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."
Oh Boy Chinese Science (Score:2, Funny)
I bet this includes some fancy use of ginseng root?
Re:Oh Boy Chinese Science (Score:4, Insightful)
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.
--PM
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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.
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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.
Viewpoint from a Chinese (Score:2, Interesting)
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
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Well, now you've gone and told everybody!!
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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
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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.
Never thought of plasma sheath as Faraday cage... (Score:2)
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.
Star Trek solution, eh? (Score:1)
So they're wiring communications to the main deflector? Interesting idea!
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"Clever and useful -- we will be able to hear clearly the screams of the next crew when they fall down in pieces."
More or less my thoughts. While I see the obvious human curiosity seeing the reentry radio silence as over-frustrating, I don't see it as "the most cruicial time of a re-entry" when comunications are of any use. How much can a ship take corrections at that stage? Before and after, yes, but what can be done in that precise stage so the comunication channel becomes the difference between live an
Re:Star Trek solution, eh? (Score:5, Insightful)
what can be done in that precise stage so the comunication channel becomes the difference between live and death?
We can send telemetry, making a difference between life and death for the *next* crew to go up.
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You assume there is still a functioning transmitter after the blackout ends.
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"We can send telemetry"
If the mission ends successfully, there's of course no need. If the mission fails, yes, you might find useful the telemetry you couldn't get otherwise. On the other hand, the only accident involving plasma at reentry that I'm aware off is Columbia's and it seems all the needed info was gathered anyway.
Mind me, I'm not saying it's not worthy, I'm saying that it's far from crucial.
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"How much can a ship take corrections at that stage? "
Quite a bit. The basic reentry designs currently in use have substantial lifting body abilities, etc. and there's the possibility of picking up stuff the crew may have missed due to operational overload
(eg: the soyuz crew who asphixiated during reentry due to a faulty valve. With warning, they could have closed their pressure visors and used suit supplies for a few minutes, but the pressure loss was so gradual that they didn't notice it and simply drift
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"eg: the soyuz crew who asphixiated during reentry due to a faulty valve. With warning, they could have closed their pressure visors and used suit supplies for a few minutes, but the pressure loss was so gradual that they didn't notice it and simply drifted off"
What a non-example! Do you really think you need the ability to send telemetry to land in order to turn on an alarm on the vehicle as result of a pressure loss detected by a sensor on the vehicle?
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There was an alarm. The crew didn't react to it, most likely due to operational overload - the same overload which probably led to the open valve in the first place.
In other hypoxia incidents people have reacted to human voices whilst still being unaware of alarms.
More to the point, with external monitoring the gradual loss of pressure (or the fact that the valve had been left open in the first place) might well have been noticed and flagged long before the alarm went off.
Having systems being able to be mon
Noise figure (Score:2)
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As long as that flippity flappity antenna doesn't short against itself and shorten the antenna length, it's not THAT much of a problem.
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Gamma matching capacitor? (Score:2)
Is this like the gamma matching 'capacitor' used in ham radio antennas, like the Halo antenna?
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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)
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)
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)
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.
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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)
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(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.
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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...
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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.
Resonance, why? (Score:3)
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.
Tow a cable? (Score:2)
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?
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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...)