Wow... Our Solar System Is HUGE

[Spacescifi]

The oort cloud is a region where the sun's gravity is more or less null and void.

The oort cloud is about 2 LY accross if I read correctly.

It would take the Voyager probe 300 years of inertia driftng just to reach the edge of the oort cloud, but by then it's instruments will be long dead anyway.

It is the edge of the solar system if you consider where the sun's influence ends.

So if you had a scifi 1g constant acceleration propellantless drive how long would it take to reach the oort cloud? From low Earth orbit?

My guess? Months. Or over a month at the fastest.

 

Reason? In scifi it could be that interstellar wormholes are only formed where star gravity is virtually nonexistent, requiring travel to the edge of solar systems.

Why go through the trouble of such long travel times? Makes near lightspeed RKV attacks via a wormhole at the edge of the solar system easier to guard against.

Plus if it hits one of those ice rocks it's probably mission killed anyway.

It also demonstrates that leaving the solar system for another at 99% lightspeed is not easy even if you can go that fast.

It is rather hard to dodge rocks in your path at that speed, and we are talking TWO light years worth of rocks scattered about. Any one of which could ruin your lovely trip.

Like you either need an UBER deflector shield to protect a vessel from asteroids or need to go in guns blazing with several antimatter particle beams to blast the rocks before they reach you.

As per the usual... offense is easier to do than defense... it would take a truly scifi deflector field to deflect rocks when you're going at 99% lightspeed.

 

Edited July 26, 2020 by Spacescifi

[KerikBalm]

The Newtonian equation would be x=1/2 a t^2

For simplicity, a = 10. Distance travelled in t seconds is 5*t^2

Do the math yourself

[KSK]

1 hour ago, Spacescifi said:

The oort cloud is about 2 Light Years accross if I read correctly.

It would take the Voyager probe 300 years of inertia driting just to reach the edge of the oort cloud, but by then it's instruments will be long dead anyway.

It is the edge of the solar system if you consider where the sun's influence ends.

So if you had a scifi 1g constant acceleration propellantless drive how long would it take to reach the oort cloud? From low Earth orbit?

My guess? Months. Or over a month at the fastest.

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.

Edited July 26, 2020 by KSK

[Spacescifi]

3 minutes ago, KSK said:

I'd say years. The clue is kind of in the name of the distance units you're using.

 

So much for that idea then LOL!

Too long for plot.

No problem I can use older ideas.

 

Yet it is fascinating how hard space travel is even with scifi abilities thst are impossible.

Long story short... we NEED FTL warp or a hyperdrive or wormhole analog to ever travel interstellar distances safely and efficiently.

Since if you tried that with constant acceleration... impossible as such currently is... you risk dying here at the oort cloud or in the next solar system's version over.

Wow.

[Guest]

Do note, two years is the "Earth time" time it takes. If we send a spaceship to Alpha Centauri at a significant fraction of speed of light, it will be about four years before it gets there, and eight before we hear back from it. However, for the crew, the trip could only take a few days. This is known as time dilation. Funnily enough, what this means that when looking from the ship, the distance to your destination will shorten as you accelerate. This is also a real effect, and is known as Lorenz contraction. A trip can be as short as you want in "Ship time", constrained only by the spaceship itself. However, from outside the ship, it will always be limited by speed of light.

However, be very careful when using that in your stories. Unless you really understand relativity at university level at least, it's easy to make mistakes and come up with something that looks very silly to someone who does have that kind of understanding. So if you want relativistic travel, research special and general relativity very thoroughly. It's an extremely nonintuitive subject that requires some getting used to, and you would ideally understand the mathematics that make it so, as well (they actually help you picture it).

[Spacescifi]

8 hours ago, Dragon01 said:

Do note, two years is the "Earth time" time it takes. If we send a spaceship to Alpha Centauri at a significant fraction of speed of light, it will be about four years before it gets there, and eight before we hear back from it. However, for the crew, the trip could only take a few days. This is known as time dilation. Funnily enough, what this means that when looking from the ship, the distance to your destination will shorten as you accelerate. This is also a real effect, and is known as Lorenz contraction. A trip can be as short as you want in "Ship time", constrained only by the spaceship itself. However, from outside the ship, it will always be limited by speed of light.

