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It's been more than 40 years since NASA launched Voyager 1 & Voyager 2. With more advanced technology, wouldn't it now be a good time to continue sending more sophisticated Voyagers out there? Wouldn't it be a good way to gather more data? It would increase the chances of letting them (if they exist) know about our presence.

Did NASA stop sending off probes?

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    $\begingroup$ I don't get what you mean by "it will increase the chances of letting them (If they exist) our presence, right?" Are you talking about Aliens? That wasn't the purpose of the Voyager missions. $\endgroup$ – James K Dec 15 '18 at 8:01
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    $\begingroup$ As I recall, the voyager crafts were sent when the planets were properly aligned for gravity assists. That probably doesn't happen very often. I also think we learn a lot more by having spacecraft orbit a planet vs fly by a planet. There's not all that much to gain by sending a probe out of the solar system, not that they should never do it, but it's not a top priority. I would also add that if contact is the goal, a tiny spacecraft isn't a likely way to do it. Sending radio-waterhole transmissions or listening for them is more likely. $\endgroup$ – userLTK Dec 15 '18 at 9:59
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    $\begingroup$ You need to remember that "out there" wasn't the Voyagers' mission. The "gold record" and images on the spacecraft were just lagniappe ("an extra or unexpected gift or benefit") since they'd be heading out into interstellar space after their mission was complete. I don't suppose anyone really expected they'd still be sending back data 40 years later. $\endgroup$ – jamesqf Dec 15 '18 at 18:05
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    $\begingroup$ Re, "letting them [know of] our presence." Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. Seriously. Thinking that the voyager spacecraft will alert extra-terrestrials to our presence here on Earth is somewhat like thinking that a microscopic speck of dust, attached to the front of your house, will let somebody standing on the Moon see that you are home. $\endgroup$ – Solomon Slow Dec 15 '18 at 19:59
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    $\begingroup$ Possible duplicate of Are there any successors to Voyagers underway currently? $\endgroup$ – Hobbes Dec 17 '18 at 14:53
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Space probes are expensive. When your budget is limited, you have to compare what you can achieve with a space probe against what you can achieve simply by building a bigger, better telescope on Earth.

The Voyager probes cost 865 million USD, a number I believe is not inflation adjusted. Adjusting for inflation gives 3.6 billion USD. That compares to the cost of, e.g., the Extremely Large Telescope which is slightly over a billion Euros.

If you are the US government, how do you decide which project to fund? Chances are you'd ask the scientists to come up with ideas for what either project might discover, and then compare them to the costs. If the ELT is expected to produce as many results as the Voyager missions, it wouldn't make sense to fund the Voyager missions! Something like this is already what is being done: scientists propose projects, they are peer reviewed, and the consensus best ones get funded. Unfortunately the fact is, realistically, space probes are usually just not worth the money for the expected returns. It's for similar reasons that we've not sent more manned missions to the Moon or to Mars (I am confident that a manned Martian mission is possible with current technology, and the reason we haven't done it is because of $$$).

A fair question is why NASA sent out the Voyager probes in the first place. At that time, we didn't know as much about the outer planets, and going from 30% knowledge to 80% is a much larger improvement than going from 80% to 90% (these numbers are meant to be illustrative, not authoritative). Other reasons: these space missions capture the public imagination, which might make it worth doing anyway for publicity purposes (see Breakthrough Starshot, which is sending a probe to another star, something which is unlikely to be economically sensible also). Back in 1977 when the Voyager probes were launched, the US was in the midst of the Cold War. Space exploration was good for political points, making it more attractive. You can see from NASA's budget history that its budget then as a fraction of the federal budget was twice what it is today, and a few years before 1977 it was even higher (when getting Neil Armstrong onto the Moon was a Very Big Deal).

If you care about these space probes, support an initiative to increase NASA's budget. Example of such an initiative.

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It does:

Galileo: Launched in 1989, orbited Jupiter for 7 years.
Cassini-Huygens: Orbited Saturn for 13 years.
New Horizons: Fly-by of Jupiter and Pluto.
Juno: Currently in orbit around Jupiter.

NASA (and ESA) have created multiple outer planet probes. But they are costly and there is no reason to repeat what has already been done. So each mission has a different aim and purpose. Often this means not doing a fly-by, but getting the probe in orbit around the planet.

