Here is a powerpoint presentation on the orion project, mag orion (1999) and minimag orion from Andrews Space
The original concept from the 1960s was to toss nuclear bombs out the bottom of a space ship and then explode them and have the blast hit a large metal pusher plate. Tests with a metal sphere showed that the basic concept would work and there were many designs. Super Orion was a large version that could move millions of tons and used fusion bombs. (A large planned container ship would have 14,000 containers (TEUs) which average 14 tons loaded. A million tons would be 5 of those large ships loaded.) The case for Orion is described here. I agree with the case for Orion.
Mag Orion would have detonated 100 kiloton bombs 2 kilometers behind the space craft and had a superconducting magnetic sail interact with the blast to generate 1,000,000 newtons at 30,000 ISP.
Mini-mag Orion would use sub-critical explosions with Z pinch technology. 5 tons of explosive power with a 5 meter magnetic bottle. Specific Impulse of 21,500 sec and thrust 625,000 Newtons.
There has been follow up work on updating the Orion concepts:
Pdf from 2002. Project Orion and Future Prospects for Nuclear Pulse Propulsion, G. R. Schmidt; J. A. Bonometti; C. A. Irvine Journal of Propulsion and Power 2002
Here is a summary of the minimag Orion plan. Pulsed nuclear fission propulsion achieves the combination of high thrust values and specific impulse necessary for crewed exploration mission to both the inner and outer planets of the solar system. This mission capability would be sufficient for a 100 metric ton payload to reach Mars in 60-90 days.
There is a proposed follow on to the minimag orion work.
They have plans to increase the yield fraction (estimated at 10% of the fissionable material from MCNP results). It could be increased with a deuterium-tritium fusion boost. This will allow for a smaller package and allow for a greater amount of thrust for a given quantity of fissionable material. They would investigate how the magnetic bottle will change under these conditions as well.
This site explains how the space shuttle works. The solid rocket boosters have about 11 million newtons of thrust each. All three engines have about 30 milion newtons