[X] My Assistant

[vikingmars]

With a little image processing, one can easily see the final descent trajectory of the Phoenix Lander with its plumes disturbing the top layer of the Martian surface. After the release of the lander from the backshell, the effect is barely seen first, but is becoming more obvious, until the final strong pulses before landing. Any better estimates ? Enjoy !

[CosmicRocker]

I'm a bit out of my element in this thread, but when I saw the .csv data series files I couldn't help but dive in and see if I could do anything with such easily accessible data. I'm hoping I can take the lat/long/alt data at face value. I started out trying to make a 3D plot of the descent, but settled for this anaglyph rendition of the trajectory.

Does this even appear to be close to what you folks would expect? If it is, I'd like to find a way to plot this above a rendering of the Martian globe. With the white background, it's a bit stark as anaglyphs go. It might appear more clearly to to those of you who can double-up on the density of your red/cyan filters.

[jmknapp]

I'm hoping I can take the lat/long/alt data at face value.

FYI, the values are planetocentric coordinates of the "near point" on Mars from Phoenix. The SPICE library calls:

subpt_c("near point","MARS",et,"LT+S","PHX",scsubpt,&alt) ; // get Phoenix subpoint, IAU_MARS rectangular coords
reclat_c(scsubpt,&subrad,&sublon,&sublat) ; // convert to rectangular to latitudinal (radius, longtitude, latitude)

For Mars there's not a big difference between planetocentric and planetographic.

[mcaplinger]

For Mars there's not a big difference between planetocentric and planetographic.

Remind me not to let you navigate my spacecraft.

[jmknapp]

Remind me not to let you navigate my spacecraft.

Just going by this web page:

Planetocentric coordinates are referred to the equatorial plane of the body concerned and are much used in the calculations of celestial mechanics. Planetocentric longitude is measured around the equator of the body from a prime meridian defined and adopted by international agreement. (The prime meridian may be referred to a visible feature in the case of a solid-surfaced body such as Mars, but in the case of a gaseous planet such as Jupiter it is a purely hypothetical concept.) Planetocentric latitude is measured in an arc above or below the equator of the object in the usual way.

Planetographic coordinates are used for observations of the surface features of those planets whose figures are not truly spherical, but oblate. They are referred to the mean surface of the planet, and are the coordinates actually determined by observation. They can readily be converted to planetocentric coordinates if required. As the oblate planets are symmetrical about their axes of rotation, there is little difference in practice between planetocentric and planetographic longitudes. However, the differences between planetocentric and planetographic latitudes are quite significant for very oblate bodies such as Jupiter and Saturn.

[mcaplinger]

Just going by this web page:

I'd have to say that reference is a little questionable. For Mars an areocentric latitude can be almost 0.4 degrees different from an areographic one, which corresponds to a distance of over 20 km. It may not matter for what this thread is talking about, but there are plenty of times when it does.