Europe's Swarm magnetic field mission set for launch
BY STEPHEN CLARK
Posted: November 21, 2013
Three identical European-built satellites are packed aboard a Russian rocket for launch Friday on a $280 million mission to map the Earth's magnetic field, an invisible bubble around the planet serves as a shield protecting life from solar and cosmic radiation.
"I am very happy that we are at this stage," said Roger Haagmans, Swarm's project scientist at ESA, in a phone interview Thursday. "I've worked the last 11 years toward this launch, so you can imagine I am very excited and hopefully very happy after tomorrow's launch."
The three spacecraft each weigh about 1,040 pounds when filled with freon propellant. The satellites will be lofted into a 304-mile-high orbit by a Russian Rockot launcher, a decommissioned nuclear missile upgraded to put spacecraft into orbit.
"We are all set and ready to go," said Rune Floberghagen, Swarm's mission manager at ESA, in an email with Spaceflight Now. "Thumbs up for tomorrow!"
The 95-foot-tall Rockot vehicle is set for launch from the Plesetsk Cosmodrome in northern Russia at 1202:29 GMT (7:02:29 a.m. EST). About 91 minutes later, after completing one lap around Earth, the Rockot's Breeze KM upper stage will simultaneously deploy the Swarm satellites in orbit from a custom-built connecting adapter built by Khrunichev, the Rockot and Breeze KM contractor.
View the launch timeline for more details on the Rockot's flight sequence.
"We are ready to get going, that's for sure," Floberghagen said. "Having said that, of course, we can only trust that all the work that needs to be done to give us a reliable upper stage has been carried out."
ESA's Swarm mission has been grounded more than a year to wait on an opportunity for a launch on the Rockot's backed-up flight manifest. A series of failures with the Breeze upper stage triggered several delays, and the Russian military put higher priority on launches for the Russian government, leaving Swarm to wait its turn.
The Rockot's commercial flights are managed by Eurockot, a joint enterprise between Khrunichev and EADS Astrium based in Bremen, Germany.
"The Rockot still has a very good track record," Floberghagen said in an interview with Spaceflight Now. "On the other hand, we know this Breeze family of upper stages has been rather, shall we way, beleaguered in the last few years and there has been trouble in the industrial consortium and the programmatic setup for these upper stages. People are taking it seriously, and we can only count on the fact that this job has been done properly."
"The main field of the magnetic field is originating in the Earth's core, deep inside the earth at 3,000 kilometers (1,864 miles) depth," Haagmans said. "It's like a big dynamo."
There are signs that the magnetic field is diminishing, and the unexplained weakening could be an indication the field is about to flip - something that has occurred on average every 250,000 years. The last time it happened was 800,000 years ago, so Earth is overdue.
"The weakening is so fast that it looks like it's going through a reversal, but this is a very open question and this is one of the things we are going to look at with this mission," Haagmans said.
Scientist have a murky understanding of what causes the magnetic field to erode or flip, and Haagmans said there has never been a mission like Swarm, which is designed to distinguish the drivers of Earth's magnetism.
The field behaves like a bar magnet with a north pole and south pole with magnetic field lines stretching into space, creating a bubble known as the magnetosphere. On the day side of Earth, the solar wind compresses the magnetosphere and charged particles stream around the planet and follow field lines into the poles, spawning the colorful auroras.
On the side of Earth facing away from the sun, the magnetosphere is blown out like the tail of a comet.
The primary force behind the magnetic field is the Earth's internal dynamo, where convection produces electric currents that spiral out of Earth, through the atmosphere and thousands of miles into space.
But there are other contributors.
Rocks in Earth's crust retain "remnant magnetism" that adds to the magnetic field generated deep within the planet. And the oceans create their own magnetic field from tides and circulation patterns, according to scientists.
"All of these currents and induced magnetic fields are part of what Swarm will see in space," Floberghagen said. "The trick is to make sure we have a constellation that is able to separate between what is the contribution from the main field, to understand the geodynamo and geophysics, what is the contribution from the Earth's crust and what is the contribution from these current systems that move around in geospace."
One satellite is not capable of examining the inputs of all the magnetic field sources, so Swarm's three spacecraft will offer unique insights.
"You are never going to be able to do it with a single satellite because then you have to use models to separate the components," Floberghagen said. "If you have spacecraft that measure at the same time in different local solar times - that means some are at night, some are in daylight and so forth - you are able to see the variation due to the ionosphere and also due to the magnetospheric activity."
In the first few months after launch, ground controllers will guide each of the satellites to different orbits. Two of the spacecraft will drop down to about 285 miles in altitude, and the third satellite will boost its orbit to about 329 miles, according to Floberghagen.
Built by EADS Astrium in Germany, each of the satellites could be plugged into any position in the Swarm constellation.
The two lower satellites will fly less than 100 miles apart, each receiving magnetic field signals at slightly different locations in space to map the field's global variation. The higher-altitude satellite will orbit on an entirely different trajectory to see how the field changes over longer time scales.
The satellites each carry an extendable 4-meter, or 13-foot, boom holding two magnetometer instruments to detect the magnetic field. Built in Denmark and France, the sensors will provide the highest accuracy magnetic field measurements ever made in space, according to ESA.
Engineers designed the satellites, which have their own magnetic fields, with special care to eradicate as many of their magnetic disturbances as possible. The engineers went over the rest of the satellites' components and analyzed how they might throw off Swarm's magnetic field data, creating a catalog allowing scientists to compensate for known measurement errors.
Technicians tested the satellites in a clean room with wooden floors, minimizing the potential of metals to disturb Swarm's magnetometers. In an extra measure of caution, the magnetic test facility was also in the middle of the forest away from other buildings that could have magnetic influence.
"We think we have an [error] effect that is low, in the order of 100 picotesla or so," Floberghagen said. "If that will be the case, the data from Swarm will be truly spectacular."
A tesla is a unit used to measure the magnetic field.
Scientists say the Swarm mission will help them learn how the magnetic field is evolving, why it is weakening and the data could be used in navigation and communications applications involving satellites, which are sensitive to changes in the magnetosphere.
"The whole point of Swarm is to make measurements more precise than other satellites but also to make them in a constellation, such that we can actively separate out the various contributors in a much better way than any other mission has been able to do in the past," Floberghagen said.
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