm (gigameter: 1 billion meters) or Mm (megameter: 1 million meters)
So a 10Gm satellite can connect to a receiver 10 billion meters away, that is 10.000.000 Kilometers.

A dish has to connect with a radio receiver on the other end. If the signal becomes to weak it cannot receive that signal. Stacking multiple dishes doesn't help as it's just sending the same weak signal but then multiple times.

[eatU4myT]

27 minutes ago, Aeroboi said:

That's not true. You can't stack antennas of a certain rating to magically extend their range.

That's news to me?  I thought that all antennas were combinable, for diminishing returns in increased power?

Thanks

[Aeroboi]

4 minutes ago, eatU4myT said:

That's news to me?  I thought that all antennas were combinable, for diminishing returns in increased power?

Thanks

IIRC it doesn't work like that in real life. But I'm not sure of all that is possible so I might be wrong. It would be nonsensical anyway because if you need more range you just get a bigger antenna. Regardless, it doesn't work like that in KSP. One antenna has a specified strength and range. Just as in real life you would want to get a bigger one.

44 minutes ago, eatU4myT said:

Its difficult, becuase I do want to bother, I just think I'm missing something.

I guess maybe what my question really is (other than perhaps "have I got something wrong in my rough calculations") is "what were radio communications like with the Mariner 2 spacecraft...?!"

Thanks

In real life there is signal delay. So vessel controls and instrument inputs were transmitted in advance based on the precalculation of the probes orbit. If you install the remote tech mod this signal delay function will be simulated.

KSP commnet is simple. If you really want to know all about it you can read this https://wiki.kerbalspaceprogram.com/wiki/CommNet
For a interplanetary probe you want a relay satellite around Kerbin and a Satellite dish on the probe. But because the satellite around Kerbin can also be on the other side of Kerbin you want several satellites that relay to one another around Kerbin to make sure your probe can always connect with the KSC.

To create full relay coverage there are 2 ways.
The 1st way is simple. Just send a dozen satellites into a high kerbin orbit that all have 3 dishes on them. That way your bound to always have a connection.

The 2nd way is more elegant but more tricky. It is much cheaper though.

That is to launch 3 satellites around Kerbin in a Semi-synchronous orbit. These are 3 equatorial satellites that have the same orbital period. That means they take the same amount of time to make one orbit around the planet. That means they always stay at the same distance relative to one another. You can use mods such as mechjeb to auto calculate the orbital period. If the orbital periods of all the 3 satellites are similar they shouldn't drift apart.

To create a semi-synchronous orbit around Kerbin you want to read this https://wiki.kerbalspaceprogram.com/wiki/Synchronous_orbit

[eatU4myT]

26 minutes ago, Aeroboi said:

IIRC it doesn't work like that in real life. [...] Regardless, it doesn't work like that in KSP.

To clarify, it was only KSP I was talking about re: stacking antennae - I was pretty sure they did stack.

I'm fairly comfortable with constellation designs and how they establish line of sight, its really just range that I'm not understanding.  Any further insights about this would be very welcome!

Doing some reading online, I think perhaps that DSN groundstations were better established in the early 60s than I thought they were, and that part of the answer I'm looking for is that there wasn't as much down time as I imagined to ground stations.  Perhaps I should turn the additional ground stations back on in KSP!

Thanks

[Kryxal]

Another potential answer is to delay your arrival at your destination ... a burn which combines radial and prograde/retrograde will adjust that without overly affecting your arrival point if you do it right.  Just be sure to plan out Kerbin's position and facing at your arrival, and you only need to change it by maybe 2 hours.

[HebaruSan]

The wiki is a good source (and it contradicts 90% of what @Aeroboi just said ).

Quote

Connection range of a antenna is pronounced in Gm (gigameter: 1 billion meters) or Mm (megameter: 1 million meters)
So a 10Gm satellite can connect to a receiver 10 billion meters away, that is 10.000.000 Kilometers.

