For Questions That Don't Merit Their Own Thread

[PB666]

3 hours ago, peadar1987 said:

Short answer. No. Xenon-135 has a half-life of about 9 hours. About 6% of U-235 fissions to Xenon-135. Half of this transmutes to Xenon-136 through neutron capture. You're going to get about 3% of the mass of the U-235 in the fuel as Xenon. At 4% enrichment, that's 0.0012% of the nuclear fuel. You're not going to produce enough Xenon to make any sort of meaningful difference.

Say 1/100 th of your ship is nuclear, if you could eject at c (ignoring the lorenze transformation) 

3 x 4 x 1 / million = .000007       ln (1/.999993)  is roughly ln 0.000007. 

c x 0.000007 300 e 6 x 7 e -6 = 2100 dV 

But seriously the MW transformation would be rediculous. 

 

Edited July 8, 2016 by PB666

[RocketSquid]

4 hours ago, peadar1987 said:

Short answer. No. Xenon-135 has a half-life of about 9 hours. About 6% of U-235 fissions to Xenon-135. Half of this transmutes to Xenon-136 through neutron capture. You're going to get about 3% of the mass of the U-235 in the fuel as Xenon. At 4% enrichment, that's 0.0012% of the nuclear fuel. You're not going to produce enough Xenon to make any sort of meaningful difference.

I was assuming you either use the Xenon as it is produced or deliberately turn 135 into 136.

[peadar1987]

9 hours ago, PB666 said:

Say 1/100 th of your ship is nuclear, if you could eject at c (ignoring the lorenze transformation) 

3 x 4 x 1 / million = .000007       ln (1/.999993)  is roughly ln 0.000007. 

c x 0.000007 300 e 6 x 7 e -6 = 2100 dV 

But seriously the MW transformation would be rediculous. 

 

If you can eject your exhaust at c, you're firmly in science fiction territory. Current ion engines have a maximum exhaust velocity of about 50,000 m/s, or about 0.016% of c.

8 hours ago, RocketSquid said:

I was assuming you either use the Xenon as it is produced or deliberately turn 135 into 136.

In that case you can double the amount of Xenon available for propulsion, but it's still a pretty tiny amount.

Running the numbers, if your entire ship is made of fuel rods, you get about 120 m/s of delta-V over the lifetime of the reactor, 60 of that due to Xenon-136, and 60 due to Xenon-135.

The Russian Topaz reactor had a mass of 320kg, 12kg of which was fuel rods, to give some idea of the ratios you'd be working with in real life.

[PB666]

23 minutes ago, peadar1987 said:

If you can eject your exhaust at c, you're firmly in science fiction territory. Current ion engines have a maximum exhaust velocity of about 50,000 m/s, or about 0.016% of c.

The limit on ion drives is not exhaust velocity, its power, you can increase the number of plates, but there is a feasible limit of power per crossectional area of about 100 KW per meter. When you look at the ion drive equation you quickly realize that higher ISP requires proportionally more power but delivers per each higher thrust it become impractical with the power generation capabilities. In the case of xenon, bevause its a fraction of the fissile products it can be used but, again, you are not going to ever get 2100 dV from near c accelerated ION drive from a uranium fission reactor, no way, thier current in-space efficiencies are way too low.

Given the these ion drives weigh a few kgs, if you had something like a cyclotron you could, lol. I'm talking theoretical here, not realistically, lets just be clear. And not only would you eject xenon, you would be ejecting literally anything that could be sucked out of the uranium, so you could get dV higher. But thats not the problem. Fissile energy conversion is not that good and is very heavy so you MW efficiency per ship mass is going to be lousy, its not going to happen. 

The technology that really makes sense is fusion, because the products are pretty much all gases and can be used dirctly as propellants and I calculated the maximum efficiency point is to about 0.1 c. Even anti-matter explosion powered you want to accelerate to about 0.7 c, which is the credible limit of space travel which is about double the credible limit of space travel. This is my interest in these matter-antimatter quarks, because if they can be made stable then this is a source of fuel for interstellar travel. 

Fusion power Electric Propulsion

Will work for extended periods in space?

Mass fraction of reactor. Major

Ion accelerators. In the 0.1c range. Mass fraction of cyclotrons, efficiency.

Spent fuel + Accelerant fuel lowers the mass fraction cost of the reactor, but decreases ISP. Bigger ship, dueterium storage. 

Fusion heat to MW conversion efficieny? 

 

[todofwar]

On 6/28/2016 at 7:21 PM, andrewas said:

If you are far enough away from it, you can orbit it more or less as normal. The gravity will be non-spherical which means that orbits will precess, and since the mass distrbution is much more extreme than Earth's, this precession will be much faster than it is in Earth orbit. I'm not sure how low you can go and still have a stable orbit.

