Commercial alternatives to DSN?

[gongora]

Here is one dish for Lunar support:
1661-EX-ST-2023

Pursuant to Section 5.61(a)(1) of the Federal Communications Commission’s (“FCC” or “Commission”) Rules, the Ronald G. Eaglin Space Science Center (“SSC”) at Morehead State University (“MSU”), provides this narrative statement to justify its request for Special Temporary Authorization (“STA”) to transmit a 250 kHz emission Earth-to-space centered at 2035.594 MHz to support the Intuitive Machines 1 (“IM-1”) mission to place and test the Nova-C lunar lander on the south pole of the Moon.

[Jim]

Having big antennas on Earth is a problem. They are not viable to operate commercially.

Huh?  and a large relay satellite at Sun-Mars L4 or L5 would be?

Might be, if there's enough radio traffic to relay. Say, from a large surface base or two on Mars.

Then Earth ground stations would be even more viable.  They could support other missions in addition to Mars.

[Jim]

Put another set in Earth orbit.

No, that makes no sense either.

It depends on how well a laser link from Mars can operate through the earth's atmosphere.

Psyche is 1/2 the minimum distance to Mars and its laser link has been working.

[DanClemmensen]

Put another set in Earth orbit.

No, that makes no sense either.

It depends on how well a laser link from Mars can operate through the earth's atmosphere.

Psyche is 1/2 the minimum distance to Mars and its laser link has been working.

My knowledge of in-space laser links is restricted to the research reading I did over the course of about six months for this patent:
    https://patents.google.com/patent/US9866324B2/en
This reading does not make me an expert, and I did not suddenly become a professional in the field just because I was getting paid. The nice thing about being an old guy with a reputation for being indispensable is that the company will pretty much keep paying you no matter what you do.

One big advantage of staying in space is no worry about clouds. Another big advantage is the receiving telescope sees the transmitter against a dark background instead of having Earth as the background. For the Earth-orbit Mars relays, put maybe two of them in high enough orbits so one is always far enough away from Earth. Perhaps two in the same Molniya orbit but out of phase by 180 degrees?

[whitelancer64]

Here is one dish for Lunar support:
1661-EX-ST-2023

Pursuant to Section 5.61(a)(1) of the Federal Communications Commission’s (“FCC” or “Commission”) Rules, the Ronald G. Eaglin Space Science Center (“SSC”) at Morehead State University (“MSU”), provides this narrative statement to justify its request for Special Temporary Authorization (“STA”) to transmit a 250 kHz emission Earth-to-space centered at 2035.594 MHz to support the Intuitive Machines 1 (“IM-1”) mission to place and test the Nova-C lunar lander on the south pole of the Moon.

The largest radio dish Morehead has is a 21 meter antenna.

[tbellman]

Oh. The relay satellite should be at Sun-Mars L4 or L5.

I thought that was obvious, that way Mars radio dishes always stay low mass, low power.

The Sun-Mars L₄ and L₅ Lagrange points are at a distance of approximately 1.5 astronomical units (au) from Mars.  That's a long way.  It is about three times the distance between Mars and Earth when they are at their closest.  Even during solar conjunction (when Earth and Mars are on opposite sides of the Sun), the distance to L₄/L₅ is about 60% of the Mars-Earth distance.

So if you need e.g. a 17m dish on Earth to pick up signals from Mars during solar conjunction, you will need a 10m dish on the relay satellites.  That's a fairly large antenna to put on a deep space probe, so it won't be cheap.

Much better to put relay satellites in orbit around Mars.  Put three of them in a somewhat high orbit around Mars, do optical inter-satellite links, and optical links towards Earth.  With three satellites, you can make sure that one is always above the horizon for any position on Mars unless too close to the poles, and at least one satellite will be outside of Mars shadow as seen from Earth.  The radio antennas for communicating with assets on the surface (and other satellites in orbit around Mars) can be kept at reasonable sizes, and the optical links between the relays and towards Earth allows higher bandwidth for the same size than radio links.

You want a somewhat high orbit to get good coverage of the surface with just a few satellites.  A somewhat high orbit also helps with the optical links towards Earth: you get spatial separation between the satellite and the bright planet, so the receiving telescope can avoid being blinded by reflected sunlight.  Something like areostationary orbit (about 17000 km altitude) should do fine in terms of altitude, but you might want to go higher, well outside the orbit of Deimos, to lower the amount of stationkeeping needed.

This will still give an outage during solar conjunction, but that's just a couple of weeks every 26 months.  Not worth solving until we have a sizable number (hundreds) of humans on Mars.


A small handful of relay satellites around Earth would also be helpful, to ensure that you always have at least one in sight of Mars (outside solar conjunctions), and to avoid the optical links being blocked by clouds, but that's optional, especially early on.


This would of course only solve communication with Mars.  Other things the Deep Space Network communicates with, e.g. Voyager, New Horizons, Dragonfly, et.c, won't be helped directly.  However, my understanding is that DSN spends quite a lot of time communicating with Mars, so such a relay constellation would free up time on the DSN for non-Mars things.

Now we only need to figure out how to get NASA, ESA, JAXA and others to get money to pay for it...