For Questions That Don't Merit Their Own Thread

[kerbiloid]

A toxic mirror with poisonous engines...

Hope, at least the tent hood is not venomous.

Astronomers are such astronomers... 

Wait...

Spoiler

 

A thing to add...

Spoiler

 

... if there was air to hear the sounds.

 

Edited January 4, 2022 by kerbiloid

[DDE]

1 hour ago, wumpus said:

Fun fact - the mirrors of the JWST are beryllium (covered with something non-reactive).  For when you really, really, want light weight (also helps if they aren't going to almost always be in a clean room or otherwise outside of an oxidizing atmosphere).

There seem to be national favorites:

Quote

The similar diameter of Sevan’s primary mirror does not necessarily translate into the same ground resolution as that achieved by America’s spy satellites. Other factors that come into play are the quality of the mirror and the image sensors. The material used for the construction of the primary mirror (and, presumably, the others as well) is SO-115M, also known as Sitall or Astrositall. This is a crystalline glass-ceramic material developed back in the Soviet days and has been used for many Russian space-based mirrors, including the 1.5-meter mirrors flown on Araks and Persona. LZOS publications acknowledge that materials such as silicon carbide (used by ESA’s Herschel and Gaia observatories) and beryllium (used by the James Webb Space Telescope) are superior in performance, but they point to the relatively low cost of Sitall and its ultra-low coefficient of thermal expansion.

https://thespacereview.com/article/4006/1

[kerbiloid]

Daedalus was going to carry a beryllium erosion shield.

[wumpus]

17 minutes ago, DDE said:

There seem to be national favorites:

https://thespacereview.com/article/4006/1

Since Huble's was glass, I'd suspect that the similar keyhole mirrors were glass.  Or possibly they didn't, and used a rookie company to polish the lens (thus the error).  More likely, all the Keyhole birds have the same abberation, but it doesn't matter for looking at Earth.  I suspect that NASA checked this time for previous experience, and that somebody had ground similar mirrors for NRO.

[DDE]

16 minutes ago, kerbiloid said:

Daedalus was going to carry a beryllium erosion shield.

If we're going away from mirrors, beryllium was a Soviet favorite for expandable Mars entry shield frames.

[SunlitZelkova]

1. What are the potential applications of rotary detonation engines in space? Japan tested one in space in August 2021, and China is working on one too.

2. What makes a mission control center? As long as the communications equipment is there, can you just set up computers in any room and control a spacecraft? Or are they purpose built rooms with computers integrated into the building?

I ask the second question as I wonder whether the growth in spaceflight missions in the 2020s will require construction of new mission control centers or if existing facilities can be converted.

[kerbiloid]

3 hours ago, SunlitZelkova said:

whether the growth in spaceflight missions in the 2020s will require construction of new mission control centers or if existing facilities can be converted.

The tower.

[DDE]

7 hours ago, SunlitZelkova said:

1. What are the potential applications of rotary detonation engines in space? Japan tested one in space in August 2021, and China is working on one too.

Energomash showed off a kerolox subscale demonstrator (Ifrit) half a decade back, too. The rhetoric is that it's all-around better - more thrust, better combustion, smaller chamber - but the specific impulse reported was a measly 290 sec.

https://fpi.gov.ru/projects/fiziko-tekhnicheskie-issledovaniya/ifrit/

[kerbiloid]

If take both "rotary detonation engine" and "rotary magnetoplasm(/at/on)ic engine", the trend is obvious: the thing should be a ring of bursts.

Because.

[JoeSchmuckatelli]

Found this interesting: https://www.bloomberg.com/news/features/2018-10-04/the-big-hack-how-china-used-a-tiny-chip-to-infiltrate-america-s-top-companies

It's a good read.  At first I thought it explained the JPL hack - but that was 'an unauthorized raspberry pi device attached to a server'. 

https://www.forbes.com/sites/daveywinder/2019/06/20/confirmed-nasa-has-been-hacked/?sh=16c68e9adc62

 

Scary thing is how deep some of it could get 

... 

"The somewhat huge challenge that NASA faces from the cybersecurity perspective shouldn’t be underestimated though. Scientists tend to default to collaboration after all. “Imagine trying to do cybersecurity focused on advanced threat actors when many of the members of the scientific community work in those adversarial countries,” Ian Thornton-Trump, head of security at AmTrust International, says. “You can’t simply turn Russia off at the firewall, for example, when you are partnered with Russia,” Thornton-Trump concludes, “it’s almost mission impossible for NASA from an infosecurity point of view.” "

 

[caecilliusinhorto]

Is there any advantage to an engine which has multiple combustion chambers and a single nozzle, and has an engine like this ever existed?

