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Jerry
2006-Jan-16, 07:11 PM
Sciences - primary research - regards the interity of the product as the highest metric. But there are other metrics that often interfere.

This near demise of Spirit is according to Bruce Moowmaw:

http://www.unmannedspaceflight.com/i...52&#entry32452



Given how close MER-A (I refuse to use that cornball name "Spirit") came to disaster because of the unexpectedly low density of Mars' upper atmosphere -- even after its hasty last-minute reprogramming to open its parachute earlier, it came within 3 seconds of opening the chute too late to avoid a crash --

As far as I know, this has never been reported officially - as of December NASA had not released reconstructions of either MER-A or MER-B EDLs.

There are many, many other examples of near misses and anomalies that are invariably downplayed or omitted completely in official reports. I mentioned this trend to a collegue, who explained it this way:

Science is also a business, and competition for research dollars is high. Principle investigators who make predictions about the expected results of a mission, and then report all results are within expectations receive higher metric marks than those who don't and ultimately more funding. So regardless of the result of the program, the investigator will highlight the data that is consistent with the test plan and down play any unexpected observations.

The net result is riskier programs are rarely proposed, more rarely funded, and we end up with a watered down scientific yield.

That's one scientist's opinion. Here is another one:

Not only are anomalous results down played, in many cases they are ignored. For example, in the NASA TV play around the Stardust mission, when a scientist was ask what the results of Deep Impact were, the scientist responded 'pretty much what we expected - we can see the sublimation pools that are responsible for the jetting...'

Here are the facts:

Deep Impact demonstrated that the thermal inertia of Tempel 1 is extremely low. This means the dust on the surface is highly insulating, and very little heat from the sun penetrates beyond a few centimeters into the comet, before it rotates and releases the energy on the dark side. How this leads to jetting is difficult to explain.

No one expected the primary ejecta from the impact to be dust - clays and silicates, not water and organics.

The "sublimation pools" looked much more like craters, and showed no evidence of recent activity. There was jetting, but the source of the jets happened to be on the opposite side during closest appoarch, so no direct observations were made. (Partly too, because the probe is near-sighted.)

I am not saying that the mission was not a success. I think it was extremely successful. But I don't think the observational evidence is 'pretty much what we expected'. I think they are a stunning example of new data raising new questions: Where exactly is the water, how much is there, and how is the comet nucleus finding enough energy to create high velocity, periodic jets?

When Jessica Sunshine was interviewed by the Planetary Society, and ask if there were any surprises, she said that the layering was a big surprise - but she did not mention any of the unexpected results posted above.

When the data does not fit the model, it is still a scientific success. Researchers must put there preconceptions back into the bottle when analyzing the data. The model must be changed to accomidate new facts. New facts must not be ignored, and must not be neglected when discussing the results in public forums.

Doodler
2006-Jan-16, 08:51 PM
Few things:

1) The link 404'd me.

2) Is there no third party source describing this issue with Spirit? One guy with an apparent chip on his shoulders is not a credible enough source for a one legged defense.

3) The "3 seconds" thing sounds to me like the chute opened within designed tolerances, so what's the point he's trying to make? Extensive deconstruction of the entry profiles of the rovers would seem to have the pre-ordained conclusion of "worked as intended".

4) As far as the ejecta analysis of the Deep Impact, you've got to establish how they were wrong. Does the fact that the composition of the nucleus is more silicate that water on the surface imply that there is not a robust presence of water on the comet? Even if the nucleus were a core of ice with an accumulated layer of dust hardened over the surface through cementation as I described in my geode comparison, would this still not be a defensible postion for the "dirty snowball" model? The location of the jets would simply be weak spots in the dust surface.

5) In response to the issue of the comet's rotation preventing heat absorbtion due to rotation, is that rotation so rapid that the "dark" side isn't dark long enough to radiate all absorbed heat? Is there a threshold point of proximity to the Sun where the amount of absorbed radiated energy exceeds the surface dust's ability to prevent thermal transfer? Are the energy absorption properties of the dust directly over the jet openings similar to the properties of the remainder of the comet? Mind you, active jets will have a substantially lesser dust covering.

Questions may well exist, but even the dustiness of Deep Impacts ejecta cloud is not enough to completely unseat the currently theorized model.

Nowhere Man
2006-Jan-17, 04:08 AM
Are you talking about "silence" or "science?"

Fred

01101001
2006-Jan-17, 05:15 AM
This near demise of Spirit is according to Bruce Moowmaw:

http://www.unmannedspaceflight.com/i...52&#entry32452

As far as I know, this has never been reported officially - as of December NASA had not released reconstructions of either MER-A or MER-B EDLs.

Refresh our memories, please. How far outside of the expected window of parachute deployment was Spirit's?

I remember EDL being described as "six minutes of terror" and that a lot was happening throughout. As I recall the main chute deployed 3 or 4 minutes after entry into the atmosphere, so the window couldn't have been all that large to begin with.

Were those 3 seconds from doom, 3 long seconds or 3 short seconds? I mean, if the mandatory window for deployment was like a couple of minutes long, then 3 seconds from the end might sound like cutting it pretty close. If the mandatory window was 10 seconds long, 3 seconds from the end sounds just dandy. What was Spirit's like?

I've designed enough real-time systems to know there are margins and there are margins. I remember testing a system that when measured succeeded on average 5 milliseconds from disaster. And, we laughed with relief. 5 whole milliseconds! Plenty to spare!

