Share this page!

Enter URL or ID to Unroll

You can paste full URL like: https://x.com/threadreaderapp/status/1644127596119195649
or just the ID like: 1644127596119195649

How to get URL link on X (Twitter) App

  1. On the Twitter thread, click on or icon on the bottom
  2. Click again on or Share Via icon
  3. Click on Copy Link to Tweet
  4. Paste it above and click "Unroll Thread"!
  5. More info at Twitter Help
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.

• • •

Missing some Tweet in this thread? You can try to force a refresh
　

Keep Current with Dr. Phil Metzger

Dr. Phil Metzger Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @DrPhiltill

Dr. 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
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

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

Send Email!

Become Premium to read this thread!

Read all the old archives from Twitter by becoming our Premium member for only $3/month! Read more »

Become Premium

Already a Premium member? Login to access this thread

:(