Wow... Our Solar System Is HUGE

[SOXBLOX]

Of course you need radiators! You misunderstood me. Your radiators do not need shielding from comets because there are not enough comets to fill the Oort cloud to the densities which make a hit remotely probable.

Since you are ignoring this fact (not "sticking with known science"), I was handwaving the issue and asking how you want to "solve" it.

Are you saying moving waste heat to an alternate dimension is your solution? Cool, but Lord Kelvin is glaring at you now.

[Spacescifi]

2 minutes ago, SOXBLOX said:

Of course you need radiators! You misunderstood me. Your radiators do not need shielding from comets because there are not enough comets to fill the Oort cloud to the densities which make a hit remotely probable.

Since you are ignoring this fact (not "sticking with known science"), I was handwaving the issue and asking how you want to "solve" it.

Are you saying moving waste heat to an alternate dimension is your solution? Cool, but Lord Kelvin is glaring at you now.

 

Hey..  you gotta break a few eggs to make a setting remotely plausible.

Another solution would be a fictional gas that literally converts heat into solid mass.

And as you probably are aware, it would take a while before the gas room was chock solid of some solid mass (let's make it ice).

Since energy into mass perfect conversion no heat losses is fiction for us, but it would also be very handy for such a vessel.

 

Edited July 28, 2020 by Spacescifi

[kerbiloid]

I guess, the sequel is about the invaders from another dimension who are trying to stop us from polluting their world with waste heat.

***

Though, as i suggested here a couple of years ago, let's stick out our nozzles into the parallel universe, to get a jetless starship.

***

Btw, we can do this with smoke pipes.

[KerikBalm]

5 hours ago, Spacescifi said:

Even 1% waste heat requires VAST radiators with 1g photon rockets.

Typo, was supposed to be 99.99%

As I said, I can accept super high efficiency before I can accept FTL

5 hours ago, Spacescifi said:

That is about the most energy inefficient drive known theoretically.

Only if you don't count the energy of the rest mass of discarded propellent in other drives.

5 hours ago, Spacescifi said:

The bussard ram jet last I read does not have enough hydrogen in interstellar space to make it practical. 

Sure it does. The local bubble around the sun is lower density than normal, but that just requires a bigger scoop

[Gargamel]

On 7/26/2020 at 10:08 AM, pmborg said:

Sometimes an image talk more than a thousand words:

But the problem with logarithmic scales is that they severely distort scale and distance.   That pic makes it look like our oort cloud extends all the way into AC's "SOI", to misuse a term.   But for those that can read it, it's a nice pic. 

[Spacescifi]

32 minutes ago, KerikBalm said:

Typo, was supposed to be 99.99%

As I said, I can accept super high efficiency before I can accept FTL

Only if you don't count the energy of the rest mass of discarded propellent in other drives.

Sure it does. The local bubble around the sun is lower density than normal, but that just requires a bigger scoop

 

A bigger scoop?

If this is anything like the massive rad fins imply, what... an epic magnetic field that stretches hundreds of kilometers ahead deflecting stuff?

At some point this reality mod became a monstrousity of a vessel... now that it has rad fins longer than some countries and magnetic fields that stretch as far.

 

So yeah... it probably could work... but it turns into such a station sized monstrousity that it hardly looks anything like scifi.

Might as well call it  Rad-ship, which while kinda cool sounding, betrays the fact that the ship's glowing red rad fins dwarf it in size by a factor of a 1000×.

In other words, from a distance the ship will appear tiny compared to it's massive glowing radiator wings.

 

 

Edited July 28, 2020 by Spacescifi

[KerikBalm]

1 hour ago, Spacescifi said:

A bigger scoop?

If this is anything like the massive rad fins imply, what... an epic magnetic field that stretches hundreds of kilometers ahead deflecting stuff?

Yes... but such a thing is also a planet killer. Do you want cheap planet killers?

Also, the magnetic scoop is largely non physical, the magnetic field stretches very wide, less so the actual material structure.

Quote

At some point this reality mod became a monstrousity of a vessel... now that it has rad fins longer than some countries and magnetic fields that stretch as far.

If its a bussard scramjet, you don't need much in the way of radiators, because the fusion need not takeplace within the vessel.

