Friday, February 13, 2015

KARI Lunar Orbiter concept

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 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 ;-)

Continue reading...

This article was originally published on the Celestial Matters forum.

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