鈥淲HEN you watched Neil Armstrong walking on the Moon, it was like watching a
TV show shot through someone鈥檚 nylons,鈥� recalls Bill Foster. Yet, he admits,
those blurred shots fired the public鈥檚 passion for space travel. Now, 32 years
on, Foster plans to reignite those flames with footage so clear and crisp you
could be scaling the mountains of Mars from your sofa.
Foster is chairman of Dreamtime, the company that is helping NASA exploit its
vast archive of space images. Part of Dreamtime鈥檚 plan is to send
high-definition television cameras into orbit. Eventually, though, it wants to
film on planets in the outer reaches of the Solar System鈥攖o create the
ultimate experience in 鈥渆dutainment鈥�.
Before the opening credits can roll, however, engineers must find a way of
transmitting film back to Earth up to 100 times faster than is possible now.
Many people think the best way to do that will be to replace radio waves with
narrow beams of laser light. This will be no mean feat. Engineers will have to
turn their space probes into mobile lighthouses. They鈥檒l even have to learn to
hit a communications satellite just metres across with laser beams shot across
billions of kilometres of space. But if all goes to plan, by 2020, film footage
with the quality of an IMAX movie could be streaming back from space to your
living room on a thread of light.
Advertisement
When NASA鈥檚 Mars Pathfinder probe arrived on the Red Planet in 1997, you鈥檇
have been forgiven for thinking that making movies in space had already made
great progress. Millions of people logged on to the Internet to watch Sojourner
trundle about the Martian surface and marvel at the short film it sent back.
鈥淎ctually, that was faux video,鈥� says Rodney Grubbs, a digital television expert
at NASA鈥檚 Marshall Space Flight Center in Huntsville, Alabama. 鈥淲hat you saw was
a sequence of 3D images taken with a stereo still camera,鈥� he says. NASA
technicians simply strung the images together and posted them on the website as
a movie.
NASA had little choice. Pathfinder had a small antenna and only a limited
supply of sunlight to power it in the dusty Martian atmosphere. On a good day,
the images trickled back on a microwave beam at just a few kilobits per
second鈥攁bout 20 times slower than the modem on your home PC.
And most of the energy in this signal had already leaked away. NASA鈥檚 Deep
Space Network struggled to collect just a fraction of the power that Pathfinder
sent back, says Hamid Hemmati. By the time it reached us, he says, the microwave
beam had spread out so much that it was hundreds of times wider than the
diameter of the Earth.
Hemmati leads the optical communications group at NASA鈥檚 Jet Propulsion
Laboratory in Pasadena, California. Ideally, Hemmati believes, you鈥檇 take film
recorded by a high-definition camera on a space probe, turn the images into a
stream of digital information and beam it back to Earth encoded in a laser beam.
Laser light beats radio waves hands down since the frequency of light is much
higher than the frequency of microwaves鈥攕o it can carry more digital
information. Since laser light has a shorter wavelength, it also spreads out
less with distance. This means it will stay as a narrow, collimated beam, says
Hemmati. 鈥淵ou could never get that with microwaves.鈥�
Because you can collect far more of the signal, you needn鈥檛 beam out so much
power in the first place. What you end up with, Hemmati calculates, is a laser
communicator that needs just half the mass and power of an equivalent radio
communications system, occupies about a fifth of the volume on a spacecraft but
can beam data back up to one hundred times faster.
With this potential, it鈥檚 hardly surprising that the fledgling technology has
already made it into orbit. The US military operates satellites that communicate
with each other by laser beam, and in just a few months the European Space
Agency will put this technology through its paces when it launches a satellite
called Artemis. The French SPOT 4 imaging satellite is already in orbit and will
take photographs of Earth and shoot them to Artemis on laser beams at 50
megabits per second.
