# Lasers may be able to propel spacecraft to Mars at a significant fraction of the speed of light

#### wiyosaya

##### TS Evangelist
An object in motion tends to stay in motion; an object at rest tends to stay at rest - it is the "law" of inertia and applies whether or not the "object" is in a gravitational field. https://en.wikipedia.org/wiki/Inertia Therefore, any object would experience the effects of acceleration and deceleration regardless of whether it was in a gravitational field or not. With schemes like this, an acceleration of 1G would produce a gravity like effect for anyone inside the craft, and applied over sufficient periods of time, could allow a craft like this to reach the speeds they cite in the article. I'm not versed on the specific instance, so I do not know what their planned acceleration is.
Speed is not the issue... it's speed/distance/time....
I see you read my post carefully. At least I am not the only one slow to catch up. BTW - you would not hurl anything. Hurling something, in other words, imparting momentary instantaneous acceleration, would result in a constant speed in a microgravity environment. Nothing we know of could possibly impart anything even close to c on such a large object with a "hurl".

As others have noted, the laser idea is nothing new. It has been around for ages and relies on imparting a constant acceleration. It is the same concept that made Deep Space 1 so successful.

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#### wiyosaya

##### TS Evangelist
An object in motion tends to stay in motion; an object at rest tends to stay at rest - it is the "law" of inertia and applies whether or not the "object" is in a gravitational field. https://en.wikipedia.org/wiki/Inertia Therefore, any object would experience the effects of acceleration and deceleration regardless of whether it was in a gravitational field or not. With schemes like this, an acceleration of 1G would produce a gravity like effect for anyone inside the craft, and applied over sufficient periods of time, could allow a craft like this to reach the speeds they cite in the article. I'm not versed on the specific instance, so I do not know what their planned acceleration is.
Jeez, I made that misstatement quite awhile ago, just catching up with it now? Clifford called me on it right away! I do recall seeing how a space station could be made to have "gravity", through centrifugal force.

However, such artificially produced gravity, would cease as soon the the craft stopped accelerating, and the ship along with its occupants would return to a weightless state. (Not that it would matter).

Since, "a significant fraction of light speed", is a completely unusable constant in any equation, let alone one centered on determining the g-force derived from an unknown coefficient of acceleration, neither one of us needs to take calculus 6 to try and figure it out...

What is impressive, is someone trying give Musk's grandiose rhetoric a run for its money, so to speak.
My my, sensitive aren't we Crank. Musk can't even get anything up these days.

#### wiyosaya

##### TS Evangelist
The cited paper does not address the deceleration issue. Like so many have stated, deceleration is a problem that must be overcome if any craft is going to actually stop at Mars. While the paper is keen on current laser technology, nowhere does it specifically mention deceleration. In fact, the title of this paper is "A Roadmap to Interstellar Flight". The paper specifically states that "wafer sized craft" would pass Mars at 30-minutes. The operative word being "pass" not "stop at."

Unfortunately, I think some journalist that has no knowledge of physics got as far as the part about reaching Mars, and concluded that whatever uses this method would just magically stop there. Maybe that journalist should have consulted Neil DeGrass-Tyson first before publishing their article.

Yes, the advances in lasers are amazing, and yes, it theoretically could propel large craft to places like Mars and far beyond. Stopping anywhere from that velocity with an Earth-based propulsion system is one part of the equation that the cited paper fails to address.

In other words, the article was little better than click-bait - at least as I see it.

cliffordcooley

#### captaincranky

Oh look at that @wiyosaya, you almost have the whole page to yourself.

As for the article being, "click bait", I can't help but notice this will be post #105, and you're still clicking away. Ironic, ay?

Maybe we passed by a black hole, and we're caught in its gravity well. Our fingers and mice locked in a death dance as we accelerate toward oblivion. Someone, somehow, manages to struggle toward the distress beacon and press its big red button.

We know our destiny, and as the ship approaches light speed, we face it with grim resignation while the ship's klaxon blurts out the ancient Morse code....." .*** _ _ _ **_* S.O.L......S.O.L.......S.O.L......." A very last thought flickers and dies in everyone's mind before the blackness overcomes us, "weren't we supposed to stop at Mars"......

(Now I'm not sure if, "S.O.L.", means "Save Our Laser", or more probably, "S*** Outta Luck")!

#### Squid Surprise

##### TS Evangelist
The problem with the article was that it was claiming to summarize a 52 page paper... I'm going to guess that very few posters here read the 52 pages (I read the first 12 and gave up), so just assumed that the writer accurately summed it up.

Fortunately, the paper did have its own synopsis (conveniently placed on the first page - the abstract) which basically states that this is for interstellar exploration. Mars is only mentioned as a point of reference!! That is, that on a journey to the stars, it would pass Mars in a short time... The paper makes no claim about being able to send manned flights to Mars, nor does it mention deceleration at all - it's focused on sending small unmanned probes.

#### captaincranky

You just can't launch these laser powered missions in the middle of July when everybody's running their air conditioners....

The tome of the continuing posts in this thread are beginning to mirror the stages of grief!

https://en.wikipedia.org/wiki/Kübler-Ross_model

#### wiyosaya

##### TS Evangelist
Oh look at that @wiyosaya, you almost have the whole page to yourself.

As for the article being, "click bait", I can't help but notice this will be post #105, and you're still clicking away. Ironic, ay?

Maybe we passed by a black hole, and we're caught in its gravity well. Our fingers and mice locked in a death dance as we accelerate toward oblivion. Someone, somehow, manages to struggle toward the distress beacon and press its big red button.

