If the rocket stage happened to impact on a surface which was far off the horizontal, the ejecta plume coming out would be substantially less than predicted. For instance, an impact into the side of a cliff or steep slope, or the side of a big boulder, would see most of the initial ejecta thrown downwards. Only a small part of the rebound from that would end up exiting the crater, with greatly reduced energy. This might explain the lack of observed plume.

Of course, the chances of this also happening to the chaser satellite are low. However, given its much smaller size, I'm not sure what the initial expectations were of a plume from that, if any.

I'd hate it if NASA got so conservative that they didn't alert people to the possibility of something spectacular. All they really needed to do here was to say, up front, "Well, there's a possibility that no one will see anything from the ground, but there's ALSO a possibility that it'll be visible in telescopes as small as 10 inches, so it's worth taking a chance and watching." I'll bet a dollar to a doughnut there were scientists who strongly advised NOT hyping this, given the uncertainties, but they were overruled by PR types.

I can't entirely blame the PR guys, since public support is essential for funding, but it wouldn't have been THAT hard for them to hedge a little bit. Heck, someone once tried to explain to me why people watch things like football, basketball, baseball, etc. by saying that sports are fun to watch because "no one knows what will happen." Putting in some uncertainty in their claims might make these events MORE popular.

@nprev are we showing our age by remembering Kohoutek? Even a Geraldo reference seems dated now! :-)

--Greg

Of course the meteor hits might be easier to see from Earth since they wouldn't usually be hidden from direct view in the floor of a crater. On the other hand the shepherding craft should have seen more having that direct view.

And as a colleague asked me, if the Centaur was oriented sideways, would it be less likely to be buried?

If I understood correctly, a sideways hit (as well as a hit where the Centauri would be vertical) were unfavorable. An angled hit would allow for more ejecta. As for impact flash? No idea.

Not really comparable, but Lunar Prospector (far less mass, less speed --> less kinetic energy) made an almost grazing hit in 1999 but it also failed to raise any detectable plume

I think there are two variables here, one is the trajectory of the spacecraft, and the second (that I was wondering about) is the attitude or orientation of the spacecraft.

With an impact in such a permanently shadowed region, how high should the plume ejecta rise so that they can reflect sunlight? Was there any prediction for that? I just think there is not much light there to reflect the plume dust, even if the plume is extended. Still, the detectors at other wavelengths should have seen more...

As kenny said, the details of the particular terrain it hits matter too. This was mentioned in the post impact press conference.

It appears the LCROSS team believed there was a high probability that it would visible in modest size telescopes, but I'm sure they knew other outcomes were possible. They probably didn't communicate this as well as they could have, but such subtlety would almost certainly have been lost on the press anyway.

Elias: There definitely were predictions and models. You can find some of them on the lcross site.

Without time to digest the science result, that would be an absurd statement to make . Given that a bright plume was considered a possibility, NASA would be taken flack had it happened and the didn't alert people. Many people thought SL-9 would fizzle. What if NASA had played it down because we might not see much?

As (sort of) a member of "the media," I feel like I should speak up here. I had figured that people with telescopes on the smaller end of the scale probably wouldn't see anything. But given that there was a big effort to organize amateur astronomers (or at least provide plenty of relevant, up-to-the-minute information to them), and the organized events run at bigger observatories, I never, ever, once imagined that the biggest telescopes on the planet wouldn't be able to see anything. Frankly I'm still surprised and confused about the fact that even Palomar didn't see squat. I think it's totally reasonable to be surprised about that.

From my point of view, reporting on this event, I was never particularly interested in the view from telescopes of any size. I was wholly focused on the shepherd spacecraft. Everything seemed to function spectacularly. And yet there was basically no indication of any impact on the screen. Even the people doing the color commentary for NASA TV were confused about that. We were all geared up for a climax that never came.

When you get excited, and expect something that doesn't come, you're disappointed. That's basically the definition of disappointment!! And I think there's no incompatibility between understanding that the mission was successful and still being disappointed about the lack of any sign that the impact happened during the live event.

--Emily

Seemingly, the PR impact has been greater (if in an unexpected way) then that of the physical event...didn't realize that the title of this thread would become a pun...

Maybe LCROSS was swallowed up by hundreds of meters of 'snow'.

...swallowed by snow or some other unexpected surface feature in the shadow was my first impression. Maybe the combination of cold and H2O condensation inside the shadowed crater created a cushion type textured surface that is very deep. Who knows?

The impact did occur and on target, but no fireworks. There has to be a logical explanation.

The simplest explanation, completely consistent with all the available data (once you strip off the hype) is that there were simply no significant volatiles at the impact site.

But shouldn't there have been "fireworks", even without ice?

