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

[Moomoocow76]

Why not send a normal manned mission to mars and setup a similar laser. So you propel at one end, turn around and use the laser to slow down at the other end. Then of course coming home u use the mars laser to go shifty shifty and then use the earth based beam of doom to slow down. Screw it warp drive it is!!!!!, Im sure its just as easy!!! lol

 

[Squid Surprise]

That's what I said already.... Will be complicated to calculate planetary spin and orbit, but I'm sure it could be done...

 

[Ivangela]

And I can drive my car to the store at a significant fraction of that speed.

1/14,911.111 isn't significant, it's negligible.

1/14,911,111

that's what I mean

 

[Technician]

1/14,911.111 isn't significant, it's negligible.

They said they will be able to travel

Why not send a normal manned mission to mars and setup a similar laser. So you propel at one end, turn around and use the laser to slow down at the other end. Then of course coming home u use the mars laser to go shifty shifty and then use the earth based beam of doom to slow down. Screw it warp drive it is!!!!!, Im sure its just as easy!!! lol

Before or after the space elevator is complete?

 

[captaincranky]

The laser would be earth based, right? So how they suppose to stop at the destination?

Nobody in their right mind would design a space capsule without retro rockets, or would they?

Come to think of it, let's play it safe and not let the Chinese build it for us.

 

[captaincranky]

What I want to know is how long would it take to gain that much speed. We should all know we are limited to the amount of acceleration our bodies can withstand. So how long would we be under physical stress while accelerating or decelerating?

I believe acceleration and deceleration are only an issue when considered against a force of gravity. If you're weightless in space, how much acceleration would be necessary to mimic the forces encountered when earth bound. This should have been evident with the pictures sent back from out moon landings, with astronauts taking 20 foot strides easily. Now if you were trying to take off from a base on Jupiter, you might encounter lethal forces of (wild guess), say 50 G's.

A pivotal issue becomes, "how much gravity is the person accustomed to", which would depend on how long has the individual been in space, before the start of the trip.

https://en.wikipedia.org/wiki/Gravitation_of_the_Moon

 

[cliffordcooley]

https://en.wikipedia.org/wiki/G-force

In the absence of gravitational fields, or in directions at right angles to them, proper and coordinate accelerations are the same, and any coordinate acceleration must be produced by a corresponding g-force acceleration. An example here is a rocket in free space, in which simple changes in velocity are produced by the engines, and produce g-forces on the rocket and passengers.

Now if you were trying to take off from a base on Jupiter, you might encounter lethal forces of (wild guess), say 50 G's.

I don't believe the lethal G-Force rating would ever change.

 

[captaincranky]

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.

 

[Squid Surprise]

Even in Gravity-less space, when you accelerate, you produce g-forces.... In sci/fi, you'll note that they usually say the ship is accelerating at 6G, or whatever.....

So whatever the human tolerance for G forces, that would have to be your max acceleration... Not your max SPEED though, as that doesn't matter (unless you hit something!).

With the laser thingy, I would think that it would be the decelerating that would produce the most g-force - just need someone (or many someones) to do the math to make sure the passengers aren't pulp...

 

[luvantique]

"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.

Not with this propulsion. The power is ground-based, so you would have to have a like-laser pre-positioned on Mars.

 

[captaincranky]

Not with this propulsion. The power is ground-based, so you would have to have a like-laser pre-positioned on Mars.

Yes but, there's no fixed wisdom here which says you can't use more than one type of propulsion. You could certainly accelerate with the ground based laser, and decelerate with on board retro firing rockets.

Here is something to consider when proposing to power with light for an extended period of time:

"The Institute of Laser Engineering (ILE), Osaka University, has succeeded to reinforce the Petawatt laser "LFEX" to deliver up to 2,000 trillion watts in the duration of one trillionth of one second (this corresponds to 1000 times the integrated electric power consumed in the world)."

Power necessary vs. power available over time vs. power available in a small enough package to be portable. I think that's why we don't have practical death rays yet. (Although I'm not on the Pentagon's briefing list, so I can't be sure).

 

[luvantique]

Yes but, there's no fixed wisdom here which says you can't use more than one type of propulsion. You could certainly accelerate with the ground based laser, and decelerate with on board retro firing rockets.

Here is something to consider when proposing to power with light for an extended period of time:

"The Institute of Laser Engineering (ILE), Osaka University, has succeeded to reinforce the Petawatt laser "LFEX" to deliver up to 2,000 trillion watts in the duration of one trillionth of one second (this corresponds to 1000 times the integrated electric power consumed in the world)."

Power necessary vs. power available over time vs. power available in a small enough package to be portable. I think that's why we don't have practical death rays yet. (Although I'm not on the Pentagon's briefing list, so I can't be sure).

