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31
The Reality of Apollo / Re: Chandrayaan-2 views Apollo
« Last post by BertieSlack on September 09, 2021, 09:16:06 AM »
That Apollo 11 image is actually really good, but you know what the HBs are going to say, where are the footprints? I would reckon that no argument about light angles, size or resolution would placate them.

The are several LRO photos of the Apollo 11 landing. The astronaut foot-trails seem much more visible in the those photos taken when the sun is high in the sky above Tranquillity. The sun is low in the Chandrayaan 2 image.
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The Reality of Apollo / Re: Chandrayaan-2 views Apollo
« Last post by onebigmonkey on September 08, 2021, 01:48:24 PM »
That Apollo 11 image is actually really good, but you know what the HBs are going to say, where are the footprints? I would reckon that no argument about light angles, size or resolution would placate them.

To say it's a screengrab of a powerpoint presentation slide it holds up very well against the LRO's shots of the same place.
33
General Discussion / Re: Boeing Starliner
« Last post by jfb on September 08, 2021, 01:32:58 PM »
To pull things back onto topic, can I point out a couple of Scott Manley videos in the last week, covering launch failures by a couple of new companies - Astra and Firefly (I assume you've all seen the sideways lift-off of the Astra). Which just goes to show that it's not just well-established companies that can suffer from rookie errors...

I'm still amazed at the Astra's ability to recover; that could have been a wrecked pad.  The guidance and control guys deserve a case of beer over that.

Agreed! I was so struck by what I saw that I showed the video to my kids. I explained to them that there are videos of spectacular rocket failures from the 1950s and 1960s where engine shutdowns straight after launch resulted in pretty much complete loss of control and big explosions close to the ground. Even they (after their fashion) were impressed by the Astra recovery - and laughed at Manley's "flamey-end down, pointy-end up" comment.

Having said that, as one commenter pointed out: just as well it wasn't the opposite-side engine that failed, otherwise the rocket would have slid sideways into the launch tower...

And regarding the Firefly launch, I was surprised the rocket survived its tumbling motion as long as it did. I thought rockets travelling other than straight ahead disintegrated quickly.

Yeah.  I don't remember if it was Manley or someone on another forum, but they had a comment to the effect that was a sign the stage was a bit over-engineered and could afford to shed some weight. 
34
General Discussion / Re: James Webb Space Telescope
« Last post by bknight on September 08, 2021, 01:25:12 PM »
Yes I read where it was readied for shipment via the sea.  I'm still hoping all will go well.
35
General Discussion / Re: Work after COVID
« Last post by LionKing on September 08, 2021, 01:12:54 PM »
Poor you. I hate cold weather.
Here we have a saying that describes each month. In Arabic they rhyme so they are memorizable.

September has its end wet in rain.
Between October and November there is another Summer.
(Both december and janjary are kenoun the first and kenoun the second), so in the kanouns stay in your home and increase your bread and oil. Also in kenoun keep the embers in the kanoun (another word for where you put the embers for grill-it means for warmth)
February, no matter how much it hit or kicked, it has the smell of Summer.
In March keep your big logs (for warmth), it has 7 big snows, not to mention the small (not anymore though)
The water of April enlivens the person

I forgot what there is for May and June

In July the water boils in the cup

August is flamy





36
General Discussion / Re: James Webb Space Telescope
« Last post by molesworth on September 08, 2021, 12:27:04 PM »
There's now an "official launch date" of 18th December, although whether it'll slip again remains to be seen.

https://www.nasa.gov/press-release/nasa-readies-james-webb-space-telescope-for-december-launch

Quote
NASA plans to launch the James Webb Space Telescope into orbit Dec. 18, 2021, to serve as the premier deep space observatory for the next decade.

The agency set the new target launch date in coordination with Arianespace after Webb recently and successfully completed its rigorous testing regimen – a major turning point for the mission. The new date also follows Arianespace successfully launching an Ariane 5 rocket in late July and scheduling a launch that will precede Webb. The July launch was the first for an Ariane 5 since August 2020.
37
General Discussion / Re: Work after COVID
« Last post by jfb on September 08, 2021, 12:03:18 PM »
So how much education you get should depend on your climate.  Check.

 ;D  I guess that doesn't bode well for us in damp, drizzly Scotland then...

There aren't seasons better than others?

Well, there's mist season, rain season, snow season and sleet season, but we do get at least three days of sunshine per year  ;D

Seriously though, we do get reasonable Summers, and this year it's managed to get up to the high 20's, with long dry periods.  We have a special word for Winter though - "dreich" (ch as in loch) - which captures the climate in a sound.

Heh.  I always joke that Texas has two seasons, Summer and Not Summer, but it actually breaks down more like this (thanks to a meme someone posted in Facebook):

Winter
Fool's Spring
Icepocalypse/Snowmageddon
Spring of Deception
Third Winter
The Pollening
Actual Spring
Noah's Ark
Summer
Hell's Front Porch <- we are here
False Fall
Second Summer
Actual Fall

38
General Discussion / Re: Work after COVID
« Last post by gillianren on September 08, 2021, 10:54:29 AM »
So how much education you get should depend on your climate.  Check.

 ;D  I guess that doesn't bode well for us in damp, drizzly Scotland then...

We've apparently got roughly the same weather here in Western Washington.  There are definitely a few months where school outside isn't a ludicrous concept, but not as many as there are in other places.  It's as though buildings were invented for a reason.
39
General Discussion / Re: Boeing Starliner
« Last post by molesworth on September 08, 2021, 07:50:08 AM »
I guess we've wandered way off topic from the thread's original subject, but I think the most outstanding piece of optimisation I've ever seen, and which still blows my mind, is the Fast Inverse Square Root.  The code looks like complete nonsense but gives a result within a percent or two of the actual value, and back in the days when Pentium processors were top of the range it was huge performance improvement, especially for graphics processing where 1/sqrt(x) is used a lot.  Even today it's still faster than general-purpose processors or libraries can achieve.

A good article on it is - https://medium.com/hard-mode/the-legendary-fast-inverse-square-root-e51fee3b49d9 - see if you can figure out how it works before reading the explanation  :) 
(Warning - code contains sweary word...)

Most general purpose processors now have square root or reciprocal square root instructions that are considerably faster and more accurate. x86 has had such instructions for over two decades now. This algorithm is mainly only of significance today for historical interest or small embedded processors. (And in those, even the Cortex M7 I'm writing code for now has a VSQRT instruction.)

Good point - hardware FPUs are a lot better nowadays, and GPUs are just mind-bogglingly fast.  I guess I've spent too much time working on what are really low-performance processors recently, not on more widely used systems...  :)

However, even as a historical artefact the algorithm is a great example of brilliant optimisation and ingenuity.
40
The Reality of Apollo / Re: Chandrayaan-2 views Apollo
« Last post by Mag40 on September 08, 2021, 06:06:41 AM »
That Apollo 11 image is actually really good, but you know what the HBs are going to say, where are the footprints? I would reckon that no argument about light angles, size or resolution would placate them.
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