PDA

View Full Version : Writing myself into a radioactive corner



Noclevername
2015-Jun-24, 11:29 AM
Forgive me, for I have made a story setting with FTL.

The Jump Drive (imaginative name) produces a wormhole around the vessel accompanied by a strong burst of Hawking radiation. The starships have to be heavily shielded; the conventional wisdom for armoring a spacecraft against radiation is designed to prevent cosmic rays, solar flares, and other cumulative natural hazards from harming the crew. But to deal with the hot gamma and hard x-rays of the method I've chosen, a different solution is needed, or at least an additional one.

I thought of having a hull layered with (from outside to in) graphite, hydrocarbons, and heavy metal, with additional protection given by water pipes and storerooms inside. The outermost carbon layer, however, would gradually get ablated away and reduce its protection each time the jump drive is used. This is obviously not desirable.

Now, I know the easiest solution would be to do away with the radiation, but I'm too stubborn it's there for a plot reason. I'd just like suggestions as to what the outer layer could be made of to protect the outer hull from being eroded away by the jumps, and without exposing the crew to Bremsstrahlung from conventional cosmic rays and natural sources between jumps.

Cougar
2015-Jun-24, 12:41 PM
If you had the craft generate a strong magnetic field around itself, this could redirect the particles so they never touch the ship. I'm not so sure about the gamma rays... :think:

Noclevername
2015-Jun-24, 12:53 PM
If you had the craft generate a strong magnetic field around itself, this could redirect the particles so they never touch the ship. I'm not so sure about the gamma rays... :think:

I had considered a magnetic shield for charged particles, but I would prefer a fairly fail-safe design in case of a power failure or malfunction that can't be repaired on the spot. These are deep space explorer ships that stay away from the nearest docks for years at a time, so it needs something fairly simple and reliable; the KISS principle is in full effect.

Swift
2015-Jun-24, 01:15 PM
The outermost carbon layer, however, would gradually get ablated away and reduce its protection each time the jump drive is used.
Why? What is the mechanism of carbon ablation? Is it simply heating from absorbed gamma-rays and vaporization? Why is it the outermost layer? Why not make the heavy metal (Pb?) the outermost layer?

Noclevername
2015-Jun-24, 01:18 PM
Why? What is the mechanism of carbon ablation? Is it simply heating from absorbed gamma-rays and vaporization? Why is it the outermost layer? Why not make the heavy metal (Pb?) the outermost layer?

Yes, it is vaporization.

I was told that lead on the outermost layer is a bad thing, as cosmic rays tend to produce Bremsstrahlung radiation when they hit heavy metals; hence why there's a hydrocarbon buffer zone outside of the metal inner hull, to absorb those particles.

Noclevername
2015-Jun-24, 01:34 PM
Maybe a coating of something with boron? Borosilicate or a boride alloy?

Swift
2015-Jun-24, 01:35 PM
Maybe you can change the vaporization of the carbon? Change the composition so it has a higher boiling point.... coat it with diamond maybe?

Noclevername
2015-Jun-24, 02:30 PM
Maybe.

I briefly thought of having some kind of oil or coolant sprayed over the hull to carry off the heat, but that would be less simple to implement than the magnetic field idea, plus they'd run out of coolant.

Side question: If I do go with a magnetic shield, would the ship's hull need to be conductive?

Swift
2015-Jun-24, 03:38 PM
I briefly thought of having some kind of oil or coolant sprayed over the hull to carry off the heat, but that would be less simple to implement than the magnetic field idea, plus they'd run out of coolant.

What about pumping a heat exchange fluid between the outer carbon layer and the next inner layer. Most heat exchange fluids are hydrocarbon liquids, so that could also act as your hydrocarbon layer. That way you wouldn't run out of fluid, it would just be cycled around. The problem is what to do with the waste heat - maybe you store in sort of system in the interior of the ship (like a tank of rocks that you warm up by pumping the heat exchange fluid through). After the jump, you would deploy some sort of radiator, and pump your heat exchange fluid through your bed of hot rocks and into the radiator, and dump the excess heat out into space. Your limitation is now taking the time to get rid of the waste heat.

