Paul,

So - may I ask what ISAAC is? 

The question of shielding entirely depends on what is flying. COTS covers a very wide range of fabrication nodes (Pentiums were 350nm) - it rather depends on the shelves that you find things on!

Can you identify the parts for us, and the approximate mass budget available?

Your shielding has to perform two tasks.

1) Put enough low mass nuclei in the way to scatter beta

2) Put enough heavy Z nuclei in the way to mop up x-rays and stop heavy nuclei.

Laminating light materials with dense isn't a bad idea.

James:

Thank you for the reply.

I am working on a proposal to a NASA request for instrument designs to fly on a Korean Lunar orbiter. Instrument for Soil Analysis Assessment and Characterization (ISAAC)'s aim is to use electromagnetic waves to characterize the Lunar regolith (soil) for potential future human exploration missions.

Where COTS electronics come in is specifically as a cost-saving measure. I am researching the Lunar radiation environment, but I am looking for research into shielding for COTS electronics (computers and radios, specifically) to see if it would be possible to use these lower-cost devices for my instrument.

I have to submit a pre-proposal by the end of the month, and I am not too worried about this particular part of my project, I am just thinking ahead to the final proposal at the end of October.

Thank you, again.

Paul B. Huter

Paul,

Okay, time for nitty-gritty details.

Is this a radar altimeter of some sort?

(if so, what power, transmission band...)

I'm struggling to see what a simple radar would reveal that, for example, infra-red spectroscopy would not...

(unless it's a polar orbiter, in which case polarization studies of the return may tell you something about water-ice enriched regolith concentrations).

If you can minimize the amount of onboard processing, you reduce the cost of both the payload and its shielding. I appreciate that you'll need to do *some* (quantization, packet assembly, etc.) but less is more.

Ah, this ties in with your interest in dielectrics.

Okay. Well, I suggest that you'll want to look at the power budget first and foremost - if this is nadir pointing then there are quite a few studies about the reflectivity of the lunar surface at a variety of radar bands - and given some COTS RF amplifiers, you can work out what scale of power you need to transmit at.

That's the easy part.

The hard part is finding a receiver with radiation dose statistics. I doubt that the average Rx maker knows the SEU rate for their kit when bathed with soft x-rays.

:)

So you might need to make some quick and nasty tests with the help of a friendly dentist.

:)

Or dig deep and find the SEU rates on the discrete components of the receiver, and build some basic attenuation models. Any chance for hiding the receiver deep inside the craft, with just the antennae protruding?

Hi Paul,

Just a quick point in the past if we have been concerned about the radiation susceptibility of certain parts we have used spot shielding using Tantalum, I think we did this over an ADC at one point for the Cluster mission. This combined with the aluminium chassis helped reduce the risk to an acceptable level.

Thank you, Barry. I have seen some similar research on using materials in conjunction with aluminum for shielding.

James:

In answer to you question -

My premise is based on this paper:

Arulanandan, K., Anandarajah, A. and Meegoda, N. J. (1983). "Soil characterization for

non-destructive in situ testing." Symposium Proceedings Part 2: The Interaction

of Non-Nuclear Munitions with Structures, U.S. Air Force Academy, Colorado,

69-75.

I found a doctoral dissertation that uses that paper as part of the research into using electromagnetic waves to analyze various soil properties, specifically through the dispersion of the waves through the dielectric (soil/regolith). I am trying to work through ResearchGate to get that particular paper from the author to get some more details and fill in the necessary holes.

Basically, by measuring the angles of incidence and reflection, it appears that it is possible to calculate the dispersion of the electromagnetic waves (generally between 1-100MHz) through the soil, and from there analyze things like compressability and water content.

Paul,

Any terrestrial soil studies will be dominated by the presence of liquid water - with a relative permittivity of 80 or so, water in a liquid phase is the dominant effect in soil's radar return.

The moon is essentially free of liquid water - so what you'll be measuring is indeed some complicated factor of bulk density, surface roughness, mineralogical content, and subsurface masscons. It is *not* a trivial matter to deduce anything about makeup, given the near-absence of data on bulk density and the difficulty of modelling roughness.

I am sure that you've scoured NASA ADS, the technical report server, and the LPSC archives.

So, there's nothing wrong with another dataset :D and so I wish you well.

Note, I would hesitate to say that compressibility (of the bulk regolith) is deducible without knowing composition - and spectroscopy only gets you so far with that. Mechanical compressibility depends on grain *size* and not just simple bulk density (presuming that one can deduce density from IR spectra - which is a mug's game!)

Short of poking the surface with a cone penetrometer, I'd leave compressibility out of it.

James:

Yes, the "compressibility" part of the theory does rely on knowing what it is made of. But the dissertation I am looking at (and hopefully that paper, if I can get it) have about 20 different characteristics that can be measured by electromagnetic waves, so I hope to find some characteristics to measure.

Thank you for the well wishes.

Paul,

20? Golly.

I'm struggling to get past four.

I've a pile of references from my work on the Huygens sonar/altimeter - what paper are you trying to find? And may I ask what budget you have in terms of mass *and* money?