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Re: [Orekit Developers] Status of the Android application -- 2

Hi Alexis,

First of all, I'm sorry to be rather slow to answer these days, but I am on holidays and working in my house. Pascal is the backup mentor and can help you in most cases. I will try to be more responsive :-(

Alexis ROBERT <alexis.robert@gmail.com> a écrit :

On Thu, Aug 11, 2011 at 6:15 PM, pascal parraud <pascal.parraud@c-s.fr> wrote:
You don't need to extract an orbit to feed a KeplerianPropagator (which is inappropriate), you will rather use the TLEPropagator on its own by adding the ImpulseManeuver event to it and then propagate the same way you did with the KeplerainPropagator. You're lucky, with the last Orekit versions, for about a month, the TLEPropagator is a full propagator with all those nice features ...

Thanks, it worked :)

If you want to test impulse maneuver support, I've published a new
snapshot with it :

I am still not able to install this version. My personal tablet keeps telling me « Orekit n'a pu être installé. Libérez de l'espace et réessayez. », despite I have only 206Mbytes used and 1.7GBytes available on the sdcard (and 6.6Gbytes available on an additional mounted sdcard). I have tried both versions from today (included the -2 one) and the version from two days ago. I think the problem lies in my tablet which still forec close most applications and ask for accounts reconfiguration at each reboot. I did not yet try to retrieve the syslog using adb.

By the way, I noticed you used the wrong logo for Orekit. The pink one was a variation suitable only for the forge theme. The proper logo is here: <https://www.orekit.org/forge/projects/orekit/repository/revisions/master/entry/src/site/resources/images/orekit-logo.png> (I can also send a scalable SVG version if you prefer).

Also, the date selector now automatically fills the fields with the
current date in the UTC time zone if no date was selected, meaning you
can fill the forms faster -- before, no time zone conversion was made
and the time scale was left unset. (I also added a Vector3D widget,
which is basically the conversion of the x/y/z entry seen in the Frame
conversion part (when it requests a position & velocity) in a
standalone widget so I could re-use it in the Impulse maneuver part,
but that's unnoticeable when you use the application)

Fine. I think we will need to input many vectors in the final application.

Concerning the other questions you asled earlier, I agree with everything Pascal said. I would stress out the fact TLE is really something weird. It is unfortunate it is so widely used as from a space flight dynamics points of view it has really many drawbacks. The reason why Pascal advised you to avoid extracting the orbit from TLE and put it in a Keplerian model is due to one of these drawbacks. This is probably out of scope, but as a summary the rationale is that TLE is not an orbit per se, it is a combination of an orbit *and* a propagation model, and the orbit part is filtered to work with the mathcing model and only with the matching model (it is a kind of what we call « mean orbit » with some specific high frequency parts removed, the removed parts being propagation model dependent). Using an orbit extracted from TLE with another propagation model (i.e. Kepler, Eckstein-Heschler, Brouwer, Lyddanne, numerical propagator, DSST, or anything else) does not work.

Concerning usability, I agree that when we will have all features available, TLE will be entered by direct download, by copy-paste, by importing files ... but probably not by painful manual typing in a virtual keyboard.

Concerning bad TLE, there are some checksums at the end of each line and every character is important (including blanks), so you may have mad a very minor mistake that changed the checksum.

Concerning numerical keypad, I think the compromise to have numbers and not scientific notation is the least inconvenient one. Perhaps in the future we will have some default settings for huge values like attraction coefficient, so we may avoid entering it each time and simply select it from a list (you can have a look at the Constants class, which provides a few useful constants for our field, like several mu values and also Earth equatorial radius, flatness ...).

I will try to look at the source code you put on the forge when I find some time.

best regards,


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