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Phil Metzger Profile picture
Phil Metzger
@DrPhiltill
Director, Stephen W. Hawking Center for Microgravity Research & Education @UCF. Prev: co-founder NASA KSC Swamp Works. Space Mining. Space Settlement. Science.
15 subscribers
Mar 14 • 10 tweets • 5 min read
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
Mar 5 • 5 tweets • 2 min read
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.
Mar 4 • 40 tweets • 13 min read
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
Feb 6 • 21 tweets • 7 min read
One time testing the Space Shuttle landing strip at White Sands, NM, the thought of this happening really scared me. We had just flown from Florida to Holloman Air Force Base in NM, which is 1.25 km above sea level. I asked the pilots about the barometric altimeter setting… 🧵/1 2/ because “0 feet” altitude above the runway in New Mexico is a lot lower barometric pressure than 0 feet at Cape Canaveral where we took off. The pilots explained how it is set whenever they are at a new airport. I was just wondering and thought no more of it till that night. Image
Dec 14, 2024 • 14 tweets • 6 min read
Great question. I don’t think the Moon can have solid sheets or lenses of ice like the Earth and Mars have. The absence of an atmosphere means everything on the lunar surface gets pummeled by meteorites and broken into granular material to 10s of meters depth. /1 2/ We saw evidence of this at the NASA LCROSS mission’s impact into Cabeus crater in 2009. The target soil was so soft that the spacecraft apparently buried into the soil 2-3 meters deep before meeting much resistance. This caused three observable:
Jul 18, 2024 • 17 tweets • 5 min read
A little background. The earlier version of this mission was the Resource Prospector Mission. When Jim Bridenstine was appointed NASA Administrator, NASA cancelled it without his permission just hours before he was sworn in. I can’t confirm this, but rumors say he was livid! /1 2/ Mr. Bridenstine was appointed by Pres. Trump, and the Trump Transition Team had people assigned to plan space policy. They were calling people for input. I got one such call and the person told me they not only WEREN’T going to cancel Resource Prospector, but instead…
Jun 22, 2024 • 14 tweets • 4 min read
Ok, here’s a little thread of some of the recent, awesome fluid dynamics content on here.

1. Checkout the computer modeling of airflow over an aircraft!

1/N 2. Vortices made visible by water vapor

/2
Jun 12, 2024 • 9 tweets • 3 min read
Four other problems with landing on a flat pad, even if it is a steel with water deluge.

(I’m assuming the larger size of the Super Heavy booster is why they can’t use flat concrete like ordinary booster landings.)

The four problems: … /1 1/ You need enough surface area around the base of the rocket for the gas to flow out, or the engines will choke. Imagine a cylinder extended below the rocket to the ground. The exterior of that cylinder must exceed the exit area of all the rocket nozzles that are firing. Image
Jun 10, 2024 • 14 tweets • 5 min read
If I had to guess it would be this: same exact material as the existing tiles but just a wee bit thicker. Here is why…

1/N 2/ Here is what they look like on the inside. They are something like 98% empty space, and the rest is a glass fiber. The fibers touch each other along small contacts, so thermal conductivity is very low. (The scale bar is 100 microns, or 0.1 millimeter.)
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Jun 4, 2024 • 18 tweets • 7 min read
This was the same reaction the science team had during the Apollo program — surprise that bone-dry soil could have so much cohesion! See the clods in the footpad image, especially. Short 🧵 1/N 2/ Closeup image of the clods. These are likely very porous, low density clods — very fluffy material — that will easily fall apart between your fingers. Yet they are in blocky shapes somehow held together as the footpad impacted and disrupted the ground. Image
Apr 28, 2024 • 15 tweets • 5 min read
Untrue. This does touch on something related that actually happened, which people have apparently distorted and used to prop up the dumb conspiracy theory. I will explain… 1/N 2/ First I’ll tell you what I know about the videos, then the telemetry.

