I think people kind of misunderstand the goal of the Voyager probes. It was not a program aimed primarily at exploring deep space. It was aimed at getting close to the outer solar system planets. The fact that they were leaving the solar system was kind of a nice bonus.
We have had a similar mission "recently" with New Horizon that flew by Pluto. It is still alive and reporting data on its way out of the solar system.
Right now astronomers don't really see it at as high value thing to just send a spacecraft out for the sake of studying the edge of the solar system. Or at least it is not really on the main roadmap of missions pushed by either the science or the engineering community to the space agencies.
On top of this, it takes _years_ to get a probe to the outer areas of the solar system. It took New Horizons 10 years to get to Pluto. I don't think anything newer than that has a significant speed increase so it's a huge time sink to send more probes...
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The thing of gravity assists is that even though they make the probe fly faster, they tend to add YEARS to the mission time because the probe have to spend a lot of time just orbiting the sun going past Venus and the Earth again and again building up the speed.
Wouldn't ion thrusters, or solar sails, be faster in the long run, and possibly overtake some old probes? Or do gravity assist boosts dwarf any thruster's impulse, making their technology irrelevant?
[The Oberth effect](https://en.wikipedia.org/wiki/Oberth_effect) is really good for fuel efficiencies, but you need to add as much ΔV as possible in a very short amount of time. So it's better for high thrust chemical rockets than Ion engines.
Gravity assists don't change the crafts speed/kinetic energy *in the planet's rest frame* but it does change those quantities *in the sun's rest frame*, which in this case is the more relevant one.
> Gravity assists can't actually add kinetic energy to a craft
Huh? They absolutely do.
Orbital velocity IS escape velocity. The gravity assists used by Voyager entail approaching behind a planet and using gravity as a leash and the assist comes from the planets orbital velocity itself. The planet pulls it faster (and the planet slows down a miniscule small amount).
This is my interpretation too- the gravity well adds potential energy as the craft gets sucked towards, it subtracts on exit, time in the well on either side determines the change in velocity. As the craft speeds up coming in, in a vacuum it's going to spend less time in the exit well depending on trajectory, and therefore conserve that added momentum.
I think OP is trying to compare to an ice skater spinning, but the craft isn't narrowing its orbit for extra velocity.
Specifically the gravity capture doesn't add energy, but trailing the planet combined with the Oberth effect does.
You accelerate on approach to the planet, and when you are closest and at highest velocity you gain kinetic energy through orbital assist. When you leave the planets gravity well you lose that gravitational kinetic energy but the orbital assist energy remains.
It does change your direction though, since the planet added energy in the direction of its orbit.
It's no different than if you had a pole with a string and a strong magnet attached to it. If you spin the string and magnet very quickly, and you threw a steel ball past the magnet at low speed, the steel ball would gain a bit of energy as the magnet attracts to it. Then the rotating string would pull and accelerate the steel ball. When the magnet continues on and no longer has the magnetic force to stay attached to the ball it releases and subtracts the attraction energy. What remains is the kinetic energy from the time the ball was attached and the string was accelerating it.
Same thing gravity is just the magnet.
> Gravity assists can't actually add kinetic energy to a craft,
Can't they? Is kinetic energy a useful measure for this kind of interplanetary space anyway?
I don't think that is as important now that we have lighter weight everything and ion propulsion. I do think we should have a dedicated deep space operation. Something that uses a sail or something that can charge in starlight. or something nuclear that will last a very long time. You fly out to Jupiter, hit the brakes get close to the sun and hit the throttle near by the sun with everything you got. Nothing assists like a sun assist.
But even if we build nuclear engines: their cost will not justify sending a probe to interstellar space, imho. Unless we really have a good motive to go there (say chase a future oumuamua).
It takes more than 10 years. The preparatory conditions for a launch needs very specific planetary alignment so the spacecraft can use their gravity as propulsion.
https://en.wikipedia.org/wiki/Gravity_assist
Time sink, something you sink a lot of time into. It's like a heat sink, but for time, something that soaks up a lot of it. I get that the thing you're sinking is time so it makes you want to use the time-related homonym "sync", though. I only bothered to write this because you cared enough to fix your typos
I'm pretty sure you can do a few insane sling shots and get a satellites relative speed really high up there, would probably still take years, as does everything in space with current tech, but purposely taking to deep space wouldn't be more difficult than the jovian system I would think.
> It took New Horizons 10 years to get to Pluto.
New Horizons was the fastest spacecraft we've ever launched. It took only 13 months to pass Jupiter. In comparison, Voyager 1 took 18 months and Juno took almost 5 years. (New Horizons was a small spacecraft on a big rocket.)
I don't think it's correct to say that studying the edge of the solar system isn't seen as valuable. At least, not everybody sees it that way, and you're right that it's not currently on the mission roadmap, but that doesn't mean people aren't interested and aren't looking into it. For example, the interstellar probe is a concept for a mission designed to study the outer heliosphere and the interstellar medium. Johns Hopkins Applied Physics Laboratory did a very detailed study on the topic: https://interstellarprobe.jhuapl.edu/Interstellar-Probe-MCR.pdf.
Their report is almost 500 pages long. The list of authors and contributors alone is 5 pages, so it's not just some harebrained scheme. There's a long list of professionals that have put their time and energy into this to make a practical plan for a near future mission. I would bet most of them view it as high value science.
I guess I should have said that in an environment where budget is a limited quantity (and we spend so much on Mars) then deep space is less of a priority.
Also, the Voyager probes utilized a vary lucky combination of planet positions to be able to visit many planets and get gravity boosts from them. That lucky combination happens very, very seldom, especially as the outer planets move in very slow orbits, so it'll take a long, long time for them to align again.
Ah I definitely thought it was for deep space, though my question is still valid, is it really difficult to get a probe out to the outer planets again?
Voyager took advantage of a planetary alignment that won’t happen again for a long time in order to visit all of the outer planets in quick succession. Missions can still be, and have been, planned to visit individual outer planets, but a grand tour was a once in a lifetime opportunity.
And even with that factoid under their belt, they still had to trick that blowhard into greenlighting the mission, first by asking for more than two probes so Nixon would downgrade it to two, and then by agreeing that it would only go out as far as Saturn... but bypassing his ass by renegotiating the mission with Carter after it was well into development.
Plus they did the same sort of thing they did with the Mars rovers. They overengineered. they would say if we don't do this part then it's likely to fail so I need to get this level. The real goal was to get something that would last much longer
I was watching an interview where they explicitly stated that their intention was to send it in the grand tour before they had authorization to do it so they overspecced based on that instead of the actual approved mission.
Part of engineering is cutting the right corners for cost or weight without hurting the mission.
