DART in transit to Vandenberg Space Force Base ahead of November 2021 launch

by Lee Kanayama

After completing months of tests and assembly, NASA’s Double Asteroid Redirection Test (DART) is in transit to Vandenberg Space Force Base (VSFB) in California ahead of its launch. DART is a first-of-its-kind NASA mission to demonstrate an asteroid deflection via a kinetic impact.

The probe will launch on a flight-proven Falcon 9 rocket from Space Launch Complex 4 East (SLC-4E) at VSFB no earlier than November 23 at 22:20 PST (06:20 UTC on November 24).

DART is NASA’s first planetary defense demonstration. It will attempt to impact Dimorphos, a moonlet of the asteroid Didymos.

The vehicle is a technology demonstrator built by the Johns Hopkins Applied Physics Laboratory (APL). APL completed the assembly of the primary spacecraft in November 2020. One of the final steps was the installation of NASA’s Evolutionary Xenon Thruster-Commercial (NEXT-C) ion engine. Thermal blankets and the high-gain antenna were later installed.

In February 2021, the nearly completed spacecraft began a months-long thermal and environmental test campaign. This confirmed that the spacecraft would survive the harsh environment of space. DART completed environmental testing in the spring of 2021, clearing the way for the APL team to integrate the spacecraft’s final components.

Following testing, DART was placed back inside the cleanroom at APL. The APL team then installed the spacecraft’s twin Roll-Out Solar Arrays (ROSA). The two ROSA panels will be used to power the spacecraft throughout its mission. The panels themselves are one of the technology demonstrations onboard DART.

DART after installation of its Roll-Out Solar Arrays (ROSA). (Credit: NASA/Johns Hopkins APL)

The ROSA solar arrays are next-generation solar panels developed by Redwire. ROSA is designed to be more efficient and less bulky than other designs of solar panels and uses a flexible and rollable modular “wing” to extend the array. This wing will be lighter, more compact, and stiffer than traditional solar arrays.

The ROSA array was first tested onboard the International Space Station (ISS) after a successful launch on the SpaceX CRS-11 mission in 2017. This test array completed all but one mission objective – returning to its stowed configuration. It was jettisoned from the Station in its deployed position.

Today, a larger version of the ROSA, iROSA, is being used to help provide power to the ISS. Twin ROSA panels will also be used on the Power and Propulsion Element on NASA’s Lunar Gateway station.

A small portion of DART’s ROSA will use Transformational Solar Array technology, an experiment using higher-efficiency solar cells and reflective concentrators. Combined, these aim to provide three times more power than current solar array technology.

At the same time as the ROSA’s installation, the Didymos Reconnaissance and Asteroid Camera for Optical (DRACO) navigation camera was installed on the spacecraft. The DRACO camera is DART’s primary and only instrument.

DRACO is derived from the Long Range Reconnaissance Imager (LORRI) used on the New Horizons mission. The camera will be used for navigation and to conduct observations of Dimorphos. The camera will also be used to locate the impact site and the moonlet’s geologic properties.

LUCIACube is being installed on DART. (Credit: Johns Hopkins APL)

Another version of LORRI will also be used on NASA’s Lucy Trojan explorer. This version will be called Lucy LORRI (L’LORRI). Lucy is currently preparing for launch as well, targeting liftoff on October 16, 2021.

Following the installation of both ROSA and DRACO, DART underwent another set of vibration tests to ensure the entire spacecraft was secure and ready for the stresses of launch. DART successfully passed these tests and was prepared for shipment to VSFB.

On September 8, the APL team installed the Light Italian CubeSat for Imaging Asteroids (LICIACube). LICIACube – a 6U CubeSat weighing 14 kg – was built by the Italian Space Agency (ASI). It is equipped with two optical cameras for imaging DART’s impact from a distance.

The two cameras, the LICIACube Unit Key Explorer (LUKE) and the LICIACube Explorer Imaging for Asteroid (LEIA), will capture scientific data and information on the microsatellite’s position as well as the effects of the impact, including the plume of ejecta and impact crater.

About 10 days before DART’s impact, LICIACube will be ejected from the host spacecraft, using a spring-loaded box, at a velocity of 1.1 m/s. LICIACube will then use its onboard propulsion to allow itself to fly past Dimorphos about three minutes after DART’s impact. Following the flyby, LICIACube will investigate the backsides of both Didymos and Dimophos.

