Pons_Aelius comments on NASA can’t talk to its Mars robots for two weeks because the sun is in the way

[–] Pons_Aelius@kbin.social 7 points 2 years ago (3 children)

The problem you face with that idea is that the satellites will have to have enough power to retransmit signals.

While the Mars > L3/L4 > Earth route is not much of an issue as the large receivers on earth can deal with a small power output at Lagrange. A signal moving in the other direction will have to be quite powerful to reach the small receivers on the Mars end.

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[–] TheFerrango@lemmy.basedcount.com 4 points 2 years ago

Looks to me like a perfectly good reason to devote a few extra trillions to the public space program

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[–] threelonmusketeers@sh.itjust.works 1 point 2 years ago

L3

Did you mean L5? L3 is always in line with the sun, so it doesn't seem like it would be useful for communication.

A signal moving in the other direction will have to be quite powerful to reach the small receivers on the Mars end.

Would it be easier to have a separate satellite for each direction, one at the Earth-Sun L4 point, and one at the Mars-Sun L4 point? Could we get a large enough dish to the Earth-Sun L4 point?

Alternatively, could we use lasers instead of radio? The SpaceX Starlink satellites have laser inter-links, and NASA just sent up the ILLUMA-T payload to the ISS last week.

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[–] Sigmatics@lemmy.ca 1 point 2 years ago (2 children)

"would have to be quite powerful" doesn't mean it's not feasible?

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[–] Pons_Aelius@kbin.social 6 points 2 years ago (1 child)

Pretty much. For it to be effective as a relay it would need some large dishes and a large power supply (large solar array) plus a good amount of propellant for station keeping.

So it would be a quite expensive option when it is only really required for a few weeks a year.

Also with the mass it would likely have to be I doubt there was a heavy lift rocket that could do the job in recent times until Falcon Heavy came along.

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[–] threelonmusketeers@sh.itjust.works 1 point 2 years ago (1 child)

plus a good amount of propellant for station keeping

Aren't L4 and L5 naturally stable points? A large propellant budget shouldn't be required for station keeping.

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[–] Pons_Aelius@kbin.social 2 points 2 years ago* (1 child)

They are much more stable than other locations but are not completely stable, so station keeping is required. In a theoretical two body system Lagrange points would be perfectly stable but that is not the case with the solar system. Eg: The orbit of the moon ever so slightly effects the Sun - Earth Lagrange points.

The JWST is a good example. The expected observational lifespan of the telescope is based on how long it is able to remain at L2.

NASA Says Webb’s Excess Fuel Likely to Extend its Lifetime Expectations

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[–] threelonmusketeers@sh.itjust.works 1 point 2 years ago* (last edited 2 years ago)

The JWST is a good example. The expected observational lifespan of the telescope is based on how long it is able to remain at L2.

I thought L1, L2, and L3 were unstable but L4 and L5 were stable. Hence why asteroids and other detritus tend to collect at L4/L5.

Edit: Huh, it looks like the stability of L4 and L5 are dependent on the mass ratio of the two bodies. The ratio works out for the Sun-Earth system, so it should also work for the Sun-Mars system.

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