If EM Drive works, how long to get to nearest Star?

originally posted by: rajas
a reply to: ketsuko

Mmm.. think about nature with only a handful of humans, i would love that..

With only a handful of humans, you would witness the very worst of human nature. Be careful what you wish for.

a reply to: Wide-Eyes

hmmm.. I think you are right

originally posted by: Tripnman
a reply to: muSSang

I'm just riffing here, but couldn't we use some sort of gravitational breaking at the destination end of the trip, slowing down faster than just reversing thrust vectors at the half-way point?

Yeah, the craft would need to find a close planet to do an aerobraking maneuver, and boom. let smaller nav rockets take over.

originally posted by: eriktheawful
a reply to: Tripnman

On the other hand, I'd shrudder to think what would happen to an object traveling that fast to get to the nearest star if it tried aerobraking.

My best hypothesis - to an observer on the ground on a destination planet, the aerobraking would look like the show the Taurids have been putting on for us this week.

a reply to: Tripnman

Nah. Taurids are way slow. Even for meteors. Around 30 km/sec.
Would take a very long time to get where you're going at that rate. Interstellary speaking that is.

I am sure they would calculate at what point to stop accelerating and coast or even reverse thrust the rest of the way, in order to be able to slow down on the other end. Not sure if they calculated that in the 100 year trip hypothesis however.

Just being able to quickly survey all the asteroids in the asteroid belt for resources would surely create a robotic mining industry if not human mining.

Tech like this seems like it could allow us to at least start gathering solar system resources and human outposts could be readily resupplied in timely fashion.

For Probes I would think it would sling shot around while surveying each star system and possibly move on to the next or return to earth all the while broadcasting what it finds. If it detects Earth like planets on the way in to a system it could swing past and return images and sensor data. Of course it would be future generations that would receive the signals but at least humanity would be moving forward.

originally posted by: Iamnotadoctor

originally posted by: Teikiatsu
I imagine a combination of gravity slingshot and solar sail could allow reverse thrusting to be held off until the 2/3 or 3/4 point of the journey.

You have quite an imagination then.

I like to think that I do, especially since this discussion is theoretical. I also prefer to use 'could' instead of 'should' or 'would' when there are unknown variables at the point of destination.

Really interesting thread, just wish I had the math, a constant acceleration of 1 G must build into a huge speed, and then at the half way point a flip over to use the 1 G to slow down, all the while still coasting towards the 'target' , Anyone got a CRAY computer?

Whenever one of these motive design theories comes forward people always start speculating about deep space travel, but they always conveniently leave out one critical (albeit depressing) reality about the whole concept. Deep space travel, no matter how you slice it, will always be a one-way affair.

First, deep space travel at orbital speeds is not really practical for humans because it would take thousands of generations to complete. These speeds are relatively low when compared to the vast distances involved in such a journey. The known hazards of long term space travel would render the travelers to globs of traveling "goo" after such an endeavor reducing the value of such an effort to zero.

Second, and most importantly, inter-stellar space travel really only becomes a reality when / if mankind develops the ability to travel at high percentages of the speed of Light...but there's a catch, a BIG catch. When / if such velocities are achieved, good ol' Relativity kicks in making the 'trip' a value only to the traveler, not to those left behind.

Without getting into too much complex mathematics, high speed travel affects the traveler differently than those left behind. Specifically, the traveler ages at a much different, much slower, rate relative to the non-traveler. And, there's no way to "un-do" this phenomenon when the trip is complete.

The analogy I use to explain this concept to people is as follows:

Let's say mankind miraculously devises a spaceship capable of traveling at 99% the speed of light (we'll forget the mass and energy requirements implications for a moment just for the sake of discussion). So, Buzz Lightyear hops in his new space Ferrari and heads off to Proxima Centauri with hopes to save the human race on Earth. His journey takes him roughly 5 years to get there. Once there, Buzz finds a planet just like Earth, but far more advanced (let's call it Earth Redux). Earth Redux has infinite energy reserves, all diseases have been cured, there is no war, no starvation...and the streets are paved with pure gold. In short, Buzz has found Utopia. The people of Earth Redux give Buzz the comprehensive instruction manual on how to fix Earth. The mission has been a smashing success...so far.

