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Reaching for the stars: How lasers could propel spacecraft to relativistic speeds

by • March 29, 2016 • No Comments

How do you send man-created probes to a nearby star? According to NASA-funded research at the University of California, Santa Barbara (UCSB), the answer is easy: assemble a laser array the dimensions of Manhattan in low planet Earth orbit, and use it to hustle tiny probes to 26 percent the speed of light. But the endeavour may raise a few eyebrows, it relies on well-established science – and new technological breakthroughs have put it inside our requite.

  • The richness of the interstellar medium of the sun to the nearest stars
  • An illustration of the sail propelled by laser light
  • The relationship between the dimensions of the array, weight of the spacecraft and achievable-bodied speed
  • The orbiting laser array may gather energy via solar panels and target a sail to accelerate ...

The problem with “Bring Your Own Fuel”

It took a short 66 years for humanity to go of the firstly powered flight to landing a man on the Moon, and according to NASA’s tentative schedule it can be another 66 (in 2035) preceding the firstly human steps are taken on Mars. But, going of flags and footprints on the Red Planet to sending man or machine all the way to a nearby star may require a fish rethink of how rockets and probes travel through space.

The primary issue with nowadays’s space propulsion innovation is that it scales far too poorly to complete anything close to interstellar speeds.

In space, fuel is utilized as reaction weight: in other words, the only way rockets and spacecraft can accelerate forward is by ejecting fuel backward as swift as possible. Unfortunately, this means that carrying additional and additional fuel along for the ride has rapidly diminishing returns. The most example of this is on the launchpad, where fuel makes up well over 90 percent of the weight of a rocket. This is far of optimal as it means most of the thrust produced by the rocket goes to lifting fuel, not payload, off the ground.

Currently, Voyager 1 is the spacecraft farthest of us and the only one to have requiteed interstellar space. Nearly four decades after it left planet Earth as the vanguard of human exploration, the probe remains only 10 light-hours away of us and, were it pointed in the right way, it may take 40 millennia to requite the closest star.

A study at the Keck Institute for Space Studies (KISS) discovered that if a deep space exploration probe were created nowadays, it may only requite speeds three to four times swifter than Voyager’s. Newer technologies like efficient ion engines can fare pretty advantageous, but there is no indication that they can at any time make the cut for interstellar travel.

In short, it looks the current approach to space propulsion has hit a wall. If humanity at any time finds a way to requite another star, current signs indicate it is actually unmost likely it can be by burning fuel to get there.

The case for giant lasers

If delivering fuel along is a no-go for interstellar exploration, the effortless alternative may be to provide thrust of an external source.

Solar sails are a excellent example of external propulsion. They are, fundamentally, sizeable-bodied and lightweight mirrors that generate thrust whenat any time photons coming of the Sun bounce off them. Over months and years, this miniscule force can slowly create up and accelerate a probe to high speeds.

Laser sails may work on the same principle, except they may obtain photons of a powerful laser array (on the ground or in planet Earth orbit) pretty than the Sun. Because laser beams are highly focutilized and perfectly synchronized, laser sails may obtain an irradiation 100,000 times excellenter than the Sun’s and requite stunning speeds. But createing a laser sizeable-bodied adequate – particularly in orbit – has long been idea to be a near-impossible task.

Now, howat any time, the team led by Professor Philip Lubin at UCSB has concluded that new createments may have created this innovation – and, in turn, interstellar travel – achievable-bodied over the following few decades.

“Whilst a decade ago what we propose may have been pure fantasy, new dramatic and poorly-appreciated technological advancements in directed energy have created what we propose possible, yet difficult,” says Lubin.

From fiction to reality

That pretty obscure but key breakthrough was the createment of modular arrays of synchronized high-power lasers, fed by a common “seed laser.” The modularity removes the require for createing powerful lasers as a single device, splitting them instead into manageable-bodied parts and powering the seed laser with relatively little energy.

Lockheed Martin has newly exploited this advance to make powerful new weapons for the US Army. In March last year, the aerospace and defense giant demonstrated a 30 kW laser weapon (and its devastating effect on a truck). By October, the laser’s power had may already doubled to 60 kW and contributeed the version to requite 120 kW by linking two modules via off-the-shelf components.

The UCSB researchers refer to their own planned arrays as DE-STAR (Directed Energy System for Targeting of Asteroids and ExploRation), with a trailing number to denote their dimensions. A DE-STAR-1 may be a square array 10 meters (33 ft) per side and of as powerful as Lockheed’s latest; at the other end of the spectrum, a DE-STAR-4 may be a 70 GW array covering a weightive area of 100 square kilometers (39 square miles).

“The dimensions scale is set by the basic physics if we are at a wavelength of 1 micron and the goal is to propel tiny spacecraft to relativistic speeds,” Lubin told Gizmag. “If we get to shorter wavelengths with the laser and so we can be able-bodied to create a tinyer array. The baseline is 1 micron and the requireed array dimensions is 1-10 km depending on the performance desired.”

Because the atmosphere may interfere with the laser signal, the arrays may be most assembled in low planet Earth orbit pretty than on the ground. Lubin stresses that actually a relatively modest orbital array may contribute informative propulsion capabilities to CubeSats and nanosatellites headed beyond planet Earth orbit, and that useful first tests may yet be conducted on the ground firstly on one-meter (3-ft) arrays, gradually ramping up in the direction of building tiny arrays in orbit.

