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Space China Communications

Plasma Resonance Could Overcome Radio Silence For Returning Spacecraft 62

Zothecula points out this article about a workaround for a long-standing problem with space-flight communications: some of the most cruicial time of a re-entry is also time when the craft cannot send data to or receive instructions from the ground controllers. From the article: Returning spacecraft hit the atmosphere at over five times the speed of sound, generating a sheath of superheated ionized plasma that blocks radio communications during the critical minutes of reentry. It's a problem that's vexed space agencies for decades, but researchers at China's Harbin Institute of Technology are developing a new method of piercing the plasma and maintaining communications. This means coupling the craft's antenna to that plasma sheath, "[causing] the sheath to act as an inductor. Together, they create a resonant circuit."
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Plasma Resonance Could Overcome Radio Silence For Returning Spacecraft

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  • I bet this includes some fancy use of ginseng root?

    • by PeterM from Berkeley ( 15510 ) <petermardahl@@@yahoo...com> on Sunday June 21, 2015 @03:05PM (#49957465) Journal

      The Chinese are getting better every year, year in and year out. How do you climb the tech ladder? The logical way is that first you learn from what others have done, and reproduce it. Then, when you are caught up, you start to lead.

      And with a billion people, the Chinese have their share , or maybe more than their share, of first class brains. Their culture doesn't sneer at science, either.

      The Chinese are on the fast track to being the dominant world power if their own misgovernment doesn't screw them up.


      • Re: (Score:1, Interesting)

        by Anonymous Coward

        How do you climb the tech ladder? The logical way is that first you learn from what others have done, and reproduce it.

        What's logical about that?

        Then, when you are caught up, you start to lead.

        Why are they catching up? Did Chinese just pop into existence 20 years ago?

        And with a billion people, the Chinese have their share , or maybe more than their share, of first class brains.

        And far less than their share of results.

        • Re: (Score:2, Insightful)

          by Anonymous Coward

          I'll just point out; It's always a mistake to underestimate your competition. Just as it's always a mistake to overestimate your competition. This sort of argument may work to keep children on the playground from challenging bullies and may keep bullies feeling smug in the short term, but it does not intimidate a mass of one billion people with ambitions to succeed at all costs.

          • by Anonymous Coward

            I am a Chinese

            Although I do not enjoy the attitude displayed by those racists towards the Chinese, I do hope that there are even more of them --- the more of them look down on us, the more of them won't even notice what we have accomplished

            We Chinese have a saying --- stay low but work diligently

            In other words, the more we stay under the radar the more we can progress without Obama and his anti-Chinese gang looking over our shoulders

            • Re: (Score:2, Funny)

              by Anonymous Coward

              Well, now you've gone and told everybody!!

            • China has a very long history of technological innovations exported to the rest of the world. It's only since the start of the industrial revolution that it's fallen behind and even then only slightly.

              The biggest stumbling block in the last few decades has been communism discouraging "tall poppies" - now that the brakes are off it's only to be expected that innovations would start pouring out.

              (The world would benefit greatly from china being treated as an equal in space. Locking the chinese govt out of ISS

      • Japan was once considered a third world country, with third rate science and technology. They deliberately worked to fix both those problems, and now they are considered world leaders of science and technolgoy. Given strong central contol and plenty of dollars from their massive manufacturing industry they will achieve their goals.
    • You seem to have the Chinese confused for the North Koreans. You'll be better off if you learn the difference. One, we take seriously. The other claims they've got the cure to AIDS, some forms of cancer, and Ebola from a drug they devised from ginseng.

  • Turning the shield (conductive layer around the craft) into an antenna? I like this idea. And with the full paper freely available through the link in the source article, I could in principle learn more -- if only my math and EM physics were up to it. Sigh.

  • by Anonymous Coward

    So they're wiring communications to the main deflector? Interesting idea!

  • Interesting for TX, but the noise figure for RX would be horrendous.
    • A directional ground based antenna with high output power will overcome the RX noise. The military use for this technology is obvious, you can re-target your balistic missiles (or abort) or use radar to see incoming interceptors and avoid them.
  • Is this like the gamma matching 'capacitor' used in ham radio antennas, like the Halo antenna?