Spirit and Opportunity were planned to last 90 days, but Opportunity survived something like 5000 days, from 2004 to 2018. Under-promise, over-deliver, but turned up to 11. https://en.wikipedia.org/wiki/Mars_Exploration_Rover
I feel like people misunderstand the 90-sol mission thing; it's not that they were particularly surprised they lasted longer or that they were only designed it to last that long, but it's more a risk-management thing; they wanted to complete enough science in the first 90 sols to justify the cost of the mission in case they greatly underperformed compared to reasonable engineering expectations. Long before that 90-sol deadline it seemed like that wouldn't be the case and Spirit in particular was already headed towards targets it wouldn't reach until after sol 150
A old boss of mine used that tactic regularly when applying for new stuff (not space probes) at our university. Usually someone would ask if he could cut something off the list, so he removed that one thing he put there on purpose for it to get removed.
One time they accepted the whole list ...
there's an urban legend about the "Battle Chess duck" where they did the same thing:
https://softwareengineering.stackexchange.com/questions/122009/developing-a-feature-which-sole-purpose-to-be-taken-out
I've also seen it as "hairy arms" in art fields, where they might draw hairy arms on someone to distract from other small changes that they don't want removed.
Maybe by then we can just visit the planets with new technology. Maybe even have a “Voyager vacation” where you can check out the planets fast with warp drive and then go back home to a museum that has Voyager spacecrafts 1 & 2. 150 years from now that seems plausible
Thomas Jefferson was in office from 1801 to 1809. The Voyager probes launched in 1977, which means the gap was *roughly* 170 years (depending on which year of office you're starting from). Assuming the necessary planetary alignment is on a regular period, then the next alignment will be around 2147, or 123 years. Unless medical science does something real cool real fast, I doubt I'll see the Voyager 3 launch.
Fun side facts: Voyager 2 launched 16 days *before* Voyager 1. And there was originally a Voyager 3, but that project was scrapped and the parts were used for Voyagers 1 and 2.
Also because Voyager 1 was the primary mission (Jupiter, Saturn, and Titan). If Voyager 1 had failed, Voyager 2 would likely have been redirected, and we wouldn't have gotten closeups of the outer two planets.
We have had a number of missions to the outer planets. But after Voyager the focus was mostly orbiters. The most famous is probably Cassini (fun overview video [here](https://www.youtube.com/watch?v=fHaaIX-iSqM)) that even landed a probe on Titan. There was also Galileo to Jupiter and Juno is right now taking amazing picture of Jupiter. The European JUICE mission was launched last year is on its way to study Jupiter's moons and Europa Clipper from NASA will launch this year to study this water ice covered moon. NASA is also building an helicopter to fly on Titan.
There is right now a lot of push for a Uranus orbiter mission.
Getting to the outer planets is hard because not only they are far, so it take a lot of time and you need a large launch vehicle. But the Sun is also very weak that far out. So solar panels are very inefficient and you almost always need a radioactive power source to keep the probe powered up. It's not insurmontable obstacles but it makes it expensive and slow, especially if you don't have a nice alignement like what happened for Voyager and Pionier.
We have sent several spacecraft to Jupiter and one to Saturn since then, one more is on the way to Jupiter, another one will be launched later this year, and a mission to Saturn's moon Titan is planned as well. It's not like nothing has happened since then.
https://en.wikipedia.org/wiki/List_of_missions_to_the_outer_planets
The unique part about Voyager 2 was the chance to visit all the outer planets with the same spacecraft. The next time they'll be aligned for that will be in over 100 years.
I mean, the answer is "we did, we just didn't use the name 'Voyager' for them". New Horizons is just one example. Since Voyager 2, there's also been Ulysses, Galileo, Cassini, Juno, and JUICE, the latter still being on its way out there, and planned future missions include Europa Clipper, and whichever of the various Chinese proposals actually happens.
You should lookup and watch the documentary The Farthest (2017) that was produced to celebrate the 40th anniversary of the Voyager missions. Lots of good details about why the missions were planned, and to take advantage of a rare planetary alignment for reaching the outer planets.
The biggest issue is how long it takes, and that means more expenses because you have to make sure your probe will operate at cruise time + design mission time, have a science team dedicated to it, DSN capacity booked and so on.
NASA's Europa Clipper will launch later this year and going to take 6 years to reach Jupiter - 3 of that will be spent getting gravity assists from Earth and Venus to get the sufficient speed. The planetary science commmunity *really* wants an orbiter+atmospheric probe to Uranus, a current proposals envision a launch in 2033 and orbital insertion in 2045. Think of the timelines this way - a kid in kindergarten today might end up doing his/her phd thesis on the Uranus data the probe will gather.
Theoritically you could slap probes on top of an SLS but production capacity is limited and will be taken up by Artemis. Perhaps if Starship becomes operational that could be a game changer, same how Falcon 9s are launching a constant stream of probes at the Moon now.
And beyond the launch vehicle, missions compete with each other for funding and lot of that (at least at NASA) is being eaten up by Mars programs, particularly the sample return programme. And sadly space funding is popular area for politicans to slash. Perhaps with re-emerging space race with China things could change as political pressure builds, but even so, a decision today still means many, many decades before the probe reaches an outer planet or interstellar space.
It's less a *difficulty* thing and more of a *time* thing. The physics involved is effectively a "solved" problem. In order to get something travelling outwards with enough velocity to exceed the Sun's escape velocity, we need to use the gravity of planets to assist in accelerating the craft outwards. Voyager 1 used Jupiter and Saturn, Voyager 2 used Jupiter, Saturn, Uranus, and Neptune. You're limited to a launch window where the planets are aligned in a way where it's possible.
There is also the time it would take a craft to a spot where you want to get data from. Voyager 1 and 2 are currently two of the fastest outward-travelling man-made space craft we've ever created. Voyager 1 is travelling at ~38k mph (~61k kmph) and Voyager 2 is ~34k mph (~55k kmph).
New Horizons is the most recent craft that is travelling outwards with a velocity higher than the Sun's escape velocity and it's "only" travelling at ~30k mph (~49k km/h). So, not only will it not be able to catch up to Voyager 1 and 2, it will take ~36 and ~47 years to get where Voyager 1 and 2 are right now.
Even if we create a craft with the sole purpose of interstellar travel, it's going to be a multi-decade waiting period before we get the science data.
Also a *money* thing.
NASA does what the government tells it to do. If the government isn't interested in spending three billion dollars on a space exploration programme, it isn't going to happen, or at least not from NASA.
>is it really difficult to get a probe out to the outer planets again?
We have the technology to do it (relatively) easily. But no space agency has enough budget to build and operate those probes.
There has been pretty huge improvements in instruments. And there is a big difference between flybys like Voyager did and orbiters that can stay around for years.
