For Questions That Don't Merit Their Own Thread

[ARS]

Kinda weird how energy shields commonly referred as deflector shield in the first place when it doesn't deflect stuff at all

[Spacescifi]

32 minutes ago, ARS said:

Kinda weird how energy shields commonly referred as deflector shield in the first place when it doesn't deflect stuff at all

 

Energy shield itself is a paradox. A shield made of lasers?! A shield that shields against lasers? Steel does that LOL. Longer if you spin it anyway 

Remember not to think about buzzwords too much.

It's a buzz word with little real meaning.

Like the light saber, or turbolasers that are NOT lasers.

[K^2]

36 minutes ago, magnemoe said:

The typical scifi shield is fantasy, you can use magnetic field to deflect charged particles.

If you have a strong magnetic field and are moving fast enough, you can ionize incident matter, so this isn't just for charged particles. Obviously, at that point, you are adding ionization energy to net drag, but this might be the only viable option for traveling at relativistic speeds, and the faster you go, the less significant is ionization energy loss compared to ram pressure. You do need a beam core AM or some variant of black hole drive to have the kind of power you need to make it work, but it's physically possible, at least, and it's unlikely you'd be getting to speeds where it's crucial to have without something like it anyways.

[FleshJeb]

45 minutes ago, K^2 said:

If you have a strong magnetic field and are moving fast enough, you can ionize incident matter, so this isn't just for charged particles. Obviously, at that point, you are adding ionization energy to net drag, but this might be the only viable option for traveling at relativistic speeds, and the faster you go, the less significant is ionization energy loss compared to ram pressure. You do need a beam core AM or some variant of black hole drive to have the kind of power you need to make it work, but it's physically possible, at least, and it's unlikely you'd be getting to speeds where it's crucial to have without something like it anyways.

If you're riding a laser sail, you could regularly displace from your path (or close the sail), and let the laser cannon(s) in home system clear the way. That should accelerate any small particles in your direction of travel, although I doubt it would vaporize them outright. Any overspill around the sail during regular travel might even be enough to intercept most things crossing your path. You'd certainly know by the reflections if you were going to run into a dust cloud. You could even find the relative velocity by reading the frequency shift from the bounced light. It pays to have your propulsion system also work as a sensor.

I imagine mitigating impacts is more about the total rate of impacts and magnitude thereof, rather than avoiding them entirely. The question is: Does the laser cannon in home system put out enough power for this to be an effective mitigation strategy. Is the acceleration of the incident matter significant? What power level is required to also ionize the incident matter? It would require A LOT more than having it onboard, but what a mass-savings.

If anyone feels like doing the math for that one. ;-)

[K^2]

2 hours ago, FleshJeb said:

If you're riding a laser sail, you could regularly displace from your path (or close the sail), and let the laser cannon(s) in home system clear the way. That should accelerate any small particles in your direction of travel, although I doubt it would vaporize them outright. Any overspill around the sail during regular travel might even be enough to intercept most things crossing your path. You'd certainly know by the reflections if you were going to run into a dust cloud. You could even find the relative velocity by reading the frequency shift from the bounced light. It pays to have your propulsion system also work as a sensor.

This is fine while you're riding out of the system, since you're going with general direction of the solar wind, but once you're out in interstellar space, at about 90-100AU out, you're going to hit a "cross wind" sufficient to carry in matter from outside your direct path. Of course, you are unlikely to be using laser propulsion at these distances anyways, but in either case, you can't rely on this technique outside of Sol system. And, of course, you're going to have a whole new problem on arrival, as you're going to hit the solar wind of target star head on. The good news there, however, is that you'll actually want that drag to help you slow down, so using magnetic shielding is absolutely the right thing to do at destination. If you don't have active propulsion in interstellar, however, magnetic shielding might be generating too much drag...

[FleshJeb]

Interesting thoughts.

14 minutes ago, K^2 said:

unlikely to be using laser propulsion at these distances anyways

Robert Forward's plan was 20 years of pushing to 0.2c, then coasting for 20 years, then braking by detaching the outer ring of the sail.

Short version: https://en.wikipedia.org/wiki/Rocheworld#Forward's_light_sail_propulsion_system

More detailed explanation: https://www.centauri-dreams.org/2013/08/20/key-issues-for-interstellar-sails/

First page of the actual paper: https://arc.aiaa.org/doi/10.2514/3.8632

Looks like @MatterBeam also covered it at some point: 

 

[K^2]

2 hours ago, FleshJeb said:

Robert Forward's plan

Ok, yes, if you have a flawless lens hundreds of km across and a laser source with coherence length several times that, you can project the beam to 10ly. I hope I don't need to explain why that's problematic from engineering perspective. Also, lasers with that fidelity don't exist, but we can get up to about 100km, so maybe that can be pushed a little. We might be able to do a lot better with microwaves, because we can actually adjust phases dynamically to create an effect of perfect lens of such size, which might be just as good for propulsion, but it won't be helpful in clearing the path at all, as the absorption is going to be pitiful.

