September 17, 2019

Experimental British satellite tests harpoon in orbit


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A British satellite released from the International Space Station last year has successfully demonstrated a harpoon that could be used on future missions to clean up space debris, officials announced Friday.

The harpoon fired out of the RemoveDebris spacecraft Feb. 8, striking a target plate extended from the satellite on a 4.9-foot (1.5-meter) boom. The experiment was one of the main objectives of the $17 million (15.2-million-euro) RemoveDebris mission, conceived as a testbed for technologies engineers hope will allow future satellites to tidy up busy orbital traffic lanes by collecting dead satellites and rockets and driving them back into Earth’s atmosphere to burn up.

In a dramatic video released by Surrey Satellite Technology Ltd., the harpoon is seen catapulting out of the RemoveDebris spacecraft at a velocity of about 45 mph — 20 meters per second — and spearing its target. A cable attached to the harpoon kept the device from flying off and becoming its own piece of space junk.

“This is RemoveDebris’ most demanding experiment and the fact that it was a success is testament to all involved,” said Guglielmo Aglietti, director of the Surrey Space Center at the University of Surrey, and principal investigator for RemoveDebris. “The RemoveDebris project provides strong evidence of what can be achieved with the power of collaboration – pooling together the experience across industry and the research field to achieve something truly remarkable.”

Operated by controllers at SSTL’s campus in Guildford, England, the RemoveDebris satellite is shaped like a cube and measures about 3 feet (1 meter) on each side. But it punches above its weight, with a mission that has already successfully tested a net that could capture space debris, and completed trials with a laser and camera system to identify and navigate toward objects — such as space junk — in orbit.

The harpoon was developed by Airbus Defense and Space in Stevenage, England.

“Successful in space demonstration of the harpoon technology is a significant step towards solving the growing issue of space debris,” said Chris Burgess, harpoon lead engineer at Airbus Defense and Space.

The RemoveDebris satellite deployed from the International Space Station on June 20. Credit: NASA/NanoRacks/Ricky Arnold

The RemoveDebris satellite launched inside a SpaceX Dragon cargo craft in April 2018. After delivery to the space station, the satellite was mounted on a deployer by astronauts, then moved outside the station’s Japanese airlock for release in June.

The RemoveDebris spacecraft released a tiny CubeSat target that was snared with a net during an experiment in September, then deployed a second CubeSat in October for a tracking experiment using a color camera and laser rangefinder to determine the location, speed and orientation of the target.

“While this experiment may not be as eye-catching as its predecessor, it could prove to be just as consequential,” Aglietti said in an October statement announcing the navigation system test. “What we have proved with this successful test is that the vision-based-navigation system is able to provide accurate information about a piece of debris, its behavior and its flight of travel – information crucial in an active debris removal mission.”

Engineers expected the harpoon experiment would pose more hazards, due to the velocity and dynamics of the spear as it fired out of the RemoveDebris satellite and pierced its target. On a real satellite, the harpoon would have to be aimed away from fuel tanks to avoid the risk of uncontrolled leaks, or explosions.

“Maybe it’s a bit more risky because you have to hit your debris in a place that is suitable to be captured by the harpoon,” Aglietti said in an interview before the launch of RemoveDebris. “Clearly, you have to avoid any fuel tanks … That would produce some undesired effects.”

Experts were eager to gauge how the harpoon moved in zero gravity, collecting data that was difficult to obtain during ground testing.

“We have harpoons, we have nets,” said Jason Forshaw, RemoveDebris’ former project manager at SSTL, in a TEDx talk in 2017. “These all seem like simple concepts, and they are. They’ve been used for thousands of years underwater to capture things such as sea creatures. However, taking technologies that are mature on Earth, in the oceans, and actually bringing them up there into space and seeing (if) these concepts work for the first time — nobody has ever used a net or a harpoon for these purposes in space before.”

The final experiment in the RemoveDebris mission is scheduled for March, when the satellite will open an expandable sail to act like an airbrake or spoiler, generating drag from collisions with air molecules in the rarefied outer atmosphere. From an altitude of around 250 miles (400 kilometers), the dragsail will bring the RemoveDebris satellite back into the denser layers of the atmosphere, where it will burn up.

The braking mechanism will allow RemoveDebris to re-enter the atmosphere within about eight weeks of unfurling the dragsail, not the estimated two-and-a-half years it would take to de-orbit naturally.

The CubeSats released by RemoveDebris last year for the net and navigation trials were also predicted to naturally re-enter the atmosphere within months.

“All the elements of the mission should be de-orbited very quickly,” Aglietti said. “Clearly, for a mission like ours, we don’t to further contribute to the problem of space debris. We want to make sure that all the pieces we are putting up there are going to come down pretty quickly.”

The RemoveDebris mission was partially funded by the European Commission. The rest of the project was paid by the 10 companies involved in the demonstration, including SSTL, Airbus Defense and Space, and ArianeGroup.

“Space debris can have serious consequences for our communications systems if it smashes into satellites,” said Chris Skidmore, the UK science minister, in a statement. “This inspiring project shows that UK experts are coming up with answers for this potential problem using a harpoon, a tool people have used throughout history.”

Experts currently estimate more than 8,000 tons of junk and debris are orbiting Earth, a mass equivalent to the Eiffel Tower. Derelict satellites, spent rocket stages and other bits of junk could collide with other spacecraft, such as the space station, putting astronauts and property at risk, and risking the creation of more debris.

Officials hope RemoveDebris can prove cleaning up space junk can be accomplished at a relatively low cost, within the budgets of commercial service providers and governments with limited funding.

“Once the whole campaign is finished, and the (RemoveDebris) satellite is de-orbited, it would be great if companies offered this as a service, and there will be bigger missions when they will go and capture a real piece of debris using some of the technologies we have demonstrated,” Aglietti said in an interview last year.

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Follow Stephen Clark on Twitter: @StephenClark1.


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