How efficient is iron smelting ?
Acroduster there is a newer class of solid rockets that CAN be throttled/shut off, and restarted again. They are hybrid rockets with a solid rubber fuel similar to the SRB mix, but with a liquid/gaseous oxidizer that is injected down the bore of the rocket instead of using ammonium perchlorate. they are more complex than simple solid rockets but less complex than liquid fuelled rockets with cryo-fuels. they occupy a specific impulse range about midway between the two I believe.
booster, that was my comment. once you had a facility to process it. why send it all over looking for material to process? go harvest it from the asteroid beld and bring it back to the facility. in that case, the mountian WILL come to mohammed.....