For Questions That Don't Merit Their Own Thread

[kerbiloid]

Some pics of the Energiya Martian ship project (click the links to enlarge)

https://www.energia.ru/energia/mars/condition.html

[ARS]

If there's an asteroid detected on collision course not on earth, but the dark side of the moon (with the debris small enough to not pose a hazard on earth reentry, basically a spectacle), how the world's scientific community will react?

[Gargamel]

5 hours ago, ARS said:

dark side of the moon

Aside from them taking issue with the term "dark side" (I have no issue with it, as long as you understand what we mean by it), I think, given enough lead time, they'd get a probe up there to watch.  Without enough lead time, not much. 

[ARS]

55 minutes ago, Gargamel said:

Aside from them taking issue with the term "dark side" (I have no issue with it, as long as you understand what we mean by it), I think, given enough lead time, they'd get a probe up there to watch.  Without enough lead time, not much. 

Yeah I know that the term "Dark side" is rather incorrect compared to "Far side" (Since that side still receives sunlight). Anyway, the last time there's a large-scale event involving impact on celestial body in solar system is during Shoemaker-Levy-9 comet impact with Jupiter. My next question is, what kind of scientific data that can be gained from observing impacts? Just curious

[Shpaget]

People smarter than me can deduce composition and mass of the smaller body, or in case of known impactor and relatively small bigger one the compostion and mass of the larger one. If you can land some seismic sensors on the bigger one, those brainy folk can figure out physical structure of the body as well.

[Spacescifi]

If there was a medium where light's speed could be accelerated dramatically, how much faster would the speed of light need to be to generate thrust on par with SRB's?

Also, what side effects would occur on the medium (gas or solid, whichever you prefer)?

I think heat exchange is a possibity since the medium is doing work on the light.

What are your answers and thoughts?

Edited June 3, 2019 by Spacescifi

[Cunjo Carl]

On 6/3/2019 at 1:24 PM, Spacescifi said:

If there was a medium where light's speed could be accelerated dramatically, how much faster would the speed of light need to be to generate thrust on par with SRB's?

Also, what side effects would occur on the medium (gas or solid, whichever you prefer)?

I think heat exchange is a possibity since the medium is doing work on the light.

What are your answers and thoughts?

Ironically, we'd need light speed to be lower to get more thrust out of a photon rocket with a given power and efficiency. It would have lower Isp, but more thrust.
for a photon Momentum = Energy/c
so for a photon rocket, Thrust = Efficiency*Power/c   (with Thrust in Newtons, Efficiency as a number from 0 to 1, Power in Watts, and c in m/s)

Light would need to go very slow to get meaningful thrust out of it though. Maybe as slow as 17m/s   https://www.nature.com/articles/17561. Now if only we had some clouds of dense nano-Kelvin sodium BEC gas to fly through...

(Note, I'm not 100% clear if the c in the above equations are medium dependent. I think for this specific relationship it is because the slowing of light in media is dependent on interactions, which means momentum exchange right? In other words, the light pushes off the medium, though without scatter, permanent absorption or reflection. If there's any theoreticians out there, is that the correct interpretation?)

 

 

[Spacescifi]

2 hours ago, Cunjo Carl said:

Ironically, we'd need light speed to be lower to get more thrust out of a photon rocket with a given power and efficiency. It would have lower Isp, but more thrust.
for a photon Momentum = Energy/c
so for a photon rocket, Thrust = Efficiency*Power/c   (with Thrust in Newtons, Efficiency as a number from 0 to 1, Power in Watts, and c in m/s)

Light would need to go very slow to get meaningful thrust out of it though. Maybe as slow as 17m/s   https://www.nature.com/articles/17561. Now if only we had some clouds of dense nano-Kelvin sodium BEC gas to fly through...

(Note, I'm not 100% clear if the c in the above equations are medium dependent. I think for this specific relationship it is because the slowing of light in media is dependent on interactions, which means momentum exchange right? In other words, the light pushes off the medium, though without scatter, permanent absorption or reflection. If there's any theoreticians out there, is that the correct interpretation?)