Note that I talk about a Bussard SCRAMjet, not a RAMjet. The ramjets have a maximum speed equal to the exhaust velocity of the reaction products. They scoop up the hydrogen, accelerating it to the same speed as the vessel, then shoot it out the back - although it has been suggested that the process of accelerating the hydrogen up to the speed of the ramjet would generate a massive electrical current, that you might be able to use to accelerate the reaction products further than just their velocity from the fusion reaction...

A scramjet would just direct particles laterally inward, without collecting the particles in the ship/accelerating them to the velocity of the ship, where they would hit each other and fuse, and then the reaction is contained by magnetic fields.

With superconducting magnets (getting literally no resistance, which would generate heat if there was resistance), you would have very little heating from the fusion reaction. You'd still be able to decelerate the incoming H+ stream a little to generate power, but again with superconductors, this should generate almost no heat. Then you'd need to run your ionizing laser, so you basically just need radiators sufficient to deal with your laser's waste heat.

Anyway, this is all just to get a tech that you already stipulated: a drive capable of accelerative at 1g to high fractions of c.

You seem to be arguing against a tech that you wanted yourself...

None of this relates to the fact that traversing the Oort with a very high degree of success with a sort of technology that you specified, is trivial.

[pmborg]

4 hours ago, Gargamel said:

But the problem with logarithmic scales is that they severely distort scale and distance.   That pic makes it look like our oort cloud extends all the way into AC's "SOI", to misuse a term.   But for those that can read it, it's a nice pic. 

We are used to have a vision of Solar System as an island, including Oort Cloud as a final frontier of solar system:

Is nice to see beyond that!

Edited July 28, 2020 by pmborg

[KerikBalm]

8 hours ago, Gargamel said:

But the problem with logarithmic scales is that they severely distort scale and distance.   That pic makes it look like our oort cloud extends all the way into AC's "SOI", to misuse a term.   But for those that can read it, it's a nice pic. 

Well, consider that the alpha centauri system (the binary stars, ignore proxima) has 2x the mass of our sun, Its SOI must be as large as ours, and should in fact be significantly larger

AC is currently 4.4 LY away...

And some estimates of the Oort cloud give it an outer radius of 3.2 LY... that would be in the SOI of AC if the 3.2 figure refers to a sphere (if referring to a disk, then it depends on the orientation of the disk relative to AC)

So, just taking the mass and proximity of AC, I really have to doubt that the oort cloud extends that far.

*** Whelp, I looked at the graphic, and AC seems to be something other than Alpha centauri, but it doesn't get around the objection that the oort cloud would seem to be extending into alpha-Cen's SOI.

[Exoscientist]

On 7/26/2020 at 3:19 AM, KSK said:

I'd say years. The clue is kind of in the name of the distance units that you're using, assuming that your drive isn't FTL capable.

Even at a constant 1g, it takes most of a year to accelerate to lightspeed, assuming that your drive laughs in Einstein's face and that we can ignore relativistic effects

Back of an envelope calculation. V = U + AT, where V = final velocity, u = initial velocity, a = acceleration and t = time.

Assume that we're starting from rest. Which makes no real sense but it does make the calculation easier. Besides orbital velocity is negligible compared to lightspeed.

Therefore V = AT or V/A = T

Final velocity = speed of light = 3x10⁸ ms-1

Divide by 10 for convenience rather than 9.81

T = 30,000,000 seconds = 500,000 minutes, 8,333.3 hours, or 347 days.

 The time is actually shorter, and it doesn't quite reach light speed. It's surprising how fast and how far you can go by just 1 g acceleration:

 A nice way to remember the distance of a lightyear is that it's about 10 trillion km, which equals 1x10¹⁵ meters. Use equation x=1/2 a t², and round off 1 g acceleration as 10 m/s². Then 2x10¹⁵ m = (1/2)*10*t². So t = 2x10⁷. That's 231.5 days. The speed reached is v = at =10*2x10⁷ = 200,000 km/s, less than lightspeed of 300,000 km/s. 

Bob Clark

Edited August 3, 2020 by Exoscientist

[sevenperforce]

On the topic of how big the solar system is, I've always found this to be helpful.

https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html

[kerbiloid]

3 hours ago, Exoscientist said:

which equals 1x10¹⁵ meters.

1x10¹⁶

[SOXBLOX]

So a light year is, to massacre the SI, a "decapetameter". Cool.

