Four astronauts on board the International Space Station ended their mission early after one of them had a medical issue.
The crewmembers splashed down in the Pacific on Thursday. The nature of the health problem is not clear, but the event highlights an ongoing concern: How, if humans want to settle beyond Earth, do we manage health problems without running back to Earth all the time.
The 2023 book A City on Mars noted the many dangers astronauts will face as we leave Earth — radiation, microgravity, poisonous chemicals on Mars, or lethal razor-sharp dust on the Moon — and most places we want to go are a lot further away than the ISS, which is only about 300 miles up.