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Targets for LRO
jmknapp
post Jul 13 2009, 02:00 PM
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QUOTE (Paul Fjeld @ Jul 11 2009, 12:32 PM) *
I am certain the beta angle changes completely through the whole mission or they wouldn't need to do a 180 yaw at the midway point to get the solar arrays shifted to the other side. Plus you wouldn't need that beta gimbal joint on the arrays.


Just verified that per the "mission baseline" SPICE data. The beta angle on the descending node (currently very low) increases to ~90 degrees in about 3 months, goes back to zero at 6 months, then the ascending node will be in sunlight, increasing to ~90 degrees at 9 months & back to zero at the end of one year. So I guess that means that LRO completes a sweep around the moon in one sidereal period (27.3 days) rather than the full moon to full moon period of 29.5 days.


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Phil Stooke
post Jul 13 2009, 02:16 PM
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"Good! You answered me what I was searching about the Moon phase when Apollo 11 landed on Moon.
I knew that the Moon was either as waxing crescent or waning crescent. Now I see it. "

Spacelistener - that image does not show the phase at the time of the Apollo 11 landing - in fact it was almost the opposite, a waxing crescent. In other words, very early morning at the landing site.

Phil Stooke


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SpaceListener
post Jul 13 2009, 02:31 PM
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QUOTE (Phil Stooke @ Jul 13 2009, 08:16 AM) *
Spacelistener - that image does not show the phase at the time of the Apollo 11 landing - in fact it was almost the opposite, a waxing crescent. In other words, very early morning at the landing site.

Thanks Phil,
Why did NASA select that the landing Apollo 11 time was in early morning? Due to temperature reasons? I don't see difference temperature between early, noon and late day of Moon since it has no atmosphere but I am still figuring it out.
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djellison
post Jul 13 2009, 02:34 PM
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You want to have the sun fairly low, so that when landing, the craters and boulders stand out well.

I would suspect that you target for the beginning of the lunar day, giving you a few days until the sun gets too high.
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SpaceListener
post Jul 13 2009, 02:59 PM
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Full inline quote removed - ADMIN

Your post sounds very reasonably.

That is for a better visibility during the landing and EWA which is very important for security reasons since the Moon light is so intense, that, I imagine, a person would have lots difficulties to discern the surface line.
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Phil Stooke
post Jul 13 2009, 03:29 PM
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You need the low sun to discern surface features, as Doug said. The most important reason for targeting early morning rather than late evening was to allow the approach to the site to occur over the illuminated region for navigation updates - they tracked landmarks to update their position. Also this will allow for landing delays. If you have some little problem that prevents landing on one orbit you can go for the next, or the next again. In the evening, miss an orbit or two and you will be on the surface during the night. That would be even more important for the longer missions.

Lighting is much more important here than temperature.

Phil


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djellison
post Jul 13 2009, 03:37 PM
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I'm sure I've read one astronaut, probably from a J class mission, comment that just from one EVA to the next, the lighting change was so significant that the place looked very very different on the ground.
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Phil Stooke
post Jul 13 2009, 04:03 PM
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Right, it's very apparent in the surface photos. So it makes perfect sense to land with the lowest sun angles and see all the hazards (except for the blowing dust... but that's a different issue), and allow the sun to get higher during the EVAs. It makes no sense to land with washed-out topography and run the risk that a landing delay would mean the last EVA would have to be cancelled due to approaching night.

Phil


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SpaceListener
post Jul 13 2009, 04:04 PM
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Fantastic, Doug and Phil statements have closed very well about all reasons for early morning landing on Moon.

However, for just confirmation of my hipothesis is that the Moon surface temperature on that time on Sun side is so hot as over than 100 centigrades Celius, isn't it?
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djellison
post Jul 13 2009, 04:48 PM
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http://www.solarviews.com/eng/moon.htm
Mean surface temperature (day) 107C
Mean surface temperature (night) -153C
Maximum surface temperature 123C
Minimum surface temperature -233C
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SpaceListener
post Jul 13 2009, 05:57 PM
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Thanks Dougs for the links. I knew about these temperatures and I am sorry that I didn't explain thoroughly about the hypothesis. As the Apollo 11 landing time was on early morning, close to the Lunar Terminator, and am suppossing that the real temperature must be lower than the maximum.

By the way, I have seen a picture taken by the LCROSS, from infrared camera during its approach to the Moon. It showed that the temperature starts to lower at the Terminator. See the next link: LCROSS Infrared Camera.

Well, I hope that one of the LRO instruments, DIVINER would be able to map the Moon surface temperatures. Patience! wink.gif

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Phil Stooke
post Jul 15 2009, 06:36 PM
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The first radar image from LRO has been released:

http://www.nasa.gov/mission_pages/Mini-RF/..._turned_on.html

Phil


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Guest_Sunspot_*
post Jul 15 2009, 06:58 PM
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Guests






And an interesting article from space.com

http://www.space.com/missionlaunches/09071...nding-site.html
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glennwsmith
post Jul 16 2009, 04:12 AM
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Speaking of radar, and in anticipation of the LCROSS impact, can someone briefly explain (or point me to an explanation of) how the Arecibo observatory has been able to map the poles of both the Moon and Mercury, finding water at the latter but not the former? Seems like it would have the same (impossible) tangential view that we do from earth. Or is its radar sufficiently robust to be able to penetrate the poles "from the sides" and obtain useful reflections that are processed tomographically?
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nprev
post Jul 16 2009, 04:31 AM
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In the case of Mercury I'd guess that Arecibo's acuity there is at least partially a function of the planet's orbital inclination with respect to the ecliptic (7 deg.), which allows a slightly better look angle at the poles at certain times.

Arecibo's radar isn't nearly powerful enough to do a CAT-scan of the lunar poles, though. (I don't think that any ground-based radar yet built could do that.)


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