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4 hours ago, K^2 said:

Cold isn't a problem. If the primer goes off, the round will fire. And since primer usually has its own casing, it should be perfectly functional even if it becomes brittle. I am familiar with some primary explosives that can crystalize out in low temperatures which causes them to become more unstable. I don't think that can happen to mercury fulminate or lead azide, but I'm not certain.

High temperatures are a problem, of course, but if it's stable enough to be left out in the sun on Earth, it's hard to imagine conditions where it'd overheat dangerously in space.

I think, if temperature is a problem at all, it's going to be due to making the frame too brittle and possibly failing after a few shots. But I'm confident you can get a single shot out of a firearm in space pretty much no matter what.

At what temperature (s) do steel, aluminum and polymer become brittle enough that they might fail under use?

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5 hours ago, DDE said:

Thank you for all the responses, but I was mostly worried about the thermal stability of modern gun propellants.

I was basically thinking about the minimum list of possible precautions, and not carrying a round in the chamber was one of those.

That's a good point, temperature is going to be an issue as well. Ambient temperature can affect chamber pressure when the firearm is discharged. Generally the higher the temperature, the higher the pressure, although how much so depends on the powder used. Most military powders are specifically formulated to be relatively temperature insensitive, but that is for Earth-normal temperature ranges. Out in space, where the firearm could be exposed to open sunlight for extended periods of time with no atmosphere to remove the heat buildup, it could get quite hot, with a distinct possibility of increasing the chamber pressure to dangerous levels on discharge, even with a normally temperature-insensitive powder. This could be overcome by insulating the firearm, designing it to pull heat away from the chamber, formulating special powders, etc.

I still think the criteria above would hold: If it's a one-off, if you're going to shoot the firearm once and throw it away, yeah, you could get away with just about any off-the-shelf firearm. Any quality firearm should be able to shoot a hot load once without failing. Once. I wouldn't push my luck. (And you might want to leave the Hi-Points and Lorcins at home.) If you're going to use it on a regular basis your health insurance plan would probably appreciate it if you would use a purpose-built firearm.

Not carrying the round in the chamber? (Israeli-carry) Might help. But the barrel and chamber will still be hot when the round goes off. And the rounds will still heat up in the magazine. Again, metal conducts heat, and there's no atmosphere to remove it. Using a plastic Wonder-9, like a Glock or a M&P, might help with the heat issue. Or it might be a worse idea. (What temperature does Glock polymer soften at?)

11 minutes ago, JoeSchmuckatelli said:

At what temperature (s) do steel, aluminum and polymer become brittle enough that they might fail under use?

Depends on the alloy. Each one is going to have a Nil Ductility Temperature, which will determine the point at which it transitions from failing ductile to failing brittle. In general, the harder the alloy, the higher the NDT. 

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Would the ammo temperature significantly differ from the suit temperature and be +/-100°C?
If so, I guess the thermal instability of the powder is not the greatest problem of the shooter.

Also the spacegun would probably be attached to the suit with a cable (at least to keep it from getting lost), so keeping it warm is probably not a problem, mostly heating is.

Does the space gun really need the energy of the atmospheric bullet when there is no gravity or air drag, but any hole in the opponent's suit is a deadly problem.

Edited by kerbiloid
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Not sure where to put this so I'm just going to drop this here...

Mostly older clips, but at 3:56  I haven't seen that two-wheeled logistics 'bot before. Some intriguing stuff; Atlas is getting pretty agile.

Good thing Atlas and Spot don't have tempers though, or that guy with the hockey stick would have gotten cross-checked

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The robots can't properly shoot until they get able to put the index finger along the barrel.
It gives +10 to the Shooting skill and the Sacred Bless Of Holy Wood Archers.. 
Having it on the trigger causes: -1 to Dexterity, -2 to Agility, -3 to Morale, and 1d4 chance of diarrhea on every shot until the next day.

BD should equip them with a special extendable finger.

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How does the Atlas rocket that carried John Glenn into orbit work? I keep hearing it is a "one and a half" stage rocket, which doesn't make sense to me. I also heard that the Atlas had a "sustainer" thing. What is that?

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1 hour ago, AeroSky said:

How does the Atlas rocket that carried John Glenn into orbit work? I keep hearing it is a "one and a half" stage rocket, which doesn't make sense to me. I also heard that the Atlas had a "sustainer" thing. What is that?

