IMAGE CREDIT: DARPA
AS IMAGINED BY BREAKGROUND

SATELLITE SERVICING

HOW ROBOTIC ARMS WILL CHANGE
THE INFRASTRUCTURE OF SPACE,
BOTH NEAR AND FAR

STORY BY: DAVID PARK
PHOTOGRAPHY AND DESIGN: AARON SILVERSTEIN

IMAGE CREDIT: DARPA
AS IMAGINED BY BREAKGROUND

SATELLITE SERVICING

HOW ROBOTIC ARMS WILL CHANGE
THE INFRASTRUCTURE OF SPACE,
BOTH NEAR AND FAR

STORY BY: DAVID PARK
PHOTOGRAPHY AND DESIGN: AARON SILVERSTEIN

Low Earth Orbit must have been a lonely place in 1957. The only thing remotely human out there was Sputnik I, the world’s first artificial satellite in space, which looked like a wrecking ball in a slingshot without the handle hurtling 25 times the speed of sound. For three months, it orbited Earth 1,440 times 350 miles above the surface of the planet with nary another spacecraft in sight, before dipping back into the atmosphere and bursting away in a blaze of glory.

Back then, the race to space was a sprint between the two fastest sovereignties in the world. Today it’s the starting line of a marathon, with over 4000 spacecraft traversing the very trail Sputnik I blazed by its lonesome. Over the past two decades alone, governments, universities, private companies, and perhaps even your next-door neighbor have contributed to the launch of nearly 600 satellites into space. Low Earth orbit (LEO) and Geosynchronous Earth (GEO) orbit are the busiest streets in the Solar System. Nearly all of the estimated 1100 active artificial satellites make their daily commute through LEO and GEO, giving directions to motorists, delivering text messages to girlfriends, broadcasting 24-hour news cycles, and enabling Siri to define “Sputnik” on demand. In essence, satellites provide pulp to the otherwise empty husk of nearly all modern consumer technology.

The majority of satellites in space also do absolutely nothing, shuffling aimlessly in a celestial purgatory without fuel or a place to go. There are roughly 2600 decommissioned satellites in near-Earth orbit, and about 1/3 of the satellites launched in the new millennium have already gone offline. Even if everything works out perfectly, most satellites work anywhere from 5-20 years with little downtime, no vacations, and a lousy retirement plan – they could really use a union.

This quietly accepted practice is criticized as a “launch and leave” strategy, not unlike driving a car off the lot knowing the gas tank is sealed with enough juice to last a year and then walking away from it wherever it sputters to a stop. Our roads and highways would quickly become cluttered in such a system. Satellites expend a great deal of fuel, or propellant, just to reach their destination orbit. Whatever is left goes into “stationkeeping”, a term for the periodic thrusts that maintain each satellite’s specific swimming lane, orientation, and velocity as atmospheric drag and gravity relentlessly conspire to pull them back to Earth. As the tank approaches empty, most satellites are programmed to either slow down and sink back into the atmosphere or set a course thousands of miles above GEO to a supersynchronous orbit – the Graveyard orbit, as it is more poetically known. Even those maneuvers require propellant, creating big, expensive, and potentially dangerous drifting debris if there are any miscalculations. The prospect of an ever more unwieldy near-Earth infrastructure is now giving rise to the idea of on-orbit servicing, a concept that has been discussed since the dawn of space exploration but lacked the technology to make it possible.

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In 2011, communications and space robotics company MacDonald, Dettwiler and Associates (MDA) announced the Space Infrastructure Servicing (SIS) program, a sort of roadside assistance in space that can extend the life expectancy of satellites and perhaps even bring the defunct ones back from the dead. As these things go, the development process started years earlier in 2006 when the US Defense Advanced Research Projects Agency (DARPA) contracted MDA to lend a hand to FREND (Front-end Robotics Enabling Near-term Demonstration). The main directive for this revolutionary robotic arm with seven degrees of freedom (DOF) and a neighborly acronym was to enable a service probe to refuel and reposition satellites that were not designed for post-launch engagement.