However, be very careful when using that in your stories. Unless you really understand relativity at university level at least, it's easy to make mistakes and come up with something that looks very silly to someone who does have that kind of understanding. So if you want relativistic travel, research special and general relativity very thoroughly. It's an extremely nonintuitive subject that requires some getting used to, and you would ideally understand the mathematics that make it so, as well (they actually help you picture it).

 

No intention to go full relativistic.

Not once I learned that solar systems carry their own WHIPPLE SHIELDS to kill incoming relativistic masses flying at ludicrous speeds.

2 LY of oort cloud dodging or blasting is hardly a nontrivial concern LOL.

 

Make that 4 yrs or more if you count the next system over.

I have a sneaking suspicion that most solar systems have oort clouds, some with more rocks, some with less.

Edited July 26, 2020 by Spacescifi

[KerikBalm]

5 hours ago, Spacescifi said:

Long story short... we NEED FTL warp or a hyperdrive or wormhole analog to ever travel interstellar distances safely and efficiently.

No, you don't.

You just need it for a plot that goes from settings in different star systems in short times.

You don't need FTL to get to epsilon eridiani, much less alpha centauri.

[kerbiloid]

Also, a sociopathic space nomad never needs an FTL, he is happy with unlimited source of fuel onboard to get ultrarelativistic, and never returns to the places already visited.

[Kerbart]

6 hours ago, 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.

But then, it’s two light years across, not away. So the distace to travel is much smaller.

And while relativistic effects do make it harder to get closer to c, they also dilate time, so in ship time it wouldn’t take nearly that long, I assume. Although a round trip to the edge of the Oort Cloud may leave you finding a long-dead Earth on return, with the last traces of civilization having vanished eons ago.

[pmborg]

7 hours ago, Spacescifi said:

The oort cloud is a region where the sun's gravity is more or less null and void.

The oort cloud is about 2 LY accross if I read correctly.

It would take the Voyager probe 300 years of inertia driftng just to reach the edge of the oort cloud, but by then it's instruments will be long dead anyway.

It is the edge of the solar system if you consider where the sun's influence ends.

So if you had a scifi 1g constant acceleration propellantless drive how long would it take to reach the oort cloud? From low Earth orbit?

My guess? Months. Or over a month at the fastest.

 

Reason? In scifi it could be that interstellar wormholes are only formed where star gravity is virtually nonexistent, requiring travel to the edge of solar systems.

Why go through the trouble of such long travel times? Makes near lightspeed RKV attacks via a wormhole at the edge of the solar system easier to guard against.

Plus if it hits one of those ice rocks it's probably mission killed anyway.

It also demonstrates that leaving the solar system for another at 99% lightspeed is not easy even if you can go that fast.

It is rather hard to dodge rocks in your path at that speed, and we are talking TWO light years worth of rocks scattered about. Any one of which could ruin your lovely trip.

Like you either need an UBER deflector shield to protect a vessel from asteroids or need to go in guns blazing with several antimatter particle beams to blast the rocks before they reach you.

As per the usual... offense is easier to do than defense... it would take a truly scifi deflector field to deflect rocks when you're going at 99% lightspeed.

 

 

Sometimes an image talk more than a thousand words:

 

[StrandedonEarth]

6 hours ago, Dragon01 said:

If we send a spaceship to Alpha Centauri at a significant fraction of speed of light, it will be about four years before it gets there, and eight before we hear back from it. However, for the crew, the trip could only take a few days. This is known as time dilation.

This effect also leads to the postulation that if relativistic, non-FTL aliens have been visiting Earth throughout history, the same individuals could be returning to visit Earth 10,000 years later. After all, it could only be a few years or decades of ship time to return to Earth after 10,000 years surface time.

Perhaps to see how their genetic engineering experiment is doing...

[Guest]

Even better, it opens up interesting possibilities of human travelers returning to Earth in a different age than the one they left from. Lem's "Return from the Stars" and the first book of Hyperion Cantos both explore variations on this theme, and they're just the ones I can remember offhand (in the latter case there was FTL involved, but it didn't eliminate time dilation). Basically a hard SF time travel story.

Edited July 26, 2020 by Guest

[Spacescifi]

3 hours ago, KerikBalm said:

No, you don't.

You just need it for a plot that goes from settings in different star systems in short times.

