If you like TV, you’ll love the Mars Channel. Take your seats for the network premiere of interplanetary telly. Ben Iannotta reports
“When you watched Neil Armstrong walking on the Moon, it was like watching a TV show shot through someone’s nylons,” recalls Bill Foster. Yet, he admits, those blurred shots fired the public’s 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’s 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-to create the ultimate experience in “edutainment”.
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’ll 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.
When NASA’s Mars Pathfinder probe arrived on the Red Planet in 1997, you’d 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. “Actually, that was faux video,” says Rodney Grubbs, a digital television expert at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “What you saw was a sequence of 3D images taken with a stereo still camera,” 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-about 20 times slower than the modem on your home PC.
And most of the energy in this signal had already leaked away. NASA’s 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’s Jet Propulsion Laboratory in Pasadena, California. Ideally, Hemmati believes, you’d 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-so 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. “You could never get that with microwaves.”
Because you can collect far more of the signal, you needn’t 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’s 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 “light bridge”. But adapting this technology for deep space will be difficult, warns Gotthard Oppenhäuser, 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-the time it takes signals to travel between Earth and Mars-to tell the deep space probe to realign its beam, says Oppenhäuser. 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’t 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? “That really is the primary concern,” says James Lesh, who leads JPL’s telecommunications and mission operations technology group. “Can you point such a narrow beam accurately enough?”
Beam me up
To prove it can work, Hemmati’s 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’s 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’t 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-on the ground, at least. Several months ago, Hemmati’s 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’s Table Mountain Facility.
Table Mountain is also the site of an experiment designed to make sure a laser beam can get through Earth’s atmosphere in the first place. Even when it’s not cloudy, atmospheric gases swirl in unpredictable ways-which 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-together with two similar sites in California and Arizona-has 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’s notoriously cautious managers to embrace the new technology. “Any time you try to do something different it’s a difficult sell. People are anxious to see it done, but usually on someone else’s mission,” Lesh says.
Right now, the team’s proposal is one of eight bids under consideration for NASA’s New Millennium programme which tests out exotic technologies. Hemmati should find out this August whether his team’s device has made it. But even if they don’t 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 TVpictures, making them a potent tool for planetary exploration, says Chad Edwards, chief telecommunications engineer for NASA’s Mars programme. “Pathfinder was very constrained. It couldn’t bring back a full panorama in a day.” You’re going to miss big opportunities if you can’t look around you, he says.
In particular, it’s impossible for geologists to put still photographs of an alien landscape into the right context to really understand a planet’s geology. If you can’t 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-with a format 10 times larger than normal film-only 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 “pick up” a rock and examine it on a screen that’s 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’d be able to maintain contact with people back on Earth, Edwards says. “Or if you want to show them how to fix something, you could send up video directions.”
Once you establish a “live” 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. “We might even be able to measure a quantum state of bacteria that we find on Mars, and transmit it back to Earth,” 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-which 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’ve 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. “I don’t know anyone whose mouth doesn’t open when you show them images from space,” says Foster. “When you see high-definition pictures of Mars on TV, it will blow your mind.”
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. “You’ll be able to see what Mars looked like 20 minutes ago,” says Foster. “Teachers 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.”
Grubbs, too, is confident this new view of our Solar System will change the world forever. “There’s no doubt in my mind,” he says. “The 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 incredible.”
Ben Iannotta is a journalist based in Florida
New Scientist issue: 24th March 2001
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