For Questions That Don't Merit Their Own Thread

[Chemp]

2 hours ago, JoeSchmuckatelli said:

Got something for you Math Nerds:

Does the windshield of a car travelling at 60 mph hit more raindrops in one second than the windshield of the same model parked collects?

  Reveal hidden contents

FWIW - I tried to figure this out; 

• at 60mph, the windshield travels at 88 feet per second.
• raindrop terminal velocity is about 32 feet per second
• 2 foot tall windshield at 45 degrees has a surface area...
• math something
• volume
• dis...
• ...
• ask the smart guys.

•  

There's an episode of MythBusters related to this:

 

[darthgently]

10 minutes ago, Chemp said:

There's an episode of MythBusters related to this:

 

As I recall, it mostly depends on how long you spend in the rain.  Moving faster between dry points A and B can result in getting less wet because you spend less time in the rain.  But moving will cause you to collide with more drops horizontally so there is an eqn to minimize in there.

Edited December 5, 2023 by darthgently

[kerbiloid]

If both windscreen and rain are vertical, and the car is motionless, then no drops can hit the windscreen except from the top edge or by ricochet.

Thus, a moving car by definition has more chances to catch a drop with the windscreen.

Because the car motion makes the vertical rain tilted.

P.S.
The post hasn't been merged with the previous one, even when being posted just a minute later.
This makes me frustrated, but I'm still trying to keep my faith in humanity.

Edited December 6, 2023 by 18Watt
Behold my post merging powers.

[kerbiloid]

There is a known from literature phenomenon of St. Elmo's fire.

Usually they tell about the electric fires on cathedrals, ships, and other close static objects with sharp vertical things.

But when I google for a video, there are only lightnings, seen from an airplane cockpit, or a thunderstorm far away.

What happened? Is this phenomenon still available? Had somebody actually seen it irl? Maybe there are youtube videos with a cathedral with the St. Elmo fires on pikes?

In my city there are metal vertical things, and some of them on top of gothic-style buildings, but I've never seen it. Maybe, the buildings are not enough high. But as here are people from places with medieval architecture, maybe some of them have seen it?

Edited December 8, 2023 by kerbiloid

[SunlitZelkova]

7 hours ago, kerbiloid said:

There is a known from literature phenomenon of St. Elmo's fire.

Usually they tell about the electric fires on cathedrals, ships, and other close static objects with sharp vertical things.

But when I google for a video, there are only lightings, seen from an airplane cockpit, or a thunderstorm far away.

What happened? Is this phenomenon still available? Had somebody actually seen it irl? Maybe there are youtube videos with a cathedral with the St. Elmo fires on pikes?

In my city there are metal vertical things, and some of them on top of gothic-style buildings, but I've never seen it. Maybe, the buildings are not enough high. But as here are people from places with medieval architecture, maybe some of them have seen it?

Not a building but here is a pic, perhaps an artificially produced version from a lab.

https://x.com/roaneatan/status/1146392689811681281?s=46&t=Jd73T2beq0JLNtwTy1uR5A

I was able to find this video by searching in Japanese. It shows the phenomena coming from a Southeast Asian temple, but it’s a little blurry.

Also that lightning might look far away in the plane videos, but it is actually occurring over the surface of the plane. This image from Japanese CNN illustrates it better.

[kerbiloid]

7 hours ago, SunlitZelkova said:

an artificially produced version from a lab.

Yes, the lab experiments are documented fine.

And the views from the plane as well.

But I mean that this phenomenon looks usual for the medieval people, who were watching it right on the churches, cathedrals (with their metallic pikes), and on the wooden ship masts. 
As the thunderstorms and the medieval cathedrals look same, I was expecting a lot of videos on youtube, but I can't see anything but planes and thunderstorms.

Edited December 8, 2023 by kerbiloid

[monophonic]

1 hour ago, kerbiloid said:

Yes, the lab experiments are documented fine.

And the views from the plane as well.

