Math of Exobiology: Exploring Interstellar Travel Possibilities

[Fizica7]

I see there are a few similar topics in this subforum so I guess this is the best place for this topic... Unless there's a dedicated exo/astrobiology subforum.

Keeping it very simple:
a) we are sentient multicellular organism on a random planet in a random galaxy.
True or false...
b) we are the only ones everywhere.
True or false...

If a and b are true then we are the rarest thing in the universe.
If a is true and b false then we contemplate c)

c) a vehicle coasting at considerable fractions of c ( v/c ), then according to relativity the t' (traveler time increment) to t (observed time increment) is:

v/c ---- t'/t
0.0 ---- 1
0.866 ---- 0.5
0.900 ---- 0.436
0.990 ---- 0.141
0.999 ---- 0.0447
0.9999 ---- 0.01414
0.99999 ---- 0.00447
0.999999 ---- 0.00141
1 ---- 0

Ignoring 1c and 0, the last line of the table for obvious energy requirements, if vehicle is traveling at 0.866c it will traverse 1 light year in 0.5 years... aka vehicle appears to travel for 1 real Earth clock year, but inside occupant clock only measures 0.5 year of elapsed time, 6 months.
If it's 0.999999 then 1 light year will effectively last 0.00141 years or 12.5 hours onboard, while the destination wait 1 actual year for vehicle to arrive.
If these calculations are correct then I don't see why distances are a problem for interstellar travel as long as the traveler has no intention of ever returning home to find every loved one has aged... If exploration is the ultimate objective then then onboard time is obviously insignificant.

edit: I've inserted some lines in that "table" cause I'm not sure how it looks in desktop, on my Android it doesn't allow desktop mode for the forum.

 

[mfb]

How do you accelerate to 0.999999 c?

If acceleration is not an issue at all, then interstellar travel is not hard. Still with the caveat that you won't ever see anyone you know again, apart from those on the same ship. Unless we find ways to make humans live significantly longer, or just go to the nearest stars within a lifetime.
But that's like saying winning any competition is not hard - just beat all opponents, the rest (??) is trivial.

 

[Fizica7]

100g for minutes/days/weeks(depending on ly distance) acceleration then coasting at 1g, then reverse 100g before destination.

Edit: Not necessarily 100g, but for example
5g 275 days= 0.999c...or
10g 225 days=0.9999c...or
20g 110 days= 0.9999c etc.

 

[Alltimegreat1]

It's an interesting idea, but nothing we can reasonably expect to become feasible in the next 100+ years. We can, however, take action right now and begin seeding nearby celestial objects with microscopic life. As discussed in other posts, this could involve releasing hardy microbes on both poles of Mercury. We must ensure that every planet, moon, and asteroid within reach fulfills its maximum potential for sustaining complex life forms.

 

[phinds]

100g for minutes/days/weeks(depending on ly distance) acceleration then coasting at 1g, then reverse 100g before destination.

Have you done ANY research on how many G's the human body can stand and for how long?

 

[Ophiolite]

Have you done ANY research on how many G's the human body can stand and for how long?

Or, indeed, quite what propulsion system is going to deliver this acceleration for a sustained period. Generation ships would be more plausible a solution.

 

[Fizica7]

Have you done ANY research on how many G's the human body can stand and for how long?

The amount people can withstand without blacking out depends on the direction of the g-loading.
Also a very small person, like the world's smallest person from Guinness records, say 1m tall will feel g-loading half that of a person that is 2m tall, no ?
And as for the propulsion, are we talking spherical acceleration type field or virtual static field(magnetohydrodynamic) ? Or even better 2 fields superimposed(variable) to cancel out the g-loading on crew?

Edit: What's this paper from NASA about?
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjSjYjUrqrLAhXMOhQKHbkHANEQFgghMAA&url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800010907.pdf&usg=AFQjCNH24VmCX4a-WUE6hviVoZ4B-TNo8Q&sig2=VPD4Jm0NSyKS37PKhMGXLQ

Edit: And what I'm unsure of if it's an actual real quote from an undisclosed "Dr. B" is:
"We also have the next level of propulsion, it is called virtual field, which are called hydrodynamic waves…”.

 

[phinds]

The amount people can withstand without blacking out depends on the direction of the g-loading.

We're not talking about blacking out we're talking about sustained level G force.

Also a very small person, like the world's smallest person from Guinness records, say 1m tall will feel g-loading half that of a person that is 2m tall, no ?

