[♪ INTRO]
Star Trek envisioned a high-tech future of starships and space stations.
And more than ever, our real technology is reaching for the stars
to realize some of that sci-fi future.
But some of the most ambitious programs actually rely on technology
that’s been around for hundreds of years.
Like the innovative 19th century optics from lighthouses
that could help to take us to the moon… and beyond.
Star Trek’s series ‘Deep Space Nine’ aired in the 90’s,
and portrayed life on board a huge space station in the 24th Century.
So maybe NASA was going for a very early start on that
when they launched their Deep Space 1 mission in 1998.
The mission was a technology demonstration that spent more than three years
in space, visiting an asteroid and a comet while it tested out a slew of brand new
methods for the next generation of space exploration.
Notably, it was the first spacecraft to be powered by an ion engine
rather than traditional rocket fuel.
Normally, spacecraft burn fuel to push themselves around in space.
But that means that you'd have to take all the fuel that you’d need for a long journey,
which is heavy, so it requires more fuel… you can see where this goes.
So Deep Space 1 tried out a new type of engine that used ions
instead of conventional exhaust gases.
The idea is that small quantities of xenon gas could be electrically charged,
and then accelerated by an electric field.
The individual ions would be ejected from the spacecraft
at speeds of up to 144,000 km per hour.
In the test flight, that was enough to accelerate DS1 by up to 4.3 km per second.
The engineers think they could have gone even faster,
but there was more to DS1’s mission than just going super fast!
Nonetheless, ion drives were a breakthrough in spacecraft propulsion,
especially for long-distance or long-duration missions,
as only tiny quantities of xenon are needed.
But to make DS1’s enterprising ion engine work,
the spacecraft needed a very strong and reliable source of power.
And that’s where the 200 year-old lighthouse tech comes in!
In the mid-19th century, French Engineer Augustin-Jean Fresnel
figured out a way to use lenses to make lighthouses more effective.
A lens could theoretically bend and collect the lighthouse’s light
and make it visible from farther away.
But a convex glass lens big enough to do the job would have been
far too heavy to mount at the top of a tower.
Fresnel figured out that you didn’t need a big thick lens
to get the same bending of light, just its outer curved profile.
So he effectively hollowed it out, and then flattened the once-curved surface
into a series of concentric circular prisms.
The light passes through and is bent exactly as it would be with a thick curved lens,
but with just a fraction of the materials and weight.
So these Fresnel lenses were used in lighthouses to collimate the light:
to take the diverging light rays from a lamp
and straighten them out into one concentrated beam.
Collimating: make it into a column, I guess.
This was a huge victory for maritime safety and navigation.
But over the years, Fresnel lenses also found other applications.
They can be used as lightweight, slimline magnifying sheets.
And if they’re turned around, they can focus the incoming light down to a point.
Which proved to be just the thing to supercharge DS1’s ion engines.
Because the spacecraft also sported
brand new, so-called multi-junction solar panels.
Made of different materials layered together, they were able to absorb
more of the sun’s wavelengths than traditional silicon photovoltaic cells.
In fact, they can theoretically produce the same wattage
with just one eighth as much surface area.
But to get the most out of them, these revolutionary new cells
needed to have a high intensity of light falling onto them.
So engineers turned to Fresnel lenses to design what they called a solar
concentrator with refractive linear element technology, or SCARLET for short.
SCARLET was a component that sat above the multijunction cells
with the sole purpose of concentrating the sun’s light.
NASA scientists made the already slimline lenses even more lightweight,
to reduce the cost of launching them into space.
And they curved an extended sheet of Fresnel lenses
so that even more light could be focused on a single point.
DS1 ended up using 720 of these lenses to focus light onto 3600 solar cells.
That was enough to generate about 2500 watts of continuous power,
which is about the same as three microwave ovens.
That might not sound like much,
but it’s much more than most solar system probes run on.
It was enough to power DS1’s instruments and its groundbreaking ion engines.
So it was thanks to these 200-year old lenses
that DS1’s advanced technology mission was considered a resounding success.
The Fresnel-enhanced solar cells were a revolution in space power,
but back on Earth, it soon became much cheaper
to make normal silicon photovoltaic cells.
So for most applications, the traditional variety are used,
rather than solar concentrators.
But the high-efficiency cells are still being considered for larger-scale projects,
like solar power plants in sunny places like Arizona and Colorado.
In space, however, SCARLET’s Fresnel lenses and DS1 did demonstrate
the viability of a new kind of propulsion using only solar electricity
and a few high speed ions.
And these ion engines are now widely used
for positioning satellites in Earth’s orbit.
And also, they’re planned to propel the Gateways support mission to the moon,
in preparation for the future Artemis program of manned lunar missions.
And who knows, they may even have a use on a space station
300 years in the future named Deep Space 9!
In the meantime, however, if you’d like to experience Deep Space One
up close and personal, you can, because it’s this month’s Pin of the Month!
From the time this episode goes up through the end of February,
you can pre-order this Deep Space 1 pin for your very own.
We’ll take pre-orders through the end of the month, and then we will ship,
and then we will never make that pin again.
Never fear though, we will make another one in March.
So look forward to the next one,
and check out the link in the description to learn more.
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