DART (Double Asteroid Redirection Test)
|24 Nov 2021
|End of life date
|26 Sep 2022
DART (Double Asteroid Redirection Test) MissionSpacecraft Development Status Launch Sensor Complement References
DART is a NASA space probe with the goal to demonstrate the kinetic effects of crashing an impactor spacecraft into an asteroid moon for planetary defense purposes. The mission is intended to test whether a spacecraft impact could successfully deflect an asteroid on a collision course with Earth. A demonstration of an asteroid deflection is a key test that NASA and other agencies wish to perform before the actual need of planetary protection is present. DART is a joint project between NASA and the JHU/APL (John Hopkins University/Applied Physics Laboratory) of Laurel MD, with support from the NASA centers: JPL (Jet Propulsion Laboratory), GSFC (Goddard Space Flight Center), and JSC (Johnson Space Center). As of summer 2018, the DART mission is in Phase B, led by JHU/APL and managed by the Planetary Missions Program Office at MSFC (Marshall Space Flight Center) for NASA’s PDCO (Planetary Defense Coordination Office). 1) 2)
Under the auspices of the PDCO, an international cooperation between NASA and ESA was formed, named the Asteroid Impact & Deflection Assessment (AIDA). For AIDA, NASA provides the DART (Double Asteroid Redirection Test) mission element. 3)
DART is a planetary defense-driven test of one of the technologies for preventing the Earth impact of a hazardous asteroid: the kinetic impactor. DART’s primary objective is to demonstrate a kinetic impact on a small asteroid. The binary near-Earth asteroid (65803) Didymos is the target for DART. While Didymos’ primary body is approximately 800 meters across, its secondary body (or “moonlet”) has a diameter of about 150 m, which is more typical of the size of asteroids that could pose a more common hazard to Earth.
The DART spacecraft will achieve the kinetic impact by deliberately crashing itself into the moonlet at a speed of approximately 6 km/s, with the aid of an onboard camera and sophisticated autonomous navigation software. The collision will change the speed of the moonlet in its orbit around the main body by a fraction of one percent, enough to be measured using telescopes on Earth. The kinetic impact will occur in October of 2022 during a close approach of Didymos to Earth.
DART completed Phase A in mid-2017,Phase B in mid-2018, and is currently in Phase C with the mission Critical Design Review (CDR) scheduled for June 2019.
Even as a low-cost, focused planetary science mission, DART will return fundamental new information on the mechanical response and impact cratering process at real asteroid scales, and consequently on the collisional evolution of asteroids with implications for planetary defense, human spaceflight, and near-Earth object science and resource utilization. DART will return unique information on an asteroid's strength, surface physical properties and internal structure. Numerical simulation studies will support Earth-based optical and radar observations of the DART impact event. A CubeSat, a potential contribution from the Italian Space Agency (ASI), is under consideration to image the ejecta and the DART impact site. 4) In addition, the ESA Hera mission concept is being considered, which would observe the impact site a few years after the DART mission is completed. 5)
DART Mission Rationale
Four primary strategies are identified as sufficiently mature to warrant consideration as approaches to mitigate an asteroid impact threat [6)]: civil defense warning, sheltering, and evacuating populations; impulsive deflection by a stand-off nuclear explosion; gradual orbit change with a nearby massive spacecraft (the “gravity tractor” concept); and impulsive deflection via a sudden addition of momentum (the “kinetic impactor” concept). DART is designed to be the first demonstration of a kinetic impactor for planetary defense.
DART is needed because there are key unanswered questions about the kinetic impactor technique and because it, like the other primary strategies for asteroid deflection, requires some level of validation and demonstration before it is considered viable for implementation in the event of an impact emergency. Studies of asteroid mitigation 7) suggest kinetic impactors are useful in situations where an asteroid deflection Δv of mm/s to cm/s would be appropriate, namely, when an impact threat of up to hundreds of meters size is identified years to decades before the Earth impact date. This warning time is sufficient for the kinetic impactor deflection to cause the asteroid to miss the Earth.
The imparted Δv from a kinetic impactor is a small fraction of a typical Near-Earth Object’s heliocentric speed, which is several tens of km/s, and measuring this small change is a challenge (e.g., it was a cost driver for the former ESA Don Quijote mission concept). The innovation used by DART to overcome this challenge is to target the secondary member of a binary asteroid system for the kinetic impactor demonstration. The Didymos system undergoes periodic dimming episodes called “mutual events” as the primary and secondary move in front and behind each other. These episodes can be precisely timed. Asteroid satellites typically have orbital speeds of tens of cm/s around their primaries, and a change of orbital speed by mm/s from the kinetic impactor changes the binary orbit period by an amount easily measured by an accompanying spacecraft or by ground-based telescopes by analyzing the timing change of the mutual events.