No, I can't even begin to figure how you came to that conclusion.

And as for the propulsion, are we talking spherical acceleration type field or virtual static field(magnetohydrodynamic) ? Or even better 2 fields superimposed(variable) to cancel out the g-loading on crew?

Now you're getting into magic not physics and that's not a good idea on this forum.

Edit: What's this paper from NASA about?
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjSjYjUrqrLAhXMOhQKHbkHANEQFgghMAA&url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800010907.pdf&usg=AFQjCNH24VmCX4a-WUE6hviVoZ4B-TNo8Q&sig2=VPD4Jm0NSyKS37PKhMGXLQ

Edit: And what I'm unsure of if it's an actual real quote from an undisclosed "Dr. B" is:
"We also have the next level of propulsion, it is called virtual field, which are called hydrodynamic waves…”.

 

[Fizica7]

I'll get back with the thing about passenger height.

What about that paper from NASA(link is downloading straight from NASA server) which is impressive:
https://www.google.co.uk/url?sa=t&r...UE6hviVoZ4B-TNo8Q&sig2=VPD4Jm0NSyKS37PKhMGXLQ

Also is the info here reliable ?
https://en.wikipedia.org/wiki/Field_propulsion

 

[mfb]

100 g are both unrealistic and unnecessary. Anyway, it is not about the passengers, it is about the propulsion system.

Accelerating a single human to 0.999999 c needs an energy of about 5*10²¹ J. That's the current world energy consumption of 10 years. And this number is only the single human, not the spacecraft , food and so on.
To make things worse, there is no way to accelerate a spacecraft in such a way that all the energy goes to the spacecraft . Even if you would convert the whole mass of all matter in the solar system (including the sun) to a massive nuclear rocket with 100% efficiency, it would not be sufficient to reach that speed.

Also is the info here reliable ?
https://en.wikipedia.org/wiki/Field_propulsion

The parts that are not overly speculative (and marked as those) yes, but those do not allow accelerations to such high speeds.

 

[Fizica7]

What about that NASA paper? It's also mentioned in the wiki article.
Is nobody curious to see what actually it contains and give a layman description in a sentence or two?

 

[mfb]

It is from 1979. It mentions in the abstract (and everywhere in the main text) that the concept is highly speculative. If something would have been behind the idea, there would be follow-up studies.
They even put "propulsion" in quotation marks.

 

[Fizica7]

Is that kind of study normal for those years, or was it ahead of its time but classified until recently? I mean does anyone remember such thermology being used in the '70s in public research institutions?
I've heard somewhere that the military/black projects are 30-50 years ahead of the public ones... any truth in that?

Edit: Aren't follow up studies in effect the ones NASA is doing with solar flare activity ?

 

[mfb]

A lot of weird things get studied all the time, and then get dropped - because they do not work.
"I've heard somewhere" is not a reliable source.

 

[Fizica7]

Yeah I know it's not reliable... that's why I'm asking those with possible connections if, and only if, there is some truth to that.
So the paper mentions magnetic line merging and something to do with solar flares and there being a very big unexpected output of energy or something at the point of the magnetic lines merging.
Doesn't NASA have like at least one dedicated camera that monitors solar flares 24/7? They've been doing it for years.

 

[mfb]

There are tons of cameras monitoring the sun. Including the side that is not visible from Earth, via the STEREO satellites (or currently satellite, as connection to one doesn't work).
I don't see how this would be relevant to the topic.

Yeah I know it's not reliable... that's why I'm asking those with possible connections if, and only if, there is some truth to that.

What do you expect? Someone joining the discussion with "yeah all those rumors are true, I'm working on [whatever] which is so top secret so I cannot tell you about its existence"?
Sure, some military research projects develop things that you cannot buy on the market. But you cannot be decades ahead with projects, simply because military research relies on civil research way too much.

 

[Fizica7]

Accelerating a single human to 0.999999 c needs an energy of about 5*10²¹ J. That's the current world energy consumption of 10 years.

What does that mean in therms of the best source of energy like matter antimatter annihilation? How many kg/tons ?

 

[mfb]

With matter/antimatter annihilation and if you magically manage to fully convert it to photons that leave the rocket in a collimated way, you would still need something like 1500 times the payload mass as fuel, half of it antimatter. And that's only the acceleration part. Want to decelerate? 3 million times the payload mass.

