QUESTION:
Why couldn't the Mars Surveyor get launched by the shuttle?
Isn't it more wasteful to use a rocket? 

ANSWER from Mark Adler on January 30, 1997:
Mars Global Surveyor (MGS) could have been launched by the shuttle, though it  
would have needed some modifications to allow it to fly on a human-rated  
vehicle, and that would have increased the cost of the spacecraft somewhat.
It turns out to not be more wasteful to use an expendable rocket of the sort  
used for MGS, because they are much cheaper than a shuttle launch, even though  
much of the shuttle is reusable.  Furthermore the shuttle is a valuable and  
limited national resource whose use should be and is limited to those missions  
that take advantage of the shuttle's unique capabilities.  Launching MGS  
would not have taken advantage of those capabilities.