QUESTION:
I study Computer Science, and would like you to tell me about the history
and trade-offs that led you to choose C (with some assembler) as the
language for the lander and the rover.

Several other choices come to my mind: Forth for compactness, C++ for more
"modern" programming, pure assembler, etc.
 
Also, Java is now touted to be good for both distributed computing and
toasters. Do you expect Java to become the language for rovers or landers in
the future?

ANSWER from Jesse Wright on August 4, 1997:
I can answer for the lander. First remember that we started 5 years ago on
our development. We needed a language that would work on these platforms:

* Wind Rivers VXworks for 68000 -- hardware tests with flight s/w
* Sun OS 4.1.2 -- high level flight s/w tests
* IBM R6000 workstations/cards -- low level flight s/w test & compile/link
* Wind Rivers VXworks for IBM RAD6000 -- final configuration
  (note: flight computer built by Loral)
 
The Wind Rivers VXworks operating system was the main driver. It only had
support for C until recently. Also we had to pay for the port and test of
VCworks for IBM R6000 and IBM RAD6000 machines. C++ was not an option
because we did not have a compiler for it when we needed one.  Assembly just
does not give the right "bang-for-the-buck" -- it is very costly to write
and test.
 
We rejected other languages mainly for 2 reasons: (a) it would be very
difficult to hire people with that language experience, and (b) other
languages, at the time, would not enhance peoples chance of advancement.
 
What we did do is design the software in an Object-Oriented manner using C.
(David Smyth, one of the team members has presented some professional papers
on the subject). This gives us most of the advantages of C++ with using C.
 
The gain we had in productivity on Mars Pathfinder s/w development was
mainly from using Object-Oriented designs. As you know people can code C++
without out really using objects.
 
We are in process of developing the next generation of flight/ground
computer system design using C++ for the high speed servers and
computationally intensive code, and Java for the analysis, command, and
display code. This might migrate to pure Java as Java "native code
compilers" become available.
 
In my view, the gain is to use better object-oriented techniques for
"better-faster-cheaper". The languages C++ and Java, right now are suited
for our applications. C++, for various technical reasons (multiple
inheritence, operator overloading, ...) make it less suited for our work
than Java (multiple person development teams, long life cycle, multiple
platform, distributed, time-sensitive). Java is also Hot -- we can hire
people with Java experience, and Java experience on a resume will help
people get jobs.
 
For the next series of launches (98), the flight software is directly
inherited from Mars Pathfinder and is in C. The new systems should be in the
2001 Mars launches, and earlier on some other flights.