HANSCOM AIR FORCE BASE, Mass: A series of early March flight tests has validated a two-and-a-half year effort and set the course for significantly enhanced airborne communications capability.
A team of specialists from the Electronic Systems Center, MITRE Corporation and MIT Lincoln Laboratory used a 707 test bed aircraft to evaluate the transmission capabilities of a prototype waveform developed as part of the High Data Rate Airborne Terminal program, known as HDR-AT. It was the first time an airborne system has successfully accessed the high-capacity Ka-band portion of the new wideband global satellites, which offer wider bandwidth and higher throughput than other military satellites.
This development is especially important for the “Global Hawk-class of unmanned aerial systems,” which will be first in line for receiving the capability once it’s been perfected and transferred to the defense industry, said Dr. Tom Macdonald of Lincoln Lab.
As reliance on these high-altitude surveillance aircraft increases, a key challenge has been figuring out how to get the collected data out to operators quickly. This new capability will make that task much easier.
“With this waveform, they should have the ability to move hundreds of megabits of sensor data per second off the platform to users beyond direct line-of-sight,” Doctor Macdonald said.
When the platforms lose line-of-sight connectivity, they have to rely on satellite communication to move their data to where it’s needed.
“Right now, that mostly requires relying on commercial satellites, which means paying a per-minute charge and living with data-rate limiting constraints of those systems,” Doctor Macdonald said. “This new capability will give them a fast, dedicated military solution.”
Before ever engaging in a flight test, a lot of up-front work had to be done, according to ESC program manager Bill Lyons. First off, the team had to figure out if putting very high data rates through the wideband global satellites was feasible. They started by adapting an existing commercial waveform for military use and testing it in the lab.
“It’s like satellite TV, only flipped around and running backwards,” said Doctor Macdonald. “With satellite TV, there’s a big, fixed ground station that sends data to a satellite which relays the signal to many users with small antennas. We run from one small antenna up to the satellite and then to many big terminals, and we hit the gas and make the waveform run a lot, lot faster.”
During earlier lab testing, the team saw rates as high as 300 megabits per second, which is much higher than the standard desktop user experiences. The question for the flight tests centered on what kind of results could be achieved from the first-of-a-kind airborne terminal. During the flight tests they were able to get to 40 Mbps, which was predictable due to a number of constraints in the test set-up. For one thing, the 2-foot antenna on the 707 was only half the size of the projected Global Hawk antenna.
During the testing, the team also was able to use ground stations to show communications at about 200 Mbps per second through the WGS. That rate, the team expects, is more indicative of what could be achieved with a 4-foot Global Hawk antenna and the more powerful Global Hawk amplifier. With the next generation of WGSs, this data rate will increase to almost 300 Mbps for Global Hawk users.
While the flight test was a great success, it allowed team members to identify areas needing additional work. The team hopes to schedule another flight test late this summer, to verify solutions and improvements.
From here, Mr. Lyons said, the challenge is to transition this effort to industry. That process will begin with an Analysis of Alternatives on the way-ahead. The program team also is planning to do some early risk-reduction, or proof-of-concept testing, with the Global Hawk.
“We’ll basically take what we’ve got now and work with Global Hawk program managers to improve it,” Mr. Lyons said.
Once the AoA is complete, the program office will go out with a Request for Proposal, which likely will lead to some industry prototyping, and eventually to development programs.
“The good news is that so much leg work has already been accomplished,” said Mark Tsarouhas of the MITRE Corporation, a member of the program team.
“In addition to the waveform work, we have been pushing the amplifier industry to develop the necessary power at the right frequencies and investigating the effects of radiation at high altitudes of common digital processing elements. Now when the government asks for those speeds in its formal request to industry, these capabilities will already exist.”