That said, if you're just sending an unmanned probe, maybe you just take the beating. Build your electronics with enough heft and redundancy to take the abuse from radiation and don't even worry about it. It's still going to be generating considerable drag, and you'll have to account for it in your acceleration phase, but even if you just cut out a cylinder 10ly long and 1,000km across, there's only about 125kT of matter. For comparison, if you made the 1,000km sail out of heavy duty kitchen foil, it would have a mass of 50MT. So if you don't get into hyper-relativistic speeds, you'll only lose a small amount of your velocity to drag on such a mission.

On the net, my only correction to above would be replacing a laser with a maser, and this is with help of hindsight that we've developed way better means of manipulating microwaves compared to what we can do with optics at relevant power densities.

There have been more recent proposals for probes with a lot more acceleration and, therefore, much shorter travel distance before they start coasting. These can be done with optical lasers, since you only need to project the beam, maybe, a few AU. Of course, these designs assume no return trip and either a rapid fly-by of target system or a completely independent braking mechanism.

[JoeSchmuckatelli]

I posted a 'game theory' question in The Lounge section for anyone willing to help me.  I like poker, and understand that certain strategies 'win over time' even if they lose in a given hand... so I'm the non-math guy trying to apply that concept in a different game.  Appreciate any assistance.

[ARS]

On 5/18/2021 at 5:50 AM, Spacescifi said:

A shield made of lasers?! A shield that shields against lasers?

Now that makes me think, if an energy shield is really made out of lasers, does it really shield against actual laser? Against solid projectiles and missiles I can accept it as they simply vaporized when in contact with the shield, but against lasers? Lasers will simply pass through each other unimpeded, although their point of intersection may experience any constructive or destructive interference between the two beams depending on the characteristics (wavelength and phase) of the lasers involved, but does that interference sufficient to neutralize incoming laser attack (in ship-to-ship combat scale)? Especially since the laser used against those shielded by energy shield in the first place is usually ship-grade high-power laser weapon

[kerbiloid]

That's exactly why I wasn't answering the initial question, lol.
Lasers pass through any magnetic field except of somewhat apocalyptictic strength, while SW deflectors look protecting from the lasers.

Probably, one should form and support some kind of partially ionized opaque dust cloud.

(Ionized - to keep it around the ship by a magnetic field and to make it more opaque).

Also the dust could protect from speedy projectiles.

Finally, the space battle will looks like a fight of two swarms of bees.

Edited May 19, 2021 by kerbiloid

[JoeSchmuckatelli]

Since we've been in the realm of the fantastic for a while... 

In SF most warp or hyper drive tech is there to solve the distance or 'space' problem in getting from one system to another - getting past the light speed limit found in Relativity.

Since Relativity ties space and time together into spacetime, is there any theoretical way to 'solve for time' (rather than solving for speed /distance) that might get future explorers to and from a distant system in a similar manner? 

 

(i.e. Are SF writers looking at the wrong side of the equation?) 

[Spacescifi]

1 hour ago, JoeSchmuckatelli said:

Since we've been in the realm of the fantastic for a while... 

In SF most warp or hyper drive tech is there to solve the distance or 'space' problem in getting from one system to another - getting past the light speed limit found in Relativity.

Since Relativity ties space and time together into spacetime, is there any theoretical way to 'solve for time' (rather than solving for speed /distance) that might get future explorers to and from a distant system in a similar manner? 

 

(i.e. Are SF writers looking at the wrong side of the equation?) 

Orbiting a rogue moving black hole could do it.

Yet there is a limit to how close you can get unless you are SF enough to survive that too.

That limits your time warp.

 

Now I have a question!

 

Do all 1g planets have atmospheres even if they are not habitable?

I tend to think it may not always be true, but is more often than not, since 1g is more than strong enough to hold down atmosphere as we will know.

Edited May 19, 2021 by Spacescifi

[tomf]

31 minutes ago, Spacescifi said:

 

Do all 1g planets have atmospheres even if they are not habitable?

I tend to think it may not always be true, but is more often than not, since 1g is more than strong enough to hold down atmosphere as we will know.

It's going to depend on the temperature, close in to a bright star with a strong wind it is going to be hard to hold on to anything

Edited May 19, 2021 by tomf

[JoeSchmuckatelli]

37 minutes ago, Spacescifi said:

 

Do all 1g planets have atmospheres even if they are not habitable?

I tend to think it may not always be true, but is more often than not, since 1g is more than strong enough to hold down atmosphere as we will know

Atmosphere is a difficult issue from what I can tell - and we have so few terrestrial 'worlds' to view closely. 

From a simple 'can 1g hold gas to the surface' standpoint - yes.  But how much and the composition is decided by other factors. 

