Using Spacex BFR to rapidly and affordably build interplanetary photonic railway by the 2030s

The Lubin UCSB laser propulsion system efforts have been funded by Breakthrough Starshot for $100 million. They are working working to demonstrate proof of concept for light-propelled nanocrafts.

A large scale network of several 70 Gigawatt lasers on Earth, Earth Orbits, the moon Mars and asteroids is not as distant as one might think because of several converging systems and technological shortcuts.

A laser power of 70GW (without photon recycling) can send a 100 kg craft can be propelled to 1AU in approximately 3 days achieving a speed of 0.4% the speed of light, and a 10,000 kg craft in approximately 30 days.

The full scale DE-STAR 4 (50-70 GW) will propel a wafer scale spacecraft with a 1 meter laser sail to about 26% the speed of light in about 10 minutes (20 kgo accel), reach Mars (1 AU) in 30 minutes, pass Voyager I in less than 3 days, pass 1,000 AU in 12 days and reach Alpha Centauri in about 20 years. The same directed energy driver (DE-STAR 4) can also propel a 100 kg payload to about 2% c and a 10,000 kg payload to more than 1,000 km/s. While such missions would be truly remarkable, the system is scalable to any level of power and array size where the tradeoff is between the desired mass and speed of the spacecraft.

Photon Recycling was a 5X in 2015 and 100X seems doable

The NASA funded Directed Energy Propulsion for Interstellar exploratioN in 2015 and 2016 tested a photon recycler.

The team also tested a photon recycler, a device that reuses photons from the laser by shining them on a reflector cavity. “We have a second mirror at some distance away that bounces the photons back and forth like a ping-pong ball onto the spacecraft reflector.” Brashears said. “In effect, we’re recycling these photons to achieve a force multiplication that allows the vehicle to go even faster. So far, with a simple implementation, we have achieved an amplification factor of five. Much more is possible with refinement. This works as predicted, though implementing it into the full flight system will be complex.”

Photon recycling works better for laser pushing larger objects because they have slower acceleration and stay within range of the reflections for a longer time.

Photon recycling could reduce the size of the laser array and power systems needed to achieve the desired performance or to increase the performance for the same sized system.

20X size reduction to about 3.5 GW for the laser array and power systems seems doable.

10 GW PLT with a thrust multiplication factor of 1,000, would generate a thrust of 66.7 kN, which can accelerate 6.8 ton Spacetrain at 1.0 g, a comfortable cruising acceleration.

Improving lasers, solar and batteries make the whole system lighter

Lasers are approaching 1 kw per kg, solar weight to performance (also approaching 1 kw per kg) is also improving and solid state batteries with initially 500 watts per kg could reach 1000 watts per kg.

Large scale 3D printing and robotics are being developed for assembly and manufacturing on the moon and in space.

Spacex can make the BFR for reusable affordable heavy lift to the moon, Mars, Titan and other locations

All of Spacex resources will go to develop the 150 ton reusable payload capacity BFR rocket.

Let us assume one 150 payload for 50 tons of lasers, 50 tons of solar and 50 tons of batteries and another 150 tons for robotics, 3D manufacturing and other astronauts and other systems.

50 tons of lasers at 1 kilowatt per kilogram would be 50 Megawatt and the same for the solar and batteries.

20 such payloads would be 1 gigawatt.

70 would be 3.5 gigawatts. 3.5 gigawatts with a photonic reflection amplification of 20 times would be 70 gigawatt system performance.

Spacex is targeting $5-10 million per BFR launch. The launching of each system would be about $1 billion total if Spacex achieves those costs.

One Spacex BFR launch per week could put such a system with the assembly robotics and other systems up into orbit within 2 years.

Another dedicated Spacex BFR could place a system on the moon within 2 years.

Three or four dedicated Spacex BFRs could put the receiving system on Mars within 2 years of launches and effort.