Within the ring, gravity will be towards the near side of the ring, and towards the plane of the ring. There are no stable orbits within the ring. At the center point all gravity cancels, but the slightest perturbation will result in you leaving that center point and gravity will accelerate you towards the ring.

If I'm remembering mechanics correctly any point inside the ring will not feel a gravitational pull towards any side of the ring, same reason a sphere around the Sun would drift relative to the Sun. But extending it to 3d, I don't know about being inside a cylinder. I want to say you get an attraction to the plane intersecting the middle of the cylinder. 

[peadar1987]

49 minutes ago, todofwar said:

If I'm remembering mechanics correctly any point inside the ring will not feel a gravitational pull towards any side of the ring, same reason a sphere around the Sun would drift relative to the Sun. But extending it to 3d, I don't know about being inside a cylinder. I want to say you get an attraction to the plane intersecting the middle of the cylinder. 

Yeah, you'll fall towards the centre of the long axis of the cylinder, and tend to just oscillate about that (while drifting in the x-z plane)

[todofwar]

7 minutes ago, peadar1987 said:

Yeah, you'll fall towards the centre of the long axis of the cylinder, and tend to just oscillate about that (while drifting in the x-z plane)

So would you then "orbit" that point (probably not the right word, it wouldn't be eliptical) until you hit a side assuming you don't have the energy to exit the cylinder?

Edited July 8, 2016 by todofwar

[SuperFastJellyfish]

4 hours ago, todofwar said:

So would you then "orbit" that point (probably not the right word, it wouldn't be eliptical) until you hit a side assuming you don't have the energy to exit the cylinder?

I picture it in my head acting like this, but with the needle being the long axis of the cylinder.  Edit:  I had it backwards in my head.  It seems the gravitational net force inside a cylinder would be towards the closest wall.  See, Andrewas's post below.  I'll leave the video though, as it's interesting.   

 

Edited July 8, 2016 by SuperFastJellyfish

[peadar1987]

1 hour ago, todofwar said:

So would you then "orbit" that point (probably not the right word, it wouldn't be eliptical) until you hit a side assuming you don't have the energy to exit the cylinder?

It would look more like a bungee jumper, you'd basically just look like you were bouncing up and down with the midpoint of the bounces half way along the cylinder

[andrewas]

4 hours ago, todofwar said:

If I'm remembering mechanics correctly any point inside the ring will not feel a gravitational pull towards any side of the ring, same reason a sphere around the Sun would drift relative to the Sun. But extending it to 3d, I don't know about being inside a cylinder. I want to say you get an attraction to the plane intersecting the middle of the cylinder. 

You are not remembering correctly.

http://www.alcyone.com/max/writing/essays/why-niven-rings-are-unstable.html

 

[K^2]

The video of droplets orbiting a needle requires a clarification. The droplets are neutral, so the attractive force is due to polarization, which is 1/R³ force. When orbiting a long cylinder, however, the net force in the transverse plane integrates to 1/R², which allows droplets to orbit as if around a gravitational attractor in the transverse plane, while moving freely in the longitudinal direction. Picture changes near the ends of the cylinder, of course, but that's a more complicated discussion.

[DDE]

Jumping onto the xenon bandwagon, why doesn't the ISS use the hydrogen from electrolytic oxygen generators for some sort of electric propulsion?

[RainDreamer]

I think they don't want to because they would have to re-rigged the current propulsion system which has been there forever to use electric propulsion, or replace them entirely, both of which would be costly and not worth it for something that would be going down in 2020.

My very simple question: Organic matters are matters that are carbon-based, yes? So can I tell people who keep hounding me with the "eat organic" lines to eat coal and shut up?

[p1t1o]

5 hours ago, RainDreamer said:

My very simple question: Organic matters are matters that are carbon-based, yes? So can I tell people who keep hounding me with the "eat organic" lines to eat coal and shut up?

There are 3 meanings to the word "organic":

In chemistry, as you say, it means involving carbon-containing compounds.

In biology (or otherwise outside of chemistry) it refers to biological material.

In food, it is used to refer to...actually its pretty hard to pin down as there are no regulated definitions of "organic", you are free to come up with your own. The only restriction if if you want a badge or logo saying "certified organic" or whatever, then your food has to meet the various specifications of that particular certificate or badge. Its generally perfectly legal to put the word "organic" on any food at all, the only time you need to fill certain criteria is if you want a specific badge or certificate to put on there as well. This is true at least in the UK, and if things havn't changed drastically in the last couple of years or so.

 

So basically if someone is talking to you about "eating organic" you should tell them not to be such a slave to marketing and just eat healthy.

There is limited evidence that certified organic food prevents any health issues or provides any benefit, and whilst there is also only limited evidence of increased microbial contamination, there have been outbreaks of E.Coli that have been attributed to organic foods (due to unwashed, untreated food, fertilised with manure).