My biggest counter to that is I wonder if you can cool the outer carbon layer enough to really make a difference in its evaporation.

JohnD
2015-Jun-24, 05:26 PM
This gets into that "Name that story" thread, but I'm sure I recall a tale where the "Jump" locked the ship and everything in it into an impervious shell.
A macguffin of the tale was that the jump could not be too long, else heat would build up dangerously, but tat was just waste heat from engines and crew.

John

Solfe
2015-Jun-24, 07:35 PM
If your FTL drive could produce gamma rays in pairs, the process could be aligned with the ship's long axis so that one beam is "vented" forward and one goes out the back. The net effect on the ship would be zero and shielding for them wouldn't be necessary.

If you need a plot device to prevent too many jumps too quickly, make the FTL device a clock-like structure that only aligns with the vents every so often. You could have a tiny bit of "play" in the alignment. If the captain is willing to expose parts of the ship to a gamma ray blast, he could jump when the beam would pass through the shortest axis of the ship. The cost would be quick crew evacuations and fried electronics.

The beams could be paired with the sensors to produce a weak ghost like images of stuff directly to the front and back, while the main sensors are under protective covers for the jump. Picture the Mars landing where they took pictures through the frosted camera lens covers on the wheels to confirm orientation and touchdown. It was basic orientation, as in "is the rover right side up?", not which way was it pointing.

Noclevername
2015-Jun-24, 07:44 PM
If your FTL drive could produce gamma rays in pairs, the process could be aligned with the ship's long axis so that one beam is "vented" forward and one goes out the back. The net effect on the ship would be zero and shielding for them wouldn't be necessary.


It's the wormhole around the ship that produces the radiation. It doesn't come from inside the vessel, it surrounds the outside.

Solfe
2015-Jun-24, 07:56 PM
Nanotechnology, that's the ticket! The hull has a layer of carbon laden nano-structures which shield the ship from a jump. The structures are like microscopic whipple armor and the nano-structures are completely passive during the shielding process. The carbon is hammered down into the nano-structure like a ball and cup game. When the jump is complete, the ship generates a massive electromagnetic field that lifts the carbon back to position where it waits for the next jump. This takes a lot of time depending on the plot.

It wouldn't be 100% effective, but what is?

As a bonus, I suspect the ship would look like a fireball when emerging from the jump.

Jeff Root
2015-Jun-24, 08:14 PM
How thick is the shield? Can't you just make it thick enough
to do the job? Thickness is what makes Earth's atmosphere
effective at blocking stuff, including gamma rays.

It doesn't have to be solid, either. A Whipple shield.

-- Jeff, in Minneapolis

Ken G
2015-Jun-24, 08:25 PM
I was told that lead on the outermost layer is a bad thing, as cosmic rays tend to produce Bremsstrahlung radiation when they hit heavy metals; hence why there's a hydrocarbon buffer zone outside of the metal inner hull, to absorb those particles.But you have radiation anyway, from the wormhole, so why worry about bremsstrahlung? Hawking radiation will populate each radiation mode equally in a given energy bin. So I say, put the gamma radiation shield inside the heavy metal shield, and bring on the bremsstrahlung.

cjameshuff
2015-Jun-24, 09:19 PM
How about just not making the radiation environment so severe that carbon shielding ablates substantially over a small number of jumps? There's a wide, wide range between "requires shielding" and "is like being surrounded with thermonuclear detonations".

Some kind of refreshable graphite or polymer coatings would require consumables, but they would also be feasible to manufacture from raw materials with shipboard machinery. Is there something wrong with stopping every hundred jumps or so to refresh the outer hull?

Solfe
2015-Jun-24, 10:39 PM
But you have radiation anyway, from the wormhole, so why worry about bremsstrahlung? Hawking radiation will populate each radiation mode equally in a given energy bin. So I say, put the gamma radiation shield inside the heavy metal shield, and bring on the bremsstrahlung.

