How to Land a Spaceship on a Comet in Eight Steps

If successful, it would be scientists’ first-ever landing and a major boon to space explorers. If not, it could be a mighty big bang.

Rosetta will orbit 67P/Churyumov-Gerasimenko before sending a probe to land on it.
National Journal
Alex Brown
Jan. 22, 2014, 7:57 a.m.

Sci­ent­ists are try­ing to land a probe on a comet mil­lions of miles from Earth that is trav­el­ing at roughly 10 times the speed of a bul­let. Here’s their plan:

Step 1: Wake up your space­ship. The Rosetta craft, hi­bern­at­ing for nearly three years, was 500 mil­lion miles from the sun — way out past Jupiter. Now, it’s closer to 400 mil­lion miles away, and near enough to pick up the sol­ar power it needs to keep it­self go­ing. On Monday, sci­ent­ists pulled Rosetta out of its slum­ber.

Comets are con­sidered the “prim­it­ive build­ing blocks of the sol­ar sys­tem,” yet much is still not known about them. Ac­cord­ing to NASA’s Sam Gul­kis, the mis­sion will “cre­ate the most com­plete pic­ture of a comet to date, telling us how the comet works, what it is made of, and what it can tell us about the ori­gins of the sol­ar sys­tem.”

Step 2: Find your tar­get. By May, when Rosetta is 1.2 mil­lion miles from the ap­proach­ing comet, the European Space Agency ex­pects it to start send­ing back im­ages of the 67P/Chury­u­mov-Ger­asi­men­ko, a two-and-a-half-mile-wide comet that’s about to enter our sol­ar sys­tem. As it gets closer, NASA says, it will “trans­form from a small, frozen world in­to a roil­ing mass of ice and dust, com­plete with sur­face erup­tions, mini-earth­quakes, bas­ket­ball-sized, fluffy ice particles, and spew­ing jets of car­bon di­ox­ide and cy­an­ide.”

Step 3: Get in po­s­i­tion. At the end of May, Rosetta will be­gin lin­ing it­self up for a ren­dez­vous with the 67P. A comet land­ing has nev­er been done be­fore — all pre­vi­ous six comet en­coun­ters were in the form of brief flybys, two of them by Rosetta. But ESA, with help from some NASA in­stru­ments, thinks it’s ready to give it a try.

Step 4: Catch your comet. The fate­ful meet­ing is ex­pec­ted to take place in Au­gust. If all goes well, Rosetta will park it­self in or­bit around 67P and fol­low it in and out of the sol­ar sys­tem for 16 months.

Step 5: Find out what makes your comet tick. As Rosetta or­bits the comet, its three NASA-provided in­stru­ments will come in­to play. A mi­crowave in­stru­ment will sense tem­per­at­ure and chem­ic­als, as well as gaseous activ­ity. Alice, a spec­tro­met­er, will meas­ure the ul­tra­vi­olet por­tion of the spec­trum to test for wa­ter, car­bon monox­ide, and car­bon di­ox­ide. And an ion and elec­tron sensor will help define the comet’s plasma at­mo­sphere.

Step 6: Pre­pare for land­ing. The real mo­ment of truth will come Nov. 11. That’s when the tiny Philae lander, hon­ing in on a land­ing spot chosen by Rosetta‘s map­ping, will try to touch down on the comet. The 220-pound probe will de­ploy ice screws and har­poons as it hits the sur­face, be­cause 67P’s min­im­al grav­ity is not enough to keep it anchored.

Step 7: More test­ing — up close and per­son­al this time. If the land­ing goes well, Philae will start send­ing back high-res­ol­u­tion pic­tures. Then it will be­gin ana­lyz­ing ice and ma­ter­i­al samples, drilling up to nine inches be­low the sur­face.

Step 8: Stick around, en­joy the ride. Philae‘s job com­plete, Rosetta will stay along­side 67P as it nears the sun, watch­ing its ice re­act as the comet heats up. It will even­tu­ally get around 115 mil­lion miles from the sun, “roughly between the or­bits of Earth and Mars.”

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