Taking a sample from most earthy objects is easy using either a scooping or coring method. But in outer space, sample collection is a different ball game due to a lack of gravity and moving object.
Comets in particular could be especially hard, considering they are often spinning and traveling upwards of 150,000 miles per hour. NASA deems these as reason enough to think up an alternative to landing on comets for sample collection.
The idea it has developed so far? Harpooning comets. NASA reports in a news release that it's developing a harpoon to shoot at comets and pull back a sample. The concept is currently be researched in a laboratory setting using a ballista:
In a lab the size of a large closet stands a metal ballista (large crossbow) nearly six feet tall, with a bow made from a pair of truck leaf springs and a bow string made of steel cable 1/2 inch thick. The ballista is positioned to fire vertically downward into a bucket of target material. For safety, it's pointed at the floor, because it could potentially launch test harpoon tips about a mile if it was angled upwards. An electric winch mechanically pulls the bow string back to generate a precise level of force, up to 1,000 pounds, firing projectiles to velocities upwards of 100 feet per second.
Here's more about the harpoon concept and current research:
Right now, NASA reports that it is looking into how much energy would be required to shoot the harpoon at a comet at different depths and with different compositions. NASA Donald Wegel, lead engineer on the project, said that researchers aren't exactly sure what they're going to be met with in terms of comet composition, so its harpoon will need to be ready for anything:
The team is working out the best tip design, cross-section and explosive powder charge for the harpoon, using the crossbow to fire tips at various speeds into different materials like sand, ice, and rock salt. They are also developing a sample collection chamber to fit inside the hollow tip. "It has to remain reliably open as the tip penetrates the comet's surface, but then it has to close tightly and detach from the tip so the sample can be pulled back into the spacecraft," says Wegel. "Finding the best design that will package into a very small cross section and successfully collect a sample from the range of possible materials we may encounter is an enormous challenge."
Wegel says that comet samples would give researchers more materials to analyze about to the origins of our solar system, as comets are thought to be composed of materials form its formation.