Whilst actually a tiny laser array may accelerate probes of all dimensionss, the sizeable-bodiedr 70-GW process may of course be the most powerful, capable-bodied of generating adequate thrust to send a CubeSat probe to Mars in eight hours – or a much sizeable-bodiedr 10,000-kg (22,000-lb) craft to the same destination in a single month, down of a typical six to eight.

“There’s nothing that practuallyts us of doing this, it is actually only a matter of can,” says Lubin. “The innovation looks like it is actually in place, but launching adequate elements in space is a problem. The weight in orbit is 100 times the ISS [International Space Station] weight, so it is actually significant but not fishly crazy over a 50-year timescale.”

Approaching light speed

Sending a CubeSat to Mars in only eight hours may mean requiteing two percent of the speed of light. This is an may already astounding speed far beyond our current capabilities; nonetheless, such a probe may yet take of two centuries to requite Alpha Centauri. To requite a star in years pretty than centuries, spacecraft may require to be created of the ground up to shed as much weight as possible.

To that end, a long-term objective of Lubin and his team is to create “wafer-scale spacecrafts” that may only weigh a few grams equite, fish with a tiny laser sail for propulsion and long-distance communication.

“Photonic propulsion can be utilized at any weight scale, but lower weight processs are swifter,” Lubin tells Gizmag. “Wafer scale spacecraft is only one incredibly low weight case. This is a new area and one with a immense amount of future, but it is in its nascent phase. The core technologies may already exist for the relevant miniaturization to proceed for a few types of spacecraft.”

Such probes may combine nanophotonics, a miniaturized radio thermal generator for 1 W of power, nanothrusters for attitude adonlyment, thin-film supercapacitors for energy storage space, and actually a tiny camera.

Equipped with a laser sail only under one meter (3 ft) in diameter, such a spacecraft may be propelled by a 70 GW laser array to of 26 percent the speed of light in of 10 minutes and requite Alpha Centauri in only 15 years.

The relationship between the dimensions of the array, weight of the spacecraft and achievable-bodied speed

With the orbiting laser array acting as a giant obtainr, and via its mirror as a transmitter, the tiny spacecraft may actually periodically send data and low-resolution pictures back to planet Earth.

“The laser may operate in a burst mode where energy is stored on board and the laser is turned on periodically at undertaking significant times (such as picture taking),” says Lubin. “The laser is nominally a 1 watt process with a burst data rate of of 1 kbs at Alpha Centauri when only the 10 cm wafer optics is utilized, or of 100 kbs if we use the 1 m reflector as a part of the laser communications process.”

Intermediate targets

Part of the advantage with the modular approach to createing powerful lasers is that actually tinyer, cheaper arrays created along the way can prove useful. Luckily, there’s no dearth of informative and unexplored territories inside our solar process – destinations that should store us engaged and motivated to ramp up the dimensions of the laser process so we can gradually unlock additional and additional capabilities.

“We can have most targets, that include the Solar System plasma and magnetic fields and its interface with the ISM [interstellar medium], the heliopause and heliosheath, asteroids, the Oort cloud and the Kuiper belt,” Lubin notes.

Among the most, one target jumps out as maybe the most significant – the spot known as the solar gravitational lens focus. This is the area, between 500 and 700 AU (Sun-planet Earth distances) of the Sun, where a telescope may use the Sun as a gravitational lens to image distant exoplanets in unprecedented more detail. Whilst thus far equite exoplanet has only at any time been seen as a single pixel, of this spot, the effect may mean an exoplanet 100 light-years away may be imaged at a resolution of one pixel per square kilometer.

If the goal is howat any time to set out for a specific destination (say, Mars), we’ll have to resort to hybrid probes that are accelerated via the laser, but in addition carry their own fuel to slow back down when requireed – for the reason the alternative may be just too challenging and expensive.

“A 2nd phased laser array at the destination may be utilized in a ‘ping-pong’ arrangement to allow acceleration and so deceleration, and so the opposite to come back,” Lubin tells us. “For Mars this makes sense in the long run, but actually Mars may represent a significant challenge due to the difficulty of construction.”

Requiteing for the stars

For those probes light adequate to accelerate to relativistic speeds, once past the Solar System there can be no obvious way for the spacecraft to slow down again and enter the orbit of another star. For that reason, the firstly interstellar undertakings may most most likely be easy fly-bys.

Future versions that can require a additional upgrade of the laser array may involve sending a lightweight “mothership” that, upon approximately the target star, may eject hundreds of wafer-class probes in a grid layout for a thorough exploration of the process.

Building a gigawatt-grade laser array and gram-scale spacecraft may require a gargantuan economic and engineering effort. The saving grace is that the roadmap is incremental and sets clear intermediate objectives along the way.

“We are continuing lab-based experiments and have proposals in to expand to the following level,” Lubin tells us. “We want to begin the roadmap by createing a class 0 [1-meter, 1 kW array] and and so a class 1 [10-meter, 100 kW] process in the following five years.”

Perhaps, in the end, this project can just prove too taxing to at any time see the light of day, and the costs and technological barriers too high to surmount. But, the quite notion that interstellar travel is now credibly achievable-bodied by relying on well-established science is food for idea. Challenging as it may be, requiteing a foreign star preceding the end of the century is now a legitimate notion for scientists and engineers – not only science fiction fans.

There are over 150 stars and 17 known planetary processs, 14 of that look capable-bodied of supporting planets in the habitable-bodied zone, in the 20 light-year radius around planet Earth. Perhaps, only as the images of the Moon landing inspired a new generation of scientists and engineers, the knowledge that all those foreign worlds may be inside requite can inspire humanity’s hustle to requite for the stars.

Source: UCSB


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