Phil Metzger Profile picture
Oct 6, 2023 9 tweets 3 min read Read on X
I got word today that our research into the Starship launch pad anomaly is being forwarded uphill to NASA HQ. They are focusing on what we learned about launch/landing pad failure modes and how we can make lunar landings safer. /1
2/ What we found is that the pressure that built up beneath the launch pad was comparable to a volcanic eruption when the buildup of hot gas that evolves from the magma busts apart the caprock and expels it. (Pic: Fagents & Wilson, Geophys J Int 113(2): 359.) Image
3/ The theory on these volcanic eruptions predicts a range of velocities that matches what was measured for the ejected chunks of concrete from the Starship launch pad — about 90 m/s. Image
4/ But to explain the mass of gas needed to expel at this velocity, we had to conclude that groundwater under the pad was vaporizing. We estimated the water based on crater volume and permeability of the sand under the pad. It is in the range that agrees with theory. Image
5/ This raises the question about ice in lunar polar soil under a launch pad. If the pad cracks and hot gas is pushed through (like we think happened for Starship) then vaporization of the ice may create a similar situation. Ice can be as much as 5%wt (actually higher), which…
6/…predicts that ejection velocity of a lunar launch pad could be even faster than what happened for Starship. 5 wt % vs 1 wt % on this plot. Image
7/ So we need to develop methods to prevent this. It shouldn’t be hard to do. Examples: make the pad thicker. Measure the ice before construction. Put vents under the pad. In fact… Image
8/…we are already collaborating with Cislune on a project to develop these technologies. “Deflector cone and vented launch pad” — read more here: spaceref.com/science-and-ex…
9/9 So that’s how the Starship launch pad anomaly, while not *desired* ofc, turned out to produce insights for engineering lunar landing technology. This is the message that got attention and is being sent up to NASA HQ.

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More from @DrPhiltill

May 18
1/ Let’s walk through a mining competition cycle. The students take their robots to the judge station for inspection and weigh-in. (More points awarded for lower-mass robots.) Image
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2/ They set their robots on the forklift platform to lift into the arena. Image
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3/ Robots are placed on the regolith in an orientation chosen randomly by the judges (so the robotic autonomy can’t be cheated).
Read 12 tweets
May 17
@bobster190 @DJSnM @WilliamShatner The paper has all the citations to other work inside it. I linked the paper because it wouldn’t make sense to duplicate that in a tweet. The paper wasn’t about Pluto. It was only about asteroids. We wrote a second paper that discusses Pluto and I think answers your objections. /1
@bobster190 @DJSnM @WilliamShatner 2/ That 2nd paper is here (no paywall so it is accessible):

It does discuss the arguments surrounding the IAU’s vote in 2006. I think we did a much better and more complete review of the issues than any other publication on the topic. Most other papers…sciencedirect.com/science/articl…
@bobster190 @DJSnM @WilliamShatner 3/ …include patently false information about why Pluto was voted down by the IAU. For example, the claim that asteroids were demoted because they share orbits is utterly nonsensical. Even a cursory review of the publication history shows this. Also the claim that the Moon…
Read 16 tweets
May 6
Here is something that hints strongly at how human scientists and engineers are already doomed by AI. 🧵

I noticed this tonight while using Grok for technical research. I asked it a complex question and Grok understood it completely and gave a sophisticated and highly believable answer, but when I asked for specific references so I can write it into a paper for a journal, none of the references Grok provided exactly support the answer it gave me. Instead, they hint at something deeper.

In this case, I am quantifying the loss of signal margin in a Moon-Earth communications link as a function of how many times you landed near the communication system so the rocket plume sandblasted the electronics' thermal coatings, causing them to operate hotter than designed. There is a real cost to sandblasting your hardware on the Moon, and I am trying to quantify it.

Grok gave me many quantified effects, including that the frequency oscillator will drift about 10 to 50 ppm per deg C of temperature rise outside its operating range and that the Signal to Noise Ratio of the overall communications link will drop about ~0.1–0.5 dB for small drifts (<10 kHz) in particular modulation schemes. This is a great result that I can use to quantify sandblasting damage on the Moon, and the result is totally plausible, but it doesn't appear in ANY reference that Grok provided. Nothing discusses this.

So I suspect Grok actually derived that relationship itself during the LLM training. I think the relationship is probably correct, because the many references hint around the edges of this relationship in the right magnitude. I think Grok noticed the patterns of many performance metrics including temperature, input power and frequency, outputs, etc., for many devices and how they are connected in typical systems, and it stored as a higher-level symbol the result that you get 10 to 50 ppm per deg C performance loss. I think it solved that during training as it sought the higher-order symbols to store everything it had learned. IOW, its learning process included a heckuva lot of valid inference on these technical issues, and it now knows more about the performance of communications equipment than even the published literature knows.

I asked Grok if this is true, and it says it is correct (screenshots).

/1Image
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2/ I then asked Grok to derive this relationship the same way it probably did during the LLM training, and it did. So now, if I want to use this key result in my paper, I have to use the many references that Grok used when it derived the relationship, and I have to show the derivation explicitly in the paper, or I can't publish it per the rules of scientific publishing (which of course were created in the days before reliable AI, and we still don't have totally reliable AI, but we can see it is coming fast).Image
3/ So here is the derivation, which it says replicates the process it did during its LLM training, which led it to believe in the quantified relationship between frequency shift and signal to noise ratio. I'm including this just to show its character. Image
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Read 4 tweets
Mar 14
I think it’s likely the Outer Space Treaty will be voided within the next few decades as nations will claim (effectively) national territory on the Moon and Mars.

Here’s why I think this…

/1 Image
2/
The OST is part of the International Rules-Based Order that emerged post-WW2. The IRBO was originally multipolar with the US-led NATO and Soviet-led Warsaw Pact. The collapse of the latter left the US as the main power wanting to keep the IRBO. China/the CCP hates this.
theguardian.com/world/2023/oct…Image
3/ The CCP claims the rules-based order was set up when China was weak so it is unfair and needs to be replaced. They are aggressive at claiming territory in their national interest, disregarding the existing rules-based order by rejecting rulings of the international court. lowyinstitute.org/the-interprete…
Read 10 tweets
Mar 5
I’d like to reemphasize this. The dust you see is not settling. It is still going uphill when it flies over the horizon and out of view. It is like a rocket that has curved below the horizon but is still climbing. If you get this, it makes sense why it clears the view so fast. /1
2/ It has so much grandeur when your mind can see it for what it is. It is not a humble cloud sinking to the ground. It is a vast, high energy phenomenon covering hundreds of kilometers in just a few seconds. In the vacuum of space nothing impedes its flight.
3/ I know some will object to the idea of regolith flying so fast that it escapes completely off the Moon, but the finest dust does. In fact, you can only see dust finer than about 1 micron in this video, and rocks bigger than a centimeter or so. >99% of the mass of the flying regolith is actually invisible in this video.
Read 5 tweets
Mar 4
This is superb! Will be a treasure for quantifying plume-surface interactions during lunar landing. There are some things I don't understand yet and will take a while to unpack. (Note: I'm not supporting the mission so this is just my private musing.) 🧵/1
2/ I don't understand three things about the shadows.
First, there is a huge upward flow up the centerline. The plume itself should be clear and invisible, since it cools as it leave the engine and without an atmosphere to collimate it the shock structures in the plume are... Image
3/ greatly reduced. So when I look at this, I think that central shadow up the center is not the plume but is dust, what we call "fountain flow". Now the lander has only one main engine, so if it was firing then there shouldn't be any fountain flow... Image
Read 40 tweets

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