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

luvantique

TS Rookie
No, you're not wrong. Mars' "escape velocity", is less than half of that of our earth. To escape earth's gravity, (from low earth orbit), requires accelerating to about 25,000 mph. Accordingly, (rough estimate), Mars' escape velocity, should be on the order of perhaps 11,000 mph.

"Capture velocity", (also distance dependent from the target), would be roughly the same, but you would still have a protracted period where the craft would decelerate slowly to orbital velocity. (Obviously, retro rockets would need to be used, the same as our lunar missions, to hasten braking)..
No, oortcloud is correct. Dennis Young said: "For slowing down, gravity drag in the Martian atmosphere will work, but if the craft is traveling at the speeds discussed, would likely take weeks or months to slow down. The other way would be to whip around Mars and use the laser to slow it down every time it comes out from the planet's shadow. This, too, would take time."

He probably meant atmospheric drag, since the statement as it reads is essentially meaningless, but in any event, as he posed the suggestion, a ship traveling at the speeds being discussed would barely notice Martian gravity, and even a brush with the atmosphere would create a spectacular and very final torch of the ship (not to mention pancaking the crew). As for "whipping around Mars," you would have to slow down to orbital velocity in the first place to be able to get around Mars, so that point is moot as well. It's not like banking an aircraft into a tight turn. So you (Captain Cranky) are correct at least in that rocket deceleration would be necessary before any other braking methods could be used.
 

luvantique

TS Rookie
Again, not really... there are other ways of decelerating that might not necessitate the loss of all the fuel... perhaps using a gravity well to spin off of, perhaps a cool orbiting do-hickey... it's all conjecture anyways...
I can't imagine what other kind of deceleration you could use. You can't use the gravity well to do more than deflect the course of the ship. Mars' gravity won't brake a ship traveling at the velocities in question (even the lower practical velocity limit that would make this "speculation" work). It would simply send the ship off on a deflected course as it blew past Mars. There is no other way until you get that second laser in place.
 

patenteux

TS Rookie
"For example, how would we slow down a spacecraft as it approaches its destination?"

Do what they've always done in space. Turn the aircraft around and use the propulsion in the opposite direction.
But it's being propelled by lasers based on or around earth. We'd have to put earth in front of the spacecraft to slow it down
If the laser are only 5Kg why aren't they on the craft, then one can do as Raz says
I presume it's because the power source would be the grid due to the immense power requirements and therefore have to be Earth based.
Combine both an on board laser and earth laser. Small power source on board and grid power source on earth. Best of both worlds.
 

cliffordcooley

TS Redneck
All this talk and I'm still not convinced laser propulsion is possible. Does anyone have links to successful space flight using laser propulsion?
 

Squid Surprise

TS Evangelist
I can't imagine what other kind of deceleration you could use. You can't use the gravity well to do more than deflect the course of the ship. Mars' gravity won't brake a ship traveling at the velocities in question (even the lower practical velocity limit that would make this "speculation" work). It would simply send the ship off on a deflected course as it blew past Mars. There is no other way until you get that second laser in place.
No offense, but that's why we're just guys (and girls) who post on this website and uber smart scientists are the ones working on space flight... just because we can't imagine it, doesn't mean the way doesn't exist.

For all WE know, there's some "as-yet-undiscovered" particle that can be used to attain lightspeed without any G-Force at all...
 

patenteux

TS Rookie
I had in mind a dual system of on board fuel propulsion engine and earth based laser. Since action/reaction canceling out would prevent using on board laser and sail !
 

luvantique

TS Rookie
Combine both an on board laser and earth laser. Small power source on board and grid power source on earth. Best of both worlds.
What would you do with a laser on board? It's not going to propel anything, any more than you can propel a sailboat by mounting a fan on the stern. Doesn't work that way.
 

luvantique

TS Rookie
No offense, but that's why we're just guys (and girls) who post on this website and uber smart scientists are the ones working on space flight... just because we can't imagine it, doesn't mean the way doesn't exist.