No, antennae are not rated in meters in KSP. The "m" part of the unit is specifically left off, and the ratings are in k, M, or G. This is to avoid giving the impression that the rating is to be interpreted as a simple distance. This is the formula for calculating the maximum range of two endpoints once you know their individual vessel power (from the wiki page you linked):

Quote

A dish has to connect with a radio receiver on the other end. If the signal becomes to weak it cannot receive that signal. Stacking multiple dishes doesn't help as it's just sending the same weak signal but then multiple times.

This is mildly wrong because it ignores the receiving side, where stacking multiple dishes is most definitely a thing IRL:

https://en.wikipedia.org/wiki/Interferometry

(I'm guessing that it's equally valid for transmitting, but I can't prove that with a source.)

3 hours ago, Aeroboi said:

You can't stack antennas of a certain rating to magically extend their range.

2 hours ago, Aeroboi said:

Regardless, it doesn't work like that in KSP. One antenna has a specified strength and range. Just as in real life you would want to get a bigger one.

Wrong, multiple antennae do stack, and this is the formula for combining their power (again from the wiki page you linked):

It looks complicated, but if you let the exponent equal 1 (I think it's 0.75 in practice), then the "strongest" factors cancel each other out, and vessel power is just the sum of the strengths of the vessel's antennae. So you can use that as a first approximation in your head when building craft.

Quote

KSP commnet is simple. If you really want to know all about it you can read this https://wiki.kerbalspaceprogram.com/wiki/CommNet

You should have read it before commenting!

Quote

To create a semi-synchronous orbit around Kerbin you want to read this https://wiki.kerbalspaceprogram.com/wiki/Synchronous_orbit

Note that synchronous orbits don't matter here. It's a thing in real life because it's convenient to be able to point a static satellite dish at one spot in the sky without active tracking, but KSP's dishes track automatically for free. Commnet only requires line of sight, which means you can put your relay satellites into any orbit as long as their orbital period is the same.

Edited September 24, 2018 by HebaruSan

[Tyko]

4 hours ago, eatU4myT said:

I arrive at Eve some time later, and oh dear, I don't have line of sight to KSC (Kerbin facing the wrong way etc.)

Line of sight is a real issue and can be managed by timing your missions. This is a problem for real world mission planners too.

As @Aeroboi mentioned above, if you're performing a Hohmann transfer Kerbin won't be far behind your spacecraft and should be on the same side of the Sun. You also have to contend with being in the shadow of Eve, and again that's a real world issue. One solution is to plan your first Eve mission to enter a polar orbit. This way your circularization burn will occur somewhere above Eve's Pole and won't be in Eve's shadow. If there's a relay on that polar satellite it's a lot easier to plan later equatorial missions to be able to see either the polar satellite or Kerbin.

[eatU4myT]

Thanks everyone for the input!

So, to summarise, antennae do stack, probably in real life and certainly in KSP.

I think what I have been doing that has made it feel odd to me is turning off the extra ground stations. This has made me look at relays around Kerbin, which would therefore need to match DSN power in order to work. Since it appears that there were several ground sites even as far back as late 50's, I won't feel too bad turning them back on! I had thought I was making the game harder, but actually I was making the game unrealistic. Bad move!

I'll save my relay building efforts for putting around my target planets, when I get to the stage of trying to make landings.

Out of interest, does anyone know how realistic the DSN power really is? Is there a modifier level that people prefer to use to match real world capabilities?

Thanks

[bewing]

In stock, you can still perform burns while in a communication "blackout". The assumption is that you have reduced control from not having LOS, but you don't have zero control (unless you change some settings). Or have a pilot onboard.

If you turn off the Kerbin groundstations, then yes you'd better research something more powerful than an RA2 pretty quick to create a Kerbin orbital comm network -- before you go launching a bunch of interplanetary robotic missions.

On the other hand, if you leave the Kerbin groundstations turned on, then what you always need is a relay network at the other end of your journey. Kerbin has plenty of antennas, and doesn't need more from you. So you always have to launch a relay sat along with your interplanetary mission.

Even if you have the Kerbin groundstations turned off, you still don't want your relay sats anywhere near Kerbin. L4 and L5 (60 degrees ahead and behind Kerbin on orbit around Kerbol) might be much better choices.

