Re: [Orekit Users] 2015 International Space Apps Challenge - a project that can use Orekit /and/ Rugged?

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

Michael Turner <michael.eugene.turner@gmail.com> a écrit :

> I'm involved in a project for the 2015 International Space Apps Challenge.
> I'm listing both Orekit and Rugged as possible resources. Orekit proved
> useful (thanks to the help of the Orekit team) in winning a prize at the
> Tokyo Space Apps Challenge in 2014.

Hi Michael,

> http://tokyo.spaceappschallenge.org/2014/img/release/PressRelease_H_20140423_02.pdf
>
> This was for the project Sprite Orbits
>
>   https://github.com/ProjectPersephone/SpriteOrbits
>
> This year, I want to be involved in something more related to remote
> sensing. The premise is remote sensing from equatorial LEO satellites, so
> that visitation rates are high, permitting /potentially/ meaningful
> oversampling if the effects of transitory shadows can be filtered out.
>
>   https://github.com/ProjectPersephone/Moombi
>
> I'm very new to remote sensing and satellite image analysis. It seems to me
> that, for /some/ of what Moombi is about (flood and landslides, and their
> ecological effects), Rugged might be ideal. Landslides can cause slight
> changes in terrain, and more significant changes in coloration. Flooding
> might be considered similarly. I'd like to get some opinions on this. Am I
> on the right track?

Perhaps, Rugged may help, I am not sure. One of the main input of Rugged
is a Digital Elevation Model, and the library will compute geometric  
correction
grids that will be fed into an image processing chain to compute  
ortho-rectification
(another open-source library, Orfeo Toolbox  
<http://www.orfeo-toolbox.org> may be
helpful there. Digital Elevation Models accuracy is often in the range  
10m-20m (see
<http://geodesy.curtin.edu.au/local/docs/Rexer_Hirt_2014_DEM_AJES_av.pdf>. We
have already used Rugged with both SRTM (using a link to the GDAL library to
load the DEM) and ASTER (using a custom loader I can provide to you if  
you want,
it is in the history of the git repository).


> There are a few orbital dynamics issues in this -- for example, it would be
> nice to model a whole ELEO remote-sensing satellite mission from launch to
> reentry, maybe even the spacecraft orientation problem. But I think terrain
> mapping has to be where we concentrate. I just want to be sure that Rugged
> can be useful to us. If it is, well, the Apps Challenge is the beginning,
> not the end, for the Moombi project.

In any case, I think that your needs would also involve mostly image
processing, the terrain modeling would be just one step of the process.
I agree the Orekit/Rugged pair is a good starting point, mainly as Orekit can
simulate accurate meta-data (orbit, attitude) to provide to Rugged and build
the full geometric model. You do not need to have a complex set of  
applications
or already built reference data: this helps a lot during initial  
definition and
design. As per version 7.0, Orekit also provides the DSST  
semi-analytical propagator
that can be used for very long term propagation, up to full spacecraft  
lifetime.
For ELEO orbits, I guess you will not get too much out-of-plane perturbations,
so a simple periodic semi-major axis with a pair of tangential maneuvers to
compensate for atmospheric drag would probably be sufficient if you intend to
have a spacecraft that has thrusters for station-keeping. This can be done
easily as our implementation of DSST fulfill all the requirements of Orekit
propagators and hence supports both events (to trigger maneuvers when altitude
goes below a specified minimum) and impulsive maneuvers triggered by  
such events.

best regards,
Luc

> Regards,
> Michael Turner
> Executive Director
> Project Persephone
> K-1 bldg 3F
> 7-2-6 Nishishinjuku
> Shinjuku-ku Tokyo 160-0023
> Tel: +81 (3) 6890-1140
> Fax: +81 (3) 6890-1158
> Mobile: +81 (90) 5203-8682
> turner@projectpersephone.org
> http://www.projectpersephone.org/
>
> "Love does not consist in gazing at each other, but in looking outward
> together in the same direction." -- Antoine de Saint-Exupéry