by Staff WritersParis (ESA) Jun 26, 2018
 In 2022, NASA's Double Asteroid Redirection Test (DART) collides with the smaller body of the Didymos binary asteroid system in an attempt to measurably shift its orbit. ESA's Hera mission, now under study, will examine the aftermath of this impact to help determine whether humans can deflect threatening asteroids. Hera will also demonstrate the ability to operate at close proximity around a low-gravity asteroid with some on-board autonomy similar in scope to a self-driving car, going on to deploy Europe's first deep-space CubeSats, and potentially also a micro-lander, to test out a new multi-point intersatellite link technology. Hera will be highlighted during Asteroid Day on 30 June, an annual opportunity to raise awareness of the threat and opportunity posed by the numerous rocky bodies traversing space. As part of the UN-recognised Asteroid Day, hundreds of regional events take place world wide, with 78 countries so far having hosted concerts, community events, lectures and much more. This year, the European Southern Observatory (ESO) and ESA will team up to co-produce a packed webcast, streamed live from the new ESO Supernova Planetarium and Visitor Centre in Munich, from 13:00 CEST. The programme will highlight some of the most recent activities in the global hunt for risky asteroids, as well as conversations with ESA planetary scientists, asteroid experts and a variety of guest presenters. Fascinating insights into the 2013 Chelyabinsk event will be presented, as well as discussions around the possibility of one day sending humans to asteroids. Watch live via esa.int/asteroidday. |
Planning for humankind's first mission to a binary asteroid system has entered its next engineering phase. ESA's proposed Hera mission would also be Europe's contribution to an ambitious planetary defence experiment.
Named for the Greek goddess of marriage, Hera would fly to the Didymos pair of Near-Earth asteroids: the 780 m-diameter mountain-sized main body is orbited by a 160 m moon, informally called 'Didymoon', about the same size as the Great Pyramid of Giza.
"Such a binary asteroid system is the perfect testbed for a planetary defence experiment but is also an entirely new environment for asteroid investigations. Although binaries make up 15% of all known asteroids, they have never been explored before, and we anticipate many surprises," explains Hera manager Ian Carnelli.
"The extremely low-gravity environment also presents new challenges to the guidance and navigation systems. Fortunately we can count on the unique experience of ESA's Rosetta operations team which is an incredible asset for the Hera mission."
The smaller Didymoon is Hera's main focus: the spacecraft would perform high-resolution visual, laser and radio science mapping of the moon, which will be the smallest asteroid visited so far, to build detailed maps of its surface and interior structure.
By the time Hera reaches Didymos, in 2026, Didymoon will have achieved historic significance: the first object in the Solar System to have its orbit shifted by human effort in a measurable way.
A NASA mission called the Double Asteroid Redirection Test, or DART, is due to collide with it in October 2022. The impact will lead to a change in the duration of Didymoon's orbit around the main body. Ground observatories all around the world will view the collision, but from a minimum distance of 11 million km away.
"Essential information will be missing following the DART impact - which is where Hera comes in," adds Ian.
"Hera's close-up survey will give us the mass of Didymoon, the shape of the crater, as well as physical and dynamical properties of Didymoon.
"This key data gathered by Hera will turn a grand but one-off experiment into a well-understood planetary defence technique: one that could in principle be repeated if we ever need to stop an incoming asteroid."
The traditional method of estimating the mass of a planetary body is to measure its gravitational pull on a spacecraft. That is not workable within the Didymos system: Didymoon's gravitational field would be swamped by that of its larger partner.
Instead, Hera imagery will be used to track key landmarks on the surface on the bigger body, 'Didymain', such as boulders or craters. By measuring the 'wobble' Didymoon causes its parent, relative to the common centre of gravity of the overall two-body system, its mass could be determined with an accuracy over 90%.
Hera will also measure the crater left by DART to a resolution of 10 cm, accomplished through a series of daring flybys, giving insight into the surface characteristics and internal composition of the asteroid.
"Hera benefits from more than five years of work put into ESA's former Asteroid Impact Mission," comments Ian.
"Its main instrument is a replica of an asteroid imager already flying in space - the Framing Camera used by NASA's Dawn mission as it surveys Ceres, which is provided by the German Aerospace Center, DLR.
"It would also carry a 'laser radar' lidar for surface ranging, as well as a hyperspectral imager to characterise surface properties. In addition, Hera will deploy Europe's first deep space CubeSats to gather additional science as well as test advanced multi-spacecraft intersatellite links."
NASA's DART mission meanwhile has passed its preliminary design review and is about to enter its 'Phase C' detailed design stage.