In simpler terms: it would throw two of the three/five engines away. The remaining centre engine would be the sustainer.

e1dh431xx6661.jpg

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Liquid-hydrogen research found early support from the Department of Defense. The Air Force sponsored a series of liquid-hydrogen rocket experiments by Johnston and his students in which they applied the principle of regenerative cooling by circulating liquid hydrogen in passages that surround the thrust chamber prior to injection and firing of the rocket. They also discovered that ball bearings cooled by liquid hydrogen did not require lubrication—a phenomenon rediscovered by engineers at Pratt & Whitney during the development of the RL10 engine.

From a book about the Centaur upper stage. The reference (Liquid Hydrogen, by Sloop) doesn't provide much clarification on this process either (as far as I can tell).

How does this hydrogen lubrication work? Is liquid hydrogen itself an effective lubricant? Do the cryogenic temperatures reduce friction? Is there some beneficial chemical process going on between the metals used in turbomachinery and the hydrogen?

 

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1 hour ago, Silavite said:

How does this hydrogen lubrication work? Is liquid hydrogen itself an effective lubricant? Do the cryogenic temperatures reduce friction? Is there some beneficial chemical process going on between the metals used in turbomachinery and the hydrogen?

While I suspect LH2 has very low viscosity, you usually want large molecules for lubrication, hence oils, to prevent direct contact between metals, so I don't think LH2 would be a good lubricant. I'm also not aware of any reason why cooling itself would reduce friction. It's true that friction between two perfect lattices would go to zero as temperature does, but that's just not a thing that exists in any mechanical system, and imperfections in metals will always exist at any temperature, and that will cause friction. For the same reason, no solid coating would help, so idea of chemical reaction seems dubious.

This is a stab in the dark, but having discarded other ideas, and running with "cooled by liquid hydrogen," which usually involves evaporative cooling, I'm going to guess a variation on Leidenfrost Effect, with pockets of hydrogen gas forming around metal parts suspending moving parts and driving friction to almost nothing. It's most certainly a phenomenon that can happen and can be used to avoid needing to lubricate bearings under the right conditions, but I do not know enough about the rocket engines and specifically about which bearings would require cooling to say whether this is, indeed, what's happening.

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I always had a feeling that it's something very wrong with the CBM dimensions.

Everywhere (even in the wiki) they write that its diameter is 71" (~1.8 m).

But it's known very well that it's designed to match the rounded-square hatch which is 50" (127 cm) wide.
And these 50" / 127 are also not random, it's a full internal diameter of an IDSS-compatible docking adaptor tunnel when they unmount its mechanics, making it empty.
So, a cargo of 50" can freely pass the docking node tunnel and the squared hatch behind the CBM adaptor.

But every time I measure the CBM photos in Inkscape and calculate the scale taking 127 cm as the squared hatch width, I get the CSM ring diameter ~198 cm on top and ~205 cm  at bottom.
No "71" / 1.8 m" even close.

One small picture tells that the docking port on the bottom of the Cupola is 2025 mm wide.

 

And what do you think?

https://www.ehdavis.engineering/Exegeses/common-berthing-mechanism-core-design-description/

Spoiler

cbm-cbm_wall_final-1024x641.jpg

That's exactly so!

The top of the ring is officially 77.696" (197.3 cm), the bottom is 79.73" (202.5 cm), exactly like what my measurements give.

That everyone's 71" is just the 70.9", the diameter of the hole opening.

If we can't believe wiki, then whom at all can we believe?!
Only one small picture was containing the truth, and this perfect article has revealed it totally.

Edited by kerbiloid
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38 minutes ago, ARS said:

Does explosive-tipped arrow makes sense or actually useful in real life?

Probably a low-yield equivalent to the under-barrel grenade launcher and requiring more skill to use, but not making any noise at the origin  point.

Might be especially useful for espionage if you use time-delayed charges, should there be a target that is visible but not reasonably reachable for hand-placed charges(which could be both larger and precisely placed)

 

So, probably useful in a niche scenario or two, but probably not worth actually stocking or using unless your sniper likes to bow-hunt on the weekends.

 

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54 minutes ago, ARS said:

Does explosive-tipped arrow makes sense or actually useful in real life?

Depends on what you define as useful. Are there tasks, including such as demolition or assassination, that can be accomplished with an explosive arrow? Yes. Are there any tasks for which it is the optimal tool? Almost certainly not. The small amount of explosive you can reasonably deliver with an arrow will have to be placed directly on target and detonate on impact to do anything. So you don't really get advantage of stealth. And barring that, a rifle or grenade launcher will work way better.

