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this post was submitted on 13 Nov 2023
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Can we put some relay satellites at the L4 and L5 Lagrange points already? It seems like something we should have done years ago...
Can we? Yes. Should we do it right now? That's debatable.
The question is how much this would cost vs getting a two weeks offline every 26 months?
These two weeks do not create any additional requirements (you already have to make sure the probes can survive for a few weeks without comms), science does not fully stops during these two weeks. And it gives an opportunity to do long duration maintenance on the ground segment.
Frankly, there is little need to spend >$100M for such relays satellites until we actually have a permanent human presence on Mars.
Even when we have a permanent human presence on Mars, there isn't a great necessity to maintain contact for those two weeks. Even if something goes wrong, it's not like anyone could send help. Essentially it would be just so we knew what was going on, but that's not really a full time requirement.
You've for the start of a sci Fi movie there : Mars comes out from behind the sun to find communication from Earth has stopped
Marvin got his hands on the Q35 space modulater didn't he?
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.
Looks to me like a perfectly good reason to devote a few extra trillions to the public space program
"would have to be quite powerful" doesn't mean it's not feasible?
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.
Aren't L4 and L5 naturally stable points? A large propellant budget shouldn't be required for station keeping.
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
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.
But is it necessary?
If Musk ever gets to Mars the lack of communication for two weeks will be the best part of the project.
They should try something with magnets.
I want to agree with this but I don't know enough about how magnets work to reasonably dispute it
No one knows. That's why we should try.
Did you mean L5? L3 is always in line with the sun, so it doesn't seem like it would be useful for communication.
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.
There's no pressing time urgency. It's okay to wait 2 weeks so yeah we could but it's an enormous expense and not worth it
We use very large radio dishes to communicate with craft at Mars, so that the spacecraft can use smaller dishes and less power. In order to add a relay at L4/L5, that relay would also need very large dishes and high power usage to reach the craft at Mars. Probably larger than anything we have in earth orbit today.
Could we use lasers instead of radio, like the Starlink laser inter-links or the NASA ILLUMA-T/LCRD demonstration?
Maybe in the future, but the existing Mars orbiters need to hear a strong radio signal. And laser communication has not yet been tested outside of Earth orbit. It will need to be significantly scaled up to handle the 2-3AU distance.