Buzz hops back in his space Ferarri and heads back to Earth with the instruction manual to save mankind. With no time to waste, Buzz accelerates to maximum velocity and races back to Earth. Five years later, when he arrives back on Earth he excitedly jumps out of his spaceship, instruction manual in hand, and exclaims "I MADE IT...I'M BACK!" as he holds the manual to save mankind above his head. Puzzled, Buzz looks around and wonders why no one is there to greet him after his long journey. Stranger still, the birds look different and, and...and, everything looks different. Very different.

You see, the 'Earth' Buzz returned back to is not the same Earth Buzz left 10 years ago. Buzz was only gone 10 years, but in that 10 years (for Buzz) the Earth aged hundreds of years. The Earth Buzz returned to had long since forgotten about Buzz and his journey, Buzz was, at best, some distant memory written down in a history book somewhere. Buzz's great grandchildren had grown old and died while he was gone. The Earth that Buzz returned to had either already unlocked the secrets Buzz brought back with him or had evolved in such a way that those secrets were no longer relevant.

...and Proxima Centauri is a really "close" star (relatively speaking). At further distances this effect is even more pronounced.

a reply to: Xeven

Then I think it would be wiser to explore our solar system first . Maybe we can find this element 115 Bob was talking about..

a reply to: pikestaff

Really interesting thread, just wish I had the math, a constant acceleration of 1 G must build into a huge speed,

Gets you to lightspeed in about a year. But wait...it can't.

Anyone got a CRAY computer?

Excel works fine.

An em drive would put you directly in the sun because the earth is the center of the universe and is protected by a giant ball of fire. Any attempts to use an em drive will cause the sun to suck up any outbound traffic. That is only if you survive the fall from going over the edge of earth.

originally posted by: muSSang
Don't forget you need the same amount of power/thrust to slow it down, so multiply the time of arrival by 2.

strictly speaking this is true but it assumes no other technology is involved in deacceleration. The EM drive is compact and light weight even if it must be scaled up to be a practical primary propulsion drive. this means there is fudge room for the mass of the rest of the package mass of the craft. So there is nothing to preclude you from adding a M2P2 generator the size of a coffee can to the craft. and that means you can use a tens to 100s of kilometer diameter magneto-plasma sail parachute on the deacceleration phase. This works best inside the "helio"sphere of the target star but can significantly boost deacceleration and shorten deacceleration time. And of course you can use it to accelerate at the beginning of the trip too.

originally posted by: Flyingclaydisk
Whenever one of these motive design theories comes forward people always start speculating about deep space travel, but they always conveniently leave out one critical (albeit depressing) reality about the whole concept. Deep space travel, no matter how you slice it, will always be a one-way affair.

First, deep space travel at orbital speeds is not really practical for humans because it would take thousands of generations to complete. These speeds are relatively low when compared to the vast distances involved in such a journey. The known hazards of long term space travel would render the travelers to globs of traveling "goo" after such an endeavor reducing the value of such an effort to zero.

Second, and most importantly, inter-stellar space travel really only becomes a reality when / if mankind develops the ability to travel at high percentages of the speed of Light...but there's a catch, a BIG catch. When / if such velocities are achieved, good ol' Relativity kicks in making the 'trip' a value only to the traveler, not to those left behind.

Without getting into too much complex mathematics, high speed travel affects the traveler differently than those left behind. Specifically, the traveler ages at a much different, much slower, rate relative to the non-traveler. And, there's no way to "un-do" this phenomenon when the trip is complete.