Hamlet
2006-Jan-18, 03:13 AM
The Mars Exploration Rovers Entry, Descent, and Landing Trajectory Analysis (http://techreports.larc.nasa.gov/ltrs/PDF/2004/aiaa/NASA-aiaa-2004-5092.pdf) paper shows the data that has been reconstructed so far. Pages 5 and 6 of the paper have tables with the simulated and reconstructed values for the various EDL parameters.

Indeed parachute deployment was at the high end of the ranges for Spirit, but still within them. The parachute deployment for Opportunity was slightly outside the predicted ranges.

The authors took note of this on page 7:


Note, due to an observed dust storm on Mars just weeks prior to arrival, the targeted parachute deployment dynamic pressure was increased from the 700 N/m2 to 725 N/m2 for the “Spirit” entry and to 750 N/m2 for the “Opportunity” entry to raise the deployment altitude. This modification was made to hedge against the possibility of encountering a lower density profile than predicted which would reduce the parachute deployment altitude, and thus, the descent timeline from parachute deployment to RAD firing.


The authors acknowledge a few parameters that were outside the predicted range:


However, there are a few parameters that are near or slightly exceed the 3-σ variation bounds (e. g., time of and αTat parachute deployment).


Here is the reason why:


For both the “Spirit” and “Opportunity” entries, the time of parachute deployment was later than predicted because a lower density atmosphere was experienced. Based on preliminary atmosphere reconstruction estimates, approximately an 8% lower density profile (correlating to roughly a 1-σ low profile) was encountered in the maximum deceleration region during the “Spirit” descent, while approximately a 12% lower density profile was encountered during the “Opportunity” descent. This greater reduction in the density profile for “Opportunity” (as compared to “Spirit”) is consistent with the observed later time of parachute deployment.


These predicted ranges aren't black and white. A slightly out of range parameter does not mean near or total disaster. There is some conservatism built into the design to account for conditions that aren't totally predictable.

There is no silence.

Argos
2006-Jan-18, 01:32 PM
As some people might use the contents of this thread to strengthen conspiracy views I think that a reassurance that NASA is utterly transparent reporting the development of its programs, without any interference whatsoever of competition and/or personal agendas is needed for the sake of the general public, but I´m affraid to be unable to provide it.

R.A.F.
2006-Jan-18, 01:54 PM
A slightly out of range parameter does not mean near or total disaster.

Nor does it mean that we must employ "new physics" as an explanation.

It simply means that we are exploring new places. And when we do that, we should expect new discoveries/surprises. That's part of what scientific discovery is.

Jerry
2006-Jan-19, 09:29 PM
Bruce cites as his source a meeting with mission scientists - and this is their characterization, not his. Bruce is highly reliable, so even though this is hearsay, the assessment that the late deployment was nearly fatal is "official". They scrambled, in the week following Spirit's landing, to raise the altitude at which the parachute of Opportunity was deployed. (From Spirit's significant event log.)


Notice that there are a lot of blank slots in the "Reconstruction" column of the Mars Exploration Rovers Entry, Descent, and Landing Trajectory Analysis referenced above - this report is a year old - when will the reconstruction be completed? Is the unposted data more-or-less out of family than the data included in the report?

Yes I mean the success of silence: Playing up the results when the mission performs as expected, while ignoring the shortcomings. That is to be expected. What I do not understand is downplaying scientific results that are significantly at odds with an unproven hypotheses.

At Tempel 1's current distance from the sun, it is absorbing virtually NO solar energy - reradiating everything that hits it. This was unexpected, and should be reported as such. When Stardust Mission Scientists go on NASA television and say the results of Deep Impact were 'pretty much what we expected.' I think that is only true if all we expected was for the probe to hit the nucleus and stuff to come out. There was much more dust, much less water, and many more questions raised than answers.

Jerry
2006-Jan-19, 09:46 PM
Few things:

1) The link 404'd me.

sorry:

http://www.unmannedspaceflight.com/index.php?showtopic=1868&st=30

If that does not work, go to www.unmannedspaceflight.com and select the Mars & Missions > Orbiters > Mars Express & Beagle 2 thread - (page 3)



2) Is there no third party source describing this issue with Spirit? One guy with an apparent chip on his shoulders is not a credible enough source for a one legged defense.

A better description of Bruce is candid. Yes, an offical or third party source would be appreciated.



4) As far as the ejecta analysis of the Deep Impact, you've got to establish how they were wrong. Does the fact that the composition of the nucleus is more silicate that water on the surface imply that there is not a robust presence of water on the comet? Even if the nucleus were a core of ice with an accumulated layer of dust hardened over the surface through cementation as I described in my geode comparison, would this still not be a defensible postion for the "dirty snowball" model? The location of the jets would simply be weak spots in the dust surface.

Not wrong - the mechanism may be exactly as expected, but the mission results are inconsistent with a solar heating mechanism...If the prelimnary reports on the thermal inertial stand.



5) In response to the issue of the comet's rotation preventing heat absorbtion due to rotation, is that rotation so rapid that the "dark" side isn't dark long enough to radiate all absorbed heat?
according to the preliminary report - I think you can find a summary in the planetary societies pages, the comet only took a few minutes to return to cold thermal equalibrium after rotating away from the sun. This is like the desert, the sand is only hot on the very surface. One would not expect a vapor explosion on the desert in the middle of the night, and that appears to be what is happening in comets. Cool mystery!


Questions may well exist, but even the dustiness of Deep Impacts ejecta cloud is not enough to completely unseat the currently theorized model.
Absolutely! But the way you phrase this is a far cry from 'pretty much what we expected'. Is a mission that raised more questions than answers a success? Of coarse...but only if we follow it up with another mission, since we have a better idea of what to expect. If the results were 'what we expected', why bother?