typodupeerror

## Hypersonic Radio Black-Out Problem Solved88

Posted by Soulskill
from the ending-the-five-minute-panic-period dept.
KentuckyFC writes "Russian physicists have come up with a new way to communicate with hypersonic vehicles surrounded by a sheath of plasma. Ordinarily, this plasma absorbs and reflects radio waves at communications frequencies, leading to a few tense minutes during the re-entry of manned vehicles such as the shuttle. However, the problem is even more acute for military vehicles such as ballistic missiles and hypersonic planes. Radio blackout prevents these vehicles from accessing GPS signals for navigation and does not allow them to be re-targeted or disarmed at the last minute. But a group of Russian physicists say they can get around this problem by turning the entire plasma sheath into a radio antenna. They point out that any incoming signal is both reflected and absorbed by the plasma. The reflected signal is lost but the absorbed energy sets up a resonating electric field at a certain depth within the plasma. In effect, this layer within the plasma acts like a radio antenna, receiving the signal. However, the signal cannot travel further through the plasma to the spacecraft."
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## Hypersonic Radio Black-Out Problem Solved

• #### Black out? (Score:1, Insightful)

by Anonymous Coward

Is this PC? Maybe use "slave out"? What do you think, Linda?

• #### Re: (Score:2)

Montag remains incredulous over this.

• #### Re: (Score:2)

WTF are you talking about. Clearly in the US this gets replaced with "African-American Out."

• #### Re: (Score:2)

What about all those African-Americans in Africa?

• #### No, they haven't. (Score:2)

The SNR and BER of that scheme are going to suck.

• #### Re: (Score:2)

Very very little:1 is still better than 0:1
• #### Re: (Score:2)

No, it isn't. Noisy telemetry is balls. It will mislead you. And you can't make an error-correcting code to handle the number of bits that will be borked by this system (which is why I mentioned BER). Not that you'd waste your bandwidth on elaborate error-correcting codes anyway.

Best strategy: save up the data and read it later. There's not much you can do in real-time at that point anyway. It knows where to go, and you're not going to need to change that during that phase of its flight.

• #### Re: (Score:2)

I don't know, "Maybe we shouldn't have launched that nuke after all" seems like it would be a nice command to be able to send. This solution might not work, but it's still a useful problem to work on.

• #### Re:No, they haven't. (Score:5, Informative)

<bughunter&earthlink,net> on Friday January 07, 2011 @01:33PM (#34794176) Journal

FTFA:

Korotkevich and co say the weakness of the transmission signal doesn't matter because ground-based receivers can be made hugely sensitive, certainly much more so than mobile ones.

Considering we can communicate with interplanetary (and now some technically interstellar) probes with received signal strengths on the order of -200 dBm [baylorschool.org], and we can build arbitrarily large transmitters/receivers on the ground, and health and status telemetry doesn't require huge bandwidths (on the order of 10^2 bps), I'd say he's right.

• #### Re: (Score:1)

You do realize that these things go so fast that you have to track them across large swaths of ocean, right? You can't really build an arbitrarily large receiver in the ocean for a reasonable cost. Heck, you can't even put a ton of arbitrarily sized trackers on the ground either without massive expenditure, probably larger than a lot of the hypersonic test projects budgets.
• #### Re: (Score:2)

You need that for interstellar probes because you have no other choice. And you can accept that data rate because you have nothing but time. And it fits into your power budget besides.

But that's a much lower-noise situation.

This will be like trying to talk while standing in jet wash. The 1 in 10 words you can make out will not be enough information to be useful in the time during which you're still in the jet wash. Better to wait until you've stopped tumbling down the tarmac and the plane is gone and th

• #### Re: (Score:2)

Considering a typical terrestrial noise floor is about -90dBm, your talking in a jet wash analogy is not inaccurate for either scenario.

Because SNR is SNR (assuming we're not getting into the realm of ECM or correlated noise).

SNR and channel bandwidth (and a few other things we can hold constant in this example) give you your BER. If your BER is too high, then you either need to talk louder, narrow your bandwidth, or use an error correcting code. Usually some combination of all three. There are solutions

• #### Re: (Score:2)

Thanks for the Voyager transmitter link info...that was a really interesting read.

Cheers!

• #### Re: (Score:2)

I know this is /. but '100' is actually fewer characters than '10^2'.

• #### Re: (Score:2)

well since this is slashdot, the parent post said 10^2bps and that is way fewer than 100 characters which might be 6, 7, usually 8 (ASCII), or 16 bits each.

