Slashdot Mirror
Busy Signals for Deep Space Experiments
lionchild writes "Just when you hated getting those 'Network Busy' signals on your Cell Phones..imagine what it's like to deal with communications in deep space after all these years of putting satellites and probes out there into the space lanes. Check the article out on space.com
" The saddest part is the poor state that the deep space network of dishes is in, with some of the 70 meter antennae approaching their fifth decade with no repair funds on the horizon.
Just put Ham equipment on those things, and let us do the rest...
I'm sure we could get something to work.
-twb
How's ET supposed to phone home now?
You asked how often these antennas break down. While I don't know any statistics, I can give you an idea of what sorts of things make up one of these installations.
First of all, the antenna has to be pointed at the satellite that it's tracking. This is not an easy task, since the satellite is moving and it's a long way away. To make matters worse, the beam width of the antenna is damn small, so you have to point it very accurately. Doing this involves some tricky work, when you consider how much a 70 meter antenna weighs. And you can't ignore the wind in the desert, though to be fair they do stow the antenna when the wind gets above 20 or 30 miles per hour, as I recall. So in addition to having to move a lot of steel, you have to position it very accurately. Take a complex polynomial to describe the trajectory in azimuth and elevation (or is it right ascension and declination? I don't remember) and servo all that steel to track.
OK, that's the mechanics.
Now let's talk about the transmitter. The satellites you're talking to are rather far away. Remember our friend one-over-r-squared? Well, when r is large, the energy falls of a hell of a lot. So when transmitting you try to have as much power as possible. Think megawatts. Megawatts at microwave frequencies. How do you generate such power at those frequencies? You take a vacuum tube that stands about six feet high and you put a lot of current into it. You cool that sucker with a lot of water. Did I mention that the antenna is out in the middle of the desert?
OK, now you have an idea about the transmitter.
Ah, yes, the receiver. Well, the satellite can't afford to transmit a megawatt of power. If it's lucky, it can muster ten or twenty watts. At planetary distances, the energy arriving at the antenna is comparable to the amount of energy that arrives at the moon when you hold up a lit match. Not much!
How do you make a receiver that will detect a signal that weak? This is a very complicated topic, but let me summarize by noting that the key component is a superconducting maser. This is basically a chunk of copper hollowed out, evacuated, and then cooled down to a very cold temperature. In the desert.
To coordinate all of this you have to have some computers. When I last visited the control room at Goldstone it seemed pretty darn big to me. It had something like six or seven rows of 19" racks, each row with something like thirty or forty racks. That was over 20 years ago, so I might be off by a factor of two or more.
Oh, yes, how about some facilities for the people who support the installation and the project people from JPL.
And it's out in the desert. The control electronics at the big antenna are in one building and the people who drive the antenna sit in another. There's a long tunnel between the two. You're out in the desert, so keep an eye out for scorpions when you go into the tunnel. I never saw a live one, though I did see several dead ones.
So in answer to your question about maintenance, yes, there is some stuff that needs maintenance.