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Dr. Phil Metzger Profile picture
@DrPhiltill
Dec 3, 2017 • 15 tweets • 4 min read • Read on X
Another story on forgotten requirements in the space program. During NASA’s Constellation program, we all knew the Apollo Lunar Modules had a requirement that they couldn’t land on terrain more sloped than 11 degrees. (Or was it 10.5? I’m no longer sure.) But nobody knew why. 1/n
2/n Even the lead designer for the Altair lunar lander told me that he didn’t know why Apollo Lunar Landers had that requirement, although he knew that it was in fact their requirement. It was another requirement whose rationale was long lost in the mists of time.

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More from @DrPhiltill

Dr. Phil Metzger Profile picture
Dec 14, 2024
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:
3/ First, the visible flash that we expected to result from the impact was entirely suppressed. I remember watching it in realtime. It was a big disappointment because the satellite images in the visible spectrum showed absolutely nothing at impact. Image
Read 14 tweets
Dr. Phil Metzger Profile picture
Jul 18, 2024
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…
3/ …they were thinking about having MANY Resource Prospector missions. We talked about what would be the scientific, engineering, and economic value of building multiple copies of the mission. There was strong interest in the lunar ice to support building a sustainable program.
Read 17 tweets
Dr. Phil Metzger Profile picture
Jun 22, 2024
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
3. Just awesome! Look how the rings pull each other toward the end.
Read 14 tweets
Dr. Phil Metzger Profile picture
Jun 12, 2024
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
2/ With more engines firing you would need longer legs to keep that area large enough. If not, then the flow will choke meaning it goes subsonic and super high temperature and pressure, comparable to inside the combustion chamber, which can destroy the nozzles or engines.
Read 9 tweets
Dr. Phil Metzger Profile picture
Jun 10, 2024
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.)
Image
Image
3/ This is an extreme case of a “granular material” where the grains are long fibers. I did research on shuttle tiles when I worked in a physics lab at NASA, and I did research on thermal conductivity through granular materials, so I can report something interesting about this. Image
Read 14 tweets
Dr. Phil Metzger Profile picture
Jun 4, 2024
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
3/ The first hint of this came from the famous boot print made by @TheRealBuzz. Scientists’ jaws dropped when they saw the clean, vertical sidewalls of this print in such dry, fluffy material! How could the sidewalls stand straight without any moisture?! Image
Read 18 tweets

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