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NASA is working on laser-based propulsion


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Hmm. At these sort of (relativistic..?) speeds? My understanding is that gravity slingshots/slowdowns have many limitations, including that you need to find something going (fast) in the right direction, and you also need to get very close if you need a major speed change. And of course for a solar wind slowdown, well, you need a Star in the right place and a big sail that you have to bring... I ain't a practising expert on those topics, but I do know that slowing down is as big a problem as speeding up, if you are talking about a spacecraft that has occupants...

The solar wind braking would have to be in another solar system, where the star would be directly in front of you when you started braking. A minimal amount of solar braking is available within the same solar system because of the angles.

You wouldn't be using such great speeds around our solar system. The article simply stated that such a speed could be reached in 10 seconds at the power output currently used. The benefit of the method is in the energy savings. Obviously, payload has to shrink.

Missions are done as flybys though. Just bring the probe up to the speed you would have reached by rocket and it's the same mission with a lighter payload for less money. Note that the overall mass can be so reduced that it would make up for a lot of the payload loss, since the craft wouldn't necessarily have to withstand launch via rocket and a solar sail is pretty light.

The only missions where you have to worry about slowing down would probably be manned and this tech is a long way from doing that.

Harte

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Will someone check my maths here?

Philip Lubin is described as a "NASA scientist". If he is I am assuming he has been misquoted.

Firstly, there is the sentence: "We're struggling to even accelerate spacecraft to beyond 3% [of the speed of light]. The speed of light is 300,000 km/s. 3% of that is 9,000 km/sec. Which spacecraft have ever flown that fast?!

Secondly, he talks about accelerating spacecraft to 30% of the speed of light in ten minutes. The basic equation of motion is v = at, so this can be changed to a = v/t.

So, (using the speed of light in m/s) a = 0.3 x 300,000,000/10 x 60. Hence a = 150,000 m/s^2. That is 15,000 g!!!

I can't imagine a space probe could survive an acceleration like that, let alone people.

Edited by Derek Willis
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That calculation was energy-based. The claim was that the power expended in a typical probe launch would translate into that acceleration with the new tech.

If you used that much power in a laser, you'd first need to ensure the probe wouldn't incinerate.

Harte

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That calculation was energy-based. The claim was that the power expended in a typical probe launch would translate into that acceleration with the new tech.

If you used that much power in a laser, you'd first need to ensure the probe wouldn't incinerate.

Harte

The article says: "In the ten minutes it will take to get the SLS into orbit, photonic propulsion could propel a spacecraft to the unheard of 30 percent of the speed of light - and it would also use a similar amount of chemical energy (50 to 100 gigawatts) to do so."

It is pretty straightforward what is being said: the laser could propel a spacecraft to 30% of the speed of light in ten minutes.

But this is why I suggest Lubin is being misquoted. If the article was only referring to the energy - i.e. the same amount of energy used to get the SLS into orbit in ten minutes could accelerate a spacecraft to 30% of the speed of light over a far longer time, then fine. But that is not what the article says.

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How would this even move something in zero G?

The laser would be pushing against a sail attached to the spacecraft in exactly the same way that wind pushes against a sail attached to a sail-boat. However, unlike the sail-boat which has to push through the friction of the water, the spacecraft experiences no friction so this space-sail would be much more efficient at accelerating the spacecraft.

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The article says: "In the ten minutes it will take to get the SLS into orbit, photonic propulsion could propel a spacecraft to the unheard of 30 percent of the speed of light - and it would also use a similar amount of chemical energy (50 to 100 gigawatts) to do so."

It is pretty straightforward what is being said: the laser could propel a spacecraft to 30% of the speed of light in ten minutes.

But this is why I suggest Lubin is being misquoted. If the article was only referring to the energy - i.e. the same amount of energy used to get the SLS into orbit in ten minutes could accelerate a spacecraft to 30% of the speed of light over a far longer time, then fine. But that is not what the article says.

Again, it's a calculation based on power expended.

With a 100GW laser, a probe with a small mass could be accelerated to 0.30c in ten minutes.

I don't see where he recommended doing so.

I took the quote as being for the purpose of comparing power requirements.

