NASA’s Double Asteroid Redirection Test (DART) spacecraft has been moved to its secondary launch window as it begins thermal and environmental testing. The new launch date of November 24, 2021 is a delay from an original target of July 21.
DART is NASA’s first planetary defense demonstration, planned to change an asteroid’s orbit by a kinetic impact. DART is a simple technology demonstrator which will attempt to impact Dimorphos, a moonlet of the asteroid Didymos.
NASA’s Science Mission Directorate (SMD) senior leadership requested a risk assessment to determine the viability of the primary and secondary launch windows. After this assessment was completed, teams determined the primary launch window was no longer viable and the DART team was told to pursue the secondary date.
“At NASA, mission success and safety are of the utmost importance, and after a careful risk assessment, it became clear DART could not feasibly and safely launch within the primary launch window,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate.
A part of the decision to move to the secondary date stems from the technical challenges of two main mission critical components: the Didymos Reconnaissance and Asteroid Camera for Optical-navigation (DRACO) imager and the roll-out solar arrays (ROSA). DRACO needs to be reinforced to handle the stress seen during launch and ROSA has had its delivery delayed due to supply chains impacted by the COVID-19 pandemic.
“To ensure DART is poised for mission success, NASA directed the team pursue the earliest possible launch opportunity during the secondary launch window to allow more time for DRACO testing and delivery of ROSA, and provide a safe working environment through the COVID-19 pandemic.”
While not the sole factor, the pandemic has made a large impact to the safety of personnel. The delay allows extra flexibility for the remaining spacecraft testing schedule, prioritizing the safety of people alongside mission success.
NEXT-C engine lifted to be placed on the DART spacecraft – via John Hopkins/APL
In the meantime, DART has completed major testing milestones. In November 2020, NASA and Aerojet Rocketdyne personnel installed the NASA Evolutionary Xenon Next-Commercial (NEXT-C) ion engine onto the spacecraft at the John Hopkins Applied Physics Laboratory (APL) .
“The biggest part of that process was lifting the thruster bracket assembly off of the assembly table and positioning it at the top of the spacecraft,” said APL’s Jeremy John, the lead propulsion engineer on DART.
“This took some care as the thruster’s propellant lines extended below the bottom of the bracket ring and could have been damaged if the lift was not performed properly.”
Once the engine was lowered onto DART’s central cylinders, fasteners were installed to secure the thruster to the spacecraft. This then allowed APL to connect the electrical harnesses and propellant lines between the thrusters bracket assembly and DART. Afterwards, APL spent several days preparing and testing critical components to ensure a good integration.
With the NEXT-C engine installed, the spacecraft had both of its propulsion systems onboard. Along with the NEXT-C engine, it will use hydrazine thrusters as its primary propulsion system. The thrusters were installed in May 2020.
More of DART’s final systems then underwent integration as the spacecraft was prepared for environmental testing. After a pre-environmental review was held in January, the DART team was approved to begin thermal vacuum testing.
“We’ve worked very hard to get to this critical point in the mission, and we have a great idea of spacecraft performance going into our environmental tests,” said APL’s Elena Adams, DART mission systems engineer.
“We have an experienced team that is confident with the spacecraft’s ability to withstand the rigors of testing in the next month,” added Ed Reynolds, DART project manager at APL.
DART undergoes electromagnetic interference testing – via John Hopkins/APL
Thermal vacuum testing will be done throughout spring. Once testing is complete, the spacecraft will then be equipped with the ROSA and DRACO. After those are installed, additional vibration and shock testing will take place before it is delivered to Vandenberg Air Force Base in California for launch on a SpaceX Falcon 9.
DART will launch from Space Launch Complex 4-East (SLC-4E) on a flight-proven Falcon 9, B1063. The booster first supported the Sentinel-6 Michael Freilich mission in November 2020. B1063 may support other missions from Vandenberg prior to launching DART in November 2021.
SpaceX’s Vandenberg manifest includes a pair of commercial launches: the SARah-1 mission for the German military, and the WorldView Legion Flight 1 launch as early as September.
Additionally, SpaceX will launch their second dedicated rideshare mission for their smallsat rideshare program, Transporter-2, no earlier than June. The classified NROL-87 mission for the National reconnaissance Office is also scheduled for no earlier than June.
