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Comment by bjelkeman-again | Hacker News Reader

So imagine it was actually Rama (I1, Oumuamua) and Rama II (I2). We’d be sitting here watching them zip by and not be able to do anything other than watch longingly at them. I suppose we’d get a perspective change on life in the Universe. Maybe it would increase space budgets.

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ESA is planning a "Comet Interceptor" mission that will loiter at the Sun-Earth L2 point for up to three years for something reachable to fly-by:

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

Maybe a few more probes like this in suitable locations would give us a better chance of intercepting interesting stuff passing through the solar system.

As a general rule, having an interceptor already in an orbit is slower than launching a new one. If the target is coming in on a random orbit, the interceptor floating off in space is in no better a position, on average, than earth. So it is generally more efficient to launch from earth into a more targeted orbit than redirect a craft already in a less-than-ideal position.

That said, having dozens or hundreds of probes in random orbits would be advantageous, but still much more costly.

Maybe faster to reach it but accounting for prep times to ready the probe and rocket the equation probably changes. L1-3 are actually pretty good spots for it though because they're unstable and small perturbations will drastically change the orbit.

Parking one is also predictable in budgets where a random emergency launch isn't and will cost more than a planned launch just to get things done quickly.

The L points are 'easier' but not any faster. A probe at an L point won't be able to get anywhere any faster than if it were launched from earth directly[1]. And sending a probe on a rocket to park itself at an L point wastes delta-v, as opposed to launching the same rocket directly from earth to the target.

[1] Excepting maybe a target that appears conveniently a the same L point.

The point is that you can't leave a rocket on the pad fueled and ready to go 24/7/365 because those pads are in use for other rockets and keeping them ready to fly is fairly labor intensive.

So the advantage of already being in orbit is that you don't have to go through all of the logistics of getting the rocket to the pad, prepping it for flight, getting launch permission, etc... That's a difference of a couple of weeks.

Here's a silly thought: why can't we put the spacecraft on top of an ICBM in a silo and launch when the next extrasolar object is detected? The American and Russian armed forces worked out 24/7 launch readiness in the 1960s.

Nobody wants to pay for the personal needed to staff that silo.

Because an ICBM doesn't have anywhere near the power needed for such a mission. A timely flyby of an interstellar object would need something akin to the Saturn-V or Falcon Heavy, or perhaps multiple launches of said. An ICBM is a firecracker in comparison.

I see that now. With the two booster stages, the Ulysses spacecraft weighed > 15 tons in LEO, and the Dnieper rocket has a capacity of 4.5 tons to LTO. And you do need to get to Jupiter to turn the orbital plane of the spacecraft out of the ecliptic.

ICBMs could only launch a very small probe into orbit and not even a sun centered one. They're meant for basically sub orbital ballistic trajectories for nukes and you don't need the power to put something into orbit for that.

Because launching it could trigger a response?

You can't intercept an interstellar object from a loitering orbit around the sun, with something that has basically zero delta-v (in terms of this context) onboard. The loitering orbit, by necessity, has a fairly tightly constrained velocity vector, and the interstellar object, by virtue of having escape velocity from our sun, must have a much higher velocity vector by a certain large number of kilometers per second at a minimum, basically unbounded on the upper end.

By the time you have something like a nuclear rocket in space that has the requisite delta-v, there becomes no particular reason to station it around the sun, since you can get to the right vectors from anywhere in the system.

I was wondering how the Comet Interceptor could accelerate to follow the same path as some comet thing. The short answer is https://en.wikipedia.org/wiki/Solar_electric_propulsion. It's a pretty cool technology in space, but you wouldn't want to use it for your commute to work here on Earth.

If we can see them, we can study them. We could aim radars at them to image their size/shape. We could aim lasers at them to study their surfaces. We could measure any impacts they have on magnetic fields or the solar wind, perhaps giving us insight into their means of propulsion. Sin short, if we are ready there is much that can be done short of physical contact. The real question is whether we would want to take such risks.

If you are an alien civilization with interstellar capabilities why risk a fly by from a planetary system which could easily be detected, or even intercepted, even by less advanced beings instead of just park a probe in the outskirts of the Solar system and collect as much data as you like undetected.

If then again Oumuamua was a probe traveling for millennia in search for alien life then there's no point of sending two in the same planetary system.

I'm not saying it was - but what if Oumuamua was some kind of "derelict" - an intergalactic equivalent of the "Mary Celeste" - a ghost ship from deep space?

Imagine a civilization that is maybe 500 years more advanced than ours in space travel - perhaps they have nearly conquered their solar system. Instead of building ships the regular way, they instead carve up asteroids or other similar "space rocks" and attach engines to them in some way. But something went wrong - maybe the engines got stuck "on" or something, and the entire thing was launched out beyond their system, never to be seen by them again...

...and it floated for however many of our millenia before briefly tumbling through our system. To us, it looks like a rock - we can't even optically resolve it properly, it's too fast and too far away. In (fantasy) reality, though, on board is a bunch of technology that we could probably understand, that would allow us to "leap" to hands-on human exploration (and exploitation) of our own solar system.

It might be both a blessing and a curse.

Again - sheer fantasy - and most likely it was just a shard of rock and nothing more. But is it far fetched to think that there isn't "large scale" ships or probes of some nature just drifting through space, probably completely broken down and relatively inert, moving at sub-light speeds due to various reasons, but made out of rock because it's easy to get, provides relatively good protection from space, easy to modify, etc?