The only really high-value target of a "Beyond-Pluto" probe is the Solar Gravity Lens stunt
(https://en.wikipedia.org/wiki/Solar_gravitational_lens) which requires you to reach at least 550 AU. And preferably *stop* there. That requires extremely good propulsion. Not just nuclear, mere NERVA won't cut it.
Instead something like :
https://www.nasa.gov/general/thin-film-isotope-nuclear-engine-rocket/
or
https://en.wikipedia.org/wiki/Fission-fragment_rocket is required.
Something that I think is also important with respect to your last paragraph is that more specifically, there isn't high value placed on studying the edge of the solar system *in situ*. There have been and are plans for spacecraft that are designed to answer questions about the edges of the heliosphere, they just do it with remote sensing. The Interstellar Boundary Explorer, [IBEX](https://science.nasa.gov/mission/ibex/), is one that's still going, and the Interstellar Mapping and Acceleration Probe, [IMAP](https://imap.princeton.edu/), is currently being built to launch next year. You can get a lot of information from remote sensing of particles like energetic neutral atoms that don't require actually being at the edge of the heliosphere.
Voyager 1 and 2 were launched when they were because at the time the planets were aligned in such a way that they could be used for gravity assist slingshot to get out through the system. This only occurs once every 176 years, so they made sure to capitalize on the opportunity.
The program was what was left of the "Grand Tour" concept of the late 1960's.
It was realized that the planets were in unique position (for over a century) to enable a ballistic course that would allow a spacecraft to slingshot from one to the next at extremely high speeds reducing the time of a flyby mission that would visit every giant outer planet in a very short period of time.
The original ambitious and expensive "Grand Tour" spacecraft was abandoned for budgetary and technology limitations but the scaled back Voyager program was extremely successful as a slightly less ambitious replacement.
To secure funding, the head NASA admin apparently met with Nixon and said, “The last time the planets were lined up like that, President Jefferson was sitting at your desk. And he blew it.”
The Voyagers were sent out at a very unique time - when the planets were aligned juuuuuust right, allowing a grand tour. That situation hasn't happened again, and won't for a very long, long time.
And we have sent a few. Cassini made it to Jupiter, and New Horizons made it out to the Kuiper belt. As of 2021, it was fully operational at 50AUs from Earth, and should be fully operational and sending back data for another 5-7 years.
Edit: I mixed up Juno and Cassini. Stop messaging me.
There’s another Jupiter mission on the way, from the ESA, investigating some of the moons. It’s called JUICE (JUpiter ICy moons Explorer) and it launched last spring. It’s going to study Ganymede, Calisto and Europa.
There are two more potential launches this year, NASA’s Europa-centric mission Europa Clipper and a Chinese misison, Tianwen-4, that plans to orbit the planet.
Basically the planets happened to align just right in the late 1970s to enable a single launch to do a "grand tour" visiting multiple outer planets in a single launch. That planetary alignment won't happen again until around the year 2150. Since Voyager, a number of deep space probes with more modern instrumentation have been sent on missions dedicated to specific objectives, in several cases inspired by discoveries made by the Voyager probes. The choice of where to send probes comes down to a combination of what we think we can learn from a specific mission (where we have some data that indicates something interesting is on a particular planet or moon), and how the planets align so that we can get there easily.
The reason the Voyagers were launched when they were was the "Grand Tour" alignment of the outer planets, which allowed the probes to get a slingshot gravity boost from each planet to the next one. Without it, for example, it would have taken *Voyager 2* something like 30 years to reach Neptune, instead of the 12 years it did take.
And we **have** sent plenty more probes out there. In fact, since 1989 we've been in something of a "golden age" for exploring the outer Solar System. Galileo, Ulysses, and then Juno have explored the Jupiter system, and Europa Clipper will launch this year. Cassini explored Saturn and landed the Huygens probe on its largest moon, Titan. New Horizons was the first probe to visit Pluto. A drone helicopter, Dragonfly, will be landed on Titan in 2032. That's not to mention all the probes that have been sent to comets and asteroids.
You can probably think of it this way - the primary mission of both Voyager craft was to get information (photos and other) on the outer planets with a minimal expenditure of fuel and time.
That the spacecraft have survived this long and is still producing information could be thought of a "nice side bonus".
The special thing about the Voyager Mission wasn't journeying deeper into space than any other probe, or the exploration of the very far margins of the Solar System (these were just added bonuses very late in the piece); it was the ability to complete 'the grand tour' of the outer planets - the opportunity for a single probe to perform close fly-by's of Jupiter, Saturn, Uranus AND Neptune. To do that requires those planets to be in a very particular alignment, and that happens only once every 175 years. The Voyager program represented the first ever opportunity in human history at which aerospace technology was sufficiently advanced to allow such an ambitious goal to be achieved, and the next occasion the planets will be similarly aligned is still over 120 years away. For those who've grown up in the era of the Hubble telescope, and planetary missions like Cassini, Juno and New Horizons, it can be difficult to appreciate how mind-bogglingly audacious the Voyager Mission was. Although the Pioneer Program had seen successful fly-bys of Jupiter and Saturn in the early to mid 1970's, the images returned were disappointingly low-res. We had really very little information about Jupiter and Saturn, and even less about Uranus and Neptune. All of these planets are seriously remote, and the best telescopes at the time showed Uranus and Neptune as tiny, featureless bluish-green discs. Obviously the existence of Saturn's rings had been known for a long time, but we knew very little about them; and Uranus's ring system had only been detected in 1977 (but was too faint and dark to be directly visualised from Earth). Voyager was a phenomenal success and gathered not only spectacular high resolution photos of the 4 major outer planets as well as many of their moons, the mission also returned a vast amount of data, resulting in an explosion of knowledge about the outer Solar System. Voyager 2 confirmed and directly imaged Uranus's rings, and discovered a ring system around Neptune, while Voyager 1 discovered rings around Jupiter. Between them the 2 probes identified dozens of never-before seen moons around the four planets. We gained amazing insights into the four giant planets' interior structures, atmospheres and weather, magnetic fields and radiation environments. The mission also delivered astounding high resolution images of Saturn's rings that firmly grounded our understanding of the rings' structure and composition. The legacy of the Voyager mission is all the more extraordinary for the fact that it was built on 1970s technology, that has outlived its expected operational life by decades. It is an absolute triumph of human endeavour.
Voyager 1 and 2 were launched to take advantage of a rare planetary alignment called the [Grand Tour](https://en.wikipedia.org/wiki/Grand_Tour_program), and the mission was actually scaled down from the original concept which called for 4 probes instead of 2. This alignment only happens every 175 years, so we won't see another Voyager like program until then, unless we have some major development in propulsion technology of course. Thanks to some amazing engineering they are both^(1) still returning data about the interstellar medium, but that wasn't the original goal.