[Tyko]

1 hour ago, eatU4myT said:

Thanks everyone for the input!

So, to summarise, antennae do stack, probably in real life and certainly in KSP.

I think what I have been doing that has made it feel odd to me is turning off the extra ground stations. This has made me look at relays around Kerbin, which would therefore need to match DSN power in order to work. Since it appears that there were several ground sites even as far back as late 50's, I won't feel too bad turning them back on! I had thought I was making the game harder, but actually I was making the game unrealistic. Bad move!

I'll save my relay building efforts for putting around my target planets, when I get to the stage of trying to make landings.

Out of interest, does anyone know how realistic the DSN power really is? Is there a modifier level that people prefer to use to match real world capabilities?

Thanks

Yep, and not only ground stations either. During early missions they'd place ships at sea spread across the Pacific to act as "ground" relay stations.

[Rocket In My Pocket]

4 hours ago, HebaruSan said:

It looks complicated, but if you let the exponent equal 1 (I think it's 0.75 in practice), then the "strongest" factors cancel each other out, and vessel power is just the sum of the strengths of the vessel's antennae. So you can use that as a first approximation in your head when building craft.

I've often heard a "rule of thumb" quoted with diminishing returns for antennas, being that it takes four extra of a given antenna to double the power of the first? Is that correct? Ie. If I had one RA-2 it would take an additional four RA-2 (so five total) to give me double the strength of a single RA-2?

Or are there no diminishing returns on antenna? They stack at a flat rate? So five RA-2's are five times as powerful as one?

Edited September 24, 2018 by Rocket In My Pocket

[HebaruSan]

23 minutes ago, Rocket In My Pocket said:

I've often heard the "rule of thumb" with diminishing returns for antennas being that it takes four extra of a given antenna to double the power of the first? Is that correct? Ie. If I had one RA-2 it would take an additional four RA-2 (So 5 total.) to give me double the strength of one RA-2?

As far as I can tell, that's somewhat overkill. Let P=power of one of the antennae you're using and N=how many; then to double it we let the vessel power equal 2 * P, the strongest antenna is P, and the sum is N * P:

2 * P = P * ((N * P) / P) ^ 0.75

2 = N ^ 0.75

N = 2 ^ (4/3) ≈ 2.52 antennae needed to double power

That should work out, but I did have to correct two algebra errors while working it out, so I won't claim infallibility.

Edited September 24, 2018 by HebaruSan

[swjr-swis]

2 minutes ago, HebaruSan said:

2 * P = P * ((N * P) / P) ^ 0.75

 

Or, if math gives you the hickups... check the handy spreadsheets / charts made by others.

 

[Rocket In My Pocket]

12 minutes ago, HebaruSan said:

As far as I can tell, that's somewhat overkill. Let P=power of one of the antennae you're using and N=how many; then to double it we let the vessel power equal 2 * P, the strongest antenna is P, and the sum is N * P:

2 * P = P * ((N * P) / P) ^ 0.75

2 = N ^ 0.75

N = 2 ^ (4/3) ≈ 2.52 antennae needed to double power

That should work out, but I did have to correct two algebra errors while working it out, so I won't claim infallibility.

I won't pretend I understood any of that but the the last bit, but thanks! Two and a half does seem more reasonable.

9 minutes ago, swjr-swis said:

 

Or, if math gives you the hickups... check the handy spreadsheets / charts made by others.

Indeed lol, I'm certainly more of a Pilot/Engineer than a Scientist. Thanks!

[HebaruSan]

4 minutes ago, Rocket In My Pocket said:

I won't pretend I understood any of that but the the last bit, but thanks! Two and a half does seem more reasonable.

