New Curiosity Rover Landing Target May Save Months Travel to Prime Destination 64
coondoggie writes with an update on the Mars Science Laboratory. From the article: "Even as it hurtles towards an August 5 rendezvous with the red planet, NASA's Mars Science Laboratory (MSL) is being fine-tuned for a more precise landing and better operations once it reaches its destination. NASA today gave a status report for the MSL which was launched November 2011, and is still over 17.5 million kilometers away from Mars. Of major interest today was the fact NASA said it has narrowed landing target for the Mars rover, Curiosity letting it touch down closer to its ultimate destination for science operations, but also closer to the foot of a mountain slope that poses a landing hazard, the agency said."
From NASA: "The larger ellipse, 12.4 miles (20 kilometers) by 15.5 miles (25 kilometers) was already smaller than the landing target area for any previous Mars mission, due to this mission's techniques for improved landing precision. Continuing analysis after the Nov. 26, 2011, launch resulted in confidence in landing within an even smaller area [handy diagram], about 12 miles by 4 miles (20 by 7 kilometers). Using the smaller ellipse, the Mars Science Laboratory Project also moved the center of the target closer to the mountain, which holds geological layers that are the prime destination for the rover. ... 'We're trimming the distance we'll have to drive after landing by almost half,' said Pete Theisinger, Mars Science Laboratory project manager ... 'That could get us to the mountain months earlier.'"
Re:Why?? (Score:5, Informative)
Because they completed an engineering analysis and determined that the reduced operational costs and increased science opportunities were balanced by the increased risk. Heck, for all you know there is no significant increase in the risk, and the old landing area selection was based on unnecessarily conservative estimates of the landing precision, so landing further away would be purely detrimental.
Re:Techniques for guiding a landing on Mars? (Score:4, Informative)
Range, Doppler, and VLBI, all from Earth (and all done by the DSN). I don't believe that this mission is using Optical Navigation. No (other) Mars spacecraft participate directly in this, although of course the Mars ephemeris is dominated by data from them. It is an iterative process, where an initial trajectory is refined by course corrections and monitored more or less continuously, with the measurement tempo increasing as Mars entry gets near.
If you want to drill down into this, here [gatech.edu] is a good starting point focusing on Mars entry navigation.