NASA Probe Blasts 461 Gigabytes of Moon Data Daily 203
coondoggie writes "On its current space scouting mission, NASA's Lunar Reconnaissance Orbiter (LRO) is using a pumped up communications device to deliver 461 gigabytes of data and images per day, at a rate of up to 100 Mbps.
As the first high data rate K-band transmitter to fly on a NASA spacecraft, the 13-inch-long tube, called a Traveling Wave Tube Amplifier, is making it possible for NASA scientists to receive massive amounts of images and data about the moon's surface and environment.
The amplifier was built by L-3 Communications Electron Technologies in conjunction with NASA's Glenn Research Center. The device uses electrodes in a vacuum tube to amplify microwave signals to high power. It's ideal for sending large amounts of data over a long distance because it provides more power and more efficiency than its alternative, the transistor amplifier, NASA stated." It kills me that the moon has better bandwidth than my house.
better bandwidth? (Score:3, Informative)
1 - http://www.vendian.org/envelope/dir0/light_delay.html [vendian.org]
This is not exactly a new device... (Score:5, Informative)
Traveling Wave Tubes have been a mainstay of microwave communications and radar systems for the better part of a century. They're a very efficient way of amplifying microwave signals to the very high power levels needed to cross long distances.
Re:This is not exactly a new device... (Score:1, Informative)
I mean, TWT's were used on the VERY FIRST COMMUNICATION SATELLITE, and they have been used on virtually every single communication satellite since!
Gah! This is like saying that a space-based computer might use what is known as "RAM", and then explaining RAM.
I understand that a lot of
Re:better bandwidth? (Score:4, Informative)
Slow news day from what it sounds like... (Score:4, Informative)
TWT amps have been used in microwave systems since the 2nd world war. The use of TWT in satellites are recent, as in 25-30 years ago. The NSA's LACROSSE and the new ONYX satellites use TWT amps in the finals on their radar systems. The Soviet ROARSAT's probably use them as well, or something similar, they love to overbuild their stuff.
Hell, the YF-12a used 2 TWT's in tandem in its Hughes AN/ASG-18 radar, putting out over 10MW of raw power.
But they are power gobblers, The YF-12A's ate over 40KVA of juice to operate.
Re:This is not exactly a new device... (Score:3, Informative)
Yes. But it's not easy. A TWT is, in many ways, very similar to a linear acclerator, except that instead of using RF to put energy into an electron beam to make it faster, it takes energy out of a fast electron beam to amplify an RF signal. So whip out those books on linear accelerator design and construction, and have at it. You need an electron gun and some electron optics to make the beam, and then the section where the RF interacts with the beam, either a helix or a series of coupled resonant cavities. A helix would probably be easier for homebrew. You'll need all the usual stuff: vacuum pumps, HV power supplies, etc. I also wouldn't start with K band, because it's so small. Do something easier like 2.45 GHz.
Amplifiers like the one on LRO run about a million bucks a pop, but a lot of that is because it has to work in space and survive the test campaign. Kind of difficult to make a service call to replace it if it fails.
Re:Vacuum Tube? (Score:4, Informative)
Re:Vacuum Tube? (Score:5, Informative)
When you need to make serious power, tubes are still the way to go. Transistors have a significant reliability benefit.
Also, for 99% of applications, transistors are better. For the other 1%, you have very application-specific tube designs such as TWTs and magnetrons, which rearrange the tubes in such a manner as to negate its usual disadvantage (large size USUALLY translates to nasty frequency limits - TWTs and magnetrons are exceptions that use various Neat Tricks to allow microwave operation from a large device.)
BTW, one of the other common microwave tubes (magnetrons), while it is a "niche" device, it is a VERY widely deployed niche - basically all microwave ovens use magnetron tubes.
Re:Spam (Score:4, Informative)
Vacuum tubes have always had higher frequency limits than transistors, since WWII in fact. Take a look at THz radiation sources, all tubes. No tranny is going to touch that for a while. And then tubes will have gotten better too.
http://en.wikipedia.org/wiki/Backward_wave_oscillator
Tubes just have more geometric freedoms to create bizarre fields and strange structures to do whatever you need.
Re:This is not exactly a new device... (Score:3, Informative)
And these have been used in space applications since the early 60's. In fact every satellite program that I have worked on used TWTA amplifiers. People are always looking for alternatives because they are very squirrely devices, but it's pretty difficult to generate much power at microwave frequencies with solid-state alternatives.
Brett
Re:This is not exactly a new device... (Score:5, Informative)
You need an electron gun and some electron optics to make the beam,
Check, old 19" TV tube... all the parts are there.
and then the section where the RF interacts with the beam, either a helix or a series of coupled resonant cavities.
Again, can be found in other surplus tech.
but screw it, just buy one....
http://cgi.ebay.com/NEC-LD7306A-B61-Travelling-Wave-Tube-TWT_W0QQitemZ200255211587QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea0240843&_trksid=p3286.c0.m14 [ebay.com]
Re:Insane (Score:3, Informative)
no, they couldnt risk having a Verizon tech punching the oribter in the face if they needed onsite service
Re:Insane (Score:5, Informative)
5.46MB/s is close to half of a 100BaseT.
Re:This is not exactly a new device... (Score:4, Informative)
Cause Joe Sixpack never heard of them? And with the possibility of NASA losing some more budget [newscientist.com], it's best to keep talking up all that cool tech that's been around since the Stone Age, makes people think you just found something cool.
Re:Vacuum Tube? (Score:4, Informative)
Because the tube would get contaminated by the pollutants & particles in the atmosphere, and some of that won't outgas as the probe gets into a decent vacuum. Also, the solar wind [wikipedia.org] kicks particles out as well, and some of those could also contaminate the tube, threatening its lifespan and/or performance.
Good idea, but it just won't work in practice.
if not, the tube would be ruined before launch (Score:5, Informative)
curious thing about tubes, they don't become useful until they're sealed in vacuum, and boiled out in a high RF magnetic field to take impurities off the elements. and then you have to flash the last of the gases off by igniting a getter inside the envelope.
that provides a higher vacuum on earth, inside the tube, than you can ever develop in space. and the electrons can do their work, instead of hitting stuff and just making a useless glow.
Re:Spam (Score:1, Informative)
A travelling wave tube amplifier is not your standard amplifier circuit. It is similar in concept to an all-optical evanescant wave amplifier used in undersea fiber optic cables. In those cases, the laser beam is sent through sapphire or some other medium that is pumped with high-power unmodulated laser light. The weak, modulated beam gains energy as it passes through the pumped media, emerging on the other side without any optical-electrical-optical conversions, with the modulation intact.
For the travelling wave tube amplifier, the modulated data is launched into one end of an evacuated tube, and power is pumped into coils of wire wrapped around the tube in special configurations. I don't recall exactly how at the moment, but the energy is transferred from the energy-pumped coils into the emerging waves as they travel down the tube from the launch point, without circuitry. The waves exit the tube at high power. This amplifier serves as the antenna as well as the final-stage power amplifier and can have pretty high directivity, which assists the communication range and speed. Similar transmitters are used on earth satellites, as well.
Re:Insane (Score:3, Informative)
My question is why you need a vacuum tube in a vacuum?
You're laboring under the idea that space is empty. But it's not, and throwing highly charged particles around (required for RF transmission) is going to attract the wrong kind of folk to the party. -_-