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General Discussion / Re: Kids say the darnedest things...

« Last post by Peter B on March 14, 2025, 04:54:27 PM »

14YOS and I were talking about vaccinations. The context was that all three of the kids (and my wife) have just had chicken pox despite being fully vaccinated.

14YOS: So, why are people opposed to vaccinations?

Me: A variety of reasons, none of them really good. Some people think the diseases aren't dangerous. Some people are worried about additives to vaccines. Some people prefer to expose their kids to the actual disease rather than the vaccine.

14YOS: I've heard that some people reckon the vaccines contain microchips to control everyone. Though that doesn't make sense, they could just put them in the  water supply...

Me: And anyway, people seem willing to control themselves with their addiction to social media...

We both look at 12YOD, whose head is buried in her phone.

She looks up blankly.

12YOD: Huh?

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General Discussion / Re: Kids say the darnedest things...

« Last post by Peter B on March 12, 2025, 04:31:19 PM »

Someone doesn't like maths...

All Australian school kids are required to do standardised testing in English and Maths in Years 3, 5, 7 and 9, known as NAPLAN, and it's happening at the moment.

At breakfast this morning, 12YOD informed me she had her NAPLAN maths test today. Then, she mournfully added, "...and I have a maths class too, and they're not at the same time!"

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The Reality of Apollo / Re: Command module/Service module connection

« Last post by Peter B on March 10, 2025, 04:23:01 PM »

Cool, thank you! I didn't expect that level of connection through the heat shield.

I mean, I was aware of the connections around the outside of the heat shield. But I thought they were all that were involved, as I assumed it would be necessary to avoid any sort of interruption in the material of the heat shield.

The things you learn...!

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The Reality of Apollo / Re: Command module/Service module connection

« Last post by JayUtah on March 08, 2025, 10:59:20 AM »

Here is as complete an explanation as you're likely to get anywhere.

https://space.stackexchange.com/questions/41958/apollo-command-module-heatshield-tube-what-was-it-for

Tl;dr—yes there were stainless steel bolts that passed through the ablative portion of the heat shield in three places. But to be pedantic, this connects the CM to the SM, not to the Saturn IV-B stage. "Tension tie" is functionally equivalent to "bolt" in this application, although it's still ambiguous whether it was cylindrical or not. It seems to be, but other commentators describe it as a "strap." The illustration labeled Figure 11 is the most helpful. The compression pad (not labeled) is tightened until it presses upward hard on the CM, putting the tension tie in, well, tension. This compression-tension strategy is very much like how bombs are attached to airplane wings. It keeps them from wiggling around.

At separation, the linear shaped charge cuts the tension tie, the CM end of which stays there and gets very, very hot during reentry. The portion of the heat shield around the compression pads and tension ties are composed differently, and there is thermal isolation on the CM side.

The video also gives a very informative close-up of the fluid and electrical connections that went around the heat shield and were guillotined apart at separation.

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The Reality of Apollo / Command module/Service module connection

« Last post by Peter B on March 08, 2025, 03:06:18 AM »

Were there any connections between the CM and SM which passed through the CM's heat shield?

I don't think so, but a conservator in this Adam Savage's Tested video thinks it was. Savage is looking at the A11 CM sitting on a cradle, and the CM appears to be bolted to the cradle through the heat shield. The conservator says that these were "the same bolt holes that were used to attach it to the Saturn 5 rocket".

It occurs at about a minute into this video:

Thank you!

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The Reality of Apollo / Re: Apollo 11 and 17 imaged by South Korea

« Last post by onebigmonkey on March 06, 2025, 01:35:41 PM »

Apollo 15 imaged February 22 last year, released today. This is the calibrated version, the RAW file is flipped horizontally.

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The Reality of Apollo / Re: Everyday Astronaut video about Apollo

« Last post by JayUtah on March 06, 2025, 11:18:20 AM »

Rockets had been a practical reality for some time by then. The Hale rocket was available starting in the mid-1800s as a gyrostabilized missile that could be fired from a breech-loaded canon. They weren't very accurate. Nevertheless, the notion of constraining a rapid combustion was nothing new, and the mass production of a practical (if dubiously effective) rocket had already occurred.

Tsiolkovsky gets the most credit in my estimation for being an excellent physicist. It's one thing to experiment and note results that you can then harness. It's another thing to understand, quantify, and characterize the elementary principles by which something operates. He answered the question, "What's really going on here?"

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The Reality of Apollo / Re: Everyday Astronaut video about Apollo

« Last post by Dalhousie on March 05, 2025, 11:38:06 PM »

Its astonishing to me that Konstantin Tsiolkovsky published his Rocket Equation in May 1897, over six years before the Wright Brothers flew, and almost 30 years before Robert Goddard launched the first liquid fueled rocket.

He must have been some engineer!

"Just" a humble school teacher!

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The Reality of Apollo / Re: Everyday Astronaut video about Apollo

« Last post by smartcooky on March 03, 2025, 04:02:37 AM »

Its astonishing to me that Konstantin Tsiolkovsky published his Rocket Equation in May 1897, over six years before the Wright Brothers flew, and almost 30 years before Robert Goddard launched the first liquid fueled rocket.

He must have been some engineer!

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The Reality of Apollo / Re: Everyday Astronaut video about Apollo

« Last post by bknight on March 02, 2025, 08:32:50 PM »

After sleeping I reran the video and I have a question concerning Tim's calculations concerning the rocket equation.  In all of his calculations Tim used the Earth's gravitational constant of 9.8 m/sec^2.  I wonder if the Moon's gravitational constant should be used for the CSM/LM while entering/leaving Lunar orbit and the LM's landing/takeoff.  What's the verdict?

Short answer: no, you don't change g₀ to be that for the Moon. This comes up all the time while teaching rocket science. A moment's thought reveals that specific impulse and exhaust velocity have nothing to do with the gravity of anything your rocket might be operating near. All that works in deep space too.

g₀ appears in the rocket calculations to normalize the answer for differences in physical measurement units. "Specific" anything in science wants to be as dimensionless as possible. So something labeled "specific impulse" should be considered dimensionless even though it has units in seconds. To get there, you have to do undo all the physically-based measurements such as for mass, velocity, and force. Time in seconds is the only common thing in that relationship among all the measurement systems, so the physically-measured quantities are normalized to a "specific" quantity using something that exists as the same conceptual relationship in all systems. This is arbitrarily chosen to be Earth's gravity-based acceleration. It's a relationship that's defined in all systems and incorporates units of force, mass, time, and velocity—the quantities we care about when trying to measure rocket performance in terms of propellant behavior.

It's important to understand that this is arbitrary. It doesn't have anything to do with operating a rocket near Earth or anything to do with what the Earth's gravity is doing to the rocket. If you're working in SI, you undo the normalization for your units by using g₀ in SI units. If working in EES, you undo the normalization for pounds-force, gallons, firkins, and cable-lengths by applying g₀ in EES units to get exhaust velocity (for example) in feet per second instead of meters per second.

Short answer, ok.