BTW, 30% of light speed isn't fast enough for relativistic effects to come into play. I just wanted to note that, since earlier someone brought up "relativistic speeds."

Harte

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Again, it's a calculation based on power expended.

With a 100GW laser, a probe with a small mass could be accelerated to 0.30c in ten minutes.

I don't see where he recommended doing so.

I took the quote as being for the purpose of comparing power requirements.

BTW, 30% of light speed isn't fast enough for relativistic effects to come into play. I just wanted to note that, since earlier someone brought up "relativistic speeds."

Harte

The statement is: "In the ten minutes it will take the SLS to get into orbit, photonic propulsion could propel a spacecraft to the unheard of 30 percent of the speed of light."

We will have to agree to disagree on what that statement means. Like I said, I think Lubin has either been misquoted or the author of the article misunderstood what he meant. The author also wrote that we currently struggle to accelerate spacecraft to 3 percent of the speed of light. That is obviously nonsense - 0.03 percent is nearer the mark.

BTW It wasn't me who mentioned relativity.

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BTW It wasn't me who mentioned relativity.

It was mentioned by ChrLzs and me here: http://www.unexplained-mysteries.com/forum/index.php?showtopic=291899&st=15#entry5779124

I used the term relativistic speed as it is a term that is often used when discussing interstellar space travel, as a way to distinguish fast spacecrafts from generation ships. Strictly speaking any speed is relativistic, but you have to get fairly close to the speed of light before it becomes noticeable. Sorry if I caused any misunderstanding.

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Why is that out of context? Several folks (inc. the article itself and you, Harte) were raising scenarios of travel beyond our solar system, and if the speeds aren't *substantial*, then that is pretty much a no-go. I was responding to that extended scenario, and I quite tentatively raised it anyway, thus:

At these sort of (relativistic..?) speeds?...

and tried to make it clear I was referring to its potential for extrasolar / manned craft.

The article was clearly hinting at huge speeds, with these quotes:

While we're able to propel particles to close to the speed of light in the lab, we're struggling to even accelerate spacecraft to beyond 3 percent of that.

...Lubin explains .. that the system could easily be scaled up.

...Electromagnetic acceleration is only limited by the speed of light while chemical systems are limited to the energy of chemical processes.

..But the real benefit of photonic propulsion comes over longer distances, where the spacecraft has more time to speed up, and could eventually take us outside our Solar System and to neighbouring stars.

....

If all that is not hinting at 'relativistic' speeds, then I am lacking in reading comprehension...

And while it is true that you don't get get major relativistic effects at 30%, it is most certainly becoming measurable, eg relative time will be passing slower for the craft (be it manned or unmanned) by about 5%, iirc. (I'm too tired (aka lazy) do do the calc.. - corrections welcome, but bring the maths!)

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ohh laser based solar sails :) love it..

remember reading about a scifi book about a alien race that used it.. actually read a few like that over the years but always enjoyed this one

https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye

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And while it is true that you don't get get major relativistic effects at 30%, it is most certainly becoming measurable, eg relative time will be passing slower for the craft (be it manned or unmanned) by about 5%, iirc. (I'm too tired (aka lazy) do do the calc.. - corrections welcome, but bring the maths!)

4.60608%. Whilst it wasn't me who mentioned relativity, I agree that roughly 5% is easily measurable. If we men woke up 5% shorter I am sure our wives/partners would notice. (I am talking about height, BTW - 5% of six feet is over three inches).

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Sure this could be used to send humans to Mars. If it's only 3 days, can send 1 person at a time and then subsequent trips for extra food/supplies and probably equipment to send the people back.

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The statement is: "In the ten minutes it will take the SLS to get into orbit, photonic propulsion could propel a spacecraft to the unheard of 30 percent of the speed of light."

We will have to agree to disagree on what that statement means. Like I said, I think Lubin has either been misquoted or the author of the article misunderstood what he meant. The author also wrote that we currently struggle to accelerate spacecraft to 3 percent of the speed of light. That is obviously nonsense - 0.03 percent is nearer the mark.

BTW It wasn't me who mentioned relativity.

I realize that. I just wanted to get that in there because, as I said, someone brought it up in an earlier post.

