In the early 20th century, it would have been unimaginable to think of going to the moon.
Scientists however succeeded in the late 60's, to send a manned mission, to the moon.
Now scientists are exploring the possibility of sending an unmanned mission, to a neighbouring star.
As of now this ambition might look impossible.
Undeterred by this, scientists are actually working on a project to make this possible.
Even today, we call something which is very unlikely, as a moon shot.
Now scientists are aiming for the next level, a star shot.
Alpha Centauri is one of the nearest stars, to our sun.
It is about 4.37 light years away.
A light year is about 9 trillion kilometers.
If we travel by the fastest rocket, it will take thirty thousand years, to reach Alpha Centauri.
No man made object has ever reached a distance even comparable to this.
Success is not guaranteed for this mission called breakthrough Starshot, yet scientists are going to try their best.
This spaceship is unlike what we would imagine.
Starshot is a cloud of tiny multifunction chips called StarChips.
Each chip would have a tiny light sail.
A laser beam will be aimed at the light sail.
It would accelerate the StarChips to 20% of the speed of light.
The speed of light is about 300 thousand kilometers per second.
At this speed it will take about 20 years for the StarChip to reach.
The StarChip is designed to flypast the star, and transmit pictures back to Earth.
There is another star close to Alpha Centauri.
It is called Proxima Centauri.
Scientists have recently discovered a planet going around Proxima Centauri.
It is possible that StarChip might pay a flying visit, to this planet.
The technology to launch this mission, is not yet available.
A range of specialist scientists are discussing possible ways, to make this technology feasible.
Even the time required to launch this mission, is not clear.
Some think it could be done in 20 years.
Some others believe it could take much much longer.
The basic concept behind this mission, is to have a large number of small lasers.
The light from all these small lasers would combine into a covalent single beam.
The laser beam would be aimed, at a light sail of these StarChip.
This would accelerate the chip to a large speed, about 20% of the speed of light.
The aim is not to launch one StarChip but a cluster of them.
It could be hundreds or thousands of them.
A launch vehicle will launch these flying StarChips.
The idea of having many StarChips, is that a loss of a few,
due to many hazards that they will face, will not endanger the mission.
Each StarChip would be hit by the laser, and accelerated to 20% of speed of light, in a few minutes.
The laser would then be cut off, and the StarChip would sail, with a velocity it had acquired.
There are countless challenges facing the mission.
Each chip has to be very tiny, roughly weighing about a gram.
This tiny chip should carry its own power supply,
and be able to collect and send back data.
Each chip would carry maybe four cameras.
Using conventional lenses is not possible.
Scientists are now thinking, to use a diffraction grating, called the planar Fourier capture array.
This will break the incoming light, from the light sensor, into wave lengths,
which can be reconstructed by a computer, to any focal length.
The StarChip may also have a spectrograph.
To identify the chemistry of the planets atmosphere.
It might also have a magnetometer, to measure the stars magnetic field.
Another challenge is the chips, would have to transmit pictures, over interstellar distances.
Currently satellites use single watt diode lasers, to transmit information.
To target the Earth from the star, the laser's aim needs to be extraordinarily precise.
During the four year trip, from star to Earth, the signal will dilute significantly.
Only a few hundred photons, will finally reach the Earth.
The scientists are thinking of one possible solution.
That is to transmit the pictures by relay.
The signal will get transmitted from one StarChip to a series of StarChips,
flying at regular intervals behind, the leading StarChip.
According to the current plan, a conventional rocket will be sent in to an Earth orbit.
It will launch one StarChip once a day.
This it will continue to do, for more than 3 years.
All the StarChips will fly towards the star, one behind another.
An array of hundred million small lasers, spread over one square kilometre,
will be located on Earth.
All these lasers will combine their light into a single beam.
It is called a phased array laser.
This laser beam is aimed at the light sail of the StarChip.
They will be propelled by the recall from the beamed laser light.
This will accelerate the StarChip to 20% of the speed of light.
This will be about 60 thousand kilometers per second.
The StarChip will need batteries to power the computers, camera etc..
They need to be operational during the 20 year voyage.
The power they generate would be only a few watts.
The signal that the StarChip generate will weaken over a long voyage to Earth.
