3I/ATLAS: Probably NOT an alien interstellar probe

[pood]

He must realize that he can end up looking like a fool? So why risk it? Because he thinks the pay-off would be huge if he is right?

What are the odds?

Because it’s clickbait and somewhere downstream he is making money. Those people who tell you the world is going to end on such and such a date suffer no penalty for being proven wrong. They just move on to the next date. And keep their fan base.

 

[pood]

Basically I think Loeb is like a religious leader or a cult leader, like Trump. He tells people what they want to hear, and can never be proven wrong.

 

[DBT]

I suppose there is always a rationale for failure. Nobodies fault....next event please.

 

[steve_bank]

Wow, I just figured it out.

ET in orbiting in invisible spaceships are on the net posting on the forum.

That explains a lot.

 

[Loren Pechtel]

No, the point is there is no possible suspension as you can only transmit the force at the speed of sound.

Yet you can continuously apply 16000 gs to a tardigrade for a full minute without killing it?

No idea on the g-tolerance of a tardigrade, but what's the relevance? I'm talking about speed, not acceleration. Your 16,000g is unquestionably from a centrifuge, it's just going round and round, not smacking the atmosphere.

 

[Loren Pechtel]

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.

Two problems:

1) They're not in the right place to do this.

The setup in the question assumes that we can wait until they are, however long that takes.

2) While in theory you could get 96km/sec out of Mercury look at the periapsis. It's way, way below the surface.

Sure, but we are looking for an upper bound to the achievable velocity relative to the Sun. Some assumptions are justified, such as treating planets as point masses. It's not like I am asking you to consider a spherical planet in a vacuum...

Moo!

Tables exist for the maximum velocity that can be obtained from the various planets.

 

[Elixir]

No idea on the g-tolerance of a tardigrade, but what's the relevance? I'm talking about speed, not acceleration.

Speed isn’t an issue. You don’t mind going 500+ mph in a plane because the rate of your acceleration is gradual. If you were simply placed in the way of the plane while it was going 500+ mph, you’d get “smacked” by your instant acceleration from zero to 500. In fact you’d be pizza. Not from the speed, from the acceleration.

Same deal with imbedding a terrestrial object in a fast moving interstellar object - it ain’t the speed that will get you, it’s the acceleration, aka getting “smacked”. Surviving the impact means reducing the G forces of acceleration.

It’s NOT about the speed (until you get to relativistic speeds). Kinda like how falling from great heights won’t kill you, the rapid deceleration upon impact will.

 

[Loren Pechtel]

No idea on the g-tolerance of a tardigrade, but what's the relevance? I'm talking about speed, not acceleration.

Speed isn’t an issue. You don’t mind going 500+ mph in a plane because the rate of your acceleration is gradual. If you were simply placed in the way of the plane while it was going 500+ mph, you’d get “smacked” by your instant acceleration from zero to 500. In fact you’d be pizza. Not from the speed, from the acceleration.

Same deal with imbedding a terrestrial object in a fast moving interstellar object - it ain’t the speed that will get you, it’s the acceleration, aka getting “smacked”. Surviving the impact means reducing the G forces of acceleration.

It’s NOT about the speed (until you get to relativistic speeds). Kinda like how falling from great heights won’t kill you, the rapid deceleration upon impact will.

I'm not talking about acceleration, I'm talking about slamming through the atmosphere very fast.

 

[Elixir]

What atmosphere? The interstellar object ain’t in the atmosphere and if it had one of its own the sun would probably blow it away. The ability of a tardigrade to withstand such acceleration relates to its survival chances if placed in a shock absorbing capsule in the path of 31/Atlas. Are you saying it has a thick atmosphere?

 

[Loren Pechtel]

What atmosphere? The interstellar object ain’t in the atmosphere and if it had one of its own the sun would probably blow it away. The ability of a tardigrade to withstand such acceleration relates to its survival chances if placed in a shock absorbing capsule in the path of 31/Atlas. Are you saying it has a thick atmosphere?

We were talking about launching from a planet.

 

[steve_bank]

If the capsule can be maneuvered to be in front of the object and it is low mass then having an engine to decelerate would be the thing to do.

Getting a probe or capsule directly in line with path of the object would be hard to do ballistically. There would have to maneuver engines.

Arrive in style and comfort.

moon probes have course corrections to stay on their planned trajectory
. These adjustments are made using small thrusters to make minor changes, while larger burns are used for more significant maneuvers, such as entering lunar orbit. The corrections are often pre-planned and calculated on Earth, then uploaded to the spacecraft, but some limited autonomy can also be used.

