A million years

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p1t1o
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A million years

Postby p1t1o » Thu Jul 23, 2015 10:17 am UTC

Lets say, hypothetically, that we want to build a probe - using current state-of-the-art - for an extreme duration interstellar mission.

The probe is going wherever you want, likely one of the nearer stars, its mission is whatever you like, but probably something along the lines of contemporary probes, basically scientific close-recon.

Whatever the destination or mission, the idea is that the probe is designed to function for at least a million years.


Do we, in present day, have the capability to:

Build a power supply that will operate for a million years?
Build electronics, and other components, that will continue to function in deep space for a million years?
Build a communications system capable of transmitting data over relevant distances? (say, 10^12 kilometers?)

What other technological challenges would the timescale introduce? For example, how long before interstellar medium and radiation reduce the physical structure of the probe to dust?

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Re: A million years

Postby >-) » Thu Jul 23, 2015 11:54 am UTC

10^12 kilometers is a fraction of a light-year -- it's nowhere near enough to get to any star.

The communication at 10^12 kilometers should be easy -- we could probably do it now.
Communication at tens of light-years is harder, but we can simply wait a million years for the technology to get there before the probe starts transmitting.

Overall I'd say we can't do it.

There's a closely related topic here. It's just not over a million years.

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Re: A million years

Postby sevenperforce » Thu Jul 23, 2015 2:34 pm UTC

I daresay your energy budget is going to be extraordinarily problematic.

The Innovative Interstellar Explorer is a proposed interstellar probe which would be equipped with an Am-241 radioisotope thermal generator capable of providing power for 1000 years. Here's a really fantastic presentation on the various challenges of such a mission. But extending the generator's lifetime a thousand fold might be a bit prohibitive.

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Re: A million years

Postby cyanyoshi » Thu Jul 23, 2015 2:35 pm UTC

The big issue that jumps out to me over such a long time scale is radiation. The probe would need one heck of a radiation shield to prevent its electronics from degrading. One of the main reasons I've been told that New Horizons is just doing a single flyby over Pluto is because less time flying through space means less shielding needed, which means less mass, less fuel, and less money. Then there is the issue of power. Even the best modern solar panels may get degraded on the time scale of hundreds on years when they are in use, so the probe may need to be powerless for very long time scales. Maybe that could work if the destination is another star. Nuclear power could be an option if there is a (nearly?) prohibitively large amount of radioactive material, but again, shielding is a problem. This spacecraft has to be huge regardless.

A thousand-year probe may be doable with state-of-the-art technology. Not that such a thing would ever get funded, but that's a different issue. Ten thousand years is really pushing it (not too many things are meant to last that long). A million years is just out of the question.

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Re: A million years

Postby p1t1o » Thu Jul 23, 2015 2:40 pm UTC

I definitely made a mistake, I meant to put 10^15 km. I chose that fairly arbitrarily by multiplying 20km/s - roughly ball-park how fast Voyager I is leaving us - by a million years.

10^15km is around 100 light years.

The distance, and therefore the likely mission, is less important, the question is more about can we build a something that will function for that long - even if it is just a box with a blinking light and a radio that transmits a beep every [unit of time] or so.

Can we build a blinking beeper that will still be blinking and beeping in a million years, can it survive space travel for that long and could we still detect its beeps given that it will be some arbitrarily long distance away?

I feel like the biggest challenge would be the power source, and ability to withstand a million years of wear-and-tear - ***EDIT** as the two previous posts mention.


Is it possible that *small* may be the way to go? A micro-probe might intercept less radiation and fewer particles and require less power? Though I think that the limitations on power are given by the half-lives of various things rather than the wattage required. Solar power is definitely out due to fragility of panels I suspect, though the dormant-whilst-travelling might be a good plan.

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Re: A million years

Postby meat.paste » Wed Jul 29, 2015 9:47 pm UTC

Given civilization is only 5-10 thousand years old, and it has been an enormous technical challenge to create a clock that will last 10,000 years, I think we are a long way from building something that will last 100x longer than that.

A thermogenic power source that lasts for 1E6 years must have a radio isotope with a half like longer than 100,000 years. I also want the energy from the decay to be beta or alpha decay (gamma would leave the probe without much heat being generated). U-234 might work. It decays via alpha emission (each alpha particle is 4.8 MeV, or 7.7E-13 J) and has a half life of 246 kyears. If I want a 100W transmitter, and I send out a pulse every year, then I need to get about a 1/3 J of energy per day. If the energy storage and heat to electrical energy is 10%, then I need 4.3E12 decays per day at the end of the journey. I need to start with a lump of U-234 that generates 16.5 times more decays at the starts of the journey, or 7.2E13 decays per day or 2.6E16 decays per year. The lump of U234 would have to lose about 3ppm of it's atoms to decay in the first year, so the initial lump would have to contain 9E21 atoms, which is less than a mole and would weigh about 4 grams.