2*10²⁵ J. The world energy consumption of 40000 years.
With current efficiencies of antimatter production, more like a few trillion years of the current world energy consumption.
Again, just for a single human body (of 80 kg, but a factor of 2 doesn't really matter here).

Can we agree that this is a problem?

 

[Fizica7]

Why accelerating is 1500 times and decelerating 3 mil times ?
Edit : is it because of the increase in energy(kinetic?) you get by approaching c?
I mean if you actually wrote 3 mil seriously... Then say it takes 1500 units of energy to spin a flywheel close to c, then when I want to slow it down via an electric generator, I get 3 million units of energy? That's a deal I could take : )

 

[mfb]

It is a result of the rocket equation. A rocket is not a flywheel, you have to carry around fuel. To change the velocity by 0.999999 c, you have to use 1499/1500 of the rocket mass as reaction mass. Starting with 3 million times the payload, you reach the speed with 2000 times the payload mass - sufficient to change your speed by 0.999999 c again (with some safety margin). You need most of the fuel to accelerate more fuel.

There are some concepts that avoid carrying around fuel, but those are all highly speculative, and most of them won't work if you go somewhere for the first time because no infrastructure exists there yet.

 

[Fizica7]

I just don't see it... You start out with a total 1500 tons, 1 ton ship/crew/instruments and 1499 tons fuel. You get to 0.999999c then you have to decelerate so you're thinking... oooops have no fuel left to decelerate... so you go back in time lol and put an extra 1499 tons of fuel for decelerating, only now you weigh 2999 tons... So wait... Your initial 1499 tons won't cut it to accelerate to 0.999999 so you add more fuel instead of initial 1499 but then you'll need even more fuel than 1500 to decelerate... do we have a catch 22?

Edit: can't we use a solar sail in reverse like an air brake... sure space is empty but not a perfect vacuum... so even the smallest particles, striking out "brake parachute", will either rip it to shreds or get us from 0.999999 to maybe 0.99 still a huge difference on the deceleration fuel needed, no?

 

[mfb]

You get to 0.999999c then you have to decelerate so you're thinking... oooops have no fuel left to decelerate... so you go back in time lol and put an extra 1499 tons of fuel for decelerating, only now you weigh 2999 tons... So wait... Your initial 1499 tons won't cut it to accelerate to 0.999999 so you add more fuel instead of initial 1499 but then you'll need even more fuel than 1500 to decelerate... do we have a catch 22?

Sort of. But you can directly consider the 1500 tons as "payload" you have to accelerate to 0.999999c, in order to be able to decelerate 1 ton later.
If accelerating 1 ton needs a 1500 ton rocket, then accelerating 1500 tons needs a 1500^2 ton rocket.

Edit: can't we use a solar sail in reverse like an air brake... sure space is empty but not a perfect vacuum... so even the smallest particles, striking out "brake parachute", will either rip it to shreds or get us from 0.999999 to maybe 0.99 still a huge difference on the deceleration fuel needed, no?

Oh well, realistic conditions make it even worse, because you need a ridiculous amount of shielding against anything. Every grain of sand impacts with the energy of a nuclear weapon.

 

[Fizica7]

Well this is interesting... so a ship impacting a grain of sand at 0.999999 is like a nuke... what about the impacting something 1 mil times smaller in mass like a single particle... surely we child have the front of the ship armored to support a RPG blast... then at the destination we manufacture a new front armor and replaced the damaged one... like replacing the used disk brake on a car.
Problem is if we send a single particle(or more) ahead of us, would we be able to deliberately rear end it out would it still be going 0.999999 or would it surpass that and get maybe 0.999999999 or 1? But really concerned with that... I'm hoping there is a particle which is so massive of cumbersome that it naturally never travels at c or even 0.9 but maybe 0.899 so then even if we true it in front, it will somehow lose speed and we'll get our brake.

 

[mfb]

Individual particles hitting will lead to radiation damage in the material, most notably at the front.

Problem is if we send a single particle(or more) ahead of us

It will fly off and then it's gone. Where is the point?

But really concerned with that... I'm hoping there is a particle which is so massive of cumbersome that it naturally never travels at c or even 0.9 but maybe 0.899 so then even if we true it in front, it will somehow lose speed and we'll get our brake.

That does not make sense.

Note that there is no absolute speed. Speed is always relative. And particles do not care about arbitrary reference frames. The physics is the same in every reference frame.

 

[Fizica7]

Individual particles hitting will lead to radiation damage in the material, most notably at the front.
It will fly off and then it's gone. Where is the point?
That does not make sense.

