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posted by chromas on Friday July 30 2021, @03:06PM   Printer-friendly

No Antenna Could Survive Europa's Brutal, Radioactive Environment—Until Now

Ultimately, when NASA's Jet Propulsion Laboratory (JPL), where I am a senior antenna engineer, began to seriously consider a Europa lander mission, we realized that the antenna was the limiting factor. The antenna needs to maintain a direct-to-Earth link across more than 550 million miles (900 million km) when Earth and Jupiter are at their point of greatest separation. The antenna must be radiation-hardened enough to survive an onslaught of ionizing particles from Jupiter, and it cannot be so heavy or so large that it would imperil the lander during takeoff and landing. One colleague, when we laid out the challenge in front of us, called it impossible. We built such an antenna anyway—and although it was designed for Europa, it is a revolutionary enough design that we're already successfully implementing it in future missions for other destinations in the solar system.

[...] I've mentioned previously that the antenna will need to transmit signals up to 900 million km. As a general rule, less efficient antennas need a larger surface area to transmit farther. But as the lander won't have an orbiter overhead with a large relay antenna, and it won't be big enough itself for a large antenna, it needs a small antenna with a transmission efficiency of 80 percent or higher—much more efficient than most space-bound antennas.

So, to reiterate the challenge: The antenna cannot be large, because then the lander will be too heavy. It cannot be inefficient for the same reason, because requiring more power would necessitate bulky power systems instead. And it needs to survive exposure to a brutal amount of radiation from Jupiter. This last point requires that the antenna must be mostly, if not entirely, made out of metal, because metals are more resistant to ionizing radiation.

The antenna we ultimately developed depends on a key innovation: The antenna is made up of circularly polarized, aluminum-only unit cells—more on this in a moment—that can each send and receive on X-band frequencies (specifically, 7.145 to 7.19 gigahertz for the uplink and 8.4 to 8.45 GHz for the downlink). The entire antenna is an array of these unit cells, 32 on a side or 1,024 in total. The antenna is 32.5 by 32.5 inches (82.5 by 82.5 centimeters), allowing it to fit on top of a modestly sized lander, and it can achieve a downlink rate to Earth of 33 kilobits per second at 80 percent efficiency.

By way of comparison, consider that the V.34bis standard (which allowed a top speed of up to 33.6 kbit/s bidirectional data transfer over phone lines) was finalized and issued in February of 1998. It was in September 1998 that the first draft of V.90 was announced and which finally enabled faster speeds. See the extensive history of modems on Wikipedia.

It bears noting that landlines presented much less of a challenge to communications than what would be experienced by the lander. Especially since light (or a radio wave) takes up to 50 minutes to get from Earth to Jupiter!


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  • (Score: 2) by MIRV888 on Friday July 30 2021, @05:16PM (7 children)

    by MIRV888 (11376) on Friday July 30 2021, @05:16PM (#1161405)

    I should have went into astronomy.

    • (Score: 2) by DannyB on Friday July 30 2021, @05:48PM (4 children)

      by DannyB (5839) Subscriber Badge on Friday July 30 2021, @05:48PM (#1161415) Journal

      To boldly go where none of the various genders have gone before!

      --
      People today are educated enough to repeat what they are taught but not to question what they are taught.
      • (Score: 3, Interesting) by Tork on Friday July 30 2021, @06:04PM (2 children)

        by Tork (3914) Subscriber Badge on Friday July 30 2021, @06:04PM (#1161423)
        Heh.. wait.. was there was a bunch of people freaking out in 1987 over Patrick Stewart saying "no one has gone before..."?
        --
        🏳️‍🌈 Proud Ally 🏳️‍🌈
        • (Score: 0) by Anonymous Coward on Friday July 30 2021, @06:08PM (1 child)

          by Anonymous Coward on Friday July 30 2021, @06:08PM (#1161426)

          Not really, a few people said "nothing should change at all!" but most thought it was fine.

          • (Score: 1, Flamebait) by Tork on Friday July 30 2021, @06:35PM

            by Tork (3914) Subscriber Badge on Friday July 30 2021, @06:35PM (#1161437)
            Ah.. was about to say, if someone is sensitive to gender portrayals there's no incarnation of that show they'll fully enjoy.
            --
            🏳️‍🌈 Proud Ally 🏳️‍🌈
      • (Score: 0) by Anonymous Coward on Saturday July 31 2021, @12:45AM

        by Anonymous Coward on Saturday July 31 2021, @12:45AM (#1161568)

        You are, like, totally disgusting, man.

        Kinda hot.