Back in the seventies, I loved the "Bring on Bremsstrahlung". Those screeching guitar solos and the drums were almost as good as Ted Nugent. :)

So, back to the really topic. Is this drive like an Alcubierre Drive or something different?

Noclevername
2015-Jun-25, 01:41 AM
I have been doing some checking, and I may have vastly underestimated how much energy it would take to have that affect on graphite.

I probably should have done that research first.

:doh::doh::doh::doh::doh::doh::doh::doh:

Solfe
2015-Jun-25, 02:58 AM
If you spell out your parameters for FTL and follow them, you don't have to tell the reader how it works. If they must, they can figure it out on their own. I have a story where the speed of light is only exists in nature, machines can be built to go faster if one knows how. It's a total dodge - what we know today is accurate yet I can still have very fast travel times. All of the characters either know how it works or don't care, so the subject never comes up to be addressed. For the characters, the description is either like reading the ingredients of mashed potatoes or is like hearing Star Wars translated into Klingon. No one makes the attempt to verbalize it.

I can describe the process of going to FTL without saying how.

I lampshade the situation in a couple of ways, usually socially rather than scientifically. Characters sometimes use telescopes to look for a future version of their own ship. It scares the heck out them, successful or not. Since they have to deal with acceleration, no one tries to hotdog through a solar system. There is a device that predicts the future so they can dodge things coming at c or higher. It isn't all that great, it works or fails as the plot dictates. Some of the characters are actually savvy to this, and turn it off. In some cases the device is manned with adrenaline junkies to keep them out of real trouble on the ship.

Noclevername
2015-Jun-25, 04:21 AM
What about pumping a heat exchange fluid between the outer carbon layer and the next inner layer. Most heat exchange fluids are hydrocarbon liquids, so that could also act as your hydrocarbon layer. That way you wouldn't run out of fluid, it would just be cycled around. The problem is what to do with the waste heat - maybe you store in sort of system in the interior of the ship (like a tank of rocks that you warm up by pumping the heat exchange fluid through). After the jump, you would deploy some sort of radiator, and pump your heat exchange fluid through your bed of hot rocks and into the radiator, and dump the excess heat out into space. Your limitation is now taking the time to get rid of the waste heat.

My biggest counter to that is I wonder if you can cool the outer carbon layer enough to really make a difference in its evaporation.

All ship's heat radiators have to be retracted during the jump anyway. As you can imagine, it's something of an engineering nightmare getting them to work and stay working. Moving parts on the radiators are the number one reason spacers swear more than wet-navy sailors... :whistle:

Solfe
2015-Jun-25, 05:07 AM
All of this sounds sort of exciting. I'll buy a copy when your done.

Noclevername
2015-Jun-25, 05:44 AM
Since the wormhole bubble size is limited, perhaps the ship's main reactor should be designed to retract into or closer to the ship for a jump, and then extend away for normal flight to limit the crew's radiation exposure (it goes without saying that the crew and passengers would ride out a jump in the "storm cellar".) Or would a telescoping reactor boom add too much complication to an already complicated ship design?

Noclevername
2015-Jun-25, 12:04 PM
If you spell out your parameters for FTL and follow them, you don't have to tell the reader how it works. If they must, they can figure it out on their own.

Actually, where I apply this principle is in the SSTO landing boats. I never say exactly how they can land and take off again from large terrestrial planets without using boosters or stages.

Solfe
2015-Jun-25, 02:14 PM
Actually, where I apply this principle is in the SSTO landing boats. I never say exactly how they can land and take off again from large terrestrial planets without using boosters or stages.

Landers are a hard sell. In the setting I have, there isn't much combat on unsettled planets because they have to leave most of the dropship behind unless they refuel. "Assault the planet" sometimes reads like "Welcome to Laguardia, thank for for flying with us." because they have to go to airfields. I have dropships and fighters because the main ships are too big to maneuver. The big ships tend to buzz planets and deploy forces from space at key times so they don't have to waste energy slowing down or accelerating away. They sort of "sail the spaceways".