But I mean that this phenomenon looks usual for the medieval people, who were watching it right on the churches, cathedrals (with their metallic pikes), and on the wooden ship masts. 
As the thunderstorms and the medieval cathedrals look same, I was expecting a lot of videos on youtube, but I can't see anything but planes and thunderstorms.

What's changed is not only minute details on the cathedrals themselves but also the surrounding environment. Typical city around a cathedral is now very well lit, meaning the phenomenon may well still exist but is invisible in the flood of light. There are also hundreds of lightning conductors on the surrounding buildings which route their own share of the electric charge in the ground, meaning the charge available to light these fires at any single point is much less. Finally as the phenomenon is now well understood the church decorations have in many places been modified to reduce it. (Mainly to avoid lightning strikes though but the measures are the same.) E.g. sharp points have been rounded or small orbs attached at their tips.

[kerbiloid]

Sounds reasonable, probably that's it.

[Mikki]

On 12/7/2023 at 3:23 PM, kerbiloid said:

There is a known from literature phenomenon of St. Elmo's fire.

Usually they tell about the electric fires on cathedrals, ships, and other close static objects with sharp vertical things.

But when I google for a video, there are only lightnings, seen from an airplane cockpit, or a thunderstorm far away.

What happened? Is this phenomenon still available? Had somebody actually seen it irl? Maybe there are youtube videos with a cathedral with the St. Elmo fires on pikes?

In my city there are metal vertical things, and some of them on top of gothic-style buildings, but I've never seen it. Maybe, the buildings are not enough high. But as here are people from places with medieval architecture, maybe some of them have seen it?

Hi there, i can tell you from my own experience that in real life Elm`s Fire is a very, very faint happening, i have seen it twice, once as a child and once many years ago on top of a mostlikely deep frozen (living) very tall spruce. This was only visible because in this area there was basically no artificial light pollution and our eyes have been adapted to the dark for some hours. Both times it was green and it glowed from the top 1.5 meters of the tree and around the end of the topmost branches. I haven`t seen any accurate photo of this ever, maybe once a real picture that came close to it.

[kerbiloid]

Thank you, the picture looks clear now.

[magnemoe]

5 hours ago, Mikki said:

Hi there, i can tell you from my own experience that in real life Elm`s Fire is a very, very faint happening, i have seen it twice, once as a child and once many years ago on top of a mostlikely deep frozen (living) very tall spruce. This was only visible because in this area there was basically no artificial light pollution and our eyes have been adapted to the dark for some hours. Both times it was green and it glowed from the top 1.5 meters of the tree and around the end of the topmost branches. I haven`t seen any accurate photo of this ever, maybe once a real picture that came close to it.

Explains why is rarely seen now, effect is faint and ruined by light. Just using an flashlight to look for something or an phone to check position will ruin it. 
On a ship it will not work unless an warship running dark and you have an guard station outside? 

[SunlitZelkova]

The Apollo CSM was known for being a pretty capable spacecraft due to retaining the big engine originally tended to lift the entire spacecraft off the surface of the Moon.

But could a CSM have braked into Earth orbit instead of reentering directly? Or would that be too much?

[Shiki404]

8 hours ago, SunlitZelkova said:

The Apollo CSM was known for being a pretty capable spacecraft due to retaining the big engine originally tended to lift the entire spacecraft off the surface of the Moon.

But could a CSM have braked into Earth orbit instead of reentering directly? Or would that be too much?

After it did maneuver burn into suborbital trajectory to set the release of command module, I don't think it would have enough fuel left to boost it's trajectory back into earth orbit, especially since the command module need it until just before reentry (Even with automated system, by the time the umblical connection is severed, there won't be enough time or fuel left to boost it back)

Edited December 12, 2023 by Shiki404

[SunlitZelkova]

Okay, so I’m trying to figure out if a Japanese rocket could take a Soyuz and a Fregat-M upper stage to lunar orbit.

Setting aside the issue of the rocket, which I haven’t gotten to yet, I’ve found something weird with my calculations.

