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The size of MSL, Yep, it really IS that big!
MahFL
post Aug 5 2012, 11:40 PM
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QUOTE (Marz @ Aug 6 2012, 12:29 AM) *
Seems a shame to deliver an extra 75kg to mars that is dumb ballast.

5.7 hours and counting!


The problem then is you'd have to safely land all the embedded rover/landers, have comms setup for them, and teams to run the submissions, all costing many many $$$. The throw away mass is what it is, it's a needed design feature.
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mchan
post Aug 6 2012, 12:32 AM
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Ballast is typically very dense material due to the mass and volume constraints. In some cases on aircraft, depleted uranium is used. Designing a payload into ballast is just not practical from either budget or schedule.
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Explorer1
post Aug 6 2012, 12:33 AM
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Any reason it was tungsten specifically? Wouldn't lead work just as well (and be a bit cheaper)?
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MahFL
post Aug 6 2012, 12:36 AM
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QUOTE (Explorer1 @ Aug 6 2012, 12:33 AM) *
Any reason it was tungsten specifically? Wouldn't lead work just as well (and be a bit cheaper)?


To comply with the Planetary Protection Protocol they used fairly nonreactive tungsten. Lead is deadly poisonous.

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mcaplinger
post Aug 6 2012, 12:55 AM
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QUOTE (Explorer1 @ Aug 5 2012, 05:33 PM) *
Any reason it was tungsten specifically? Wouldn't lead work just as well (and be a bit cheaper)?

Lead is too soft. Tungsten (or possibly a copper-tungsten alloy which is easier to machine) is much harder. Also, tungsten is denser, allowing volume savings.

http://www.e-tungsten.com/top_10_tungsten_reasons.html

I'm unaware of any planetary protection restrictions against lead or generally toxic materials. Consider the toxicity of Pu238...


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
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MahFL
post Aug 6 2012, 01:06 AM
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The Pu238 is in protective ceramic cakes. It's highly unlikely to ever to pollute Mars. It also has a half life and will eventually decay into a less harmless compound.
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