We humans have already flung tiny objects out of our solar system - I can believe that larger artifacts might be something that could "drift away" as well (then again, one would think that if a civilization got to that level - they'd be able to go out and retrieve it before it got too far away).

Maybe it'd make a good science fiction story - from both ends (the creation of the "ship", the "loss" after trying to retrieve it, then the journey and the eventual discovery of it by another civilization "far away" - and how it changes the discoverers socially, politically, and technologically).

Even if Oumuamua was a probe how would that explain the second interstellar sucker we're discussing here? The closest star system that could harbor life is 4 light years away. So even if Oumuamua signaled home that it found a planet with little brown beings it would take them at least 8 years to send a second probe. Oumuamua was detected just two years ago.

>> The closest star system that could harbor life is 4 light years away.

Under the conclusion that space-born civilization would remain around stars. If we one day tap into other energy sources, ie whatever is powering dark energy, stars may become irrelevant or even awkward to be around. A civilization of kilometer-wide cities could be just beyond Pluto and still totally outside our perceptions.

In which case you don't need to send probes hundreds of meters long. You'd send something much more compact and undetectable. You don't have to worry for probe's longevity so to enclose it inside an asteroid since you're launching from relatively shorter distances.

Oumuamua as an alien probe sounds probable. Two of them in a span of two years, not so much. Besides contrary to Oumuamua this one has all the characteristics of a comet.

You are assuming that the civilization that sent it is trying to be stealthy. Not to mention at only 60,000 mph (Oumuamua) or 90,000 mph (C/2019 Q4) these probes need to be designed for many 100,000 years of travel if not millions. During that time they will see quasars, supernovas, and a wide variety of high energy particles. Might well make more sense to have many feet of rock as shielding instead of trying to keep a high power energy source going for that long. If you are patient gravity assisted slingshots makes quite a bit of sense.

And how does a second probe in a two year span fits this theory? If you send out probes with the intention to crawl the galaxy for hundreds of thousands of years then the chances of two of them entering the same region in a two year timespan are nonexistent.

Well lets assume there's probes somewhat equally distributed in the galaxy, and that there's many tiny probes and fewer larger probes. Assuming enough technology for replicating probes the number of probes in the galaxy is limited only by time and materials.

Presumably if you are watching a galaxy you are quite patient and a few 100,000 years is no big deal. With that kind of experience you've likely figured out what signature events are related to the rise of intelligence.

It's hard to speculate on the technology, sensors, and intelligence of the probe makers. Maybe the signature even to watch for is plankton, oxygen, and being in the Goldilocks zone (billions of years ago)? Changes in atmospheric chemistry related to clearing forests and cooking? (1000-10,000 years ago)? Emissions of radio waves (75 years)?

Whatever that threshold was, it might have been triggered in the past and a slow moving smaller ship was first (Oumuamua), now a few years later a somewhat faster (15%) larger ship is coming for a look.

Fun to think about anyways... at least we saw this one coming so anyone that wants a closer look will have the chance.

15% faster is too low. If they're far away, as the scenario with the long term probing implies, then the second probe should be orders of magnitude faster.

Well presumably anyone smart enough to mass produce interstellar probes would be able to make pretty decent sensors for a probe that's 100-1000 meters long (Oumuamua). Might even pick an asteroid that's long and thin and core it out and put a big telescope inside.

At least some speculation on Oumuamua lead to the conclusion that it had unusually low mass for an object so large.

Oumuamua might well have reported something interesting 1000 years ago when it was 0.09 light years away. Maybe changes in the atmospheric chemistry related to human activity.

Also note C/2019 Q4 is approaching at about 50% faster than the previous. It looks like it's a comet with a tail... or is that a retrorocket?

Send two in case one fails.

Distance might be so difficult that a "ballistic approach" within a margin of error is the only practical plan.

Dunno. There's an efficiency in making this less than perfect. It might well be more efficient to make 100 probes that have a 90% chance of making it 1 million years than trying to make 10 probes that have a 99% chance.

Not to mention there's likely some hierarchy of probes. The smallest ones relay to the bigger ones, the bigger ones can related to the huge ones, and the huge ones can report back home.

So maybe somewhere within 100 light years a factory started converting asteroids to probes and launching them at 100k miles an hour and lobbed a few our way. That would have been some 600,000 years ago.

If I were designing Rama, I’d probably make the craft change directory and/or slow down on entry into a star system. This would indicate its artificial nature, give inhabitants a better chance at intercept, and protect it from collision.

>I’d probably make the craft change directory

How do you know that the ETs use a hierarchical filesystem?

The Ramans do everything in trees.

I really appreciate this joke. Good job.

Slowing down or changing direction (in space) is equally as much work as accelerating the craft in the first place.

You don't need to slow/change direction by very much to demonstrate a very high probability of artificial origin.

Yes, but the Ramans are vastly more capable.

Of course! We should put some speed limit and CCTV warning signs at the orbit of Pluto :)

But on the serious note why would you do that if your mission is only observation, data collection or maybe launching micro probes?

Moreover, why exactly would you want to announce your presence to the beings you're observing? It's probably only going to cause chaos and upheaval in their society anyway.

Well are we seeing a comet's tail? Or a retrorocket?

I'm guessing from this book?

https://en.wikipedia.org/wiki/Rama_II_(novel)

Eh. The first one, Rendezvous with Rama, was a lot better in my opinion: https://en.wikipedia.org/wiki/Rendezvous_with_Rama

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