The analogy I use to explain this concept to people is as follows:

Let's say mankind miraculously devises a spaceship capable of traveling at 99% the speed of light (we'll forget the mass and energy requirements implications for a moment just for the sake of discussion). So, Buzz Lightyear hops in his new space Ferrari and heads off to Proxima Centauri with hopes to save the human race on Earth. His journey takes him roughly 5 years to get there. Once there, Buzz finds a planet just like Earth, but far more advanced (let's call it Earth Redux). Earth Redux has infinite energy reserves, all diseases have been cured, there is no war, no starvation...and the streets are paved with pure gold. In short, Buzz has found Utopia. The people of Earth Redux give Buzz the comprehensive instruction manual on how to fix Earth. The mission has been a smashing success...so far.

Buzz hops back in his space Ferarri and heads back to Earth with the instruction manual to save mankind. With no time to waste, Buzz accelerates to maximum velocity and races back to Earth. Five years later, when he arrives back on Earth he excitedly jumps out of his spaceship, instruction manual in hand, and exclaims "I MADE IT...I'M BACK!" as he holds the manual to save mankind above his head. Puzzled, Buzz looks around and wonders why no one is there to greet him after his long journey. Stranger still, the birds look different and, and...and, everything looks different. Very different.

You see, the 'Earth' Buzz returned back to is not the same Earth Buzz left 10 years ago. Buzz was only gone 10 years, but in that 10 years (for Buzz) the Earth aged hundreds of years. The Earth Buzz returned to had long since forgotten about Buzz and his journey, Buzz was, at best, some distant memory written down in a history book somewhere. Buzz's great grandchildren had grown old and died while he was gone. The Earth that Buzz returned to had either already unlocked the secrets Buzz brought back with him or had evolved in such a way that those secrets were no longer relevant.

...and Proxima Centauri is a really "close" star (relatively speaking). At further distances this effect is even more pronounced.

you have time dilation wrong you know. from the rest frame (proximal start point of trip) there is no difference in the passage of time generated by the act of sending a relativistic ship. on the ship (depending on how close to c it travels) the crew experiences something weird. the trip appears to only take (for example) a few weeks despite the ships clocks appearing to run normally. but when they get back they will find that ten years has passed at home. they will have about ten years of food water and other consumables left on thier ship that they did not use.

if time dilation worked the way you think it does we would all be dead and the universe gone right now because all photons travel at light speed including ones travelling from here to alpha proxima and there to here. on top of that there are many natural phenomenon that accelerate massive particles to the applicable range of light speed. these facts coupled with your misunderstanding of relativity would ensure that every point in the universe and thus every earthling in the universe undergo infinite aging acceleration of trillions and trillions of years.

originally posted by: Xeven
I am sure they would calculate at what point to stop accelerating and coast or even reverse thrust the rest of the way, in order to be able to slow down on the other end. Not sure if they calculated that in the 100 year trip hypothesis however.

Just being able to quickly survey all the asteroids in the asteroid belt for resources would surely create a robotic mining industry if not human mining.

Tech like this seems like it could allow us to at least start gathering solar system resources and human outposts could be readily resupplied in timely fashion.

For Probes I would think it would sling shot around while surveying each star system and possibly move on to the next or return to earth all the while broadcasting what it finds. If it detects Earth like planets on the way in to a system it could swing past and return images and sensor data. Of course it would be future generations that would receive the signals but at least humanity would be moving forward.

Some things to consider:

does the trip use acceleration and deacelleration to generate artificial gravity for the crew? if so then you may want to accelerate all the way to the halfway point although there are some alternatives. this is the general assumption for such conjectures.

