Category Archives: solar sails

PopSci: Lasers Could Send A Wafer-Thin Spaceship To A Star

Lasers and photon drives have been a staple of science-fiction for 150 years.

Now finally, laser-driven star probes are in the main-stream of science.

Lasers are now advanced enough to help launch interstellar space probes, researchers say.

Scientists calculate that a gram-sized laser-propelled space probe could reach more than 25 percent of the speed of light and arrive at the nearest star in about 20 years.

The Voyager 1 spacecraft launched in 1977 is finally leaving the solar system after 37 years of flight at a speed of roughly 38,000 miles per hour or less than 0.006 percent the speed of light. This suggests that with conventional propulsion technology, humanity will never reach even the nearest stars, says experimental cosmologist Philip Lubin at the University of California, Santa Barbara.

Lubin and his colleagues suggest that, instead, lasers could accelerate small probes to relativistic — that is, near-light — speeds, reaching nearby stars in a human lifetime. “No other current technology offers a realistic path forward to relativistic flight at the moment,” Lubin says.

The problem with all thrusters that current spacecraft use for propulsion is that the propellant they carry with them and use for thrust has mass. Interstellar spacecraft require a lot of propellant, which makes them heavy, which requires more propellant, making them heavier, and so on.

Photon drives instead involve equipping spacecraft with mirrors and depending on distant light sources for propulsion. Solar sails rely on light from the sun, while laser sails count on powerful lasers.

Lubin acknowledges that photon drives are nothing new — in a letter to Galileo Galilei in 1610, Johannes Kepler wrote, “Given ships or sails adapted to the breezes of heaven, there will be those who will not shrink from even that vast expanse.” What is new, Lubin says, is that recent, poorly appreciated breakthroughs in laser technology suggest they can now accelerate spacecraft to relativistic speeds.

Breakthroughs in laser technology suggest they can now accelerate spacecraft to relativistic speeds.

The advance that Lubin’s approach depends on involves laser arrays. Instead of building one extremely powerful laser — a technologically challenging feat — researchers now can build phased arrays that are made of a large number of relatively modest laser amplifiers that can sync up to act like a single powerful laser. This strategy also eliminates the need for a single giant lens, replacing it with a phased array of smaller optics.

The researchers envision a phased array of currently existing kilowatt-scale ytterbium laser amplifiers that can scale up gradually, adding lasers over time. For instance, a current 1- to 3-kilowatt ytterbium laser amplifier is about the size of a textbook and weighs roughly 5 kilograms.

Eventually, the scientists calculate that a 50- to 70-gigawatt array that is 10 kilometers by 10 kilometers large in Earth orbit could propel a gram-sized wafer-like spacecraft with a 1-meter-wide sail to more than 25 percent of the speed of light after about 10 minutes of illumination, which could reach Mars in 30 minutes and Alpha Centauri in about 20 years. The researchers suggest this array could launch roughly 40,000 relativistic wafer-sized probes per year — each “wafersat” would be a complete miniature spacecraft, carrying cameras, communications, power and other systems.

The same array could propel a 100-ton spacecraft — about the mass of a fully loaded space shuttle, sans rockets — with a 8.5-kilometer-wide sail to about 0.2 percent of the speed of light after about 15 years of illumination. However, it would take about 2,200 years to reach Alpha Centauri at those speeds. Lubin suggests a larger array would make more sense for a human interstellar trip in the distant future, “but I personally do not see this as a priority until many robotic probes have established a need to do so.”

A major problem with this strategy is braking — the researchers currently have no way to slow down these laser-driven spacecraft enough for them to enter into orbit around the distant planets that they are dispatched to. The first missions that accelerate to relativistic speeds may have to simply fly by targets and beam back their data via lasers, Lubin notes.

Lubin notes there are many additional uses for such a laser array other than space exploration. For example, it could deflect asteroids away from Earth, or blast debris out of orbit to prevent it from threatening spacecraft, astronauts and satellites.

They are currently testing to show that small lasers can stop asteroids from spinning.

The researchers stress that they are not proposing to immediately build the largest system. They are currently testing small lasers on asteroid-like rock samples to show that such systems can stop asteroids from spinning, work that could help one day wrangle asteroids for exploration.

If lasers are the only practical route for interstellar travel, Lubin and his colleagues suggest that alien civilization may currently use lasers to help explore the cosmos. They suggest that SETI projects should look for telltale signs of such technology.

