3I/ATLAS: Probably NOT an alien interstellar probe

[bilby]

I mean, if we're being serious, that's going to be the absolute easiest way to get out of the solar system by far.

I think you mean it's the easiest way to send something out of the solar system. It lets you "get out" of the solar system exactly as effectively as does any other flight of fancy, stimulated though it may be by actual signals of actual distant origin. We could probably figure out how to tag something onto an interstellar intruder like that 31/Atlas thingy, but so what?

if we can make a rocket that can catch up to one of these why would we need to tag a ride?

I didn’t specify what was to be “sent” - No way anything is going to “catch” an interstellar interloper there would HAVE to be a super violent impact, and it might take kilotons of rock to absorb and accelerate a few grams of earth matter to near it’s speed. Hopefully the impact doesn’t slow the object down enough for it to be captured… if it does, go lighter or get a bigger interstellar object!

I didn’t say “catch” it, I said “catch up to it”. How else will you “tag something to it” unless you can match its speed and position? And if we can get something up to that speed then we don’t need to tag along with it because we are already on the same trajectory, no?

Maybe I misunderstood what you were suggesting. Sorry.

Intercept courses with small payloads. Imagine a gun on the end of a rocket or somesuch: you just have to cross paths with it, depending on the payload.

Ok. I guess I was assuming a softer “tag”. Where you might want the thing being tagged onto it to survive the impact of what would likely be a massive delta v.

Many things impact earth and even after the impact, are still cold.

Two points:

1) what’s the delta v in these cases? Neither object is moving at a velocity that can escape the solar system.

2) the earth has an atmosphere, so the impact happens over a large distance and the impactor goes through a lot of ablation.

3) what do you mean by "cold"? Anything arriving from deep space is at a couple of Kelvins; It will arrive at the Earth's surface at more like hundreds of Kelvins. That sounds pretty "hot".

 

[bilby]

The idea is that once the rock has been infected, there are thousands of years during its transit to fully affect any change necessary to spread spores our during a pass-through on the next system.

Getting those spores the delta-v needed to escape the interloper, and arrive on a planet, is going to be exactly as problematic as getting them to the interloper to start with - but instead of starting with the technological base of an entire planet of humans, you are trying to solve the problem with the technological base of a small cold rock with some frozen tardigrades on it.

This seems like an even less tractible problem than the one we started with, and thousands of years don't seem like anywhere close to sufficient.

 

[Shadowy Man]

I mean, if we're being serious, that's going to be the absolute easiest way to get out of the solar system by far.

I think you mean it's the easiest way to send something out of the solar system. It lets you "get out" of the solar system exactly as effectively as does any other flight of fancy, stimulated though it may be by actual signals of actual distant origin. We could probably figure out how to tag something onto an interstellar intruder like that 31/Atlas thingy, but so what?

if we can make a rocket that can catch up to one of these why would we need to tag a ride?

I didn’t specify what was to be “sent” - No way anything is going to “catch” an interstellar interloper there would HAVE to be a super violent impact, and it might take kilotons of rock to absorb and accelerate a few grams of earth matter to near it’s speed. Hopefully the impact doesn’t slow the object down enough for it to be captured… if it does, go lighter or get a bigger interstellar object!

I didn’t say “catch” it, I said “catch up to it”. How else will you “tag something to it” unless you can match its speed and position? And if we can get something up to that speed then we don’t need to tag along with it because we are already on the same trajectory, no?

Maybe I misunderstood what you were suggesting. Sorry.

Intercept courses with small payloads. Imagine a gun on the end of a rocket or somesuch: you just have to cross paths with it, depending on the payload.

Ok. I guess I was assuming a softer “tag”. Where you might want the thing being tagged onto it to survive the impact of what would likely be a massive delta v.

Many things impact earth and even after the impact, are still cold.

Two points:

1) what’s the delta v in these cases? Neither object is moving at a velocity that can escape the solar system.

