Hi guys and girls, I have an assessment task on all of my individual sciences which requires me to make propose a question and then carry out an open-ended secondary investigation. So this is my question for physics:

“Are methane-fuelled rocket engines feasible for interplanetary space travel?”

This question (proposal) has been approved by my physics teacher and I am confident to extract data and carry out a secondary investigation, but before I do that I need to plan out everything otherwise it could get a bit messy.

Referring to my question, I believe there are several factors which affect the feasiblility of a rocket-engine, including the following:
- cost
- safety
- its effectiveness

My question is, what else can I include regarding the factors which affect the feasibility of a rocket-engine? ^ if that made sense. Like aside from safety and cost, etc, what else?

Much thanks