By Denise M. Stefula
The Human Exploration Telerobotics 2 project has reached another milestone in its numerous overlapping tests of four free flying robot prototypes for the Astrobee technology. In this “iterative” method, one test’s results inform requirements and design for the next version. The importance of having these incremental prototype milestones is to develop a technology in the most efficient manner possible while accepting the proper amount of risk for that stage of development.
“Our ultimate goal is to be on track to deliver certified units ready to meet the technical needs of a project,” says Mary Beth Wusk, acting program manager for Space Technology’s Game Changing Development Program. “This approach, called iterative design, is used in many projects, not just Astrobee, because it provides a path to integrate the subsystems that are being developed concurrently and ensure the integrated system is progressing as planned.”
Future human space missions in Earth orbit, to the Moon, and to distant destinations offer many new opportunities for exploration. However, astronaut time will always be in short supply, consumables (e.g., oxygen) will always be limited, and some work will not be feasible, or productive, for astronauts to do manually. Robots such as Astrobee can complement astronauts by performing this work under remote supervision by humans from a space station, spacecraft, habitat, or even from Earth.
“One goal is to reduce the workload on astronauts using these highly functioning, remotely controlled robots capable of performing routine housekeeping and in-flight maintenance jobs so the astronauts can focus on the more important science missions at hand,” says Wusk. “The Game Changing Development Program is well on its way to deliver these Astrobee units to the International Space Station in order to improve the way humans live and work in space.”
Astrobee is an assistive, free flying robot being developed for use on the International Space Station to help save crew time and serve as a research platform. In space, every moment counts and alleviating crew members of conducting tasks robots can easily do frees up valuable time for engaging directly in research activities rather than setting up and tearing down equipment to do so.
“The most recent set of tests took place with Astrobee Prototype 4 (P4),” says Chris Provencher, project manager for the Astrobee technology at NASA’s Ames Research Center. “This prototype is the first to attempt a flight-like hardware design; the previous prototypes were ‘open-structure subsystem test platforms.’ P4 is the first to truly integrate all of the subsystems and the first that will really tell us if the robot can do what we expect it to. It’s also the last prototype before we build the certification unit.”
The primary purpose for P4 is a risk reduction activity on various features/components wherein the team is ensuring the hardware design will meet requirements, a critical milestone for this prototype, which reflects a flight-like hardware design. All bench testing, but with a big impact.
P4 was put through the same tests the team would run on the certification unit. The milestone testing included checking that processors can read data correctly from navigation sensors, command the nozzles which in turn need to produce sufficiently for propulsion, and confirm the motors don’t overheat. Also tested were network connectivity and ensuring the free flyer can receive power from and communicate through the dock.
“The testing was very successful in that we demonstrated that the hardware design works. But, we also identified areas of the design that require modifications, and that’s what we needed to find out now rather than later. This gives us time to make corrections to the design before it’s too late,” explains Provencher. “One example of an area that requires design modifications is in the thermal management system. Astrobee’s biggest heat source is the processors. We are using smartphone quality processors, and our analysis indicated that they would provide enough heat that we had to do something about it.”
The tests revealed a few flaws in the thermal management system design that need to be addressed, such as rerouting cables so that they don’t impede air flow, installing mechanical louvers to direct the air over the processors, and improving the contact between the processors and their heat sink.
“Developing iterative prototypes has been a very effective development approach for us over the past 1.5+ years,” says Provencher. “It allows us to address and reduce risks in a prioritized manner, we can focus on a subset of the robot subsystems instead of everything at once, we can make incremental changes to the design, and it reveals integration issues sooner rather than later.”
Provencher likens the approach to that of a college student preparing throughout an academic year for that big exam. Smaller tests through the year gauge progress and help students and instructors identify which areas need more attention—“better to see what you’ve done wrong on the practice test than getting it wrong on the big exam,” he says.
What makes Astrobee’s milestone a big splash? P4 had a secondary purpose; it allowed the team to practice how to do the integration, assembly and testing of the certification unit. This was important because the central core module presented a real integration challenge. “We’re trying to fit a lot of avionics components into a small volume. The order in which you assemble things makes a big difference,” says Provencher. “We experimented with a few different sequences, then documented the way that worked best. Those draft procedures now set us up for successful assembly and testing with the certification unit. Astrobee’s Prototype 4 really was the ultimate practice test.”
Once the hardware testing was complete, the team began testing software and control of the free flyer. All of the simulator work paid off, and the software testing looks promising so far.
“We are now able to ‘fly’ the robot in our lab on a testing table that is similar to a giant air-hockey table. This table allows the robot to translate in two axes and rotate about one axis. So far we’ve successfully commanded the robot to move about the table in a very controlled manner. Next we will test the accuracy of our navigation by having the robot perform an automated docking,” Provencher recounts.
Completing this testing milestone was a tremendous accomplishment for the team. Earlier prototypes were impressive, but they only tested subsets of the system, and they looked nothing like the final robot will.
“This prototype is a great technical achievement because it shows that the hardware design works, and that brings a huge sense of relief to the team. I’m really impressed with our project team. They’ve accomplished so much in the past year and a half,” says Provencher. “And now we have something that we can point to and say, that’s it…that’s what Astrobee looks like.”