2) the earth has an atmosphere, so the impact happens over a large distance and the impactor goes through a lot of ablation.

3) what do you mean by "cold"? Anything arriving from deep space is at a couple of Kelvins; It will arrive at the Earth's surface at more like hundreds of Kelvins. That sounds pretty "hot".

When a meteor impacts the Earth's atmosphere it starts as a big, "cold" rock. As it quickly travels through miles of atmosphere, the outer surfaces ablate away, and by the time whatever is left hits the ground, there may be parts of it interior that did not get substantially heated in the process.

When an objects hits an asteroid or comet with no atmosphere, all the kinetic energy gets dissipated in a single massive explosion (as evidenced by missions like DART), but it is in principle possible that some microscopic piece of the impactor could stay close enough to the object to be retained by it gravitationally and be carried out of the solar system.

I think that unless one is closely matching the velocity (speed and direction) of the so-called interloper, the delta-v could likely be very high (like order of 10 km/s) and there won't be much left of the impactor. If one can actually nearly match the speed of the interloper then it would seem that one could just escape the solar system without the interloper. That was the crux of my confusion on the logic of the proposal.

 

[Swammerdami]

I have a hypothetical question unrelated to the present interstellar comet. Assume a space-craft launched from Earth with only a limited amount of stored energy aboard. After achieving a desired initial trajectory it has enough fuel left for some course corrections. (Instead of wasting matter on impulse, suppose it steers magnetically.)

My question is: ASSUMING that some of the major planets line up propitiously for the space-craft to approach them dozens of times in a long series of ever-changing ellipse-like trajectories, gaining more and more energy from the "sling shots" what is the maximum speed it could have when it finally escapes the solar system? Assume that the missionaries are very patient and are willing to spend hundreds of centuries on the "sling-shotting." (Assume as well, perfect computation of future orbits.)

 

[Shadowy Man]

I have a hypothetical question unrelated to the present interstellar comet. Assume a space-craft launched from Earth with only a limited amount of stored energy aboard. After achieving a desired initial trajectory it has enough fuel left for some course corrections. (Instead of wasting matter on impulse, suppose it steers magnetically.)

My question is: ASSUMING that some of the major planets line up propitiously for the space-craft to approach them dozens of times in a long series of ever-changing ellipse-like trajectories, gaining more and more energy from the "sling shots" what is the maximum speed it could have when it finally escapes the solar system? Assume that the missionaries are very patient and are willing to spend hundreds of centuries on the "sling-shotting." (Assume as well, perfect computation of future orbits.)

Without thinking through it more deeply or having any expertise in orbital mechanics, my initial response to this is I doubt there’s much to be gained after just a handful of flybys.

 

[bilby]

The maximum velocity increase achievable relative to the Sun, by gravitational slingshot from a planet, is twice the planet's orbital velocity. So the best you can do in the Solar System with a single manoevre is about 96km/s (twice the orbital velocity of Mercury).

Each slingshot manoevre is effectively a perfectly elastic 'bounce', transferring momentum to your spacecraft from tne planet. As far as I can see, if you have infinite time for the task, you could keep doing such manoevres until you have stolen all of the momentum from everything in the Solar System, and all the planets have fallen into the Sun.

Your final velocity would be huge in such a scenario; although your accelerations would get very small as your probe's mass increased due to its speed. You should achieve a sizable fraction of c for any probe with a reasonable rest-mass.

 

[bilby]

Of course, once you get above solar escape velocity, it starts to require more energy to get back for your next slingshot than you can gain from it.

My guesstimate is that the maximum practical velocity relative to the Sun will therefore be the Solar escape velocity, plus twice the orbital velocities of the planets you can arrange to pass on your way out; For a perfect setup, that's going to be all eight planets, plus maybe a few dwarf planets.

 

[lpetrich]

I have a hypothetical question unrelated to the present interstellar comet. Assume a space-craft launched from Earth with only a limited amount of stored energy aboard. After achieving a desired initial trajectory it has enough fuel left for some course corrections. (Instead of wasting matter on impulse, suppose it steers magnetically.)

