NASA Takes Streaming Into Space
Hard Choices and Hard Tests
Choosing technologies and off-the-shelf video software and hardware for the Space Video Gateway was a laborious process, involving a great deal of deliberation and testing, says Hames. The project began several years ago, and at that time the choice of MPEG-2 was a no-brainer. Things have changed since then, but Hames is still not sorry he picked MPEG. "We started specing the system about two years ago, and at the time MPEG-2 was the only thing out there for a PCI card," he says. "And the reason we went with a PCI card is because we had other PCI cards in the PC, and that sort of forced the architecture on us."
But by consolidating everything into a single laptop PC, NASA found it could save both money and space by using standard equipment. In a space vehicle, onboard real estate is precious. "It's very, very expensive to launch things into space, so we have to keep things as small and light as possible," says Hames. "We looked at flying standalone encoders and packetizers and all that kind of stuff, and it just got to be really heavy. We couldn't justify the launch cost."
One important part of the SVG is the LSI Logic HDTVxpress Compressor PCI board. It enables contribution-quality video (4:2:2 iFrame and long GOP encoding) and distribution-quality video (4:2:0 MP@HL long GOP encoding) and includes HD-SDI input (SMPTE 292M) and a DVB-ASI transport output.
For standard-definition realtime video encoding, NASA chose the Digital Rapids Stream Encoding System, but only after "a wide ranging market survey," according to Hames. "The big advantage we found in the Digital Rapids card is that it has a FireWire input, so it could handle FireWire or NTSC right out of the box. And that meant we only had to fly one card instead of two," says Hames. "It's an extremely capable card, and we keep dreaming up stuff to do with it as we move along."
Both the Digital Rapids and the LSI cards had to go through rigorous NASA "environmental" testing. NASA has to put electronic hardware through testing to see if it can stand up under the extreme environment of space. "Part of our test process is to check the susceptibility of electronics to ionizing radiation," says Hames. "High-energy protons come from the sun. The sun is always spitting out protons, and on the ground the earth's magnetic field protects us from that," Hames explains. "But in the Space Station you get less protection from such radiation, so as part of our winnowing process, we have to test hardware by bombarding it with radiation on the test bench."
Hames says NASA looks for equipment that will hold up well against both "single-event upset" radiation problems (which are less serious) and against "latch up" problems, which are disastrous. A latch up usually "burns up part of the board," says Hames. He says that during single event upset testing, the Digital Rapids card's "colors got a little weird then straightened out. No big deal. What we didn't see was a latch up." And that was important.
More Plans for More Video
As mentioned earlier, the first use of SVG-supplied footage will be for public affairs broadcasting, which NASA will first provide to partners NHK and the Discovery Channel.
"After that time, it's going to be a mixture of stuff," says Hames. "We may have some more public affairs events coming up. We also have some interest from the scientific community which wants to view their experiments in high definition. And we have potential for some earth observation stuff, pointing the camera out the window and looking at the earth, and we may be looking at some crew activities."
Crew activity footage will be an important part of NASA research, says Hames. "We have a separate group called human factors that deals with how humans can get their jobs done in zero gravity," says Hames. "This includes a lot of things you just don't think about. It can be very interesting to move heavy equipment around in zero gravity, just to get your job done. And by viewing these routine attempts to work and move things around in high-def, they (human factors personnel) get a much better feel for what's going on, just because the picture content is so much better."
Hames also foresees the Space Video Gateway eventually augmenting the Space Station’s overall video system. "At standard definition we'll be able to take one of the station's NTSC cameras (their closed circuit TV cameras) and route it through our system. And then we’ll be able to make bit rate versus quality trade offs and look at more efficient compression." Hames says that during testing, the SGV has streamed at about 6Mbps. "At 6, we're beautiful, and we've dropped it down to 1.5Mbps and still have a usable picture. So for operational functions, at 1.5, you can still tell what's going on. And when we go up to 6, it looks great. So we’ll be able to do those kinds of tradeoffs."
It will also be possible to plug the crew's handheld camcorders into the SVG, which will provide some advantages, says Hames. The Space Station astronauts are currently using Sony DSR-PD100 Handycam DVCAM digital camcorders, he says. "Right now if they want to show the ground what they are doing with their camcorder, they can output it through the NSTC port on the PD100 and get real-time minus light speed delay (about a second and some change). And that works pretty good, but it takes a lot of bandwidth. They can also save the file onto the laptop and do a file transfer down, but that's not real time." But by using the SVG, the astronauts will get the best of both worlds. "What we can do is we can plug their PD100s in and get the real high quality for the low bandwidth, in essentially real time."
"So operationally, I think the use of the SVG is going to be very interesting," says Hames. "When the crew has a particular task they want to do and they want to show the flight controllers on the ground what they are doing, we can send them real-time video and get some immediate feedback. In a way they can do this right now, but with the SVG we can get better quality. And that's what the experiment is all about. We want to find out how useful this stuff is, and I think that will justify the upgrading later on."
And so it’s onward and upward for NASA. And it looks like we’ll all be seeing moon footage streamed live in high resolution, thanks to the pioneering efforts of NASA’s Space Video Gateway.
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