# I wanna go to Neptune **URL:** \ **Category:** In My Humble Opinion\ **Created:** [October 16, 2026, 8:37pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901 "2026-10-16T20:37:17Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 16, 2026, 8:37pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/1 "2026-10-16T20:37:17Z")
I was reading an article about how impractical it is to get a resident probe to Neptune, when a thought occurred to me. What if you sent a pair of probes to Neptune, maybe using an ion thruster to get them up to ridiculous speed so that they could get there in our lifetimes. Then, when you get there, one of the probes pushes the other one down into orbit, bleeding off a large fraction of its speed, thereby getting pushed out into deep space (Oort cloud or whatever) for other fun exploration.        I am guessing this would involve a massively explosive separation (with appropriate shielding, of course). Is there a practical way to accomplish this? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [October 16, 2026, 8:56pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/2 "2026-10-16T20:56:14Z")
You do know that we sent a probe to Neptune in 1989, don’t you? Ion thrusters are incredibly low thrust, so they take a long time to get up to speed. But by the time the probes eventually get there, they could be travelling very fast. A flyby gravity-assist could allow the probes to attain even greater speeds, but I don’t think pushing one of the probes into Neptune’s atmosphere would help very much here. But maybe you could elaborate on the mechanism a bit more. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [October 16, 2026, 8:59pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/3 "2026-10-16T20:59:14Z")
> [@eburacum45](#): > > You do know that we sent a probe to Neptune in 1989, don’t you? - Someone made a mistake. Exploratory spacecraft go to Neptune. Probes go to Uranus. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [October 16, 2026, 9:41pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/4 "2026-10-16T21:41:11Z")
The OP used the term “resident probe” which I’m not sure I understand but they may be referring to an orbiter rather than a fly-by. I think the proposal is to use some kind of explosive separation of two probe components to accelerate one while decelerating the other (relative to the planet), as a way of reducing the fuel requirement necessary to slow an orbiter in the traditional way. I’m dubious that any craft could be designed to survive the instantaneous acceleration produced by such a maneuver. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 16, 2026, 9:42pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/5 "2026-10-16T21:42:29Z")
Well, I was not really talking an atmospheric descent probe, because the kind of speed it would have to shed would be: a lot. Though, I suppose the separation angle could shoot the non-resident device skimming the upper atmosphere to gather extra data before sailing off into the dark.        I was trying to envison an expanding tube for a linkage, to contain as much of the explosive separation energy for as long as possible. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [October 16, 2026, 9:52pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/6 "2026-10-16T21:52:25Z")
I’m not sure how different this is from just carrying extra fuel and decelerating with a traditional rocket. You need enough explosive material to jettison the discarded stage with sufficient velocity, which off the top of my head seems like it would be roughly equivalent to the amount of fuel needed to decelerate traditionally. Might even be worse than using a rocket, since you’re carrying this inert stage that provides nothing except reaction mass and doesn’t provide any deceleration the way that an equivalent amount of fuel would. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 16, 2026, 10:46pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/7 "2026-10-16T22:46:19Z")
Yeah, this is basically what a rocket is, except that usually you use something cheaper than a second probe for your reaction mass. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [October 16, 2026, 10:57pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/8 "2026-10-16T22:57:05Z")
> [@eburacum45](#): > > You do know that we sent a probe to Neptune in 1989, don’t you? Those spacecraft have left the solar system. Sure, Neptune is a long trip but clearly doable in our lifetime (cuz we have done it already). ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [October 16, 2026, 10:59pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/9 "2026-10-16T22:59:25Z")
> I wanna go to Neptune Prove to us you know they way. Can you find Uranus? 🤣 ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [October 17, 2026, 11:43pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/10 "2026-10-17T23:43:32Z")