How would magnetic steering work? Spacecraft are "steered" by rocket engines.

My question is: ASSUMING that some of the major planets line up propitiously for the space-craft to approach them dozens of times in a long series of ever-changing ellipse-like trajectories, gaining more and more energy from the "sling shots" what is the maximum speed it could have when it finally escapes the solar system? Assume that the missionaries are very patient and are willing to spend hundreds of centuries on the "sling-shotting." (Assume as well, perfect computation of future orbits.)

Only one flyby is necessary for going into interstellar space, though that flyby is a flyby of Jupiter. New Horizons, for instance.

 

[steve_bank]

Haven't heard this one before.

Spacecraft use magnetic steering primarily through magnetorquers, which are electromagnetic coils that create a controllable magnetic field to interact with a planet's magnetic field. This interaction produces a torque, allowing for attitude control (orientation) and de-tumbling without using propellant. While this method is low-cost and propellant-free, it produces weak torque and its effectiveness is limited to areas with a strong magnetic field, like low Earth orbit.

Magnetorquer - Wikipedia

en.wikipedia.org

Regardless of what methods you use you can't get around LOT.

Energy required equals the work done on the spacecraft plus efficiency losses.

Spacecraft use gyroscopic steering, often with Control Moment Gyros (CMGs), to change orientation by tilting a spinning flywheel's axis of rotation, which causes a torque on the spacecraft. This leverages the principle of angular momentum: changing the direction of the wheel's angular momentum produces a reactive torque on the spacecraft that rotates it. CMGs are efficient for reorientation, while reaction wheels provide fine-tuning and thrusters are used for large or backup maneuvers.

Control moment gyroscope - Wikipedia

en.wikipedia.org

When riding a bicycle or motorcycle you apply force on the axle of the front wheel and it pre4cesses.

Gyroscopic precession on a motorcycle is the phenomenon where a force applied to the front wheel's axle causes the wheel to move 90 degrees in the direction of the spin. For example, pushing the left handlebar to turn the wheel left causes the bike to lean to the right. To turn a motorcycle, a rider uses counter-steering which, despite its counterintuitive nature, relies on this principle: they push the handlebars in the opposite direction of the turn, which initiates a lean in the intended direction.

An oldie but a goodie. Using a spinning wheel to turn a chair on a swivel.

Google Search

 

[Loren Pechtel]

The question is whether we can "tag" an interstellar rock like this one on its way through with something that can soak up enough energy somewhere along its pathway to activate and hijack it, ride that out of the star's gravity well, and then when in a relatively gravitationally neutral environment, select a nearby destination somewhere in the cone of deflection given the previously collected energy, and then give the rock a bit of a kick, and doing some math/observation on the way to determine fine tuning on trajectory to get info, and maybe make a gravity acceleration or get more energy from the star.

Orbital mechanics--you can't hitch a ride like this. You'll burn just as much catching up with the rock as if you simply launched directly to interstellar space. Don't be mislead about the proposals for hitching a ride on Earth-Mars cyclers. Those actually cost you delta-v, they don't save it. The reason for the proposal is to leave your living quarters out there looping around rather than boosting them for each trip. Likewise, Apollo, it was about not taking the return supplies down to the lunar surface.

And you can't use a passing star for acceleration. Gravity boosts only work when you're operating in a different frame of reference than the object you're using for a boost. Anything heading beyond Jupiter uses Jupiter for a gravity maneuver but it's only possible because the craft is operating in the reference frame of the solar system. If you were sitting on Jupiter and measuring the spacecraft you would see it change course due to the flyby but leave with exactly the same energy it started with. Think of throwing something bouncy at a car. If the car is sitting still it comes back with the same energy you threw it. If the car is moving towards you it comes back faster, if the car is moving away it comes back slower. But anyone in the car always sees it head back out with the same speed it came in.