Scientists expect only a few photons to reach the Earth.
No technology exists today, for batteries required by the StarChip.
Scientists are exploring whether tiny nuclear batteries can be used.
The interstellar medium has a small amount of gas and dust.
Another possibility is to tap the energy, the sail gains,
from the friction, as it travels through the interstellar medium.
The interstellar medium also poses a threat.
If a StarChip travelling at 60 thousand kilometers per second,
collides with a grain of dust, it could be potentially disasters.
Scientists are still thinking of a way to protect the Chip.
But they are resigned to the fact, that they will lose some StarChips,
due to collision.
Their hope is that out of the hundreds or thousands of Chips sent,
at least some will survive, the journey and make it.
Another challenge is the design and production of the light sail.
The StarChips would be propelled by the recoil of light reflected by the sail.
The light sail will be about 4 meters across.
The need to be extremely light weight and strong.
They also need to have reflectivity of 99.9999.
Any light that does not reflect, will heat up the sail.
Even if a small fraction of the energy of the laser beam,
heats the sail, it could be disasters.
Solar sails, are which reflect the light from the sun,
have been used to propel some experimental spacecraft,
around the solar system.
The light sail for the StarChip has to be much thinner and lighter.
Its thickness has to be measured in atoms.
It will probably have the thickness of a soap bubble.
Scientists have experimented with accelerating a sail made of a carbon sheet,
using a microwave beam.
They have achieved an acceleration of 13 g's.
One g is the acceleration felt on Earth by gravity.
Achieving 13 g is the current cutting edge of technology.
But the StarChip will need an acceleration of 60 thousand g's.
It also faces the risk of collision.
The design of the sail required, offers a challenge, which current technology,
is not able to address.
Scientists are also thinking about how to mount the sail to the Chip.
The sail needs to be accurately positioned, to receive the laser beam.
Once the actual acceleration is achieved, the sail needs to fold up,
for the rest of the journey.
This will render it less vulnerable to collisions, during the journey.
After it reaches Alpha Centauri, the sail is supposed to unfold.
It needs to adjust its curvature, like a telescope mirror, or an antenna,
to send messages back to Earth.
The scientists have a bag full of challenges, in the light sail alone.
The light beam that will push the sail, offers its own challenges.
To achieve the required acceleration, the laser beam, has to be extremely powerful.
Scientists estimate the required power, to be about 100 giga watt.
Though more powerful lasers have been developed,
they shine for only one billionth or one trillionth of a second.
The StarChip however requires the light beam, to be operational for several minutes.
To reach this power for so long, small fibre lasers can be grouped together,
into an array.
The light beams from all the arrays, have to be phased together,
to provide a single coherent beam.
Current technology in phased arrays produce only tens of kilo watts.
To achieve 100 giga watts, it would require 100 million kilo watt scale lasers.
The lasers would be located in about a square kilo meter, on the Earth.
The challenges do not end here.
The hundred million micro lasers, would be deflected by the normal turbulence,
of the atmosphere.
Each beam could be deflected in different directions.
Scientists need to bring all of the together,
and focus it on a 4 meters square light sail,
at a distance of 60 thousand kilometers.
On top of all this the beam has to hit the sail evenly.
If it is not even, the sail would go into a spin.
Scientists are examining a potential solution for the turbulence problem.
Large telescopes cancels out the distortion, created by the atmosphere's turbulence,
by using a flexible mirror, which creates a equal and opposite turbulence.
In the case of Starshot, they need to minutely adjust each laser fibre,
to make the atmospheric correction.
When measuring the objects in the sky, scientists use the angle subtended,
in arcseconds or milli arcseconds.
Current technology at best, resolves a point about 30 milli arcseconds.
Starshot has to focus the beam within 0.3 milli arcseconds.
This has never been done before.
This is one of the many challenges that scientists have to overcome.
We have being discussing the challenges, that individual subsystems pose,
in the starshot mission.
Making all the technologies work together as a whole system,
is a challenge in its own right.
What is the possibility of the Starshot mission succeeding?
No one knows for sure.
But scientists have always been exploring the unknown.
Many of the things that we take granted today,
is because, some scientist at some point, chose to venture into the unknown,
to discover it for us.