> [@eschereal](#): > > What if you sent a pair of probes to Neptune, maybe using an ion thruster to get them up to ridiculous speed so that they could get there in our lifetimes. Then, when you get there, one of the probes pushes the other one down into orbit, bleeding off a large fraction of its speed, thereby getting pushed out into deep space (Oort cloud or whatever) for other fun exploration. > I am guessing this would involve a massively explosive separation (with appropriate shielding, of course). Is there a practical way to accomplish this? No. The amount of energy it would take to accomplish what you are proposing is comparable to the energy imparted to the probes to accelerate to that speed in the first place. And even if you could do that with an explosive separation, the resulting acceleration alone would destroy the probes. > [@eburacum45](#): > > You do know that we sent a probe to Neptune in 1989, don’t you? Right, this one utilized a once-in-a-lifetime planetary alignment in order to do a gravity assist. However, it was necessarily only a flyby. The difficulty noted in the OP to orbit Neptune is that there is no easy way to slow down once you get there. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 17, 2026, 11:45pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/11 "2026-10-17T23:45:22Z")
There’s always lithobraking, but as you said about the explosive separation, it’s kind of hard on the instruments. 😁 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 17, 2026, 11:50pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/12 "2026-10-17T23:50:35Z")
If you’re not going too fast, and you’re clever about it, you can do a capture maneuver with the moons. Or if you are going too fast, combine that with aerobraking. Remember, Neptune is short on lith. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 17, 2026, 11:57pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/13 "2026-10-17T23:57:05Z")
No lith, but the ice in the center is probably kinda hard too. At a high enough velocity it doesn’t greatly matter how hard it is or isn’t. I just couldn’t think of the Latin term for ice and even if I knew it, I’m not sure most of the audience would. Some Googling now tells me it’d probably be close to glacobraking. Still hard on the instruments. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [October 18, 2026, 12:24am UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/14 "2026-10-18T00:24:22Z")
> [@Chronos](#): > > Remember, Neptune is short on lith. > [@LSLGuy](#): > > No lith, but the ice in the center is probably kinda hard too. Keep up, guys! > **[Scientists Think Uranus and Neptune May Not Be the Ice Giants We Imagined](https://gizmodo.com/scientists-think-uranus-and-neptune-may-not-be-the-ice-giants-we-imagined-2000778382)** > > The so-called ice giants might not be as ice-rich as many astronomers believe. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [October 18, 2026, 8:52am UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/15 "2026-10-18T08:52:12Z")
Some magic with extra-long rotating tethers might assist this problem. Attach two probes to the ends of a very long, and very strong, tether; dip one of the two probes into the atmosphere, and allow the outermost probe to escape after most of the momentum is transferred to that end of the array. Not sure if this would be more efficient than ordinary aerobraking, but tethers must be good for something. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [October 18, 2026, 2:38pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/16 "2026-10-18T14:38:55Z")
Voyager 2 [flew by Neptune at 19.7 km/s](https://science.nasa.gov/missions/voyager-program/voyager-2-prepares-for-1989-neptune-flyby/) (and still took 12 years to get there). That’s a lot of velocity to scrub off in order to put it into orbit. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [October 18, 2026, 2:47pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/17 "2026-10-18T14:47:21Z")
You do want to keep some of the velocity in order to maintain orbit. Note that Artemis lost 11km/s by aerobraking alone. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 18, 2026, 3:11pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/18 "2026-10-18T15:11:44Z")
> [@Whack-a-Mole](#): > > Sure, Neptune is a long trip but clearly doable in our lifetime (cuz we have done it already). When we did it before, we used a rare alignment of the gas planets to get there in a relatively short time. That same alignment occurs every 175 years, so it’ll be mid 22nd century before we can return to Neptune the way we got there in the first place. [![](https://img.youtube.com/vi/URUwhOdpFh4/maxresdefault.jpg "Why Going Back to Neptune Is Almost Impossible") ](https://www.youtube.com/watch?v=URUwhOdpFh4) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 18, 2026, 4:02pm UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/19 "2026-10-18T16:02:33Z")
That specific alignment is rare, but there are other alignments that can be used. In fact, almost any alignment can be used, if you’re patient enough (which often results in counterintuitive paths like multiple Earth flybys). ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 19, 2026, 2:16am UTC](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901/20 "2026-10-19T02:16:07Z")
> [@eburacum45](#): > > Some magic with extra-long rotating tethers might assist this problem. I had been mulling some sort of tether strategy right before I saw your post. But, at Neptune’s distance, you need a fairly non-small dish to communicate with Earth, and a tether would impart a certain amount of spin to the probe that would have to be corrected in order for us to send instructions and receive data. [Next page](https://boards.straightdope.com/t/i-wanna-go-to-neptune/1033901.md?page=2)