 

[Loren Pechtel]

I mean, if we're being serious, that's going to be the absolute easiest way to get out of the solar system by far.

I think you mean it's the easiest way to send something out of the solar system. It lets you "get out" of the solar system exactly as effectively as does any other flight of fancy, stimulated though it may be by actual signals of actual distant origin. We could probably figure out how to tag something onto an interstellar intruder like that 31/Atlas thingy, but so what?

if we can make a rocket that can catch up to one of these why would we need to tag a ride?

I didn’t specify what was to be “sent” - No way anything is going to “catch” an interstellar interloper there would HAVE to be a super violent impact, and it might take kilotons of rock to absorb and accelerate a few grams of earth matter to near it’s speed. Hopefully the impact doesn’t slow the object down enough for it to be captured… if it does, go lighter or get a bigger interstellar object!

AFIAK you can't build something to survive a supersonic impact--measured using the speed of sound in the object, not the environment. Force can't be transferred faster than local sound velocity, thus any possible crush mechanism on the front can't slow down the payload. In the real world we see this with armor-penetrating weapons. Once the weapon is hitting the target all that matters is mass and energy. Strength only matters to the extent that you need to hold things together--note that plasma jets are plasma, they have no strength whatsoever. Lithobraking is usually treated as a joke, in practice it's never been used beyond tens of miles an hour. (Those Mars rovers that were basically wrapped in airbags.)

 

[Loren Pechtel]

Things to do when traveling on an interstellar rock:

1. Take a walk around the rock in a space suit.
2. Gaze at the stars.
3. Contemplate meaning of life.
4. Go to #1.

"Walk" implies that you won't simply throw yourself off the rock and it implies a surface strong enough to stand on.

 

[Jarhyn]

The idea is that once the rock has been infected, there are thousands of years during its transit to fully affect any change necessary to spread spores our during a pass-through on the next system.

Getting those spores the delta-v needed to escape the interloper, and arrive on a planet, is going to be exactly as problematic as getting them to the interloper to start with - but instead of starting with the technological base of an entire planet of humans, you are trying to solve the problem with the technological base of a small cold rock with some ftozen tardigrades on it.

This seems like an even less tractible problem than the one we started with.

Well, that's the whole point: only life itself tends to have the kind of deployment package that could do it.

It also tends to produce the only viable deployment packages for containing a whole human organism worth of information in a package smaller than a grain of dust.

I would expect that the majority of space is, as you say, quite cold and empty with few opportunities to collect energy.

The question is whether we can "tag" an interstellar rock like this one on its way through with something that can soak up enough energy somewhere along its pathway to activate and hijack it, ride that out of the star's gravity well, and then when in a relatively gravitationally neutral environment, select a nearby destination somewhere in the cone of deflection given the previously collected energy, and then give the rock a bit of a kick, and doing some math/observation on the way to determine fine tuning on trajectory to get info, and maybe make a gravity acceleration or get more energy from the star.

Orbital mechanics--you can't hitch a ride like this. You'll burn just as much catching up with the rock as if you simply launched directly to interstellar space. Don't be mislead about the proposals for hitching a ride on Earth-Mars cyclers. Those actually cost you delta-v, they don't save it. The reason for the proposal is to leave your living quarters out there looping around rather than boosting them for each trip. Likewise, Apollo, it was about not taking the return supplies down to the lunar surface.

And you can't use a passing star for acceleration. Gravity boosts only work when you're operating in a different frame of reference than the object you're using for a boost. Anything heading beyond Jupiter uses Jupiter for a gravity maneuver but it's only possible because the craft is operating in the reference frame of the solar system. If you were sitting on Jupiter and measuring the spacecraft you would see it change course due to the flyby but leave with exactly the same energy it started with. Think of throwing something bouncy at a car. If the car is sitting still it comes back with the same energy you threw it. If the car is moving towards you it comes back faster, if the car is moving away it comes back slower. But anyone in the car always sees it head back out with the same speed it came in.

