Given the timeframe of interstellar travel, it makes sense to consider the possibility of uploading the minds of the crew rather than trying to take care of their fragile bodies:

The very high cost of a crewed space mission comes from the need to ensure the survival and safety of the humans on-board and the need to travel at extremely high speeds to ensure it’s done within a human lifetime.

One way to overcome that is to do without the wetware bodies of the crew, and send only their minds to the stars — their “software” — uploaded to advanced circuitry, augmented by AI subsystems in the starship’s processing system.

The basic idea of uploading is to “take a particular brain [of an astronaut, in this case], scan its structure in detail, and construct a software model of it that is so faithful to the original that, when run on appropriate hardware, it will behave in essentially the same way as the original brain,” as Oxford University’s Whole Brain Emulation Roadmap explains.

It’s also known as “whole brain emulation” and “substrate-independent minds” — the astronaut’s memories, thoughts, feelings, personality, and “self” would be copied to an alternative processing substrate — such as a digital, analog, or quantum computer.

An e-crew — a crew of human uploads implemented in solid-state electronic circuitry — will not require air, water, food, medical care, or radiation shielding, and may be able to withstand extreme acceleration. So the size and weight of the starship will be dramatically reduced.

This strategy has a long history in science fiction. In his 1962 story Think Blue, Count Two, sf legend Cordwainer Smith describes this very idea as a way to pilot interstellar vessels. You may consider his choice of computer system to be idiosyncratic: meet the laminated mouse brain computer:

...Tiga-belax came in, very cheerful indeed... In his right hand there was a black plastic cube wih shimmering contact-points gleaming on its sides...

"This brain isn't frozen... It's been laminated. We stiffened it with celluprime and then we veneered it down, about seven thousand layers. Each one has plastic of at least two molecules thickness. This mouse can't spoil. As a matter of fact, this mouse is going to keep on thinking forever. He won't think much, unless we put the voltage on him, but he'll think. And he can't spoil..."

And, uploaded into the laminated mouse brain is the mind of the pilot:

"Do you need the mouse any more?" said the first technician.

"Yes," said Tiga-belas. "One-third of a millisecond at forty megadynes. I want him to get her whole life printed on his left cortical lobe... "I'm putting the girl's whole lifetime into one-third of a millisecond at top power. It will drain over into the mouse-brain inside this cube."

More recently, Charles Stross has been playing with the same idea. In his 2005 novel Accelerando, a tiny starship - a Starwisp - is propelled by a light sail, and visits a nearby star system with an e-crew of 63 uploaded crew members:

Here we are, sixty something human minds. We’ve been migrated — while still awake — right out of our own heads using an amazing combination of nanotechnology and electron spin resonance mapping, and we’re now running as software in an operating system designed to virtualize multiple physics models and provide a simulation of reality that doesn’t let us go mad from sensory deprivation!

And this whole package is about the size of a fingertip, crammed into a starship the size of your grandmother’s old Walkman, in orbit around a brown dwarf just over three light-years from home.