This seems ridiculously light. If the efficiency is much less than 10%, then the mass of the fuel would get big pretty quickly. I may also have made a math error. I'll check it later.
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Re: A million years

Postby Flumble » Wed Jul 29, 2015 10:37 pm UTC

meat.paste wrote:This seems ridiculously light.

Well, you did assume that you're sending one single pulse once in a year and that something on the ship can simply collect the full 1/3 J/day and not lose it over the course of a year.
These are ridiculous assumptions compared to the activities of every satellite launched so far. The on-board electronics aren't designed for 0 K, so they require ~30 W* to keep themselves warm.
But assuming the whole satellite is a lump of uranium surrounded by a capacitor connected to an antenna, chances are 4 grams of U-234 is sufficient.

*either my memory serves me well, or I'm completely making this number up.

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Re: A million years

Postby p1t1o » Thu Jul 30, 2015 1:09 pm UTC

"a lump of uranium surrounded by a capacitor connected to an antenna"

Incredibly simple designs such as these are probably the way to go, and are a totally valid answer to the initial question :)

To go very "stone-age", is there a material that would make it possible for the "probe" to be a single monolithic piece of matter, of radioactive nature, such that its own radioactivity serves as the "signal" - able to be detected even as it approaches its maximum seperation at 1000000years?

It hardly fits the definition of "probe" but we are talking a million years, so some sacrifice (!) of complexity is required...

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Re: A million years

Postby Elmach » Thu Jul 30, 2015 6:01 pm UTC

p1t1o wrote:"a lump of uranium surrounded by a capacitor connected to an antenna"

Incredibly simple designs such as these are probably the way to go, and are a totally valid answer to the initial question :)

To go very "stone-age", is there a material that would make it possible for the "probe" to be a single monolithic piece of matter, of radioactive nature, such that its own radioactivity serves as the "signal" - able to be detected even as it approaches its maximum seperation at 1000000years?

It hardly fits the definition of "probe" but we are talking a million years, so some sacrifice (!) of complexity is required...


One problem: it is really hard to transmit data long distances. I think New Horizons is near the limit before getting drowned by the background radiation (near might be a few orders of magnitude, however). It would need to emit a lot of radiation to be able to be seen from earth with a telescope.

A single monolithic piece of matter will emit radiation in all directions [citation needed] so it would need to emit a lot of radiation. Of course, we would know where it is, unless we forgot.

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Re: A million years

Postby cyanyoshi » Thu Jul 30, 2015 10:14 pm UTC

What if you just launched a disco ball into space, shooting a laser at it every so often? Would that count?

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Re: A million years

Postby sevenperforce » Fri Jul 31, 2015 1:17 pm UTC

The flux from the CMB is 3.01e-6 W/m2. To match this by pure undirected radiative emission alone at a distance of 1e15 km or 100 light years, our "probe" will need to be putting out 3.39e31 W of power...roughly 100,000 times more than the power output of the sun, if I've done my math right.

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Re: A million years

Postby speising » Fri Jul 31, 2015 4:21 pm UTC

sevenperforce wrote:The flux from the CMB is 3.01e-6 W/m2. To match this by pure undirected radiative emission alone at a distance of 1e15 km or 100 light years, our "probe" will need to be putting out 3.39e31 W of power...roughly 100,000 times more than the power output of the sun, if I've done my math right.

How do we see simple stars, then?

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Re: A million years

Postby sevenperforce » Fri Jul 31, 2015 4:49 pm UTC

Stars radiate in the visible spectrum. One reason we have trouble finding brown dwarves that could be lurking very close to us is that they radiate closer to the microwave spectrum, where there's more background noise.

At least that's what I think -- I could be wrong.

The flux requirements would be lower if the "probe" was radiating in a different spectrum, but I'm not sure what the noise levels are like in other EM regions; I was just calculating the CMB because that's an easy one. There's far less noise in the visible spectrum, but producing a visible emission requires significantly more power, which is why some sort of lasing is a much better option.