[DDE]

2 hours ago, JoeSchmuckatelli said:

an unauthorized raspberry pi device attached to a server

From what I've read over at Kaspersky's ATP blog, it's enough to leave a covert raspberry pi device on the premises and let it make friends with the local wi-fi for a while.

2 hours ago, JoeSchmuckatelli said:

You can’t simply turn Russia off at the firewall, for example, when you are partnered with Russia

Not to mention it's a bit naive to think blacklisting Russian IPs is an effective counter-hacking or counter-DDoS measure.

4 hours ago, kerbiloid said:

If take both "rotary detonation engine" and "rotary magnetoplasm(/at/on)ic engine", the trend is obvious: the thing should be a ring of bursts.

 

[kerbiloid]

3 hours ago, JoeSchmuckatelli said:

but that was 'an unauthorized raspberry pi device attached to a server'. 

Be happy, it's not on Arduino.

38 minutes ago, caecilliusinhorto said:

Is there any advantage to an engine which has multiple combustion chambers and a single nozzle, and has an engine like this ever existed?

http://www.astronautix.com/a/a9a10.html

A10 was going to have six.

Probably, the only real advantages are:
1) when it's cheaper to design based on the existing chambers than do it from scratch;
2) when you can't design stable combustion process in a bigger chamber.

Anyway that's from need, not from desire.

And there was an opposite design: a toroidal chamber with four turbopumps and 24 or so throats and a ramjet nozzle in the middle.

[JoeSchmuckatelli]

35 minutes ago, DDE said:

Russian IPs

Russian 'alternative businessmen' are smart enough to use sites in Africa, India and other places - including trailer parks in the US. 

 

But why single out just the Russians? 

https://www.google.com/amp/s/www.wlky.com/amp/article/companies-face-lawsuit-from-indiana-ags-office-for-routing-illegal-robocalls/37973455

Edited January 6, 2022 by JoeSchmuckatelli

[Hyperspace Industries]

For a while I’ve had an idea for powering a Lunar base at a pole by launching large “tin foil” (it won’t actually be tin foil, just a thin flexible sheet of reflective material like jwst’s sunshield or a solar sail) mirrors into orbit around the moon to reflect sunlight onto the pole. I used tin foil for some basic educated guessing and in that case, I think it would be cheaper to launch big mirrors up into orbit and concentrate light onto smaller solar arrays on the surface (solar panels are much more expensive than foil) than to use bigger solar arrays on the surface (that you have to land), especially on the poles.

You can either use multiple solar reflectors in low orbit, arranged so that when one goes below the horizon, one comes up, or one larger reflector in an elliptical orbit which has a low periapsis above the opposite pole, and a high apoapsis above the base, making for short breaks where batteries are used.

Would this work, could it work, what have I inevitably overlooked?

[wumpus]

On 1/6/2022 at 12:07 PM, caecilliusinhorto said:

Is there any advantage to an engine which has multiple combustion chambers and a single nozzle, and has an engine like this ever existed?

I don't think there is any advantage to a single nozzle.  I've only seen that method done with multiple combustion chambers.  With multiple chambers/nozzles, you have less combustion instability issues (unsure of the disadvantages).  There are also hard limits to the size of expansion (see RL-10) turbopumps, but that is only based on the maximum size of the combustion chamber and nozzle, not the total volume of each.

[Lisias]

On 1/6/2022 at 2:07 PM, caecilliusinhorto said:

Is there any advantage to an engine which has multiple combustion chambers and a single nozzle, and has an engine like this ever existed?

Yep. As a matter of fact the first jet engines were exactly like that! (the comparison sticks because a combustion chamber is a combustion chamber - what the engine does with the thrust after it another problem).

Spoiler

(half the plane was the jet engine!!!)

Each one of that "cylinders" on the colder end of the engine is a combustion chamber.

The reason was that, at that time, they didn't have materials that would withhold all the pressure that would be generated by a single combustion chamber to do the same job. Valves, pumps, ducts, all of that:

 

2 hours ago, wumpus said:

I've only seen that method done with multiple combustion chambers.  With multiple chambers/nozzles, you have less combustion instability issues (unsure of the disadvantages).

Complexity and failure rates. The more combustion chambers you have, more ducts and pumps you need to keep everybody fed and happy, and the more mechanical parts you have moving, the more mechanical parts prone to jamming you have.

The jet engines of that era were terribly unreliable due exactly this.

There's also weight: more ducts + more chambers == more weight. One big duct/chamber is usually lighter than many smaller ones for the same job.

Edited January 8, 2022 by Lisias
Forum had bit me!!!!

[K^2]

Distinction between multiple combustion chambers and single chamber with multiple combustion zones can get rather academic for jet engines. Cannular designs are pretty common. They have multiple combustion areas, but a shared cooling channel. Do you call that a single combustion chamber or multiple? Does it matter?

