Dr. Phil Metzger Profile picture
Director, Stephen W. Hawking Center for Microgravity Research & Education @UCF. Previous: co-founder of NASA KSC Swamp Works. Space Mining. Space Settlement.
Tomáš Kafka Profile picture Ireneusz Kozłowski Profile picture R. Chitwood 🇺🇸🇺🇸🇺🇸 Profile picture RJ Profile picture @AlgoCompSynth@universeodon.com by znmeb Profile picture 15 subscribed
Jun 22 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

Jun 12 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 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.)
Jun 4 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 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 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 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 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.
Mar 29 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.
Mar 18 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 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!

Feb 27 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 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 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 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.
Jan 27 19 tweets 7 min read
This is a fun and fascinating thread. I’ll add one thought. Latif says that some objects are dynamical and move about but the “regular” planets & moons aren’t that way, but really it’s just a matter of timescales. Everything changes orbits. 1st read Latif’s thread then mine…🙂/1 2/ An example of a moon that changed orbits: Triton. It is currently a moon of Neptune but previously it was a primary planet orbiting the Sun directly (albeit a small planet…a dwarf planet like Pluto). Neptune captured it! Image
Jan 23 31 tweets 7 min read
This was a fun read but I have this response. The piece says that Turner’s Frontier Thesis is a strong motive of people who want to move civilization beyond Earth. But that’s not true. It is merely *adjacent* to the actual strong motives. Discarding it makes no difference. /1 2/ As the article explains. Turner’s thesis is that the US Western frontier created an open democratic society of self-reliant individuals with strong moral fiber. It says the western frontier values diffused back east to keep the rest of the US from falling into degeneracy, too.
Dec 31, 2023 9 tweets 2 min read
Here’s the problem with trying to respond to Dr. Kirkpatrick’s request. Many technologists (myself included) believe we have reached the point where technology is changing so fast we cannot even guess what it will look like beyond a few decades. Any alien civilization that…/1 2/ …is so far ahead of us that they could travel between stars is way, way beyond the point that it becomes completely unpredictable. Therefore, any models we might create for what the tech could look like (how they might get here, how they might refuel…) are unconstrained.
Nov 22, 2023 9 tweets 3 min read
Apologies for the crude markup (did this on my phone). Your eye can pick out these features better in the video than in a single snapshot, so watch the video and look for these annotated features (short thread). 1/N
Image 2/ Each nozzle has a plume (a jet) that is slightly mismatched relative to surrounding air pressure, so they oscillate in diameter, widening and narrowing to try to match pressure, but overshooting each time so they oscillate. These are the Mach diamonds.
Nov 3, 2023 4 tweets 1 min read
Just today I was advising a PhD student and told him something very similar. We were discussing experimental results that seem irrational, contrary to theory, and showing no pattern at all. Over the course of my career I’ve learned that whenever you’re in this situation… /1 2/…you have to tell yourself that nature is not irrational; there is always an explanation, and it can always be found. Someone will find it, and that person can be me.

If you don’t believe that, you won’t persevere and you won’t find the answer. But in my experience,…
Oct 6, 2023 9 tweets 3 min read
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