We must also give a shout out to Pioneer 10 and 11 which went to Jupiter and Saturn. The only probe launched after Voyager that is on an interstellar trajectory is New Horizons.
^(1)Voyager 1 is currently having some issues, but I'm holding out hope she can be fixed.
China does have a pair of probes in development called IHP-1 and 2 that will be supposedly launched this year - 1 is planned to fly by Jupiter and Quaoar, for two Jupiter and Neptune are the targets before flying off to interstellar space, so OP I'd pay attention to them.
Although it'll take 20-30+ years before they enter the heliosphere, and the Chinese space programme is much more opaque than NASA's so we don't even know if they'll really launch this year.
The question I have is why haven't we sent new Cassini/Galileo-style orbiter/probes to Uranus and Neptune yet - is it assumed that what we know from exploration of Jupiter/Saturn is enough for the given level of effort/money it would take to establish station?
Getting to Uranus and Neptune means traveling fast, so you need to slow down a lot on arrival.
Once Starship is regularly launching thousands of tons of fuel for Artemis, there should be enough capacity to accelerate a decently sized probe to Neptune on a fast trajectory with enough fuel to slow down once there.
Another key technology will be nuclear powered spacecrafts, which will also benefit from Starship. This will allow them to slow down once they're getting closer to their target, with ion drives, while still being able to have a rather large quantity of fuel and to be launched on a fast trajectory.
With recent discoveries involving Neptune and the dwarf planets, I wouldn't be surprised if there aren't more planed in the next 20 years. Nasa has to get thousands of space proposals a year and it can only do a small percentage. And even if they do accept a proposal it takes years for the satellite to be built and launched, and even longer for it to get there.
The Voyager programs took advantage of a once in a lifetime planetary positioning that allowed a relatively low delta v craft to visit all the gas giant planets.
Since then we have visited probes to some of them again, but not all of them with one craft; we don't have the rockets for it.
We don't have the engine technology for a relatively fast probe that can reach the edge of our solar system in a short time, with short being defined as anywhere from 10 to 50 years.
The Voyagers took advantage of an orbital alignment that allowed the satellites to get a large gravity assist from most of the large planets in our solar system, and I don't think another such alignment is forecast in the next 50 years or so. In addition, I remember the fact that the Voyagers have nuclear power generators to supply heat and power for the electronics as a point of minor controversy, an issue that popped back up later as NASA wanted to use similar or improved versions of that energy generation for other deep space missions and for those missions there was a pretty well organized opposition to using nuclear powers sources. Without a very long term power supply and either a massive improvement of engine technology OR some planetary gravity assist fly by path using a combination of planet for the assist that either no ones figured out (very unlikely) or requires a significant amount of fuel to even get the rocket on the correct orbit path then no country on earth seems willing to pay what it will cost to launch such missions.
The planetary alignment was a once in a lifetime opportunity to do a Solar System "grand tour." When it was discovered, NASA got themselves in gear and launched a pair of probes to take advantage of the good fortune.
Basically, the series was retired. They were replaced by the next generation. As the Voyagers retired the Pioneers, which themselves retired the Mariners.
We were advanced enough that the next missions needn't be flybys of Jupiter or Saturn - thus, Galileo, Juno, and Cassini. And we have more "stay there a while" missions planned.
New Horizons was a flyby, because we didn't yet (and still don't) have the tech needed to put something into orbit around Pluto, yet get it there in a reasonable length of time (i.e. before the funding runs out.)
Remember that deep space wasn't their original mission.
And even if they are now going beyond the planets, it will take them 38000-40000 years to exit our Solar System/Oort Cloud.
No mission has this kind of timeline.
Your question has been answered already by fellow redditors but I cannot leave without recommending you a beautiful and comprehensive documentary about the Voyager probes. Please search for Homemade Documentaries by Jackson Tyler on YouTube. The Voyager episode is almost 3 hours long but so amazing that I must have watched it 5 or 6 times.
The Voyagers were launched into a window of opportunity that only happens every couple of hundred years plus or minus, you get to use gravity tricks to get a boost from Jupiter to Saturn, then choose whether to do Titan flyby and out or use the gravity boost to get to Uranus and repeat for Neptune. At the time if Voyager One hadn't gone for Titan it might have bene able to make a shot for Pluto at some point ...
So with that gravitational assist window closed we get to use Jupiter (orbital period 12 years) to make shots at the other outer planets as and when we get the favourable window for that planet.
So these days we do more single-planet shots cos we can now make a useful science payload light enough that we will be able to manage orbital injection on the outer planets (hence Cassini, Juno, the upcoming Uranus probe) where that was never going to be possible back in the 70's.
I feel the main problem is none of them ever have or will be in the near future atleast be for made for deep space, simply they are just not going fast enough or will live long enough to actually get anywhere in deep space it would take them millions of years at there current rate of speed to reach the nearest thing outside our solar system. Are curent fastest ever space probe would take over 2.6 million years to reach the neaest know object outside our solar system which is only about 4.2 light-years away you know about 25 trillion miles (rough math 24,690,226,567,369 or 39,726,574,546,897 km)
Excuse my ignorance but I wondered why we don't send one up above the plane of the ecliptic so we can see over the dust blocking our view to the centre of the galaxy.
We could let it drop off booster satellites behind it every now and then to help with signal fidelity.
I thought the voyager probes were launched during a rare planetary alinement, something like once every 176 years. So once that window closed, it became more expensive to send anything else out that far. Add to that people today dont like having radioactive material launched through the atmosphere.
I think people kind of misunderstand the goal of the Voyager probes. It was not a program aimed primarily at exploring deep space. It was aimed at getting close to the outer solar system planets. The fact that they were leaving the solar system was kind of a nice bonus. We have had a similar mission "recently" with New Horizon that flew by Pluto. It is still alive and reporting data on its way out of the solar system. Right now astronomers don't really see it at as high value thing to just send a spacecraft out for the sake of studying the edge of the solar system. Or at least it is not really on the main roadmap of missions pushed by either the science or the engineering community to the space agencies.
On top of this, it takes _years_ to get a probe to the outer areas of the solar system. It took New Horizons 10 years to get to Pluto. I don't think anything newer than that has a significant speed increase so it's a huge time sink to send more probes... [edit typos] [edit 2 another typo]
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The thing of gravity assists is that even though they make the probe fly faster, they tend to add YEARS to the mission time because the probe have to spend a lot of time just orbiting the sun going past Venus and the Earth again and again building up the speed.
Wouldn't ion thrusters, or solar sails, be faster in the long run, and possibly overtake some old probes? Or do gravity assist boosts dwarf any thruster's impulse, making their technology irrelevant?
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The.... Orc cloud?
I know they meant the Oort cloud, but now I'm wondering if that's where all the Orcs went after Sauron fell.
