Comment by jacquesm | Hacker News Reader

Comment by jacquesm | Hacker News Reader

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It's mostly a function of how well your antenna is able to amplify the signal, how precise you can aim that antenna and how slow you transmit. If you have a very good antenna with lots of gain and a very precise mechanism of aiming it (at an object whose location is very well known, and Voyager is a moving target) it will take much less power than if either one of those elements is not optimal.

The idea here is that any radio energy that does not end up in the vicinity of the target was wasted and at 21 billion Km that gives you plenty of opportunity for mis-alignment.

Receiving the signal has similar challenges, with the added complication that this time the sender is sending with a power level that puts its signal under the noise floor by the time it reaches Earth.

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

Fun fact: this goes for the GPS satellites as well by the time their signal reaches your pretty little hand-held receiver and it takes nothing short of magic (to me, not to the people that design that stuff) to recover the signal.

If we launched a proxy satellite into the solar system to help communicate with these probes, would it make things easier/better? Or is it better to just communicate directly from the Earth?

For Voyager-like mission profile building useful network of such data relay satellites/probes would be prohibitively expensive.

For missions where that makes sense (mars probes, STS, ISS and IIRC even original Apollo moon landings) relay satellites or even networks of them are/were used. To some extent for such constructions to be useful it has to be constructed of satellites that orbit something which is near to target of the probe, which is impractical for probes that are on highly eliptical orbits around sun, not to say probes that are on exit trajectory like Voyager.

Isn't Voyager on an an angle relative to the ecliptic that is large enough that a single satellite could have it in view at all times?

See the other thread :). Such satellite would need impractically large Rx sensitivity and Tx power. Doing that on surface of earth is simpler and significantly cheaper.

Are there bots that downvote comments on HN? Why would anyone downvote this comment?

I think it would make things worse, the only advantage I see is that if you got it to work at all you could do away with the requirement that you'd need three base stations on Earth. A single Geostationary satellite should be able to keep both the base station and the Voyager in sight at the same time. But that's a lot of money to spend for very little advantage.

There is no launch vehicle that is capable of launchibg anything remotely similarly sized as typical DSN antenna, not to mention of similar mass. Also station and attitude keeping of such an satellite would be non-trivial problem at sufficiently high orbits for such thing to be useful.

Edit: TLDR: for the amount of money required to design, build and deploy such relay satellite in geosynchronous or such orbit you can do several manned missions to mars or some other planet of your choosing

It would not nearly have to be as heavy as it would have to be on Earth (no gravity to withstand so skeletal build will do just fine) and a 20KW transmitter could be powered on a satellite with relative ease. There have been quite a few proposals for antennae that unfold in space.

As for your edit: very heavy satellites cost (including launch) ~$250M whereas a manned Mars mission is estimated to cost $6B.

I really don't see how you could do 'several manned missions to Mars or another planet of your choosing' for the same budget as a single relay satellite, even a large one.

The problems I see with such a design are simply that it does not give you any advantage for spending all that money and actually stands a fair chance of making things worse. More stuff, so more stuff that can go wrong and if it does it is in a place where you can't fix it. Limited life-span as well compared to the Voyager itself because of the larger complexity (must keep two antenna's aimed at the same time while moving itself).

Unfolding some lightweight structure is certainly possible, but the attitude-keeping requirements are harsh.

Uplink path of DSN is capable of significantly higher power levels than 20kW, several orders of magnitude more. Also the whole transceiver electronics are especially fiddly, with various cryogenically cooled and/or high-power microwave valves without meaningful solid-state replacements, which is not something you want to have in GSO without any chance of mainteance.

> but the attitude-keeping requirements are harsh.

Yes, that's exactly what I wrote upthread, that's the hard requirement. And that is what will fail and then you've got a very expensive doorstop in an orbit outside of any repair capability. Inability do do maintenance / repairs is the killer.

My point was that the actual payload is mainteance-heavy.

On the other hand it is certainly true that RCS of such satellite would require exceedingly large stores of RCS supplies which will invariably run out and have to be somehow replenished.

Edit: even hall thrusters require stores of xenon and with the precision required the amount consumed is far from practical.

Interesting! Thank you for the info, I'll ruminate over that for a while!

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