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Author
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Topic: Apollo 10: Bringing "Snoopy" home
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jklier
Member Posts: 54
From: Austin, Texas
Registered: Aug 2007
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posted 09-16-2010 02:47 PM
   
I know this isn't feasible (at least not right now) so this is just me wishing out loud.I was just looking at the orbit of the Apollo 10 ascent module using Celestia. It appears that every few years it makes a relatively close pass to earth, probably several million miles in 2014. It could likely be closer at another pass. Wouldn't it be fantastic if at some future date this artifact could be recovered at put back on the ground for all to see? |
SpaceAholic
Member Posts: 4494
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 09-16-2010 03:00 PM
There was never accurate ephemeris captured on Snoopy so am curious how Celestia is modeling its orbit...I would take the estimated CPA strictly for entertainment value only |
jklier
Member Posts: 54
From: Austin, Texas
Registered: Aug 2007
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posted 09-16-2010 03:21 PM
Yes, I agree. The author of the file said in his README that the estimation is rough (see below for more info on its creation). It's still something I'll dream about seeing sometime in the future!From the README file... The computation of the actual orbit elements of LM 4 was done in a three- step process. From technical references about the Apollo program there is enough information to calculate the delta v of the LM. "Snoopy" didn't land on the moon, so most of the propellant of the ascent engine wasn't yet needed when Mission Control fired it at May 23, 1969 at 6:07 UT. The engine ran until burnout. Delta v can be calculated to 1150 m/s. - Under the assumption the LM accelerated parallel to the orbital tangent, the delta v adds to the circular velocity of Apollo around the moon (note the Apollo orbits were retrograd). By this, an escape hyperbola and its asymptotic velocity and angle can be calculated. Snoopy left the moon's gravity well at 1336 m/s and an angle of 58.5 deg against the orbit tangent/moon center.
- By a vector addition of the moon's orbital speed one gets the LM's trajectory in a geocentric coordinate system, and doing the same procedure as above for earth again one has the LM's velocity vector with respect to sun center.
- Now I had a point in space (vincinity of the moon) and a velocity vector at a certain time (May 23, 1969, 6:00). It was now possible to calculate the elements of a sun orbit by means of common formulas of celestial mechanics [10].
Nevertheless some fine adjustments in the .ssc file had to be done - I also desire the LM to be in the vincinity of the moon on May 23, 1969 but obviously some of the assumptions I made were only rough approximations of what really happened. So please note the calculated orbit is only a rough approximation of where "Snoopy" would be located really today - despite of any bugs in the calculation I might have done. |
ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 09-18-2010 11:00 AM
At best, Snoopy's orbit can be described as "chaotic". |
Max Q
Member Posts: 399
From: Whyalla South Australia
Registered: Mar 2007
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posted 09-18-2010 08:27 PM
It makes me wonder why more in depth information wasn't recorded at the time. Was it seen as irrelevant or was NASA not truly aware of its place in history at the time? |
ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 09-19-2010 04:34 PM
Even miniscule and unanticipated ventings or thruster firings would cause the errors in estimated position to accumulate very quickly. Examples are the extra impulse that Eagle got in separating from Columbia when the docking tunnel wasn't completely depressurized, resulting in the landing being several km long, or the venting from Aquarius' water tank which caused the continued drift in Apollo 13's position on the leg home from the Moon. Also, I'm sure a lot more concentrated effort was being spent on bringing the crew home than on tracking a discarded piece of the spacecraft which was expected to crash into the Moon shortly thereafter. |
SpaceAholic
Member Posts: 4494
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 09-19-2010 06:44 PM
LM guidance and navigation was not completely autonomous, a man in the loop was required to establish a frame of reference (via optical fixes) for the G&N system to do its job and establish position and velocity. Also return of telemetry after undocking to calculate accurate ephemeris would hinge on retention of S-Band lock with the Manned Space Flight Network (initial acquisition required manual slewing to the 12.5 degree capture angle) or LOS VHF relay to S-Band via the CM; neither viable once RCS fuel was depleted even if automated processes were in place to emulate actions which would have been otherwise taken by an on-board crew due to the tumbling spacecraft, geometry and opening range between the LM/CSM. The LM's radar cross section wasn't large enough for Earth based radars to independently resolve and track the ascent stage as it departed from lunar orbit. |
Max Q
Member Posts: 399
From: Whyalla South Australia
Registered: Mar 2007
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posted 09-20-2010 02:00 AM
Thanks for the reply SpaceAholic and ilbasso, much clearer now. |
jklier
Member Posts: 54
From: Austin, Texas
Registered: Aug 2007
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posted 09-20-2010 11:46 AM
Great replies! Thanks!That leads me to another thought. How close would Snoopy have to pass Earth for it to be detected by some of the sensors looking for NEA such as WISE? It seems that I've seen data showing NEA sizes around 30 meters. If that's the case I don't think it would be a stretch for Snoopy to be sighted if it's orbit brought it close to earth. Would we know what it was if it were spotted or would it look like any other object floating around out there? |
ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 09-20-2010 02:36 PM
Near-Earth Object J002E3 is the spent S-IVB stage of Apollo 12. It was originally identified as a Near-Earth Object (a.k.a. 'asteroid'), and then analysis of its spectrum (i.e., pretty much the same as white paint) led to its identification as Apollo 12's 3rd stage.One factor mentioned in the NASA article was that solar radiation pressure is not constant over time, which further confounds the ability to predict the position of an object in orbit around the Sun, Moon, and Earth. |
Blackarrow
Member Posts: 3160
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 09-20-2010 04:20 PM
Let's just be content knowing that there is a flown Apollo lunar module ascent stage up there somewhere, orbiting the sun. All the others were destroyed. |
jklier
Member Posts: 54
From: Austin, Texas
Registered: Aug 2007
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posted 09-21-2010 08:46 AM
I think we can be content knowing she's up there and talk about laying eyes on her again.  I've been enjoying this discussion. Learned a few things I didn't know before. |
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