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Voyager Probes Give Us ET's View
astroengine writes "For the first time, scientists have been able to measure a type of radiation streaming out from the Milky Way that in other galaxies has been linked to the birthplaces of young, hot stars. There was no way to make our own galaxy's measurement of the radiation, known as Lyman-alpha, until the Voyager probes were about 40 times as far away from the sun as Earth — any closer and the solar system's own emissions drowned out the fainter glow from the galaxy."
Pictures of young, hot, stars?! Count me in!
Voyager has to be the coolest space probe ever. It's been operating for 34 years straight and is LEAVING OUR GALAXY, still receiving commands from Earth and still transmitting data back. If that's not marvelous, I don't know what is. Anyone interested should read: http://en.wikipedia.org/wiki/Voyager_1
You never know when such research will pay off. The US and EU is scrapping programs now while China, India and a few others try to get into space, you can bet that a lot of cool research will be coming from that side of the globe in the next 30 years.
Imagine if we could launch a probe now with what we have available. We could cheaply launch 10's of much faster probes with incrementally better sensors for the price of the voyager program (~$3B in today's dollars).
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That must be one of the most successful space exploration projects so far, too bad it's running out of juice!
It receives commands from Earth, and it's 34 years old. What's to keep enemies of the United States from sending it bad instructions, or from collecting all data it sends back to us? I realize that Voyager isn't of any military importance, but I guess this is more of a hypothetical question. Does it use some type of encryption? Is that encryption still unbreakable today? The keys haven't been compromised after all this time? Just curious.
Last I heard, the voyagers are about 100-110 AUs from the sun. Is the summary incorrect or do you only need to be 40 AUs from the sun to make these measurments? In which case, why is it news now and not in the 80s/90s when they reached this distance?
A surprisingly large part of me feels good that those amazing spacecraft are so far away, nearing the depths of interstellar space and will continue on for as near as makes no difference to forever. An even larger part of me regrets that I won't be around to see the day when they make contact with another civilisation.
You're confusing antenna angular resolution with antenna effective area. The problem with reception of the Voyager probes isn't being able to discern them among other relevant signals. The problem is that the signals are so weak that they need an antenna with large area just to collect enough energy per bit to reliably overcome noise generated in the receiving system. Until you do this, you can't get a signal strong enough for your correlator to work on -- all you'll get out of the correlator is noise, because that's all that's going in to the correlator from your receivers.
Ergo, the 70m dishes.
This seems to be a pretty good description of the Voyager telecom system. Based on this, the X-band transmitter provides 18 watts to the high-gain antenna, which has a gain of 48 dB, for an effective radiated power of just over 18 * 10^(48/10) = 1.1 megawatts. (At least at launch; I assume the output power will have fallen somewhat over the intervening decades, as the RTG output falls and RF components age.)
This sounds like a healthy amount of power, and it is, but keep in mind that antenna gain comes easy at X-band (8 GHz), and such ERP levels are common in terrestrial point-to-point microwave links. Also keep in mind that the half-power beamwidth of the high-gain antenna is only 0.5 degrees, so any alien not in that narrow beam would hear substantially nothing.
Also, to answer your direct question, the frequencies and beam shapes are different, and one has to consider the shielding effects of the ionosphere vs. frequency, but just to compare (US regulations, YMMV): AM broadcast stations (~1 MHz) are usually limited to 10 kW with more-or-less 0 dB gain antennas, for an ERP of 10 kW; but UHF TV stations (~500 MHz) may have an ERP of up to 5 MW.
Of course, there are a zillion broadcast stations, all transmitting non-coherently (some would say incoherently), but only two Voyagers, so that would have to be taken into account, too.
Out of interest, are there many computers down here on the planet that have been operating constantly for 34 years?
I'm sure there are embedded and industrial control systems that have been running that long, if only though sheer dumb luck. It would need reliable power, but there's a lot of that around. The computers that run security alarm systems come to mind. Most of them will have had something happen by now, but I bet someone's gotten lucky. Same for industrial control systems which have battery backup and run a continuous process.
Telecom would be another. The older digital telco switches are basically big computers. They're highly redundant and as simple as possible, and practically never go down. I'd bet money there are some with uptimes like that.
But the main reason I feel confident for saying so is that there are so many of those sorts of systems. With a large enough population, even rare events become common.
The Voyager craft are somewhat unique in that there are only two of them . (And they're not exactly reachable for sustaining maintenance.)
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I'm as big a fan of the smaller, faster, cheaper paradigm as anyone but there is one thing about ALL these space probes that CAN'T be miniaturized.
It's the communications subsystem, most notably the antenna. I'm pretty sure that it can't be miniaturized due to the laws of physics dictating aperture and gain etc. (Unfortunately, I am not an physicist :( Also, ever since the Galileo probe antenna DISASTER (I call getting much less than one-hundredth the bandwidth a disaster) caused by the fact that the antenna didn't unfurl properly, means NASA is very conservative about using lightweight technologies. So unless the probe is designed to return to earth-space, bandwidth requirements will dictate a large (and heavy) antenna. (Still I'm not sure if the weight-bandwidth rule applies to coherent laser/maser communications, I understand that an upcoming mars orbiter will test using a laser link for much higher bandwidth).
That said, the advances in miniaturization (which extends to sensors and complete lab-on-a-chip) are extremely encouraging. Perhaps probes of the future will have a main "mothership" which will provide the communications link to lots of semi-autonomous micro-probes.