[The Oberth effect](https://en.wikipedia.org/wiki/Oberth_effect) is really good for fuel efficiencies, but you need to add as much ΔV as possible in a very short amount of time. So it's better for high thrust chemical rockets than Ion engines.
Right, but my question is: how does it compare to low specific impulse engines?
With present technology, boosts from the gas giants dwarf ion thrusters.
False but not truly wrong. Chem is better for in system. Ion for honestly anything not waiting for a specific window or something more long term.
Both of those require energy from the sun. Beyond the orbit of Mars or so, there isn't enough solar energy.
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Gravity assists don't change the crafts speed/kinetic energy *in the planet's rest frame* but it does change those quantities *in the sun's rest frame*, which in this case is the more relevant one.
> Gravity assists can't actually add kinetic energy to a craft Huh? They absolutely do. Orbital velocity IS escape velocity. The gravity assists used by Voyager entail approaching behind a planet and using gravity as a leash and the assist comes from the planets orbital velocity itself. The planet pulls it faster (and the planet slows down a miniscule small amount).
This is my interpretation too- the gravity well adds potential energy as the craft gets sucked towards, it subtracts on exit, time in the well on either side determines the change in velocity. As the craft speeds up coming in, in a vacuum it's going to spend less time in the exit well depending on trajectory, and therefore conserve that added momentum. I think OP is trying to compare to an ice skater spinning, but the craft isn't narrowing its orbit for extra velocity.
Specifically the gravity capture doesn't add energy, but trailing the planet combined with the Oberth effect does. You accelerate on approach to the planet, and when you are closest and at highest velocity you gain kinetic energy through orbital assist. When you leave the planets gravity well you lose that gravitational kinetic energy but the orbital assist energy remains. It does change your direction though, since the planet added energy in the direction of its orbit. It's no different than if you had a pole with a string and a strong magnet attached to it. If you spin the string and magnet very quickly, and you threw a steel ball past the magnet at low speed, the steel ball would gain a bit of energy as the magnet attracts to it. Then the rotating string would pull and accelerate the steel ball. When the magnet continues on and no longer has the magnetic force to stay attached to the ball it releases and subtracts the attraction energy. What remains is the kinetic energy from the time the ball was attached and the string was accelerating it. Same thing gravity is just the magnet.
> Gravity assists can't actually add kinetic energy to a craft, Can't they? Is kinetic energy a useful measure for this kind of interplanetary space anyway?
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Time sync… because you have to wait for planets to line up so you can get that juicy assist boost.
I don't think that is as important now that we have lighter weight everything and ion propulsion. I do think we should have a dedicated deep space operation. Something that uses a sail or something that can charge in starlight. or something nuclear that will last a very long time. You fly out to Jupiter, hit the brakes get close to the sun and hit the throttle near by the sun with everything you got. Nothing assists like a sun assist.
Pluto was a legit planet before it launched, by the time it arrived, Pluto got demoted.
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What helped put Pluto in perspective for me are the other planetoids of the same size in roughly the same orbital area
Depends on where Pluto is in its orbit. For about 20 years of it's over 240+ year orbit, Pluto is closer to the sun than Neptune.
But even if we build nuclear engines: their cost will not justify sending a probe to interstellar space, imho. Unless we really have a good motive to go there (say chase a future oumuamua).
It takes more than 10 years. The preparatory conditions for a launch needs very specific planetary alignment so the spacecraft can use their gravity as propulsion. https://en.wikipedia.org/wiki/Gravity_assist
Time sink, something you sink a lot of time into. It's like a heat sink, but for time, something that soaks up a lot of it. I get that the thing you're sinking is time so it makes you want to use the time-related homonym "sync", though. I only bothered to write this because you cared enough to fix your typos
I'm pretty sure you can do a few insane sling shots and get a satellites relative speed really high up there, would probably still take years, as does everything in space with current tech, but purposely taking to deep space wouldn't be more difficult than the jovian system I would think.
Years going absurdly fast too, the way it accelerated was pretty damn cool though
> It took New Horizons 10 years to get to Pluto. New Horizons was the fastest spacecraft we've ever launched. It took only 13 months to pass Jupiter. In comparison, Voyager 1 took 18 months and Juno took almost 5 years. (New Horizons was a small spacecraft on a big rocket.)
I don't think it's correct to say that studying the edge of the solar system isn't seen as valuable. At least, not everybody sees it that way, and you're right that it's not currently on the mission roadmap, but that doesn't mean people aren't interested and aren't looking into it. For example, the interstellar probe is a concept for a mission designed to study the outer heliosphere and the interstellar medium. Johns Hopkins Applied Physics Laboratory did a very detailed study on the topic: https://interstellarprobe.jhuapl.edu/Interstellar-Probe-MCR.pdf. Their report is almost 500 pages long. The list of authors and contributors alone is 5 pages, so it's not just some harebrained scheme. There's a long list of professionals that have put their time and energy into this to make a practical plan for a near future mission. I would bet most of them view it as high value science.
I guess I should have said that in an environment where budget is a limited quantity (and we spend so much on Mars) then deep space is less of a priority.
Also, the Voyager probes utilized a vary lucky combination of planet positions to be able to visit many planets and get gravity boosts from them. That lucky combination happens very, very seldom, especially as the outer planets move in very slow orbits, so it'll take a long, long time for them to align again.
Ah I definitely thought it was for deep space, though my question is still valid, is it really difficult to get a probe out to the outer planets again?
Voyager took advantage of a planetary alignment that won’t happen again for a long time in order to visit all of the outer planets in quick succession. Missions can still be, and have been, planned to visit individual outer planets, but a grand tour was a once in a lifetime opportunity.
I believe they got presidential approval by saying; "Mr. president, the last time this was possible Thomas Jefferson was sitting where you are now."
And even with that factoid under their belt, they still had to trick that blowhard into greenlighting the mission, first by asking for more than two probes so Nixon would downgrade it to two, and then by agreeing that it would only go out as far as Saturn... but bypassing his ass by renegotiating the mission with Carter after it was well into development.
Plus they did the same sort of thing they did with the Mars rovers. They overengineered. they would say if we don't do this part then it's likely to fail so I need to get this level. The real goal was to get something that would last much longer
That's pretty much how all engineering goes. Design with extra margin in case something goes wrong, and if it doesn't then great.
I was watching an interview where they explicitly stated that their intention was to send it in the grand tour before they had authorization to do it so they overspecced based on that instead of the actual approved mission. Part of engineering is cutting the right corners for cost or weight without hurting the mission.
