I was wondering how much delta-v would be practical to achieve if you can have "unlimited" fuel avaiable in orbit?<br /><br />Lets say we use lunar regolith to fabricate liquid hydrogen and oxygen, and then send it to orbit. When done automated and routinely it would be very cheap, at least compared to sending it up from earth surface (let's not discuss the feasibility of this plan, lets just say it's possible).<br /><br />Then lets say we want to send a 10-tonnes craft to Mars. How long would it take if we used 100 tonnes of fuel? A 1000 tonnes? 10 000 tonnes? Where would it not be practical anymore (because of the weight of the fuel)?