Relay satellite

[eatU4myT]

I have just entered a Duna window, and sent of a little fleet of probes for a first trip to a new planet. The first one out is a relay, which is headed for a nice high eccentric polar orbit of Duna with a big relay antenna, while all the rest have smaller direct antennae so will be using this first relay to phone home. So...

1) Have we ever actually launched a dedicated relay satellite, whose sole purpose was to enable other satellites to contact home?

2) What combination of antenna/dishes do/would they have?

Obviously in the game, the big relay dish just does the job for me, but I presume in real life I would need one big powerful dish pointing back at Kerbin, and then... What? A number of smaller dishes tracking the satellites that the relay was supporting? An omnidirectional antenna that could talk to all the satellites in range?

[DerekL1963]

5 hours ago, eatU4myT said:

Have we ever actually launched a dedicated relay satellite, whose sole purpose was to enable other satellites to contact home?

No.  The closest we've ever come is TDRS.  Several Mars probes have given over part of their payload to act as relays as well.

[DDE]

12 hours ago, eatU4myT said:

1) Have we ever actually launched a dedicated relay satellite, whose sole purpose was to enable other satellites to contact home?

Well, let's start with the basics. Usually, there is a direct radio link between a lander or rover, and Earth. A relay is not normally involved. Heck, the doppler shift of the lander's signal was used in lieu of an accelerometer on the early Soviet Venera missions to find out what it landed onto. Sometimes there is a relay... but it's the orbital section/probe bus the lander rode on.

As a rule, relays come into play when there's an issue of line of sight, not distance. Which is why you get NASA's TDRS(S):

And Roscosmos has Luch:

And the there's the National Reconnaissance Office and its Space Data System:

Spoiler

Please look here:

And then the Russian military has the 14F136 Harpoon series, reportedly derived from this platform:

Spoiler

*furrows brows sternly*

None of them are designed to work past high orbit.

Edited September 5, 2020 by DDE

[mikegarrison]

I believe China launched some sort of lunar orbiter to function as a relay to their probes on the far side of the moon. And as mentioned, some of the Mars orbiters have been designed to function as relays for probes and rovers on the ground, but they aren't dedicated in the sense of that being their only job.

I mean, if you already have an orbiter, why not include a camera and use it to take pictures with as well as relay?

https://en.wikipedia.org/wiki/Chang'e_4#Queqiao

Here it is. Yes, it's a relay parked at the Earth-Moon L2 point. (Or rather, in a halo orbit that is centered on the L2 point.)

Wikipedia says it is primarily a relay, but also has another science package:

Quote

Additionally, this satellite hosts the Netherlands–China Low-Frequency Explorer (NCLE), an instrument performing astrophysical studies in the unexplored radio regime of 80 kilohertz to 80 megahertz. It was developed by the Radboud University in Netherlands and the Chinese Academy of Sciences. The NCLE on the orbiter and the LFS on the lander work in synergy performing low-frequency (0.1–80 MHz) radio astronomical observations.

KSP does not have an L2 point because it doesn't do 3-body gravity.

Edited September 6, 2020 by mikegarrison

[tomf]

One of the mission objectives for the Mars Reconnaissance Orbiter is to provide hish speed data relay for rovers on the surface of mars, which technically aren't satellites themselves are close enough.