How Lockheed Martin's SPIDER Blimp-Fixing Robot Works

Airships, which are distinct from blimps by being much more rigid and sounding much less silly, are one of those unusual technologies that has been undergoing a resurgence recently after falling out of favor half a century ago. Airships have potential to be a very practical and cost effective way to move massive amounts of stuff from one place to another place, especially if the another place is low on infrastructure and has a reasonable amount of patience.

Lockheed Martin’s Skunk Works has been developing a particular kind of airship called a hybrid airship, which uses a combination of aerodynamics and lifting gas to get airborne, for the last decade or so. The P-791 technology demonstrator first flew in 2006, and a company called Hybrid Enterprises is taking Lockheed’s airship technology to commercialization. Their LMH-1 will be able to carry over 20,000 kilograms of whatever you want, along with 19 passengers, up to 2,500 kilometers, and it’s going to be a real thing: Hybrid Airships recently closed a US $480 million contract to built 12 of them for cargo delivery.

As part of the construction and ongoing maintenance of an airship, it’s important to inspect the envelope (the chubby bit that holds all the helium) for tiny holes that, over time, can have a significant impact on the airship’s ability to fly. The traditional way to do this involves humans, and like most things involving humans, it’s an expensive and time consuming process. To help out, Lockheed Martin has developed “Self-Propelled Instruments for Damage Evaluation and Repair,” or SPIDERs, which are teams of robots that can inspect airship skins for holes as well as representing one of the less ludicrous robot acronyms that we’ve seen recently.

For details on SPIDER, we spoke with hybrid airship engineer Ben Szpak about where the idea came from, how the robot works, and what their plans are for the future.

IEEE Spectrum: Can you tell us about this history of this project? Where’d you get the idea for the design of the robot, and were there other designs that you tried before finalizing this one?

Ben Szpak: Airships have been inspected for pinholes in the same way ever since they were first designed. A crew of workers partially inflates the envelope and locates holes with a bright light while the team on the inside patches them up.

The SPIDER concept originated when the P-791 Hybrid Airship demonstrator flew 10 years ago. The idea of eliminating the pinhole check, a serial step in the production schedule, is attractive when you are producing a significant number of large airships each year. SPIDER allows this check to be performed in parallel with the airships final assembly.

The SPIDER design grew organically through many iterations into the robust and simple approach you see in SPIDER. We tested everything from stabilized two wheeled batons to centrally pivoting four wheeled designs before settling on our design. We were able to use our expertise in advanced manufacturing to 3D print parts on demand, allowing us to rapidly build and test new designs and learn from our successes and failures.

Why is the task that SPIDER performs important, and why did you decide that a team of robots was the best way to tackle it?

Helium is a very small molecule and a lot of effort is put into developing helium-tight fabrics for the envelope. Pinholes can be a huge problem if they aren’t eliminated, and they are hard to detect with the human eye. The process of patching the pinholes over a large envelope is also very time consuming and tedious. Robots have the advantage of running continuously and operating on the bottom, top, and sides of a fully inflated envelope where it can be difficult for people to reach. Since SPIDERs have evolved to a rather small robot in order to operate over curved surfaces and climb the envelope, a team of SPIDERs allow for an even faster inspection and repair process.

What are some unique challenges about operating robots across the skin of an airship, and how does SPIDER solve them?

SPIDER has to operate over a non-uniformly curved surface while also propelling itself up, down, and upside-down. We handle the curved surface by designing the chassis to comply with the envelope, twisting and bending slightly to ensure a tight coupling to its mating half. The challenge of driving in strange orientations on the envelope and still accurately measuring movement is done using optical encoders watching the envelope pass rather than shaft encoders which are susceptible to wheel slippage. We also use the known shape of the envelope to approximately locate the robot on the envelope with accelerometers.
“We’ve learned a lot about autonomous inspection and repair with SPIDER, and . . . we are working on more ideas, like SPIDERs roaming around in-flight for larger airships.”—Ben Szpak, Lockheed Martin

How many robots (and how much time) does it take to cover the airship, and how does the patching mechanism work? Are these robots that would be monitoring the airship continuously, or would they be deployed to perform maintenance at specific intervals?

We expect to utilize five to six SPIDERS on the LMH-1 vehicle, which has roughly 80,000 square feet of envelope, in less than five days depending on the number of pinholes found. The manual process of locating and patching pinholes can take about ten days and doesn’t happen in parallel with the production process, which is a major benefit of SPIDER. The patching mechanism works similarly to a handheld label applicator, applying a patch over the hole once the SPIDER is positioned. We will deploy the SPIDERS during airship final assembly and at major maintenance checks.

Can you talk about the future of SPIDER? Are there ways in which you’d like to upgrade or improve the robots, or will the success of these robots lead to other robotic systems being developed in this space?

We’ve learned a lot about autonomous inspection and repair with SPIDER, and those lessons will be applicable as more opportunities arise in this field. We are working on more ideas, like SPIDERs roaming around in-flight for larger airships.

Anything else cool about these robots that you can tell us?

We were able to build SPIDER with almost entirely off-the-shelf components, while designing our own critical parts, and integrating them together. This demonstrates the amazing growth of the robotics community in the past few years and demonstrates that with the right applications robotics can be used to solve a vast set of challenges.

Fulltext of the article by Evan Ackerman in IEEE SPECTRUM.