IIRC the reason the Deep Impact impact was so spectacular was because of the amount and fineness of the dust. The lack of any visible curtain probably tells us something pretty significant about the nature of the substrate but I'm not sure what it is. Mcaplinger, correct me if I'm wrong, but I don't think it's the presence or absence of volatiles (which weren't expected to have been present at more than a couple percent as far as I understand) but the grain size and porosity of the material at the impact site that contributes most to the size of the ejecta curtain. When Deep Impact was about to happen, there was lots of discussion of Peter Schultz's experimental work on impacts into different kinds of materials, and I think their biggest concern was that they'd impact into a cohesionless target where there hardly be an ejecta curtain at all, just sort of a backward squirt out a deeply punched transient crater. (I think that was a "compression-controlled" impact as opposed to "gravity-" or "strength-controlled."

Funny, while I was researching that last sentence I was reminded of the manner in which the Deep Impact impact was unexpected. The Society ran a contest to see who could guess closest to the actual size of the impact crater, but the Deep Impact ejecta curtain turned out to be so spectacularly large and dusty that they were never able to see the crater. So we were forced to pick at random an entrant who'd been among the many who'd predicted a size between 100 and 250 meters, which pissed a lot of people off. Guess that goes to show you that making predictions is a bad idea

--Emily

I hope the Society kept the list. In mid-February 2011, you might have another chance to make the award a second time, albeit belatedly.

The size, perhaps, but not necessarily the visibiliity. See http://lcross.arc.nasa.gov/docs/Colaprete....SS-overview.ppt page 14 for a discussion of the "vapor cloud" which contributes in some not-well-explained way to the impact visibility through excitation of OH- and H2O+.

I read http://www.lpi.usra.edu/meetings/leagilewg...pm/Bart4050.pdf but it's not clear there how volatiles were expected to contribute to plume visibility; all of the predictions were based on 1%.

At any rate, I don't claim to be especially knowledgeable on this topic and could well be wrong, but to my eye these results aren't lending a lot of credence to the already fairly poor case, prior to LCROSS, for there being a lot of ice at the lunar poles.

That's a pretty good point re excitation of ions; if there were a lot (& I mean a LOT) of volatiles in the impact plume, you'd expect it to light up like a neon sign once it was exposed to the solar wind.

I think the issue is whether there was a plume of any significance or not, though. Evidence thus far seems to indicate that there wasn't, and I'm not sure if the often-cited hypothetical 1% H2O content would have been a player in that at all if it does in fact exist; seems like too small a concentration to affect the material properties of the soil (if the Centaur in fact hit soil) at the impact site.

All we really seem know right now is that at that specific place where the impact occurred there was less material ejected then expected, reason unknown. The spectroscopic data should shed some light (ta-da, da!) on the ejecta's chemical composition but probably won't yield much information about its pre-impact physical properties. And when the dust finally settles (please, somebody stop me!), all the data & analysis will again only be truly relevant to that very specific point on the Moon's surface, and it might be erroneous to extrapolate the results as representative of the entire South Polar region.

I just thought of something. Some say that there wasn't much ejecta because maybe LCROSS hit something very hard like a boulder. Well, the hydrogen signature is definitely there in that crater. Most believe it is water ice...perhaps only 1% of H2O in the soil. That's an assumption, right? What if the concentration is a lot greater than that?

Water ice in space is much different than here on Earth. It cannot form crystals in a vacuum. We call this form 'amorphous ice'. It is very much like hard glass only far colder. Imagine LCROSS hitting a block of hard glass that is 50 or more meters thick. It might as well as hit a solidified lava flow. Am I right?

I'm sure there would have been some damage to the block. But the forces involved in the impact would have been directed differently than expected. Wouldn't there be a lot less ejecta going upward in such a case? Wouldn't most of the forces be directed more horizontally and the ejecta would be less likely to get above the rim? I'm not an expert on impact dynamics, so help me out on this one.

LCROSS could only be considered a failure in the sense that the Michelson-Morley experiment to detect "luminiferous ether" was a failure. Rather, both experiments were executed flawlessly and disproved the existence of the hoped-for substance (in this case volatiles). So disappointment rather than failure is indeed the bottom line.

A 50m thick layer of ice would have been unambiguously detected by one of the many previous spectrometers and other instruments to overfly the poles.

Everyone here should agree: Good science and successful experiments tell us what is there, not what we wish was there.

However, I think you're premature in saying what the experiment has proved or disproved. No visible debris cloud does not equal no volatiles. That information is found in the spectroscopic data which has yet to be reported on. What I got from the press briefing was that spectra of the flash were obtained. I don't know if those are ideal or sufficient for detecting volatiles. Also, although there was no visible cloud, I don't know if it has been stated that there was no spectrographic data collected in the aftermath of the flash from invisible products of the impact.

I think we should wait for the results before making any conclusions. I've read that they obtained good data and need to process it thoroughly before making anything public.

