travelling near light speed

Photonic Propulsion Could Get Us to Mars in a Month, But?

Our journey into the final frontier is still in its infancy. Russian cosmonaut Yuri Gagarin was the first human to venture into outer space in 1961. Fast forward to today and we have men and women living aboard a space station orbiting 249 miles above Earth. Private companies such as SpaceX are pushing the boundaries of what’s possible with reusable rockets. Probes like New Horizons are studying the distant bodies of our solar system. But, how do we take that next step?

One potential answer is photonic propulsion. Basically, using lasers as propulsion.

Professor Philip Lubin from the University of California Santa Barbara gave a talk at the 2015 NIAC Fall Symposium last October. In it, he tackled the prospects of photonic propulsion and what it could mean for interstellar travel and exploration.

Lubin tells us we can already get to relativistic speeds (a speed that is a sizable proportion of the speed of light) in the laboratory. Think the Large Hadron Collider in Europe. That uses electromagnetic acceleration.

Then we get to things we use to travel in everyday life – cars, airplanes and rockets. And “we are pathetically slow,” according to Lubin. This is where photonic propulsion could come into play.

Now, this isn’t your typical propulsion system. Think about NASA’s Dawn and New Horizons spacecraft. The propulsion systems are attached to the spacecraft. What Lubin is proposing is building a laser array to propel a spacecraft. The array and the spacecraft start in low-Earth orbit. But, then the spacecraft is propelled away while the array stays in Earth orbit. Here’s an image that illustrates what’s going on.

photonic propulsion

You see how the craft is much further away from the laser array? That simulation was using a 20 m diameter array with power of 272 kW propelling a 1 g payload. What makes this system so intriguing is it’s scalable. You could create a bigger array to power a bigger payload.

When the SLS launches in the next few years, it will rise off the launch pad at between 50 and 100 gW (gigawatts). “Turns out, to get to relativistic speeds with the spacecraft we’re talking about, you basically need the same power level,” says Lubin. “And for about the same amount of time. It takes 10 minutes to get to orbit with the shuttle. It takes us 10 minutes to get to 30% the speed of light with about the same power level, just using different technology.”

This technology could propel a 100 kg spacecraft to Mars in three days. Something the size of a shuttle? About a month.

“There are recent advances which takes this from science fiction to science reality,” says Lubin. “There is no known reason why we cannot do this.”

The potential uses for photonic propulsion are nearly endless. From planetary defense to SETI. You can imagine how handy this technology would be for pushing asteroids or comets on a potential impact course away from us.

How do you stop?

And therein lies the rub. “If you ever watched Spaceballs, you know on the back it says ‘we stop for nobody.’ So we stop for nobody,” Lubin joked at his NIAC Fall Symposium talk. One idea is an Alpha Centauri flyby mission.

exploring the cosmos

Getting to Mars in three days sounds great, but placing an object in Mars orbit is trickier. You would need a second array on the surface or orbiting the red planet to slow down the spacecraft. But, using this propulsion for manned missions is a very long ways off. It would be better suited for flybys of objects outside of our solar system.

Watch the entire talk by Lubin to learn more about the ins and outs of photonic propulsion.

15 comments
  1. what happens when the laser stops working or is interrupted, the astronauts are stuck without anyway to get anywhere… great…

  2. This is only experimental. Things evolve! Technology changes!!! If you existed 100 years ago, the modern automobile would not have seen the light of the day!

  3. If all that’s needed is a (de)propulsion system in Mars orbit to slow the craft down, that seems like that’s what the NASA priority should be – just using conventional tech to get it there, like we’ve done a dozen times or so already.
    From there – the economy generated by such fast turn-arounds would easily justify the effort.

  4. I think a better analogy for you would be “If you existed 100 years ago we would of still be improving steam engines”… there are much much more promising theoretical propulsion systems. Lets not forget lasers suffer from propagation loss and will eventually fall prey to the inverse square law, this is by far the biggest challenge of this system, using for take off and initial acceleration may be, but getting back is a problem again. By the time they develop a practical application with this, we will be traveling between star systems, again something like this would be useless at that point.