But other options are available: accelerate as fast as possible to as close to light speed as you can manage at the beginning of the trip and likewise delay deaccelleration at the end of the trip to the last possible moment. assuming an appropriate propulsion system you can accelerate to just short of light speed at one g in about one year (and deaccellereate in a like amount of time.) if your acceleration system can do more than one G it would take less time to accellerate or deaccelelerate. So this trip mode would only add a couple of years to the trip time. Conceivably a human crewed craft could get there in about 7 or 8 years this way. unmanned craft could withstand more Gs and could accelerate and deaccellerate faster. Smart artillery rounds electronics survive a near instant acceleration of thousands of gs.

Maybe we can slow it down with this Electric Sail

"Over periods of months, this small force can accelerate the spacecraft to enormous speeds — on the order of 100-150 km/s (~ 20 to 30 AU/year)."

If we had enough of these I would think we could use them to slow a ship down on way into a star system?

originally posted by: pikestaff
Really interesting thread, just wish I had the math, a constant acceleration of 1 G must build into a huge speed, and then at the half way point a flip over to use the 1 G to slow down, all the while still coasting towards the 'target' , Anyone got a CRAY computer?

What you need is a space travel calculator. Acceleration at 1G makes interstellar exploration very possible, Round time trip time for closest star will take something like 13.5 years (earth time) including deceleration before destination and deceleration on return to earth, For the space travelling occupants it would feel like 10 years because of time dilation.

Stormbringer’s right about the time dilation thing. If you were a photon on a trip from Earth to Alpha Centauri it would seem virtually instantaneous to you, while over 4 years would have passed on Earth.

I think for interstellar travel to be at all practical we will have to engineer a technology capable of exploiting loopholes in currently known laws of physics. Something like discovering some means of navigating spacetime via shortcuts, allowing us to “effectively” surpass the universal speed limit. To achieve ftl performance, though, may require we devise some means of traveling with (or along the edge of) spacetime, rather than through it. Possibly something along the lines of an Alcubierre warp drive? I realize there are currently unanswered questions with the Alcubierre drive design. For one, if we could solve, or work around, the exotic matter/negative energy density problem, it would be a huge breakthrough. Although quantum physics allows for the existence of exotic matter, we’ve only been able to generate very tiny amounts via the Casimir vacuum and the squeezed vacuum technique. Quantum laws place tight constraints on the amount of fluctuation energy that can be passed (loaned) from one region of spacetime to another. It may be the limitations are too servere to allow for generation of the needed negative gravitating energy for an Alcubierre drive to work. Another potential snag is that Alcubierre based his drive design entirely around relativistic principles. Should a theory of quantum gravity emerge, it may very well invalidate the drive design entirely.

And even if we do come up with something similar to an Alcubierre drive, there’s also the matter of communications. That’s a whole other hurdle to get over.

So, I wouldn’t hold my breath as far as interstellar travel goes. The EM Drive, however, sounds like something that might be nice for tooling around the solar system.

a reply to: Xeven

Say 4.3 ly to nearest star (Alpha Centari cluster)
Say 9.5 x 10^15 m
Say 2g acceleration (EM drive benefit is constant engine thrust due to infinite 'fuel', 2g is less than current ground launch TWR)
This gives us 22,000,000 seconds, or 254 days.

At 4g (very uncomfortable to humans) this would take 161 days.

Then again that would exceed c ...

Considering that is has unknown effect exhaust velocity, it would likely be possible to accelerate to high%s of c.

Dawn has 1,240 kg of mass and 92 uN of thrust (425kg of mass is fuel). This gives us 0.000,074 m/s2 thrust while full and 0.000,11 m/s2 while empty. Most of Dawn's acceleration came from slingshots afaik.

a reply to: Nodrak

Considering that is has unknown effect exhaust velocity, it would likely be possible to accelerate to high%s of c.

Yes, about 72%. If you maintain that acceleration.
And, as you get to significant % of c, your mass will increase. With increased mass you will lose acceleration unless you increase thrust.

That increased mass also means you have to reverse thrust sooner in order to slow down, assuming you'll want to visit.

Fuel is not the only problem with constant acceleration. Relativity gets in the way.