NASA is about to light its biggest-ever fire inside a doomed space garbage truck.

The purpose of this test is simply to "see what happens," writer Maddie Stone at Gizmodo reports.

Why? The space agency has no idea what'd happen if a big fire broke out on a spacecraft. And if you're exploring the final frontier with people, fire is a pretty important risk to understand.

The space agency will light the controlled fire inside an experiment aboard a discarded Cygnus resupply vehicle. The bus-size spacecraft safely disconnected from the International Space Station (ISS) on Tuesday at 9:30 a.m. ET, and NASA will light the spark around 2:30 p.m. ET.

Here's how the fire-in-space experiment, called Saffire-I, is going down.

Lighting a controlled fire in space

A Cygnus spacecraft floating above Earth. NASA Over the past few months, astronauts moved all the supplies aboard the Cygnus into the ISS — then packed the spacecraft full of garbage.

NASA has since undocked the spacecraft and propelled it away from the space station. Mission controllers also put it into a different orbit.

Once the Cygnus maintains a safe distance — NASA hasn't said exactly how many miles — officials on the ground will remotely spark a fire inside Saffire-1: a sealed, three-foot long box full of "cotton-fiberglass composite." (The goal is not to set the entire ship aflame.)

The fire should burn for about 15 to 20 minutes, according to Gizmodo.

Meanwhile, special temperature, carbon dioxide, and oxygen sensors will record the whole thing. A camera will also film the blaze, and heat sensors will gather data from both sides of the flame.

There won't be a live video of the fire, but all of this data will beam back to Earth before the ship deorbits, breaks up in the atmosphere, and is completely destroyed — so NASA should release some kind of footage in the hours, days, or weeks to come.

What the fire will look like

NASA Astronauts have intentionally sparked small, controlled fires in space before, but nothing bigger than a candle or match-size flame. A three-foot-long controlled flame in zero gravity is the biggest NASA has ever attempted.

Fire behaves differently in space than it does here on Earth. If you light a match on Earth, the flame is long and pointy because hot gases rise upward from the flame, keeping it straight and sticking up.

But in space, buoyancy does not exist — so the flames spread out in all directions.

NASA scientists know space fires can be erratic, but they don't fully understand the properties and mechanics. That's because — up until now — experiments like this have been extremely dangerous. They've also (luckily!) never sparked such a large fire on a spacecraft to learn from.

Read more about NASA's Saffire-I experiment here, and watch NASA's footage of the Cygnus spacecraft detaching from the ISS on June 14:

Julia Calderone contributed to this post.