Robert Romanofsky, Senior Scientist, Antenna and Optical Systems Branch
- Tuesday, 02 February 2010
NTB: You mentioned earlier the Space Communication and Navigation architecture for future space exploration missions. What can you tell us about this effort and how far along we are on it?
Dr. Romanofsky: I’m probably not the best person to respond to that, but I do know that the Space Communications and Navigation program will eventually be responsible for providing all of the communications and navigation technology for flight missions that will eventually be located throughout the solar system.
NASA Glenn has a very significant role in an important experiment that’s underway called “CoNNeCT” (Communication, Navigation and Networking Reconfigurable Testbed) and they’re basically endeavoring to fly, to demonstrate, a series of software defined radios on the International Space Station, and this will be a prelude to what the SCAN project is trying to accomplish, and that is to establish a common framework of protocols, as well as security methods, and ultimately develop a so-called Internet in the sky.
NTB: You currently hold five patents, one of which covers a MEMS reflectarray antenna for satellite applications. What makes this antenna unique and how does it work?
Dr. Romanofsky: That’s actually the ferroelectric reflectarray antenna that I alluded to earlier. In a conventional phased array antenna, the signal is distributed via some type of manifold to, perhaps, thousands of elements in the array. Each one of the channels is amplified and then it’s applied to a radiating element. The physics of a phased array requires that those elements are spaced nominally half-a-wavelength apart, so it’s an extremely dense electronics box and because of the inefficiency, dissipating heat becomes an issue. In addition, the way they are constructed currently is quite labor intensive and requires very special manufacturing capabilities that lead to high costs.
The ferroelectric reflectarray is a planar structure; it’s fed quasi-optically, meaning that there is no beam-forming manifold, so the manufacturing is simplified. And our novel ferroelectric phase shifter is unique in the following way – the finest feature size on our device is on the order of 10 microns. If you wanted to build phase shifting devices at the frequencies that we’re interested in, using conventional transport devices – that is, transistor devices – the feature sizes would be sub-micron, so the lithography on our antenna is much simpler, and that also leads to lower costs. So it’s a combination of factors that the ferroelectric reflectarray offers that promises a reduction of cost of at least, I believe, a factor of ten, and a significant savings in prime power.
NTB: We’ve been hearing a lot lately about space debris and the damage it can do to satellites and spacecraft. Given their size and shape, how susceptible are satellite antennas to being damaged by space debris, and can anything be done to protect them?
Dr. Romanofsky: That’s a good question. I think we’ve been lucky so far. Obviously, we had an event this past January where there was a Russian communications satellite and, I believe, an Iridium satellite that collided. One of the problems is, we have the ability to track objects that are, perhaps, 10cm in diameter. Things that are smaller than that, I don’t think we really understand the distribution.
I think future events are going to be inevitable. One of the biggest problems is, it doesn’t take a very large particle to do a lot of damage because you’re dealing with relative velocities that are in excess of 10 kilometers per second. A good example of that comes to mind back in the early 80s when there was a paint flake that struck the window of, I believe it was Challenger, and actually caused a “crater”. This was an extremely small particle, but because of the very high relative velocities it did a remarkable amount of damage.
The inflatable antennas are going to be particularly susceptible because if we have a micrometeorite penetration – and again, I’m not even talking about orbital debris or manmade orbital debris; I’m talking about natural phenomenon – but if we have a small micrometeorite piercing the membrane, it would, of course, cause the inflation gas to leak. The differential pressure is actually quite small, so it’s not something that’s going to deflate very rapidly. Nevertheless, rigidization is something that would be required so that if we do have an impact, the antenna would survive.
NTB: With a flexible antenna, how do you make it rigid once you deploy it in space?
Dr. Romanofsky: There are several techniques. We’ve been working with a company that used to be called SRS – it’s now Nexolve, in Huntsville, Alabama. There are certain resins, or polymers, for example, that will rigidize upon exposure to ultraviolet light. That’s one technique.
Again, the inflatable membrane technique is only one of several approaches that we’re looking at. Another very promising technology is the shape memory polymer antenna where you don’t have an inflation gas. You rely on the stored energy of the polymer material. What happens is, if you heat the material up above what’s called the glass transition temperature it becomes elastic, it can be folded and stowed, cooled down, and it becomes plastic. If you heat it up one more time, it deploys to the proper shape. That technology would be a lot less susceptible to these micrometeorite types of incidents.
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