Typically, force on solar sails is enumerated as the Solar power density per square meter at 1 AU. AT 1 AU, the Sun's power comes to around 160 Watts per square meter. At that value, acceleration of a solar sail maxes out at about 1 cm/s2 , with the best sail design. That doesn't include any payload.

100 GW is a million times more power. You can look into whether or not such numbers indicate an acceleration that would result in the stated speed after ten minutes. You'd know if he was misquoted then.

But, the article mentions recent advances. Not knowing exactly what those are might make the exercise a waste of time.

Harte

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Why is that out of context? Several folks (inc. the article itself and you, Harte) were raising scenarios of travel beyond our solar system, and if the speeds aren't *substantial*, then that is pretty much a no-go. I was responding to that extended scenario, and I quite tentatively raised it anyway, thus:

and tried to make it clear I was referring to its potential for extrasolar / manned craft.

At 30% c, that's a little over 12 years to Proxima Centauri. Voyager 1 and 2 were launched almost 40 years ago.

As I said, manned craft would present a problem and is likely not doable with a light sail. At least, not extrasolar.

The article was clearly hinting at huge speeds, with these quotes:

....

If all that is not hinting at 'relativistic' speeds, then I am lacking in reading comprehension...

And while it is true that you don't get get major relativistic effects at 30%, it is most certainly becoming measurable, eg relative time will be passing slower for the craft (be it manned or unmanned) by about 5%, iirc. (I'm too tired (aka lazy) do do the calc.. - corrections welcome, but bring the maths!)

About 4.8%. You need the equation?

The same percentage of mass increase, by the way. Of course, that's at speed, and not along the way while accelerating.

Huge speeds are certainly possible over long time periods. However, approaching the speed of light would also be a problem for acceleration, with the mass increase. At around 70% c, that 4.8% becomes 40%, reducing the acceleration. Doesn't mean we'd have to up the power though, since acceleration would still be happening.

Then you get into the previously mentioned problem of slowing down so you'll have time to see what you just whizzed by.

Harte

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ohh laser based solar sails :) love it..

remember reading about a scifi book about a alien race that used it.. actually read a few like that over the years but always enjoyed this one

https://en.wikipedia...te_in_God's_Eye

I read that. Pretty good.

I liked the way the Engineers altered the coffee pot.

Niven and Pournelle wrote several Sci Fi novels. All of them worth reading.

Harte

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When the craft is out of the laser's reach you will stop accelerating but you won't stop moving. You won't be stranded you will just have reached your maximum velocity.

Which is all fine if you are already pointed at the destination, but what about if you need to make any manuevers or want to come back someday?

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That's a problem isn't it. That's why I said manned missions are unlikely.

Harte

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Posted (IP: Staff) ·

Which is all fine if you are already pointed at the destination, but what about if you need to make any manuevers

With a conventional rocket the rocket runs out of fuel in only a few minutes, the spacecraft does not become stranded. If it needs to manoeuvre it will use small thrusters to do that. There is no difference here.

or want to come back someday?

As has already been pointed out by Chrlzs, for interstellar missions this technique is really only useful for unmanned flyby missions, so the question of returning isn't an issue. If, however, you are to use this technique for interplanetary missions, to Mars for example, then the solution is simple, build another laser at Mars.

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I actually thought of this decades ago. Use a laser to push and pull your spacecraft by grabbing objects. The push part is easier than the pull part however. Seems like half is becoming a reality.

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Lasers don't "grab."

Harte

I am very curious too about how you pull something with a laser ?

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Posted (IP: Staff) · (edited)

Focused beams of gravity to pull and push, working like a laser. Same principal.

No, it's not the same principle, particularly as no one has ever produced a "focused beam of gravity".

Edited to add:

And just as Noteverythingisaconspiracy is curious to know how you pull something with a laser I'm curious to know how you push something with gravity.

Edited by Waspie_Dwarf
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I am very curious too about how you pull something with a laser ?

You say "Come this way or I'll laserize ya!"

Harte

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No, it's not the same principle, particularly as no one has ever produced a "focused beam of gravity".

Edited to add:

And just as Noteverythingisaconspiracy is curious to know how you pull something with a laser I'm curious to know how you push something with gravity.

You put some gravity (mass) on the other side of it. This is actually one of the long-term methods I mentioned.

Harte

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