After LICIACube was installed into the spring-loaded box, DART departed from Maryland to VSFB in late September 2021. Once it arrives, the spacecraft will undergo final testing ahead of its November 2021 launch.

DART will liftoff on a flight-proven Falcon 9 from SLC-4E. The Falcon 9 booster for this flight will be B1063-3. This booster previously supported two missions, Sentinel 6 Michael Frelich from VSFB in November 2020 and Starlink v1.0 L28 in May 2021.

Falcon 9 will carry DART, massing 610 kg, into an Earth-escape trajectory.

As the spacecraft coasts to Dimorphos, it will communicate to Earth via the Radial Line Slot Array (RLSA) antenna. RLSA is a low-cost, high-gain antenna that enables high-efficiency communications in a compact, planar form.

To reach its target, DART will use its NEXT-C ion engine along with its primary hydrazine thrusters. The NEXT-C engine is a brand-new ion engine developed by NASA’s Glenn Research Center, in partnership with Aerojet Rocketdyne.

NEXT-C is designed to have improved performance, thrust, and fuel efficiency compared to other ion engines. While NEXT-C is not the primary propulsion system, its inclusion on DART will help demonstrate the thruster’s potential for use on future deep-space missions. The engine is based on the NASA Technology Application Readiness (NSTAR) engine used on the Dawn and Deep Space 1 missions.

To control itself during its mission, DART will use the Small-body Maneuvering Autonomous Real-Time Navigation (SMART Nav) guidance, navigation, and control (GNC) system. The SMART Nav system is a GNC algorithm developed by the DART team to autonomously detect the Didymos system. The optical navigation system will work with other GNC elements to distinguish Dimorphos from Didymos roughly an hour before impact.

All of this will be controlled by DART’s CORE Small Avionics Suite (CORESAT). CORESAT is DART’s single-board computer and interface module. Both use field-programmable gate array-based electronics to allow flexible control over the data handling onboard the spacecraft.

After a several-month journey to the Didymos system, DART will target Dimorphos and impact at 6.7 km/s. The impact will take place in early October 2022 and is expected to alter Dimorphos’ 12-hour orbit around Didymos by several minutes by changing the moonlet’s orbital velocity by 0.5 millimeters per second.

Dimorphos is the moonlet of asteroid Didymos (Greek for twin). The Didymos system was discovered in April 1996 by the Kitt Peak National Observatory during a close pass of Earth. It was originally thought to be a single asteroid until 2003. In June 2020, Dimorphos was given its name. The system is currently in a 1 x 2.2 AU orbit around the Sun.

During the system’s next closest approach to Earth following impact, ground-based instruments will be used to study the altered bodies. However, DART is not the only mission set to reach the binary system.

DART is part of a joint NASA and European Space Agency (ESA) program called Asteroid Impact & Deflection Assessment (AIDA). AIDA’s main goal is to understand the effects of an asteroid impact by a spacecraft.

For its part, ESA will conduct a follow-on mission called Hera. It will launch onboard an Ariane 6 rocket with an Astris kick stage in 2024. Hera will arrive at the binary system in 2027 to get up-close observations of the changes made to Dimorphos after DART’s impact.

Artist Impression of Hera’s mission at Dimorphos. (Credit: ESA)

Hera itself is a simple spacecraft. It will mass just 870 kg and be equipped with multiple cameras and a LIDAR altimeter to determine how effective DART’s impact was.

The probe will also test new autonomous GNC systems while at Dimorphos for use in future interplanetary missions.

Hera will also carry two CubeSats of its own. The first is Milani, which will perform surface measurements of the two asteroids. This will be based on a 6U XL CubeSat and will have a mass of 12 kg.

The second CubeSat is called Juventas. It will line up with Hera to perform a satellite-to-satellite radio experiment and undertake a low-frequency radar survey of the asteroid’s interior. Toward the end of its month-long mission, the satellite will attempt to land on Dimorphos. Juventas will also be based on a 6U XL CubeSat and will have a mass of 12 kg.

DART is one of many future NASA missions to visit an asteroid. Before DART lifts off, the Lucy probe will launch to visit seven different asteroids – of which six are trojans of Jupiter.

Following DART’s launch, NASA’s Psyche mission will launch in August 2022 to the asteroid 16 Psyche, a metal-rich asteroid theorized to be the exposed metallic core of a protoplanet.

Data from these missions will help paint the picture of what the early solar system was like, as well as its evolution over time.

(Lead image: DART departing the Johns Hopkins Applied Physics Lab. (Credit: NASA/Johns Hopkins APL)

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