Re: "How do you stop?" The simplest answer is to construct another laser array at Mars. If regular commerce between Mars and Earth becomes a reality then an infrastructure will be established on the red planet. This would include laser breaking and launch capability. Re reduced gravitation and low density atmosphere on Mars also makes many other technologies feasible. Studies of the Martian surface indicate that most of the elements necessary for an industrial society are present in abundance and if our theories of planetary formation are any where near correct the more rare elements are there as well. Automated mining, refining and manufacturing are likely to be high priority activities early in the Martian colonization strategy. Constructing an orbiting laser array would be an obvious part of that plan.
I have been doing some consulting for some companies that are pursing asteroid mining and "exotic" propulsion systems. These and many more issues are receiving their close attention.

Remember, this is a sail, and applying nautical principles, it could tack to change the resulting thrust vector. Not so much braking, but a planned steering trajectory to place it on an intercept course. Of course, that would probably extend the flight time beyond the sensational three day claim.

I didn't post the link because I got an e-mail from here that seemed to discourage posting links.

The problem there is that when you start dealing in relativistic speeds you run into Einstein's classic mass to energy conversion problem: that it starts taking exponentially more energy to move a massive object the closer you come to the speed of light. It is for that reason that even electrons only travel at speeds approximating the speed of light. Though your initial thought is good, the practicality is that the speed would eventually taper off to the point that even though you were constantly expending energy in thrust, your velocity increase would cease.

My own concept was a series of orbiting rings that would sequentially boost an object's speed as it passes through them similar to a rail gun. Each ring would dramatically boost the speed of the object and after three or four boosts it would be projected toward its target. Then the "ship" would only have to worry about slowing down on the other end. Oh, and not liquefying any kind of compressible/organic material like say... the pilot... ;)

Yes, some are absurd or rely on principles of "magic", but there are other sci-fi authors who were meticulous in their application of science in their stories. Star Trek: The Next Generation faded off quickly when it all disintegrated into "which new particle can we invent to save the day!"

Then again, the original Star Trek communicator led to the cell phone. See also (http://entertainment.howstuffworks.co...) I would also note that most good sci-fi has some basis in reality - see Star Trek V as a pointed example of the absurdity of some sci-fi, where The Martian was rigorously researched.

When I worked at NASA one of the more interesting projects was interstellar mission planning.

(http://interstellar.jpl.nasa.gov/inte... )
(https://ntrs.nasa.gov/archive/nasa/ca...)

The two greatest challenges were propulsion and spacecraft autonomy. We considered light sales and lasers but the technology at the time was not up to the task. More recent advances in materials science and laser systems make the concept not only feasible but doable.
The options for Mars mission propulsion can be classified as "self contained" and "external source". Self contained would be any type of rocket where the reaction mass was contained within the vehicle and expelled to produce thrust. Chemical as well as nuclear powered ion drives would come under this category. External would include solar, laser and microwave powered systems where the photonic pressure directly provided thrust. Nuclear or solar powered ion rockets such as the VASIMR could reduce Mars mission times from months to weeks and a laser powered sail could reduce the mission time to a few days. Very impressive.

http://earthsky.org/
That's easy for even me dino to look up. Thanks!

From the Allosaurian Dictionary~
Science fiction: Contemporary fairy tales weaved from both speculative and silly science

I came up with an idea to test light speed travel/ warp drive a while back. Not sure how valid this is:

I'm under the impression that if something accelerates in space, it would keep accelerating so long as it had thrust since there would be few forces to slow it down. How about launching a small rocket, albeit with a long term power source- nuclear or whatever. Point it in a safe direction and let it fly. With a consistent thrust, I would think it would continue to accelerate, perhaps faster than any space craft has gone before. Have equipment on it to send back data to Earth as it heads out of our solar system. It might be interesting to see how fast continuous acceleration would take it.

Some hazards for the craft involved: We likely couldn't control it well so it may run into a planet, asteroid or whatever. Plus, at those speeds, it could be a collision with a pea sized piece of space debris could prove catastrophic. But, hey, you have to start somewhere.

Gave you a point because I see your point.
Nevertheless, there is a percentage of dreamers who invent what they dream of. Never say never.
I've met some who live and breathe "never" to the point of denying that man ever went to the moon.

If you're interested in daily facts about space and such, look up Earth/ Sky News. Tells you all about the astronomical events going on each day.

I've obviously had an interest in such things.
This post I have created has caused me to realize that, in my zeal for mankind to find a way to reach the stars, I never really considered how the heck do you stop when you get there.

One of the things that we take for granted as well is conservation of momentum. In Star Wars and Star Trek one pops out of hyperspace going the same speed one popped in. One thing I do appreciate in Star Wars is that they do have strictly tasked navigational computers which map a "safe" path through the galaxy to the destination so as to avoid flying through a star. This comes up in several instances. Other sci-fi genres (Dune) take a different tack and vehicles are stationary (in real space) while transiting "hyperspace". There the operative principle is not really hyperspace but space folding.

Overall, I think your article reminded me most of a Star Trek: Deep Space 9 episode where Cisco and his son travel from Bajor to Cardassia in a solar sailer similar to this design. Now to see if we hit any tachyon bursts which warp us out into the galaxy! ;)

You're obviously a space buff like me.

I'm suddenly thinking of all the times I've space movie entire fleets come out of that warp drive thingie.
It never occurred to me until now that must be a lot harder to do than all the times I've seen entire fleets go into "warp drive."

interesting how concerned some are about stopping when in reality nobody is ever going to get off the ground for this excursion.

Gravitational attraction does not provide braking, however. It takes either reverse thrust or an atmosphere to bleed off the energy. It's all fine and good to accelerate, but one always has to consider the other end as well. That's why hyperspace travel from a sci-fi perspective is so appealing because one simply shifts from propulsion in normal space at one set of speeds to propulsion though hyperspace at huge speeds.

Bad choice of words. I was thinking a craft attempting to decelerate from light speed by using atmosphere would have to loop an earth-sized planet many, many times.
A pilot or better a computer would have to fly the thing. That's what I meant by a "controlled orbit" or flown loops around a world.
Can't see this happening due to the speed of light entry speed into an atmosphere.
Ship may just blow up. I once saw a meteor do that before it could become a full-fledged meteorite.
That's what happens when an airplane dives straight into water at high speed. As a former water skier, I have bounced off water that felt like concrete at rare times I've skied that fast and fell.

What do you mean by a "controlled orbit"?

Whatever velocity you have when you arbitrarily enter the "gravitational field" of a ponderous body determines the shape of your orbit.

If you are going really faster, you get a hyperbola and off you go.
A little less fast and you get a parabola and off you go.

More manageable and you have an ellipse, the axes of which are determined again by the initial velocity.

Get that v just right and you have a circle.

oh... one more... the one in this problem: straight line... impact.

https://www.google.com/search?q=%3D+2...
If the target is the atmosphere of that earth sized planet, I wonder how a spacecraft can even stay in a controlled orbit coming down from such a speed.

How do you stop?
Good question.
The usual method is to aim for something soft.
This could be the atmosphere of the target. But there is an enormous amount of energy to get rid of.

3 days for a few hundred pounds. Not quite the transport system in Galaxy Quest, but a step in the right direction.
(How does it brake?)

Good point.
The speed of light is incredibly fast.
Sigh.
Would NASA be holding back something?

How do you stop? Several Heinlein stories have "torchships" with constant acceleration. At 9.8 m/s/s at the end of three days, you would be going 2,540,160 m/s which is fine and all, but then what?

Heinlein's ships swung about so that the drive unit could counter the direction of motion. How do you do that with a solar sail?