A way to mitigate the risks of a crewed mission to Mars is reducing the time of transfer to and from the planet, with the downside of a meaningful increase in the mass required to achieve faster travel. In this work it was considered the possibility of producing the propellant needed for the return journey for such a rapid crewed mission on the surface of Mars, taking advantage of In Situ Resources Utilization (ISRU) technology. Although ISRU is typically considered as way to reduce mass when designing a mission to Mars, it was not clear whether this would be the case when the quantity of propellant to produce is very large.