While preparing this mission concept, I also took the opportunity to generate a fresh 32k normal map of the Moon using the latest 2014 LOLA data.
A previous version from 2011 is available from http://imbrium.mit.edu/EXTRAS/CELESTIA/ and also the Celestial Motherlode.
Like the 2011 version, I used LDEM_128.IMG from here: http://imbrium.mit.edu/DATA/LOLA_GDR/CYLINDRICAL/IMG/
Then I used Fridger Schrempp's nmtools to generate a DXT5nm virtual texture. I took the opportunity to compile nmtools again for the Mac in order to try out nmtilesDXT (a nmtools program that generates DXT5nm tiles). This worked, although I had to change the Makefile and also compile NVIDIA texture tools from scratch.
Anyway here is a side-by-side comparison of the original 2011 version vs the 2014 normal map generated by me:
As you can see, there is a clear improvement in quality in the 2014 data.
Details are sharper, and there are less artifacts as compared to the 2011 data. It goes without saying that the DXT5nm compressed format also saves disk space: 589 MB vs 946 MB for the 2011 version (which uses PNG).
I think that the smoothed velocities are correct (i.e., the unsmoothed velocities with gaps are wrong).
Here is a plot comparing the smoothed and unsmoothed velocities of the spacecraft at launch time:
For both, the velocity profiles can be broken down into 3 main parts:
Launch: Steep increase in velocity
LEO orbit: Constant velocity (circular orbit)
Trans-lunar Injection (TLI): Delta-v increase to push spacecraft towards the Moon
For the unsmoothed profile, the velocity evens out at only ~5.5 km/s, and the delta-v of TLI is only about +2 km/s. These numbers are too small, especially considering that a typical orbital velocity of a circular LEO should be ~8 km/s.
By comparison, the smoothed profile flattens out at ~7.8 km/s, which is a reasonable velocity for LEO. Also, TLI delta-v is roughly +3 km/s, which is also in the ballpark for typical TLI delta-v's. :D
I noticed that with the provided trajectory .xyz file, the spacecraft would periodically speed up, slow down, then speed up again, etc.
To illustrate, here is a Octave (Matlab) plot of the spacecraft velocity:
It seems that the time (first column) was not written with sufficient number of decimal places, causing several rows to have the same time.
So I tried to simply delete any rows with duplicated times. But this didn't work, because it caused the [b]distance[/b] between the same timestamps to vary.
In the above example, deleting duplicate .207 and .209 entries would cause the distance to jump suddenly between .207 and .208, and .209 to .21.
Since velocity=distance/time, this causes the velocity to jump suddenly also.
The solution was to recalculate all the timestamps. I simply took the total time interval between the first row of the .xyz file and the last row, and divided by the total number of .xyz entries minus 1. Then I made all the timestamps increment by this constant time interval.
This is the resulting plot:
As you can see, there are no more gaps and moreover the velocity curve is smooth. The motion of the spacecraft in celestia.Sci is also much smoother. However, the velocities are also higher than the original; I'm still investigating why.
I've been working with an engineer at KARI (Korean Aerospace Research Institute - the Korean space agency) on an addon simulating the Korean Lunar Orbiter mission concept in celestia.Sci.
(the addon also works just fine using Celestia trunk code)
KARI has just begun developing a lunar orbiter and has set a goal of 2018 for launching it on a US launch vehicle (originally the plan was to launch on Korea's next gen launch vehicle KSLV-2, but budget cuts this year make that unlikely). The orbiter will be followed up by a surface rover.
This is a YouTube of the mission concept (produced before the switch to a US launch):
The KARI engineer provided me with a medium-res 3ds model and .xyz trajectory. Using Blender, a free 3D modeling program, I split the 3ds model into different movable components such as the body, solar panels, and high-gain antenna and converted the lot to cmod (Celestia Model format) using 3dstocmod and cmodfix:
Blender has a high learning curve and the 3ds output requires hand-editing to remove extraneous opacity attributes (after conversion to ascii cmod format). I wish there was something better that is also free and works on the Mac...
In the .ssc (Celestia solar system catalog file defining the addon), I then linked all the components together using BodyFixed frame directives.
Here is the spacecraft in LEO (missing the upper stage), along with the trajectory overview:
I had to use the Spice orbits for the Earth and Moon, by following the instructions given in the CM Spice Kernel Files forum. There are some differences between the default orbits and Spice ones that prevent the .xyz trajectory from lining up with the default orbits.After testing again, the default orbit does provide a good match for the .xyz trajectory, so there is no need to use the Spice orbits! I must have mixed up something when testing previously.
The solar panels automatically align themselves to the Sun. This is achieved by setting the target of one the axes of the BodyFrame of the solar panels to "Sol":
This is the orbiter in the dark side of the Moon. Eclipse shadows on the spacecraft are handled correctly.
The spacecraft follows a roughly polar lunar orbit, coming as close as about 100 km from the lunar surface. I used John Van Vliet's LRO WAC color map and a normal map generated from the latest 2014 LOLA (Lunar Orbiter Laser Altimeter) data at http://imbrium.mit.edu. Planetographic grid has been turned on to show lunar longitude and latitude.
Note that the orbiter trajectory appears to intersect the Moon, but that's ok because the Moon will move away along its own orbit to prevent a premature crash ;-)
Bug fixes: Better handling of premultiplied/unpremultiplied alpha
Due to this fix, I've removed the premultiply alpha user option. Squish should automatically do the right thing in most cases, but let me know if there's a case it can't handle.
Mipmap export is limited to the TIFF format, for now. PNG mipmap export has subtle bugs that I hope to fix in a future release.
New features: Mipmap tile export to separate images, and image assembly from mipmap tiles. This allows you to fine-tune individual mipmap levels by hand.
Bug fixes: Allow Quit and Help when Export options panel is open
As Celestia 1.6.0 nears release, here is a list of what's new in the Mac version:
Bundled data files for planets and stars (CelestiaResources) moved inside the Celestia app bundle. This simplifies installation - just drag and drop the app, no need to copy an extra folder. Nothing has changed for advanced users who wish to create their own addons; Celestia will continue to look for custom extras and scripts inside ~/Library/Application Support/CelestiaResources or /Library/Application Support/CelestiaResources.
SPICE support added - Celestia will now recognize SPICE spacecraft trajectories allowing you to recreate actual missions easily.
Here is a new build of Celestia, with Chris Laurel's experimental reference marks feature enabled: Celestia UNOFFICIAL build 2007-12-24 Update: Reference marks are now a standard feature of Celestia.