 

 

 

I dunno. Interestingly a tachyon rocket is basicslly the same idea. Superluminal exhaust means high thrust and high delta v according to this article.

https://www.tor.com/2018/08/17/when-will-sf-learn-to-love-the-tachyon/

I used quotons since I figured FTL photons should be more or less harmless compared to FTL particle exhaust.

Would not wanna be in that ship's wake.

 

 

Edited June 5, 2019 by Spacescifi

[DDE]

What have they done to A-235's cold-launch system? It's wailing!

 

[kerbiloid]

8 hours ago, DDE said:

What have they done to A-235's cold-launch system? It's wailing! 

If watch it in VLC at 0.06^x speed, it seems to be two flashes.

[DDE]

2 hours ago, kerbiloid said:

If watch it in VLC at 0.06^x speed, it seems to be two flashes.

The first clip is definitely doctored, probably to avoid the shots where the airframe is visible.

[ARS]

If we compare between medieval-era cannon (On the variety that can be towed around like WW2 PaKs AT gun, using spherical cannonball roughly the size of softball) against modern anti-material rifle (assuming the caliber is 12.7 mm, pointy round), shooting at target 100 meters away, assuming the shot hits the target dead-on, will the size and mass of spherical (non-pointy) shape of cannonball compensates for it's low velocity and focused impact of modern rounds?

Edited June 6, 2019 by ARS

[Flibble]

Cannon varied a lot between the medieval period and later.

Assuming a 300 m/s muzzle velocity (probably in the right ballpark, later guns had had higher velocities) and a 9 lb shot (which would be around 4 inches diameter).

KE as it leaves the muzzle is then KE = mv²/2 = 4.08 * 300² / 2 = 183.6 kJ.

KE for the rifle shot (varies on which exact bullet is used, assume 45g bullet, 908 m/s) is KE = 0.045 * 908² / 2 = 18.55 kJ.

It's pretty much guaranteed that the cannon ball will have more energy. Shape isn't actually that important, other than for range.

Put another way, the cannon shot has equivalent energy to the bullet at 3 m/s - you could pretty much just drop it on the target and do much the same damage.

[ChrisSpace]

Is there any way Plutonium-239 could be used as a replacement for Uranium-238 in nuclear power stations? If not, why?

[Flibble]

17 minutes ago, ChrisSpace said:

Is there any way Plutonium-239 could be used as a replacement for Uranium-238 in nuclear power stations? If not, why?

Nuclear reactors burn Pu-239 as part of their normal cycle (around a third of the power is from Pu-239 fission).

However Pu-239 doesn't occur in quantity in nature, so without U-238 to make it from there is no fuel source.

[James Kerman]

28 minutes ago, ChrisSpace said:

Is there any way Plutonium-239 could be used as a replacement for Uranium-238 in nuclear power stations? If not, why?

There is the potential for molten salt reactors powered by thorium. There was some research done in the 60's that has recently been enjoying a resurgence by various agencies around the world.

[magnemoe]

3 hours ago, Flibble said:

Cannon varied a lot between the medieval period and later.

Assuming a 300 m/s muzzle velocity (probably in the right ballpark, later guns had had higher velocities) and a 9 lb shot (which would be around 4 inches diameter).

KE as it leaves the muzzle is then KE = mv²/2 = 4.08 * 300² / 2 = 183.6 kJ.

KE for the rifle shot (varies on which exact bullet is used, assume 45g bullet, 908 m/s) is KE = 0.045 * 908² / 2 = 18.55 kJ.

It's pretty much guaranteed that the cannon ball will have more energy. Shape isn't actually that important, other than for range.