DART’s target, the secondary member of  Didymos, will also allow the kinetic impactor demonstration to be conducted at a realistic scale for planetary defense. The target body, at a diameter of ~160 m, is large enough to be a Potentially Hazardous Asteroid (PHA) in its own right if it were a single body. There are an estimated ~6700 PHAs at diameter ~140 m or larger, 8) most of which have not yet been discovered.
DART will also answer a key question about the kinetic impactor technique, which is that the magnitude of the resulting deflection is highly uncertain, owing to the poorly understood contribution of recoil momentum from impact ejecta. The impact ejecta carries momentum back in the incident direction, so that the momentum transferred to the largest remaining fragment exceeds the incident momentum by a factor that may be as much as 3to 5. 9) Determinations of the momentum transfer from the DART impact will allow centimeter-scale laboratory experiments to be tested at sizes many orders of magnitude larger, and will help validate models and numerical simulations.
DART will be the first high-speed impact experiment at an asteroid and at a realistic scale for planetary defense, and the impact conditions and the physical properties of the projectile are well known. DART will determine, from terminal approach imaging, the impact location on the target asteroid, the local surface topography and the geologic context.
The DART mission will impact the secondary member of the Didymos binary system during its close approach to Earth in October, 2022. For a period of several weeks around the time of the DART impact, Didymos is within 0.08 AU from the Earth and is bright enough for useful data to be obtained by small ground-based telescopes. The DART impact will change the binary orbit period by an amount sufficient to be quantified by ground-based observations.
Didymos satellite orbits its primary with a period of 11.9 hours, with a semi-major axis of 1.1 km, and a nearly circular orbit. 11) The primary has a diameter of 780 m, the secondary 160 m. The presence of a satellite has allowed the density of the primary to be estimated as 2.1 g/cm3 with ~30% uncertainty. Ground-based reflectance spectroscopy of Didymos shows it to be a member of the “S complex” of asteroids, the most common compositional group of near-Earth objects.
The impact of the ~560 kg DART spacecraft at 6 km/s will produce a binary orbit period change greater than 7 min (assuming that the incident momentum from the impactor is simply transferred to the target without enhancement). This change in binary orbit period can be measured within a week given expected observing conditions.
The DART spacecraft uses the NASA Evolutionary Xenon Thruster Commercial (NEXT-C) electric propulsion system, which allows for tremendous flexibility in trajectory design. The DART spacecraft will be launched on an Evolved Expendable Launch Vehicle (EELV) into a low-energy escape (possibly as a rideshare). 12) However, the mission can also use a higher-energy trajectory paired with a corresponding reduction in the operational time of the NEXT-C thruster. The Didymos encounter for the electric propulsion mission occurs in the same time frame and a similar geometry as for the chemical design (Ref.9). 13) The EELV selection is progressing with Launch Services Provider (LSP), and will constrain the large trajectory design space afforded by using the NEXT-C engine in the spacecraft design.
June 15, 2021
PHA (Potentially Hazardous Asteroid) flyby
March 06, 2022
Arrival relative speed
Maximum Earth distance
0.95 AU – 1.03 AU
Earth distance at impact
Solar phase angle at impact
Impact angle to orbit plane
DART’s primary launch window extends from mid-June 2021 through mid-October 2021. Three NEXT-C thrust arcs are currently planned for the interplanetary trajectory to target an asteroid flyby and arrival at the Didymos system. The DART reference mission design for launch on June 15, 2021 is summarized in Table 1 and shown in Figure 4.
The DART spacecraft is shown in Figure 5. The spacecraft has two ~7 m gimballed Roll-Out Solar Arrays (ROSA) to power the low-thrust engine and spacecraft components. The X-band communication system consists of two hemispherical low-gain antennas, and a gimballed Radial Slot Line Antenna (RLSA) for high-gain communication. An IMU and star tracker are used as the primary attitude sensors, and five digital Sun sensors provide Sun-direction information for safe mode. DART is carrying two propulsion systems: chemical and electric. The chemical system is currently used for launch clean up, trajectory correction maneuvers and attitude control. It is a monoprop hydrazine system that consists of twelve thrusters and uses helium as the pressurant. The electric propulsion targets the asteroid flyby and provides flexibility in launch options. It uses xenon for the propellant and its accommodation is a principal driver in the spacecraft and mission design. 14)
DART is a simple, low-cost spacecraft. The main structure of the spacecraft is a box with dimensions of roughly 1.2 x 1.3 x 1.3 meters, from which other structures extend to result in measurements of roughly 1.8 meters in width, 1.9 meters in length, and 2.6 meters in height. The spacecraft has two very large solar arrays that when fully deployed are each 8.5 meters long. DART will navigate to crash itself into Didymos B at a speed of approximately 6.6 km/s.
