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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

Phil Metzger Profile picture
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
Phil Metzger Profile picture
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
Phil Metzger Profile picture
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
Phil Metzger Profile picture
Feb 6
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
3/ We were scheduled to fly out of Holloman at midnight to perform landing tests on the Shuttle runways repeatedly until dawn, two nights in a row. The flights were at that dark shift to avoid conflict with Air Force flight traffic. It was home of the F-117A stealth fighter. Image
Read 21 tweets
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
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

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