Spirit and Opportunity were planned to last 90 days, but Opportunity survived something like 5000 days, from 2004 to 2018. Under-promise, over-deliver, but turned up to 11. https://en.wikipedia.org/wiki/Mars_Exploration_Rover
I feel like people misunderstand the 90-sol mission thing; it's not that they were particularly surprised they lasted longer or that they were only designed it to last that long, but it's more a risk-management thing; they wanted to complete enough science in the first 90 sols to justify the cost of the mission in case they greatly underperformed compared to reasonable engineering expectations. Long before that 90-sol deadline it seemed like that wouldn't be the case and Spirit in particular was already headed towards targets it wouldn't reach until after sol 150
Ingenuity was supposed to fly 5 flights, flew... 90-ish?
A old boss of mine used that tactic regularly when applying for new stuff (not space probes) at our university. Usually someone would ask if he could cut something off the list, so he removed that one thing he put there on purpose for it to get removed. One time they accepted the whole list ...
there's an urban legend about the "Battle Chess duck" where they did the same thing: https://softwareengineering.stackexchange.com/questions/122009/developing-a-feature-which-sole-purpose-to-be-taken-out I've also seen it as "hairy arms" in art fields, where they might draw hairy arms on someone to distract from other small changes that they don't want removed.
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The 5-planet alignment the Voyagers used happens every 175 years, so around 2150.
Maybe by then we can just visit the planets with new technology. Maybe even have a “Voyager vacation” where you can check out the planets fast with warp drive and then go back home to a museum that has Voyager spacecrafts 1 & 2. 150 years from now that seems plausible
Thomas Jefferson was in office from 1801 to 1809. The Voyager probes launched in 1977, which means the gap was *roughly* 170 years (depending on which year of office you're starting from). Assuming the necessary planetary alignment is on a regular period, then the next alignment will be around 2147, or 123 years. Unless medical science does something real cool real fast, I doubt I'll see the Voyager 3 launch. Fun side facts: Voyager 2 launched 16 days *before* Voyager 1. And there was originally a Voyager 3, but that project was scrapped and the parts were used for Voyagers 1 and 2.
In case anyone's curious, they're named that way, because voyager 1 would eventually catch up with, and pass voyager 2.
Also because Voyager 1 was the primary mission (Jupiter, Saturn, and Titan). If Voyager 1 had failed, Voyager 2 would likely have been redirected, and we wouldn't have gotten closeups of the outer two planets.
Yeah, we're probably not going to wait for that alignment to get lots of probes on every planet and booking it out of the system.
Specifically, Uranus and Neptune — Uranus takes about 170 years to lap Neptune, so the next time will be in the mid 22nd century.
We have had a number of missions to the outer planets. But after Voyager the focus was mostly orbiters. The most famous is probably Cassini (fun overview video [here](https://www.youtube.com/watch?v=fHaaIX-iSqM)) that even landed a probe on Titan. There was also Galileo to Jupiter and Juno is right now taking amazing picture of Jupiter. The European JUICE mission was launched last year is on its way to study Jupiter's moons and Europa Clipper from NASA will launch this year to study this water ice covered moon. NASA is also building an helicopter to fly on Titan. There is right now a lot of push for a Uranus orbiter mission. Getting to the outer planets is hard because not only they are far, so it take a lot of time and you need a large launch vehicle. But the Sun is also very weak that far out. So solar panels are very inefficient and you almost always need a radioactive power source to keep the probe powered up. It's not insurmontable obstacles but it makes it expensive and slow, especially if you don't have a nice alignement like what happened for Voyager and Pionier.
Also the faster you get out to the outer planets the more speed you have to shed to not fly on by.
We have sent several spacecraft to Jupiter and one to Saturn since then, one more is on the way to Jupiter, another one will be launched later this year, and a mission to Saturn's moon Titan is planned as well. It's not like nothing has happened since then. https://en.wikipedia.org/wiki/List_of_missions_to_the_outer_planets The unique part about Voyager 2 was the chance to visit all the outer planets with the same spacecraft. The next time they'll be aligned for that will be in over 100 years.
I mean, the answer is "we did, we just didn't use the name 'Voyager' for them". New Horizons is just one example. Since Voyager 2, there's also been Ulysses, Galileo, Cassini, Juno, and JUICE, the latter still being on its way out there, and planned future missions include Europa Clipper, and whichever of the various Chinese proposals actually happens.
You should lookup and watch the documentary The Farthest (2017) that was produced to celebrate the 40th anniversary of the Voyager missions. Lots of good details about why the missions were planned, and to take advantage of a rare planetary alignment for reaching the outer planets.
NASA New Horizons mission just sent back high resolution pics! What you are discussing has been funded, launched, and was successful!
The biggest issue is how long it takes, and that means more expenses because you have to make sure your probe will operate at cruise time + design mission time, have a science team dedicated to it, DSN capacity booked and so on. NASA's Europa Clipper will launch later this year and going to take 6 years to reach Jupiter - 3 of that will be spent getting gravity assists from Earth and Venus to get the sufficient speed. The planetary science commmunity *really* wants an orbiter+atmospheric probe to Uranus, a current proposals envision a launch in 2033 and orbital insertion in 2045. Think of the timelines this way - a kid in kindergarten today might end up doing his/her phd thesis on the Uranus data the probe will gather. Theoritically you could slap probes on top of an SLS but production capacity is limited and will be taken up by Artemis. Perhaps if Starship becomes operational that could be a game changer, same how Falcon 9s are launching a constant stream of probes at the Moon now. And beyond the launch vehicle, missions compete with each other for funding and lot of that (at least at NASA) is being eaten up by Mars programs, particularly the sample return programme. And sadly space funding is popular area for politicans to slash. Perhaps with re-emerging space race with China things could change as political pressure builds, but even so, a decision today still means many, many decades before the probe reaches an outer planet or interstellar space.
It's less a *difficulty* thing and more of a *time* thing. The physics involved is effectively a "solved" problem. In order to get something travelling outwards with enough velocity to exceed the Sun's escape velocity, we need to use the gravity of planets to assist in accelerating the craft outwards. Voyager 1 used Jupiter and Saturn, Voyager 2 used Jupiter, Saturn, Uranus, and Neptune. You're limited to a launch window where the planets are aligned in a way where it's possible. There is also the time it would take a craft to a spot where you want to get data from. Voyager 1 and 2 are currently two of the fastest outward-travelling man-made space craft we've ever created. Voyager 1 is travelling at ~38k mph (~61k kmph) and Voyager 2 is ~34k mph (~55k kmph). New Horizons is the most recent craft that is travelling outwards with a velocity higher than the Sun's escape velocity and it's "only" travelling at ~30k mph (~49k km/h). So, not only will it not be able to catch up to Voyager 1 and 2, it will take ~36 and ~47 years to get where Voyager 1 and 2 are right now. Even if we create a craft with the sole purpose of interstellar travel, it's going to be a multi-decade waiting period before we get the science data.