Of course even lasing itself is still problematic. This post suggests that the divergence of a space communications laser is on the order of 3.5 microradians. A pencil-thin beam coming off a laser and traveling 100 lightyears would expand into a circle with a radius of 22.2 AU, a little more than the orbit of Uranus. You're going to need a pretty hefty power supply to put out enough flux for such a beam to still be detectable from Earth. Even if you set up an orbiting receiver telescope with a reflecting mirror the size of Texas, it would still only be able to pick up 2% of a trillionth of the laser's power ouput.

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Re: A million years

Postby Eebster the Great » Sun Aug 02, 2015 8:59 pm UTC

Presumably if you're using radio communication you wouldn't choose a band close to the cmb.

If you're just talking about a decaying lump of metal, that's probably gamma radiation (I can't see how else we could detect it remotely), and I don't think gamma ray telescopes have the required sensitivity, though I could be wrong about that. I suppose it depends on the size of the chunk of metal. You also have to consider that a lot of the emissions from the interior will just be absorbed as heat and reradiated slowly in the infrared spectrum.

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Re: A million years

Postby p1t1o » Mon Aug 03, 2015 2:54 pm UTC

cyanyoshi wrote:What if you just launched a disco ball into space, shooting a laser at it every so often? Would that count?


Yeah, good call, but only if we could still detect the reflections at its million-year distance and as long as it remains shiny after a million years of space travel 8-)

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Re: A million years

Postby Sableagle » Mon Aug 03, 2015 6:07 pm UTC

sevenperforce wrote:Of course even lasing itself is still problematic. This post suggests that the divergence of a space communications laser is on the order of 3.5 microradians. A pencil-thin beam coming off a laser and traveling 100 lightyears would expand into a circle with a radius of 22.2 AU, a little more than the orbit of Uranus. You're going to need a pretty hefty power supply to put out enough flux for such a beam to still be detectable from Earth. Even if you set up an orbiting receiver telescope with a reflecting mirror the size of Texas, it would still only be able to pick up 2% of a trillionth of the laser's power ouput.

That does at least save the probe the challenge of figuring out where in the Earth's orbit to aim in order to get the signal home.
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Re: A million years

Postby mfb » Tue Aug 04, 2015 11:11 pm UTC

Forget radioactive decays as signal. There is significant cosmic background, even our whole nuclear inventory [i]on Pluto[i] would probably be impossible to distinguish from background on Earth.

What about a nuclear explosion? Electronics is needed anyway. The nuke also needs chemical explosives that are stable for a million year, and a suitable neutron source. Plutonium+Beryllium could make a long-living neutron source.

A 24 MT bomb (heavy!) would release 1017 J of energy. In a distance of 10 light years, this is 70 eV/m^2. A single detected x-ray doesn't help and there are no telescopes that could hope to find more than one. If we magically make the whole energy get radiated away with a sun-like spectrum in a millisecond, we get 11fW/m^2, roughly a magnitude 15 star or the same energy we get from a magnitude 25 star in 10 seconds, or from magnitude 35 in a day. Might be visible to telescopes today, but not easy. Hubble sees stars down to ~31, but only with very long exposure times (weeks). E-ELT will be able to collect much more light.

A directed beam with a narrow wavelength can reduce the required power significantly.

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Re: A million years

Postby >-) » Tue Aug 04, 2015 11:36 pm UTC

I haven't been able to find any data on this but are there any EM spectrum wavelengths that just don't appear at all from natural sources? If there is such a frequency, sending just one photon back should be enough to transmit data.

For example, ELF radio waves have energy on the order of 1E-32 joules. Suppose your transmitter broadcasts evenly over one steradian. A 1000 sq km telescope* at 10 light years is 1E-25 steradians, so you get a cost of 1E-7 joules per photon, which is pretty cheap.

Even if your transmitter only has 1% efficiency and you can only detect one in ten thousand photons, you end up with ~1J/photon

*which I assume will be trivial to construct in a million years

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Re: A million years

Postby Eebster the Great » Wed Aug 05, 2015 12:54 am UTC

ELF radio requires a gigantic detector anyway, so 1000 sq km is not an issue even with today's technology. Unfortunately, the ISM is opaque to ELF. Besides, the antenna would have to be thousands of miles long iirc.

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Re: A million years

Postby sardia » Wed Aug 05, 2015 1:38 am UTC

What about using machines that created new machines, maybe with some random changes. As each reached maturity, they simply create more machines. You could power the whole contraption with a massive proton-proton chain fusion reactor as it made its sojourn around the galaxy. Estimated duration, approx 4 billion years.

