University Lowbrow Astronomers

From the Desk of Roger Tanner (Mars Pathfinder Update as of Mid October 1997).

by Roger Tanner
Printed in Reflections:  November, 1997.

I haven’t forgotten about writing for the newsletter, I was waiting for the Super Pan to be finished to send the latest high res images with the text.  I don’t know if you have heard, but we lost contact with the lander on Sep 27.  The battery died abruptly and dragged the power bus down to such a low voltage that the computer wouldn’t run.  The problem is the computer has to run to set the switch to disconnect the battery from the power buss.  Kind of a catch 22.  JPL had been sending the message to do that repeatedly at Mars local noon where the lander solar panels had the max power output and the computer had the best chance to restart.  Monday Oct 7th, they got a LGA link for 20 minutes that didn’t transmit any data but it turned off and on at the commanded times which indicated it ran the battery disconnect sequence.

The next step was to reconfigure the lander to run without the battery.  This will mean that operation will only occur during the day when there is enough solar power to run the instruments and the computer and the data taken can be down linked to the earth before the sun sets.  This is necessary because all the data is stored in dynamic ram.  Meanwhile the rover has probably not been able to make contact with the lander and its default program in this case is to make a circle around the lander trying to reestablish contact.  So who knows where the rover is?  This would be an autonomous traverse as the rover dudes call it.  It would have to find its own way around any obstacles.

They haven’t made any more contact and they think the problem now is the transmitters and receivers are not operating at the right frequencies because the crystals are getting much colder than planned with out heat from the battery at night.  The battery also heated the computer at night and that has been getting down to -80 deg C (-112 deg F) instead of the -55 deg C it has been tested to.  Our camera has been tested to -110 deg C and operates ok at this temperature.  JPL has been trying wider and wider frequency sweeps on both transmission and receiving without success.  The latest odds are only about 10% that we will regain contact.

When the Mars Global Surveyor reaches its final orbit and starts mapping the Pathfinder site, we might see the lander and a circular trench from the rover as it continuously cruises around the lander.  The Global Surveyor has 1 meter resolution, so the lander should be several pixels across and the backshell and parachute should also show up.

The two stereo images I sent are from the super pan with some resolution enhancement.  Unfortunately the Xerox copies don’t do the images justice.  The color image is from the presidential pan which is about 2:1 compressed in the red, blue, 4:1 in green.  The super pan is the first pan with the red (670 nm) and blue (440 nm) filters uncompressed and all of the geology filters (11 filters in the visible and near IR) at 2:1 Jpeg compression.  This results in a huge amount of data which took most of the downlink bandwidth until the battery failure.  The result is more detail in the images and the possibility of a better superresolution result.  Superresolution involves taking all of the images of one spot in each filter and processing them such that you get a monochrome image with about 2-3 times the resolution of our images.  This will allow more resolution in distant objects like the apparent terracing in the hills.

I will write again, when I hear more.

Clear skies.


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