Deep Space Deployers Developed for Hera Mission

A pair of Deep Space Deployers developed by Dutch firm ISISPACE for ESA’s Hera asteroid mission for planetary defense have been by far its most challenging project. The two systems need to keep their nanosatellite cargo alive and healthy, before releasing them on a precisely staged basis – at a velocity of just a few centimeters per second. Any faster and Hera’s CubeSats would risk getting lost in space.

“The reason for deploying this way is that in Earth orbit there are ground stations available to communicate immediately with newly-deployed CubeSats." Ralph Slootweg, ISISPACE

Ralph Slootweg, ISISPACE

Once Hera travels to the Dimorphos asteroid it will not go there alone. It will carry with it two CubeSats to gather additional data on its target: the Italian-led Milani CubeSat is equipped with a hyperspectral imager to perform mineral prospecting of the body’s surface while the Luxembourg-led Juventas CubeSat will perform the first subsurface radar probe of an asteroid, going on to touch down and measure surface gravity levels.

To keep these nanosatellites in good health through Hera’s two-year cruise phase through deep space and then to check out their independent functioning before releasing precisely as required within the asteroid’s ultra-low gravitational field, the mother spacecraft is equipped with a pair of Deep Space Deployers, built into opposing ends of Hera’s topside.

Deep Space Deployers Require Longevity, Precision

Standard deployers employed for CubeSat missions to low-Earth orbit serve as a kind of supportive exoskeleton for these tiny items during their turbulent ride to space, then inject them into orbit. Hera’s Deep Space Deployers must operate for much longer. They then have to release their cargo in a gradual and carefully engineered manner.

“In complexity terms, our Deep Space Deployer design is equivalent to another onboard instrument,” explains Hera’s ESA system engineer Franco Perez Lissi. “Instead of releasing its CubeSat with a big spring like a standard deployer, pushing away from the parent at around two meters per second, we need to release two orders of magnitude more slowly, because the asteroid gravity is less than a millionth of Earth’s. If we release any quicker then the CubeSat could well miss the asteroid altogether.

“In addition, the two DSD will be used to communicate with their CubeSats, throughout Hera’s approximately two-year voyage to Dimorphos, exchange telemetry and telecommands, update software, charge batteries, test reaction wheels and perform final health checks.”

“Then, when we get ready to deploy each CubeSat, this does not happen all at once. We begin with springs that push the CubeSat up to the top of the DSD, but it will remain linked to Hera through an umbilical for power and communications," said Ralph Slootweg, lead mechanical design engineer at ISISPACE. "Over an approximately 24-hour period each CubeSat will have its systems activated and checked out while exposed to space – including the inter-satellite links that will be used to communicate back with Hera – before undergoing their final release, intended to occur not only slowly but also precisely, minimizing any imparted rotation which would need precious onboard cold-gas propellant to correct.”

“The reason for deploying this way is that in Earth orbit there are ground stations available to communicate immediately with newly-deployed CubeSats. Out at Dimorphos there will only be Hera.”

The DSD’s CubeSat Release System that will give each CubeSat their final push away had to be tested in terrestrial gravity, which meant employing a pendulum-based rig plus high-speed cameras to validate that the desired velocity would be reached at Dimorphos.

The overall DSD design also had to be subjected to a full qualification campaign, including environmental testing to check if it can survive the launch and cruise phases.

(Source: ESA news release. Images provided)