For all WE know, there's some "as-yet-undiscovered" particle that can be used to attain lightspeed without any G-Force at all...
Sorry but this goes to basic Physics, and the rules are pretty cut and dried. There are no magic alternatives out there. I've always said people shouldn't argue against things they don't understand, but it's becoming clear that they probably shouldn't argue for things they don't understand, either. The science involve in this problem is pretty basic.
 

cliffordcooley

TS Redneck
I'm surprised out of all this conversation no one has mentioned the potential for reflecting the laser beam from the front of the craft. There is no need in using gravity, petroleum, or spinning the craft around. Only the sails need to be turned, and the beam controlled by mirrors. That is if this concept works at all.
 

captaincranky

TechSpot Addict
All this talk and I'm still not convinced laser propulsion is possible. Does anyone have links to successful space flight using laser propulsion?
Personally I see many many problems. The first not insignificant obstacle, is what's to stop the laser from burning through the sail. A surface can't reach 100% reflectance, and at the power levels being discussed, a stray 1% of absorbed light might be enough to destroy the sail.

Second, all current extreme power lasers, have pulse durations measured in tiny fractions of a second. Where are we getting the tech, or for that matter the energy, to sustain a laser beam for a couple of days, or weeks for that matter, in case the system isn't as efficient as the hype.

Third, this guy is talking in terms of, "bringing resources back from Mars to replenish out dying supplies. News flash, there's no oil on Mars, (it never had enough atmosphere to sustain life with which to produce the carboniferous period needed to produce it). There's no organic matter for food, and fairly limited water. What's left, you ask? Well, we might find the raw materials for concrete, but what the hell would we have to build to haul that back?

So, this "space sail s***", has been done many times in science fiction, with ideas as far fetched as "sailing on solar winds"?

Bottom line here, this isn't actually a new concept, just a simple retread.
 
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patenteux

TS Rookie
"For example, how would we slow down a spacecraft as it approaches its destination?"

Do what they've always done in space. Turn the aircraft around and use the propulsion in the opposite direction.
But it's being propelled by lasers based on or around earth. We'd have to put earth in front of the spacecraft to slow it down
If the laser are only 5Kg why aren't they on the craft, then one can do as Raz says
I presume it's because the power source would be the grid due to the immense power requirements and therefore have to be Earth based.
Combine both an on board fuel reactor and earth laser. Small power source on board and grid power source on earth. Best of both worlds.[/QUOTE

When on Mars install another laser for future deceleration. The first travel would have to be made my a more conventional way. Send a probe equipped with a laser and atomic power source ?
 

captaincranky

TechSpot Addict
Junior, you need to work on your posting technique ^^^^^^, before trying to attempt to solve problems as conplex as the topic of this thread.

The short answer is, "say wut"?

I mean it's a brave tactic to challenge five members at once, but you can't ignore the mechanical aspects of putting coherent information up on the screen....:p
 

cliffordcooley

TS Redneck
When on Mars install another laser for future deceleration. The first travel would have to be made my a more conventional way. Send a probe equipped with a laser and atomic power source ?
That's right fire a laser back at Earth. Lets hope the guidance system never screws up.
 

captaincranky

TechSpot Addict
That scratches the idea of putting a Penal Colony on Mars.
Not really. You just don't let the inmates have anything stronger than a laser pointer and some AA batteries. It would take an eternity to escape back to earth using a laser pointer aimed at a stolen bed sheet for a sail. Even El Chapo wouldn't get out of that prison..

Of course the humane thing to do would be to let the ladies have D batteries. Were that to be the case, they'd probably be glad to stay on Mars, long after the men left. ;)
 
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Lurker101

TS Evangelist
And yet not one post mentioning the consequences of a collision with space dust whilst travelling at a 'significant' fraction of the speed of light which could impact with the potential force of a nuclear warhead.
 