    • Re: (Score:2, Informative)

      by Anonymous Coward

      The effect is the same. Usually the capacitance is adjusted to series resonate with the inductance from length of feedline going to the drive point tap. Whether it's a physical series capacitor, or the effective capacitance of a coupling sleeve doesn't change the theory. Obviously the feedpoint impedance will vary with the length of the plasma plume. The transmission line length will be relatively short, so mismatched impedance isn't a problem there. The interfacing electronics needs to tolerate wide v

  • What issue? (Score:4, Informative)

    by Dereck1701 ( 1922824 ) on Sunday June 21, 2015 @04:48PM (#49957889)

    I thought this was no longer an issue? I think continuous communication had been in use for over a decade with the space shuttle before the end of the program. The solution was to use satellites, being on the other side of the plasma sheath, as relays to communicate between a reentering craft and the ground..

    • Re:What issue? (Score:4, Interesting)

      by AmiMoJo ( 196126 ) <mojoNO@SPAMworld3.net> on Monday June 22, 2015 @04:25AM (#49960319) Homepage Journal

      This way you don't need to rely on a satellite for communication. Cheaper, less to go wrong. A low cost improvement.

    • Couple of things (Score:4, Interesting)

      by Laxator2 ( 973549 ) on Monday June 22, 2015 @05:22AM (#49960491)

      The article specifies that spacecraft re-enters at about 5 times the speed of sound.

      1) The spacecraft on low Earth orbit have orbital velocities of about 8km/sec, and the speed of sound is about 0.34 km/sec. That makes the spacecraft about 23 times faster than sound on re-entry. I remember reading bout the Columbia disaster, that the shuttle entered the atmosphere at about 26 times the speed of sound. That makes sense, as the potential energy of the above-atmosphere orbit is transformed into kinetic energy at the altitude of hitting the atmosphere.
      For the Apollo spacecraft, they re-entered at even higher speed, close to the Earth escape velocity of 11.2km/sec. That makes them about 33 time faster than sound.

      2) The plasma sheet forms a very narrow cone with the spacecraft at the tip of it, effectively enveloping the spacecraft. The angle is given by:

      sin \theta = speed of sound / speed of spacecraft.

      At mach 23 it is about 6 degrees. Plus the plasma is turbulent, so it is very difficult to aim a signal along this cone and hit a satellite.

      • Whenever you see "xyz is going at N times the speed of sound" - it's the speed of sound at sea level (standard temperature and pressure), not the speed of sound in the local environment.

        Media always dumb this down. "Journalists" are not reknowned for their comprehension skills for the most part.

        (Whenever you see media massively screwing up reporting of stuff you know lots about, bear in mind that every expert in every field has the same gripe about them)

        • (Whenever you see media massively screwing up reporting of stuff you know lots about, bear in mind that every expert in every field has the same gripe about them)

          This is an important point you raise and one I frequently remind people of. The News is best assumed to contain a non-insignificant quantity of fiction with lashings of misses-the-point and at least a touch or two of just-plain-wrong.

        • Then what is the speed of sound at the point where re-entering spacecraft hit the atmosphere? (I realize that "hit the atmosphere" is a relative term, so I suppose the question is what the speed of sound is at the point the spacecraft starts generating enough plasma to interfere with radio.) My guess is that it's nowhere near 8 km/sec / 5. But that's a guess...

          • Somewhere between "non-existant" and a few metres per second at most.

            Sound transmission requires that movement can be transferred between molecules (Just like a newton's cradle)

            At the altitudes concerned, gas molecules are so widely dispersed that collisions are occasional to rare, despite giving enough friction to generate a plasma.

  • by Pinky's Brain ( 1158667 ) on Monday June 22, 2015 @02:10AM (#49959999)

    The resonant frequency is just going to dance around any way. Why not just modulate the voltage on the plasma directly? (Relative to the metal super structure of the craft.) If you do it with a square wave you can very easily recover the energy the same as if you were using resonance ... and these guys don't have to worry about the FCC.

  • I'm sure people far more clever than me have thought of this, but why couldn't you just tow a cable behind the craft and use that to communicate? I presume the cable wouldn't get too hot as it's long and straight, and behind whatever heat shield you have. I have no idea how long the plasma tail runs to, but presumably you could make the cable long enough to get into a bit that was 'washy' enough to communicate?

    • At hypersonic velocities a trailing antenna is going to flail around so much that it'll probably snap.

      I wouldn't be at all surprised to find that NASA tried something like this back in mercury days, as I've spoken with some of the scientists who worked on the unmanned and chimp craft. Many are now long-dead, but they had a lot to tell which isn't in any history file (such as desperately giving CPR to a chimp...)

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