Put another way, the cannon shot has equivalent energy to the bullet at 3 m/s - you could pretty much just drop it on the target and do much the same damage.

yes the cannon ball has more energy and would do more damage, just having an larger bullet helps a lot here as an .50 is likely to pass trough an unarmored target. 
Not sure about armor penetration, the BMG might win over the cannon ball in some settings 
 

[Flibble]

1 hour ago, magnemoe said:

Not sure about armor penetration, the BMG might win over the cannon ball in some settings 

I could see it being better against armour yes. The BMG applies energy to a much smaller area so will likely cause a higher pressure spike which could rupture the armour, where a cannon ball would just dent it.

[Mitchz95]

On average, how much physical damage does a supernova do to the planets orbiting it? Are they physically shattered/vaporized, or "merely" have their surfaces melted but remain mostly intact?

[Spacescifi]

3 hours ago, Mitchz95 said:

On average, how much physical damage does a supernova do to the planets orbiting it? Are they physically shattered/vaporized, or "merely" have their surfaces melted but remain mostly intact?

It has been said that a nova (NOT a supernova) would erode our atmosphere from all the radiation and cosmic particles). Googled it.

I am rather certain that a supernova will plow through and vaporize it's immediate solar system

 

[Flibble]

8 hours ago, Mitchz95 said:

On average, how much physical damage does a supernova do to the planets orbiting it? Are they physically shattered/vaporized, or "merely" have their surfaces melted but remain mostly intact?

Depends on the planet and the star.

Inner planets like Earth are likely to be destroyed as they will receive a huge amount of energy which will exceed the binding energy of the planet. They will be torn to pieces and anything that isn't will heat up until it vaporizes.

Outer plants can potential survive if they are far enough relative to their mass. A large gas giant like jupiter can withstand a lot more incoming energy before flying apart.

Another factor is that there might not be much to orbit, or the force of the supernova may perturb the orbit enough to eject surviving planets from the system.

There's a bunch of maths on it here: https://worldbuilding.stackexchange.com/questions/19000/can-a-planet-survive-a-supernova

 

[VoidCosmos]

On 6/8/2019 at 8:36 AM, Spacescifi said:

It has been said that a nova (NOT a supernova) would erode our atmosphere from all the radiation and cosmic particles). Googled it.

I am rather certain that a supernova will plow through and vaporize it's immediate solar system

Oh good to know

[Spacescifi]

3 hours ago, Nigel J. Cardozo said:

Oh good to know

 

Googled it once and it said between 50 and a hundred lightyears is the safe distance between Earth and a supernova.

30 lighyears away (further than Proxima Centauri) is still considered deadly, since the gamna rays and cosmic rays would wreck our atmosphere and us with radiation.

Granted, that gives us 30 years to prepare. Some of the rich could likely survive under the ocean as the ocean would absorb a lot of radoation.

Many more commoners would die of cancer it seems.

 

[DDE]

Anyone knows which OTV study this is?

[kerbiloid]

2 hours ago, DDE said:

Anyone knows which OTV study this is?

Tineye found similar pic here

Also they say that

Quote

Orbit-to-Orbit Transportation (LEO to GEO, Lunar Orbit, Asteroids, or Mars Orbit and back)

Orbit-to-Orbit transfers within cislunar space can be handled by OH rockets. See figure 4 [Orbit Transfer Maneuver]. A series of space-based orbital maneuvering vehicles (OMVs) and orbital transfer vehicles (OTVs) is now being considered by NASA.

Aerobraking, which uses aerodynamic, effects to lower orbit, may be significant in cislunar space transportation. this technology will be used primarily with high-energy systems, such as OH rockets, to slow spacecraft returning to the Earth (or entering the Mars atmosphere), reducing their need for propellant. See figure 5 [Aerobrake used to slow down unmanned spacecraft returning from Mars]. This technology is under development but has not been tested in the context of GEO, lunar, asteroid, or Mars missions. No paper on aerobraking was produced during the workshop, but the principles and prospects of aerobraking have been discussed by Scott and others (1985) and Roberts (1985).

Pat Rawlings' drawings about the Mars.

Edited June 11, 2019 by kerbiloid