Celestia Forums

In trying to design a (very rough) mission trajectory for my interstellar colony ship(s) to Terra Nova (formerly known as Tiamat to those familiar with my pet project...I'll have to request the original add-on be removed form the motherlode until the final version is done), and I've discovered something rather odd in Celestia. It seems that relative to the Solar System, my planets around 82 Eridani seem to be severely inclined (i.e. if viewed from Earth, we would be looking almost right on top of the system). Is 82 Eridani's rotational axis actually inclined like this, or is this some kind of glitch in the .stc file (or perhaps in my .ssc file)? I've been unable to find data on 82 Eridani's actual rotational axis in the literature, and have also found at least one paper claiming that determining a star's rotational axis is very difficult at best. Link: http://adsabs.harvard.edu/full/1985PASP...97...57S

So, if it is truly inclined like this, this would pose several problems. the first of which is the planetary system's discovery. My knowledge of exoplanet detection is that generally the system has to be aligned roughly line-of-sight with Earth (exactly for a transit, mostly aligned for accurate Doppler spectrometry). If it was this inclined, how could the fictional exoplanets I've put there even be discovered for them to be explored?

In addition, in what ways would such an inclination impact any kind of mission there? I would think that the ship would be, in effect, like a long-period comet (albeit one with a very high inclination) who's orbit would circularize over time (like how we go into orbit around other planets.) After the orbit is circularized, I think it would then just do an orbit transfer to Terra Nova and preform the required burns to enter orbit around it. But if the system is so highly inclined with respect to Earth, would this then extend the actual trip length due to having to make the ship's orbit coplanar with the plane of the ecliptic? (Not to mention add a whole lot more fuel for the burns and course-corrections).

Perhaps I'm over-thinking things, but this is a hard sci-fi project. Scientific accuracy is something I take some pride in. (And something I should be able to a lot better on my own with once I start college! )

My knowledge of exoplanet detection is that generally the system has to be aligned roughly line-of-sight with Earth (exactly for a transit, mostly aligned for accurate Doppler spectrometry). If it was this inclined, how could the fictional exoplanets I've put there even be discovered for them to be explored?

The inclination issue isn't really that prohibitive to the detection of the planets until the inclination begins to get real close to 0° or 180°.

MRV = Mtrue · sin i

The planets at ? Andromedae were detected, despite a couple of them having inclinations < 10°.

Furthermore, inclination places no constraint on astrometric detection or direct imaging.

Edit:
M[sub]RV[/sub] = M[sub]true[/sub] · sin i <---- broke?

The default Celestia coordinate system is the ecliptic coordinate system, so if you are not specifying Inclination/AscendingNode, the system will appear to be orientated parallel to the ecliptic plane. The same goes for the default rotation axis for objects which is by default perpendicular to the ecliptic plane. Since the rotation of 82 Eridani is not specified in any of the Celestia catalogue files, it will use this default rotation (together with a default rotation rate that is set based on the spectral type). In ecliptic coordinates, 82 Eridani has a latitude of -58 degrees so the default orientation will be highly-inclined relative to the plane of the solar system.

Would such detection methods work with Earth-mass planets however? (although, given the time period my project takes place in, it could be assumed that we have developed means of detection orders of magnitudes more sensitive and accurate than today's methods.) For direct imaging to work, the planets have to be particularly large and bright (like Fomalhaut b, for example), unless you're using a REALLY sensitive telescope (maybe something like a solar focus telescope that uses the sun's natural gravity lens out at 550 AU).

ajtribick wrote:The default Celestia coordinate system is the ecliptic coordinate system, so if you are not specifying Inclination/AscendingNode, the system will appear to be orientated parallel to the ecliptic plane. The same goes for the default rotation axis for objects which is by default perpendicular to the ecliptic plane. Since the rotation of 82 Eridani is not specified in any of the Celestia catalogue files, it will use this default rotation (together with a default rotation rate that is set based on the spectral type). In ecliptic coordinates, 82 Eridani has a latitude of -58 degrees so the default orientation will be highly-inclined relative to the plane of the solar system.

Yep, I realized this when I went back and looked at both systems a second time. This just leaves the problem of the colony ship's mission trajectory. The way I have it pictured in my head, it would enter orbit around the star itself (obviously highly inclined) and proceed to make it's orbit coplanar with 82 Eridani's equator before doing some kind of Hohmann transfer to Terra Nova. But I'm not sure if I'm over-thinking things. Surely there is a simpler method? Perhaps I should have chosen a star that was more-or-less coplanar with our solar system...