Lubin presented his latest work in a talk on January 25 at Harvard.

Lubin however fails to mention how the Military-Industrial-Complex invested billions and billions of dollars to make lasers into a combat grade weapon, which lasers of this type obviously are.

Which begs the question of “Will the government allow space probes of this type to be used?”

And who or whom would be allowed to construct them?

Original article

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Laser Powered Bussard Interstellar Ramscoops

We do a change of pace today as we move from the UFO Community to the mainstream ( sort of ) of Paul Gilster’s Centauri Dreams and Tau Zero’s discussion of real life interstellar propulsion methods and starflight.

Here Robert Bussard’s ramjet is linked with Robert Forward’s idea of laser-powered starflight and a more efficient method of vehicle acceleration –  and more importantly ‘deceleration’ at the appointed destination:

Many of the interstellar concepts I write about in these pages take on a life of their own. After the initial brainstorming, the idea gets widely enough disseminated that other scientists take it on, looking to modify and improve on the original concept. That’s been true in the case of solar sails and the more recently devised ‘lightsails,’ which use beamed energy from a laser or microwave source to drive the vehicle. We continue to study magnetic sails — ‘magsails’ — and various nuclear options like the inertial confinement fusion that powered Daedalus and perhaps Icarus. Sometimes insights arise when ideas are grafted onto each other to create a hybrid solution.

The idea I want to examine today, a hybrid design combining a Bussard-style interstellar ramjet with laser beaming — exemplifies this mix and match process. Working with Daniel Whitmire, A. A. Jackson, a frequent commenter and contributor here on Centauri Dreams, pondered the various issues the Bussard ramjet had run into, including the difficulty in lighting the proton/proton fusion reaction Bussard advocated early in the process. Writing at a time not long after he had finished up a PhD in relativistic physics (at the University of Texas), Jackson conceived the idea of beaming energy to the spacecraft and discovered that the method offered advantages over the baseline Bussard design. The laser-powered ramjet is a fascinating concept that has received less attention than it deserves.

Image: Physicist and interstellar theorist Al Jackson, originator of the laser-powered ramjet concept.

Bussard’s ramjet, you’ll recall, lit its fusion fires using reaction mass gathered from the interstellar medium by a huge magnetic ram scoop, which itself has proven problematic given the drag issues such a scoop introduces. The other way to power up a starship using an external source of energy is to beam a terrestrial or Solar System-based laser at the departing craft, which has deployed a lightsail to draw momentum from the incoming photons. Jackson and Whitmire found the latter method inefficient. Their solution was to beam the laser at a ramjet that would use reaction mass obtained from a Bussard-style magnetic ram scoop. The ramjet uses the laser beam as a source of energy but, unlike the sail, not as a source of momentum.

Running the numbers and assuming all photons transmitted by the laser will be absorbed by the ship, the authors discovered that the laser-powered ramjet (LPR) is superior to the baseline Bussard ramjet at low velocities, while superior to the laser-pushed sail at all velocities. The Bussard design becomes the most efficient of the three at velocities equal to and above about 0.14 c. The laser-powered ramjet, then, solves at least one of the Bussard vehicle’s problems, the fact that it has to get up to a significant percentage of lightspeed before lighting its fusion reaction. LPR propulsion could be used up to 0.14 c, with the vehicle switching over to full interstellar ramjet mode to achieve high efficiency at relativistic velocities.

The laser-powered ramjet offers other advantages as well. Think back to some of Robert Forward’s laser sail concepts and you’ll recall the problem of deceleration. With the sail powered by a laser beam from the Solar System, it’s possible to reach velocities high enough to take you to the nearest stars in a matter of decades rather than centuries. But how do you slow down once you arrive? Conceiving a manned mission to Epsilon Eridani, Forward came up with a ‘staged’ solution in which the sail separates upon arrival, with the large outer sail ring moving ahead of the vehicle and reflecting beamed laser energy to the now smaller inner sail, thus slowing it down. It would be so much easier if the beam worked in both directions!

But with the laser-powered ramjet, a round trip can be made using a single laser beam because the beam is being used as a source of energy rather than momentum. Jackson and Whitmire showed that the efficiency in the deceleration phase of the outbound journey as a function of velocity is the same as for the acceleration phase. And on the return trip, the energy utilisation efficiency is more favorable in both the acceleration and deceleration phases because the ship is traveling into the beam. In fact, the laser-powered ramjet is superior to both the laser sail and the Bussard ramjet even at high fractions of the speed of light when traveling into the laser beam.