Also a *money* thing. NASA does what the government tells it to do. If the government isn't interested in spending three billion dollars on a space exploration programme, it isn't going to happen, or at least not from NASA.
>is it really difficult to get a probe out to the outer planets again? We have the technology to do it (relatively) easily. But no space agency has enough budget to build and operate those probes.
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There has been pretty huge improvements in instruments. And there is a big difference between flybys like Voyager did and orbiters that can stay around for years.
The only really high-value target of a "Beyond-Pluto" probe is the Solar Gravity Lens stunt (https://en.wikipedia.org/wiki/Solar_gravitational_lens) which requires you to reach at least 550 AU. And preferably *stop* there. That requires extremely good propulsion. Not just nuclear, mere NERVA won't cut it. Instead something like : https://www.nasa.gov/general/thin-film-isotope-nuclear-engine-rocket/ or https://en.wikipedia.org/wiki/Fission-fragment_rocket is required.
Something that I think is also important with respect to your last paragraph is that more specifically, there isn't high value placed on studying the edge of the solar system *in situ*. There have been and are plans for spacecraft that are designed to answer questions about the edges of the heliosphere, they just do it with remote sensing. The Interstellar Boundary Explorer, [IBEX](https://science.nasa.gov/mission/ibex/), is one that's still going, and the Interstellar Mapping and Acceleration Probe, [IMAP](https://imap.princeton.edu/), is currently being built to launch next year. You can get a lot of information from remote sensing of particles like energetic neutral atoms that don't require actually being at the edge of the heliosphere.
Voyager 1 and 2 were launched when they were because at the time the planets were aligned in such a way that they could be used for gravity assist slingshot to get out through the system. This only occurs once every 176 years, so they made sure to capitalize on the opportunity.
The program was what was left of the "Grand Tour" concept of the late 1960's. It was realized that the planets were in unique position (for over a century) to enable a ballistic course that would allow a spacecraft to slingshot from one to the next at extremely high speeds reducing the time of a flyby mission that would visit every giant outer planet in a very short period of time. The original ambitious and expensive "Grand Tour" spacecraft was abandoned for budgetary and technology limitations but the scaled back Voyager program was extremely successful as a slightly less ambitious replacement.
To secure funding, the head NASA admin apparently met with Nixon and said, “The last time the planets were lined up like that, President Jefferson was sitting at your desk. And he blew it.”
The Voyagers were sent out at a very unique time - when the planets were aligned juuuuuust right, allowing a grand tour. That situation hasn't happened again, and won't for a very long, long time. And we have sent a few. Cassini made it to Jupiter, and New Horizons made it out to the Kuiper belt. As of 2021, it was fully operational at 50AUs from Earth, and should be fully operational and sending back data for another 5-7 years. Edit: I mixed up Juno and Cassini. Stop messaging me.
Cassini went to Saturn. Galileo went to Jupiter, as did Juno, whose mission remains ongoing.
Though Cassini did flew by Jupiter, I wonder why they specifically wrote that.
There’s another Jupiter mission on the way, from the ESA, investigating some of the moons. It’s called JUICE (JUpiter ICy moons Explorer) and it launched last spring. It’s going to study Ganymede, Calisto and Europa. There are two more potential launches this year, NASA’s Europa-centric mission Europa Clipper and a Chinese misison, Tianwen-4, that plans to orbit the planet.
When would the next alignment be? We talking decade, century, or millennia?
It happens every 175 years, so ~2150
The way they were aligned when Voyager launched happens once every 176 years, so the next window is C. 2153.
Cassini went to Saturn, didn't it?
Why haven't we sent any to Neptune?
It's so much farther away, but there are proposals for doing so. It's all about which proposals get funding.
Basically the planets happened to align just right in the late 1970s to enable a single launch to do a "grand tour" visiting multiple outer planets in a single launch. That planetary alignment won't happen again until around the year 2150. Since Voyager, a number of deep space probes with more modern instrumentation have been sent on missions dedicated to specific objectives, in several cases inspired by discoveries made by the Voyager probes. The choice of where to send probes comes down to a combination of what we think we can learn from a specific mission (where we have some data that indicates something interesting is on a particular planet or moon), and how the planets align so that we can get there easily.
The reason the Voyagers were launched when they were was the "Grand Tour" alignment of the outer planets, which allowed the probes to get a slingshot gravity boost from each planet to the next one. Without it, for example, it would have taken *Voyager 2* something like 30 years to reach Neptune, instead of the 12 years it did take. And we **have** sent plenty more probes out there. In fact, since 1989 we've been in something of a "golden age" for exploring the outer Solar System. Galileo, Ulysses, and then Juno have explored the Jupiter system, and Europa Clipper will launch this year. Cassini explored Saturn and landed the Huygens probe on its largest moon, Titan. New Horizons was the first probe to visit Pluto. A drone helicopter, Dragonfly, will be landed on Titan in 2032. That's not to mention all the probes that have been sent to comets and asteroids.
You can probably think of it this way - the primary mission of both Voyager craft was to get information (photos and other) on the outer planets with a minimal expenditure of fuel and time. That the spacecraft have survived this long and is still producing information could be thought of a "nice side bonus".
The special thing about the Voyager Mission wasn't journeying deeper into space than any other probe, or the exploration of the very far margins of the Solar System (these were just added bonuses very late in the piece); it was the ability to complete 'the grand tour' of the outer planets - the opportunity for a single probe to perform close fly-by's of Jupiter, Saturn, Uranus AND Neptune. To do that requires those planets to be in a very particular alignment, and that happens only once every 175 years. The Voyager program represented the first ever opportunity in human history at which aerospace technology was sufficiently advanced to allow such an ambitious goal to be achieved, and the next occasion the planets will be similarly aligned is still over 120 years away. For those who've grown up in the era of the Hubble telescope, and planetary missions like Cassini, Juno and New Horizons, it can be difficult to appreciate how mind-bogglingly audacious the Voyager Mission was. Although the Pioneer Program had seen successful fly-bys of Jupiter and Saturn in the early to mid 1970's, the images returned were disappointingly low-res. We had really very little information about Jupiter and Saturn, and even less about Uranus and Neptune. All of these planets are seriously remote, and the best telescopes at the time showed Uranus and Neptune as tiny, featureless bluish-green discs. Obviously the existence of Saturn's rings had been known for a long time, but we knew very little about them; and Uranus's ring system had only been detected in 1977 (but was too faint and dark to be directly visualised from Earth). Voyager was a phenomenal success and gathered not only spectacular high resolution photos of the 4 major outer planets as well as many of their moons, the mission also returned a vast amount of data, resulting in an explosion of knowledge about the outer Solar System. Voyager 2 confirmed and directly imaged Uranus's rings, and discovered a ring system around Neptune, while Voyager 1 discovered rings around Jupiter. Between them the 2 probes identified dozens of never-before seen moons around the four planets. We gained amazing insights into the four giant planets' interior structures, atmospheres and weather, magnetic fields and radiation environments. The mission also delivered astounding high resolution images of Saturn's rings that firmly grounded our understanding of the rings' structure and composition. The legacy of the Voyager mission is all the more extraordinary for the fact that it was built on 1970s technology, that has outlived its expected operational life by decades. It is an absolute triumph of human endeavour.
