[Marika (OP)]

Donald wants to know:

For long-term spaceflight, would it be reasonable to really fatten up the crew so eating calories isn't necessary? Saving on food, packaging, storage, diapers, etc.

What do you think?

[alancalverd]

If that were possible, I'd be on my way to Mars already, or at least standing in the queue with a bunch of other overweight, time-expired aviators and sumo-sized scientists.

You won't save on diapers unless you reduce the astronauts' total metabolism. AFAIK diapers are only worn for short single trips: a Mars ship is more likely to have recycling toilets which will certainly be needed on arrival. If we could find the key to effective hibernation and transfer it to humans, it would solve a whole lot of problems including boredom and possibly even radiation damage. "2001" and many other deep-space scifi plots use hibernation but the reality still seems some way short of fiction. Maybe the answer is to train grizzly bears to do whatever it is we want done on other planets?

[jeffreyH]

Are we talking about Mars or Mars bars?

[evan_au]

One of the essential factors in "living off your fat" is that your size reduces over time.
- But a long-duration spaceflight will require maintenance activities, including outside the spacecraft.
- The astronaut must fit into his/her spacesuit, or the repairs won't be possible.

Fat has very high energy density. And it has pretty much the same energy density whether it is sitting around your waist, or sitting in the cupboard.
- If they carried blocks of butter in the cupboard, it would have the same effect, but at least it wouldn't be furring up their arteries!
- But a diet of butter is not a balanced diet for humans
- and butter won't feed a healthy microbiome very well.

There is some reduction in energy consumption from living in reduced gravity. But astronauts in microgravity have to compensate by exercising vigorously for 2 hours every day. Maybe if the spacecraft ran on Mars gravity on the way there, and then ramped up to Earth gravity as they were returning to Earth?

As Alan said, efficient conservation and recycling of air, water and waste, and maybe growing some food on the way would be useful techniques to reduce liftoff weight.