Uranus and Neptune have not been re-visited. They are very distant. Getting a probe out to them is possible. Getting something out to them in a reasonable amount of time and then getting it in orbit is much harder, and they are, perhaps, less intrinsically interesting than Jupiter and Saturn.

The voyagers did carry gold disks, but this was not a serious attempt to contact alien intelligence. It has a symbolic purpose. A record of humanity will exist somewhere in the galaxy long after we are gone.

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  • $\begingroup$ The gold disks (and their carriers) won't have moved outside of our galaxy by the time humanity is expected to no longer exist? $\endgroup$ – horse hair Dec 15 '18 at 18:51
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    $\begingroup$ No, the voyagers are not travelling fast enough to escape from the galaxy's gravitational well, so will remain in the Milky Way. Eventually a stellar collision is possible, but stars are small (compared to space, which is really really big). So the voyagers will travel in the galaxy for billions of years, longer than life will continue on Earth. $\endgroup$ – James K Dec 15 '18 at 19:42
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    $\begingroup$ @horsehair Even if they could leave the galaxy, they're moving rather slow. If we ignore they don't have nearly enough velocity (as if gravity no longer affected the probe), galactic distances are rather great. If we assume the Voyager travels in the galactic plane, it would have to cross at least 12 kilo parsecs (which already considers only "X% of stars are in this volume, not interstellar matter or dark matter). That would mean about 700 million years; the known human civilisation has only really existed for ten millennia or so. 700 million years ago, there were no animals on land. $\endgroup$ – Luaan Dec 15 '18 at 19:56
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    $\begingroup$ I like much more that version of the future, that we once find the Voyagers and take it back to home, into a museum. $\endgroup$ – peterh Dec 16 '18 at 1:30
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    $\begingroup$ @peterh In Elite Dangerous you can actually go visit the probes. They were left alone as moving museums. I like to think we'd do that when we're truly spacefaring. $\endgroup$ – Lightness Races in Orbit Dec 17 '18 at 10:34
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Like James K's answer details, probes have been sent to the outer planets even after the Voyagers.

However, the specific trajectory used by Voyager missions has not been reused. In fact, it was the specific position of the planets that inspired the whole program, initially called the Grand Tour.

Voyager trajectory, from Wikipedia (public domain)

The relative position of the outer planets in their orbits in late 1970's allowed a space probe to visit many of them and to achieve great speeds using a sequence of gravity assist maneuvers. This position only repeats once every 175 years, so it is very likely that future space probes in 2150's will take advantage of it.

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    $\begingroup$ There's not really much point in a “Grand Tour” trajectory any more. Sure, a mission to the outer solar system will always benefit from a gravity assist from Jupiter, but there's not much another flyby at Saturn or Uranus would gain you. For more thorough science than has already been done, you'll need orbiting probes like Galileo / Cassini / Juno. It's really serendipitous that the Grand Tour was possible in exactly the decade where it was most useful. $\endgroup$ – leftaroundabout Dec 15 '18 at 14:09
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    $\begingroup$ Surely the monumental advances in imaging in the intervening 175 years could make another flyby worthwhile. $\endgroup$ – nasch Dec 15 '18 at 17:50
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    $\begingroup$ @nasch Hopefully such missions won't be nearly as expensive as they are now, and we can do one as a sort of nostalgia mission. It can be earth's little once-every-175-year tradition. $\endgroup$ – corsiKa Dec 15 '18 at 19:05
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    $\begingroup$ @nasch, flybys in general aren't worthwhile. You only do a flyby if, for some reason, you can't do an orbital mission. Hopefully 175 years of engine design or probe miniaturization will let us send orbital surveys to Uranus and Neptune. $\endgroup$ – Mark Dec 16 '18 at 9:03
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    $\begingroup$ One might imagine e.g. a large probe on a Grand Tour trajectory, launching small cubesats to orbit each planet it flies by. $\endgroup$ – jpa Dec 16 '18 at 12:02
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It's a question of science return on investment. As @JamesK's answer notes, NASA has done several orbiters since the Voyagers. You get greater ROI when your probe can stay near the body you're interested in and continue to observe it for a long time. The only Voyager type probe in that list is New Horizons, in the sense that Voyager type probes only do a flyby. In the case of Uranus, and points more distant, as @JamesK noted, it's extremely hard to get there in a reasonable time, and then slow down enough to enter orbit. So for them Voyager type probes have an advantage.

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