Do you mean interstellar probes? The Voyager missions were primarily planetary exploration missions, which NASA and other space agencies continue to run with new probes every few years. The interstellar exploration piece was kind of a secondary feature of the missions taking advantage of high speeds from all the gravity assists along the way.
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.
The propulsion technology for an interstellar mission is available today, there are proposals for probes powered by RTGs or even nuclear reactors and driven by ion engines. Jupiter-Saturn conjunctions that can be exploited for gravity assists happen every 20 years or so: https://en.wikipedia.org/wiki/Interstellar_probe#Proposed_in...
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.
In nuclear engines the fuel and propellant is separate. I keep wondering how much gas a rocket needs to take with it in order to have something to push against. Nuclear fuel is incredibly energy-dense, but the density of the gas used for propulsion in a nuclear rocket can't be much different from what's used in conventional rockets.
The JIMO mission was supposed to have 12 tons of xenon on board, a substantial amount of the yearly production (~ 70 tons). You do wonder how Elon Musk's Starlink madness will affect the xenon price.
The StarLink satellites use krypton thrusters instead of xenon [0]. They need more electic power to run, but produce higher specific impulse [1]. And krypton is cheap.
There's a (partly funded!) project to send a 'chain' of probes to α Centauri[1], as long as they don't need to slow down when they get there, they can shoot right through and relay results back, as I understand it.
With launch costs plummeting it may be possible to launch a bigass booster and give an interstellar probe a real kick even without a magical planetary alignment.
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"?
As per the article, exploring the trailing edge of the heliopause would be interesting and is something that hasn't yet been done. But yes, presumably instrumentation has also improved over the last 50 years, so hopefully we could get better data as well.
Most of the thrust of rocket is loss to get out of the earth gravity well.
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.
You're trying to compare apples to apples here, when the situation we have is actually apples to oranges ;).
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.
There's a saying among KSP players: "Orbit is halfway to anywhere".
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.
This is correct. On my astrodynamics written qual, one of the questions was whether it would be more energy efficient to solve Earth’s trash problem by launching garbage into the sun or into deep space. Surprisingly, the answer turned out to be deep space, and it wasn’t that close.
> Wouldn't it be possible if we launched from the moon instead?
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).
> 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.
It's kind of hilarious that the hardest thing to find in the inner solar system, off Earth (and, of course, the Sun), isn't precisely water but hydrogen.
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.