Let’s go over that again: Jackson and Whitmire’s calculations focus on the energy utilisation efficiency parameter, showing that the laser-powered ramjet is superior to the laser sail at all velocities, whether the ship is receding from the beam or approaching (moving into the beam). The LPR is also superior to the Bussard ramjet at velocities less than about 0.14 c when receding from the beam, and superior to the Bussard design at all velocities when approaching. Add to this that the LPR concept requires no onboard proton-burning reactor — the authors assume the use of Whitmire’s ‘catalytic’ ramjet using the CNO (carbon-nitrogen-oxygen) cycle — and that the LPR’s power requirements are less than those of the laser sail.

As this talk is more ‘mainstream’ than usual, the idea of spotting interstellar craft incoming to this Solar System is easy to spot, given the power output of the craft. Any invasion would be highly visible.

But the UFO phenomenon excludes that – no incoming craft are visible until they are already in the atmosphere.

So is wormhole technology being used, or are other folding door type technologies ( if one can call such things technology ) being utilized?

A Laser-Powered Interstellar Ramjet

Long Bet Update

I’ve been surprised by the sizable reaction to my bet with Tibor Pacher, not just in terms of comments here but in related e-mails. For those of you who missed the original post, I found Tibor’s prediction that the first interstellar mission would be launched by 2025 to be an irresistible target. Tibor posted the prediction on the Long Bets site, and the way this works is that someone willing to make a bet on the prediction puts down the money upfront and challenges the predictor to match it.

Negotiations follow, the outcome being that if the terms are worked out and the bet is accepted, it is finalized. Both parties send in their money, and the money grows over the years in a long-term investment portfolio called the Farsight Fund. Ultimately, either the Tau Zero Foundation or (Tibor’s choice) the SOS-Kinderdorf International, will enjoy the result.

Now that Tibor and I have finalized the terms, the details will go up on Long Bets as soon as our funds arrive (which should be in a few days). Until then, I thought you might be interested in some of the details we settled upon. Among other things, we have agreed that:

  • The mission can be a manned or unmanned, either a flyby probe or a spacecraft intended to be captured by the target star’s gravitational field. The mission will have been designed expressly as a mission to another star, and as not an outer-Solar System mission that simply keeps going, with a star more or less along its route of flight.
  • The allowed launch location of the spacecraft is any place in the Solar system within the orbit of Neptune, either from the surface of a Solar System body or from any orbital position.
  • The mission duration must be less than 2000 years.
  • As a minimum requirement for the mission the spacecraft shall be capable of delivering data for at least one scientific measurement.

The actual text of these details and a few other matters will be posted soon on the Long Bets site — I’ll provide the link once it’s available. And as I’ve told more than a few people, I would be delighted to be proven wrong on this matter, for it would mean that our technology is advancing at a far faster clip than I currently assume, and also that enough public support will exist to make such a mission possible. That sort of optimism (even though I think it’s premature) is a bracing tonic after the weekend’s loss of NanoSail-D, a solar sail deployment experiment.

I have to hand it to Paul and Tibor, they have a lot more optimism than I can claim, or wish to have. The loss of the light sail experiment makes number three loss that I know of ( previous Russian and Japanese experiments were destroyed during failed launches ). And of all provable mainstream concepts, this one is sure to work. If we can only get the damn things into orbit to test them!

Then maybe centuries hence, our descendants can have their own legend of The Lady Who sailed The Soul.

Of Solar Sails, Bets and Optimism

A Plug for the Tau Zero Foundation

Now we take a break from our regularly scheduled tinfoil to plug for an organization that just might literally take us to the stars, the Tau Zero Foundation.

The name is taken from a Poul Anderson tale about a starship crew, using a Bussard ramjet type spacecraft, literally approaches tau zero, relativistic light speed. It outlives the Universe actually. But anyway, the Foundation is a collection of writers, businesspeople, scientists, engineers and other volunteers who are dedicated to finding, and funding ways to build actual, realistic interstellar probes. Any and all ideas are encouraged, though ideas within actual technological reach are given first consideration ( warp drives and wormhole gates are acceptable, but laser driven solar sails are given first dibs! ).

Paul Gilster of Centauri Dreams is lead journalist and one of its first members. The Foundation is close to launching its website and since its an all volunteer group, donations are necessary to kick start this bad-boy and send it on its way! So give if you’re able.

