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More on the Pluto-Kuiper Express

Posted by michael on from the stopping-at-chambers-and-14th-st dept.

addie writes "Scientific American has a great, extensive article about Pluto and the possibilities of exploring it in the near future. Neat descriptions of Kuiper Belt and what we can learn about solar system birth and growth from the tiny planet."

2 of 89 comments (clear)

  1. tech details from the article... by bedessen · · Score: 5, Interesting
    Like most of these it was light on hardware details, but this was hidden in one of the captions:


    The spacecraft has a design mass of 416 kilograms (917 pounds) and is about the size of a small lifeboat.

    On the journey to Pluto, the probe will reach a top speed of about 70,000 kilometers per hour.

    The craft's computers will be able to store 48 gigabits of data and transmit the information to Earth at up to 770 bits per second from Pluto (16,000 bits per second from Jupiter).


    48 gigabits of radiation-hardened memory must cost a fortune...I seem to remember that Flash ram is not suited to this kind of thing since its especially susceptible to energetic particles (alpha, gamma rays) dislogding the charge trapped in the gate dielectric (which holds the information.) Anyone know how data storage is usually carried out on these things? I can't imagine using anything with moving parts, and since the craft is supposed to be powered down for most of the time while it drifts, I'd think you'd want something non-volatile. I would hate to think what would happen if there was a brief power shortage or something and all the readings from the entire mission that were queued up to be sent were lost.

    As to the 770 bits/s, I'm amazed it's even that fast. Consider that the RF power decreases as 1/r^2, where r is about 7.5 billion km. They are using a directional 2.5m antenna, lets say that's 100 dBi gain. Still, even if they managed to transmit 10W at the satellite (which is a lot for radio), we'd receive about a picowatt (1e-12) of it here on earth. I've heard that number thrown around before as a typical power level that we receive from deep space, and it boggles the mind that we can detech such faint signals... guess that's why it takes arrays of gigantic dishes with supercooled LNAs to do it. And it's great example of how power and bandwidth are related in communications. The more power your signal has at the receiver, the more information you can convey (bandwidth.)
    1. Re:tech details from the article... by stevelinton · · Score: 5, Interesting

      Actually the received power levels are much LOWER than that.

      10W at the antenna, say it's at 1cm wavelength (not sure about this, but it should be within a factor of 10). Thats a 250 wavelenth tranmitting dish, so the signal is spread over a 4 milli-radian diameter cone. At 7.5e12 m that is
      9e20 m2 spot, so a 250m dish on Earth receives
      125^2*pi / 9 e20 of the signal, which is about
      5 e-16 W.about half a femtoWatt, ignoring any imperfections in either dish, noise, absorbtion, etc.

      By radio astronomy standards this is actually quite a powerful signal. I think they work down to 10^2? W for fairly small values of ?. On the other hand, they need a 770Hx bandwidth here, which is relatively wide.

      Someone else commented on the time it would take to dump 48Gb of data over this link. This fits the mision profile beautifully. They fly past Pluto/Charon in a few hours, recording frantically on all instruments, then the slowly download the results, which coasting out into interstellar space. This mission is a fly-past, not an orbiter.