>> 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.

To provide the context: I wrote the above in response to pictures of Mars
(from Celestia) being posted and talk about Apollo missions, i.e. having
interplanetary missions in mind. (Jon actually knows that, because I
explained it later in the thread :-) ) - something which my wording
'orbital flight' actually doesn't reflect.

I will be convinced that stability is not an issue here if someone
demonstrates to me that a 4 month fast-forward running the simulation at a
factor 1.000.000 time acceleration gets you a few 100.000.000 km later
precisely where you're supposed to be. Gravitational slingshots require an
incredible precision - you can't be 100 km off at target.

Cheers,

* Thorsten


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