MDA is no stranger to space rendezvous. Besides designing, testing, and outfitting every NASA Mars rover with a robotic arm, they are also responsible for the Canadarm, Canadarm 2, and two-limbed Dextre on the International Space Station (ISS), all of which performed operations like grappling supply delivery shuttles and installing replacement parts without the need to put astronauts at risk. Each arm provided a new baseline for more advanced robotic extremities.

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The plan for on-orbit servicing is a ballet of precision, math, and adjustments. As the service craft approaches a target satellite using its own thrusters, the onboard camera and Light Detection And Ranging system (LIDAR – the same technology that guides Google’s autonomous car) will begin to scan for orbital dynamics, velocity, distance, topology, orientation, and familiar details like the launch vehicle adapter (nearly every satellite has one) in real time. Keeping a safe distance, the servicer will begin to fly along with and orbit the target satellite like a tetherball winds around a pole.

Meanwhile, the collected data is beamed down to a ground team that will review and assess where and how the service arm will make contact to perform the necessary procedures. If all that didn’t seem hard enough, there’s also a 1 to 3 second delay as the video feed travels between GEO and Earth. Once a plan is devised, the craft can move within reach, a range called the capture envelope, and the arm can take action through a combination of supervised autonomy and teleoperation.

SEVEN DEGREES OF FREEDOM (7-DOF) MDA ROBOTIC ARM ATTACHED TO A TEST EXERCISE ROBOT.

PHOTO CREDIT: NRL, MDA

There are aspects of the primarily titanium and carbon fiber composite arm that could be considered biologically inspired, but as Chief Technologist of MDA’s Pasadena and Boulder Offices Sean Dougherty will tell you it’s really about “whatever works best” – it just turns out that human-like arms make a lot of sense. Dougherty is an expert at paraphrasing complex notions using simpler terms with the friendly, laid back nature of a modest engineer – the kind who used to train astronauts for extra-vehicular activity (EVA) in the neutral buoyancy pool at NASA’s Johnson Space Center. “I think it’s inspired by a whole bunch of different inputs,” he laughs, “including a lot of different team member’s experience.”

For instance, the average human arm is one meter, equally divided between the upper and lower halves. The service arm is also equally divided but two meters long to expand the capture envelope and broaden the margin of error, like a baseball catcher with extremely long arms. Its seven degrees of freedom is congruous to the movement of human joints: three at the shoulder, one at the elbow, and three more at the wrist. The entire apparatus is punctuated with an “end effector” that administers tools like a hand, and is outfitted with a “force torque sensor” that acts like a sense of touch to determine the right amount of force needed for every action. Some of the tools include grippers, a refueling plug for nozzles, and clippers to make incisions in the thermal blankets that are often wrapped around satellites.

In certain situations, distressed satellites could be tumbling at an erratic rate. The service craft can mimic that wild spin cycle like two bowling balls rolling down the same lane, enabling the robotic arm to reach out and impose a safer amount of torque. “If you try to instantly stop an object with that much mass, you’re going to impart a lot of force onto your robotic arm,” says Dougherty. Called “nulling the rates”, the service craft will set its thrusters in reverse once the arm is attached to gently decelerate the tumbling satellite’s inertia as it simultaneously slows its own rotation.

The key to making such a maneuver work is largely thanks to the arm’s seventh degree of freedom. But as Dougherty points out, “Our innovation really was simplifying the math so that equations could be solved more quickly.” When the task at hand involves hardware worth millions of dollars and thousands of miles away, it’s safe to say that time is of the essence.

