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Plasma Resonance Could Overcome Radio Silence For Returning Spacecraft
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."
I bet this includes some fancy use of ginseng root?
Mod me down, my New Earth Global Warmingist friends!
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.
So they're wiring communications to the main deflector? Interesting idea!
Interesting for TX, but the noise figure for RX would be horrendous.
But how do you handle the harmonic distortion within the phased array? Reverse the polarity in tandem with the frequency modulator?
Send audio messages from the edge of the atmosphere, a needed technology for later "commercial" space flights. Imagine the price of ads for national elections.
Now I want you all to go to the windows of your spacecraft, turn on the plasma speakers, and yell "I'm mad as hell and I'm voting for Bernie Sanders"
https://en.wikipedia.org/wiki/...
I came here for a better reverse polarity joke.
Is this like the gamma matching 'capacitor' used in ham radio antennas, like the Halo antenna?
All rites reversed 2010
So, using the deflector shields to transmit a message? I think I've seen this plot point before somewhere..
Those of us who are old enough remember the radio blackouts during Mercury, Gemini, and Apollo reentries which also occurred on the earliest shuttle flights and then remember how cool it was when the shuttle program implemented its solution and we could hear the crews through most of reentry. Early in the shuttle program, NASA launched the network of TDRS (Tracking and Data Relay Satellites) in a ring around the Earth to lower costs by replacing the Earth-based network (which had included not only the big dish antennas on land but also ships at sea). Spacecraft could thereafter communicate with the nearest TDRS which would relay the traffic to the one over the ground station.
The TDRS network had the additional benefit of enabling comms during reentry. During reentry, the plasma formed by aerodynamic compression of atmosphere ahead of the falling orbiter, became the usually-opaque-to-radio barrier below and around the orbiter - but that plasma barrier had a hole in it above and behind the shuttle which allowed upward-facing antennas on each orbiter to communicate with the overhead TDRS network. The very short blackouts during shuttle reentries were when the orbiters were at high roll angles (they steered an S-shaped curve during parts of descent to aid in deceleration) and their up-facing antennas were pointed away from the TDRS network.
The best joke is the form of a trolling. Bravo to the parent AC!
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..
Back in the days of "ground control" for everything, and dumb spacecraft, being able to send and receive data from the re-entry was important. Today, though, it's not so important. The spacecraft can be smart enough to maneuver itself during re-entry, and things happen so fast (or are so far away light time-wise) that it has to be autonomous anyway.
Sure, if "something goes wrong" you want to get telemetry from the blackout period, but that's not exactly rocket science these days. It's not like you can't have a memory to store the telemetry and always be sending telemetry from now, and repeating the telemetry from X seconds ago. Sure, that doesn't fit in the 1970s model of "dumb spacecraft with tape recorder", but I think we can do that now.
Of course, it would require that you send 2x-3x the data rate (e.g. live data, plus delayed data), but in a re-entry scenario, the range is typically short, and with modern technology, doubling or tripling the data rate isn't a big deal. It's not like we strain every fiber to get 8 bits/second through on a earth lander.
It would be a huge imposition on the ground systems data handling though. What do you mean you're resending telemetry frames? How will we keep them organized, if they have the same frame number? What will we do with our hand crafted over the last 30 years telemetry processing software.
Bah..
Meh, why not retransmit the telemetry that was blocked during plasma blackout?
It's not like Apollo days when you'd need a magnetic tape/wire recorder to do this.
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
There are plenty of examples of coupling to an electrically produced plasma, such as an arc or corona discharge. It's controlled, but still really difficult.
Who has managed to couple to a thermally produced plasma? It's absurdly difficult to create a matching circuit for, let alone actively adjust the matching circuit. If these guys figure out how to do that, they're going to be using it for much more "interesting" things than spacecraft communications during re-entry (which is not an actual problem once you have satellites in orbit, and is obviously not the problem these guys are being paid to solve... it's the problem they're allowed to talk about).
This method lets you receive or transmit at ONE frequency, which is dynamically determined by the plasma properties. The article didn`t give any typical examples, but it sounds like:
1) You need to be able to rapidly vary the frequency the spacecraft transmits at. (So you need quite a fancy transmitter).
2) There is no reason why the frequency should be a good choice for propagation though the atmosphere.
It _could_ be used for two-way transmission, the ground station would have to track the spacecraft's current frequency window.
But, if the spacecraft is not transmitting, good luck guessing what frequency needs to be used for the ground station to get through the plasma.
So it does not sound useful for the case of a space capsule passively listening for a ground station... there is no practical way for the ground station to figure out the right frequency in general.
Also, when receiving through all that plasma, there will be a lot of noise. For transmitting through plasma, it might work.
The plasma sheath is all enveloping on many re-entering spacecraft. Sure, the gas gets ionized on the leading surface, but that ionized gas flows around the entire body.
Pretty much, you're incommunicado for the short time.
And the Chinese in a few decades do? What are they getting paid for again?
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?
I get confused about my shirts being ironed.
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.