We know our destiny, and as the ship approaches light speed, we face it with grim resignation while the ship's klaxon blurts out the ancient Morse code....." .*** _ _ _ **_* S.O.L......S.O.L.......S.O.L......." A very last thought flickers and dies in everyone's mind before the blackness overcomes us, "weren't we supposed to stop at Mars"......

(Now I'm not sure if, "S.O.L.", means "Save Our Laser", or more probably, "S*** Outta Luck")!
Don't you just love those pesky journalists? In such cases, would you not rather have someone say, hey, @captaincranky we passed Mars three light-seconds ago. Were you expecting us to stop?

Next time a ship owned by the captain looks like it is in the grips of the Schwarzschild radius, I'll keep it in mind that some may take the miraculous appearance of light from the big red button as an evil and impossible apparition.

#### ANTEATER

##### TS Rookie
I don't believe the lethal g-force rating would ever change.
Not sure what you mean here. I don't expect human physical tolerance to g-force would change, but that the large body, (Jupiter), would cause the necessity for more g-force than would be tolerated to be applied, if trying to leave. Jupiter's "escape velocity" is much higher than earth's. Higher escape velocity would require higher acceleration, therefore produce higher relative g-force. No?

This is partly science fiction wisdom/nonsense, but didn't you ever notice someone who is from a heavy gravity planet, can always beat everybody else up?

And then there's what's behind "door # 3". There does at least the possibility that the guy who is putting forth this idea, has never taken into account what effect accelerating to the predicted speed might have on humans. It wouldn't be the first time NASA screwed up the math. They destroyed a Mars rover, by calculating the landing velocity in meters per second, and applying those numbers to feet per second. As you could quickly guess, going 10 meters per second is traveling a whole lot faster than 10 feet per second.
I think NASA launches straight up because it is the most fuel efficient, straight line and all. The amount of time to reach a required "escape" velocity could be lengthened using a launch angle less than 90 degrees and making 1 or more orbits at increasing speed each orbit...hopefully you don't run out of fuel before you "clear" the gravitational pull...

#### captaincranky

I think NASA launches straight up because it is the most fuel efficient, straight line and all. The amount of time to reach a required "escape" velocity could be lengthened using a launch angle less than 90 degrees and making 1 or more orbits at increasing speed each orbit...hopefully you don't run out of fuel before you "clear" the gravitational pull...
Well, if you think the Leaning Tower of Pisa is a marvel, just consider what the lateral forces would be holding a Saturn 5 booster on the pad at an angle.... So, you can't launch it anyway but straight up. And don't listen to Elon Musk, it needs too much fuel for the launch payload, to carry enough to land it back on earth in one piece. They're not reusable, period!

Back to the launch. I'm ancient enough to have seen these launches live, and you would be surprised at how early in the trajectory the rocket starts to curve toward the horizontal attitude it will assume at its arrival at orbit. I actually think the Saturn 5 1st stage itself only has about a "three minute shelf life, so to speak, as there is an intermediate stage torched off before orbital velocity is reached. The Saturn 5 had the worst gas mileage ever

The fury of the Saturn rocket blasted into a clear sky can be seen some 60+ miles down range, IIRC

In any event, the flight goes pretty much as you suggest, save for the fact the capsule and final stage are placed in low earth orbit for at least one pass around the globe before escape velocity is attempted. So, final acceleration is only from 18K mph to about 25K mph.

Should any of this interest you: https://en.wikipedia.org/wiki/Saturn_V

Oddly, or perhaps ironically, German ex-pat Wernher Von Braun assisted in the development of this rocket, as well as pretty much everything else we used in the "space race". And yes, Albert Einstein worked for the German government as well, before working on the "Manhattan Project", toward the A-bomb. Just be thankful the allies won WW2, or we'd all be goosestepping around the craters which used to be American cities.

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#### Raoul Duke

Hehehe... well, when they start asking me for money to fund this laser... that's when I start to get suspicious
I heard someone say once, when they say "we will pay any price, bear any burden.." you can be sure they are not the one paying either the price or bearing the burden, little off topic, but that especially applies to military adventures

#### hrowder

##### TS Enthusiast
Well, you could hurl all the buckshot and ball bearings you want at Mars, but that wouldn't make it a viable planet. Tack on another billion years to allow the of evolution of carbohydrate synthesizing organisms, then maybe it might sustain an apex predator like Homo Sapiens.

But then again, the sun represents a "point source" of illumination As such, the inverse cube law determines the intensity of light reaching any point in the solar system. The further away from the sun you go, rthe lower the foot candle reading will be. Our noon daylight, (IIRC), is 16,000 foot candles. @ 5600 degrees Kelvin. The sun's color temperature is affected least by atmospheric spectral absorption, when its light is at a 90 degree angle to the surface. So, the greatly reduced available light at Mars' surface, would make growing weed there pretty much out of the question. (Along with a whole host of annual summer food staple crops).
I agree with you about the lack of solar light in the short term, even if the planet were not too cold as it stands to raise plants like we might bring for the purpose of food etc. My imagined bombardment of Mars with asteroids and comets to render it large enough and with a molten core is, of course, currently a non-starter because we don't possess the technology to hurl space objects at Mars even if we wanted to. However, in the long term, if asteroid hurling was feasible, and allowing for the million years or so that it would take the planet to cool again, we would find the sun enlarged and perhaps hot enough to give Mars enough light and heat to allow for plants to be raised there. By that time we should have the technology to travel there with enough materials to do a certain amount of terraforming and also find the need to leave earth entirely as the sun's increasing size and heat would make life all but impossible here on earth. So... go ahead and send out those laser powered probes. By the time they report back and we have the ability to follow them to new worlds we will most likely need to get out of here anyway.