This is my first time doing anything like this ever btw so go easy on me if there is something wrong. I watched this video in order to be able to do some very rough calculations. I’m not trying to literally design a spaceship, just do some general checks to make sure an idea for a story is reasonably plausible.

So, I used Soyuz TMA-M and Fregat-M. I assumed whatever was needed to allow the Soyuz to remain in lunar orbit for a few months (more RCS prop, new comms equipment etc.) + ripping out the main propulsion unit in the service module due to Fregat providing propulsion would keep the Soyuz mass identical to the LEO version.

So the wet mass for “Soyuz TMA-L” is 14.12 tons. Dry mass is 8.07 tons.

Thrust of the Fregat-M’s engine is 20 kilonewtons.

With this we get 1.41643059 m/s per second “Acceleration”.

I did TWR before realizing it didn’t matter in vacuum (or so I am told).

Now exhaust velocity is ISP x Earth gravity. I did 333.2 × 9.8 for an exhaust velocity of 3265.36.

Now, here is my attempt to do the rocket equation.

3265.36 × (14.12 divided by 8.07) = 5713.blah blah blah.

I changed this km/s for delta v, so 5.713 km/s.

Now, Wikipedia seems to say to get from LLO to lunar escape velocity, you just need 0.9 km/s. But it also says that to get from TLI to LLO, you need 0.9 km/s. https://en.m.wikipedia.org/wiki/Delta-v_budget

So in theory Fregat should be able to brake the whole thing into LLO, right? But this here says the mission architecture considered for Soyuz IRL required a Blok DM stage for lunar orbit insertion (see the “scenario 2” section) https://www.russianspaceweb.com/soyuz_acts.html

What am I doing wrong here?

[magnemoe]

12 hours ago, Shiki404 said:

After it did maneuver burn into suborbital trajectory to set the release of command module, I don't think it would have enough fuel left to boost it's trajectory back into earth orbit, especially since the command module need it until just before reentry (Even with automated system, by the time the umblical connection is severed, there won't be enough time or fuel left to boost it back)

I'm pretty sure that would require something more like an Saturn 5 3rd stage, it was that needed for lunar injection after all. 

Putting the service module into orbit, yes that is more plausible especially if you drop the command module pretty early, you would need to do an radical burn to raise Pe fast, also lower Ap who is nice. Do an second burn on the way out to raise Pe and lower Ap again and you end int an very stable orbit. But I don't think the service module worked without the command module. Computers was not as common back then  

[Shiki404]

7 hours ago, magnemoe said:

I'm pretty sure that would require something more like an Saturn 5 3rd stage, it was that needed for lunar injection after all. 

Putting the service module into orbit, yes that is more plausible especially if you drop the command module pretty early, you would need to do an radical burn to raise Pe fast, also lower Ap who is nice. Do an second burn on the way out to raise Pe and lower Ap again and you end int an very stable orbit. But I don't think the service module worked without the command module. Computers was not as common back then  

There's also a matter of in-flight trajectory adjustment. While doing retro burns to prepare for reentry, you want your trajectory towards the landing site goes as planned, so having the service module still attached until just before reentry could allow the crew to make minute adjustments and corrections, because once you start the reentry, there's no turning back, no controls and no more corrections. If you drop the command module too early, you're basically gambling your fate. It's just you returning to earth like ICBM warhead purely on ballistic trajectory

[ARS]

13 hours ago, magnemoe said:

I'm pretty sure that would require something more like an Saturn 5 3rd stage, it was that needed for lunar injection after all. 