[ARS]

At which point for a high speed projectile starts to be faster than the eye? Or more appropriately, faster than the brain can process? For example, you're viewing a blank white background, and then a projectile pass before your eyes. How fast the projectile have to travel before it starts unnoticeable by human eye? Does it have to travel faster than the speed of electrical impulse of optic nerve? Or is there lower/ higher speed for such phenomenon?

[kerbiloid]

A 60 mm mortar
According to wiki, 50 ... 244 m/s

At 01:00 there is a prepared shell visible.
Somebody here more mortarly experienced can tell if it is 1 or 3 additional powder charges on it, so is it closer to 50 or to 240 m/s.

Spoiler

 

 

[JoeSchmuckatelli]

51 minutes ago, kerbiloid said:

A 60 mm mortar
According to wiki, 50 ... 244 m/s

At 01:00 there is a prepared shell visible.
Somebody here more mortarly experienced can tell if it is 1 or 3 additional powder charges on it, so is it closer to 50 or to 240 m/s.

  Hide contents

 

 

There are 3 increments visible - but it's been over 20 years since I worked with mortars so I can't get more detailed 

[kerbiloid]

Another video with bare stems, so closer to 50 m/s, but still invisible on shot.

Spoiler

 

 

So, probably the projectile itself is not visible, but depending on illumination and albedo a short metal flash can be detected by eye.

[magnemoe]

13 hours ago, K^2 said:

Distinction between multiple combustion chambers and single chamber with multiple combustion zones can get rather academic for jet engines. Cannular designs are pretty common. They have multiple combustion areas, but a shared cooling channel. Do you call that a single combustion chamber or multiple? Does it matter?

The point of the detonation jet engines is that IC engines has much better fuel efficiency than jet/ gas turbines think its 20% better also they throttle much better.
Now you can beat much of this using an steam turbine as an second stage but this is heavy and only work for large ships and power stations. Many warships uses diesel for cruise and gas turbines for flank speed,
Detonation engines will get close to IC but not adding so much extra weight. Getting 5% fuel efficiency on jet engines would be very valuable. 

[JoeSchmuckatelli]

6 hours ago, kerbiloid said:

Another video with bare stems, so closer to 50 m/s, but still invisible on shot.

  Reveal hidden contents

 

 

So, probably the projectile itself is not visible, but depending on illumination and albedo a short metal flash can be detected by eye.

Actually... no.  You can see the projectile.  Mostly as a black flicker - but you can trace the arc of fire.  Strongly depends on the angle of view and lighting.  Artillery is much easier (beeeger bullet).

 

...

Now for something weird: one time after spending a week on a rifle range, the atmospherics were just right for me to see the flight of 5.56 bullets and call the strike locations before the targets had been pulled and marked.  I really freaked out a few Marines by demonstrating that I knew, before the target marking crew did, where the bullet had hit the target.  What I was actually seeing is reminiscent of a contrail; the disturbance in the air, caused by the passage of the bullet made it clear to me where each round hit.

I only encountered similar humidity, light and temperature twice more - and that's in 20 years of professional shooting.  It only worked if I was standing over the Marine while he shot.

It's pretty cool.

@ARS Not sure if my story answers your question: but wiki shows these flying 8-900m/s. 5.56×45mm NATO - Wikipedia

Edit again: Having been on both (many?) sides of bullets flying I can tell you that you can almost never see crossing rounds.  You can see the after-image of tracers but the bullets themselves, no.  Incoming and outgoing are a different matter.

6 hours ago, kerbiloid said:

Another video with bare stems, so closer to 50 m/s, but still invisible on shot.

This is pretty clearly Marines in school (despite the narrator talking about 11 charlie (or whatever) which is an Army MOS designation).  Notice how young and clean and uniform they all are.  If you look at about 4:00 in the video you posted, they're using only a single increment.  Later on he splices in some Army crews and other Marine crews firing... but never, as far as I can see from a short view, does the camera angle get where it needs to be for you to see the round fly.

The camera angle is not set up for you to see what I describe in watching mortar and artillery fire.  You need to be in line with the gun and the angle of flight, for the most part.  With the bigger stuff, like arty, you have a bit more wiggle room, but with 60s just stand behind the tube on a sunny day, or when the lighting is just right and you can watch it arc up and away.  You generally only get to see a short bit of the flight; the upward arc.  With the rifle rounds I described above - we were shooting at about 1/2 klick.  With mortars its often farther.

Edited January 9, 2022 by JoeSchmuckatelli

[K^2]

11 hours ago, magnemoe said:

The point of the detonation jet engines[...]

What do detonation engines have to do with any of what has been discussed? The topic was conventional jet engines, unless I'm missing something.