I am leaning hard on the social-economic side of science fiction. I have a situation where it is heavily implied that the good guys and bad guys are selling military hardware to the civilians because they can't take it home. Both sides in the conflict have the mission "fight to protect the civilians". The civilians don't want military hardware, they want generic resources like food, space suits and batteries. That has all sorts of ramifications, and highlights differences between our world and the fantasy I have created.

Solfe
2015-Jun-25, 02:32 PM
Er... back to radiation. I use radiation as a plot device. There are some characters called "Psycho Sevens" that act as advisors to the military. They have serious injuries from radiation: blindness, lost limbs and organs, serious burn damage as a result of combat or ship duties. They stay on the ships because they don't want to engage in normal society any more. As a consequence some of them are "very old" thanks to relativistic effects of space ships.

Many times, they counsel the ship's captain against doing things that would cause serious harm to people, especially individuals. Sort of like a human rights advisor or legal counsel.

Noclevername
2015-Jun-25, 02:32 PM
I'm tempted to just introduce anti-gravity; the setting already has negative energy generation to provide the wormholes, it's not such an additional stretch. I'd have to make sure it doesn't get out of hand, no gravitic shields or tractor beams; those negative particles have to stay safely ensconced inside the ship's strongest thick-walled chambers.

Of course if I do that, I won't need landing boats at all; the starships themselves can land.

Noclevername
2015-Jun-25, 02:37 PM
Er... back to radiation. I use radiation as a plot device. There are some characters called "Psycho Sevens" that act as advisors to the military. They have serious injuries from radiation: blindness, lost limbs and organs, serious burn damage as a result of combat or ship duties. They stay on the ships because they don't want to engage in normal society any more. As a consequence some of them are "very old" thanks to relativistic effects of space ships.

Many times, they counsel the ship's captain against doing things that would cause serious harm to people, especially individuals. Sort of like a human rights advisor or legal counsel.

Getting radiation right is difficult. The gamma burst would cause acute radiation poisoning and radiation sickness, but as long as the exposed person does not die, they will eventually recover for the most part. Chronic or cumulative radiation, like what you get from years of cosmic rays, is what can give you the cancer. I generally have all my characters try to avoid either form of exposure as much as possible.

Solfe
2015-Jun-25, 03:09 PM
The term "Psycho Seven" comes from an ion weapon. The user should deploy the gun away from their position before using it by remote control. The ion gun incinerates targets, but the "radiation backflash" would kill the operator. Seven pulls of the trigger is considered lethal for the operator, hence the remote operation. If defending troops are overrun, they may fire the weapon even if they are standing too close. People who survive this experience get the name Psycho Seven, no matter how many times they actually pull the trigger.

There is a term for troops that refuse to deploy such weapons, "Gatlin' Doom". It is a historical reference, Custer was reported as hating gatling guns and didn't have them at his last stand. The troops in this era are history savvy, they'd rather risk losing than killing themselves.

Noclevername
2015-Jun-25, 03:10 PM
I'm tempted to just introduce anti-gravity; the setting already has negative energy generation to provide the wormholes, it's not such an additional stretch. I'd have to make sure it doesn't get out of hand, no gravitic shields or tractor beams; those negative particles have to stay safely ensconced inside the ship's strongest thick-walled chambers.

Of course if I do that, I won't need landing boats at all; the starships themselves can land.

Wait, no... If I change that, then certain important plot elements won't work.


Sigh; I guess they launch by handwave drive after all.

Solfe
2015-Jun-25, 03:16 PM
Wait, no... If I change that, then certain important plot elements won't work.


Sigh; I guess they launch by handwave drive after all.

I am pretty sure that I have done such things, 100 times over. Should I ever be published, someone is going to science-shred something I wrote.

Noclevername
2015-Jun-25, 03:34 PM
I am pretty sure that I have done such things, 100 times over. Should I ever be published, someone is going to science-shred something I wrote.

I can only hope that by the time I get published, the Skylon will actually be working and no one will find SSTO strange anymore.

slang
2015-Jun-25, 06:32 PM
Moved from Q&A as requested

Noclevername
2015-Jun-25, 06:33 PM
Thanks!