Four astronauts are on their way to the International Space Station after being sidelined by Boeing's Starliner trouble and other issues. SpaceX launched the U.S.-Japanese-Russian crew from Florida on Friday. They should reach the space station this weekend, replacing colleagues who launched in March as fill-ins for NASA's two stuck astronauts. Leading the taxi flight for NASA is Zena Cardman. She was yanked from a SpaceX flight last year to make room for Starliner's test pilots whose capsule was judged too dangerous to fly. Two of her crewmates were also training on Starliner, which remains grounded until next year.

Elon Musk is dialing back his threat to decommission a capsule used to take astronauts and supplies to the International Space Station for NASA. The threat came as President Donald Trump and Musk argued on social media on Thursday. Trump said he could cut government contracts given to Musk's rocket company, SpaceX. Musk responded by saying SpaceX will begin decommissioning its Dragon spacecraft. It was unclear how serious he was, but he later posted he wouldn't withdraw the capsule. SpaceX is the only U.S. company capable right now of transporting crews to and from the space station, using its four-person Dragon capsules.

NASA's Lucy spacecraft will soon swoop past a small asteroid. It will be the second asteroid encounter for Lucy, launched in 2021 on a quest that will take it to 11 space rocks. Its ultimate destination is the unexplored swarms of asteroids out near Jupiter. NASA considers Sunday's flyby a dress rehearsal for 2027 when Lucy reaches its first so-called Trojan asteroid near Jupiter. Looking on from Mission Control in Colorado will be paleontologist Donald Johanson, who discovered the Lucy fossil 50 years ago. The asteroid is named for him.

A NASA spacecraft will make its second close brush with the sun. The Parker Solar Probe made its record-breaking first pass within 3.8 million miles of the scorching sun in December, flying closer than any object sent before. Parker will attempt the journey again on Saturday. Scientists hope the data from Parker will help them better understand the sun's outer atmosphere and what drives the solar wind. Parker was launched in 2018 to get a close-up look at the sun and is the fastest spacecraft built by humans.

On an episode of "The Story Behind the AP Story," Associated Press space writer Marcia Dunn discusses the space odyssey of NASA's two stuck astronauts. Butch Wilmore and Suni Williams are finally on their way home after more than nine months in space. Wilmore and Williams left the International Space Station in a SpaceX capsule early Tuesday, checking out with two others. The capsule is due to splash down in the evening off the Florida coast, weather permitting. The astronauts will then be taken to Houston. The astronauts' return will close out a dramatic marathon mission that began with a bungled test flight of Boeing's Starliner capsule last June.

College students, rocket scientists and math enthusiasts around the world are celebrating Pi Day. The holiday on March 14 — or 3/14 — correlates to the first three digits of the infinite number. It's also Albert Einstein's birthday, making the pie eaten at Pi Day gatherings all the sweeter. Pi is a mathematical constant that expresses the ratio of a circle's circumference to its diameter. It is part of many formulas useful in physics, astronomy, engineering and other fields, dating back thousands of years to ancient Egypt and Babylon. Across the country, many events now take place on college campuses.

CAPE CANAVERAL, Fla. (AP) — Landing a spacecraft on the moon has long been a series of hits and misses.