Following from earlier thread's discussions on the late parachute deployment, there is a
pretty up-to-date and comprehensive discussion of Phoenix's EDL architecture from last
year's planetary probe workshop (this year's is in Atlanta next month - www.planetaryprobe.org)

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._2008012907.pdf

Interestingly, they were going to use rather more sophisticated lifting entry, but it
got descoped.

unnecessary quoting deleted [oops. sorry. JB]

Interesting article. I had wondered if/how they would attempt to avoid the parachute landing back on top of the vehicle. Do you know if vehicle state information was recorded on the way down? I'd be interested to know how wobbly Phoenix was during the final portion of the powered descent with the jets.

Jon

I would imagine that vehicle attitude information was recorded -- Phoenix sported an inertial measurement unit, which used an inertial platform to align itself to a stable matrix. With such a platform, it's very easy to record attitude information. The only thing I would not be surprised at is that the sampling rate of the attitude excursions may not be high enough to give a really good idea of the vehicle motions.

-the other Doug

I hope it was. Phoenix actually had two IMUs, and generally the difference between an IMU (inertial measurement unit) and an INU (inertial navigation unit) is that the latter has some brains, but the former does not. Phoenix's IMUs were expected and allowed to expire from cold last night.

So there is no way of knowing if we get towed away when we landed in a "no parking" zone.

That rules out using the accelerometers in them as crude seismometers, that is if the dampening factor of the units is 0 or 0.707. I suppose that was the case since it makes it easier to measure arbitrary motions. Anyone has more info on these units?

Yeah, that was precisely the same thought I had. Unfortunately, they don't have heaters & are mounted externally on Phoenix.

So, after all the nursing along of the 'plucky little rovers' with their dodgy paw, um, wheel and arthritic arm, this is the Sadistic Mission?

Let the Seven Months of Terror commence.

Indeed!

Seriously, though, with respect to the IMUs I sure hope that future stationary lander missions will give a thought to keeping at least one running (with a power budget built in) for seismology after EDL. It seems like such a waste to me to transport sensitive, expensive instruments all the way to the target and then never re-use them for a legitimate scientific application.

There's even a sort of Catch-22 involved. You know at least one IMU will be operational after landing, or else you ain't gonna be landing...

I suspect this Q has probably been answered somewhere, and if so , please excuse my inattention.... but...

Was Phoenix planning to take descent camera imagery, like the animation shows? I seem to recall the task was being deleted because of computer issues, but I don't know the final outcome...

http://www.msss.com/msl/mardi/news/12Nov07/index.html

"Hi Mike,

It is sad that we will not acquire MARDI images during "terminal descent" (landing). To be clear (as you know), the "interference" that was mentioned was not due to the MARDI instrument itself, rather it was due to a very hard to find bug in an interface chip in an electronic board inside the lander unrelated to MARDI. It was discovered (before launch) that during the MARDI image data transfer the chip design was susceptible to errors that had the unfortunate consequence (in rare cases) in causing the lander computer to reset during EDL. Phoenix (and MSL) are not able to survive landing in the event that the on-board computer resets. If it did, by the time that the reboot is complete, too many things have happened for the software to be able to figure out what to do to survive. Although the odds of a reset was on the very low side, it was decided that we should not take a chance that it would.

I am happy to say that we expect to take (lots) of images with MARDI during MSL's landing. The chip design problem will be gone by then. (I certainly hope!)

-Rob Manning

http://www.unmannedspaceflight.com/index.php?showtopic=5145

Thank you, both....