• #### The shuttle doesn't (currently) black out (Score:5, Informative)

on Friday January 07, 2011 @01:19PM (#34793990)
http://en.wikipedia.org/wiki/Communications_blackout#Reentry_communications_blackouts [wikipedia.org]

Until the creation of the Tracking and Data Relay Satellite System, the Space Shuttle would, like Gemini, Mercury, Apollo, and others, endure a 30 minute long communications blackout before landing. However, the Shuttle can communicate with a Tracking and Data Relay Satellite during re-entry. This is because the shape of the Shuttle creates a "hole" in the ionized air envelope, at the tail end of the craft, through which it can communicate upwards to a satellite in orbit and thence to a ground station.

• #### Re: (Score:3, Insightful)

thanks for the comment - I realize this quickly devolved into a discussion about what was or wasn't said in the article but it is interesting that the shape of the vehicle can create a hole in this plasma and thus provide another solution to the issue . Maybe it's not always possible to design the object involved to create this hole and the plasma antenna is a useful alternative, but in any case it was interesting to me to know this other 'solution' exists....
• #### Re: (Score:2)

It's fairly trivial to design a vehicle to create the 'hole' - the problem is that the 'hole' is fairly narrow and always pointed to where you're coming from. This isn't always a useful direction.

• #### Re: (Score:2)

It does actually black out, but for a much shorter period of time during a transition between flight attitudes. Its less than 30 seconds however it does still loose communications during the worst parts of reentry, even with a relay off its tail.

• #### Or, you could just do it this way... (Score:2)

http://www.freepatentsonline.com/3758862.html [freepatentsonline.com]

(except it's patented)...

• #### Re: (Score:1)

Filed in 1970...
• #### Re: (Score:2)

That's actually exactly what they're doing, but slightly different approaches.

Patent:
Uses adaptive impedance matching to allow signal propagation through the plasma.

This project:
Uses adaptive frequency matching to allow signal re-transmission through the plasma.

Same net effect, exploiting the same properties (The patent changes the impedance of the transmission circuit to match the plasma, while TFA describes varying the frequency until we hit an impedance match with the plasma (changing the frequency chang

• #### Not solved! (Score:3)

on Friday January 07, 2011 @01:32PM (#34794162) Homepage

I read the full summary. The last sentence that the signal cannot travel into the craft from the plasma. How is that solved?

• #### Re: (Score:3)

Sounds like all they need to do is hook something onto the ship that can read signals inside the plasma, some kind of antenna that can withstand the stresses associated.

Essentially the signal doesn't travel all the way through the plasma, thats why theres a blackout.

But we never thought about trying to receive from inside the plasma.

• #### Re:Not solved! (Score:4, Funny)

on Friday January 07, 2011 @01:38PM (#34794224) Journal

How is that solved?

A stubby little plasma antenna lives in the plasma stream. It's made of hypereutectic unobtainium, a exotic form of unobtainium unique to Russian science.

• #### TFA is revealed! (Score:5, Informative)

on Friday January 07, 2011 @02:06PM (#34794620)

Well, I read the full introduction of the paper, and the conclusion, skipping only the detailed plasma physics models & calculations. They do mention the strategy of putting an antenna through the plasma which can last as long as one fuel tank before it ablates, but they instead propose that (more elegantly) a small commercially-available 3 kW high frequency klystron amplifier (a lot less power than the radar) be placed at the surface of the aircraft, where it will disrupt a very small region of the plasma in a manner that will scatter ~.7 - 2% of the original incoming signal (which will resonates in a layer of the plasma) back to the aircraft; that is enough power for a 5 m. antenna and a commercially-available high sensitivity GPS receiver to pick it up. There is an analogous explanation for outgoing signals. They account for quite a few confounding plasma effects, acknowledge that there are some others that can't be modeled so clearly (or maybe they didn't think of), but predict that getting the system to work would be a not-so-difficult engineering challenge.

My first thought was, "Boy, I hope all the space opera authors read this preprint: no more signal attenuation from the plasma engines in the atmosphere!" Now there is one more area in which reality is exceeding a certain segment of--rather soft--science fiction (that I am only familiar with--AHEM--because of Baen's visionary no-DRM any-format ebook policy).

• #### What about subspace? (Score:1)

The cause of, and solution to, all technological problems in the 23rd century.
• #### Re: (Score:3)

I'm pretty sure it would all work out if they just reversed the polarity of the tachyon emitter.

• #### Re: (Score:1)

Of course, it's just like (incredibly simplistic 21st century metaphor). It was right in front of our eyes!
• #### Re: (Score:1)

As long as it was all channeled thorugh the front deflector, of course.

• #### Recycled news (Score:2)

At the end of TFA they give the original reference, a paper preprinted in 2007 [arxiv.org]. One way to tell if this holds water is to see if other research groups have done follow-ups in the intervening three years.
• #### Disarn missiles at the last minute? Unlikely (Score:2)

The standard argument against being able to remotely disarm missiles has been that including such a mechanism opens the door for the enemy potentially figuring out how to do it - it's not about the ability to communicate.

• #### Captain we're being hailed... (Score:1)

@MajorTom: We just started our re-entry...

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