Steve,
The museum of science and industry is a bus ride (about 30 mins) from central Chicago cant really do it on the trains. Its well worth a visit a few of us went in our free time on the same holiday, you need at least half a day there.
You can use 2 buses to get their (and back)
No10 bus - Is the Museum special and drops you at the door, you can catch this at stops along Michegan Ave between the Hancock Tower and the river near your hotel. Check timetable though because it doesn't run all year round and sometimes just weekends,
No6 bus - Is the Jackson Park Express and drops you off over the road, we had to use this one. You can catch it just over the river on Wacker Drive, Cross Michegan Ave bridge and turn left its the first bus stop you come to.
Buses are regular in each direction and not expensive.
Mick