After many delays, the European Space Agency (ESA) is ready to launch its long-awaited Swarm mission into orbit at 4:02 p.m. Moscow Time (12:02 p.m. GMT) Friday, 22 November. The projected four-year mission will utilize a “constellation” of three trapezoidal satellites in near-polar orbits to monitor the strength, direction, and variation of Earth’s magnetic field, as part of efforts to better understand our atmosphere and climate and their interaction with the Sun. Flying atop a Rockot launch vehicle from Site 133 at the Plesetsk Cosmodrome in Arkhangelsk Oblast of Russia’s far northwest, some 500 miles (800 km) north of Moscow, the satellites will be injected into an initial 300-mile (490 km) orbit, after which they will gradually maneuver to their active science orbits.
Originally proposed by a team of Danish, German, and French scientists, with support from seven European nations and the United States, Swarm was selected by ESA as an Earth Explorer Opportunity Mission in May 2002 and is tasked with performing high-precision and high-resolution studies of the strength, direction, and variations of Earth’s magnetic field. When complemented by navigation, accelerometer, and electric field measurements, Swarm’s data will allow for the development of better models of our planet’s geomagnetic field. Its key scientific objectives include investigating the dynamics of Earth’s core and its interaction with the overlying mantle, as well as the magnetic state of the lithosphere and the flow of current in the magnetosphere and ionosphere. Secondary tasks include magnetic-signature observations of ocean circulation patterns and providing new insights into Earth’s interior, climate, and interaction with the Sun.
Each of the Astrium-built Swarm satellites measures about 29.8 feet (9.1 meters) in length and carries five instruments, including a fluxgate vector magnetometer, an absolute magnetometer for calibration purposes, an accelerometer, an electric field instrument, and a laser range reflector. Original plans called for four satellites, of which two would operate from a 285-mile (460-km) orbit and two of which would operate from a higher, 330-mile (530-km) orbit, but by 2004 changes to the project refined the number of spacecraft to three, with only one in the higher orbit. At that time, liftoff of Swarm was projected for 2009.
“After climbing into space on a single launcher, the satellites will adopt orbits passing over the Earth’s poles,” ESA explained in a January 2005 news release. “Swarm-A and -B will fly side by side, simultaneously measuring the magnetic field from positions up to 150 km apart in the east-west direction near the equator. Their orbits will at first be 450 km above the surface, but by the end of the mission they will come as low as 300 km, for more accurate measurements of magnetism originating from the Earth’s crust. Swarm-C will always fly higher, remaining at more than 500 km altitude throughout the mission. Compared with its sisters, Swarm-C will give simultaneous snapshots of the magnetic field over quite different regions of the Earth, and impressions of the same region at different times of day.”
By the end of 2007, the project had evolved from Phase A/B preliminary analysis and definition into the Phase C/D finalization of designs and construction of hardware. By April 2010, when ESA contracted with Eurockot Launch Services to carry Swarm into orbit aboard one of its Rockot boosters from Plesetsk, the liftoff target date had slipped to no earlier than mid-2012. Over the course of the following year, the three Swarm satellites took shape and underwent extensive testing by engineers in Ottobrunn, Germany. These included tests in a wooden-floored, magnetically-clean environment to evaluate the performance of their scientific instruments. “In fact,” noted ESA in October 2011, “the magnetic testing facility is in a forest, far from any other buildings to minimise any magnetic disturbance.”
Rescheduled for a late 2012 liftoff, the mission’s progress had been stalled by problems with the Rockot vehicle, which suffered a launch failure in February 2011 and was only returned successfully to flight in July of the following year. Then, in January 2013, another Rockot flight suffered a performance shortfall from its Briz-KM upper stage—of similar design to the unit which will place the Swarm payload into orbit—and a further delay was enforced as investigators set to work identifying the cause and implementing corrective actions. Eventually, on 12 September, a Rockot/Briz-KM combo perfectly delivered three Gonets communications satellites into orbit, and it became increasingly likely that Swarm could be launched as early as mid-November.
Finally, on 19 September, the first Swarm satellite was airlifted from Munich, Germany, to Plesetsk, aboard an Ilyushin-76 cargo aircraft, followed by its two sisters over the following days. By mid-October, inside the Spacecraft Preparation and Integration Building, the satellites had been fueled with Freon-14 for their maneuvering thrusters, and the Rockot vehicle was transferred to the Site 133 launch complex on the 23rd. In the meantime, the Swarm trio were being prepared for installation onto their payload adaptor, when, on 30 October, Eurockot decided to postpone the launch by one week, from 14 November until 22 November, in order to replace a unit in the Briz-KM.
Aligning the final pre-flight plans with this revised manifest, engineers completed the installation of the Swarm satellites onto their payload adaptor by 6 November, producing exceptionally tight clearances of just a few centimeters between the three spacecraft. “Placing the third one on the adaptor was particularly challenging,” ESA explained, “because it had to be manoeuvred very carefully so as not to damage the two already in position.” Encapsulation within the payload fairing occurred last weekend, and the vehicle was delivered, “in a rather wintry setting,” to the pad on Monday, 18 November. Wrapped in thermal padding, the fairing and its precious cargo were hoisted to the top of the pad’s servicing tower and lowered gently into place atop the Rockot.
The booster, which stands 95 feet (29 meters) tall, is manufactured and operated by Eurockot Launch Services, an organization founded in 1995, which is today owned with a 51-percent stake by Astrium and a 49-percent stake by Russia’s Khrunichev State Research and Production Space Centre. First flown from Baikonur Cosmodrome in today’s Kazakhstan in November 1990, the Rockot has completed 21 missions, with two failures, and has the potential to deliver payloads weighing up to 4,300 pounds (1,950 kg) into low-Earth orbit and up to 2,600 pounds (1,200 kg) into Sun-synchronous orbit. Its launch history has seen it carry communications satellites, science satellites, amateur radio satellites, Earth-observations satellites—including the recently-deorbited Gravity Field and Steady-State Ocean Circulation Explorer (GOCE)—and a variety of test payloads aloft. The Rockot owes its heritage to the SS-19 Stiletto intercontinental ballistic missile, and its three stages, including the Briz-KM upper stage, are all liquid-fueled and burn a combination of nitrogen tetroxide and unsymmetrical dimethyl hydrazine.
The half-shells of the payload fairing will open about three minutes after launch and, following the separation of the Rockot’s second stage, the Briz-KM upper stage will ignite to deliver Swarm into near-polar orbit. About 91 minutes into the mission, at an altitude of 300 miles (490 km), Briz-KM will simultaneously release the three satellites, after which the European Space Operations Centre (ESOC) in Darmstadt, Germany, will assume primary control. “The Swarm team will be waiting tensely,” ESA reported on Tuesday, 19 November, “as the satellites perform their automated sequence and then come to life, beaming their first signals back to the engineers via ground stations in Sweden and Norway.”
The first three to four days of the mission will form the critical Launch and Early Orbit Phase (LEOP), during which the Swarm team will check out the health of the systems and instruments. During this period, the three 1,032-pound (468-kg) satellites will gradually—over a period of several months—separate into different orbits, with Swarm-A and -B dropping to an altitude of about 285 miles (460 km), inclined at 87.4 degrees to the equator and flying in tandem, whilst Swarm-C will raise its altitude to about 330 miles (530 km), inclined at 88 degrees. Due to the limited propulsive capabilities of their Freon-14 on-board thrusters, this process will require several months and hundreds of maneuvers to establish them in their final science-gathering orbits.