Note that there is no absolute speed. Speed is always relative. And particles do not care about arbitrary reference frames. The physics is the same in every reference frame.

I wanted to write not really concerned with that... but my predictive text...
Edit: and if we trow it in front.

 

[Fizica7]

Right... I got it... this is pure genius.

This is how you decelerate without fuel at the end.

From the example above, we only take the reinforced front end that can withstand minor impacts... we discard throwing a particle ahead of us cause suppose we never manage to bump into it.

What we do is send 2 particles ahead of us, preferably electron-positron, they annihilate, create a little plasma/shower of particles/etc and we bump into those and decelerate.
Edit: I mean when stuff gets smashed in the lhc, the resulting particles fly omnidirectional sort of... so the 2 particle we send a few cm ahead of us, will annihilate and at least 40-50% of the particles emerging will face towards us.

 

[mfb]

That needs fuel. And it is exactly the idea of a pure antimatter/matter rocket, which leads to the fuel to payload mass ratios I posted. You don't need to shoot them out, let them annihilate in some sort of nozzle.

 

[bcrowell]

Any method of interstellar exploration requires technology that's multiple centuries ahead of what we have now. With that kind of technological advance, it doesn't seem reasonable to me to imagine that our species would remain bound by the physiological limitations of a Homo sapiens body. (Science fiction tends to depict future humans like present-day humans simply because of the need for drama and characters with whom we can identify.) Therefore I don't see any point in worrying about limits on the human body's physiological ability to withstand high accelerations.

Over the course of, say, another 500 years of technological progress, I think it also gets very hard to anticipate what fundamental scientific breakthroughs might happen. As a random example, maybe we will find loopholes in the laws of thermodynamics, as we presently understand them.

So although it's interesting to try to work this out with foreseeable technology and human bodies, I don't think that's realistic.

 

[mfb]

Any method of interstellar exploration requires technology that's multiple centuries ahead of what we have now.

Show a smartphone to someone from 1916: it would appear like pure magic to them - today you can buy it in a shop. And scientific progress today is faster than in 1916.
I would not trust any prediction about human technology more than 100 years into the future.

 

[bcrowell]

Show a smartphone to someone from 1916: it would appear like pure magic to them - today you can buy it in a shop. And scientific progress today is faster than in 1916.
I would not trust any prediction about human technology more than 100 years into the future.

Your example is not really a good one IMO. I would tell them it's a handheld device containing a camera and radio transmitter and receiver, and I think they would immediately understand that. It also has the ability to let you read books, watch moving pictures, and play arcade games. 100 years is really not that long. It's been 47 years since Apollo 11, 113 years since the Wright brothers.

I agree that extrapolation far into the future is going to be unreliable. However, it seems silly to imagine that as hundreds of years pass, the physical sciences will make the kind of fantastic progress required for interstellar travel, while the biological sciences stand still so that we are still bound by limitations on the human body such as heart disease.

 

[bahamagreen]

Couple of things...

1] All the discussion about getting up close to c traveling speed might be better based from the idea of maintaining just 1g of acceleration. Without accounting for relativistic velocity addition, just plain 1g for one year just about reaches c, so with taking into account the relativistic velocity addition one can make a 500ly trip accelerating and decelerating to arrive in about 12 years passenger time.

There is a space travel calculator here to play with some assumptions...

2] While experiencing 1g is nice for the trip, experiencing the exposure to hard radiation is a problem. Heavy shielding becomes a further problem, but the human genome project is way ahead of schedule and the solution to radiation damage may turn out to be not shielding but simply continuous repair (medical nanobots, or similar).

3] Not yet space traveling, we continue to hold a tight grasp to the comfort of being in a particular "time"... clearly a serious space traveling society must learn to be comfortable with the idea that all one's possible connections must be local, at whenever the encounters occur...

 

[bcrowell]

experiencing the exposure to hard radiation is a problem. Heavy shielding becomes a further problem, but the human genome project is way ahead of schedule and the solution to radiation damage may turn out to be not shielding but simply continuous repair (medical nanobots, or similar).

If technology is such that you can accelerate continuously at 1 g for 20 years of proper time, then the technology is pretty godlike -- many centuries more advanced than anything we have. The amounts of energy involved are insane. Given that, I can't imagine that exposure to ionizing radiation is such a technologically difficult problem. We have plenty of perfectly reasonable ways of dealing with it using present or near-future technology.