Asteroid Impact & Deflection Assessment (AIDA) study

AIM and DART before impact

The Asteroid Impact & Deflection Assessment (AIDA) mission is a joint international collaboration of ESA, the German Aerospace Center (DLR), Observatoire de la Côte d´Azur (OCA), NASA, and John Hopkins University Applied Physics Laboratory (JHU/APL). The primary goals of AIDA are to test our ability to perform a spacecraft impact on a potentially hazardous near-Earth asteroid and to measure and characterize the deflection caused by the impact.

A close-Earth encounter of the binary asteroid 65803 Didymos (1996 GT) in October 2022 provides the optimal target for such mission allowing an impact on Didymos' secondary body to change its orbital period around the primary by an amount measurable both from ground observatories and from a rendezvous spacecraft.

In the context of AIDA two independent spacecraft will be sent to Didymos:

  • An asteroid impactor - the NASA Double Asteroid Redirection Test (DART) Mission led by the John Hopkins’ Applied Physics Laboratory in the United States
  • An Asteroid rendezvous spacecraft - the ESA Asteroid Impact Mission (AIM).


An equal timing of the experiment is set for both missions. Despite the joint procedure, both spacecraft are still able to pursue their missions fully independently. Therefore if for some reason one of the spacecraft cannot contribute to the joint campaign, the other will be able to achieve the individual mission goals.

Mission Concept

AIDA mission concept

The AIDA mission will be the first space experiment to demonstrate asteroid impact hazard mitigation by using a kinetic impactor to deflect an asteroid. AIDA will return vital data to determine the momentum transfer efficiency of the kinetic impact and key physical properties of the target asteroid. The two mission components of AIDA, DART and AIM, are each independently valuable, but when combined they provide a greatly increased knowledge return.

AIM measures the deflection of the binary

DART is targeted to impact the smaller secondary component of the binary system, which is already well characterized by radar and optical instruments onboard AIM. The impact of the >300 kg DART spacecraft at 6.25 km/s will produce a velocity change on the order of 0.4 mm/s, which leads to a significant change in the mutual orbit of these two objects, but only a minimal change in the heliocentric orbit of the system. This is because the target’s velocity change from the impact is significant compared to its orbital speed, about 17 cm/s, although it is quite small compared to the heliocentric orbit speed of around 23 km/s. Thus the change in the binary orbit is relatively easy to measure compared with the change in the heliocentric orbit.

AIM monitoring DART impact

AIDA will provide us with a unique insight in asteroids' strength, surface physical properties and asteroids' internal structure. Linked with the DART mission, the AIM mission (in addition to the science return AIM has by itself) will provide data on the size and shape of the crater. There is great benefit to obtain the size of the crater in addition to the momentum transfer measurement. Indeed, it is well known that effects of porosity and strength of the target are hardly separable unless both the crater size and the momentum transfer efficiency are characterized. Using data of both missions will thus allow us to probe the internal structure of the target, and determine its influence on the impact process. While the change in orbit period caused by the impact will be easily detectable from Earth, any change in orbit inclination or eccentricity will very likely be too small to be measured directly without AIM.

AIDA will return valuable information on the mechanical response and impact cratering process on the real-asteroid scale and will, therefore, have major implications for planetary defense, human spaceflight, and near-Earth object science.

Didymos Characterisation

Didymos with its moon

65803 Didymos (1996 GT) is an Apollo asteroid discovered on April 11, 1996 by Spacewatch at Kitt Peak. It has a satellite orbiting it with a period of 11.9 hours, hence the appellation "Didymos", meaning "twin". Following are some describing parameters:

  • Semi-major axis: 1.644 AU
  • Orbital Period: 770.14 days
  • Allows to cheaply achieve a 2:1 resonance (2 s/c revolutions : 1 asteroid revolution)
  • Eccentricity: 0.384
  • Inclination: 3.4 deg
  • Geometric albedo: 0.147
  • Diameter primary: 800 m
  • Diameter secondary: 170 m
  • Separation: 1100 m
  • Orbital period secondary: 11.9 h (almost circular orbit)
  • Orientation of the mutual orbital plane is known (2 solutions)

For further information please contact:

Ian Carnelli
General Studies Programme
Future Preparation and Strategic Studies Office (TEC-SF)
ESA's Directorate of Technical and Quality Management
Tel: +33 1 5369 7109
Email: ian.carnelli @

Last update: 26 February 2015

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