 

And if someone tries to push "biodynamic" food towards you, laugh in their face. Then tell them that the laughter was actually a spell to make them go away, then watch to see if it works.

[Ten Key]

Looking for a quick reality check vis-à-vis experiencing free fall in an aircraft. . .

If an aircraft is travelling along a ballistic trajectory while still inside an atmosphere and is not running its engines, the pilot will not experience "weightlessness" due to drag force on the vehicle.

If an aircraft is at very high altitude and has positive vertical velocity, but has its nose level with the horizon so it is pointed 90 degrees off the velocity vector, the pilot will not experience "weightlessness". Both the pilot and the aircraft are experiencing the same acceleration due to gravity, but the aircraft is also experiencing drag force and the pilot is not. This disparity will cause the pilot to lift upwards into the safety harness, and loose objects in the cockpit will tend to "fall" upwards towards the canopy.  

Edited July 13, 2016 by Ten Key

[Nibb31]

The weightlessness you feel in an aircraft has nothing to do with drag. It's basically the same phenomenon as when you drive over a speed bump.

[p1t1o]

8 hours ago, Ten Key said:

Looking for a quick reality check vis-à-vis experiencing free fall in an aircraft. . .

If an aircraft is travelling along a ballistic trajectory while still inside an atmosphere and is not running its engines, the pilot will not experience "weightlessness" due to drag force on the vehicle.

If an aircraft is at very high altitude and has positive vertical velocity, but has its nose level with the horizon so it is pointed 90 degrees off the velocity vector, the pilot will not experience "weightlessness". Both the pilot and the aircraft are experiencing the same acceleration due to gravity, but the aircraft is also experiencing drag force and the pilot is not. This disparity will cause the pilot to lift upwards into the safety harness, and loose objects in the cockpit will tend to "fall" upwards towards the canopy.  

 

1 hour ago, Nibb31 said:

The weightlessness you feel in an aircraft has nothing to do with drag. It's basically the same phenomenon as when you drive over a speed bump.

 

Further to what Nibbs said, aircraft which simulate freefall execute a "negative-G pushover". They dont just throttle down and coast and try and "fall", they execute a powered maneuver where the G-force produced cancels out gravity in the cabin. During the simulated freefall stage, your floating body in the cabin is following a ballistic trajectory, the plane is not, it is actively flying the exact shape of a drag-free ballistic trajectory. The plane, as you say, experiences drag, so it must use engine power and aerodynamic control to attain this curve. The whole time you are in "freefall" the plane is actively maintaining this trajectory, there is no "coast" phase.

It is almost as if the plane "lofts" you into the sky (the 1.8g pullup), and then flies in precise formation with you as you arc through the air. The pilot could look back through the cabin and control your position relative to the walls via small control inputs, if he so desired.

[RainDreamer]

What can we do with this thing? 

C2N14 - Azidoazide Azides.

Any practical use at all?

Edited July 17, 2016 by RainDreamer

[peadar1987]

25 minutes ago, RainDreamer said:

Any practical use at all?

Finger removal?

http://blogs.sciencemag.org/pipeline/archives/2013/01/09/things_i_wont_work_with_azidoazide_azides_more_or_less

" the X-ray crystal structure, for example, must have come as a huge relief, because it meant that they didn’t have to ever see a crystal again. The compound exploded in solution, it exploded on any attempts to touch or move the solid, and (most interestingly) it exploded when they were trying to get an infrared spectrum of it. The papers mention several detonations inside the Raman spectrometer as soon as the laser source was turned on, which must have helped the time pass more quickly. "

[Guest]

To all you biologists out there, now it's your time to shine:

Is ethane metabolized by humans (as in, do we digest it)?

[JebKeb]

Probably not, unless it is oxygenated into ethanol. Also, it's a gas, so transport is a bit complex.

Edited July 19, 2016 by JebKeb

[Kryten]

11 hours ago, Aperture Science said:

To all you biologists out there, now it's your time to shine:

Is ethane metabolized by humans (as in, do we digest it)?

It isn't to any significant degree, it mostly leaves through the lungs unchanged. Longer alkanes like hexane can be oxidised to alcohols by the P450 enzyme system which is why e.g. hexane is pretty toxic.

[Guest]

So if a person ingests a solution containing ethane, they most likely won't get intoxicated, right?

Edited July 18, 2016 by Guest

[PB666]

Ethane can interfere with neurobiology because it changes the permeability of membranes, ita also dosplaces oxygen, . . . . . . . .you will get buzzed from it at high enough concentrations, but then again high concentrations are also explosive. 

[JebKeb]

What does this gas processing at the top involve and where can I find a diagram for it?

Edited July 19, 2016 by JebKeb