Mars probes have in-course corrections, which are necessary to ensure they reach their destination due to the long, multi-month journey. These adjustments, performed by firing thrusters, are vital for fine-tuning the probe's trajectory after launch and can be performed multiple times before arrival to correct for external factors or the initial, less precise aim point

 

[Elixir]

What atmosphere? The interstellar object ain’t in the atmosphere and if it had one of its own the sun would probably blow it away. The ability of a tardigrade to withstand such acceleration relates to its survival chances if placed in a shock absorbing capsule in the path of 31/Atlas. Are you saying it has a thick atmosphere?

We were talking about launching from a planet.

Earth, in particular. All you need is escape velocity at the right trajectory to be intercepted. impacted and absorbed by the fast-traveling interloper. And I was only concerned with payload survival. YOU could probably do the math to figure out how long and how far the impact must last under acceleration of less than 16,000 Gs in order to reach the 218,000mph speed of 31/Atlas relative to earth … that will give you a size of compressible material and its required characteristics for a given payload to survive the acceleration of impact and go on an interstellar ride polluting the rest of the universe with the same crap that once infected this rock.

 

[bilby]

What atmosphere? The interstellar object ain’t in the atmosphere and if it had one of its own the sun would probably blow it away. The ability of a tardigrade to withstand such acceleration relates to its survival chances if placed in a shock absorbing capsule in the path of 31/Atlas. Are you saying it has a thick atmosphere?

We were talking about launching from a planet.

That's a different conversation, and is happening in another thread.

 

[bilby]

Arrive in style and comfort.

moon probes have course corrections to stay on their planned trajectory
. These adjustments are made using small thrusters to make minor changes, while larger burns are used for more significant maneuvers, such as entering lunar orbit. The corrections are often pre-planned and calculated on Earth, then uploaded to the spacecraft, but some limited autonomy can also be used.

Limited autonomy??

Apollo 13 made a mid-course correction on the way back from the Moon entirely manually, with the calculations done in Houston, and radioed to the astronauts before the manoevre; The burn was executed with two astronauts manually controlling the attitude of the (severely unbalanced) spacecraft, while the third used a stopwatch to time the burn and shut off at the appropriate time.

Attitude control was done by eye, using the Earth as a visual reference. Initial setup also used the Sun as a pitch reference.

https://www.nasa.gov/history/afj/ap13fj/19day5-themanualcoursecorrection.html

 

[Loren Pechtel]

What atmosphere? The interstellar object ain’t in the atmosphere and if it had one of its own the sun would probably blow it away. The ability of a tardigrade to withstand such acceleration relates to its survival chances if placed in a shock absorbing capsule in the path of 31/Atlas. Are you saying it has a thick atmosphere?

We were talking about launching from a planet.

Earth, in particular. All you need is escape velocity at the right trajectory to be intercepted. impacted and absorbed by the fast-traveling interloper. And I was only concerned with payload survival. YOU could probably do the math to figure out how long and how far the impact must last under acceleration of less than 16,000 Gs in order to reach the 218,000mph speed of 31/Atlas relative to earth … that will give you a size of compressible material and its required characteristics for a given payload to survive the acceleration of impact and go on an interstellar ride polluting the rest of the universe with the same crap that once infected this rock.

In vacuum .6 seconds will do it, your launcher is 30km long.

But I do not think we have a sufficient understanding of what's needed for atmospheric passage at that sort of speed. We have never done anything like it, the closest is Galileo, the probe was half ablator and burned away half of that ablator--but in the upper atmosphere and nowhere near this sort of speed.

And you have the problem that it doesn't work, anyway--velocity is a vector, not a scalar. We won't have a shot up it's ass.

 

[Swammerdami]

Distinguished Professor Avi Loeb comments on the interstellar comet's recent course correction.

The comet's perijove minimum on March 16 will be 53.44 (±0.06) million kilometers, very slightly less than the giant planet's Hill radius on that date, 53.50 million kilometers. Interior to that radius, Jupiter’s gravity dominates over the Sun’s tide.

Loeb implies this close approach will facilitate the alien's -- (if that's what it is) -- leaving behind probes to add to Jupiter's collection of satellites.

True? And why did the alien choose to intrude only so very slightly into Jupiter's Hill sphere? If Loeb's figures are correct the closeness between the perijove minimum and the Hill radius is quite a coincidence.

I am obviously not qualified to comment on Loeb's speculations. But he does seem to be having fun!

 

[Jarhyn]

I would say you need significantly less material than most of y'all are thinking to survive the impact.

You need a computer capable of calculating the impact forces within margins, a computer you could conceivably later use as ablation or reaction mass, and then a number of small events.

This is because in space, things like the hydrophobic ejection of spore capsules happens at insane velocities and does not get the ejection "broken" by the thickness of the atmosphere.

Imagine a spore container several "spores" thick. The outer container uses hydrophobics to eject an inner container that contains some water and spore containers, and suddenly you have the means to get going well beyond the speed of sound with an utterly tiny package.

