This is an artist's concept of a comet harpoon embedded in a comet. The harpoon tip has been rendered semi-transparent so the sample collection chamber inside can be seen.
Credit: NASA/Chris Meaney/Walt Feimer
WASHINGTON: A high-tech harpoon that could one day pierce a comet and bring samples back to Earth is being developed by NASA.
The idea is based on a concept developed by the European Space Agency but adds a sample chamber to the spear so it can capture dust from a fast-moving, ice-spewing comet by hovering near it and launching the space harpoon.
A spacecraft would rendezvous with a comet, "then fire a harpoon to rapidly acquire samples from specific locations with surgical precision while hovering above the target," NASA said. "Using this 'standoff' technique would allow samples to be collected even from areas that are much too rugged or dangerous to permit the landing and safe operation of a spacecraft."
Comet harpoon to collect samples
Comets are typically just a few kilometres across, and have very little gravity so landing a spaceship on them is not an option. NASA has been working out various other ways of anchoring to a comet's surface.
"A spacecraft wouldn't actually land on a comet; it would have to attach itself somehow, probably with some kind of harpoon," said Joseph Nuth, a comet expert at NASA Goddard Space Flight Centre and lead scientist on the project. "So we figured if you have to use a harpoon anyway, you might as well get it to collect your sample."
Previous NASA missions, like Stardust launched in 1999, have collected comet dust during fly-bys. In 2016 NASA will launch its Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer, or OSIRIS-REx, on a mission to collect samples from an asteroid using a robotic arm.
"The next step is to return a sample from the subsurface because it contains the most primitive and pristine material," said NASA's Donald Wegel, lead engineer on the harpoon project.
Mystery of comet's surface
The team is working out designs at NASA's facility in Greenbelt, Maryland, using a crossbow to fire a harpoon into sand, ice and rock salt to gauge how much explosive powder is needed and what the best tip shape may be. "We're not sure what we'll encounter on the comet - the surface could be soft and fluffy, mostly made up of dust, or it could be ice mixed with pebbles, or even solid rock," said Wegel.
"Most likely, there will be areas with different compositions, so we need to design a harpoon that's capable of penetrating a reasonable range of materials."
Figuring out what works
The European Space Agency plans to launch in 2014 its Rosetta mission that that will use a harpoon to grapple a probe named Philae to the surface of comet '67P/Churyumov-Gerasimenko'.
Then, a suite of scientific instruments will analyse the regolith, or the loose surface material around the comet. "We will piggyback on their work and take it a step further to include a sample-collecting cartridge," said Wegel.
The experiments are at an early, proof-of-concept stage, and only after they figure out what works will the researchers apply for funding.
