MedicalConspiracies- New NASA Spacecraft Will Be Propelled By Light

http://news.nationalgeographic.com/2016/02/160202-solar-sail-space-nasa-exploration/


New NASA Spacecraft Will Be Propelled By Light

Solar sails could travel to the outermost regions of the solar system
faster than ever before.

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Solar sails are made of ultrathin, highly reflective material. When a
photon from the sun hits the mirror-like surface, it bounces off the
sail and transfers its momentum.
Photograph by NASA/MSFC
By Mark Strauss

PUBLISHED February 3, 2016

In 1418, European sailing vessels left their ports to explore the
Atlantic Ocean, initiating a great Age of Discovery.

In 2018, a small space probe will unfurl a sail and begin a journey to a
distant asteroid. It's the first NASA spacecraft that will venture
beyond Earth's orbit propelled entirely by sunlight. This technology
could enable inexpensive exploration of the solar system and,
eventually, interstellar space.

The $16 million probe, called the Near-Earth Asteroid Scout, is one of
the 13 science payloads that NASA announced Tuesday. They will hitch a
ride on the inaugural flight of the Space Launch System—the megarocket
designed to replace the space shuttle and, one day, send the Orion
spacecraft to Mars.

It will take 2.5 years for the NEA Scout to reach its destination, a
smallish asteroid named 1991 VG. But it won't be a leisurely cruise. The
continuous thrust provided by sunlight hitting the solar sail will
accelerate the probe to an impressive 63,975 mph (28.6 km/s) relative to
the sun.

Given enough time, a spacecraft equipped with a solar sail can
eventually accelerate to higher speeds than a similarly sized spacecraft
propelled by a conventional chemical rocket.

"A sail wins the race in terms of final velocity because it's the
tortoise and the hare," says Les Johnson, the Technical Advisor for
NASA's Advanced Concepts Office at the Marshall Space Flight Center. A
chemical rocket provides tremendous initial thrust, but eventually burns
up its fuel. "Since the sail doesn't use any fuel, we can keep thrusting
as long as the sun is shining."
The light stuff

Solar sails are made of ultrathin, highly reflective material. When a
photon from the sun hits the mirror-like surface, it bounces off the
sail and transfers its momentum to the spacecraft—the same way that a
cue ball transfers its momentum when it smacks into another ball in a
game of pool.

The solar sail concept has been around since 1924, when Soviet rocket
pioneers Konstantin Tsiolkovsky and Friedrick Tsander speculated about
spacecraft "using tremendous mirrors of very thin sheets" and harnessing
"the pressure of sunlight to attain cosmic velocities." Forty years
later, science fiction author Arthur C. Clarke popularized the idea in
his influential short story about a solar sail racing tournament, Sunjammer.

NASA began investing in solar sail technology in the late 1990s. In
2010, it successfully launched a small, sail-propelled satellite into
Earth's orbit, where it remained for 240 days before reentering the
atmosphere.

That same year, the Japanese space agency demonstrated the feasibility
of solar sails for interplanetary travel. A test craft hitched a ride
aboard the Venus probe Akatsuki. The solar sail, dubbed the
Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS),
was released into space by the probe when it was 4.3 million miles away
from Earth. Six months later, IKAROS made history when it successfully
flew by Venus.
Picture of Japan Aerospace Exploration Agency's Ikaros solar sail is
seen in deep space

The Japan Aerospace Exploration Agency's IKAROS solar sail is seen in
deep space after its deployment on June 14, 2010, in this view taken
from a small camera ejected by the sail.
Photograph by Japanese Aerospace Exploration Agency (JAXA)

Solar sails have become feasible thanks to the revolution in electronics.

That's because solar sail design is hostage to Newton's Second Law of
Motion: Force = Mass x Acceleration. The force from sunlight is
constant, so, in order to achieve high acceleration, you need to have
low mass.

"Back 25 or 30 years ago, electronics were not so lightweight," says
Johnson. "You couldn't imagine building a small enough spacecraft that
didn't require a ginormous sail. With the advent of smart phones and the
miniaturization of components, we're now able to make really
lightweight, small spacecraft, which makes the size of the sail more
reasonable."

In particular, Johnson points to the development of CubeSats—boxy
mini-satellites designed to use off-she-shelf technology. The NEA Scout
will be a CubeSat roughly the size of a large shoebox, propelled by a
solar sail measuring 925 square feet (86 square meters).

Despite its modest size, the probe is packed with enough instruments to
conduct an extensive survey of asteroid 1991 VG, taking pictures and
measuring its chemical composition, size, and motion.

NASA sees such reconnaissance as an essential first step for future
crewed missions to asteroids. If an astronaut is going to explore the
surface of a space rock, NASA wants to be sure that it's rotating in a
slow, predictable way, as opposed to rapidly tumbling in multiple
directions. Likewise, the space agency needs to know ahead of time
whether the asteroid is a solid object or a pile of rubble held together
by gravity.
All the light moves

During its mission, the NEA Scout will perform at least one slow, close
flyby—reducing speed to less than 22 mph (10 meters per second) and
passing about half a mile above the asteroid's surface.