Falcon 9 B1063 may support any of these missions prior to DART. It is also possible, but unlikely, that B1063 won’t fly any missions between Sentinel-6A and DART.
Falcon 9 B1063 lands at LZ-4 following the launch of Sentinel-6A – via Michael Baylor for NSF/L2
No matter the scenario, B1063 will launch DART on a trajectory to the Didymos binary system. After liftoff, the booster will perform a Return to Launch Site (RTLS) landing at Landing Zone 4 (LZ-4), directly adjacent to the launch pad.
DART is a demonstration mission for future technologies. It is a simple spacecraft that doesn’t include any scientific payloads. Weighing only 500 kilograms, it includes one main instrument, DRACO. DRACO is a camera which will help target the Didymos system while in coast.
One of the technologies to be tested is the aforementioned NEXT-C ion engine. NEXT-C is based on the NASA Solar Technology Application Readiness (NSTAR) engine which was used on the Dawn and Deep Space 1 spacecrafts.
NEXT-C was developed by the NASA Glenn Research Center and Aerojet Rocketdyne and designed to have improved performance, thrust, and fuel efficiency compared to other ion engines. NEXT-C is not the primary propulsion system, but its inclusion on DART will help demonstrate its potential for use on future deep-space missions.
Another technology demonstration is the aforementioned ROSA solar arrays. ROSA is a new type of solar panel that is designed to be more efficient and less bulky than other standard solar panels.
ROSA was first demonstrated on the International Space Station, after launch on the SpaceX CRS-11 mission in June 2017. It completed all but one of its mission objectives when the solar array failed to lock back in its stowed configuration.
New, larger types of ROSAs will be launched in 2021 and 2022 on the SpaceX CRS-22, CRS-25, and CRS-26 missions. Called iROSA, six arrays will be launched to help power the ISS for many years to come.
Infographic of DART’s objectives- via NASA/John Hopkins/APL
DART will also be equipped with thrusters, star trackers, and several sun trackers to help navigate itself to Didymos. Once it reaches the Didymos system, DART will then target and impact Dimorphos at 6.7km/s sometime in the first weeks of October 2022.
Dimorphos is the moonlet of the asteroid Didymos (Greek for twin). The system was discovered in April 1996 by the Kitt Peak National Observatory, when the asteroid was in close proximity to Earth. Dimorphos was given its name in June 2020.
The system is currently in a 1 AU by 2.2 AU orbit around the Sun. The impact with Dimorphos should cause the speed to change by 0.5 millimeters per second and alter the orbit of Dimorphos around Didymos.
DART will carry a CubeSat called Light Italian CubeSat for Imaging of Asteroids (LICIA) which will be released five days prior to impact to provide communications and images of the impact.
DART itself is one of two missions in a joint NASA and European Space Agency (ESA) program called the Asteroid Impact & Deflection Assessment (AIDA). AIDA’s main objective is to understand the effects of an asteroid impact by a spacecraft.
Artist impression of Hera observing DART’s impact site – via NASA/ESA
The ESA will conduct a follow-on mission called Hera, launching on Ariane 6 in 2024. Hera will arrive at the binary system in 2027 to observe the changes made by DART’s impact.
Hera is also a simple spacecraft, weighing about 1,050 kilograms and equiped multiple cameras and a LIDAR Laser Altimeter to determine how effective the impact from DART was in changing Dimorphos’ orbit.
Hera will also use new autonomous navigation systems while at Dimorphos to will test better and more efficient navigation methods for future interplanetary missions.
Hera will also carry two CubeSats. The first CubeSat is the Asteroid Prospector Explorer (APEX). APEX will perform surface measurements of two asteroids. Once its main surface data is gathered, APEX will attempt to land for up-close observations of the surface.
The second CubeSat is called Juventas and will line up with Hera to perform a satellite-to-satellite radio experiment and a low-frequency radar survey of the asteroid interior.
Once Hera’s mission is complete, Hera will land on one of the two asteroids. The landing will provide insight into the surface material of the asteroid.
The AIDA program is the first one of many Planetary Defense programs for NASA and ESA. NASA currently operates the OSIRIS-REx mission, which collected a sample from the Asteroid Bennu in October 2020. The samples will help NASA protect Earth from near-Earth Asteroids. The samples will be returned to Earth in 2023.
(Lead image: Artist impression of DART approaching Dimorphos – via NASA)