Hera on course for asteroid rendezvous

The European Space Agency’s (ESA) Hera spacecraft is on its way to the only asteroids in existence whose orbits have been deliberately altered by human action.

At the Didymos binary system, Hera will help scientists answer the questions remaining after NASA’s DART spacecraft impacted Didymos’ smaller moon Dimorphos. In doing so, Hera will help to transform asteroid deflection by kinetic impact into a well-understood and repeatable technique for protecting Earth.

Hera recently completed the second of two deep-space manoeuvres on its journey from Earth to Didymos. The manoeuvre burned 123 kg of onboard hydrazine fuel and changed the spacecraft’s velocity by 367 m/s – a change comparable to an object accelerating from stationary to supersonic flight.

“We divided the deep space manoeuvre into three engine burns, plus one much smaller correction manoeuvre, carried out over a period of around four weeks,” says Francesco Castellini from the Flight Dynamics team at ESA’s European Space Operations Centre in Germany.

“This is the Hera mission’s largest manoeuvre in terms of fuel consumption, and we used it to test all of the systems that we will need during the braking and rendezvous manoeuvres later this year as we arrive at Didymos.”

Tracking data from ESA’s Estrack network of deep space antennas confirmed the success of the manoeuvre, and downlinked telemetry from the spacecraft shows that all subsystems performed as expected.

With the deep-space manoeuvre complete, the Hera team has its sights set on arrival at Didymos. Extensive onboard software updates have been designed to prepare the spacecraft for close-proximity operations at the asteroids.

The update adds and improves functionalities that Hera will need to carry out humankind’s first thorough survey of a binary asteroid, such as new software for Hera’s laser altimeter – which will continuously monitor its distance from the asteroids – and for the monitoring camera that will visually monitor and confirm the release of Hera’s two CubeSats.

“Uploading new software to Hera across deep space is like having a video call with a friend on Mars at just 0.004% the speed of a typical home internet connection and with a twenty-minute time delay between speaking and hearing your friend’s response,” says Anna Schiavo from the Hera Flight Control Team.

“Sending the software to the spacecraft, which is just the first step in the overall software update, will take around three hours.”

In October, Hera will begin a series of precisely timed burns to transition from interplanetary cruise to asteroid rendezvous.

Unlike larger deep-space destinations such as planets, Didymos and Dimorphos are small, dark and hard to see: Hera will need to actively search for the asteroids and keep them centred in its field of view as it navigates towards them.

The approach will last around three weeks and will test Hera’s guidance, navigation and control systems to the fullest.

Find out more about the Hera mission and ESA’s role in turning asteroid deflection from science fiction into science fact at the links below.