You don't need FTL to get to epsilon eridiani, much less alpha centauri.

 

If you want to avoid flying through lightyears of rocks or come back home without everything changing you do.

 

No one has even addressed how to dodge stuff at 99% lightspeed.

I think even the so-called hard scifi ignores that, pretending that it is a sure thing the vessel will fly through oort clouds without hitting any of them or having to deflect or shoot them. Like, one would either need scifi shield generators or weapons stashed right next to the engines to fire backwards as they retroburn!

Well not all scifi ignore travel collisions.... the movie Passengers showed the interstellar space vessel hit a rock along the way, though it looked as if they had a scifi shield, otherwise one hit should have nuked them.

The time dilation makes it worse, as it gives the ship even less time to make course corrections.

Edited July 26, 2020 by Spacescifi

[Bill Phil]

One light year is around 64 thousand AU - or about 9.6 trillion km. 

It would only take about two years to cross one light year at 1 g assuming you brake halfway through and only using a Newtonian model - but you would get relativistic in that flight.

The Oort cloud is extremely low density - not quite as low as interstellar space but it’s close. 

If you can solve interstellar travel you can solve traversing the Oort cloud.

[kerbiloid]

So, to travel easily through the eons one should have a ship containing his tiny private universe.
To need no returns, and to enjoy the fast travel.

One should start from KSP, Skyrim, Fallout (NV or 4), Mount&Blade, Minecraft mod collecting and adjusting.

Of course, paleontology as hobby is greatly appreciated, as it allows to check hypotheses in real time.
Also don't forget recording videos of same planets, to later sell the records to the aborigines.

Cryocams are also nice. You can catch and sell local dinos.

Also it's good to dig souvenirs under some place to reveal to the locals them thousands of years later.
(Just not too close to the coastline).

[KerikBalm]

24 minutes ago, Spacescifi said:

If you want to avoid flying through lightyears of rocks or come back home without everything changing you do.

Interstellar space is very low density.

If you're going >0.9c, you can get to epsilon eridiani and back in just over 20 years, sure going from 1980's society to 2000's would be quite different, but most people you knew would still be alive.

Time maches in, deal with it - you don't need FTL.

24 minutes ago, Spacescifi said:

No one has even addressed how to dodge stuff at 99% lightspeed.

I think even the so-called hard scifi ignores that, pretending that it is a sure thing the vessel will fly through oort clouds without hitting any of them or having to deflect or shoot them.

Its really really low density, you need to be prepared for dust grains, but not large object collision.

Interstellar hydrogen gas becomes deadly radiation... Ive seen hard sci fi propose a several meter think ice shield at the front of the ship to deal with diffuse gas and dust grains.

Then you've got bussard ramjets that are ionizing everything in fron of them and redirecting gas and dust with a magnetic field.

Hard sci fi doesn't ignore it

[StrandedonEarth]

1 hour ago, Dragon01 said:

Even better, it opens up interesting possibilities of human travelers returning to Earth in a different age than the one they left from. Lem's "Return from the Stars" and the first book of Hyperion Cantos both explore variations on this theme, and they're just the ones I can remember offhand (in the latter case there was FTL involved, but it didn't eliminate time dilation). Basically a hard SF time travel story.

There's also a Larry Niven story dealing with a solo traveller (a revived corpsicle) riding a Bussard ramscoop to the Core and back, returning 50k years later IIRC

[Spacescifi]

59 minutes ago, KerikBalm said:

Interstellar space is very low density.

If you're going >0.9c, you can get to epsilon eridiani and back in just over 20 years, sure going from 1980's society to 2000's would be quite different, but most people you knew would still be alive.

Time maches in, deal with it - you don't need FTL.

Its really really low density, you need to be prepared for dust grains, but not large object collision.

Interstellar hydrogen gas becomes deadly radiation... Ive seen hard sci fi propose a several meter think ice shield at the front of the ship to deal with diffuse gas and dust grains.

Then you've got bussard ramjets that are ionizing everything in fron of them and redirecting gas and dust with a magnetic field.

