If the robotic vehicle stays aloft until March 25, it will break the X-37B mission-duration mark of 674 days, which was established back in October 2014.

It's unclear whether that will actually happen, however; the Air Force is tight-lipped about most X-37B payloads and activities, including touchdown plans. [The X-37B's Fourth Mystery Mission in Photos]

The uncrewed X-37B (also known as the Orbital Test Vehicle, or OTV) looks a lot like NASA's now-retired space shuttle, only much smaller. The X-37B is just 29 feet (8.8 meters) long and 9.6 feet (2.9 m) tall, with a wingspan of about 15 feet (4.6 m). Two of the vehicles could fit inside a space shuttle's payload bay.

The Air Force is known to have two X-37Bs, both of which were built by Boeing. These twin craft have flown four missions to date. OTV-1 launched on April 22, 2010, and landed on Dec. 3 of that year, spending 224 days in orbit. OTV-2 started on March 5, 2011, and wrapped up on June 16, 2012, after 468 days in space. OTV-3 launched on Dec. 11, 2012, and landed on Oct. 17, 2014, after circling the Earth for more than 674 days.

Airline Secrets Revealed

It doesn’t matter if being up in the air feels like a second home to you and you’re practically an honorary pilot at this point for how much you jet set — there’s a lot you probably never knew about your commercial flying experience.

1 You’re probably flying with dead bodies.

Airlines need to make money however they can, and that includes taking on additional cargo like corpses and body parts. Ever wonder how donated kidneys make it from St. Louis to Dallas, or a body is flown from one city to another? Now you do.

--->2 You should never, ever drink the coffee or tea.

Your commercial flight has only three possible ways of getting the water for that fresh brew: bottled (too expensive, you’ll need to fly private for that), bathroom tap (the same sink someone may have used to deal with air sickness after a bout of turbulence), or from a fresh tap water holding tank that’s positioned just a few inches from the human waste and trash tank on most commercial flights. You do the math, and consider a can of seltzer or bringing your own Starbucks on board.

--->3 Cabin lights get dimmed for a reason.

It’s not mood lighting, people. It’s for the sake of your eyes adjusting more easily to the outside world in the event of a crash upon landing. Less soothing than thinking your pilot just wants to create a spa-like environment, right?

--->4 Your floatation device may be missing.

While airplane designing minds decided long ago that storing floatation devices and vests under seat cushions would be a great way to maximize space and safety, they never accounted for the popularity of thieving passengers. It turns out those vests are one of the top stolen items on airplanes, and the crew hardly has time to notice. Make sure you check under your seat before taking off.

--->5 Your cell phone won’t make the plane crash.

But the signal censors up front in the cockpit are pretty sensitive, so if your pilot is up front trying to get clearance for a takeoff and you plus 30 of your favorite seat mates can’t just enjoy airplane mode for a few minutes — you’re going to delay everyone. Don’t be that person.

--->6 Nobody can tell you not to breastfeed.

If you’re up in the air and your baby is hungry or cranky, it’s your right to feed. If the passenger next to you complains or causes a stir, the cabin crew is usually obligated to relocate them, not you.

--->7 Bad passengers are seated in the kiddie section.

If for some reason your seat changes last minute and you find yourself in the middle of a family of 14 young children, it’s likely because you did something to annoy the gate agent. Yes, they can punish you, so it's best not to be rude or demanding.

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