The thruster "plates" are exposed through the aeroshell and there is a bevelled edge to them, I guess so they don't hang up when the lander is released. I wonder if there has to be even a small gap there. But then the Delta exhaust would have to work its way up the rocket and through the fairing seals. And then once you're moving, the early part of the slipstream should keep that at bay. I think the solids are jettisoned within the sensible part of the atmosphere.

But the Star 48 is used post-main stack separation, and physically closest to the vehicle itself. I think it's sensible to consider the possibility of contamination. Not saying that it's likely, just saying that it is possible.

They're definitely considering it, per Emily L's blog:



Just wondering what the potential source is.

I just read the press kit and the solids were kicked off well within the atmosphere, before fairing jett.

So the idea is that any stray perchlorate would be driven away by the air?

How about contamination beforehand--like when the spacecraft was mated to the third stage:




Or maybe the stage isn't even fueled at that point?

EDIT: Are you sure about the launch sequence? Here's a frame from the launch animation that seems to show the fairing coming off while the 3rd stage is still burning, and apparently above the atmosphere:

The stage is fueled at this point, and while I still think contamination from the propellant is only a remote possibility, if it did happen, then it probably happened here. Not at this exact moment, but at some point while the spacecraft and third stage were being processed in close proximity.

Please note too that very little, if any, perchlorate gets out of rocket exhaust intact.

Okay I'm an idiot - I was thinking about the Delta Solids not the PAM.

Well now it is interesting: there has to be a tiny bit of the plume that goes >backwards< in vacuum so perhaps the thruster plate "gaps" (if there are any - I don't know how you seal perfectly something that separates like it seems to) could be the culprit?

Isn't the solid fuel bound into the case at the factory, then cleaned and sealed?


But it doesn't burn perfectly and towards the end of the burn I wonder how ragged it gets through the grain.

EDIT: but it is a long daisy chain of improbables to get the bits that get out, then that tiny fraction that goes backwards, then sneaks through a gap (if there are any)...

Below is a very relevant excerpt from the Viking Lander 1 mission in August of 1976. This is all documented in the NASA SP-4212 "On Mars" and I would highly recommend it regarding all the clammer lately:

Data returned by the pyrolytic-release experiment and reported by Norman Horowitz on 7 August were equally confounding. Once again, the specialists had detected a reaction, but they did not know what it meant. "There's a possibility that this is biological," Horowitz said, but "there are many other possibilities that have to be excluded." The results obtained the night before were interesting but he emphasized that they were not ready to say that they had discovered life on Mars. "The data point we have is conceivably of biological origin, but the biological explanation is only one of a number of alternative explanations." He told the press: We hope by the end of this mission to have excluded all but one of the explanations, whichever that may be. I want to emphasize that if this were normal science, we wouldn't even be here-we'd be working in our laboratories for three more months-you wouldn't even know what was going on and at the end of that time we would come out and tell you the answer. Having to work in a fishbowl like this is an experience that none of us is used to.

He also cautioned the reporters that they were being included in the analysis phase of the experiments. They were "looking over the shoulder of a group of people who are trying to work in a normal way in an abnormal environment." The scientist's caution was prompted by his knowledge that "we well might be wrong in anything we say. Anyone who has carried out a scientific investigation knows that the pathway of science is paved not only with brilliant insights and great discoveries, but also with false leads and bitter disappointments. And nobody wanted to be wrong in public on a question as important as that of life on Mars."

Perchance a person somewhat unfamiliar with chemistry, but still cognizant of the plentiful chlorides in the Martian soil revealed by the wonderful rover teams, and also aware of plentiful energetic UV on the Martian surface, might ponder some interesting chemistry and innocently characterize the results as a 'chlorine analog to ozone', but it does sorta, kinda look like that is pretty much what might be going on with the perchlorate.

Yeah, maybe 'some' perchlorate tagged along from the Star 48, but we have UV and chemy precursors in abundance, so do we give a nod to the plausibility of perchlorates naturally occurring on Mars?

How hard would it be to dust off the old Viking surface chemistry experiment and dump some perchlorate in it and 'see what happens' ??

Great quote! But I think we all get the caveats and don't hold it against any of the science team. It's a privilege to get to watch them work (and a privilege (hard earned I'm sure) for them to work on our nation's space program).

EDIT: tasp got in my way

You're right, but at some point you have to put in the igniter, and I'm not sure exactly when this is. Also, some surface contamination is a remote possibility if they didn't clean the stage thoroughly.


Here is what wikipedia has to offer up on ammonium perchlorate (NH4ClO4) ...
"Like most ammonium salts, it decomposes before melting. Mild heating results in chlorine, nitrogen, oxygen and water, while strong heating may lead to explosions." Emphasis added by me. I just have a hard time seeing intact particles of propellant surviving the enviroment of a combustion chamber, no matter how fast they come out.

But the AP is still within the binder until it is exposed to the "burn front" (I made that up) no? so it doesn't melt until it is ignited. I'm just wondering if there is some physical process like ragged shocks that could dislodge unburned bits, especially just before shutdown. I'm REALLY reaching here.

Idle speculation: What about pyros ? There had to be a bunch going off in the EDL sequence when phoenix was out in the open ?

First go bring it back, then you can worry about dusting it off (I know you mean a ground spare / or reconstruction)

It does happen, and if the chunks get too big, well, the end result is like what happened to CONTOUR.

My instincts are still that perchlorate contamination from exhaust is a near impossiblity, especially with the exacting grade of fuel used in these kinds of rockets. But we'll see soon enough. I'm sure NASA and the Phoenix team will publically address all possible sources of contamination in a timely fashion.

No perchlorates. These use explosives.

Edit: I was mistaken here. NASA often times does use a zirconium/potassium perchlorate mix as an initiator in their pyros. I have no idea if they used such in Phoenix.