That highlights another advantage of solar sails: They're very
maneuverable, sometimes outperforming conventional methods of propulsion.
Animation: New NASA Rocket Will Bring Tiny Satellites Into Space

See how a mini-satellite propelled by a solar sail will be deployed to
perform reconnaissance on an asteroid during a 2018 mission. Video: NASA

The key to steering a sail—whether it's in the Atlantic Ocean or in
space—is to create an asymmetric thrust. There are various ways do this,
using the celestial equivalents of masts and rigging. IKAROS had an
electro-optic coating that went dark when voltage was applied, absorbing
light instead of reflecting it. That made it possible to "tune" one part
of the sail so that it got half as much solar push than the other side,
causing the spacecraft to tip and tilt.

The NEA Scout will take a different approach, using a sliding mechanism
that moves the CubeSat back and forth relative to the booms where the
sail is deployed.

"If you imagine a Coke can and that's our spacecraft, and you put a
piece of paper on top of it, flat on top, that's the sail," says
Johnson. "Then, you can imagine just physically sliding the piece of
paper to the left and the right. That's what we're going to be doing."
Tilting the sail also makes it possible to adjust the speed.

The agility of solar sail spacecraft—coupled with the constant thrust
from an inexhaustible supply of fuel—opens the door to some intriguing
possibilities.

Let's say you want to send a probe above the ecliptic plane of the solar
system to study the north pole of the sun. In order to achieve the
drastic change in direction and velocity—without using precious
propellant—engineers would rely on a slingshot maneuver. "Right now,
we'd have to send a spacecraft out to Jupiter for a gravity assist to
get it out of the ecliptic plane and have a higher angle of orbit around
the sun," says Johnson. "With a sail, you can just kind of crank it up."

Another potential application, closer to home, is a "pole sitting"
satellite. At present, if you want a satellite to remain in a fixed
position relative to a certain location on the ground—which is highly
desirable for communications technology—your only option is to send it
into geostationary orbit, 22,236 miles above the Earth and directly
above the equator.

But with a sail, "you can go above the Earth's North or South Pole and
orbit the sun at the same rate the Earth is orbiting the sun," says
Johnson. "To keep the Earth's gravity from pulling you in, you tip the
sail so that it's thrusting upward all the time. That way, you appear
motionless above the North or South Pole."
Positive energy

Photons—which we see as sunlight—aren't the only spacecraft fuel
generated by the sun. NASA researchers have recently received more
funding to investigate an advanced concept for a superfast sail
propelled by charged particles in the solar wind.

It's called an electric sail, or e-sail. The idea, first proposed by
Pekka Janhunen, a researcher at the Finnish Meteorological Institute,
envisions a spacecraft encircled by 20 hair-thin wires that are each 12
miles (20 kilometers) long.
Picture of solar sail

Over time, an e-sail can accelerate to speeds on the order of 62-93
miles per second (100-150 km/s), making it possible to travel beyond the
solar system in just a decade.
Illustration by NASA

The wires generate a positively charged electrical field extending
dozens of meters into space. Protons in the solar wind, traveling at
speeds as high as 466 miles per second (750 kilometers per second), are
repelled by this electric field, thrusting the spacecraft forward as
they are pushed away. The solar wind's negatively charged particles are
discharged by means of an "electron gun," so that the e-sail maintains a
positive electric field.

The e-sail would have plenty of fuel. While the sunlight that propels a
solar sail significantly diminishes once a spacecraft reaches the
asteroid belt, the solar wind is still blowing strong. Over time, an
e-sail can accelerate to speeds on the order of 62-93 miles per second
(100-150 km/s).

That means space probes could reach Jupiter in just two years, or Pluto
in five. E-sails could enable an entirely new opportunity for
exploration by providing express travel beyond the solar system, into
interstellar space.

By way of comparison, it took the Voyager I spacecraft 35 years to reach
the boundary of the solar system. A solar sail could make the same trip
in 20 years, while an e-sail would arrive in just 10.

"I have to admit, about two and a half years ago, when my boss first
came to me and said, 'we want you to look at this,' I laughed a little
bit," says Bruce Wiegmann, a systems engineer at NASA's Advanced
Concepts Office. "Then we looked at it and said, 'this is pretty
interesting.' We went from nonbelievers to believers."

In fact, Wiegmann believes that a prototype could be launched in five
years. In the meantime, some key issues need to be addressed. Although
an e-sail doesn't need fuel, it requires a power source for the electron
gun that expels electrons. How much power would an e-sail need? That
depends on the number of electrons that the e-sail collects. NASA
researchers are studying the question with charged wire in a plasma
chamber that simulates the solar wind.

Another challenge is preventing the long, thin wires from bending as
they are pummeled by the solar wind. The solution: rotating the
spacecraft at a speed that will produce enough centrifugal force to keep
the wires taut.
Next stop, Alpha Centauri

Les Johnson has a job outside of NASA: He's also a science fiction
author. In fact, he credits the 1974 sci-fi novel The Mote in God's Eye
for sparking his interest in solar sails.

Unsurprisingly, he has big dreams for the distant future. He envisions
sending a solar sail all the way to another solar system.

"We could build a big laser," he says. "As the sail moves away from the
sun and the sunlight gets dimmer, you could then shine the laser light
on it to keep pushing it. The laser remains here in solar orbit, so it's
continuing to push the sail faster and faster as it leaves the solar
system."

Of course, there are some technical details to work out. For starters,
the sail would need to be the size of Texas. And the orbiting laser
would require an energy output comparable to the amount produced by the
whole world today.

It sounds daunting, but in a later century, it might be doable. And the
plan has the virtue of being steeped in actual physics.

The first space vessel made by humans and sent to another solar system
could arrive just like its ocean faring predecessors did during the Age
of Discovery: sails unfurled and guided by the stars.



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