HiRISE and Mars Polar Lander Options

[Guest_Sunspot_*]

Looking at the images of the Spirit/Opportunity landing site, it seems many of the features such as tracks and rocket blast markings have faded considerably often to the point of being invisible in the nearly three years since landing.

This had me thinking about the MGS images taken in the hope of finding MPL. Initially it was reported that MGS had spotted the lander, one image had a white spot/streak interpreted as the parachute and a dark patch with a spot in the centre not too far off, taken to be the blast zone of the rockets with the lander in the centre.

However another image taken 5 years later seemed to discount this theory - the features had faded or changed significantly. BUT, seeing how much the rover sites have changed in an even shorter time, wouldn't the same happen to the MPL site in 5 years - perhaps to an even greater degree with the more extreme seasonal changes at that location. Also, the latest HiRISE images show just how difficult it has been to spot the landers on the surface with MGS, the Viking sites in particular.

I hope HiRISE takes another look at this spot.

Mars Polar Lander NOT Found, MSSS article:
http://www.msss.com/mars_images/moc/2005/10/17/

[MarsEngineer]

Hi Climber,

You are correct. There was and continues to be a lot of uncertainty in our knowledge of the density variations in the altitude range that the entry vehicle does most of its deceleration (mostly between 20 and 50 km). Given that these machines enter at very shallow entry flight path angles - around 13.5 degrees for MPL - only a few percent uncertainty in our estimates of the atmosphere density means the difference of many 10s of km on the surface. The ellipse shown on the HiRISE site (made by Tim) is based on our best guess of where the vehicle was when it reached the top of the atmosphere (based on our radiometric tracking data taken in the hours and days before landing). We think these estimates were pretty good and do not depend much on what failures may have happened to the vehicle. We then use computer simulations to model entry, descent and landing using one atmosphere model (as well as slight variations in the entry initial conditions), we then do the simulation again and again using slightly different models (correctly selected statistics-wise) and then we look to see how these are scattered on the surface. The ellipse that Tim placed on that HiRISE map at the HiRISE site represents about a 2-sigma ellipse (see Emily's Blog from yesterday). So we believe that there is about an 86% probability that MPL is inside that ellipse.

Of course, people ask me; What if the cruise stage never came off? or What if the parachute did not open? What if it tumbled during entry? Well it turns out that these cases do not make a huge difference in the position and shape of the 2-sigma ellipse. It makes it a tad longer (probably moves it further south a few km as well ). As you suggest Climber, one place that we could be very wrong and would make a bigger difference in the ellipse is the atmosphere. You will also notice that the HiRISE images do not cover the right side of the ellipse. That was due to a mistake I made (an unfortunate change of longitude definitions occurred just after the post-MPL trajectory reconstruction that I was not aware of ... it resulted in our estimates of where the ellipse was painted on the surface moving a few km to the east after the HiRISE image "campaign" was well under way).

As I said before, it is there somewhere and I have some faith that it will eventually be seen. While I could be wrong (I have been many times in this biz), I doubt that it would have made a crater that did not leave equipment visibly scattered on the surface (unless subsequently covered by dust or other Mars material). Even without a parachute, it would have slowed down to very nearly it's Mars "terminal velocity" which for this vehicle is around 220 - 300 m/s (depending on tumbling attitude). That is fast but not fast enough to poke a deep hole in Mars!

If it is a needle in a haystack, I *think* it will be a bright needle. (My friends think I am an optimist.)

Cheers!

-Rob M

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These comments and opinions are solely those of the author and do not reflect the views of JPL, Caltech nor NASA.