Actually, I may have interpreted the question too literally. If by "power" you actually meant "range", as in you have connectivity from twice as far away, then we need to apply the other equation:

Let P1=original power of the vessel we want to double, and P2=the unchanging power of the "other" vessel (could be the DSN or whatever). We know that before our doubling attempt, these vessels can communicate at a range sqrt(P1 * P2). To double that range by increasing the first vessel's power by a factor of Q, we have:

2 * sqrt(P1 * P2) = sqrt(Q * P1 * P2)

4 * P1 * P2 = Q * P1 * P2

4 = Q

Hence to double the range, we need to quadruple the power rating. That's close to doubling it twice*, so we should increase our number of antennae to:

2.52 * 2.52 ≈ 6.35 antennae to double the range

* The second doubling isn't quite the same, because my previous post assumed that you're starting with 1 antenna, not 2. But it should be close enough for government work.

[Rocket In My Pocket]

13 minutes ago, HebaruSan said:

2.52 * 2.52 ≈ 6.35 antennae to double the range

* The second doubling isn't quite the same, because my previous post assumed that you're starting with 1 antenna, not 2. But it should be close enough for government work.

My bad, I did mean range!

As my grandfather would say; "It's good enough for the girls we run with."

Edited September 24, 2018 by Rocket In My Pocket

[Gargamel]

I guess this thread just proves the old adage true.  "There's no better way to get a correct answer on the internet, than to post an incorrect one". 

[eatU4myT]

Anyone able to advise on the realistic DSN power question?

Thanks

[bewing]

There really is no such thing as "realistic DSN power". In 1964, advanced researchers were still using stuff like this:

And by 1980, we already had this:

The power of the arrays was just a function of money, and this array could reach Pioneer all the way out at the heliopause.

So which of those two do you consider "realistic"?

 

Edited September 25, 2018 by bewing

[swjr-swis]

4 hours ago, eatU4myT said:

Anyone able to advise on the realistic DSN power question?

To add to @bewing's response: We already knew how to build antenna's to listen for faint space signals, and how to keep track of such signals, well before we started to send up satellites. Space communications used things we had already learned from advances in other areas, like radio/tv, space observation, radar, etc. After that, things sort of .. 'kept up'. We've generally restricted ourselves to sending craft only as far as we deemed reliable comms to be possible, because it was a requirement we set ourselves. And we developed new techniques and refinements for missions we wanted to send further.

So as long as you do the same in KSP careers (never go farther than your currently available antennae can support, and keep unlocking new tech to extend comms range), you're being 'realistic'.

 

Some reading material:

https://www.nasa.gov/directorates/heo/scan/services/networks/txt_daep.html

https://www.nasa.gov/directorates/heo/scan/services/networks/dsn

https://www.wired.com/story/meet-the-geek-who-tracks-rogue-satellites-with-coat-hangers/

https://blog.nobugware.com/post/2015/listening_to_satellites_for_30_dollars/

[Kryxal]

22 hours ago, HebaruSan said:

The wiki is a good source (and it contradicts 90% of what @Aeroboi just said ).

No, antennae are not rated in meters in KSP. The "m" part of the unit is specifically left off, and the ratings are in k, M, or G. This is to avoid giving the impression that the rating is to be interpreted as a simple distance. This is the formula for calculating the maximum range of two endpoints once you know their individual vessel power (from the wiki page you linked):

This is mildly wrong because it ignores the receiving side, where stacking multiple dishes is most definitely a thing IRL:

https://en.wikipedia.org/wiki/Interferometry

(I'm guessing that it's equally valid for transmitting, but I can't prove that with a source.)

https://en.wikipedia.org/wiki/Phased_array

It seems they're very similar, and based on constructive interference, which makes them highly directional (though steerable electronically through phase shifting).

[eatU4myT]

22 hours ago, swjr-swis said:

So as long as you do the same in KSP careers (never go farther than your currently available antennae can support, and keep unlocking new tech to extend comms range), you're being 'realistic'.

Thanks, and thanks for the links, very helpful.

I suppose my only remaining grumble then is that the antennas appear too late in the tech tree (or everything else appears to soon!)  With tier 0,1,2,3 unlocked you can reasonably expect to take Kerbals to the Mun, but you have to wait until tier 5 (solar panels) and tier 6 (RA-2 level antenna) to have much of a shot at sending a probe to Eve.  Its kind of anachronistic, no?

Thanks