It's more about getting attached to enough mass that's going that fast in that direction, preferably on a path through a place that will be hot for a while, so that you can co-opt much of that matter for the sake of decelerating with it.

The idea here is that it's astronomically easier getting a very small bit of matter to a large thing, and then modifying the big thing, than it is getting a big thing going that fast, assuming you have long periods of time to do so.

The point is to have many more tons of material going out of the system than you have resources to launch yourself.

 

[Loren Pechtel]

Something very small could achieve a nonviolent impact, I think, but ideally any deflection sends it on towards whatever alternative target, anyway.

It might take longer to wait for a suitable interloper, though, than it would to engineer a useful payload

Small enough means it's not obviously violent to the big object, but that doesn't make it not violent to the small object.

Look at shooting stars. Grains of sand, mostly hitting far slower than what would happen if you intercepted this object and hitting very thin atmosphere which carries off much of the energy.

 

[Elixir]

AFIAK you can't build something to survive a supersonic impact--measured using the speed of sound in the object, not the environment. Force can't be transferred faster than local sound velocity, thus any possible crush mechanism on the front can't slow down the payload. In the real world we see this with armor-penetrating weapons. Once the weapon is hitting the target all that matters is mass and energy. Strength only matters to the extent that you need to hold things together--note that plasma jets are plasma, they have no strength whatsoever. Lithobraking is usually treated as a joke, in practice it's never been used beyond tens of miles an hour. (Those Mars rovers that were basically wrapped in airbags.)

Interesting!
So an ablating suspension system is required? In the case of something moving a at tens or hundreds of miles per second, it might have to be a pretty elaborate so the actual payload experiences no acceleration greater than the rate at which it can be transmitted through the body of that payload… get to work Loren, I know you can figure it out!

 

[Loren Pechtel]

Many things impact earth and even after the impact, are still cold.

Because the heat burns away faster than it penetrates. And they reach terminal velocity in a very cold region of the atmosphere.

 

[Jarhyn]

Something very small could achieve a nonviolent impact, I think, but ideally any deflection sends it on towards whatever alternative target, anyway.

It might take longer to wait for a suitable interloper, though, than it would to engineer a useful payload

Small enough means it's not obviously violent to the big object, but that doesn't make it not violent to the small object.

Look at shooting stars. Grains of sand, mostly hitting far slower than what would happen if you intercepted this object and hitting very thin atmosphere which carries off much of the energy.

Well, as I see it, our current interstellar probes were harder to send because they are fairly more massive than a grain of sand.

How much mass does it actually take, though, to direct a thing the size of a grain of sand to those speeds in space over time?

Could we design a multi-stage shaped charge that will discharge slowly and at the correct angles and times to make a soft landing?

We're talking about a payload the size of a grain of sand here.

In my mind the really hard question is whether we can do the math we would need to accomplish a last-mile delivery prior to the time the last mile delivery would need to be constricted to make rendezvous.

Im not sure on that account whether it would be possible.

All I can think is that we are incapable of sending large things out, but having a large thing that is already going out would be a good idea to hitch with.

My biggest problem is that people oftentimes build thinking bigger is better? As small as you are capable of building is better, but it means you need to find resources where you are going, and that the only thing you should be trying to bring you are resources you will need that you are not likely to find elsewhere, assuming that it is expensive to send even that much.

The biggest issue in deep space travel though in my mind is shielding, because as you mention, everything it passes through is hitting it very hard, and there is a lot of radiation out there.

The biggest reason to want to catch a bigger rock may just be to have a thing you can hide inside of, from all that.

 

[Elixir]

Tardigrades can withstand acceleration forces up to an astonishing 16,000 g, or 16,000 times Earth’s gravity, depending on the species and conditions of exposure.[smithsonianmag +2]
Hypergravity Tolerance
Experimental studies using centrifugation on the eutardigrade Hypsibius dujardini demonstrated that specimens survived accelerations between 3,421 g and 16,060 g for one minute, though survival and reproduction declined at higher g-forces.

