Exploring the Galaxy Using Space Probes

astro-ph/0701238
Title: Exploring the Galaxy using space probes
Authors: Rasmus Bjoerk
Comments: 6 pages, 4 figures, accepted by International Journal of Astrobiology

This paper investigates the possible use of space probes to explore
the Milky Way, as a means both of finding life elsewhere in the Galaxy
and as finding an answer to the Fermi paradox. I simulate exploration
of the Galaxy by first examining how long time it takes a given number
of space probes to explore 40,000 stars in a box from -300 to 300 pc
above the Galactic thin disk, as a function of Galactic radius. I then
model the Galaxy to consist of ~260,000 of these 40,000 stellar
systems all located in a defined Galactic Habitable Zone and show how
long time it takes to explore this zone. The result is that with 8
probes, each with 8 subprobes ~4% of the Galaxy can be explored in
9.57*10^{9} years. Increasing the number of probes to 200, still with
8 subprobes each, reduces the exploration time to 4*10^{8} years.

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My 2 cents:

1. Aside from confiming something that we already know, that sending
probes is an incredibly difficult thing to do (even though it ignores
the enormous engineering and economic reasons why it is so hard to
explore with probes) nothing can be ruled out by this mental exercise
(ie. it's less useful than the Drake equation and does nothing to
resolve the so-called Fermi Paradox because there are too many other
factors that could affect the answer to Fermi's question.)

2. The initial stellar population estimate is from 1973 and is too low
(although perhaps his local densities are correct?)

3. The space probe longevities are impossible (as noted by the author)
making the exercise mute.

4. Space probes probably won't have to be within a stellar system to be
able to detect whether or not they are inhabited (i.e. advanced sensor
technologies should permit them to operate at considerable distances,
letting them examine multiple stars at a median distance between them
and still be able to detect civilizations with technological and
physical footprints, if, and that's a BIG IF, they are like ours, i.e.
light pollution, EM leakage, modification of planetary surfaces etc.)

5. Speculation referred to by the author about the probes turning
against their makers are old science fiction (and pre-date the sources
cited, see the Berserker series by Fred Saberhagen, HAL from Arthur C.
Clarke's 2001, NOMAD [Star Trek TV show] and V'ger [Star Trek movie]
and others) and are an interesting genre, but it doesn't help to
resolve Fermi's question (which is not a paradox) or even shed new
light on it.

Regards, Jason H.



Joseph Lazio wrote:
astro-ph/0701238
Title: Exploring the Galaxy using space probes
Authors: Rasmus Bjoerk
Comments: 6 pages, 4 figures, accepted by International Journal of Astrobiology

This paper investigates the possible use of space probes to explore
the Milky Way, as a means both of finding life elsewhere in the Galaxy
and as finding an answer to the Fermi paradox. I simulate exploration
of the Galaxy by first examining how long time it takes a given number
of space probes to explore 40,000 stars in a box from -300 to 300 pc
above the Galactic thin disk, as a function of Galactic radius. I then
model the Galaxy to consist of ~260,000 of these 40,000 stellar
systems all located in a defined Galactic Habitable Zone and show how
long time it takes to explore this zone. The result is that with 8
probes, each with 8 subprobes ~4% of the Galaxy can be explored in
9.57*10^{9} years. Increasing the number of probes to 200, still with
8 subprobes each, reduces the exploration time to 4*10^{8} years.

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Some day I need to get my response into a single, general purpose response in
favor of probes. My interest arose when I read of the energetics of probes being
less than those of RF transmitting at about 20 light years.

This is based solely upon technologies being developed today. Granted they are
still too far in the future to know their ultimate form and practicality.

Jason H. wrote:
My 2 cents:

1. Aside from confiming something that we already know, that sending
probes is an incredibly difficult thing to do (even though it ignores
the enormous engineering and economic reasons why it is so hard to
explore with probes) nothing can be ruled out by this mental exercise
(ie. it's less useful than the Drake equation and does nothing to
resolve the so-called Fermi Paradox because there are too many other
factors that could affect the answer to Fermi's question.)

It starts depending upon what one means by a probe. It seems obvious it will be
some sort of electronic system and the size of it can be established by the rate
of miniaturization. When one talks economics one does not start with house sized
probes rather with grapefruit sized probes.

How are they made? An autonomous factory on an asteroid.

How do they travel? Solar sails.

How do they report? They come home.

When does the first one leave? Less than a century from now.

When do they start coming back even with negative results? In less time than
HSS has been around.

2. The initial stellar population estimate is from 1973 and is too low
(although perhaps his local densities are correct?)

