The next generation crewed spacecrafts is about to fly in the decade of 2020. Not only those in the headline here are trying to make it, but more are being developed privately and internationally.
Orion will be able to support its crew longer than the current commercial contenders, 4 astronauts during 21 days I've heard. First of all, is that basically true? And if so, is that a deep early design choice, or just a formality of the specifications because Orion is planned to fly around the Moon while the commercial contenders are contracted for LEO only?
What would it take to extend the crew support lifetime of a spacecraft of this next generation? Say, to make Starliner and Dragon also being able to support 4 crew during 21 days. Would it be enough to extend the size of the service module in order to increase storages of consumables? Or to replace a consumed service module with a fresh one, doubling the life support time?
Do they just need more luggage or a differently designed ship?