Since momentum is conserved, why not just have a 2 of the 1 g probes strapped to each other with a spring in between. When you need a course correction at 100 AU out (or whatever). The probes calculate how much of a correction is needed, adjusts a screw that tightens or loosens tension on the spring, reorients itself appropriately with a reaction wheel, then the two probes are released from each other, begin pushed apart with the spring. One probe gets the trajectory correction it needs, and the other gets further off course. Maybe with some gravity assists with nearby objects.

https://en.wikipedia.org/wiki/Gravity_assist

also:

Roundtrip Interstellar Travel Using Laser-Pushed Lightsails

https://ia800108.us.archive.org/view_archive.php?archive=/24...

It's not skimmed over, they cover it near the end in the "Requirements and challenges" section:

> The most challenging phase of the mission may be related to how the nanocraft can transfer from an unbound to a bound orbit and start orbiting around the compact object. All possible solutions should be considered carefully. In the case the transfer is not possible, we may redesign the mission to perform the scientific tests when the nanocraft passes close to the black hole. For example, when the nanocraft is close to the black hole, it may separate into a mother-nanocraft (with a wafer and sail) and a number of small nanocrafts (without sails). The nanocrafts could communicate with each other by exchanging electromagnetic signals. The mother-nanocraft could compare the trajectories of the small nanocrafts to those expected in a Kerr spacetime and send the data to Earth.

Light sales can theoretically be used to not only accelerate away from Earth, but also decelerate at the end of an interstellar journey (see Robert L Forward's work). The practicality of that is another matter.

> It is stated multiple times across the article...

I was a bit confused by your comment, but I think the article you're referring to is not the OP, but the article the OP was commenting on: https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8...

> Does anyone have an idea how to equip a 1g spacecraft with any means to steer itself at 1/3 speed of light? The kinetic energy at that speed would seem to require something very incompatible with the weight constraint, to my understanding.

I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. That also seems incompatible with the weight constraint.

People don't realise this, but you can steer perfectly fine with a solar sail. That's because photons transfer momentum not just when they hit the sail, but also when they are emitted after reflection. So just by turning the sail at an angle, you can create a force in any direction perpendicular to the velocity vector. Using a two sail system, you can even accelerate and slow down along a single beam path. So you could theoretically travel to mars with a constant acceleration/deceleration phase (like a flip-and-burn in the Expanse) using only one beam emitter on earth.

Simply. You do Monte Carlo with the probes. You fire 1000 and one or two will have perfect trajectory so that no correction is needed.

> So the most important and blocking aspect of the mission

Idk, i think the fact they are using statistical arguments that there should be a nearby black hole, but haven't actually found any or have any idea where they are, is pretty blocking.

"steering" is a word that can lead to confusion because it leverages the intuition that we have with our ground vehicles.

A change in direction in space requires accelerating the vehicle in some direction, the effect of which is just simple vector addition of the velocity vector of the vehicle.

So if you are going with a huge velocity in one direction and you want to change direction significantly in another direction you have to change velocity (accelerate) a lot in order for the combined vectors to produce a significantly different final velocity vector

Easy fix: change the description to "Interstellar Mission to the General Galactic Vicinity of a Black Hole"

Solar sails. You can fire a shit ton of lasers from the planet (or orbit) at the probes and very,very slowly boost them up to the desired velocity.

gyroscopes?

That would be cool.

I read somewhere that a black hole with the mass of the moon will absorb about as much cosmic radiation as it emits Hawking radiation. This is a fine line between "the black hole disappears before we can examine it" and "oops, we got eaten by a black hole".

>It would be super hard to detect though.

Would it? I would've thought there is enough dust in the solar system that it would create constant xray emissions. Even if it's faint, it would stick out like a sore thumb on super sensitive xray telescopes.

We do not what such a thing anywhere near Earth though. https://arxiv.org/abs/astro-ph/9911309

I remember reading somewhere that it's possible for such a black hole to get captured by an asteroid (or vice versa, I guess), and happily live inside a rock, slowly orbiting inside the asteroid, sucking up atoms here and there.

It would be detectable as an asteroid that's twice as dense as it should be.

If it was asteroid mass, wouldn't it have the same gravitational effect of an asteroid itself? Plus, someone else mentioned it'd be like a micron across, which if my pop-sci understanding of these things is correct, it'd disappear in a poof of hawking radiation.

We wouldn't have to get lucky if it was on the last stages of evaporating. If it has reached a mass of about a billion kg it would be shining plenty bright to detect, and would only have a few thousand years to live before destroying most life on Earth with gamma radiation.

Could you find it by Hawking radiation?

You don't stop this type of craft, it's strictly accelerate and coast type of thing.

Also note that "solar sail" is a bit misleading, the (now apparently dead) Breakthrough Starshot design was a big reflector "sail" in space and very many lasers on Earth to power it, it's not actually driven by a stellar wind directly.

I don't think we can just go near speed of light. Even hard vacuum out there contains particles. Heliosphere is chock full of them, then Oort cloud has stuff way bigger than that (or any probe), even if sparsely spread out. Then there is cosmic stuff outside, as Voyager found out.

Getting hit by some random molecule when orbiting Earth or just travelling say 30,000 kmh is one thing. Getting hit by swarms of molecules with say 0.5c can be catastrophic to the material. Now imagine wading through some space dust cloud, or even plasma cloud (ie remnant of some bygone supernova).

Star trek had shields, and for good reasons. Super strong magnetic field may divert some charged particle, but helium molecule is just a helium molecule, no extra charge to play with.

> Or does it strand you halfway between stars in the doldrums where the force on both sides of your sail equals out from two stars?

This is actually I "love" to think about:

What would it be like, to be "stranded" in the space far from any stars?

or in the "voids" where there are relatively very few stars/galaxies to begin with?

There must be things drifting there right now...

It would also be the perfect place to HIDE something :)

You would fold the sail?

Time dilation is 1/sqrt(1 - (v/c)^2). So at 0.1c that’s 0.5%. Certainly much higher than any human has ever experienced! But not exactly gonna change 100y to 100,000,000y.

Time dilation is exponential. At 0.1c it's definitely measureable but not a practical problem.

No need to be snarky and especially not here re basic science. Time dilation happens exponentially, ie with 0.5c you don't have time going 1/2 slower, rather a miniscule amount. Once you keep approaching speed of light closer and closer, all things go extreme (time, energy required, mass and so on).

send 1 a day, that way you only have to communicate to the nearest probe.

A black hole may be invisible but its accretion disk and the effects on the light being deflected around it are anything but.

Considering AI-pornbots are increasing the derivate of the function, they might actually be the right move.

What are the odds the first alien probe to visit the solar system will be a pornbot or some form of marketing droid?

Well, they are both on a mission to a black hole.

AI porn sells, solar sails are a research project at best. There is no money to be made from space flight, only discovery, and unfortunately capitalist forces far outweigh curiosity.

Even the space race wasn't for science but for politically one-upping the others, doubly so because being able to bring a payload into space also demonstrates they can bring a payload anywhere on the world.

At least the AI-pornbots will operate from space. /s