Hypothetical Moral Question

[Twisp]

I was watching a movie today. 5 astronauts had crashed landed on Mars. Their positions broke down to the commander, a geologist, an astrobiologist, an engineer, and a doctor. Rescue would take a year to get there. There were enough resources for 2 people to live for a little over a year. 5 people could only live for 6 months. The commander had the doctor and the engineer stay, since they were the most vital. The engineer could keep the systems running and the doctor could keep both of them healthy until rescue arrived. The other three people volunteered to put on their space suits and leave, effectively committing killing themselves. Feel free to replace Mars within a location currently realistic.

Question: would this be considered suicide, and would you be able to morally do it to save the mission?

I know, useless question, but an interesting one, I think.