    • (Score: 1, Funny) by Anonymous Coward on Friday July 30 2021, @05:56PM (1 child)

      by Anonymous Coward on Friday July 30 2021, @05:56PM (#1161419)

      Astronomy: you can look but you can't touch.

      • (Score: 0) by Anonymous Coward on Saturday July 31 2021, @07:41AM

        by Anonymous Coward on Saturday July 31 2021, @07:41AM (#1161653)

        So it's like a strip joint.

  • (Score: 1, Interesting) by Anonymous Coward on Friday July 30 2021, @05:32PM

    by Anonymous Coward on Friday July 30 2021, @05:32PM (#1161409)

    TFA starts out with a few screens full of fluff, but then gets down to business:

    Each unit cell, as mentioned, is entirely made of aluminum. Earlier antenna arrays that similarly use smaller component cells include dielectric materials like ceramic or glass to act as insulators. Unfortunately, dielectric materials are also vulnerable to Jupiter's ionizing radiation. The radiation builds up a charge on the materials over time, and precisely because they're insulators there's nowhere for that charge to go—until it's ultimately released in a hardware-damaging electrostatic discharge. So we can't use them.

    Recommended.

  • (Score: 1, Funny) by Anonymous Coward on Friday July 30 2021, @05:33PM

    by Anonymous Coward on Friday July 30 2021, @05:33PM (#1161410)

    You know the rest, it was the same kind of warning given to Adam and Eve

  • (Score: 0) by Anonymous Coward on Friday July 30 2021, @06:14PM (2 children)

    by Anonymous Coward on Friday July 30 2021, @06:14PM (#1161428)

    But other than being about the same speed, not that comparable. Modems in the 80s (1200-9600 baud) were limited by signal processing, but by the 90s (especially at the 33.6 rate) it was more about not frying the telephone equipment. Ethernet over similar wiring was already at 100 megabits (albeit with a shorter range).

    • (Score: 1, Informative) by Anonymous Coward on Friday July 30 2021, @11:27PM

      by Anonymous Coward on Friday July 30 2021, @11:27PM (#1161528)

      There was no risk of damaging the telephone equipment despite the garbage AT&T spewed about it*. The old analog telephone network was bandwidth limited by crappy amplifiers to 33.6k or lower. The digital telephone backbone of the late 90's was standardized at 56k so that is the fastest possible speed over 'modern' POTS, but due to clocking issues analog modems are still limited to transmitting at 48k. This is why the last generation of telephone modems were 56k down and 48k up and required hardware support from both the ISP and the phone company.

      *Back when acoustic modems were your only option because AT&T phones were hard wired and using your own telephone equipment was illegal.

    • (Score: 0) by Anonymous Coward on Saturday July 31 2021, @03:33AM

      by Anonymous Coward on Saturday July 31 2021, @03:33AM (#1161610)

      Maybe it will run FidoNet? And other software optimized for modem speeds...

  • (Score: 0) by Anonymous Coward on Saturday July 31 2021, @12:18AM

    by Anonymous Coward on Saturday July 31 2021, @12:18AM (#1161552)

    ...will it be resistant to the ionizing radiation of a Monolith?

  • (Score: 2) by PinkyGigglebrain on Saturday July 31 2021, @06:53PM (1 child)

    by PinkyGigglebrain (4458) on Saturday July 31 2021, @06:53PM (#1161765)

    With exploration of the outer solar system become a long term goal it might be time for NASA and the rest to consider putting some simple dedicated rely hardware in some Lagrange points [wikipedia.org] in the outer solar system, probably Jupiter's. They would also be useful for other missions as well since they would be able to cover almost the whole solar system continuously.

    Wouldn't need to be anything fancy, a power source good for a couple decades, enough fuel for minor adjustments during that time, enough high gain antenna to cover the sky, and enough redundant local brains to stay in place and relay any radio signals it gets towards Earth during it's mission.

    --
    "Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
    • (Score: 2) by takyon on Saturday July 31 2021, @07:36PM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Saturday July 31 2021, @07:36PM (#1161775) Journal

      Laser communications should help increase bandwidth a lot.

      We also can't assume a Europa lander would have an orbiter overhead to relay signals, because adding an orbiter could very easily make the mission too expensive. Even if Clipper is miraculously still functional by the time a lander arrives, we won't assume that will be the case, as the lander would arrive well after Clipper's official end-of-mission date.

      A certain larger vehicle could help send a radiation-hardened orbiter and/or boost the mass of the lander so that it can have a larger antenna, communicate using lasers, etc. Missions in general need to get a lot cheaper than they are now. There's no good reason for Europa Clipper to cost $4.25 billion, or JWST to cost $10 billion.

      --
      [SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
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