At 7:37 am Eastern time on Saturday, a Cygnus cargo ship jam-packed with over three tons of crew supplies and hardware will blast toward the International Space Station atop Orbital ATK’s Antares rocket. ISS resupply missions aren’t just about making sure astronauts never run out of toilet paper. (Those folks keep a six month stockpile of all necessities anyway, which is why it isn’t a huge deal when the cargo ships ferrying their food and spacewalking equipment occasionally—or really, semi-regularly— go kaboom.) Where things really get interesting is in the research payloads—the science catching a ride on an otherwise logistical launch.

Deciding what gets to hitch a ride when requires ultra-careful preparation. Remember, cargo ship runs are like a giant game of space Tetris—except you have to control for three dimensions and mass. For non-essentials like research, cargo choices require NASA-wide deliberation. “We have teams from every space agency that work to balance the flow of science to the International Space Station,” says NASA spokesperson Dan Huot. They prioritize based on nuts and bolts like hardware availability, and squishier metrics like their relative importance in a given field. What bumps you up the pecking order? “Directly addressing a human health concern, or a major technology demonstration,” Huot says.

Which doesn't mean that you have to be curing cancer to get onboard. (Although it helps.) Two of the experiments blasting off Saturday were designed by kids, part of a program that has high school and middle school teams compete for research space on the ISS. "Inevitably, you do have some kids saying, 'We're going to cure cancer!'" says Michelle Lucas, founder and president of Higher Orbits, the non-profit running the program. "But we focus on making sure they get really good science back." This time around, both winning teams focused on studying the impact of microgravity on small life forms: the middle schoolers on mealworm life and reproductive cycles, and the high schoolers on biological nitrogen fixation in microclover. (Admit it, you're impressed.)

Adult projects range from enabling better DNA-monitoring aboard the ISS—see, cancer again—to setting up a VR camera for a National Geographic special. But the real scientific heavy hitters of this launch are technology-demonstrating CubeSat missions, including two designed by the Aerospace Corporation. The first is the Optical Communications and Sensor Demonstration, which will demo CubeSats' laser communication capabilities. Lasers can be more tightly focused than radio frequencies, so you can transmit a whole lot more data—100 times more, actually—with the same amount of power and mass. It's a perfect match for tiny, economical CubeSats.

The tricky part (besides developing the laser itself) was designing a system for highly accurate laser pointing. "You can get high data rates by using a narrow beam, but if you miss the target, you're not going to see anything," says Richard Welle, senior scientist at Aero's Space Science Applications Laboratory.

The Aerospace Corporation's second CubeSat leverages Welle's targeting system for an entirely different application. "Rich and I came up with a concept of putting three very small commercially available cameras together to act as a little miniature weather satellite," says Dee Pack, a researcher in Aero's Remote Sensing Department. Thanks to that fancy targeting system, the camera array should be able to see things like wildfires, oil fields, and city lights at night with greater resolution than NASA and NOAA's VIIRS (that's Visible Infrared Imaging Radiometer Suite) sensors—even while it's flying by at about 7 kilometers per second. CubeSats won't be replacing VIIRS anytime soon, though: NOAA will be beefing up the system by adding a new weather satellite due to launch Tuesday.

If everything goes according to plan, Saturday's launch will only be the first leg of the CubeSats' journey; they'll stay aboard the Cygnus transport while it's docked with the ISS, and then get boosted up to higher orbit once the cargo ship takes its leave in a few weeks. But for now, the CubeSat teams are just happy NASA's filling the gaps in its cargo ships with experiments rather than extra rolls of TP.