Progress has been made in fixing night-vision, latency and jitter problems experienced by pilots using the F-35 Joint Strike Fighter’s helmet-mounted display system (HMDS). But despite the prospect of a solution to this issue, aircraft maker Lockheed Martin also charted a possible alternative course using an HMDS with night-vision goggles (NVGs).

Last September, Lockheed Martin awarded a contract to BAE Systems to develop an alernate HMDS with detachable NVGs as an interim solution to the incumbent helmet display supplied by Vision Systems International (VSI), which the Pentagon has labeled as a program risk. Getting the HMDS right is critical, as the F-35 was designed without a pilot’s head-up display (HUD).

VSI, a joint venture company of Rockwell Collins of the U.S. and Israel’s Elbit Systems, received a contract from Lockheed Martin for low-rate initial production of its second-generation HMDS in 2009. In November, San Jose, California-based VSI said it received a contract for two additional phases in the HMDS development.

Since March 2011, VSI has been working to mitigate display jitter affecting the symbology of the Gen II HMDS, an earlier version of which first flew on the F-35 in 2007. Other fixes will improve the night-vision resolution of a fixed camera mounted in the cockpit and a helmet camera, and reduce the latency of imagery imported from the F-35’s electro-optical distributed aperture system (DAS), a set of infrared sensors flush-mounted around the aircraft to provide 360-degree spherical coverage.

The latest contract award “reaffirms the confidence that Lockheed Martin has in VSI to advance the fifth-generation [fighter] HMDS capabilities that are integral to the success of the F-35 program,” claimed Drew Brugal, VSI president. Deliveries of the enhanced HMDS are scheduled to begin in the third quarter of 2013.

F-35 Program Risk

VSI’s HMDS was identified as one of 13 causes for concern in a quick-look review (QLR) of the F-35’s flight-test progress by the U.S. Department of Defense, leaked late last year. The review found the HMDS has deficiencies in display jitter, night-vision acuity and image display latency from the DAS that detract from mission tasks and the display’s use as a primary flight reference. It rated the HMDS a “program-level high development risk.”

According to the QLR, aircraft buffeting induces HMD display jitter, “making symbology unreadable under those conditions.” The problem is “tactically significant” for visual range air-to-air weapons employment and surface-to-air and air-to-air threat reactions. The use of a micro inertial measurement unit is being considered to cancel out jitter effects, but remains to be tested. VSI said in November that it has modified the current magnetic receiver unit contained in the HMDS to detect both seat and aircraft vibration frequencies and filter them out in the system’s display processor.

The QLR said the current HMDS provides poor night-vision acuity of about 20/70 with the existing Gen II night-vision camera, lagging the 20/25 acuity of currently fielded military NVGs. System latency “is excessive and detracts from mission capability.” DAS video imagery latency is approximately 130 milliseconds (msec) and basic symbology 50 msec, lagging specifications of less than 40 msec and less than 30 msec, respectively. A full-motion simulator study will be conducted this spring to characterize the effects of different time latencies, although the effects may not be fully understood until the chosen corrective action is flight tested, the review said.

VSI declined to comment for this article. However, Steve O’Bryan, Lockheed Martin vice president for F-35 program integration and business development, discussed the progress of HMDS fixes during a January 20 teleconference on the F-35 program. “We continue to work the issues associated with the helmet and believe we are on a good path to fixing those,” he said. “There’s still more to do. Until we are certain that we will meet those warfighter requirements, we are going keep an alternate, lower risk helmet on track as well.”

Cockpit Design Changes

O’Bryan acknowledged that design changes would be required in the F-35 cockpit to accommodate the alternate BAE system. “There would be changes to the cockpit that would be required on this lower risk helmet to do that,” he said. “That is why it’s our desire to fix the helmet we have, and we are making significant progress with that–increasing the resolution of the night camera on it, as well as working the latency, the delays in incorporating the DAS or midwave IR night capabilities and stabilizing the image for the pilot. On all three issues we’ve seen progress and we’ve continued to make progress in the last 30 days.”

BAE proposes a hybrid solution combining the two-part design (inner and outer shell) of its Striker helmet used on the Eurofighter Typhoon and Saab JAS 39 Gripen, with clip-on Q-Sight holographic waveguide display positioned close to the eye to project flight symbology and mission information. The binocular NVGs swing down in front of the display for night operation. The system will incorporate an optical head tracking system to precisely monitor the pilot’s head movements and correctly position the display symbology.

“The program is going well,” Paul Cooke, BAE Systems fast-jet helmet business development lead, told AIN. “One of the reasons I think we were selected is all of the building blocks for the helmet we offered were very mature. They were TRL [technology readiness level] 6 or higher–everything.”

Cooke said one of the challenges involved with BAE’s solution would be mounting the Q-Sight display to the two-part helmet “because you’re adding a very near-to-the-eye kind of structure.” The pointing accuracy, overall field of view and brightness of a miniature display (less than four ounces) used as a primary flight reference will also be issues, as well as the preciseness of the head tracking system.

Should VSI resolve development problems with its Gen II HMDS, BAE’s alternate system likely would be terminated, said Cooke, adding, “I don’t believe it’s anybody’s intent to fly indefinitely with a night-vision goggle based solution.” But achieving the same night-vision acuity with digital inputs now possible with analog NVGs may still be years away, he said.

“The fact of the matter is, the digital input devices to visor-projected helmets, the kind of solution that allows you to eliminate night-vision goggles, the number of pixels are not equivalent to the picture you get on an analog night-vision goggle today,” Cooke said. “They will be at some point. But the bottom line is the pilots are not willing to trade that visual acuity and the clarity of the picture they get on a night-vision goggle for what the digital input devices can deliver today.

“The real limiting factor is not the VSI helmet, I think it’s really the digital input devices that generate the picture,” he said. “Until they’re equivalent or better than the analog, I think that you’re going to see night-vision goggles remain part of the equation.”

Preliminary design review of the alternate helmet display is scheduled for early this year. BAE said it will begin delivering test assets in 2012 to support F-35 integration laboratories, flight simulators and flight-test platforms.