Hard sci fi doesn't ignore it

 

Low densiity just means the rocks are spread out... it does not mean some of the rocks are not big like this:

 

A cursory google search of oort cloud object size supposes this:

The outer Oort cloud may have trillions of objects larger than 1 km (0.62 mi), and billions with absolute magnitudes brighter than 11 (corresponding to approximately 20-kilometre (12 mi) diameter), with neighboring objects tens of millions of kilometres apart.

Wikipedia › wiki › Oort_cloud

Oort cloud - Wikipedia

 

So maybe you won't hit it, maybe you wiil.

It may be closer to a 50/50 chance than it is 99% certainty you will get hit by a massive object.

But we simply do not know.

Scifi will attempt to 'splain' things meantime lol.

Edited July 26, 2020 by Spacescifi

[wumpus]

21 minutes ago, Spacescifi said:

 

Low densiity just means the rocks are spread out... it does not mean some of the rocks are not big like this:

...

Scifi will attempt to 'splain' things meantime lol.

It also only matters if you can accelerate at anything close to 1g or plan on just doing a flyby survey of another star system that happens to have its own Oort cloud.  Although presumably .1g will get you going at significant speed through the Oort cloud. 

Also hitting even small rocks at relativistic speed will really ruin your day once past a certain (probably very small) size.  Consider Randal Monroe's relativistic baseball: the description of a .9c baseball appears to deliver more energy than a large hydrogen bomb. https://what-if.xkcd.com/1/  Hitting dust will be a problem (and I'm assuming plenty of dust in the Oort cloud).  And as mentioned, hitting hydrogen/helium atoms at relativistic speeds are identical to radiation.  I'd expect much more hydrogen in the Oort cloud.

Don't forget to expect a similar (possibly worse) cloud at your destination.  This could be insolvable to flyby probes.

 

[kerbiloid]

We even don't know if the Oort cloud exists.

The first interstellar thing we must do is sending a telescope perpendicularly to the Solar system to make a selfie. An interstellar selfie stick.

Edited July 26, 2020 by kerbiloid

[KSK]

6 hours ago, Kerbart said:

But then, it’s two light years across, not away. So the distace to travel is much smaller.

And while relativistic effects do make it harder to get closer to c, they also dilate time, so in ship time it wouldn’t take nearly that long, I assume. Although a round trip to the edge of the Oort Cloud may leave you finding a long-dead Earth on return, with the last traces of civilization having vanished eons ago.

True. I do wonder how significant relativistic effects will be given that it still takes several months to get up to a decent fraction of lightspeed, even at a constant 1g acceleration but the calculations involved are beyond my ken.

3 hours ago, Spacescifi said:

The outer Oort cloud may have trillions of objects larger than 1 km (0.62 mi), and billions with absolute magnitudes brighter than 11 (corresponding to approximately 20-kilometre (12 mi) diameter), with neighboring objects tens of millions of kilometres apart.

So maybe you won't hit it, maybe you wiil.

It may be closer to a 50/50 chance than it is 99% certainty you will get hit by a massive object.

But we simply do not know.

Scifi will attempt to 'splain' things meantime lol.

I think space dust, micrometeoroids and the like are one of those things that you either assume that your protagonists can deal with using available technology, or you assume that they luck out and don't get clobbered by a rock that's big enough to kill them. Or a mixture of the two - assume they can deal with dust particles and small rocks (and throw in an explanation of why if you like) but then assume they miss the big rocks.

Is this entirely satisfactory? Probably not if you're looking to create a very detailed and plausible setting, but it's a useful narrative convenience because 'death by space rock' is a really lame way to kill off a character. 

"So what exactly did happen to the enemy flagship, Captain?"
"Uh - we picked up a short duration, high intensity radiation source on the edge of the Oort cloud, Admiral. As far as we can tell, they hit a magnitude eleven object on the way in. Feel a bit sorry for the blighters to tell the truth."
"At least it was quick."
"Aye, sir."

 

Edit.  And sometimes it’s better to use a bit of smoke and mirrors in a story anyway. Acknowledge the problem, provide a reasonably plausible (at least on first sight) answer and don’t worry about the details because digging into the details focuses a disproportionate amount of attention on them.

Using the current thread as an example, it would be weird to give a lot of page time to describing a detailed and setting-consistent way of avoiding or mitigating Oort cloud debris at relativistic speeds - and then hand waving away the problem of getting to relativistic speeds with a throwaway ‘assume we have a constant acceleration propellantless drive.’

