ESA’s Flight Dynamics team uses cutting-edge computational techniques to plan, determine and control complex spacecraft trajectories. We apply fundamental physics and mathematics to 21st century spacecraft orbiting Earth and voyaging deep into our Solar System.

We deliver precise orbital determinations enabling ground controllers to know where our spacecraft are located and prepare the manoeuvres to reach our targets like Moon, Mars, Venus, a comet or a spacecraft constellation. We also conduct mission analysis – brainstorming how robotic spacecraft can reach and return data from anywhere in our Solar System.

What we do

SMART-1 Moon orbit before impact in 2006

Flight dynamics scientists work as part of the team operating every ESA mission, whether in low-Earth orbit or soaring deep into our Solar System. We provide precise orbital calculations, determining where our spacecraft are located, which direction they’re facing, where they’re going and how far they've travelled.

This information is vital and is used every day not only by the mission controllers but also by supporting teams such as the Estrack station engineers – who have to know where to point their tracking antennas, what time to start ‘listening’ for a signal and how long a spacecraft will be visible.

We also guide our spacecraft, that is we calculate when a spacecraft needs a push from its thrusters or a blast from its engine to change the direction of travel, boost its orbital altitude, slow down or speed up. Our work focuses on optimising flight paths and minimising fuel usage so that valuable scientific and Earth observation missions not only arrive where they should, when they should, but also can operate for as long as possible, boosting the return on investment.

We also determine in which direction a spacecraft is oriented – vital for ensuring, for example, that solar panels obtain maximum power from the Sun, scientific instruments point toward their targets and delicate optics face away from the Sun. When ESA's Rosetta probe flew past asteroid Lutetia, the moment of closest approach lasted just a few seconds and it was the Flight Dynamics team who calculated when and for how long the cameras could snap images.

Finally, we also conduct mission analysis, the complex and scientifically challenging process of figuring out exactly how a new satellite can best achieve its objectives. Experts must address basic questions for every mission: When should it be launched? And with which rocket? Into what type of orbit? How long will it take to get to, say, Mars or the L2 Lagrange point? Is a Moon or planetary flyby beneficial? How much thrust will it need?

The detailed answers to these and many similar questions help engineers to determine such basics as how much fuel a satellite should carry or what sort of heating/cooling system it may need.

How we do it

We work in teams, with flight dynamics experts assigned to each mission operated by ESA. We are integrated into the daily mission planning process, and our scientists often work around the clock to provide verified and accurate information that must be radioed up to a satellite or delivered to ground station engineers within tight deadlines.

Someone did the maths: Rosetta's slew during Mars swingby 2007

We work from a number of dedicated flight dynamics control rooms at ESOC, ESA’s European Space Operations Centre. Our computer systems are networked with those of the mission controllers and other supporting teams within the Agency.

We develop and customise our own software, often starting from basic scientific principles related to gravitation, planetary dynamics, motion, relativity and astronomy.

We also work closely with flight dynamics experts at other European space agencies and at international partners such as NASA, JAXA and Roscosmos.

Case study

In 2011, it was decided that ESA’s ageing ERS-2 satellite would be shut down and deorbited. ERS-2 had suffered a number of hardware failures during its 16-year lifetime, including three of its six gyros, and controlling it to maintain stable flight was a challenge.

The satellite could not simply be commanded to burn its thrusters to decelerate into a convenient reentry trajectory.

ERS-2 (in background) and Envisat in tandem orbits 2010

Instead, ESA's Flight Dynamics team worked with the ERS-2 mission controllers to map out a complex series of 66 altitude-lowering burns conducted over several weeks in July and August 2011. Each of these had precise start/stop times and the results of each had to be fed into the calculations for the next. Restricted ground station availability meant that flight dynamics analysis had to be performed each night so that the next day's station availability would not be missed.

The results were superb, and ERS-2 achieved its planned deorbit altitude, 573 km, at the end of July without a hitch. From there, the mission control team implemented a series of long fuel-depletion burns so as to avoid the chance of any future debris-causing explosion. The fuel was finally exhausted on 5 September, and ERS-2 was shut down for good. Now, its orbit will steadily decay due to natural drag and it will re-enter Earth's atmosphere and safely burn up within a few years.

Contact

Juergen Fertig
ESA/ESOC Darmstadt, Germany
Tel. +49 (0)6151-90-2284
Email (click to view): juer...@esa.int