How fast would something be going if accelerated at 16000 gs for one minute?

“ If something were accelerated at 16,000 g for one minute, its speed would reach about 9,412,000 meters per second (≈9,412 km/s or ≈0.031 times the speed of light).”

And galactic escape velocity?

The galactic escape velocity from Earth’s position in the Milky Way is approximately 537–550 kilometers per second relative to the galaxy’s center.

So no problem there. Impact survival?

Impact Shock Tolerance
In separate experiments simulating meteorite impacts, tardigrades survived collisions up to approximately 0.9 kilometers per second, generating shock pressures around 1.14 gigapascals (GPa) — roughly equivalent to over 100,000 times atmospheric pressure at sea level. Beyond that threshold, the animals were physically destroyed.[pmc.ncbi.nlm.nih +2]

Uh oh. Sorry Mr Tardigrade.

 

[bilby]

The idea is that once the rock has been infected, there are thousands of years during its transit to fully affect any change necessary to spread spores our during a pass-through on the next system.

Getting those spores the delta-v needed to escape the interloper, and arrive on a planet, is going to be exactly as problematic as getting them to the interloper to start with - but instead of starting with the technological base of an entire planet of humans, you are trying to solve the problem with the technological base of a small cold rock with some ftozen tardigrades on it.

This seems like an even less tractible problem than the one we started with.

Well, that's the whole point: only life itself tends to have the kind of deployment package that could do it.

Not so. Life is shit at space travel. It took over three billion years to develop space travel, with an entire planetary surface - including a lot of water and a lot of atmosphere - to work with.

And our best efforts have resulted in non-life probes. Nothing on Voyager is alive. Likely nothing alive has made it past the Moon.

It also tends to produce the only viable deployment packages for containing a whole human organism worth of information in a package smaller than a grain of dust.

Not on tiny rocks in a hard vacuum, it doesn't.

I would expect that the majority of space is, as you say, quite cold and empty with few opportunities to collect energy.

I would expect that you don't grasp just how much of an understatement that is.

The majority of the solar system is completely empty, and has only the Sun to
provide energy - and for the vast majority of the solar system, the Sun is a long way away, and provides three eighths of bugger all energy.

The overwhelming majority of galactic space is far emptier, and has no nearby stars.

And the overwhelming majority of space lies between galaxies, and is emptier still.

Assume that somehow an alien civilization, keen to seed life through the universe, had managed to get some bacteria, or even some tardigrade-like life onto a rock on an interstellar (or even intergalactic) trajectory - how, exactly, is that life getting off that rock? Survival is unlikely; Evolution is even less likely - there is no source of energy, other than for a few days every several million years, when the rock passes close to a star.

If it takes billions of years for life to evolve the ability to travel through space, when it is situated a comfortable 150 million km from a nice stable star, how long will it take if it is only in such an advantageous energy collecting position for a few billionths of a percent of the time?

By the time your "information package" has managed to solve this problem, there won't be any stars or planets left to travel to.

3I/ATLAS could be teeming with wonderfully engineered alien tardigroid life, fully loaded with the genetic information needed to turn any planet into an alien biosphere to rival that of their home planet. We would never know about it; And it could no more influence any of the planets in our Solar System as it pases through, than it could have had it passed by a couple of lightyears away.

 

[Jimmy Higgins]

The biggest issue in deep space travel though in my mind is shielding, because as you mention, everything it passes through is hitting it very hard, and there is a lot of radiation out there.

The biggest issue with deep space travel is just about every issue with deep space travel.

3I/ATLAS could be teeming with wonderfully engineered alien tardigroid life, fully loaded with the genetic information needed to turn any planet into an alien biosphere to rival that of their home planet. We would never know about it; And it could no more influence any of the planets in our Solar System as it pases through, than it could have had it passed by a couple of lightyears away.

I've got to imagine a species as smart as that would likely not choose ridiculously unlikely, grossly inefficient, and random stupid luck to seed the universe.