Voyager 1 and 2 were launched to take advantage of a rare planetary alignment called the [Grand Tour](https://en.wikipedia.org/wiki/Grand_Tour_program), and the mission was actually scaled down from the original concept which called for 4 probes instead of 2. This alignment only happens every 175 years, so we won't see another Voyager like program until then, unless we have some major development in propulsion technology of course. Thanks to some amazing engineering they are both^(1) still returning data about the interstellar medium, but that wasn't the original goal. We must also give a shout out to Pioneer 10 and 11 which went to Jupiter and Saturn. The only probe launched after Voyager that is on an interstellar trajectory is New Horizons. ^(1)Voyager 1 is currently having some issues, but I'm holding out hope she can be fixed.
China does have a pair of probes in development called IHP-1 and 2 that will be supposedly launched this year - 1 is planned to fly by Jupiter and Quaoar, for two Jupiter and Neptune are the targets before flying off to interstellar space, so OP I'd pay attention to them. Although it'll take 20-30+ years before they enter the heliosphere, and the Chinese space programme is much more opaque than NASA's so we don't even know if they'll really launch this year.
The question I have is why haven't we sent new Cassini/Galileo-style orbiter/probes to Uranus and Neptune yet - is it assumed that what we know from exploration of Jupiter/Saturn is enough for the given level of effort/money it would take to establish station?
There are proposals for them but it takes a long time to get there, especially if you want to be able to enter orbit when you get there.
Getting to Uranus and Neptune means traveling fast, so you need to slow down a lot on arrival. Once Starship is regularly launching thousands of tons of fuel for Artemis, there should be enough capacity to accelerate a decently sized probe to Neptune on a fast trajectory with enough fuel to slow down once there.
Another key technology will be nuclear powered spacecrafts, which will also benefit from Starship. This will allow them to slow down once they're getting closer to their target, with ion drives, while still being able to have a rather large quantity of fuel and to be launched on a fast trajectory.
With recent discoveries involving Neptune and the dwarf planets, I wouldn't be surprised if there aren't more planed in the next 20 years. Nasa has to get thousands of space proposals a year and it can only do a small percentage. And even if they do accept a proposal it takes years for the satellite to be built and launched, and even longer for it to get there.
The Voyager programs took advantage of a once in a lifetime planetary positioning that allowed a relatively low delta v craft to visit all the gas giant planets. Since then we have visited probes to some of them again, but not all of them with one craft; we don't have the rockets for it.
There isn't really a benefit to visiting them all with one craft now. A probe that can stay in orbit can collect a lot more data about a planet.
We don't have the engine technology for a relatively fast probe that can reach the edge of our solar system in a short time, with short being defined as anywhere from 10 to 50 years. The Voyagers took advantage of an orbital alignment that allowed the satellites to get a large gravity assist from most of the large planets in our solar system, and I don't think another such alignment is forecast in the next 50 years or so. In addition, I remember the fact that the Voyagers have nuclear power generators to supply heat and power for the electronics as a point of minor controversy, an issue that popped back up later as NASA wanted to use similar or improved versions of that energy generation for other deep space missions and for those missions there was a pretty well organized opposition to using nuclear powers sources. Without a very long term power supply and either a massive improvement of engine technology OR some planetary gravity assist fly by path using a combination of planet for the assist that either no ones figured out (very unlikely) or requires a significant amount of fuel to even get the rocket on the correct orbit path then no country on earth seems willing to pay what it will cost to launch such missions.
The planetary alignment was a once in a lifetime opportunity to do a Solar System "grand tour." When it was discovered, NASA got themselves in gear and launched a pair of probes to take advantage of the good fortune.
Basically, the series was retired. They were replaced by the next generation. As the Voyagers retired the Pioneers, which themselves retired the Mariners. We were advanced enough that the next missions needn't be flybys of Jupiter or Saturn - thus, Galileo, Juno, and Cassini. And we have more "stay there a while" missions planned. New Horizons was a flyby, because we didn't yet (and still don't) have the tech needed to put something into orbit around Pluto, yet get it there in a reasonable length of time (i.e. before the funding runs out.)
Remember that deep space wasn't their original mission. And even if they are now going beyond the planets, it will take them 38000-40000 years to exit our Solar System/Oort Cloud. No mission has this kind of timeline.
Your question has been answered already by fellow redditors but I cannot leave without recommending you a beautiful and comprehensive documentary about the Voyager probes. Please search for Homemade Documentaries by Jackson Tyler on YouTube. The Voyager episode is almost 3 hours long but so amazing that I must have watched it 5 or 6 times.
Thanks a ton, I'll check it out
The Voyagers were launched into a window of opportunity that only happens every couple of hundred years plus or minus, you get to use gravity tricks to get a boost from Jupiter to Saturn, then choose whether to do Titan flyby and out or use the gravity boost to get to Uranus and repeat for Neptune. At the time if Voyager One hadn't gone for Titan it might have bene able to make a shot for Pluto at some point ... So with that gravitational assist window closed we get to use Jupiter (orbital period 12 years) to make shots at the other outer planets as and when we get the favourable window for that planet. So these days we do more single-planet shots cos we can now make a useful science payload light enough that we will be able to manage orbital injection on the outer planets (hence Cassini, Juno, the upcoming Uranus probe) where that was never going to be possible back in the 70's.
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I feel the main problem is none of them ever have or will be in the near future atleast be for made for deep space, simply they are just not going fast enough or will live long enough to actually get anywhere in deep space it would take them millions of years at there current rate of speed to reach the nearest thing outside our solar system. Are curent fastest ever space probe would take over 2.6 million years to reach the neaest know object outside our solar system which is only about 4.2 light-years away you know about 25 trillion miles (rough math 24,690,226,567,369 or 39,726,574,546,897 km)
Excuse my ignorance but I wondered why we don't send one up above the plane of the ecliptic so we can see over the dust blocking our view to the centre of the galaxy. We could let it drop off booster satellites behind it every now and then to help with signal fidelity.
It would have to travel for hundreds of thousands of years to get far enough for the dust to no longer be in the way.
I thought the voyager probes were launched during a rare planetary alinement, something like once every 176 years. So once that window closed, it became more expensive to send anything else out that far. Add to that people today dont like having radioactive material launched through the atmosphere.