Now, an incendiary arrow with a timer? That might have some very narrow and situational use case in sabotage.

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1 hour ago, ARS said:

Does explosive-tipped arrow makes sense or actually useful in real life?

I would say 'no'.  Beyond the historic record, where professional users did not generally have large warheads mounted on arrows - they're just impractical as heck. (Can't deliver much CE to the target. 

 

For a lengthy showing of someone trying to get it to work - see this;

 

 

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5 minutes ago, JoeSchmuckatelli said:

For a lengthy showing of someone trying to get it to work - see this;

I suspect that safety and federal regulations are getting in the way of making it lighter, more effective, and detonate on flesh impact, but I don't think you can do so much better that it'd make a qualitative difference in terms of practical application.

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1 hour ago, K^2 said:

I suspect that safety and federal regulations are getting in the way of making it lighter, more effective, and detonate on flesh impact, but I don't think you can do so much better that it'd make a qualitative difference in terms of practical application.

Exactly - if you have a human target you want to eliminate without giving yourself away, a bow or crossbow is effective as is. 

So then you ask - why mount an explosive?  Presumably to increase the effectiveness, right? But then you discover that for human targets - doing so actually decreases the efficacy of the original, by being less accurate, shorter ranged and less reliable. Thus you have to have a different target in mind. 

Anti-equipment?  For that, you often need a pretty big boom or lots of kinetic energy.  Bows have an upper limit to KE potential (which is why they're pretty much limited to anti personnel) - so maybe this is where adding a warhead makes sense?  Except the KE delivery limit, also limits the ability to deliver a warhead - especially one with enough CE to do any work.  I seriously doubt that anything short of a purpose built crossbow can launch anything much larger than a hand grenade and be man portable - and even then you can probably throw it almost as far (they weigh just shy of a pound)... And a hand grenade turns out to be quite poor as an anti equipment round (unless you place it just right - close doesn't count).   60mm mortar rounds (still anti personnel) are 2.5 pounds.  So to get a good anti personnel warhead with the ability to take out vehicles and stuff, maybe we bump it up to a 10 pound warhead, like the 81mm mortar?  That has a kill radius of 35m (110ft).  Not sure your crossbow can push it out that far. 

So back to @ARS-you can trust that if something like this worked, we'd still be using it today.

 

(FYI - folks tried it, but it didn't last) 

https://en.m.wikipedia.org/wiki/Sauterelle

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A bow is less loud than a silenced gun, and its sound sounds more naturally than a metal clang (though still not fully silent).

So, shooting with the arrow from 90 meters  (longest sport range) can hide the shooter's position and let him move to another place before getting found.

The explosive arrowhead produces loud noise which can disorientate the opponents for some time and let doing something while they are hearing ringing bells and looking around trying to get the archer's direction.

It can ignite something flammable.

Being shot to another corner of the opponents' camp, it can attract their attention to that direction and make them run to have a look.

Edited by kerbiloid
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9 hours ago, kerbiloid said:

A bow is less loud than a silenced gun, and its sound sounds more naturally than a metal clang (though still not fully silent).

So, shooting with the arrow from 90 meters  (longest sport range) can hide the shooter's position and let him move to another place before getting found.

The explosive arrowhead produces loud noise which can disorientate the opponents for some time and let doing something while they are hearing ringing bells and looking around trying to get the archer's direction.

It can ignite something flammable.

Being shot to another corner of the opponents' camp, it can attract their attention to that direction and make them run to have a look.

It will also make them draw guns to investigate. 

 

Video game and movie scenarios aside (you are not going to use a bow to take down 3 camps of 8-15 cartel members on the beautiful tropical island by yourself), using a bow and arrow in the incendiary and signaling roles does have a long place in the historical record.  You can also use it to help get a climbing rope lead up and over a high point. 

But shooting a boom thing in hopes of having a bunch of dummies run to the far side of the clearing and then stand around going 'whawuzdat' while you shoot them with arrows isn't smart.  You would be lucky to get off 6 to 10 well aimed shots in a minute as a professional archer in the 15th century. 

