Double Asteroid Redirection Test (DART)

The Double Asteroid Redirection Test (DART) is a NASA space mission aimed at testing a method of planetary defense against near-Earth objects (NEOs). In September 2022, a space probe is set to deliberately crash into the minor-planet moon Dimorphos of the double asteroid Didymos to assess the future potential of a spacecraft impact to deflect an asteroid on a collision course with Earth through a transference of momentum.

DART is a joint project between NASA and the Johns Hopkins Applied Physics Laboratory (APL).  It is being administered by NASA's Planetary Defense Coordination Office, and several NASA laboratories and offices are providing technical support.  International partners, such as the space agencies of European Space Agency (ESA), Italian Space Agency (ASI), and JAXA Japan, are contributing to related or subsequent projects. In August 2018, NASA approved the project to start the final design and assembly phase. The DART spacecraft was successfully launched on 24 November 2021, with collision slated for 26 September 2022.

Background

Originally, the European Space Agency (ESA) and NASA had independent plans for missions to test asteroid deflection strategies, and by 2015 they struck a collaboration called AIDA (Asteroid Impact & Deflection Assessment) involving two separate spacecraft launches that work in synergy.  Under the proposal, the European spacecraft, AIM, would have launched in December 2020, and DART in July 2021.  AIM would have orbited the larger asteroid to study its composition and that of its moon.  DART would then impact the asteroid's moon in September 2022, during a close approach to Earth.  AIM would have studied the asteroid's strength, surface physical properties, and internal structure, as well as measure the effect on the asteroid moon's orbit around the larger asteroid.

The AIM orbiter was cancelled, the full characterization of the asteroids will not be obtained, and the effects of the impact by DART will be monitored from ground-based telescopes and radar.

In June 2017, NASA approved a move from concept development to the preliminary design phase, and in August 2018 NASA approved the project to start the final design and assembly phase.

It was originally planned for DART to be a secondary payload on a commercial launch to keep costs low; however, a mission update presentation in November 2018 noted that the mission has a dedicated launch vehicle.

On 11 April 2019, NASA announced that a SpaceX Falcon 9 would be used to launch DART.

Scientists estimate 25,000 large asteroids are in the Solar System, though to date, surveys have detected about 8,000; therefore, NASA officials think it is imperative to develop an effective plan should a near-Earth object threaten Earth.

Description of Spacecraft

The DART spacecraft is an impactor with a mass of 610 kg (1,340 lb), that hosts no scientific payload other than a Sun sensor, a star tracker, and a 20 cm (7.9 in) aperture camera called Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO). DRACO is based on the Long-Range Reconnaissance Imager (LORRI) onboard New Horizons spacecraft, and will support autonomous navigation to impact the asteroid's moon at its center.

DART spacecraft uses the NEXT ion thruster, a type of solar electric propulsion.  It will be powered by 22 m² (240 sq ft) solar arrays to generate the ~3.5-kW needed to power the NASA Evolutionary Xenon Thruster–Commercial (NEXT-C) engine.  The spacecraft's solar arrays use a Roll Out Solar Array (ROSA) design, and this was tested on the International Space Station in June 2017 as part of Expedition 52, delivered to the station by the SpaceX CRS-11 commercial cargo mission.

Using ROSA as the structure, a small portion of the DART solar array is configured to demonstrate Transformational Solar Array technology, which has very-high-efficiency solar cells and reflective concentrators providing three times more power than current solar array technology.

The DART spacecraft is the first spacecraft to use a new type of high gain communication antenna, that is, a Spiral Radial Line Slot Array (RLSA). The antenna operates at the X-band NASA Deep Space Network (NASA DSN) frequencies of 7.2 and 8.4-GHz. The fabricated antenna exceeds the given requirements and has been tested through environments resulting in a TRL-6 design.

Mission and Impact

It is estimated that the impact of the 500 kg (1,100 lb) DART at 6.6 km/s (4.1 mi/s) will produce a velocity change on the order of 0.4 mm/s, which leads to a small change in trajectory of the asteroid system, but over time, it leads to a large shift of path.  Over a span of years, the cumulative trajectory change from such a small change in velocity could mitigate the risk of a hypothetical Earth-bound asteroid hitting Earth.  The impact will target the center of figure of Dimorphos and should decrease the orbital period, currently 11.92 hours, by roughly 10 minutes.

The actual velocity change and orbital shift are uncertain. There is a poorly understood "momentum enhancement" effect due to the contribution of recoil momentum from impact ejecta.  It is expected that the final momentum transferred to the largest remaining fragment of the asteroid could be up to 3-5 times the incident momentum, and getting good measurements of the effects, which will help refine models of such impacts, is one of the main goals of the mission.  Initial estimates of the change in binary orbit period should be known within a week.  A detailed reconnaissance and assessment will be performed a few years later by a spacecraft called Hera, approved by ESA in November 2019.

               https://en.wikipedia.org/wiki/Double_Asteroid_Redirection_Test