Weather, engineering, and luck permitting, the Cygnus Commercial Resupply Services 4 mission will launch at 5:55pm ET from Cape Canaveral, Florida. NASA and its scientific partners managed to pack over 7,000 pounds of gear into the nearly 1,000 cubic foot cylinder (built by Orbital ATK). Things like food, life support hardware, robot parts, spacewalk gear, and Christmas presents for the astronauts.

Oh yeah, it’s also carrying some pretty sweet science. You want a cellular biology lab capable of testing how microgravity affects human tissue? Cygnus has it. You want fire? Cygnus has an experiment testing fire on flame retardant material. You want tech that will improve oxygen and water recycling? Mark Watney, you can thank Cygnus for your fictional survival. You want microsatellites? Cygnus has three.

“If we take gravity out of the equation, we expose other forces and changes in behavior that we don’t get to see in a one-G environment on Earth,” says Kirt Costello, deputy chief scientist for the ISS. That one-G he’s talking about is standard Earth gravity, and it mucks up all sorts of scientific inquiry—particularly how things like liquids and gases flow.

Except for the satellites, fluid mechanics are the core principle being studied in all Cygnus’ experiments. “Without gravity, you’ve got non-intuitive things happening with fluid dynamics,” he says. For instance, did you know that flames are technically governed by gravity? Far from Earth’s pull, fires stay compact and develop hotter heat.

Which is why Cygnus is carrying that fabric-burning experiment, by the way. Technically called Burning and Suppression of Solids (or BASS-M, if you’re collecting acronyms), chemical company Millican is running the experiment so they can make better flame-retardant attire for people like firefighters and electrical workers. “In microgravity you don’t have a lot of convection-driven buoyancy that controls how heat flows, and you can get much higher temperatures because heat doesn’t get convected away,” says Costello. The results from these space experiments could save lives on Earth.

The human body is about two-thirds water, and that stuff isn’t just sloshing around in your belly. Water is the medium for every interaction inside every cell in your body. But those cells evolved in Earth gravity, and scientists are still trying to understand how they function in low-G.

Which is where the Space Automated Bioproduct Lab comes in. “In acronym-ese we call it SABL,” says Costello. With the mission to Mars looming, learning how long term low-G affects fluids in cells and tissues is important for astronauts. But like the fire experiment, in space, biology acts in funny ways that have applications on Earth. The next ISS resupply mission will be carrying cardiac stem cells, which for complicated fluid mechanical reasons grow a lot like those grown in a living human body rather than those grown in pressurized Petri dishes.

Speaking of pressure, life is under a lot of it on the ISS (or any crewed spacecraft). You want to keep people alive? You’ll need constant supplies of water, air, and food. Scientists have invented various filters and chemical processes to recycle the former two and grow the latter, but in space they don’t always work so well. The culprit? Not a trick question: It’s fluid mechanics again.

Without gravity, mixing liquids and gases (or liquids and liquids, or gases and gases) is tough. “Unintuitive things like capillary forces and surface tension take over,” says Costello. The trick to getting fluids to mix in space is by using things called packed bed reactors. Basically, you force whatever things you want to mix through some sort of porous material. In finding their ways through the material, the fluids are forced to mingle.

The Packed Bed Reactor Equipment (yep, that’s PBRE) does this with glass beads. “The hope and goal is to design the next generation reactor to take advantage of lack of gravity, reducing overall system mass, while increasing overall reliability,” says Brian Motil, a NASA researcher based at the Glenn Research Center in Cleveland.

And then there’s the satellites. Two are Nodes, each less than a foot per side. Their primary mission is measuring high energy particle fields. But maybe more interesting is their communications structure. See, the Nodes are a test for networked swarm satellites that can monitor a target from many angles, then autonomously decide which is in charge to send data home. If the technology gets sufficiently advanced, it can get adapted for larger satellites in larger numbers. “The computer in these satellites is a smartphone, off the shelf, programmed to control the satellite,” says Andrew Petro, chief of NASA’s Small Spacecraft Technology Program.

Similar in spirit to the Nodes’ one-size, modular ethos is the HiSat. Consisting of six equally sized and shaped modules, plus two deployable solar arrays, the HiSat’s parts (also known as SIMPL) will ride up on Cygnus, be assembled by astronauts, then launched from the ISS.

That’s a pretty novel idea, considering most satellites get launched directly from a rocket. From a practical perspective, this makes a lot of sense. For one, you can mass produce the parts. In the future, satellites could be made-to-order from orbit. The parts could maybe even be 3D printed.

The HiSat aboard Cygnus is pretty much a proof-of-concept model, but it also comes packing a few neat sensors. For instance, ham radio operators can call up to HiSat and get position reports, or relay messages to other operators who are outside their normal range. There’s also a DARPA payload for space Internet communications. Yeah, sounds legit.

Science aside, the commercial rocket industry needs a win. This summer, SpaceX left the International Space Station hanging when its resupply rocket blew up moments after launch. An Orbital Antares resupply mission similarly failed in 2014. Let’s all hope this one does better, if not for the science, then at least for the Christmas presents.

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The ISS Resupply Rocket Is Full of Sweet Science Experiments