The stars may have finally aligned for the world's only space sibling team.
Astronaut Scott Kelly is circling the planet, fresh into a 5 1/2-month space station mission. His identical twin, Mark, will join him next year, if NASA's shuttle schedule holds up.
Together, they will become the first blood relatives to meet up in space.
"It's something we hoped would happen," Mark said. "It wasn't done by design. But we're fortunate. I think it will be fun for us."
Scott is the International Space Station's next commander. He took off aboard a Russian Soyuz rocket early Friday _ texting and joking with his brother right until launch.
Mark is space shuttle Endeavour's next commander. He's due to take off at the end of February and knock on the space station door March 1. It's currently slated to be NASA's last shuttle flight.
Don't expect any handshakes when the Kellys unite more than 200 miles up. The 46-year-old brothers _ Navy captains and former fighter pilots _ have never shaken each other's hands and don't plan to start just because the space station cameras are rolling.
Rather, count on embraces and even arm-wrestling when the hatches pop open between the space station and Endeavour, and the world does a double take.
For now, anyway, there's a little difference _ Scott is clean shaven and Mark has a mustache.
The Kellys promise no gags or matching outfits in space. They insist they've never done any of that.
So how will they mark the historic occasion? The Associated Press posed the question in a recent interview.
"We're going to arm wrestle," replied Mark.
"I was going to say the same exact thing," said Scott.
They laughed, then speculated on which twin would win, and whether it might end up a draw, with the two rotating around each other in weightlessness.
"I'll win because I'll have more zero-g experience," Scott said.
"By that point, your bones will be like powder. Your muscles will be atrophied," Mark countered.
While there have been father-and-son astronauts and cosmonauts, decades have separated their space missions.
A husband and wife flew together in space in 1992 _ Mark Lee and Jan Davis _ but NASA permitted it only because they were not married at the time they were picked for the shuttle mission and had no children. They divorced several years later.
For the Kellys, it wasn't meant to come together like this.
Mark should have been up and back from space by now. Endeavour's launch had been scheduled for July, but it was delayed to make improvements to the Alpha Magnetic Spectrometer, the primary cargo.
Between them, they have five shuttle flights. Endeavour's trip will make six.
Even if NASA had agreed to put them on the same shuttle flight, which brother would be commander and which one co-pilot? "We'd have to arm wrestle again," Mark said.
Endeavour will have to hit its Feb. 27 launch date or come awfully close, if the Kellys-in-space reunion is to stay on track. Scott Kelly will return to Earth in a Soyuz in mid-March, brotherly visit or no.
They expect their parents _ retired police officers _ to be stressed out more than usual as Endeavour's flight nears, not to mention their 94-year-old grandmother, who still asks if they might prefer becoming a lawyer or dentist.
"Fortunately, my brother's the one that's going to have to deal with it because I'll be in space," Scott said.
The twins grew up in West Orange, N.J., fists constantly flying at one another. They went to different colleges, but ended up together in the Navy's 1993 test pilot school class and, on occasion, shared jet cockpits. Unable to choose between them, NASA accepted both as astronauts in 1996.
The brothers live in Houston, and each has two daughters from previous marriages. Mark is now married to U.S. Rep. Gabrielle Giffords, D-Ariz. Scott is single.
Mark will be picking up his brother's mail for the next 5 1/2 months and paying his bills.
"Flying in space is a privilege and I try not to forget that," Scott told the AP before departing the planet. Flying with his brother will be "icing on the cake."
"It will be certainly unique, won't it?" added Mark.
Scott Kelly on Twitter: http://twitter.com/StationCDRKelly
Mark Kelly on Twitter: http://twitter.com/ShuttleCDRKelly