But that negates the whole concept. The whole point of the laser propulsion is relatively rapid acceleration to shorten the trip to Mars. If you achieve that acceleration and the consequent velocities and must reverse them with conventional propulsion systems, you lose most of the advantage you were trying to gain.

 

[Squid Surprise]

But that negates the whole concept. The whole point of the laser propulsion is relatively rapid acceleration to shorten the trip to Mars. If you achieve that acceleration and the consequent velocities and must reverse them with conventional propulsion systems, you lose most of the advantage you were trying to gain.

No...you'd lose SOME of the advantages.... and until you have a matching laser system on Mars, you'd need something on the ship to decelerate...

Otherwise you're simply turning your ship into pulp when it hits Mars at "significant light speed"...

Of course, this does give us the perfect weapon to hurl at enemies millions of miles away from us...

 

[captaincranky]

But that negates the whole concept. The whole point of the laser propulsion is relatively rapid acceleration to shorten the trip to Mars. If you achieve that acceleration and the consequent velocities and must reverse them with conventional propulsion systems, you lose most of the advantage you were trying to gain.

Well, not exactly. Regardless of what you use for propulsion, the first trip will require retro rockets.

Then there's that ugly term which interferes with all these phantasmagorical bright ideas which is, "available payload".

We can barely get a few hundred pound rover to Mars now. So imagine the number of trips required to build a base, install a power station capable of powering a laser to effectively, and assembling everything.

And do yourself a favor, don't listen to Elon Musk press releases. He's flat out full of s***.

@Squid Surprise I nominate you to go and build that laser station on Mars. And make damned sure it's "eco-friendly".

...[ ]....Of course, this does give us the perfect weapon to hurl at enemies millions of miles away from us...

So Chicken Little was right when he shouted, "the Klingons are coming, the Klingons are coming, the Klingons are coming....., I'm sorry I meant the Romulans are coming ........"! After which he became number 2 on the KFC lunch menu, by inadvertently stepping in front of a laser beam.

 

[Squid Surprise]

The good thing is, if we're simply sending materials to Mars, we don't have to worry as much about G-Forces... and if we build a strong enough "case", we wouldn't even have to decelerate it much - just "shoot" payload at Mars and send guys later to dig it out and assemble it...

Obviously still lots of kinks to work out - like what can withstand a crash landing on Mars at ridiculously high speeds...

 

[captaincranky]

The good thing is, if we're simply sending materials to Mars, we don't have to worry as much about G-Forces... and if we build a strong enough "case", we wouldn't even have to decelerate it much - just "shoot" payload at Mars and send guys later to dig it out and assemble it...

Obviously still lots of kinks to work out - like what can withstand a crash landing on Mars at ridiculously high speeds...

About that:
Mars Probe Lost Due to Simple Math Error
http://articles.latimes.com/1999/oct/01/news/mn-17288

 

[Squid Surprise]

Yeah... we REALLY need to make sure we have GOOD mathematicians working on that... would hate to see a multi-billion dollar craft shot randomly into space instead of where it's supposed to go...

 

[captaincranky]

Yeah... we REALLY need to make sure we have GOOD mathematicians working on that... would hate to see a multi-billion dollar craft shot randomly into space instead of where it's supposed to go...

Things will be different when Donald Trump is president! We'll be shooting condos and casinos into space randomly and losing them, so that Trump can use them as a tax write off.

 

[luvantique]

No...you'd lose SOME of the advantages.... and until you have a matching laser system on Mars, you'd need something on the ship to decelerate...

Otherwise you're simply turning your ship into pulp when it hits Mars at "significant light speed"...

Of course, this does give us the perfect weapon to hurl at enemies millions of miles away from us...

No, you would lose all of that advantage. You forget the greater deceleration time with conventional propulsion from the greater velocity. Truth is, if you can't carry enough propulsive energy on board to accelerate to that velocity in the time stated, you can't carry enough to decelerate from high velocity either. Conventional propulsion is out as an alternative stopping method. You would have to make the slow trip to Mars first with the decel laser for this to work at all.

 

[Squid Surprise]

No, you would lose all of that advantage. You forget the greater deceleration time with conventional propulsion from the greater velocity. Truth is, if you can't carry enough propulsive energy on board to accelerate to that velocity in the time stated, you can't carry enough to decelerate from high velocity either. Conventional propulsion is out as an alternative stopping method. You would have to make the slow trip to Mars first with the decel laser for this to work at all.

No - you can't carry enough propulsion to accelerate AND decelerate.... If you're willing to compromise for the first several voyages (until you have a laser on Mars too), you simply use propulsion to decelerate and the laser to accelerate - but not as much acceleration as you will do in the future...

You still gain the benefits of "modest" acceleration without fuel on the ship itself... Once you have that laser on Mars built, you can take full advantage...

 

[OortCloud]

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.

I could be wrong, but I'm pretty sure that at the speeds it is travelling at it would not enter an orbit around Mars. It's path would deviate slightly but it would be going way too fast to be caught in Mars gravity so it would then plough on away out of the solar system!