There really is no reason to play a guessing game until we have all the information.

I don't see how a negative result from LCROSS would unambiguously disprove volatiles at the poles in general. Since we don't have any instruments that resolve down to the scale of the crater, we can't say whether we hit a representative sample. The LEND data already suggests that hydrogen concentration is variable in the shadowed craters at larger scales, and it seems reasonable to assume this would continue to smaller scales. If good spectra has been obtained from both the centaur and spacecraft impacts, that would help, but AFAIK we don't know that yet.

A positive result would tell us, yes, there is at least X percent in some places. A negative by itself doesn't tell us much, although the rest of the data might.

I didn't see it mentioned on the last several pages, but apparently the LRO detected an impact plume from LCROSS with its LAMP instrument and Diviner detected the impact crater. So it sounds like there was a plume created from the impact, but just not large enough to be seen from Earth I suppose. Hopefully they release the data from LAMP soon, if they haven't already

Some links.
http://lroupdate.blogspot.com/
http://www.diviner.ucla.edu/blog/?p=184

Although I must agree with Imipak that a 50m thick layer of ice would have been unambiguously detected by now, I like the way marsisimportant is thinking in his post about the strange physics that may go on in the vacuum and cold of the moon, which physics might prevent a ejecta cloud from forming -- and precisely because it DOES contain a lot of water.

For water, as we all know, does have a lot of enigmatic qualities from a physics standpoint.

Indeed, what happened with LCROSS might be akin in terms of science history to the recent discovery of water across the sunlit surface of the moon. Yes, theoretical physicists might know that high speed protons can interact with the oxygen atoms in rock to form water, but apparently nobody had thought of applying this arcane physics to the surface of the moon to predict the presence of water.

Likewise, there may be some arcane physics -- possibly involving water! -- which accounts for the non-appearance of the ejecta cloud. In fact, Emily recently mentioned in another context that the water molecule is very sticky.

I haven't noticed negativity in the UK media, some "Americans bomb the moon" headlines but that's to be expected over here.

Most of the after action reports seem to be highlighting the unknown factor, why didn't it produce visible results as expected? Which is OK imo.

The live coverage I heard on Radio 5 Live here in the UK was bordering on cringeworthy. The women presenter was dismissive, demanding and to be honest, offensive to the on-air expert.

They're like that with any thing to do with science - most BBC journalists come from the world of the arts or politics. Coverage of the '99 eclipse was appalling.

Water is important for us, but I feel like it is being portraited as the only kind of solidified substance we would expect to find there besides regular dust.

There is plenty of things that become volatile during the Lunar day and can freeze below 40 Kelvin. Ignoring any other constraints, it could aswell have hit a solid slab of Argon.

From the Facebook page:

LCROSS Lunar Impactor Mission.
The LCROSS science team met on Saturday and Monday to discuss the results and start putting together the story. In addition, further reports came in from the EBOC (Earth Based Observational Campaign). As true to the scientific method, data has been gathered, positive & null results are both valuable. Now is the time for analysis and comparisons with theory to explain the story. The team anticipates to report at the LEAG in Houston coming up in a few weeks and at the AGU in San Francisco in December. Meanwhile, check our mission page http://www.nasa.gov/lcross for the latest updates.
-LCROSS Facebook Team.

Paul Spudis has an interesting take on the potential science at his Air & Space magazine blog:

LCROSS: Mission to HYPErspace

The LRO observations of the impact site show that the LCROSS team made a bullseye, right in the coldest part of the crater. Spudis' claim that a negative water result says nothing, and his trashing of the whole LCROSS concept sounds more like wishful thinking, i.e., we know the water is there somewhere, negative evidence to the contrary notwithstanding. So, rovers and "hoppers" are proposed as the next best hope, that should have been done in the first place, etc.

If no water exists at the coldest part of a permanently-shadowed crater ("cold trap"), by what mechanism would it collect in any appreciable quantity elsewhere?

He was playing devils advocate. If LCROSS turns out dry - then the logical conclusion is to find some other means to explain the Hydrogen reading. The illogical conclusion that may well play out from supporters of the ice hypothesis is that it hit the wrong place and is not a negative. Paul's take on LCROSS is one I share.

Here's an observation from one paper, HYDROGEN MIGRATION TO THE LUNAR POLES BY SOLAR WIND BOMBARDMENT OF THE MOON:



In that simulation, they calculate that 7 million years would be required to for the solar wind to transport enough hydrogen to the poles to account for the LPNS reading. That would include atomic hydrogen (2.3%), molecular hydrogen (21.7%), hydroxide (66.7%) and water (6.8%).

Quick disclaimer: I'm not biased towards a wet or dry polar area; let the chips fall where they may based on the evidence.

That said, we need much more data.