  5. A laser system that big would be modular, so if individual units failed they could be replaced quickly with spares. And if the whole thing failed, we could all step outside with our laser pointers and help out.

  6. Maybe we’ll be traveling between star systems….Using Lasers!

    Space lasers don’t suffer from propagation loss in the tradition sense because they are “propagating” through a vacuum. As for inverse square losses, lasers don’t use the law in the same way that a radio or microwave signal would. Radio waves spread out in all directions from the get-go and as a result the signal intensity drops precipitously with distance, but this isn’t true for lasers. It’s true that energy “density” would depend on the beam area, but lasers don’t spread out in the same way, in fact there is no real reason why they have to spread out at all. Assuming that the lasers were exceptionally well constructed and the target sufficiently large, I don’t see why this couldn’t work at long distances. I do agree though, about your point on there being other cool theoretical drives in the works, this just seems less “theoretical” than most of the alternatives i’ve heard of.

  7. Could they first land a reflector on Mars, then bounce the light from the earth laser off it to slow down the spacecraft? Beam spread over that distance may be a problem however.

  8. I’m not a professional or anything, but couldn’t you just get the craft up to a speed that would be sustainable and, more importantly, reversible, and then use on-board chemical rockets to slow the craft when you want to enter orbit? You probably wouldn’t want to keep the laser on the target all the way to Mars or elsewhere anyway.

  9. Think about it this way, you would need an equal amount of energy to slow it down as was used to speed it up. If chemical rockets could not propel a craft to the speed that the laser could, then chemical rockets couldn’t slow it down enough to be effective.

    You would only need to keep the laser “on the target” long enough to get it up to the desired speed, there is no “air” resistance in space to counteract motion, it just needs a push.

  10. Interesting idea, but there are a couple issues.

    First, planets rotate, therefore having a planetary based array beaming to another planetary based system would not allow much time for the beam to be “synced” as it would only work while they are faced at each other.

    If they were both orbital stations you would have much more time but they would still be in orbit so there would still be a limited amount of time for acceleration/deceleration to take place. Because in this scenario, only one array is providing energy, you would compound the complication with the need for the Mars orbiter to be “in sync” with the earth orbiter so that there would be equal time/distance to decelerate as there was to accelerate.

  11. The question I have is in regards to the “orbital array”. Wouldn’t the discharge of energy from the orbital array push on the array itself with the energy equivalent to the craft it is propelling?

  12. Thanks Chris, that was kind of what I was getting at. You only need to get it to a certain speed and then shut down the laser propulsion. I was thinking, though, if you are not using “rocket fuel” for forward propulsion, you could then save it all for the brakes. Currently, most of the fuel is used for getting out of the gravity well of earth/moon. If you could save that fuel just for slowing down, you wouldn’t have to rely on end-point laser braking. Which, if it fails, is not a good thing.

    How you’d get that fuel into space to save is a whole other question. Also, probably don’t want to be traveling great distances strapped to a big bomb either.

  13. You would design the array so that it has a tendency to escape orbit and fire it at the vehicle either to speed up the orbit or to return it to the orbit, time after time after time.

  14. Not feasible to generate such laser in space at the moment. Personally I believe Ion propulsion is next rather than laser propulsion.

  15. The problem is, if you could use chemical rockets to ‘slow down’ something moving at that blistering speed, then you could use them to get to that speed in the first place and we wouldn’t need lasers. I think our first mission to mars would be ion pro-pulsed. Now lasers might be useful for fly-by satellites or even ships for two-way travel to mars IF we could establish another laser array at Mars to slow down incoming objects and send them back to earth. But we’d still need to get there by other means or find some other way aside from chemical rockets to slow down a laser-propelled craft.

    Here’s a question. What about using mar’s own gravity to sling-shot a craft back around? Or would a craft be moving at a speed too great for that?

Leave a Reply

Your email address will not be published.