Putting the service module into orbit, yes that is more plausible especially if you drop the command module pretty early, you would need to do an radical burn to raise Pe fast, also lower Ap who is nice. Do an second burn on the way out to raise Pe and lower Ap again and you end int an very stable orbit. But I don't think the service module worked without the command module. Computers was not as common back then  

IIRC, the Apollo command module is directly controlling the service module. As soon as the connection is cut off, there's no way to control the service module. The extra fuel needed to make stable orbit is more likely to hamper the actual Lunar mission

Also, I'm back

[monophonic]

On 12/12/2023 at 11:43 AM, SunlitZelkova said:

Now, Wikipedia seems to say to get from LLO to lunar escape velocity, you just need 0.9 km/s. But it also says that to get from TLI to LLO, you need 0.9 km/s. https://en.m.wikipedia.org/wiki/Delta-v_budget

So in theory Fregat should be able to brake the whole thing into LLO, right? But this here says the mission architecture considered for Soyuz IRL required a Blok DM stage for lunar orbit insertion (see the “scenario 2” section) https://www.russianspaceweb.com/soyuz_acts.html

What am I doing wrong here?

You are missing the LEO to TLI burn. In your link scenario 2 the first Blok DM send the entire stack from Earth orbit towards the Moon. The second Blok DM eases the stack to low lunar orbit. Finally the Fregat is sufficient to send the remaining vessel back towards home.

You could use the information from their mission plan to calculate approximately how much dV they have budgeted for each part of the mission. Then compare that to what you were considering.

[SunlitZelkova]

9 hours ago, monophonic said:

You are missing the LEO to TLI burn. In your link scenario 2 the first Blok DM send the entire stack from Earth orbit towards the Moon. The second Blok DM eases the stack to low lunar orbit. Finally the Fregat is sufficient to send the remaining vessel back towards home.

You could use the information from their mission plan to calculate approximately how much dV they have budgeted for each part of the mission. Then compare that to what you were considering.

Okay, I see. Thanks.

[DDE]

Hello, I'm not Roland Emmerich but I'm looking for an apocalypse.

Inspired by

One, what region today is the one most likely to become an extinction-level igneous province? Is it even possible to tell?

Two, how quickly would the catastrophe occur? Grasping onto the most recent LIP, the Columbia River group, a 500 km lava flow, is said to have occurred in less than a week, indicating rather remarkable output. What would the global timeline be, then?

[kerbiloid]

1 hour ago, DDE said:

One, what region today is the one most likely to become an extinction-level igneous province? Is it even possible to tell?

According to the 

Spoiler

 

in Russian

 

, Antarctics and Green_{temporarily white}land.

Not insisting on their conclusion of the arhitectonic nature of the described in the second part, the empiric data from the first part look reasonable.

P.S.
Both  reign of shoggoths and Neuschwabenland are in danger, but Lara "The Tomb Raider" Croft will crash everything there in advance.

[Terwin]

2 hours ago, DDE said:

One, what region today is the one most likely to become an extinction-level igneous province? Is it even possible to tell?

The yellowstone super-volcano seems like a likely prospect.

[kerbiloid]

According to the video, the yellow stone is secondary to the Greenland plume.

If I get it right.

[DDE]

14 hours ago, kerbiloid said:

According to the video, the yellow stone is secondary to the Greenland plume.

According to the maps I see, the Greenland plume is minor/offshoot to the larger Iceland/mid-Atlantic plume.

The problem is, is there even a plume? I dug beyond surface-level publications, and it seems that there are two rival explanations, likely varying on a case-by-case basis, for intra-plate volcanism. Besides plumes, there's also plate tectonics, as in the crust simply tearing up enough to admit magma to the surface. And Iceland is a rather stark example of that in action, being a 24 mln years old mini-continent, so is there even a plume involved? Other plate-related factors include the slowly melting fragments of subducted plates, but there seems to be no consensus how deep they sink.

There's also a curious lack of (known) plumes beneath Eurasia (even though the African plate is AFAIK just as, if not more, thick and stable, as the Eurasian plate).

The asymmetry seems to correspond to the mysterious large low-shear-velocity provinces, which, depending on who you ask, are superplumes fueled by slabs of ancient (750+ MYO) oceanic crust, or the remnants of Theia.

I'm getting the distinct impression we know painfully little about deep geological processes.

Edited December 17, 2023 by DDE

[Terwin]

9 hours ago, DDE said:

I'm getting the distinct impression we know painfully little about deep geological processes.

It is almost like a miles thick wall of dirt and stone is difficult to observe through.