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Poor crate training

by Deborah Bass

August 27, 2005 -

I have dogs, and have trained many of them over the years. So this analogy comes from that standpoint. One crates a puppy to potty train it, because dogs know that it is "bad" to mess in one's "den", and the crate functions as a den. The puppy learns to wait to go potty so that the den stays clean and pristine. As the puppy learns, the den is enlarged, so that eventually the whole house functions as the den. Works really well.

Unfortunately, our lander is going to mess in the den.

Our lander, unlike the MER rovers, is using a retrorocket/fuel system to land. No airbags. We spray fuel all over the landing site when we land. What is this fuel? A substance called hydrazine.

Wikipedia has a hydrazine entry (http://en.wikipedia.org/wiki/Hydrazine)
"Hydrazine is a chemical compound with formula N2H4 used as a rocket fuel."
"Hydrazine is a liquid with weak basic properties similar to ammonia."

The stuff freezes at 2 degrees Celsius.

Okay, no big deal right? Characterize the stuff and move on. Weeell, not so easy. This stuff is going to react with our soil chemistry and change what we see. What is worse, there are contaminants in the hydrazine--the stuff isn't pure! Even the really ultra-pure stuff still has organic compounds in it, and those compounds will contaminate our landing site and react with the unknown Martian soil chemistry.

Bad puppy.

Okay, so this spray will be kind of an even distribution all over our landing site, in a reasonably low concentration.
However, turns out that after we land, there will be some residual hydrazine in the hoses leading up to the spray nozzles, and based on our thermal analyses, these hoses will experience a wide range of temperatures, causing the fuel to freeze (contract) and thaw (expand). This freeze-thaw cycling is likely to cause the hoses to burst, producing a high concentration of this fuel and contaminants right in the location we plan to dig.

Very bad puppy.

How to solve this?
We're looking for puppy diapers. Lockheed Martin, who is in charge of the spacecraft, is going to put some baffling around the hoses on the side of the lander nearest our digging area. That way, it can both absorb and funnel the foul hydrazine to a location that is less important.

That way, we don't have to worry that our lander isn't house-broken. We'll just clean up the mess.

The science team is also working hard to characterize the fuel, so that we understand as much about it as possible.
Sometimes you just have to forgive puppies. At least they have fuzzy faces and lots of kisses.