Eventually, the ESA envisages laser communications playing a vital role as
satellites beam data around Earth across a high-speed information 鈥渓ight
bridge鈥�. But adapting this technology for deep space will be difficult, warns
Gotthard Oppenh盲user, Artemis programme manager at the European Space
Research and Technology Centre in Noordwijk, the Netherlands. You need to aim a
laser beam from deep space with incredible accuracy to strike a 10-metre-wide
detector on Earth, or on an orbiting relay satellite. With Mars up to 400
million kilometres away, even a small error will send the video streaming
uselessly past Earth.
Worse still, it would take a receiver 15 minutes or so鈥攖he time it
takes signals to travel between Earth and Mars鈥攖o tell the deep space
probe to realign its beam, says Oppenh盲user. With this kind of delay,
alignment is incredibly difficult in the first place.
However, Hemmati and his team believe they have come up with a wonderfully
simple solution: turn the receiver station into a lighthouse. Beam a laser
beacon out into space and a distant probe has a target to shoot for. With the
beacon in its sights, the probe can adjust its aim and maintain continuous transmission
(see Diagram).
Engineers at NASA tried out this idea in 1992, sending light toward the
Galileo probe as it swung by Earth. When Galileo opened its camera shutter, it
picked up the beam easily enough, but the experiment wasn鈥檛 really a fair test.
Galileo was never more than 6 million kilometres away and moving slowly across
the sky. In the real world, a far-flung probe would be flying fast relative to
Earth and would wobble about when it fired its thrusters. How would it keep a
steady aim and hit a receiver millions of kilometres away? 鈥淭hat really is the
primary concern,鈥� says James Lesh, who leads JPL鈥檚 telecommunications and
mission operations technology group. 鈥淐an you point such a narrow beam
accurately enough?鈥�
Beam me up
To prove it can work, Hemmati鈥檚 team has built a prototype laser
communications package that might someday be installed on a deep space probe.
Called the Optical Communications Demonstrator, it consists of a small laser, a
light sensor and a telescope that can be steered by computer. Altogether it鈥檚
about the size of a loaf of bread. The OCD is designed to bounce laser signals
precisely toward a receiver, so the computer controller must automatically
calculate the direction of an incoming beacon, compare it with the outgoing
signal beam and then adjust the telescope to keep the beacon in its sights.
Finding the beacon to begin with should be no problem, says Lesh. The trick
will be to lock onto it and correct for movements or vibrations. To do this, a
mirror takes a small portion of the incoming beacon and the outgoing laser beam
and shines them onto a small screen. This provides two bright spots that are
imaged with a light sensitive device built into the OCD.
As long as the two beams remain parallel, the spots won鈥檛 move from their
preset positions. But if the spots start to wander, the telescope will adjust
the position of the outgoing beam to keep it on target.
The OCD really seems to work鈥攐n the ground, at least. Several months
ago, Hemmati鈥檚 team set up the prototype on Strawberry Peak in southern
California and successfully sent a laser transmission across a canyon towards a
beacon beamed out from NASA鈥檚 Table Mountain Facility.
Table Mountain is also the site of an experiment designed to make sure a
laser beam can get through Earth鈥檚 atmosphere in the first place. Even when it鈥檚
not cloudy, atmospheric gases swirl in unpredictable ways鈥攚hich is why
stars twinkle even on the clearest of nights. Every twinkle of a laser beam
could ruin the data it carries.
To solve this problem, an automated atmospheric monitoring facility at Table
Mountain鈥攖ogether with two similar sites in California and
Arizona鈥攈as been taking observations of stars every day for more than
three years. This data is helping Hemmati work out what wavelengths are
transmitted by clouds and least affected by turbulence, as well as the best
locations and times for transmission. Hemmati believes it should be possible to
solve many of the problems by simply splitting the laser into four beams and
sending them up together in a square array. Whatever direction the turbulence
bends or scatters them, at least one of the beams should make it to the
receiver.