 

Although if you are, in fact, a time traveling Holy Warrior coming to save the world from a Caribbean drug dealer - it is probably best to use the tools you know well 

Edited by JoeSchmuckatelli
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I've heard that crossbows  were used to a limited extent in the Korean War (but probably not since).  Back when I was a boy scout, I learned that crossbows were more regulated than rifles in my home state.  Most of this was likely that they could easily restrict crossbows (and modern ones look scary), but also that they are silent, penetrate soft body armor, and have no muzzle flash (but do point back to their shooter when they stick in something).

2 hours ago, JoeSchmuckatelli said:

But shooting a boom thing in hopes of having a bunch of dummies run to the far side of the clearing and then stand around going 'whawuzdat' while you shoot them with arrows isn't smart.  You would be lucky to get off 6 to 10 well aimed shots in a minute as a professional archer in the 15th century. 

https://www.youtube.com/watch?v=NTJnyQ-bZLU  The ancient weapons segment of youtube went crazy over this set of videos.  A mad German engineer developed a "repeating bow" he named the "instant Legolas".  Expect 6 to 10 well aimed shots in well under 20 seconds, but don't expect the power of the 15th century bow/archer (although last I saw, they were trying to find ways to get even that.  But even just the repeating bow would have been on the edge of 15th century craftsmanship).

Edited by wumpus
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8 minutes ago, wumpus said:

I've heard that crossbows  were used to a limited extent in the Korean War (but probably not since).  Back when I was a boy scout, I learned that crossbows were more regulated than rifles in my home state.  Most of this was likely that they could easily restrict crossbows (and modern ones look scary), but also that they are silent, penetrate soft body armor, and have no muzzle flash (but do point back to their shooter when they stick in something).

https://www.youtube.com/watch?v=NTJnyQ-bZLU  The ancient weapons segment of youtube went crazy of this set of videos.  A mad German engineer developed a "repeating bow" he named the "instant Legolas".  Expect 6 to 10 well aimed shots in well under 20 seconds, but don't expect the power of the 15th century bow/archer (although last I saw, they were trying to find ways to get even that.  But even just the repeating bow would have been on the edge of 15th century craftsmanship.

That guy's videos are great!  Anyone who has that much fun is awesome

 

"point back at the shooter" only works if you hit a tree.  Living things tend to stagger around a bit, if not run a full mile before hiding in a hawthorn grove (don't ask how I know that)

Edited by JoeSchmuckatelli
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1 hour ago, JoeSchmuckatelli said:

But shooting a boom thing in hopes of having a bunch of dummies run to the far side of the clearing and then stand around going 'whawuzdat' while you shoot them with arrows isn't smart. 

You make me thinking that Rambo was wrong...

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In lieu of making a new thread (already have three on one page) I thought it best to post this here:

 

Scifi Alternative To Constant Acceleration:

 

It seems the more I know the more of a headache science gives me when it comes to scifi spaceflight.

On the one hand, I find orbital and newtonian dynamics very attractive, even graceful. On the other....the tyranny of the rocket equation is more or less a show stopper for scifi tropes.

High thrust constant acceleration drives seem like an attractive solution, but as I discussed in another thread, they would be far too dangerous to be commonplace, even if they had limited delta v. 

Solution: Time warping. Basically time forwarding like in KSP, only the crew inside the time warp experience much less time.

Example? Want to fly to Mars but only have enough food supplies to last a day?

No problem. You in orbit? Great! Plot a trajectory for Mars and once you're on course, engage the time warp.

Every minute spent inside the time warp your vessel generates makes TWO MONTHS pass by outside.

Result? You reach Mars subjectively in less than hour, after throttling the time warp back down to normal.

No longer do you need to worry about long flight time, and you can save precious propellant for when it is most needed.

Wanna know the cool thing?

Thanks to time warping, you would seem like you are traveling really fast, planets would whiz by, and you would even see them rotate several revolutions quickly in real time!

f8fd5e13de45b1544bd816f0a9ba1941.gif

 

So time warp VS dangerous constant acceleration....which would you rather be common for civilian scifi spacecraft to have?

Personallly, I think time warp is safer for the public at large. Constant high thrust acceleration is the kind of thing bad guys dream about when they want to make things go boom.

Edited by Spacescifi
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3 hours ago, Spacescifi said:

Every minute spent inside the time warp your vessel generates makes TWO MONTHS pass by outside.

So, if I don't want to wait for the next season of a show, I can jump in the time pod, set it for six minutes, and it's a year later and I can watch the show now?

Or I can get in, take an 8 hour nap, and wake up in 80 years?

 

I think getting to Mars quickly may be the less interesting effect of this invention.

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