The lasers would then be sending and receiving 100 kg packages and satellites within hours transit to the moon.
The lasers would then be sending and receiving 100 kg packages and satellites with three day transit to Mars.
Manned crew capsules could be going to Mars in 2 weeks and maybe 1 week. The size of the crew capsules should be less than 100 tons. 5 to 10 tons might be the optimal size. 1 week travel times might be stressful for regular passenger trips.

The robotic systems would be used to mine the moon, Mars and asteroids to build out massive solar arrays and laser arrays.

The Laser transportation system would be the high speed rail or subway for our solar system

The best use of the Spacex BFR and the $60 billion per year the US already spends on NASA and military space systems would be to build the interplanetary laser transportation network.

Building out to Terawatts of power with larger mirrors would enable even larger and heavier spaceships to be transported.

Professor Bae had laid out steps to Photon Propulsion for interplanetary and interstellar Flight.

The systems described here are an improvements by several orders of magnitude over regular power beaming. Recycling photons between mirrors reduces the energy requirements as does lightening the spacecraft and shortening the wavelength of the laser.

The operation distance of PLT is projected to be up to 1,000,000 km, which can cover a wide range of spacecraft maneuvering over lunar-scale distances. The diffraction limited size of the beaming lens should be on the order of 200 m and the spacecraft mirror diameter 50 m. The sizes the lens and mirror will decrease proportionally as the laser wavelength decreases. For example, a 100 time reduction in the laser wavelength will result in the lens diameter 20 m and the mirror diameter 5 m.

The Interlunar Photonic Railway with PLTs is predicted to meet the needs of the future generation of space industry market by enabling a wide range of innovative space applications involving the moon as a second step towards interstellar manned roundtrip commutes. For example, a 10 GW PLT with a thrust multiplication factor of 1,000, will generate a thrust of 66.7 kN, which can accelerate 6.8 ton Spacetrain at 1.0 g, a comfortable cruising acceleration.

Interplanetary Photonic Railway

With the Earth-Mars distance of 225 million km, the diffraction limit sets the beaming lens diameter 2.5 km, and the spacecraft mirror diameter 220 m with 1 µm lasers. For the Earth-Pluto Photonic Railway with a distance of 7.3 billion km, the diffraction limit sets the beaming lens diameter 35 km, and the spacecraft mirror diameter 500 m with 1 µm lasers. A 1,000 times reduction in wavelength will reduce both the lens and mirror diameters by a factor of 32 respectively, and the lens and mirror diameters required for Earth-Pluto Railway will be 1 km and 16

20 thoughts on “Using Spacex BFR to rapidly and affordably build interplanetary photonic railway by the 2030s”

    • Outside of the incredible engineering challenges in building this stuff in space, I agree that you will need to double up on all the hardware to slow the systems down on the receiving end. Not to mention that congress just wants to spend its money on the military industrial complex. Imagine having these lasers in space and the military and right wing fanatics not wanting to be pointing them to Earth.

  1. Just wait for fusion to mature in 10 more years and we will be able to traverse the galaxy with a real spacecraft.

    • It is unwise to wait for something that isn’t known to be certain yet to become known.

      Better work and do with whatever we have at hand. As I said before: if you have a horse, ride it. If you’ve got a car, drive it. And if you’ve got a rocket, launch it.

      And many times, one thing is the requirement of the other, or needs to happen before the other. It’s very likely some science and tech required to make fusion rockets or other revolutionary thrusters, comes precisely from an increased human presence in space, and if there aren’t enough people there, thy would probably never arrive or do it much later.

      That’s why I oppose the idea that we should wait to have better propulsion methods instead of dreaming of going to the Moon, Mars and beyond in big chemical rockets.

      Quite the contrary: use them and develop them to their technical and practical perfection.

      • Allegedly the warp drive will be functional this century. Reminds me of the slower than light speed being met by a FTL or warp ship named Serendipity in a Robert Heinlein story or book.

        • There was a classic SF short story, “Space Is Dark”, (Alas, I don’t remember the author. Campbell?) A team launches the first interstellar mission, in suspended animation. A thousand years later they arrive at their destination to be greeted by cheering crowds and a brass band, in a park with statues of themselves.