3. The space probe longevities are impossible (as noted by the author)
making the exercise mute.

Self repairing probes and self-repairing factories are sent out. And there is
also the possibility of self-replicating probes. When they arrive in a solar
system the move to convenient asteroid and manufacture planetary landing probes.

4. Space probes probably won't have to be within a stellar system to be
able to detect whether or not they are inhabited (i.e. advanced sensor
technologies should permit them to operate at considerable distances,
letting them examine multiple stars at a median distance between them
and still be able to detect civilizations with technological and
physical footprints, if, and that's a BIG IF, they are like ours, i.e.
light pollution, EM leakage, modification of planetary surfaces etc.)

Actually detection technology should increase much faster than the time it
takes to get a probe closer to a target. That is why I expect we will be looking
at the surfaces of extra-solar planets before anyone starts sending probes.

5. Speculation referred to by the author about the probes turning
against their makers are old science fiction (and pre-date the sources
cited, see the Berserker series by Fred Saberhagen, HAL from Arthur C.
Clarke's 2001, NOMAD [Star Trek TV show] and V'ger [Star Trek movie]
and others) and are an interesting genre, but it doesn't help to
resolve Fermi's question (which is not a paradox) or even shed new
light on it.

(This came out way too long but the last sentence is the bottom line. The
filler is how to get to the last sentence. Scroll down if bored.)

Fermi is not a real issue. If 1/100 of 1% of the UFO sightings are alien
visitors Earth is a popular tourist destination. What is the point of being a
tourist if can't go native? Put on your human suit or your elephant suit and enjoy!

From my thinking in soc.history.what-if with the back in time WIs I am fairly
convinced we may be nearly the last generation that has a chance of
communicating with the ancient Greeks or Romans or even Renaissance folks for
lack of common cultural references. As a kid I saw coal being handled for winter
heat and I have had to explain what little I remember it was like to the 50 year
old youngsters. Very few people today have ever ridden a horse and I haven't
since a teenager. My son never has as there was never a place to ride one near
any place we have lived. Our first hand experience with "natural" fire is the
rustic fireplace and then without newspapers forget getting a fire started.
Every other use of fire we have common experience with is something that did not
exist a couple hundred years ago. Explain to the Romans how to make flint and
the steel to strike it with.

Add a few hundred more years of technology, the kind needed to be a space
tourist, and there would be next to nothing of a technological nature we could
communicate. Go back in time to 1965 and impart integrated circuit technology?
Fat chance. The best you could say is that investing in it will pay off.

In any event trying to convey advanced technology would make you sound like
Brad Guth.

What could you possibly take back in time to Rome to gain enough money to live
on? There is really very little. Knives and swords of modern steel and sugar are
about it for one reason or another. They can't work our raw steel. Medicines
sound great but it takes a wide range of them and good diagnostic ability but
you don't know any incantations to invoke the right god so no one will trust
you. Crank powered LED flashlights are a possibility but expect people to do
dumb things with them like use them underwater and a dozen other things even our
young children know not to do.

I did not read First Contact but from what the movie showed the major flaw was
the absence of the complete manufacturing processes of each component back to
the raw materials as well as test specs and the manufacturing processes
themselves. And then all the technology to begin the manufacturing processes.
Essentially the transmission is the sum total all the entire technology and
science upon which the device is based.

Caesar likes your .45 and asks how to make more of them. Where do you start?

Say you just want to raise the locals to the next step in something. You first
trip has to totally research how they do that something already. Say for example
better quality transparent glass in the Renaissance. Totally research their
methods then look up the modern method then duplicate the old method and adapt
the modern method to it and then go back and teach it. And that is trivial
compared to a multi-technology based object.

Say you want to speed the industrial revolution by improving the steam engine.
Certainly you can introduce single improvements a few years before its time if
you think that is worth it. But to jump an early brass engine to one suitable
for a steam locomotive you have to start with improving mining techniques, the
metallurgy of iron, building factories to produce it, all the technical advances
in the engine itself and in the end you have advanced history maybe 40 years out
of 80 and you have NOT created a demand for trains as there are not enough
people or great enough distances to use them nor even the excess population to
lay the rail lines.

There are very few things in our history that could be introduced at any time
and be of major value. The chimney was invented about 1000 AD (believe it or
not) but would have been of value any time in history and could have been built
any time in history. The horse collar and stirrup are other inventions. The
compass is another. There are not many more basic inventions that would have
worked at any time in history and have been of significant value. Even the
compass would not have been that important when most commerce was in the Med or
followed the shore. The horse collar and stirrup depend upon Earth animals so
alien visitors cannot introduce them.

Which leads us back to the common tourist wisdom: Blend in and do not try to
educate the locals. It is wasted on the locals and embarrasses the tourist.

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