Nasa Set to Demonstrate X-Ray Communications in Space | Hacker News Reader

Nasa Set to Demonstrate X-Ray Communications in Space

nasa.gov

68 pointszeristor26 comments

Will be interesting to see what they use for a receiving antenna. 90 dBi gain is about the limit for single aperture reflector antennas at RF, as you contended with structure deformation at low frequencies, then surface roughness at high frequencies, not to mention tracking a fast moving object with that precision to keep it in the beam width.

At X-rays, I don’t know how you would focus it as the roughness is in on a molecular scale. So going to higher frequencies has its limits.

I don’t know what the equivalent gain of these large, optical telescopes are, but they seem to suffer from the same problems.

The plasma penetration must the the real objective. You can get thru the plasma with standard RF, it just takes lots more power, or lower data rate, but a low reset beacon is feasible, just not voice comms.

Even to x-rays, smooth surfaces become reflective at grazing incidence, so you can make mirrors that are constructed on that principle. Not simple to do, but not impossible either.

The gain falls off as the RMS surface roughness becomes a fraction of a wavelength; see figure 1 here:

https://arxiv.org/pdf/1007.4600.pdf

So it would be interesting to see how that effects it. I suppose a crystal fractured along the lattice for an atomically smooth surface.

In X-ray astronomy we often use Wolter Type 1 optics based on grazing incidence. These can be made with various techniques depending on the spatial accuracy (point spread function) required, e.g. foils for low accuracy or even stacked silicon wafers planned for the Athena telescope. The effective area of the telescope is smaller than the physical mirror size as everything has to be reflected at grazing incidence. We often use CCDs to detect the X-rays.

As ever Scott Manley made me do it:

https://www.youtube.com/watch?v=e4nXU1xF_Tg

Are there any health concerns about using X-ray constantly for communications? For example, should astronauts performing EVAs take care to avoid the area around the antenna? Or is there enough ionizing radiation in space already that adding some X-ray in the mix won't make any difference?

It depends on the dose, probably not really a thing to be concerned about.

That would depend on the transmit power, but in short, you wouldn't want to be outside the vehicle for a long time when the transmitter is on. A typical x-ray machine emits about twenty watts of x-ray power when in use with a typical shutter speed of 1/10 to 1/2 of a second. There's no data about how much power NASA is using in this experiment or how much a production model transmitter would use, but ground-to-ISS transmission over FM can be done with a 25-watt transmitter.

Now, the x-ray transmitter wouldn't be focused the right way to send maximum radiation into an astronaut and it would have a reduced duty cycle because it's not just a simple x-ray flashlight, but giving it an hour-long bear hug while it's in use would be a very bad idea.

Of course the most relevant point is that the vast majority of spaceships don't have humans on them.

A wild idea I had never even thought of, X-rays are of high enough frequncy that they can penetrate the plasmasheath of high velocity vehicles. Seemingly this is for hypersonic transport, and rentry vehicles, my mind is quite boggled.

What is the mechanism by which a plasmasheath blocks radiowaves, and why would x-rays be an exception?

https://www.researchgate.net/post/How_does_the_plasma_sheath...

> an electromagnetic wave can penetrate the plasma if the wave frequency f is higher than the electron plasma frequency.

X-rays have a much higher frequency (i.e. much higher energy) than the radio waves we normally use for communications, so it can punch through the noise of charged particles that makes up plasma.

I believe it's not a matter of "noise". Rather, metals and plasma are conductive up to a certain frequency. Beyond that frequency, resistance goes up and the material becomes transparent. This is basically because the electrons can't "keep up" with the electric field's oscillation so they are ineffective at screening it.

This is similar to how a metal box blocks radio waves, and how x rays can still penetrate it.

What kind of metal? I thought X-rays couldn't penetrate lead.

It is actually pretty simple. Plasma is conductive. Most conductive things Will block radio waves at GHz and below

If it is conductive, can't you make it part of the antenna?

yes -- https://en.wikipedia.org/wiki/Plasma_antenna

NASA not Nasa. It’s an acronym not a word.

Cool. In some places it is common to only capitalize acronyms if they are pronounced as individual letters.

This a NASA article on a NASA web site

Yes, and (now, at least) the linked article has NASA capitalized in the title. (Unless you intended to reply to @tntn)

I don't personally agree with this convention, but apparently some people do:

"A growing convention, which I first came across in Robert Bringhurst’s The Elements of Typographic Style, dictates that if an acronym is pronounced as a word, then it should not be written in all caps. (As opposed to initialisms, which are pronounced as a series of letters. Compare Nato to USA.)"

http://scratchtap.com/when-acronyms-should-not-be-capitalize...

CancerComm

> XCOM

I love it (For those not aware, https://en.wikipedia.org/wiki/XCOM:_Enemy_Unknown)

Also

https://www.xcom-labs.com/

And of course

Https://www.x.com

Link for the lazy:

https://www.x.com/

(just put a trailing / at the end)

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