So when will the OCD fly? Sometime soon, Hemmati hopes. One of the greatest
challenges has been convincing NASA鈥檚 notoriously cautious managers to embrace
the new technology. 鈥淎ny time you try to do something different it鈥檚 a difficult
sell. People are anxious to see it done, but usually on someone else鈥檚 mission,鈥�
Lesh says.
Right now, the team鈥檚 proposal is one of eight bids under consideration for
NASA鈥檚 New Millennium programme which tests out exotic technologies. Hemmati
should find out this August whether his team鈥檚 device has made it. But even if
they don鈥檛 succeed this time, they believe they can still reach their primary
goal: beaming high-definition television pictures from Mars by 2010.
HDTV images have six times the resolution of standard digital TV pictures,
making them a potent tool for planetary exploration, says Chad Edwards, chief
telecommunications engineer for NASA鈥檚 Mars programme. 鈥淧athfinder was very
constrained. It couldn鈥檛 bring back a full panorama in a day.鈥� You鈥檙e going to
miss big opportunities if you can鈥檛 look around you, he says.
In particular, it鈥檚 impossible for geologists to put still photographs of an
alien landscape into the right context to really understand a planet鈥檚 geology.
If you can鈥檛 look around, you might spot a lava flow but miss the volcano that
produced it.
Now imagine a high-resolution video camera that could point in any direction,
says Edwards. With data compression, even IMAX-quality film鈥攚ith a format
10 times larger than normal film鈥攐nly requires a transfer rate of about 20
megabits per second. A laser beam can easily manage this.
Suddenly geologists back on Earth would have a fast enough data rate to 鈥減ick
up鈥� a rock and examine it on a screen that鈥檚 15 centimetres across, says
Edwards, or in an IMAX theatre with a screen more than five storeys high. When
the first astronauts step off the ladder onto the Martian dust, an
interplanetary outside broadcast unit could be there to welcome them. You鈥檇 be
able to maintain contact with people back on Earth, Edwards says. 鈥淥r if you
want to show them how to fix something, you could send up video directions.鈥�
Once you establish a 鈥渓ive鈥� laser link with distant planets, you could even
set up an interplanetary quantum internet. Jonathan Dowling, who heads the
quantum computing technologies group at JPL which has dubbed this link Quantum
Skynet.
Distribute telescopes on space probes, hook them together with laser beams
and you could make a huge interferometer to hunt for planets orbiting other
suns. 鈥淲e might even be able to measure a quantum state of bacteria that we find
on Mars, and transmit it back to Earth,鈥� says Dowling.
Whatever the scientific value of a laser link to deep space, its true impact
will only be felt when the film footage returns. Once real-time images start to
stream in, there will be no end of viewers desperate to see them, and ready to
pay for the privilege鈥攚hich is where Dreamtime comes in.
The company has already installed HDTV cameras around the shuttle launch pad
to film each lift-off. Next it plans to get HDTV cameras on the International
Space Station in exchange for commercial marketing rights to images. We鈥檝e
already reserved 1.5 hours a week of astronaut time for filming, says Foster.
But the jewel in the crown will be the first film from Mars, or from further out
in the Solar System. 鈥淚 don鈥檛 know anyone whose mouth doesn鈥檛 open when you show
them images from space,鈥� says Foster. 鈥淲hen you see high-definition pictures of
Mars on TV, it will blow your mind.鈥�
In a decade we could have IMAX-quality film coming back from Mars, says Lesh,
from Europa or Ganymede by 2015, and from Neptune just five years after that.
鈥淵ou鈥檒l be able to see what Mars looked like 20 minutes ago,鈥� says Foster.
鈥淭eachers and scientists will use the films. New movies will use them. There
will even be computer games and TV game shows built on these images.鈥�
Grubbs, too, is confident this new view of our Solar System will change the
world forever. 鈥淭here鈥檚 no doubt in my mind,鈥� he says. 鈥淭he fuzzy images from
the Moon captivated the entire world. The images from Pathfinder were not even
video, but they captivated the world too. HDTV from other planets will be
颈苍肠谤别诲颈产濒别.鈥