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Mike Ravine, Advanced Projects Manager for Malin Space Science Systems  (Source: torynfarr/flickr)

A two-image panorama shot with the rover's 1024 x 1024 mono navigation cameras  (Source: NASA)
Reasons included the amount of data produced, the fact that they had to meet the needs of different cameras, and the team's familiarity with these sensors

NASA recently accomplished a huge feat by landing its Mars rover Curiosity on the Red Planet, but one of the questions on the minds of many was why such a sophisticated machine used 2 MP cameras.
Mike Ravine, a project manager from Malin Space Science Systems, was happy to answer that in an interview with Digital Photography Review. He said the main reasons for using 2 MP sensors in the cameras were the amount of data produced, the fact that they had to meet the needs of different cameras, and the team's familiarity with these sensors.
"There's a popular belief that projects like this are going to be very advanced, but there are things that mitigate against that," said Ravine. "These designs were proposed in 2004, and you don't get to propose one specification then go off and develop something else. Two MP with 8 GB of flash didn't sound too bad in 2004. But it doesn't compare well to what you get in an iPhone today."
The amount of data produced is a large reason for using 2 MP cameras. There just isn't enough bandwidth for anything more powerful because the cameras must share with other instruments. Curiosity sends data back to Earth via the UHF transmitter, which transmits to two spacecraft orbiting Mars. The data is then sent back to Earth, and this system only allows for 250 megabits per day to be shared amongst various instruments.
The 2 MP camera sensors also were the tools of choice for the use of four different cameras, including the MAHLI, MARDI and two Mastcams. Having four different sensors for each camera would be expensive and more difficult to maintain rather than having one type of sensor all across the board. 
The team's familiarity with the sensors was crucial, too. The team knew the behavior of Truesense imaging chips and Kodak's KAI-2020 chip, so it makes sense that they'd work with what they know. 
"We know how to clock them and drive them," said Ravine. "They're a very easy CCD to drive."
Other issues, like the low pixel count, are not an issue either since the two Mastcams will create images from multiple exposures. 
NASA rover Curiosity landed successfully on Mars earlier this week after launching from Cape Canaveral, Florida on November 26, 2011. Curiosity is a one-ton, nuclear-powered, Mini Cooper-sized science laboratory that will explore the Martian surface for the next two years. 

Source: Digital Photography Review

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RE: Still no reason why they couldn't put 8MP
By talikarni on 8/9/2012 4:09:38 PM , Rating: 0
Anyone who watched the Curiosity landing, should have overheard the comment where the satellite link maxed out at 500 bits (0.5Kb) per second.
By comparison dialup is at best 56,000 bits (56K) per second.

Now you people are talking 8MP cameras? 20MB files attempted to be sent through something 1/10th the speed of full speed dialup? You are looking at 91 HOURS (almost 4 days) per picture, and thats only if they had a full speed dedicated connection for the entire time which they do not.

So now you figure a 2MP camera at full color resolution creates images that are in the range of 500KB.
500KB = 4,000,000 bits (4Mb)
4Mb divided by 500 b/s = 8000 seconds or 133 minutes (over 2 hours) per full resolution picture.

Now the 64x64 pixel thumbnails collected just after landing were in the range of 1KB which comes to around 16 seconds per picture (if sent at the full 500 bits per sec.)

By Solandri on 8/9/2012 6:56:50 PM , Rating: 2
See my other post above. The downlink speed during landing was a gerry-rigged network of the lander to an orbiter to earth (Curiosity actually landed on a part of Mars facing away from Earth). Any time the transmitter is moving or its position isn't exactly known, the bandwidth will be much lower.

During the mission, Curiosity will transmit data to an orbiter, which will then relay it to Earth. For Spirit and Opportunity, these uplinks to an orbiter are at about 256 kbps - 2 Mbps. But are limited to a few minutes a day (when an orbiter is sufficiently high overhead).

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