I wonder if we'll someday launch a Voyager 3 & 4.
Depending on the mission there's no doubt other alignments that would give the gravity assist.
To put it into perspective, Voyager 1 has a current speed of 17 kilometers per second. So the Dawn craft has most of that trip covered without gravity assists if it wanted. AFAIK there's nothing stopping us from loading up some craft with more fuel and larger ion engines except for launch weight. And even then, if we mastered orbital refueling we could surpass that.
As it stands, the craft can carry approximately the same amount of Delta-V that the rocket that got it into space. Equivalent to tons of fuel from chemical rockets.
And the Earth has 30 km/s, yet we don't get Voyager "for free" and then some just from LEO. You can't compare speeds in different parts of the gravity well against each other because then you're ignoring the dv required to get from here to there.
The availability of Pu-238 is why European missions can't go past Jupiter without coordinating with NASA -- politically is impossible for them to produce nuclear spacecraft, but solar power becomes ineffective farther from the sun.
But given that NASA has a limited Pu-238 stockpile, they're only stocking new craft with the minimum necessary to hit the key science objectives.
There's (finally) a new program to produce more if it, but in very limited quantities: https://www.businessinsider.com/nasa-nuclear-battery-plutoni...
Of course you can't stockpile radioactive materials for too long. Their very nature limits their shelf life. So constant production is necessary if you want to use it on missions.
https://obamawhitehouse.archives.gov/the-press-office/2012/0...
"I think of the oak beams in the ceiling of College Hall at New College, Oxford. Last century, when the beams needed replacing, carpenters used oak trees that had been planted in 1386 when the dining hall was first built. The 14th-century builder had planted the trees in anticipation of the time, hundreds of years in the future, when the beams would need replacing. Did the carpenters plant new trees to replace the beams again a few hundred years from now?"
I sincerely hope we do launch more deep space probes in the near future, for our collective far future selves.
Not all such decisions are short-sighted.
Edit: I think it's been shown elsewhere that it is not the date that you launch the next probe that is important, but the speed at which it travels.
I don't think we'll see a dedicated interstellar probe for a long time. It just takes too much energy to get out that far in a reasonable amount of time without radical designs or a big leap in propulsion technology.
(Not that we're anywhere near having a rocket factory on the moon... but maybe one could be assembled and fueled in orbit?)
Which you can't. So that's a no for the moon, but something from orbit could make sense.
Have a staging area and just accumulate tons of fuel from multiple launches.
Of course you can.
> By atomic composition, the most abundant element found on the Moon is oxygen. It composes 60% of the Moon's crust by weight, followed by 16-17% silicon, 6-10% aluminum, 4-6% calcium, 3-6% magnesium, 2-5% iron, and 1-2% titanium.
You have oxygen. You have aluminum. You can now make a solid rocket. There's some magnesium there too if you want to use that instead.
Not exactly. You have aluminium oxide, which you could split into aluminium and oxygen using huge amounts of energy, like we do on earth.
Helium-3 could be interesting, though.
I believe that this is wrong.
The Earth weighs 5.96e+24 kg and has radius 3.37e6 meters. The Sun weighs 1.98e30 kg and our orbit has radius 1.496e11 meters. That means that the potential well for getting away from Earth is about 11,800,000 joules/kg while for getting out of the Sun's gravity well is about 882,800,000 joules/kg. Assuming that I did the math right, that's about 7.5 times as hard.
It therefore takes a lot more energy to climb out of the Solar System than it does to climb out of Earth's gravity well. Voyager got a LOT of energy from those gravitational slingshots.
A probe has to launch from the surface of the earth. But counterintuitively the probes start out already in solar orbit, even before they're launched -- because the earth is in solar orbit. More than half the energy required to achieve escape velocity is needed just to get into a roughly circular relatively low orbit around the gravitating body you're trying to escape from, and by virtue of being launched from the earth the probes get that velocity for free. Furthermore, the earth's orbit isn't really "low" with respect to the sun. We're fairly far out there, so the fraction of the energy needed to go from earth orbit to a solar escape trajectory is even less.
Put another way: a probe launched from the earth gets no help leaving earth's gravity well. But once it does it gets a huge automatic gravity assist from the earth itself as it enters solar orbit.
It takes a lot of energy to escape Earth's gravity well. It takes a comparatively tiny amount to escape the Sun's, as a sibling poster pointed out. It would be actually harder to visit, say, Mercury, as you now have to shed all the energy Earth has given you for free, in order to "fall" into the Sun's well.
Voyager wanted to visit multiple planetary bodies – changing orbital parameters is not cheap. But if all it wanted was to get out of the system, burning straight out would probably be cheaper (in Delta-V terms). The closer to Earth the better, for the Oberth effect.
https://www.nasa.gov/mission_pages/station/expeditions/exped...
It would be cheaper in fuel terms, and require less thrust, but it'd also require us to manufacture propellant on the lunar surface and fly everything we can't build there from Earth (and landing on the Moon is purely propulsive).
It's entirely a political problem. There is no will to fund such a mission, and what's worse is that in the US funding is approved year by year.
[0] https://www.spacex.com/sites/spacex/files/starlink_press_kit...
[1] http://ngpdlab.engin.umich.edu/electric-propulsion/krypton-H...
The question then becomes: what instruments would you put on this that would tell us something the Voyager probes have not? What is your mission beyond "making something go even further away from us"?
1: https://www.skyandtelescope.com/astronomy-news/100-million-f...