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To my knowledge, the most accurate "as-flown" Apollo mission trajectory data available today are published in Richard W. Orloff's "Apollo by the Numbers: A Statistical Reference" (NASA SP-2000-4029). Using these data, I've reconstructed the Apollo 11 as-flown trajectory following Trans-Lunar Injection (TLI) until Lunar Orbit Insertion (LOI) over the Moon's farside. By not performing LOI in the reconstruction, the coasted lunar gravity assist results in an Earth free-return "round trip" trajectory. A .xyz file corresponding to this trajectory, together with a supporting .ssc file and .cel script, can be downloaded from the following URL.

http://home.earthlink.net/~adamod/Celes ... ddOns.html

Also included in the download is a trajectory overview GIF reproduced below. I welcome feedback on the script (my first) and ideas for additional trajectory designs/reconstructions (in this solar system, for the time being).

-Dan Adamo

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Adamod:

Would it be possible to create the Apollo 13 free-return trajectory? I'd love to use it in one of my Activities.

Thanks in advance.

Frank

Frank-

Yes, an Apollo 13 reconstruction is a possibility, but it would be a challenge in at least 2 respects. First, at the time of its cryo tank explosion, Apollo 13 wasn't on a free return trajectory at all. The departure from free return had been an intentional consequence of a Hybrid Course Insertion (HCI) burn performed earlier in the mission to achieve lunar orbit leading to landing at the Fra Mauro LM touchdown site. Only by burning the LM descent engine before pericynthion (closest approach to the Moon) was anything like a free return re-established. Another descent engine burn 2 hours after pericynthion reduced transit time to Earth to provide more comfortable consumables margins and shift Apollo 13's splashdown point back to the prime recovery area in the Pacific. So, as you can see, an Apollo 13 reconstruction actually involves modeling multiple trajectories, both free return and not.

The second difficulty is the outgassing perturbing accelerations imparted by the explosion itself and the other leaks it triggered. I think all these impulses can be accounted for to a reasonable degree of accuracy, again thanks to the data Richard Orloff has published.

When would you need an Apollo 13 .xyz file to support your Activity?

-Dan

Dan:

If devising the XYZ for Apollo 13 is really time consuming and difficult, I can simply not take anyone to see it in my Activities. Someone once modeled Apollo 13 with an exploded service module bay. I have the model somewhere on my computer, and I thought it might be neat to set up at least one cel:url to take folks to it, then show them the orbital trajectory it had to take to get home. However, I don't want to put you to too much work.

As to timing, if you ever do decide to do it, I could insert it into an Activity update say ... by the end of summer, so there is plenty of time.

Thanks

Frank

Does this add-on require a specific version of Celestia? I have unpacked your ZIP archive in the extras directory of my Celestia 1.3.2 installation under Linux. When I run the apollo11fr.cel script, I don't see neither the spacecraft, nor the Moon or Earth while the script proceedes and displays its text captions. Any suggestions?


Paolo Amoroso

amoroso wrote:Does this add-on require a specific version of Celestia? I have unpacked your ZIP archive in the extras directory of my Celestia 1.3.2 installation under Linux. When I run the apollo11fr.cel script, I don't see neither the spacecraft, nor the Moon or Earth while the script proceedes and displays its text captions. Any suggestions?


Paolo Amoroso

I've tested the script using current Celestia versions for Mac OS X and Windows, but you're the first user I know to try it under Linux. The script doesn't attempt to show the spacecraft, but you should see the Moon, Sun, or Earth at virtually any point as it runs. Is the apollo11fr.xyz file in your extras\data\ directory, and is the apollo1fr.ssc file in your extras\ directory? If so, can you at least manually set time to some point during July 17, 1969 and select object Sol/Earth/apollo11fr?

Dan Adamo

adamod wrote:Is the apollo11fr.xyz file in your extras\data\ directory [...] ?

That was the problem: apollo11fr.xyz was not in the data directory. Very nice add-on, thanks.


Paolo Amoroso