 

Edited July 26, 2020 by KSK

[Spacescifi]

3 hours ago, KSK said:

True. I do wonder how significant relativistic effects will be given that it still takes several months to get up to a decent fraction of lightspeed, even at a constant 1g acceleration but the calculations involved are beyond my ken.

I think space dust, micrometeoroids and the like are one of those things that you either assume that your protagonists can deal with using available technology, or you assume that they luck out and don't get clobbered by a rock that's big enough to kill them. Or a mixture of the two - assume they can deal with dust particles and small rocks (and throw in an explanation of why if you like) but then assume they miss the big rocks.

Is this entirely satisfactory? Probably not if you're looking to create a very detailed and plausible setting, but it's a useful narrative convenience because 'death by space rock' is a really lame way to kill off a character. 

"So what exactly did happen to the enemy flagship, Captain?"
"Uh - we picked up a short duration, high intensity radiation source on the edge of the Oort cloud, Admiral. As far as we can tell, they hit a magnitude eleven object on the way in. Feel a bit sorry for the blighters to tell the truth."
"At least it was quick."
"Aye, sir."

 

Edit.  And sometimes it’s better to use a bit of smoke and mirrors in a story anyway. Acknowledge the problem, provide a reasonably plausible (at least on first sight) answer and don’t worry about the details because digging into the details focuses a disproportionate amount of attention on them.

Using the current thread as an example, it would be weird to give a lot of page time to describing a detailed and setting-consistent way of avoiding or mitigating Oort cloud debris at relativistic speeds - and then hand waving away the problem of getting to relativistic speeds with a throwaway ‘assume we have a constant acceleration propellantless drive.’

 

 

Really this thread demonstrates how difficult space travel is... even with impossible tech it is still easy to die.

So it actually encourages making stuff up... not arbitrary... necessary if you want a specific space opera plot.

What IS NOT NECESSARY: Artificial field gravity. Other realistic easier ways to do it, and while 1g constant acceleration is currently a dream, it is at least a concept readers can understand as opposed to a totally arbritary 1g field we make up with arbritray limits imposed. 

Plasma weapons: We know in previous thread why.

Basically, where necessary make stuff up, where reality does a good job... KEEP IT.

 

I actually find the idea of death by space rock amusing.

Could have been very anticlimatic:

"We are doomed! The enemy flagship outclasses us in every way!"

"We were. A space rock hit them along the way. What happens to 9000 ton space battleship when it hits a 500 ton space rock while traveling at 99% lightspeed."

"Boooom!" *Fist bump with an explosion gesture afterward*

Edited July 27, 2020 by Spacescifi

[Kerbart]

4 hours ago, KSK said:

I think space dust, micrometeoroids and the like are one of those things that you either assume that your protagonists can deal with using available technology, or you assume that they luck out and don't get clobbered by a rock that's big enough to kill them. Or a mixture of the two - assume they can deal with dust particles and small rocks (and throw in an explanation of why if you like) but then assume they miss the big rocks.

Larry Niven solved that problem by following a course above the ecliptic. Granted, the Long Shot was flying to the core of the galaxy, but similar concept.

[SOXBLOX]

Outbound trip is two and a half years with a 1g brachistochrone, ~3 years Earth time. 

Don't bother with antimatter beams, at torchship speeds, these beams (assuming you fire forwards) have your velocity relative to the target + the rapidity imparted to the beam. In other words, the rest mass of the particles becomes irrelevant.

[Spacescifi]

2 hours ago, Kerbart said:

Larry Niven solved that problem by following a course above the ecliptic. Granted, the Long Shot was flying to the core of the galaxy, but similar concept.

 

Not sure he did... science is an ongoing thing, and scifi will always need to be updated with new knowledge so long humans are not all knowing... which will likely always be.

If google is correct in what I read, the Oort cloud is a SPHERE.

Flying above the solar disc won't help, as even if you flew above the solar plane you would hit the cloud eventually.

 

It's the cloud. Absent hyperspace, wormholes or some super warp drive... deal with it. The Oort cloud.

Or don't. Which is what we have done so far.

Scifi either should... or find a way to circumvent it I believe.

Rather than ignore it as if it is not out there.

Edited July 27, 2020 by Spacescifi