Remember that there's a cube/square problem going on, where the smaller you can make the interception device, the less energy it takes to intercept at speed.

Then, having an impactor made to take the structural collapse and damage for the internal payload would complete the journey.

I will maintain that having several hundred thousand tons of material to add to or modify and which is already going somewhere, anywhere, is a much better way of having several hundred thousand tons of material launched from a planet and accelerated yourself.

Then in a few hundred thousand years (what does it matter to the probe systems? They hibernate!) when something happens you wake up and check if you have found yourself somewhere interesting, maybe shed some probes, and continue on through the universe.

In fact this particular interstellar object has its own 'coma' or micro-atmosphere as well as frozen gassy deposits which would be VERY nice to have for future probe applications, since not only are they easily accessed reaction mass, they are also useful hydrocarbon sources for whatever other features might need to be farmed up.

 

[steve_bank]

The minimum mass of 3I/ATLAS is estimated to be over 33 billion tons, which is equal to approximately \(33\times 10^{12}\) kilograms. This is based on the object's low non-gravitational acceleration combined with the mass loss rate observed by the James Webb Space Telescope.

Given a pierced change in velocity or direction the amount of energy for a propulsion system required can be calculated.

Comet 3I/ATLAS has experienced slight, expected changes to its speed and trajectory due to a phenomenon called non-gravitational acceleration caused by outgassing, rather than a significant overall change in direction. It remains on a hyperbolic orbit, meaning it is leaving our solar system permanently.

 

[Loren Pechtel]

I would say you need significantly less material than most of y'all are thinking to survive the impact.

You need a computer capable of calculating the impact forces within margins, a computer you could conceivably later use as ablation or reaction mass, and then a number of small events.

This is because in space, things like the hydrophobic ejection of spore capsules happens at insane velocities and does not get the ejection "broken" by the thickness of the atmosphere.

Imagine a spore container several "spores" thick. The outer container uses hydrophobics to eject an inner container that contains some water and spore containers, and suddenly you have the means to get going well beyond the speed of sound with an utterly tiny package.

Remember that there's a cube/square problem going on, where the smaller you can make the interception device, the less energy it takes to intercept at speed.

Then, having an impactor made to take the structural collapse and damage for the internal payload would complete the journey.

I will maintain that having several hundred thousand tons of material to add to or modify and which is already going somewhere, anywhere, is a much better way of having several hundred thousand tons of material launched from a planet and accelerated yourself.

Then in a few hundred thousand years (what does it matter to the probe systems? They hibernate!) when something happens you wake up and check if you have found yourself somewhere interesting, maybe shed some probes, and continue on through the universe.

In fact this particular interstellar object has its own 'coma' or micro-atmosphere as well as frozen gassy deposits which would be VERY nice to have for future probe applications, since not only are they easily accessed reaction mass, they are also useful hydrocarbon sources for whatever other features might need to be farmed up.

1) Tyranny of the rocket equation. Booster to payload is exponentially linked to desired velocity vs reaction mass ejection velocity. Hydrolox running rich is the best chemical propulsion that can exist. (Using fluorine produces a higher binding energy, but it binds only one atom of hydrogen. More energy per molecule but less energy per gram. Likewise, you run hydrolox rich not only to protect your engines but because hydrogen is lighter--you actually end up with a higher exhaust velocity than if you provided enough oxygen.) Innovations come from reducing weight and reducing power consumption.

2) You still haven't addressed the problem of supersonic impact.

 

[Loren Pechtel]

Distinguished Professor Avi Loeb comments on the interstellar comet's recent course correction.

The comet's perijove minimum on March 16 will be 53.44 (±0.06) million kilometers, very slightly less than the giant planet's Hill radius on that date, 53.50 million kilometers. Interior to that radius, Jupiter’s gravity dominates over the Sun’s tide.

Loeb implies this close approach will facilitate the alien's -- (if that's what it is) -- leaving behind probes to add to Jupiter's collection of satellites.

True? And why did the alien choose to intrude only so very slightly into Jupiter's Hill sphere? If Loeb's figures are correct the closeness between the perijove minimum and the Hill radius is quite a coincidence.

I am obviously not qualified to comment on Loeb's speculations. But he does seem to be having fun!

Big problem here. Ok, it's going to pass ever so slightly within the Hill Sphere. With a perfect ejection you add another satellite? Um, no--anything right at the edge of the Hill Sphere can't be expected to be remotely stable. In the real world you find nothing out there because it gets ejected in time. Earth acquires moons every so often, some bit of rock that gets nudged into our Hill Sphere. And soon gets nudged back out. Wikipedia lists only one, although my impression is there has been another more recent one.