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Re: A million years

Postby Eebster the Great » Wed Aug 05, 2015 4:17 am UTC

Doesn't the proton-proton change require, like, a whole star?

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Re: A million years

Postby Copper Bezel » Wed Aug 05, 2015 7:20 am UTC

is the joke.
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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Re: A million years

Postby >-) » Wed Aug 05, 2015 4:10 pm UTC

if not elf radiowaves, how about gamma rays. Takes about 1E20 times more energy but if you increase telescope area to 1E9 sq km, you get a manageable 1E7J/photon

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Re: A million years

Postby Eebster the Great » Wed Aug 05, 2015 6:10 pm UTC

Right, your telescope would need to be only 8 times the cross-sectional area of the Earth.

Unfortunately, gamma rays of all energies are also produced in space, so with a one-pixel resolution there would be no way to distinguish the probe from other sources.

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Re: A million years

Postby >-) » Thu Aug 06, 2015 2:47 am UTC

well then, with an alternate angle of attack, why not launch a new probe every few years to act as relay stations. the planets might not be aligned properly, making probe launch tricky, but that's nothing that can't solved with brute force.

OR, just wait a million years, and when the probe has info to transmit, send another probe toward it at ~1C, have it read the data from the original probe, and send the data back to earth using some vastly powerful transmitter and energy source i assume will be available after a million years of technological development.

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Re: A million years

Postby Eebster the Great » Thu Aug 06, 2015 6:36 am UTC

The most feasible form of interstellar communication is surely just conventional radio transmission.

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Re: A million years

Postby >-) » Thu Aug 06, 2015 3:16 pm UTC

sure, i just wasnt sure if it might get drowned out by other sources like cmb or exoplanets' magnetospheres or blocked by objects in space. As i said before, it would be nice if there was data somewhere on the "brightness" of space in all frequencies of em

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Re: A million years

Postby Eebster the Great » Thu Aug 06, 2015 7:08 pm UTC

There is a frequency band called the "water hole" between 1420 and 1666 MHz (corresponding to spectral lines for hydroxyl and hydrogen) that is apparently pretty quiet. I don't know if it's the quietest, but judging by SETI projects, it is quiet enough for modern technology to communicate with distant stars, at least in principle.

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Re: A million years

Postby >-) » Fri Aug 07, 2015 4:48 am UTC

Slightly off topic, but would you happen to know how temperature corresponds to intensity or power?

Image
this image seems to suggest that the CMB has an intensity of around 3K, but from what I know, doesn't temperature just specific a specific black body spectrum?

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Re: A million years

Postby Eebster the Great » Fri Aug 07, 2015 8:25 am UTC

Well, kelvin is a unit of temperature, not intensity. Intensity is the power per area per solid angle . . . per wavelength (W·sr-1·m-3 in SI, though you won't usually see it written that way; unfortunately intensity has many definitions in many contexts). In this sense, it is not immediately related to that graph.

The image you have confuses me, and I would be interested to see where it is from. Typically when people talk about the temperature of radiation, they mean the peak frequency emitted by a black body of that temperature. Temperature should simply be inversely proportional to frequency in that sense, so clearly this is not a graph of that (y = b/x for where b is Wien's displacement constant).There is also the notion of temperature of a photon gas, but that makes even less sense here. I really don't know what it is saying.

Someone help us understand what is going on.

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Re: A million years

Postby jaap » Fri Aug 07, 2015 8:43 am UTC

Eebster the Great wrote:Well, kelvin is a unit of temperature, not intensity. Intensity is the power per area per solid angle . . . per wavelength (W·sr-1·m-3 in SI, though you won't usually see it written that way; unfortunately intensity has many definitions in many contexts). In this sense, it is not immediately related to that graph.

The image you have confuses me, and I would be interested to see where it is from. Typically when people talk about the temperature of radiation, they mean the peak frequency emitted by a black body of that temperature. Temperature should simply be inversely proportional to frequency in that sense, so clearly this is not a graph of that (y = b/x for where b is Wien's displacement constant).There is also the notion of temperature of a photon gas, but that makes even less sense here. I really don't know what it is saying.

Someone help us understand what is going on.

The image is from here:
http://www.setileague.org/general/waterhol.htm
The page doesn't really explain it much further.

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Re: A million years

Postby cyanyoshi » Fri Aug 07, 2015 1:49 pm UTC

>-) wrote:Slightly off topic, but would you happen to know how temperature corresponds to intensity or power?