 

[luvantique]

No - you can't carry enough propulsion to accelerate AND decelerate.... If you're willing to compromise for the first several voyages (until you have a laser on Mars too), you simply use propulsion to decelerate and the laser to accelerate - but not as much acceleration as you will do in the future...

You still gain the benefits of "modest" acceleration without fuel on the ship itself... Once you have that laser on Mars built, you can take full advantage...

I assume you mean you gain the benefits of "modest" acceleration without using the fuel on the ship, but you're still not thinking this through. In your scenario, your ship must carry fuel for the deceleration phase. There is a physical limit to the amount of fuel it can carry. If you were getting there by conventional means (simplistic one way trip, for the sake of illustration), you would use half of your fuel to accelerate, and half to decelerate. If you use the laser for the initial acceleration, you have twice as much fuel available for conventional deceleration (on these initial trips). But that still means that you cannot go to a velocity higher than you can decelerate from with that available fuel, and that the deceleration must begin twice as far out. There is a consequent limit on maximum velocity, but the extended deceleration time because of the higher maximum velocity makes a huge dent in any time savings made by using the laser. And bear in mind that it isn't really a time savings because you only save fuel with the laser. Manned missions still can't accelerate outside of comfort levels, so there is no significant time advantage from the laser until you have one on both ends.

 

[captaincranky]

I could be wrong, but I'm pretty sure that at the speeds it is travelling at it would not enter an orbit around Mars. It's path would deviate slightly but it would be going way too fast to be caught in Mars gravity so it would then plough on away out of the solar system!

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).

In another vein, the premise of "starting colonies on Mars to mine its natural resources", is quite disturbing.

First off, Mars, never having sustained life on a scale with earth, won't have oil, coal, or natural gas. Second, feeding the 10 billion people on earth, (by the time the mission "gets off the ground"), can't be done with Mars rocks. And third, how much tonnage of whatever is usable would have to be transported to meet earth's needs? I seriously doubt, "we'll just build bigger lasers", is an altogether viable option.

I've been around for a long time, and I'll grant you many things which were science fiction in my childhood, have now become science fact. That said, what I'm hearing is just another scientist spouting retreaded comic book sci-fi concepts akin to, "using sails to capture the solar wind for propulsion", blah, blah, blah.

 

[captaincranky]

I assume you mean you gain the benefits of "modest" acceleration without using the fuel on the ship, but you're still not thinking this through. In your scenario, your ship must carry fuel for the deceleration phase. There is a physical limit to the amount of fuel it can carry. If you were getting there by conventional means (simplistic one way trip, for the sake of illustration), you would use half of your fuel to accelerate, and half to decelerate. If you use the laser for the initial acceleration, you have twice as much fuel available for conventional deceleration (on these initial trips). But that still means that you cannot go to a velocity higher than you can decelerate from with that available fuel, and that the deceleration must begin twice as far out. There is a consequent limit on maximum velocity, but the extended deceleration time because of the higher maximum velocity makes a huge dent in any time savings made by using the laser. And bear in mind that it isn't really a time savings because you only save fuel with the laser. Manned missions still can't accelerate outside of comfort levels, so there is no significant time advantage from the laser until you have one on both ends.

You know what junior? This whole concept is speculation, part and parcel. I wouldn't be terribly surprised if the first time they fired up the laser, it burns a big a** hole in the sail. Then too, how many windmills would we have build, or how many tons of coal would we have to burn, just to make a test flight?

This is crap on the order of Elon Musk's bull s*** pronouncement, "it wouldn't take that long to develop a flying car". Really dude? You would want to have all that prop wash and spinning propellers landing next to a condo in the city? Not to mention people who can barely drive a land vehicle, being summarily issued drivers licenses for flying cars.

I doubt if I'll live to see "space sailboats", but for those of you who are left, a provisional, "bon voyage".

 

[Squid Surprise]

I assume you mean you gain the benefits of "modest" acceleration without using the fuel on the ship, but you're still not thinking this through. In your scenario, your ship must carry fuel for the deceleration phase. There is a physical limit to the amount of fuel it can carry. If you were getting there by conventional means (simplistic one way trip, for the sake of illustration), you would use half of your fuel to accelerate, and half to decelerate. If you use the laser for the initial acceleration, you have twice as much fuel available for conventional deceleration (on these initial trips). But that still means that you cannot go to a velocity higher than you can decelerate from with that available fuel, and that the deceleration must begin twice as far out. There is a consequent limit on maximum velocity, but the extended deceleration time because of the higher maximum velocity makes a huge dent in any time savings made by using the laser. And bear in mind that it isn't really a time savings because you only save fuel with the laser. Manned missions still can't accelerate outside of comfort levels, so there is no significant time advantage from the laser until you have one on both ends.

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...