Not really. Like, micrometeors and other debris exist, but the craft is presumably built to deal with that. The modal probe to the outer planets just goes through the asteroid belt without much care, or may have a trajectory chosen specifically so it goes near an asteroid to observe it.

Something that comes to mind is how much Δv the craft has (and what that implies for what sort of trajectory is chosen and travel time). There are thermal and power concerns, though again this is normally dealt with in the design phase.

I mean we’ve sent unmanned ships there and further, they don’t seem to be suffering any crazy amounts of damage

There are probably tons of micro meteors that you would encounter on the way. You would also need enough food and water to make a two way trip, assuming a return trip. Tools and materials to repair any damage that occurs to your spacecraft while en route.

Well, it wouldn't be bombarded with meteors, because meteors are an atmospheric phenomenon.

Also, while more mundane than meteors, your target is also moving. I assume this is solvable by math but it still must be considered.

Even in the asteroid belt, the asteroids are so far apart that you are unlikely to even see one, let alone have one hit you. Space is really big and mostly empty. The Voyager probes have been travelling through space for decades with no repairs and are still doing fine.

Asteroids are not a concern. Real asteroids are not like the movies or the classic game. They are spread far apart. Even in the main belt between Mars and Jupiter they average ~1,000,000 km apart. There are a lot of them, so by happenstance you could pass relatively close to one, as New Horizons flew by an asteroid at a distance of over 100,000 km on its way to Jupiter and Pluto. (Or you could expend a potentially significant amount of fuel to deliberately fly by one at a closer but still-safe distance, as Galileo flew within 2,400 km of 243 Ida on its way to Jupiter.)

Micrometeroids are somewhat more of a concern, but mainly in low orbit around a massive object like Earth or Neptune, much less in deep space. (Neptune has faint dusty orbital rings.) For that, something like a Whipple shield would greatly reduce the risk and damage from micrometeoroids and other debris up to ~1 cm in size. (Earth has both natural and artificial debris orbiting it, so shielding is especially important for the ISS, which is spending decades in low Earth orbit.)

It's for a short story I'm writing

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Where's the spacecraft's origin? a planet's (Earth's?) surface? Then it first needs to get into orbit (I think it's 4.72 lbs of fuel/oxidizer per pound of cargo using current technology?). Once in orbit it needs to handle the planetary orbital debris. Then it'll leave the Van Allen belt, which protects against radiation, which makes the metal brittle. If it passes by Jupiter to pick up speed, it'll be exposed to the second highest source of x-rays in the solar system. Any spacecraft powerful enough to travel to another star system is not going to try using a Hohmann Transfer method...

It's not a given that a space craft will travel through the asteroid belt- it could easily pass at an angle to the solar plane, bypassing the asteroid belt. The next part is getting through the terminal shock and Heliopause. Apparently this is rather difficult for the voyager spacecraft. Not sure why, but apparently the voyager spacecraft has been bumping up against it for years. After that, we're effectively in "Interstellar Space", but we still need to get through the Oort cloud, which spans ~1/2 the distance to alpha centauri. Once in this region of space you're subjected to even more radiation than craft inside the solar system.

Depending on the type of transportation used, that matters as well. Current Warp theory states that if it were possible to travel at near-light speeds (or faster if you're into the whole Alcubierre drive and its improvements over the years), an accumulation of particles collects at the front of the ship and, bombarded with higher energy over the course of the distance travelled, become highly energetic. A sudden stop would impart momentum to the ionized particles at the front, effectively turning them into a bullet. So you get ALL the way to the planet, stop, and then potentially blow it up by shooting the shit out of it with a massive ion cannon, propelled by the energy picked up by your ship (turning around would have the same effect on earth).

.... I just realized you're talking only about neptune. Fuck it... I'm not deleting all that.

I will say, though, that Jupiter puts out a fuckton of xrays, and neptune is #3 xray producer in the solar system IIRC. So a spacewalk is probably out of the question around jupiter or neptune.

Because of the distance, solar power is likely not a good option for power, so some internal power source would be required.

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