Despite all of the pessimism that gets expressed here at times, this is one of the few things we can control, for now. Even if the Pentagon does have its own advanced military space program, a non-militaristic program is necessary to offset the war-pig B.S. Hopefully the Tau Zero Foundation can accomplish its goal of perfecting peaceful methods of exploring interstellar space and creating realistic, multigenerational projects that’ll benefit all of humanity, not just a few.

Tau Zero Foundation

Sneak Preview of Tau Zero website

Unsolved mystery, cosmic fireworks and sailing the light fantastic

After 100 years, the mystery of the Tunguska explosion that wiped out 80 million trees within a 770 square mile area is still with us. Theories range from meteors and comets to micro-blackholes and UFOs. But this morning at physorg.com I spotted one theory that was unique and unusual:

This year, the “alternativists” organised a separate conference held in a museum on Moscow’s picturesque Old Arbat street at which they sketched out outlandish theories for an event they say ordinary physics cannot explain.

Rodionov said the explosion was most likely caused by US physicist Nikola Tesla (1856-1943) detonating an underground volcano in Siberia by harnessing electric charges in the air from his laboratory tower outside New York.

I have to say the hypothetical involvement of Tesla was a surprise and that finding this in an otherwise ‘hard science’ Internet site was even more of one.

Tesla was certainly one of the great geniuses of the 20th Century and a lot of inventions that could’ve prevented the many deaths by wars were suppressed, even today are attributed to him. But to lay blame at his door of a mysterious explosion in Russia is wilder than even I or my ilk ever thought!

But hey, it ain’t any worse than blaming UFOs falling out of the sky!

Maverick scientists probe Siberian forest mystery

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My friend James Essig over at Jamesessig’s Weblog explains that highly evolved ETIs or our own descendents would still use ‘fireworks’, only on a cosmic scale:

…imagine that huge collections of hydrogen, deuterium, tritium, and other nuclear fuels or matter/antimatter composite materials, or antimatter itself, could be assembled to produce thermonuclear devices or matter/antimatter explosive devices that not only extend in the three ordinary spatial dimensions with the mass and/or volume a white dwarf, neutron star, or quark star or quark nugget, but which also extent into the fourth dimension in an extended interval equal to the diameter of a white dwarf, neutron star, quark star, or quark nugget.

Assuming that hyperspace or higher dimensional space has no discreetization or ultimate finite size quantization, then such a device would include an infinite mass of fusion fuel or matter antimatter fuel and have an infinite yield and be capable of effecting objects, bodies, or whatever that would exist in the fourth dimension.

I have to admit that James is a little difficult to read and comprehend at times, but I love the guy because he thinks outside of the box and big!

Artificial Cosmic Fireworks, How Large Can They Be?

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Finally, an old idea that might come to fruition, solar light sail propulsion. According to Paul Gilster at Centauri Dreams, this will finally be reality:

A realistic technology for future missions? Believe it. Although the push from the Sun is tiny, the effects are cumulative and quickly begin to mount. Says Montgomery:

“It’s not so much about how far a sail will go compared to a rocket; the key is how fast. The Voyagers have escaped the solar system, and they were sent by rockets, but it’s taken more than three decades to do it. A sail launched today would probably catch up with them in a single decade. Sails are slower to get started though. So, for example, between the Earth and the moon, rockets might be preferred for missions with a short timeline. It’s a trip of days for rockets, but months for a solar sail. The rule of thumb, therefore, would be to use rockets for short hops and solar sails for the long hauls.”

Think, too, about how the idea of solar sails is changing. The vast sails described by Cordwainer Smith (”The Lady Who Sailed the Soul”) or Arthur C. Clarke (”The Wind from the Sun”) were envisioned without a functioning nanotechnology to support them. Montgomery notes that today’s microelectronics make it possible to shrink the size of the sail and still perform serious missions. In a few decades, nanotech may have reached the point where smaller sails are sufficient to get assembler-laden research stations to their destinations. As we deploy NanoSail-D, let’s keep an eye on developing sail technologies, including beamed microwave propulsion, as we look to future prospects for even longer missions via laser or particle beam methods.

The launch from a SpaceX Falcon 1 rocket leaves me with an uneasy feeling though, the success rate of their rockets haven’t exactly been sterling, in spite of the great static firings of the Merlin engines.

I do hope for a successful test though, the sheer simplicity and efficiency of this concept is way too good to give up on!

NanoSail-D: Solar Sail Deployment Planned