This debate strongly reminds me of the view of Mars post-Viking & MPF until the MERs (really, Oppy) & Phoenix: 'dry & rocky everywhere, it's all the same'. This is not a perfect analogy, but the base concept is the same. There seems to be a fundamental human tendency to draw general conclusions based on limited data (call it the 'first impressions' effect?)

Just throwing that out there as a cautionary note. We now return to our regular programming.

One thing I'm not understanding here: why is it so important that the hydrogen has to be present in the form of water to be valuable? These spacecraft are picking up some kind of hydrogen signal. If it's in the form of solar wind deposited hydrogen, then fine. You can roast it out of the rocks and you have your ready made rocket fuel, without the step of having to break it out of the water. If you need water, then just combine the hydrogen with readily available lunar oxygen. And if it's a case of scientific study, well, you just go with whatever is there.

We don't yet know if there is any appreciable water. We do know the hydrogen is there.

We don't know what form it's in. It may be in a form that's hard to liberate. Furthermore - hydrogen on its own, isn't that useful* It's incredibly light so it's not much of a burden for space flight (consider the Mars Direct ISRU numbers). You tend to need something heavy (oxygen) to do something with it. If it's vast swathes of actual ice down there - then we have rocket fuel, air and water for future crews. If it's just hydrogen, you've still got to take 7/8ths the mass with you.

* apart from filling balloons - but that's not too useful on the moon

But the oxygen is there, too. And there have been lots of studies and pilot projects on how to get it. I still think, that whatever form, suitable seperation techniques would exist to get the hydrogen. Chemically bound to the rocks would be the hardest, but would also seem to be least likely, at least at the poles.

Some more info here:

http://dsc.discovery.com/news/2009/10/14/l...emperature.html

Good point.

A lot is being made of wishful thinkers' bias in explaining away any negative water results. Maybe Mars first bias explains the speed with with which some are grasping such negative results -- before they are released.

From the article:



I'm gonna wait for the release...

Interesting article about water on the Moon: http://www.thespacereview.com/article/1485/1


In 1978 Russians found water in samples brought back by Luna-24. In 1976 Luna-24 landed in Mare Crisium and drilled a core sample from about 2 m deep in Lunar surface. Their article "Water in the regolith of Mare Crisium (Luna-24)" was published in a Russian publication Geokhiimia but seems to have gone ignored.

Here's a link to the abstract: http://adsabs.harvard.edu/abs/1978Geokh......285A


Makes it even more sad to think that to day Luna-24 still is the last soft landing on the Moon.

Entire post of blue-sky engineering culled. See rules. - ADMIN

I cant understand why this post has been culled, fission engines using hydrogen as a working fluid were in the design stage in both the USA and Soviet Union in the 1950s and 60s. the Russians even tested one. If this is blue-sky then someone is lacking a bit of faith that any progress is going to be made
Seems to me there is more blue-sky engineering in harvesting water from the lunar poles than building these engines

"A nuclear engine was considered for some time as a replacement for the J-2 used on the S-II and S-IVB stages on the Saturn V and Saturn I rockets. Originally "drop-in" replacements were considered for higher performance, but a larger replacement for the S-IVB stage was later studied for missions to Mars and other high-load profiles, known as the S-N. Likewise the Soviets studied nuclear engines for their own moon rockets, notably upper stages of the N-1. However, neither design had progressed to the point where they were ready to test before the space race was ostensibly over.

To date, no nuclear thermal rocket has flown, or even reached a stage of development where it could be. The Russian nuclear thermal rocket RD-0410 went through a series of tests on the nuclear test site"
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

Ill try to repeat my original post and see if it get through this time

Hydrogen used as a propellant in a fission rocket has a much higher impulse than when you waste it by burning it with oxygen. Designs for these do exist, you would only have to carry a couple of tens of kgs of uranium and it does not have the same emotive radiation hazard that it would have if launched from Earth. Even at 6.8% water there would be plenty to drink and breathe

And would like to add in support

"Usually, with hydrogen propellant the solid-core design is expected to deliver specific impulses (Isp) on the order of 800 to 900 seconds, about twice that of liquid hydrogen-oxygen designs such as the Space Shuttle main engine."
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

I didn't see your original post, but I suspect you are off-topic. HINT: It has been my experience that the longer or more complex the post, the stronger the requirement for being on topic.

IMO: You just crossed a subjective line - by starting a discussion of nuclear propulsion in a LCROSS impact results thread. Technically the "usefulness of H2O" discussions were probably off-topic, but as in U.S. Football, it is always the player who retaliates for a foul blow that ends up getting the penalty.

Jack
If this post is deleted for being off-topic at least it is my first offense.

Thanks Spin0! This makes me disappointed, did NASA/scientific community deliberately ignored these findings because they are considered unreliable or...