When I analyzed the plume effects of the lunar landings, starting in the late 1990s and early 2000s, I tracked down the original data. One of the guys on my team worked with Houston to get the videos.
Apr 18, 2024 • 8 tweets • 3 min read
NASA now building a flight-ready lunar excavator for a resource utilization pilot plant (not a demonstration — the actual pilot plant) on the Moon. Discussing the challenges of reoeatably setting up the correct lunar soil conditions (compaction, rocks) for testing the lunar excavator on Earth. Image
Apr 10, 2024 • 4 tweets • 1 min read
I'm tired of reading in the news people proclaim that starting a city on another planet is economically ridiculous when clearly they are just guessing. So I'm finally starting to write a paper on the analysis I did a few years ago that found (to my surprise) it is quite feasible. The main thing ppl don't seem to grasp is that the cost of the extra stuff for Mars, like building a dome, recycling air, using mass for radiation shielding, washing perchlorates from dirt, etc., are utterly trivial compared to the cost of frivolous things we do in our economy.
Mar 31, 2024 • 42 tweets • 13 min read
Part 2. Another thing I think is cool in the papers I linked a few days ago. The quoted thread was about the granular physics of gas digging craters in small experiments, which I thought was cool. This new thread is about lunar geology. 🧵 1/N 2/ The papers described how those small experiments give physics insight that leads to a new equation predicting erosion rate when there is no saltation. I took that new equation and applied it to the Apollo Lunar Modules to predict how much soil was blowing.
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Mar 29, 2024 • 15 tweets • 5 min read
Here’s something I think is cool in the new papers that I linked yesterday.

My research group over the years has run many, many small scale experiments where a jet digs a crater against a window so we can see into it. 2/ Something weird we see in these experiments is that the depth of the crater is perfectly described by the logarithm function. Like I mean, perfectly. There are two parameters: a and b, the length scale and (inverse) time scale.
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Mar 18, 2024 • 10 tweets • 2 min read
I’m not so sure. The link to the prior estimate is a paper that measures the “blast zone”, which is the region around a lander where the reflectivity of the surface has changed. We have never known exactly what causes this change. Is it from gas blowing the dust texture flat? /1 2/ Or is it from blowing dust plowing across the surface? Or from engine shutoff when the last sputter of the engine cause a low velocity blanket of dust to fly out to a much smaller distance than normal? The problem has always been that this blast zone is *too small* to be…
Mar 17, 2024 • 12 tweets • 3 min read
Lots of discussion today on space radiation including errors like this one. This has confused water with regolith. Using too thin a layer of *regolith* creates secondaries, increasing the dose. But using water, or PTFE (lots of hydrogen), even very thin, always reduces the dose/1 2/ The thing about using regolith for shielding is that you use it when you are on the surface of a planet, and there’s so much available and you do t carry it on a spaceship so you have no reason to use a thin amount. It entirely solves the problem!

And…
Feb 27, 2024 • 4 tweets • 2 min read
There have been advances though. For example, NASA developed a coating that passively cools to liquid oxygen temperatures even in full sunlight at 1 AU (Earth-distance) from the Sun. 1/2 2/ The technology is a coating called Solar White, which uses Yttrium Oxide to block almost all the solar spectrum while yet allowing emission at black body temperatures for a cold object. So the object in direct sunlight continually loses net energy to space.
Feb 25, 2024 • 22 tweets • 6 min read
I could write a 50 page paper answering this :)

A few points in outline form only:

1) The rocket exhaust is expanding into vacuum, so viscosity breaks down, so the gas does not obey the Navier-Stokes equation, which is the basis of CFD (computational fluid dynamics) models. /1 2/ When I was at NASA, one of the things I was doing was writing solicitations to industry to write physics-based code to do CFD without Navier-Stokes. There are many ways to treat the fundamental physics (the Boltzmann Transport Equation) and they all work for different…
Feb 24, 2024 • 17 tweets • 4 min read
About how the lunar environment makes everything tippier…

1) I’m sure the CLPS contractors know this and designed for it. My point is that the Moon does this to your hardware, so when things go wrong (as they do) then tipping happens more often than on Earth. /1 2/

2) There are different ways you can tip. For static stability, gravity makes no difference. You fall when you are so tilted that the center of gravity (cg) is outside of your footpad. I don’t know where the Nova-C has its cg, but crudely it could handle ~54 degrees tilt. Image
Feb 3, 2024 • 35 tweets • 12 min read
I finally submitted this paper to Icarus (planetary science journal). I split it into two papers: “Erosion rate of lunar soil under a landing rocket, part 1: identifying the rate-limiting physics” and “…part 2: benchmarking and predictions.” The breakthrough was in part 1.
1/N 2/ It took 8.5 months from the breakthrough while sitting at McDonalds until I got the paper done. 😭 I had to re-do it several times. 💀

I’m not keeping the info secret before publication, so I’ll go ahead and tell a little here.