Parabolic / hyperbolic orbits

[Dirl]

Hello!

I have made the "Catalog of periodic and some other comets".

It includes only elliptical orbits.
How can I make a parabolic/hyperbolic orbit?

[Pierebean]

i already tried to input an excentricity >=1 but it didn't work, so and i don't think the soft can handle it.

[Spaceman Spiff]

How can I make a parabolic/hyperbolic orbit?

As far as I know, you can't, and perhaps that can be confirmed by checking Selden's documentation here: How to transform orbital elements into Celestia's SSC format (http://www.lns.cornell.edu/~seb/celesti ... meris.html)

However you seem to be on the right track by using PericenterDistance instead of SemiMajorAxis: the semi-major axes of parabola and hyperbola are undefined so astronomers use q, not a.

You don't need to use parabolic/hyperbolic orbits for known comets though. I think so far there is still not an officially accepted comet found to be coming from beyond a captured orbit about the sun. All measured eccentricities are in fact still less than 1 (any appearing greater are by less than the estimated error of measurement).

I think the reason why parabolic/hyperbolic orbits haven't been implemented yet (a term HyperbolicOrbit, instead of EllipticalOrbit would do) is that a developer would have to 'clip' the orbit at some distance because the two arms of the orbit extend to infinity.

I suppose so far, effort for this outweighs benefit.

Spiff.

[selden]

Hyperbolic orbits have been specifiable since Celestia v1.2.4. Orbits that are exactly parabolic (e=1) don't work, though.

Celestia's EllipticalOrbit declaration requires that you specify at least Period
and either SemiMajorAxis or PericenterDistance.

For all types of orbits, including hyperbolic, Celestia uses the definition
Period = 2Pi/mean_motion
so you need to know (or calculate) the value of the comet's Mean Motion in radians/year.

An intermediate mathematical treatment is available at http://www.tamuk.edu/math/scott/stars/d ... ssical.pdf

[Dirl]

New variant is to make an xyz file
for parabolic / hyperbolic orbits.