A big factor seems to be the degree to which the world is seismically active.  Another factor is (which may be related) if the world has a magnetosphere to shield it from solar wind.  Temperatures, distance from the star and where it formed are also factors speculated about. 

Earth has a moon and volcanoes and a dynamic atmosphere.  Venus has volcanoes and an atmosphere.  Mars, seismically inactive, no magnetosphere and very little atmosphere.  Titan?  Atmosphere. 

Pluto even has some atmosphere, even if only periodically and I've read that there is a tiny thin 'atmosphere' on the Moon - even if it's only temporary and captured gas from earth that's easily depleted by the solar wind. 

But I don't think you can make a rule that any terrestrial planet around any given star will have an atmosphere of a given density based solely on the degree of g. 

 

Edited May 19, 2021 by JoeSchmuckatelli

[Admiral Fluffy]

3 minutes ago, JoeSchmuckatelli said:

Do all 1g planets have atmospheres even if they are not habitable?

 

I don't think so, because the sheer number of planets, including rouge planets, means that some will and some wont.

[kerbiloid]

40 minutes ago, Spacescifi said:

Do all 1g planets have atmospheres even if they are not habitable?

Enough close to the star - yes.

Consisting of evaporated metals.

***

Upd.
O2 = 32 g/mol, so probably consisting of Fe, Si, and O2. Because Al, Mg, etc are lighter

Later - consisting of iron.

Edited May 19, 2021 by kerbiloid

[SpaceFace545]

12 minutes ago, kerbiloid said:

O2 = 32 g/mol,

Do you wanna do some dimensional analysis with me?

[magnemoe]

44 minutes ago, Admiral Fluffy said:

I don't think so, because the sheer number of planets, including rouge planets, means that some will and some wont.

Well Venus has quite an atmosphere, Earth has one, if you go outwards its easier to get one but you will easy end up as an gas giant or an Neptun so you are not an 1 g planet anymore because all the atmosphere. 

Now if you get very close to the star as in the easy to detect exoplanets you could easy loose the atmosphere. However you might get an new metallic one. 

[kerbiloid]

49 minutes ago, SpaceFace545 said:

Do you wanna do some dimensional analysis with me?

?

v ~sqrt(T/Mr)

The lesser is the molar mass, the greater is thermal speed, so lightweight atoms/moleculas escape sooner.

O2 = 32, Si = 28, Fe = 56

Al = 23, Mg = 24, C = 12

So, when the crust and mantle will be evaporating and become the atmosphere, surrounding the pure iron-nickel planet (in case of Earth = 1/3 of the Earth mass), other components of the atmosphere lighter than O2, Si, Fe, will escape sooner.

Edited May 19, 2021 by kerbiloid

[SOXBLOX]

3 hours ago, tomf said:

It's going to depend on the temperature, close in to a bright star with a strong wind it is going to be hard to hold on to anything

And far out, everything will be frozen. Unless your atmosphere is too huge to freeze. In which case you have a gas giant.

[JoeSchmuckatelli]

You know those rotating restaurants that used to be so popular?   Where you step onto the floor at a walking pace but near the window you get a 360 degree view by the time lunch is over? 

Given that astronauts suffer bone loss and other health problems in the microgravity of orbit - how feasible would it be to take the idea of the rotating restaurant and build a facility on earth where astronauts could live and work for a period before going to space at 1.2 or 1.5 g prior to departure to build up bone mass and maybe prevent the problems? 

 

Basically - take this concept,

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

but build it on the surface as a training and work facility. 

(logically, I know we can do it - what I'm asking is whether it would help) 

[Admiral Fluffy]

1 hour ago, JoeSchmuckatelli said:

Given that astronauts suffer bone loss and other health problems in the microgravity of orbit - how feasible would it be to take the idea of the rotating restaurant and build a facility on earth where astronauts could live and work for a period before going to space at 1.2 or 1.5 g prior to departure to build up bone mass and maybe prevent the problems? 

 

Makes since, but I'm not sure how you would keep the astronauts on the floor

[JoeSchmuckatelli]

56 minutes ago, Admiral Fluffy said:

Makes since, but I'm not sure how you would keep the astronauts on the floor

Presuming that you are dealing both with the normal gravity of Earth and the centrifugal force of the rotating habit - setting the floor at some angle between 0 and 90 should do it. 

You enter at the hub, and then with some creative design work, you can go from walking to stairs to ladders that get you to the work stations.  Heck - you might want two or more 'floors' with different 'g' for acclimatization or effect 

[kerbiloid]

The "medical" centrifuge module.

Was planned for both ISS and ROSS, both times postponed/cancelled.
For ROSS - in expandable module.

Was proposed in the ESA Martian ship draft project.

Diameter: 6- m.

(Inside the pressurized hull).

[kerbiloid]

Wooden sats...

I knew, it some day would happen...

https://techxplore.com/news/2020-12-japanese-pairing-wood-satellites.html

Next step: sats made of bamboo sticks, silk, and rice paper...