The Solar System Pony Express is a global, multi-spectral, high-resolution planetary surveyor supported by regular visits from a cycler satellite network to retrieve petabits of data for transit to Earth. The “courier” satellites use optical communications to receive 1-3 petabits from the surveyor at least once per year. They then travel close to earth where they can downlink the data quickly. By exploiting cycler orbits, the couriers need minimal onboard propulsion and can operate for decades as an augmentation to the Deep Space Network and a precursor to a Human Exploration logistics network.
A car loaded with ten petabytes of hard drives or magnetic tapes has 10,000,000 GBs of information. There are 100 weeks in two years. Cycler trajectories between Earth and Mars occur in whole-number multiples of the synodic period between the two planets, which is about 2.135 Earth years. There are about 1 million seconds in 11.5 days. You can send 10 petabits of information at 10 gigabits per second in 10 days. A close flyby of Mars would enable high bandwidth communication to a data mule. The mule would cycle back to Earth and unload 1000 times the information of slower long range transmission.
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"obscured" and "We know almost as much about the far side as we do the near" can both be true, but it takes some fancy definition creatin'. Also, as we have now seen it, we know the far side is *lighter* than the *darker* near side, by albedo measure, because of the very charcoal looking lava flows that happened more towards the Earth, on the near side. You do potentially confuse people who incorrectly think "dark" means "no light" *only*. But not those who correctly think "dark" means "no light", because it does, amongst other obscure things. They could conclude that someone is confused, however, about the obscure meanings "obscured" and "unknown" obtaining, on the far side of the Moon, lately.
"Dark" can also mean "obscured", which is still appropriate. Plus it is literally charcoal in colour.
Plus, it confuses people who think it means "no light", so that's why I keep using it.
Thank you. I expect that just searching for Aldrin would have got me lots of irrelevant stuff.
https://buzzaldrin.com/space-vision/advocacy/cycling-pathways-to-occupy-mars/
By which he means stuff like https://www.semanticscholar.org/paper/PRELIMINARY-ANALYSIS-AND-DESIGN-OF-POWERED-EARTH-Chen-Landau/d4a478673ab3bd4fddb60215579d84d62b66519b (yes, Aldrin is a co-author).
We would need sneakersats going in retrograde orbits for backup, no?
Actually, the nearest place without a direct line of sight from any particular place on Earth is the rest of the Earth, mostly. Now, with Earth to Earth power beaming, or comm sats, for that matter, a single reflector in Space gives an easy 1/3 of the way around, with one hop. This will be enuf to receive at midnite from daylight, or better, if using Earth solar cells for energy. Same for any transmission or reception from a surface, you cannot see around it even if it is a small body.
Now, the archaic use of the word "dark" as in "unknown" is no longer appropriate. We know almost as much about the far side as we do the near.
edit: "the dark side of the moon, which isn't far at all" One could also say "the far side of the Moon, which isn't dark always".
Remember Way Back? Too much data, had to stop trying.
Too much data is the *fundamental* reason that determinism aka predestination aka design is utterly impossible.
Aldrin
BTW the Earth Mars Cycler idea has always bothered me.
You can put a body into a 2 year orbit that goes by Earth at every perihelion & have it pass Mars on the 1st orbit, but then on the 2nd orbit Mars is at a different point on its orbit. To pass close to both Earth & Mars on each orbit the long axis of the cycler body's orbit has to get twisted substantially each time. Has it been demonstrated that this can be done by some sort of gravitational sling shots using Earth & Mars gravity? If so can someone point to a link that tells me the details?
SpaceX is already getting a lot of experience working with com lasers in Space and they plan to start settling Mars within a few years. It would be surprising if they didn’t set up a high bandwidth optical com link to Mars in the next 5 years.
I suspect SpaceX will put up an permanent optical link Mars to Earth and a Mars Starlink mini-constellation so there is a relatively cheap Mars ISP service – well before this is deployed.
NASA never wants to do anything unless they can push the envelope with a bespoke solution, which I can kind of sympathize with, but I think the envelope they should be pushing here is encoding schemes. You could get four or more times as many bits using twisted light, for instance.
Since the sneakernet approach is really only applicable to 2-3 planets, (The Moon is too close to justify it, and the gas giants too far away.) they'd get more bang for the buck if they just worked on increasing transmission rates.
Yes, but is the moment in history when launch costs are dropping rapidly the time to invest in getting more done with less?
Maybe NASA should be more concerned with getting more done with more?
Anyway, sneakernet is just barely feasible for Earth-Mars or Earth-Venus, once you get to the outer planets it starts to involve absurdly long cycle times.
I performed a back of the napkin calculation and came up with the following transmission characteristics:
R = 2 m (optical diameter sending laser)
Lambda = 1 micron
theta ~678 nRadians
10W laser power
P_receiver: 24 nW / m2
Receiver dish: 1000 m2
Receiver power: 24 uW
Data rate: 100 Mbit
Energy per bit: 24*10^-14 =2.4*10^-13 =240 fJ
240 fJ is typical energy per bit for a commercial optical fiber receiver, so that should be pretty easy to achieve…
Now, you may question the ease of reaching ~700 nRadians of divergence, but you have "levers" to pull to compensate for that. Increase the radiated power to 1 kW (doable with reactor power), increase the size of the receiver to ~10^4 m2 (inflatable structure), decrease the sending wavelength to 450 nm and you have already "recuperated" a factor of 4*10^3….
I question the need to transfer vast amounts of data *to* the space probe. Download images of Mars, sure.. Upload petabytes of data to the satellite… Whatever for?
So the space probe would only need a laser and a very modest telescope for receiving data. The large receiver would be orbiting the earth.
My thought exactly. You can send 3 Pb in a year with 100 Mbit per second. How hard can that be?
Use interplanetary lasers and a dedicated telescope. Note that the receiving telescope does not have to make a true depiction of the light source, only collect as much light as possible. So you could use an imperfect inflatable reflector and a wavelength filter at the sensor. Done.
I see what you mean. I guess there are places where you do not have a good line of sight back to Earth, because the Sun, or Jupiter or something is in the way.
The nearest such place being the dark side of the moon, which isn't far at all by space probe standards.
Right, but, if you're going to the trouble to send up a separate satellite for only communication, wouldn't it be more practical to have it orbit the destination and contain the decent telescope? That way it could relay information all the time rather than once a year…
I think the point is that "a decent telescope at each end" is actually a problem if we want the deep space probes to be as light and cheap as possible.
I appreciate the opportunity to test cycler orbits in practice, but is this really superior to an optical link using modern techniques, with a decent telescope at each end? Given that they're only going to use an optical link when they're nearby, anyway?
The interplanetary sneakernet, I like it.
And it's true that data transfer needs will probably surpass transfer capabilities by a long shot.
Even if laser links with interplanetary relays are created, a few Gpbs aren't enough for moving the massive amount of data robots, sensors and eventually people will create soon, forcing us to synthesize, reduce and remove anything that isn't critical from the interplanetary links.
For the rest, a bunch of cyclers carrying the proverbial tapes and getting bombarded with Tbps links when near a planet could to the trick. An still we'll have to be selective.