Cosmic Snowflakes, Population and Density

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WeBeGood
Posts: 65
Joined: Thu Aug 03, 2006 7:26 am
Location: Texas, USA

Cosmic Snowflakes, Population and Density

Post by WeBeGood »

Optical Analysis of Impact Features in Aerogel From the Orbital Debris Collection Experiment on the Mir Station, page 31, table 1

Ignoring the orbital debris impacts (Flakes in the table). For ODC tray 1 plus the additional orbital velocity of the MIR space station. The percentages of Dust tracks to Snowflake pits is:

41% Dust Tracks, 59% Snowflakes Pits

For ODC tray 2 minus the orbital velocity of the MIR space station. It's:

61% Dust Tracks , 39% Snowflake Pits

So, the average of these two would seem to indicate that there should be almost equal amounts of Dust tracks and Snowflake pits in the Stardust aerogel.

This table also tells us a lot about the density or ballistic coefficients of the particles. MIR is in low Earth orbit, where atmospheric drag can have a significant effect on particles of different densities. Low density particles will decelerate faster in the tenuous upper reaches of the atmosphere that the MIR is orbiting. Higher density particles will not, and retain much of their velocity. Drag is a function of time, so one would expect that many of the less dense impactors would be slower and some even in Earth orbit. Stardust samples may be different.

Therefore, due to density differences of the particles we see an unequal distribution in the ratio of Dust Tracks to Snowflake Surface Pits, due to the MIR's orbital velocity. Also, the Snowflakes (pits) are moving slower as there are fewer impacts on the rear facing ODC tray.

Happy dusting, but don't ignore the Cosmic Snowflakes, they're interesting too.

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WeBeGood
Posts: 65
Joined: Thu Aug 03, 2006 7:26 am
Location: Texas, USA

Post by WeBeGood »

Seems I was wrong about the density of snowflakes to dust ratio. From the MIR Aerogel data it would indicate 50% Snowflakes, 50% dust.

From the LDEF thermal shielding experiment, the ratio of Snowflakes to dust is more likely something like 95% snowflakes to 5% dust in Earth orbit.

These thermal shields are made of the following layers:

0.127 mm of FEP Teflon
0.000016 mm (1600 A) Silver
0.000004 mm (400 A) Inconel
.1 to .125 mm urethane paint

Snowflake impacts will delaminate the layers of the shield at it's weakest point, the Teflon/Silver layer. Teflon doesn't bond well to anything, even itself. The Snowflake impact shockwave travels from the outside through the Teflon/Silver/Iconel/Paint. As the shockwave travels through this material, it fails at the weakest link, the Teflon/Silver layer. Essentially, popping off the Silver/Iconel/Paint layers creating a void between the laminations.

Cosmic Snowflake impacts on Teflon/Silver thermal shield

You'll notice in the above image that almost every impact hole has a delamination area around it. There are only a few that don't have the delamination area around the hole, these would be the dust without Snowflake impacts. Also, there are delamination areas with no visible holes. These are the pure Snowflake impacts. In this picture, there is one delamination only area that is rather large and has a shape other than a circle. Like four of five snowflakes stuck together, giving the delamination area shape but no holes (large dust).
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