Re: [Flightgear-devel] The state of things in Flight Gear

[Jon S. B. <jon...@co...>]

> From: tho...@jy... [mailto:]
> 
> I think it's grossly unfair to mix these issues: Spaceflight requires
> to essentially write a space simulator. One of my first statements in the
> forum was:
> 
> "Orbital flights opens a whole new can of worms besides the need for
> different rendering - completely different physics, completely different
> numerical stability issues,... basically you want to write a new orbital
> simulator, because the amount of stuff you can really use from a flight
> simulator is pretty small."

At one time I thought this to be true, but it is not necessarily. We have
been working on JSBSim very hard over the past years (thanks to the efforts
of Fröhlich, Coconnier, myself, and others) to make sure that JSBSim can
handle orbital dynamics properly - because if orbital dynamic are handled
properly, it's a good indicator that aircraft dynamics are, as well. We can
now do a high altitude, high inclination, high-eccentricity, orbit (with the
spacecraft rotating) and after one simulated day end up a few hundred feet
from the spot in space where a well-regarded software tool (AGI's "STK"
product) says we should be. The dynamics of flight are not really different
at all. Stability is not a problem. I would disagree with your statements
above and in fact my experience has been almost the opposite, except for the
rendering problem, which I have no experience with. I have been approached
to help with testing JSBSim with Outerra, however, and obviously they are
doing rendering very well from space to ground.

> ...
> 
> I still think that is a correct statement (up to the part that JSBSim
> seems adequately equipped to get ascent and descent right, although we
> don't know about long-term orbital stability - which wasn't clear to me
> when I wrote it)- so from where I am standing, you are claiming that
> Flightgear development is failing based on the observation that people
> could not write a spaceflight simulation in 6 months or tell you how to
> do that.
>
> Just my two cents.
> 
> * Thorsten

Given the criticisms of our high-altitude atmosphere model from previous
discussions, I went ahead and revamped our atmosphere model. It's still a
work-in-progress, but the atmosphere model should eventually be much more
realistic at higher altitudes, and be useful for some limited spaceflight
use. I have no idea how well a re-entering spacecraft will track along the
expected trajectory, though. That remains to be seen.

Personally, I would like to see FlightGear to be made usable for orbital
flight, but I can imagine that would be a lot of work.

Jon