LCROSS wheat from chaff?

I was reading about the LRO/LCROSS launch on www.space.com. It was
saying that LCROSS will guide the Centaur upper stage into an impact
on the moon, which it will presumably watch until it too impacts on
the moon. My understanding is the idea is to scan the ejecta for
evidence of water.

That sounds all well and good to my peanut gallery brain, but then I
went over to the wikipedia entry for Centaur - it uses LH2 and LOX.
Does Centaur have facilities for a (verified) purge of the tanks before it
hits the moon? If not, aren't residual LH2 and LOX a concern wrt
"contaminating" their measuements?

rick jones
--
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