          It even inspired a classic flik:

          The first FTL drive was invented a few years after they left, but their ship couldn’t be caught up with and stopped, it was moving too fast to match speeds with.

          It’s a classic trope in SF, and one of the reasons that nobody is going to launch an interstellar mission until propulsion technologies have stalled. Nobody wants to be the one who spends a fortune getting there last.

        • There are several fringe-y topics being researched that can alter the landscape of space travel this century.

          The Emdrive (which is most likely an experimental artifact, we just need to be sure), Woodward’s MEGA drive, which has a good track of replications but not much in the way of thrust and several others deeper in the fringe but with some small chance of being real, or that at least are more serious in their investigation (e.g. David Pares’ warp drive).

          And of course, efforts within acceptable science and tech but that are just immature or with unknown feasibility, like fusion power for energy and rocketry.

          Any of these becoming actual proven science or technology would radically alter any prediction of the future.

          For that reason I’m not arguing for making a crewed interstellar ship in the next few decades. That can certainly wait.

          I’m rather arguing about going into the region of space we can go and settle now (the Solar System) with whatever technology we have.

    • So Captain Columbus. Why go to all the risk and expense of sailing outside of Europe looking for gold and silver when our alchemists assure us they can make it from lead with a just a couple more years of funding and research?

    • You can do both. No reason why you can’t. The moon is a good spot to build lasers (apart from dumping waste heat). Lasers are good for moving cargo slowly but that’s ok cargo isn’t in a hurry.

  2. I still don’t understand how you can point a GW laser at anything, and not have it boil up into a rapidly expanding plasma cloud?

    • You can do it if that something is specifically designed to be maximally reflective at that specific wavelength. The catch is even the tiniest imperfection, even a dust speck on your mirror, and it’s all over.

      That’s why ultra high level laser acceleration is probably only ever going to be used for unmanned probes; Even with everything going right, you’re going to lose a significant fraction of them.

      Now, what you can do for manned ships is accelerate cheap mass produced light sails to high speed, and impact them against a pusher plate on the the manned ship, to transfer their momentum. It’s a variant of “mass beam” propulsion.

      But I don’t see the concept being much used for in-system propulsion; The amount of energy you need to make it work is insane compared to something slower like beamed power driven ion engines.

  3. This is strongly dependent not just on launch mass and cost per pound to orbit (something BFR and BFS could take care of in the not so long term future), but on energy sources.

    These systems can be nuclear powered, but such energy source is controversial and I don’t see the public stance on it changing much in the foreseeable future. Even small reactors of a few megawatts will have a tough time being built and approved for use, in some eventual lunar or martian settlements, where they will be most needed.

    But there are other options. The space in the neighborhood of the Sun has lots and lots of energy in the form of light and radiation.

    And I believe such abundance will be noticed again and commercially used in the form of Solar Power Satellites (SPS) soon, at least way before we have laser launchers pushing loads betwen Earth and the Moon or Mars.

    In fact, I think they will very likely come as an offshoot of SPS. Instead of beaming microwaves to Earth-based antenna, an SPS could power these mighty lasers with some handy solar-clean Gigawatts of power.

    Once the methods and market for SPS arise, they could be moved and deployed on the Moon and Mars, enabling the required infrastructure for accelerating and braking the loads.

    All of this also fits BFR and BFS stated capabilities nicely.

  4. I don’t see anything about slowing down to land. Passing Mars at a significant fraction of the speed of light doesn’t seem very useful. For passengers you would probably need to speed up at 1g half way there and then turn the ship around to use a Mars based laser to slow down at 1g. Difficult given that Mars and Earth are moving so the laser that is meant to slow you down won’t be a straight line shot. (you would be traveling to where Mars will be when you get there, not where is actually is). God help you if something fails and you don’t get slowed down in time.

  5. Would emissions from a working system be detectable at interstellar distances? If so, there are implications for SETI. Just a thought.

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