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captaincranky

TechSpot Addict
And yet not one post mentioning the consequences of a collision with space dust whilst travelling at a 'significant' fraction of the speed of light which could impact with the potential force of a nuclear warhead.
Well, since you're essentially in a sailboat, I would think you'd just grab the tiller and steer around it.. (Oh, I'm just kidding)
IIRC, the closer you approach to the speed of light, the power required to do so increases virtually exponentially. I forget where I read that, so I can't state it as fact. It is probably worth investigating to determine whether that's fact, fiction, or just supposition.

FWIW, a trainer type RC aircraft weighing about 4 pounds and traveling maybe 35mph, contains the same kinetic energy as a .45 caliber bullet.

I realize that's way off topic, but it's something which also never gets mentioned in conjunction with the potential dangers from the proliferation of drones in our skies.

Back to topic, you're right of course, nobody here thought of that particular danger. Of course, the story itself is more about grabbing headlines. We've ventured further toward serious scrutiny of those headlines. than I expect a great portion of readers will, or did.
 
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luvantique

TS Rookie
I'm surprised out of all this conversation no one has mentioned the potential for reflecting the laser beam from the front of the craft. There is no need in using gravity, petroleum, or spinning the craft around. Only the sails need to be turned, and the beam controlled by mirrors. That is if this concept works at all.
The concept is well proven, but your version won't work for the same reason that fan won't drive a sailboat. The sails have to be attached to the ship. You can't reflect the beam off the sails for the same reason the aforementioned fan on the stern doesn't work. You can't deflect the beam from mirrors attached in any way to the ship for the same reason. There are problems with having mirrors in orbit around Mars, too (think action/reaction), but if you could get them there in the first place, you could have a laser on that end too, so that solution is essentially moot. As for the concept, it's a bit overblown here. It works, but even with the concentrated beam of a powerful laser, light pressure is a relatively tiny force. The acceleration would be slow, but more or less constant (there would be some spreading of the beam over distance). Extreme high velocities might be possible, depending on the laser, available acceleration time, and ship's mass, but the idea has traditionally been proposed for much longer flights than simply inner solar system jaunts. One other point: the sail would have to be designed to work across a broad spectrum because as the ship's velocity increases, the light from the laser will be dopplered into longer wavelengths. At relativistic velocities, the energy from the laser would be greatly attenuated and would probably cease to be a very effective propulsive force. Just one more limit on the system's effectiveness, but I don't have numbers at hand, so can't put a value on those limits, especially when there are so many variables.
 

Squid Surprise

TS Evangelist
Sorry but this goes to basic Physics, and the rules are pretty cut and dried. There are no magic alternatives out there. I've always said people shouldn't argue against things they don't understand, but it's becoming clear that they probably shouldn't argue for things they don't understand, either. The science involve in this problem is pretty basic.
Are you trying to tell me that since you know physics, this simply isn't possible?
Let's not be too arrogant here... Scientists have been coming up with stuff that VERY intelligent people have considered impossible all the time... There's always a chance that something like that could happen here...
Remember, Einstein stated that nothing could go faster than light, and we all thought, "yep, he's right"... Now scientists have particles going FTL...

Just goes to show - anything can happen... Start using your imagination instead of just assuming stuff can't be done... Maybe it can!
 

cliffordcooley

TS Redneck
The concept is well proven <snip> The acceleration would be slow, but more or less constant (there would be some spreading of the beam over distance). Extreme high velocities might be possible, depending on the laser
Yeah I was asking for links earlier to successful space flight. Though traveling to Mars in three days doesn't sound like slow acceleration.
but your version won't work for the same reason that fan won't drive a sailboat.
Thanks for letting me know the mirrors would react to the laser the same way the sails would.

Ohh and I do agree with the laser loosing strength, regardless of how concentrated the beam is. That is only part of my skepticism.