Ed said:

>Upgrade them at every chance. Build a bigger, better inflatable landing
>system to handle more weight. Put a RTG power source on the thing
>so it can stand up longer and not be so weather sensitive and have
>LOTS more power to do cool stuff.

Basically what you're describing is "Mars Science Lab" (MSL). MSL was supposed to be a super-duper-upgrade of MER. Unfortunately they've been screwing around with MSL for years and currently have a design that probably will be delayed, blow out its budget, etc. MER is no where near as sexy as MSL but has one big redeeming feature in that it works and is available now.

MER was launched by a Delta II ELV and had a launch mass of 1.063 metric tons. The Delta II payload capacity ranges from 0.891 to 2.1 metric tons to geosynchronous (very roughly the same energy requirement as for going to Mars). In theory, both MER A and B could have been launched by one Delta II. However that would have exposed the MER program to a single point launch failure (politically unacceptable). The Atlas V ELV can deliver 4.950 to 8.670 metric tons to geosynchronous. There is an obvious limitation in how many MERs can be crammed under one launch fairing but in theory eight MERs could be sent to Mars with one Atlas V launch. An obvious strategy is to crank out MERs like Volkswagen bugs (or Iridium satellites). Make twenty four of them under one contract and then shoot them out to Mars in groups of eight every two years over a total period of 6 years (use three Atlas V ELVs). I'm pretty sure there are 24 areas on Mars that the planetary science guys would love to explore. With so many vehicles, the science people could risk being aggressive and suffer a couple of failures.

Gary