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Re: [Orekit Developers] ESA space debris movie - Orekit under the hood

Cool. That seems like good performance too. Out of curiosity were the propagations multi-threaded or all occurring in the same thread?

Best Regards,

On Fri, 2017-04-28 at 10:55 +0200, MAISONOBE Luc wrote:
Hi all,

You may have noticed the news published recently about the ESA
movie about space debris. The 2D version of the movie is here:
<https://www.youtube.com/watch?v=zT7typHkpVg>. The 3D version
is here: <https://www.youtube.com/watch?v=EzrMHWjQCtc>.

In case this is of interest for some of you, here are some background
information about how Orekit was used for generating data for the movie.

The movie was created for ESA by ID&Sense and ONiRiXel, with some help
from CS and the Orekit team. Orekit was used for all the trajectories
and attitude from GEO to LEO. I don't know how the L2 or Integral orbits
were generated, I only guess ephemerides were provided for these.

As realistic simulation was desired for the 16741 debris involved,
we wanted something better than Keplerian only and needed attitude
modelling. On the other hand, as a movie shows the trajectories at
Earth scale and as the time range covered by the simulation was short
(3 hours), tiny force models were not included. We arbitrarily limited
the force model to Earth gravity with degree and order 12 . This was
probably already overkill; degree 2 and order 0 would probably
have been sufficient. Earth orientation and Sun direction were
also provided by Orekit.

As the movie clearly depicts the GEO ring, navigation satellites
and also all active LEO (but here it is less clear as LEO is
overcrowded by uncontrolled debris), we wanted to have a proper
simulation of both attitude and solar arrays orientation. When
looking at the GEO ring for example, the alignment of solar
arrays for active satellites is obvious. For defunct spacecrafts
or other junk, we  wanted to show a tumbling mode, which is also
obvious for the rocket stage that appears near the GEO ring. We
used a set of predefined attitude modes (nadir pointing with
Yaw compensation for SSO, LOF aligned for GEO, random selection
between nadir pointing with yaw steering and LOF aligned for other
active satellites, fixed rate with random initial orientation and
random rotation rate vector for other bodies). For active satellites,
the solar arrays orientation was also computed on top of the attitude
and written to the generated output files.

The files generated were written as binary particles files that
were imported directly by Blender <https://www.blender.org/> (the
open source 3D creation suite).

The simulation involved 16741 real objects from a catalog provided
by ESA. The objects were classified as follows:

  - rocket bodies:    1688
  - mission related:  1055
  - active:            981
  - defunct:          2717
  - fragment:        10300

The active set included one weird object with a perigee below Earth
surface. The numerical propagator failed for this object, throwing
an exception as the adaptive stepsize numerical propagator required a
step size lower than allowed minimum.

The generated output was about 2.3 gigabytes. It took 269 seconds to
generate all trajectories on a four years old laptop with a core-i5
processor, 8Gb ram, running Linux Debian stretch.

best regards,