Recent Posts

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General Discussion / Venus astronomy question

« Last post by Bryanpoprobson on Today at 04:33:57 AM »

In answering a silly flat Earth believer regarding the amount of time that Venus is above the horizon. He said that Venus in 2015 was viewable for 24hours. Now I dismissed that, but on reflection is it possible for Venus to be visible all night when viewed from an extreme northerly or southern latitude, when the sun stays just below the horizon just before or just after the equinoxes? Logic says that it is possible for Venus to hover above the horizon for 24 hours, but the angle to the plane of the ecliptic must be nearly 90degs. But is it a fact, if it is, it would be rare. The internet seems to be split but my logic says it is technically possible.. Thoughts…

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General Discussion / Re: Starship!

« Last post by bknight on May 28, 2023, 09:43:32 AM »

I would like some of our "rocket scientists" here have a look at this video and offer their opinions. It is an animated render and commentary giving a brief explanation of how the water-cooled steel plate system is supposed to work. Its from Alpha Tech's YouTube channel, with the computer rendering by Ryan Hansen. Credit to both of them for this excellent presentation.

Note: right-click on the link and choose to play it in a new tab. It will play a short (1m 41s) video in Dropbox

https://www.dropbox.com/s/1zi550dn801f41m/Starship%20Deluge.mp4?raw=1

As most of you already know, I am an aeronautical engineer (retired), but not an aerospace engineer. While the two disciplines share a lot of common ground, there are aspects of "rocket science" that are outside my pay-grade.
 
In particular, there are some statements made that I am doubting the accuracy of. I would appreciate any comments on some of these technical details.

1. The claimed "established temperature gradient" between the rocket exhaust at the point it leaves the ending bells and the water cooled plate
2. "In the centre of the plate, the water pressure is higher than the exhaust pressure"
3. "The exhaust never touches the plate"
4. If the water flow is maintained at a high enough rate, they can keep the temperature at the plate below 1000°C
5. In the real world, the plate never sees more than a couple of hundred degrees C

I'm not an aerospace engineer either but have some experience with high flow water rates/pressures.
It seems to me that 2,3,4 are dictated by a high enough rate to prove all the cases correct.  Since I don't know the temperature of the exhaust nor the profile of the exhaust i can't peak of those parameters.  I suspect they have either modelled or calculated the exhaust from engine bell to tip of exhaust, so they know the temperature/pressure regime that the water flow will experience and then back calculate how much flow is needed to offset the exhaust.  I don't know the diameter of the holes nor the number of the holes, but this two would be a somewhat easy calculation in fluid flow requirements.

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General Discussion / Re: Starship!

« Last post by smartcooky on May 28, 2023, 07:14:14 AM »

I would like some of our "rocket scientists" here have a look at this video and offer their opinions. It is an animated render and commentary giving a brief explanation of how the water-cooled steel plate system is supposed to work. Its from Alpha Tech's YouTube channel, with the computer rendering by Ryan Hansen. Credit to both of them for this excellent presentation.

Note: right-click on the link and choose to play it in a new tab. It will play a short (1m 41s) video in Dropbox

https://www.dropbox.com/s/1zi550dn801f41m/Starship%20Deluge.mp4?raw=1

As most of you already know, I am an aeronautical engineer (retired), but not an aerospace engineer. While the two disciplines share a lot of common ground, there are aspects of "rocket science" that are outside my pay-grade.
 
In particular, there are some statements made that I am doubting the accuracy of. I would appreciate any comments on some of these technical details.

1. The claimed "established temperature gradient" between the rocket exhaust at the point it leaves the ending bells and the water cooled plate
2. "In the centre of the plate, the water pressure is higher than the exhaust pressure"
3. "The exhaust never touches the plate"
4. If the water flow is maintained at a high enough rate, they can keep the temperature at the plate below 1000°C
5. In the real world, the plate never sees more than a couple of hundred degrees C

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

« Last post by Bryanpoprobson on May 28, 2023, 01:31:40 AM »

Proud of my granddaughter Eva, won 3 out of 3 of her Ju Jitsu matches, which considering they banned her glasses, without which she is virtually blind, was some feat.

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General Discussion / Oh my Hoya

« Last post by LionKing on May 26, 2023, 02:39:39 PM »

This is my favorite plant since childhood. It used to beplanted in Lebanon until the early 90s where it disppeared. We call it diamond plant. I used to stare at those stars mesmerized, and longed for it without hope almost.
Until 4 years ago where I doscovered that  a friend of the family has it. I too a cut and waited for three years as yester year it started blooming.
I discovered many people are obsessed with it as I am. It only gives off smell at night, as if it recognizes its stars. I put pics for the mesmerizing flowers I am so happy to own and watch. I hope you enjoy the shapes.

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General Discussion / The Hollywood-like escape of Carlos Ghosn

« Last post by LionKing on May 19, 2023, 04:53:44 PM »

https://youtu.be/vQ0Ch0-s5Wo

Perhaps should be under the "Beyond belief" section , but it happened. Lots of details and videos on the internet of him explaining his escape from Japan. The question remains though:is he innocent and was framed or indeed he was into corruption at the Nissan.

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General Discussion / Re: Starship!

« Last post by JayUtah on May 16, 2023, 02:35:38 PM »

I think the terms I was looking for were "open loop" and "closed loop" guidance. I understand the Saturn V flew under one system for the first stage, and the other for the remainder of the ascent; and I was wondering if the same was intended for Starship. And having asked that, what's the difference between the two...

Closed-loop control incorporates measurements of the property the controller is meant to control and adjusts the control input accordingly. Open-loop control applies the control according to invariant properties of the controller program.

Open-loop control is like a sprinkler system without any measurement of soil moisture content. It will dutifully come on at 4:00 AM and apply 15 minutes' worth of water control even if your entire garden is already under water. Closed-loop control would adjust the amount of watering based on how much water is already in the soil.

Open-loop guidance says to fly the rocket in Attitude A for so many seconds, then Attitude B for so many other seconds, and so forth—all regardless of whether the rocket is in the right place and moving in the right direction. Closed-loop guidance adjusts the desired rocket attitude based (in part) on whether the rocket is on the desired trajectory and whether that trajectory is getting you where you want to go. The LM ascent program was also open loop. It was the CSM's job to swoop down and find the LM ascent stage, wherever in orbit it ended up as a result.

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General Discussion / Re: Starship!

« Last post by Dalhousie on May 15, 2023, 01:30:13 AM »

Strangely, I haven't heard any complaints that they didn't put a "useful" payload on this Starship flight...

I promise you that if the launch had successfully achieved its target of a suborbital flight, the "20/20 Hindsight" brigade would be complaining.

I doubt that very much.  The stated goals were clear, reasonable, and there was no stunt involved, unlike the risible car in space of the 1st FH flight.

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General Discussion / Re: Starship!

« Last post by smartcooky on May 14, 2023, 11:53:14 PM »

Strangely, I haven't heard any complaints that they didn't put a "useful" payload on this Starship flight...

I promise you that if the launch had successfully achieved its target of a suborbital flight, the "20/20 Hindsight" brigade would be complaining.

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General Discussion / Re: Starship!

« Last post by cjameshuff on May 14, 2023, 03:08:40 PM »

Strangely, I haven't heard any complaints that they didn't put a "useful" payload on this Starship flight...