After 10 years, the Rosetta spacecraft caught up with a comet to find out more about the beginnings of the solar system. We'll tell you about the technology behind the mission.
Right this moment, there is a spacecraft orbiting around a comet that is moving at speeds up to 135,000 kilometers per hour through our solar system. When it lands on the comet in about three months, it will take samples, drill holes, and take photos, all to help us better understand the beginnings of the universe.
Rosetta — named after the Rosetta Stone, a slab of volcanic basalt found near the Egyptian town of Rashid in 1799 — is going to help scientists better understand how our solar system came to be. The researchers want this mission to help piece together lost history in the same way as the Rosetta Stone helped people figure out an ancient civilization. Comets can explain a great deal about how life on Earth began. For instance, much of the oceans could have come from comets, and they could provide more insight into the beginning of the evolution of life forms.
Comet 67P/Churyumov-Gerasimenko is a large, 4-kilometer wide, "dirty snowball," according to the European Space Agency. Its orbit around the sun takes 6.6 years. Currently, the comet is about 600 million kilometers from the sun, on its journey back to the inner solar system.
Rosetta caught up with the comet on August 6, after finally garnering enough energy from planetary orbits. No launcher alone could have gotten Rosetta into its orbit around the comet, which is outside of Jupiter, somewhere between 800 million and 185 million kilometers from the sun, so gravity assists were needed from planetary flybys. Three (in 2005, 2007, and 2009) used Earth, and one (in 2007) used Mars.
Figuring out how planets were formed is no easy feat. This has been an technology venture 10 years in the making.
Dr. Gerhard H. Schwehm has been waiting for this day for the last third of his career. He has been a part of the Rosetta mission from the beginning — March 2, 2004. Quickly after it began, he was promoted to manager of the mission. Schwehm retired in March at age 65, very proud of the work he has done for the ESA. But he's not finished yet.
"One thing I'm really excited about," said Schwehm from his home in Germany, "is in my former life I was a scientist and it's really great to see that now it's coming in and all the hard work we have done before has paid off. It's just an exciting time. [It will] take some time but it's exciting and we have to start to see what we learned today fits in the big picture we have about comets."
This mission, which was approved by the ESA in 1993, has required huge technological advancements from the beginning. Schwehm and his team had to work with a variety of industries that had nothing to do with space to learn more about how to power the spacecraft, catch up with the comet, land, and take samples. They spoke to scientists in Antarctica to learn about drilling in freezing temperatures, and the oil industry to learn about drilling in different types of rock surfaces. All in all, about 2,000 people assisted in this mission throughout the last decade.
The first thing to figure out was how to operate the first technology to operate under various intensities and temperatures. They had to find a comet far away from the sun to have enough time to chase it and study it, then figure out how to power the spacecraft at that distance and temperature as well. The team had to design solar arrays that could work far from the sun at low temperatures.
This November, the lander — called Philae — will touch down on the comet's surface. During the first phase, the lander will be able to operate on its battery power. During the second phase, it will run on backup batteries recharged by solar cells. Schwehm said they'll be thrilled if it lasts four to five months, but they can't be sure how long it will last.
The lander could get too cold when the solar arrays stop providing enough energy, because the comet's average surface temperature is -70 °C, though that's about 20 to 30°C warmer than originally predicted. As the comet travels closer to the sun, Schwehm said, the inside of the lander will get increasingly hot — there's a lot of densely packed gadgets inside the small lander. In total, there are 10, including a drill and other instruments to measure density, texture, porosity, ice phases, and thermal properties to determine how the comet changes as it travels.
The comet reaches its closest point to the sun in August 2015, and the mission officially ends in December 2015.
The tech on Earth
Around the world, space agencies are watching Rosetta's progress. Schwehm, who is in contact with the ESA around the clock — said it's not what he expected in his first months of retirement, but he is excited to see this journey come to a climax.
The most demanding part of this process is these first few weeks, when all the data about the comet is coming in. As overwhelming as it may be, the days leading up to the landing are the most important.
To land on the comet, the ESA had to figure out the best way to orbit Rosetta around it. Rosetta has to be in front of the comet for the best light conditions from the sun. Using high-resolution digital images collected from several cameras on the spacecraft, including a wide angle lens, and scientific cameras to help map the area, the team generated a triangular orbit pattern around the comet. The challenge is now to figure out the gravitational pull of the comet. A pyramid shape allows them to better receive and analyze that data, eventually figuring out the density and mass of the comet.
"When we know that, we can define the more circular orbits. We didn't know anything. Now [that] we are measuring all these things to determine the mass we can know the gravitational pull on the spacecraft and close our orbits," he said.
Rosetta is currently at a "fairly safe and predictable distance of 100 kilometers," but will soon move to 50 kilometers away and start to map the comet.
To better understand the comet, the ESA has been using 3D printers to make models of the comet as Rosetta finds out more information about it. Last week, when the first images came through, they printed a model 50 cm in diameter. It roughly showed the shape of the comet. But with clearer imaging, Schwehm expects new models to be made that show more detail each time. In a couple of weeks, the team will have much more accurate data, like the details and craters of the comet.
Even more important than that is making sure the lander doesn't collide with the nucleus of the comet. The surface needs to be fairly flat and small.
"3D models — you could say you really need them. You can have a great imagination but if you want to select a landing site and see what the conditions are, it's good to have something in hand," Schwehm said. "Computer simulation is great, but something in your hand you can play with, that helps a lot. It's much better insight and feeling of how the whole thing looks in reality."