Double Asteroid Redirection Test

The DART spacecraft is an impactor with a mass of 610 kg (1,340 lb),[11] that hosts no scientific payload and has only sensors for navigation such as 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.[12]

DART spacecraft uses the NEXT ion thruster, a type of solar electric propulsion.[6][13] 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.[14]

The spacecraft's solar arrays use a Roll Out Solar Array (ROSA) design, and this was tested on the International Space Station (ISS) in June 2017 as part of Expedition 52, delivered to the station by the SpaceX CRS-11 commercial cargo mission.[15]

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.[16][17]

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.[18]

The impact of the 500 kg (1,100 lb)[19] DART at 6.6 km/s (4.1 mi/s) [20][21] will produce an estimated 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.[22][4][23][24] 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.[25] The impact will target the center of figure of Dimorphos and should decrease the orbital period, currently 11.92 hours, by roughly 10 minutes.[11]

The actual velocity change and orbital shift are uncertain. There is a poorly predictable "momentum enhancement" effect due to the contribution of recoil momentum from impact ejecta. The final momentum transferred to the largest remaining fragment of the asteroid could be up to 3-5 times the incident momentum, and obtaining accurate measurements of the effects, which will help refine models of such impacts, is one of the mission's main goals.[26] Initial estimates of the change in binary orbit period should be known within a week.[27] A detailed reconnaissance and assessment will be performed a few years later by a spacecraft called Hera, approved by ESA in November 2019.[28][29]

LICIACube CubeSat, a companion satellite of the DART spacecraft

The Italian Space Agency (ASI) will contribute a secondary spacecraft called LICIACube (Light Italian CubeSat for Imaging of Asteroids), a small CubeSat that will piggyback with DART and will separate 10 days before impact to acquire images of the impact and ejecta as it drifts past the asteroid.[28][30] LICIACube will communicate directly with Earth, sending back images of the ejecta after the Dimorphos flyby.[31] LICIACube is equipped with two optical cameras, dubbed LUKE and LEIA.[32]

In a collaborating project, the European Space Agency is developing Hera, a spacecraft that will be launched to Didymos in 2024[33] and arrive in 2027[34] (5 years after DART's impact), to do a detailed reconnaissance and assessment.[33] Hera would carry two CubeSats, Milani and Juventas.[33]

The mission's target is Dimorphos in 65803 Didymos system, a binary asteroid system in which one asteroid is orbited by a smaller one. The primary asteroid (Didymos A) is about 780 m (2,560 ft) in diameter; the asteroid moon Dimorphos (Didymos B) is about 160 m (520 ft) in diameter in an orbit about 1 km (0.62 mi) from the primary.[6] The mass of the Didymos system is estimated at 528 billion kg, with Dimorphos composing 4.8 billion kg of that total.[11] DART will target the smaller asteroid Dimorphos. The Didymos system is not an Earth-crossing asteroid, and there is no possibility that the deflection experiment could create an impact hazard.[23]

Falcon 9 rocket's payload fairing being attached to NASA's Double Asteroid Redirection Test (DART) spacecraft on 16 November 2021

Animation of DART's trajectory
  DART ·   65803 Didymos ·   Earth ·   Sun ·   2001 CB21 ·   3361 Orpheus

Falcon 9 and DART vertical at SLC-4E

Launch preparations for DART began on 20 October 2021, as the spacecraft began fueling at Vandenberg Space Force Base in California.[43] The spacecraft arrived at Vandenberg Space Force Base (VSFB) near Lompoc, in early October 2021 after a cross-country drive. DART team members have since been preparing the spacecraft for flight, testing the spacecraft's mechanisms and electrical system, wrapping the final parts in multilayer insulation blankets, and practicing the launch sequence from both the launch site and the mission operations center at APL. DART headed to the SpaceX Payload Processing Facility on VSFB on 26 October 2021. Two days later, the team received the green light to fill DART's fuel tank with roughly 50 kg (110 lb) of hydrazine propellant for spacecraft maneuvers and attitude control. DART also carries about 60 kg (130 lb) of xenon for the NEXT-C ion engine. Engineers loaded the xenon before the spacecraft left APL in early October 2021.[44]

Starting on 10 November 2021, engineers mated the spacecraft to the adapter that stacks on top of the SpaceX Falcon 9 launch vehicle. The Falcon 9 rocket without the payload fairing rolled for a static fire and later came back to the processing facility again where technicians with SpaceX installed the two halves of the fairing around the spacecraft over the course of two days, November 16 and 17, inside the SpaceX Payload Processing Facility at Vandenberg Space Force Base in California and the ground teams completed a successful Flight Readiness Review later that week with the fairing then attached to the rocket.[45]

A day before launch, the launch vehicle rolled out of the hangar and onto the launch pad at Vandenberg Space Launch Complex 4 (SLC-4E); from there it lifted off to begin DART's journey to the Didymos system and it propelled the spacecraft into space.[44]

The DART spacecraft was launched on 24 November 2021, at 06:21:02 UTC.

Early planning suggested that DART was to be deployed into a high altitude, high eccentricity Earth orbit designed to avoid the Moon. In such a scenario, DART would use its low thrust, high efficiency NEXT ion engine to slowly escape from its high Earth orbit to a slightly inclined near-Earth solar orbit, from which it would maneuver onto a collision trajectory with its target. But because DART was launched as a dedicated Falcon 9 mission, the payload along with Falcon 9's second stage was placed directly on an Earth escape trajectory and into heliocentric orbit when the second stage reignited for a second engine startup or escape burn. Thus, although DART carries a first-of-its-kind electric thruster and plenty of xenon fuel, Falcon 9 did almost all of the work, leaving the spacecraft to perform only a few trajectory-correction burns with simple chemical thrusters as it homes in on Didymos's moon Dimorphos.[46]