SpaceX is preparing for the third-ever launch of its Falcon Heavy rocket. The mission is called Space Test Program-2 (STP-2) and it is set to propel the ashes of 152 dead people into orbit.

Celestis Memorial Spaceflights

The cremated remains come from a company called Celestis Memorial Spaceflights. The firm buys available room on spacecraft and packs it with capsules of the remains of the deceased that it refers to as "participants."

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Founded back in 1994, the firm has flown cremated remains on 15 different rockets. Celestis flew the ashes of geologist and planetary scientist Eugene Shoemaker to the moon in 1998.

It also flew out the remains of "Star Trek" actor James "Scotty" Doohan into orbit in 2008.

For this SpaceX's STP-2 mission, Celestis purchased room aboard the Orbital Test Bed satellite. It will send its cremated remains in a flat metal sleeve where the 152 capsules have been glued in.

Between 1 gram and 7 grams of ashes

The capsules range in weight between 1 gram and 7 grams and come in different sizes. They often have sayings etched into them.

Some of the inscriptions on the capsules on board the STP-2 mission flight read "Reach for the stars!" and "Space Truckin' Forever."

It costs under $5,000 to send ashes into orbital flights and $12,500 for deep-space and lunar flights.

The STP-2 mission will also propel 24 satellites into orbit around Earth. It is set to take off between 11:30 p.m. ET on June 24 and 2:30 a.m. ET on June 25.