Betameteoroids

I looked at Beta meteoroid flux online, mainly using the following site:

http://www.gps.caltech.edu/genesis/DocumentN.html

It gives a definition of beta meteoroids as being with mass below 1.4 x 10-15kg and a density of 2 gcm-3. They are negatively charged dust particles that travel with the solar wind, or at least that is what I have been lead to believe. The particles have to be from a circular orbit due the low mass. The particles are radition dominated, but this gives a lower mass limit of 10-18kg as radiation pressure drops off rapidly at this limit.

The website gives an approximation of cumulative flux, leading to a total mass flux of 1.1 x 10-17gm-2s-1. This gave a total flux in two years of 3.5 x 10-14 gcm-2. Assuming that there is consideration given to mass distribution, just changing the time period to nine months should lead to a total flux of 1.31 x 10-14 gcm-2. I don't see a way of converting this into impacts, as I don't know how the mass distribution varies. I also don't know the errors in the website calculation, so I can't give errors with this flux. I just knocked off a few decimal places. These estimates are based on a device pointing directly at the sun for a continuous amount of time.

I did some calculations assuming them to be of constant density and spherical composition to approximate the size, they follow here:

Volume = Mass/Density

Density = 2 x 103 kg.m-3 (after converting the quoted units)
Taking the upper mass limit of 1.4 x 10-15 kg, the upper volume limit was found to be 7 x 10-19m3. With a lower mass limit of 10-18kg the lower volume limit is 5 x 10-22m3.

Until told otherwise I am going to model the shape as spherical, for ease of calculation, but I will try to find out more details, and correct the data accordingly.

The next obvious step is to find the spherical radius using:

VSpherical = 4/3 x pi x R3.

This gives the largest possible radius as being 1.18 x 10-6m and the smallest of 4.9 x 10-8m.

I would suggest, that if these are the dust regiemes we are looking at, we take the resolution from being within this range. However, to decide on an exact figure, further details on mass distribution are needed, as are details on shape. I know that technically the width of the meteoroid is twice the radius, but we need more than one pixel to fire so that we know it's actually part of a response to an impact and not an instrument glitch.

The maximum cross section through one of these meteoroids (using cicular area) ranges from 1.4 x 10-12m2 to 2.4 x 10-15m2.

Again - I don't have errors in the original figures, so I cannot quantify the error in my answers. I believe that more error would come from the approximations of shape as well.

The website makes frequent references to two sources, Grun et Al 1985, and Zook and Berg 1975. Thought these might be good places to look next. (A quick look on google about the paper has links about a gallileo dust detector designed to analyse grains of sizes 10-9g to 10-19g. This easily encompasses our range and might be a line of further enquiry)

One final quick query is how abundant beta meteoroids are in LEO. I would hazard a guess that there would be very few impacts in our mission timeline. To be honest, these figures are also based on a sun facing satellite, so we are probably going to have more luck with larger micrometeorites (especially with resolution).

If there is any joy or recommendations, email me at ku.ca.el|2lmo#ku.ca.el|2lmo

Well, from what I've found to date, an MCP (micro channel plate) detector would give us an effective channel diameter of 10-15-6m. This probably isn't quite a good enough resolution for Betameteoroids, whose diameters are at most about 2.3-6m. However, it would give us plent of data on other small dust. For information on MCP detectors the following sites have been of use. Other than resolution, they seem to fit the size criteria for our satellite, even allowing for a camera to be positioned on the same face of the cube. There is no information on mass, but I can end out some emails and see what the experts have to say.

http://www.tectra.de/MCP.htm
ed.artcet|ofni#ed.artcet|ofni
http://www.sciner.com/MCP/MCP.htm
http://www.proxitronic.de

page revision: 9, last edited: 05 Aug 2007 09:26