This would have the benefit of allowing this theoretical NASA interstellar spacecraft to be much lighter and less expensive. Again though, we don't know how to do fusion yet. More than this, it's uncertain whether we could build a fusion reactor that could operate on the specific types of hydrogen isotopes available in the vacuum of interstellar space.
As noted by Science ABC, all of the antimatter ever created in history would be insufficient to bring a cup of tea to a boil. Yes, antimatter completely destroys an equal amount of ordinary matter – releasing "vast" amounts of energy in the process.
But the quantities of antimatter we've manufactured in particle accelerators are so tiny – basically individual particles – that it would be useless for building a propulsion system for interstellar travel. A NASA interstellar spacecraft using antimatter for propulsion would literally cost trillions of dollars just for the fuel. So that's clearly out.
The ships would go at a snail's pace compared to the previously mentioned options. This means that the people who reach Alpha Centauri – or whichever star system the spacecraft is aimed at – will be the descendants of those who originally set off from Earth. Depending on how long it takes the NASA interstellar generation ship to travel the enormous distance involved, centuries could have passed before the human colonists on board the ship reached their destination.
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