[Hannu2]

On 7/28/2020 at 4:56 PM, KerikBalm said:

Well, consider that the alpha centauri system (the binary stars, ignore proxima) has 2x the mass of our sun, Its SOI must be as large as ours, and should in fact be significantly larger

AC is currently 4.4 LY away...

And some estimates of the Oort cloud give it an outer radius of 3.2 LY... that would be in the SOI of AC if the 3.2 figure refers to a sphere (if referring to a disk, then it depends on the orientation of the disk relative to AC)

So, just taking the mass and proximity of AC, I really have to doubt that the oort cloud extends that far.

*** Whelp, I looked at the graphic, and AC seems to be something other than Alpha centauri, but it doesn't get around the objection that the oort cloud would seem to be extending into alpha-Cen's SOI.

There has also been many star flybys with much closer distance in lifetime of solar system. It is strange to think that stars can go through Oort cloud without destroying it during billions of years. Maybe decay is so slow that cloud can stay the whole main sequence lifetime of Sun.

[KerikBalm]

16 minutes ago, Hannu2 said:

 Maybe decay is so slow that cloud can stay the whole main sequence lifetime of Sun.

Or maybe those larger estimates are wrong, based on what it could be if there were never any other nearby stars - and the lower estimates on the order of 0.5 LY are closer to the actual situation.

[Hannu2]

1 minute ago, KerikBalm said:

Or maybe those larger estimates are wrong, based on what it could be if there were never any other nearby stars - and the lower estimates on the order of 0.5 LY are closer to the actual situation.

It may very well be true. Or at least large majority of comets are relatively close orbits and disturbances, like star flybys, regenerate some sparse far population by throwing some objects to very distant orbits from where they slowly dissipate to outer space.  I do not know on what assumptions those estimates of several light years are based on.

[mrfox]

And 1 light nano-second is just about equal to 1 foot

14 hours ago, SOXBLOX said:

So a light year is, to massacre the SI, a "decapetameter". Cool.

And 1 light nano-second is just about equal to 1 foot

[kerbiloid]

So, 1 Universal foot = 29.9792458 cm.

[Exoscientist]

On 8/3/2020 at 2:32 PM, kerbiloid said:

1x10¹⁶

 

 Right. Let me redo that calculation:

Use equation x=1/2 a t², and round off 1 g acceleration as 10 m/s². Then 2x10¹⁶ m = (1/2)*10*t². So t = 63x10⁶ s. That's 730 days. The speed reached is v = at =10*63x10⁶ = 630,000 km/s. This is double lightspeed of 300,000 km/s.

Then you would have to consider relativistic effects. At some point as you approached light speed you would need to expend a huge amount of energy to maintain that speed, still without actually reaching lightspeed. 

Perhaps someone will do the calculation about how long it would appear to take for shipboard time compared to Earthtime for the journey.

Bob Clark

 

 

[munlander1]

On 7/26/2020 at 2:44 AM, Dragon01 said:

However, for the crew, the trip could only take a few days.

This would make the logistics of space exploration so much easier.

I assume that the time dilation doesn't change the radiation levels which would mean less shielding is required for the trip.

A "few day" trip for the crew would also mean the bulk of the provisions could go towards the exploration portion of the mission and not the journey portion.  

[K^2]

3 hours ago, munlander1 said:

I assume that the time dilation doesn't change the radiation levels which would mean less shielding is required for the trip.

It does, actually. In fact, it makes it a lot worse. At sufficient speeds, things that aren't normally a type of ionizing radiation become ionizing radiation. Such things as interstellar dust, then hydrogen and protons of interstellar medium, and if you're going fast enough, light from distant stars. Coming up with a ship that can practically survive hyper-relativistic speeds is a nightmare. 

In fact, if you're traveling at 0.999999994c, which gives you time dilation factor of a little over 9,000, the microwave background radiation turns into X-Ray at an intensity of hugging a blue giant, and at 0.999999999999994c, when time dilation is over 9 million, universe shines gamma radiation at you at an intensity I'm scared to think about.

Now, on a trip to Alpha Centauri, you won't encounter anything nearly so extreme. You just don't have time to accelerate to truly ludicrous speeds. For nearby stars, it's only interstellar dust you have to worry about. Everything else you can take on with modest shielding. But the moment you go beyond our immediate neighborhood, difficulty quickly ramps up.