[image]

this image seems to suggest that the CMB has an intensity of around 3K, but from what I know, doesn't temperature just specific a specific black body spectrum?

Kelvins are used to describe noise temperature, which is proportional to intensity. Essentially, it takes less power to send a detectable signal over a frequency range that is less noisy. (As an aside, what the heck is 0 Hz doing on a log scale?)

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Re: A million years

Postby mfb » Sat Aug 08, 2015 5:20 pm UTC

I think we have to interpret the diagram as "at 1 GHz, the radiation is as intense as we would expect from a 3 K blackbody radiation", "at 100 MHz, the radiation is as intense as we would expect from a 900 K blackbody radiation" and so on.

Gamma rays are hard to focus. Lasers or radio waves are the most promising options, or nuclear explosions if we don't care about the future life of the probe.

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Re: A million years

Postby Eebster the Great » Sat Aug 08, 2015 10:11 pm UTC

Would maser communication work? Would it be more efficient than conventional radio communication?

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Re: A million years

Postby LaserGuy » Mon Aug 10, 2015 5:02 pm UTC

>-) wrote:Slightly off topic, but would you happen to know how temperature corresponds to intensity or power?


The Stefan-Boltzmann law is usually used for this.

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Re: A million years

Postby EdgarJPublius » Sat Aug 15, 2015 2:17 am UTC

Personally, I suspect that any probe we could send out on a million year mission now, would likely arrive at it's destination to find Humans already there.

As far actually designing such a probe, trying to keep it powered continuously, even minimally, is probably not possible with current technology over the proposed timescale and through interstellar space. You'd have to make the probe so that it goes dormant in interstellar space, but wakes up again when it gets close enough to star to warm up the electronics and power the solar collectors.

Likewise, receiving communications from the probe over interstellar distances is likely not possible with current technology. If there isn't anybody at the destination to 'catch' the probe, then it should be capable of navigating a return trajectory, most likely via solar sail.
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Re: A million years

Postby ucim » Sat Aug 15, 2015 6:29 am UTC

Even if we could, to me the more interesting question would be how to ensure that there's anybody listening when the probe's message is sent back.

For comparison, the time frame in question is three to five times longer than the age of homo sapiens itself. The mission would be something like having a curious early human writing a question on a cave wall, with a space for an answer, and "coming back" a million years later to see what the answer was. Think of the time capsules that were left in the past (hundred? years), right here on this planet, intending to be opened about now, whose location has been completely forgotten.

The longest lived civilizations known (to me) have been around for at most a hundredth of the time in question.

A million years is enough time for significant evolution to take place, never mind any intelligent design we may have the hubris to inflict upon our progeny.

Probably the largest time-scale thing humans have done have been things like the cathedrals (100 years). It's real hard to sustain interest in a project started generations ago, and whose payoff won't come for generations. And in this case, we're talking fifteen thousand generations on each side. Who has that kind of attention span (besides Phssthpok)?

I think if you want this thing to last a million years (and do something), it will have to be a colony of living things. But even so, when it gets there, it won't be the same as what you sent, and probably won't care about the mission you sent it on.

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Re: A million years

Postby Eebster the Great » Sat Aug 15, 2015 7:16 am UTC

Keeping the electronics warm is not a problem if you make the hull out of a radioactive material with the proper half-life. But then you run into problems with errors caused by radiation. If you can correct errors with high enough reliability (i.e. 100% reliability) with less power than is produced by the isotope, it might be possible. Cooling and rewarming is probably a better solution, but then you need extreme shielding.

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Re: A million years

Postby Beavertails » Mon Aug 17, 2015 5:41 pm UTC

Part of the premise was that we could send the probe wherever we wanted. What if we sent it on a trajectory designed to orbit our own sun at some nominal distance that is less than 1LY. (The orbit can even potentially be extremely elliptical so that it passes w/in the Earth's orbit on every flyby.)

What would that mean for the fuel requirement / or the power needed to keep the probe warm enough and/or keep the communications array functional?

Would it be more feasible then?

No one said we HAD to send it towards Wolf 359 and back to check on Borg activity after all.
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Re: A million years

Postby Eebster the Great » Mon Aug 17, 2015 7:11 pm UTC

I wonder if we could send the probe on an orbit that we could be sure would be stable for a million years. Orbits tend to be chaotic on long time scales, although I don't know if a million years really counts as "long" in that sense. Maybe we could find a stabilizing resonance for it or something.


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