What isn’t immediately obvious when looking at a robotic arm move is the math involved. Dougherty explains that “things in space can be given a three dimensional position on an X, Y, Z axes, plus a three dimensional orientation from pitch, yaw, and roll. That’s 6-DOF and completely defines the position and orientation [of the arm when it makes contact with a target].” The 7th degree of freedom provided a rolling motion to the shoulder, enabling the elbow to move freely and avoid obstacles while keeping the end effector in place. The notion could be compared to video game controllers, the earliest of which had thumbpads that could move Mario and Luigi rigidly on linear planes. The advent of more advanced hardware like thumbsticks opened up the possibility for games to have vastly more explorable virtual environments.

Of course, what the arm can do will always be at least a little different than what it will do, especially in space. This is where practice makes perfect. The team at MDA administers exhaustive tests on its robotic arms like placing them in thermal vacuum chambers that can simulate the low pressure and density of space and extreme temperature fluctuations due to the light of the sun or lack thereof. Vibration testing bears out the rough journey from the launch. “We need to see if all of our hard work will make it through the ride into space,” says Dougherty in a lighthearted “knock on wood” tone of voice. Once assembled, the arm is tested at massive facilities like NASA Goddard Space Flight Center and the U.S. Naval Research Laboratory where the physics of immense inertia in a weightless environment can be observed with full-scale models and a simulated sun. Each individual tool also undergoes subsystem as well as end-to-end testing on the fully integrated arm for contact dynamics as well as a myriad of other physical phenomena.

The level of autonomy built into the service arm is more akin to instinct developed from over a decade of testing and mission experience. “We’re not using anything too fancy like artificial intelligence or neural networks. Our automation is pretty straightforward scripting and branching. You have a bunch of conditions, and if something happens you go to a different branch of your program,” explains Dougherty. “There is an accumulation of experience and software packages built up over time after operating on Mars and the Space Station; it’s not like we threw all that out and started over. We’re building on that.”

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Literally and figuratively, innovations for space are never about just the here and now. The refueling and repairing of unprepared satellites today could only be realized through a yesterday filled with missions like Orbital Express, in which a prepared satellite was launched in tandem with a service satellite for the purposes of autonomously disconnecting, redocking, and refueling with a 6-DOF arm. Likewise, satellite servicing with 7-DOF arms could help build a tomorrow when satellites might be constructed in space or even engage natural satellites.

One of the forward-thinking ideas currently in development at MDA and its U.S. division, Space Systems Loral (SSL), involves launching pieces of geostationary satellites that can be robotically assembled off-planet. Called Dragonfly, the project would allow for bigger, more powerful spacecraft to be brought online while lowering the enormous price and incredible risk behind launching fully built payloads. This potential future event could change the economies of manufacturing, launching, operating, and maintaining satellites, and alter the very architecture, engineering, and construction of the near-Earth space infrastructure.

SSL is also taking part in a NASA mission dubbed the Asteroid Robotic Redirect Mission (ARRM). The plan is to land on an asteroid by 2020, cut out a boulder that could weigh up to 20 tons, and tow it to an orbit around the moon for manned mission exercises in a more controlled environment. By then, new robotic arms with even more degrees of freedom could be ready to facilitate the task. Asteroids may also be rich in minerals and other essential elements. While a lucrative cost-benefit model to import heavy payloads back to Earth is not in the picture yet (though reusable rockets and cargo shuttles like the SpaceX Dragon could add to that discussion), using those resources to get to other destinations like the moon or Mars would be transformative and could be a viable source of raw materials and water for establishing and sustaining an outpost.

Incidentally, if one did ask Siri to define “sputnik”, she’d likely reply that it means a series of Soviet satellites. Something she may not mention is that it loosely translates to “travel companion” in Russian, which makes sense since the Moon is as much a companion to Earth as it is a satellite. As humanity continues to extend its reach further into space, we may very well need the right satellite arms to accompany us on our journeys into the infinite.

IMAGE CREDIT: DARPA
AS IMAGINED BY BREAKGROUND

SOME DAY SOON, A ROBOTIC ARM
DESIGNED BY MDA/SSL MAY ASSIST NASA
IN EXTRACTING A 20-TON BOULDER
FROM AN ASTEROID.

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