Demonstrated on the International Space Station previously, ROSA (Roll Out Solar Arrays) provides a compact form and light mass for launch that then deploy into two large arrays once in space, each extending 8.6 meters in length. 15)
NEXT-C (NASA’s Evolutionary Xenon Thruster-Commercial): The DART spacecraft will utilize the NEXT-C solar electric ion propulsion system as its primary in-space propulsion system. NEXT-C is the next generation system that is based on the Dawn spacecraft propulsion system and was developed at NASA’s Glenn Research Center in Cleveland, Ohio. By utilizing electric propulsion, DART is able to gain significant flexibility to the mission timeline and widen the launch window, as well as decrease the cost of the of the launch vehicle that gets the mission off Earth and into orbit.
Technology Development and Demonstration
Developing and maturing new technology is also a critical part of the DART mission. The principal technology development for the DART program has been the NEXT-C thruster. In addition to the ion thruster system, the Small-body Maneuvering Autonomous Rendezvous and Targeting Navigation (SMART Nav) system was a large technology effort in Phase B and included development of new FPGA-based avionics. This system is comprised of algorithms, software, and firmware running in the FPGA-based avionics, and it is used to estimate and control the spacecraft’s asteroid-relative state. The SMART Nav algorithms and the spacecraft avionics successfully demonstrated TRL- 6. In addition, the Radial Slot Line Array HGA went through its own technology maturation effort and is now at TRL -6, and the engineering model for DART is currently in fabrication.
The spacecraft will be guided to hit the center of the asteroid using the SMART Nav algorithms. The spacecraft autonomously tracks the secondary, performing ΔV maneuvers, adjusting the spacecraft trajectory to ensure impact with the secondary. The spacecraft is in constant communication with ground via the RLSA, streaming images back to Earth at 3 Mbit/s. The high data rate is necessary in order to meet the requirement that the spacecraft take, process, and transmit at least one image in the last 17 seconds before impact.
The NEXT-C electric propulsion system drives numerous elements of the spacecraft design. The large ROSAs are needed to generate sufficient power to operate the NEXT-C thruster at the DART-specific throttle levels. The Power Propulsion Unit (PPU) supplies power to the NEXT-C thruster, and its thermal dissipation is comparable with the dissipation of the rest of the spacecraft. Accommodation of the PPU necessitated the addition of the heat pipes to the structure and a doubler to the PPU panel to redistribute the heat. A dual-axis gimbal on the thruster and single-axis gimbals on the solar arrays are required to keep the NEXT-C thrusting in the desired direction while producing manageable reaction torques on the vehicle and remaining power positive. The NEXT-C system is controlled by a DART-developed flight software application that runs on spacecraft avionics.
• November 18, 2021: When NASA’s DART spacecraft launches on 24 November on a world-first mission to deflect an asteroid, ESA’s Estrack network will play a vital role – finding, tracking and maintaining contact with the mission as it departs Earth heading toward its target, a 170-meter asteroid ‘moon’ named Dimorphos. 16)
- At about the length of one-and-a-half football fields side-by-side, Dimorphos is currently almost 500 million km away, orbiting the Sun on a path that brings it near Earth’s orbit and out past Mars’. It is part of a double asteroid system – bound by gravity to the almost five times larger Didymos asteroid.
- Both space rocks pose no threat to Earth. When DART strikes the Dimorphos in 2022 its orbit will be very slightly altered and a crater formed.
- Data from the experiment, in part provided by ESA’s follow-on Hera mission, will help an international team of scientists understand how this ‘kinetic impactor’ method could be deployed in case a large asteroid is ever discovered on a collision course with Earth. Throughout, ESA's Estrack network will play a vital role.
Hearing DART’s First Words
- The DART spacecraft weighs 620 kg, about the mass of a brown bear, and measures about 19 m across. It will be launched by a SpaceX Falcon 9 rocket from Vandenberg Air Force Base in California and thrust into an ‘Earth-escape trajectory’.
- Following lift-off, as DART climbs heavenward but Earth rotates beneath it, the spacecraft will follow a unique path in the sky. Passing first down the west coast of South America then east across the Atlantic, it will finally appear above the horizon as seen from Australia.
- About 60 minutes after launch, the spacecraft will separate from the launcher, its transponder will turn on, and ESA’s 4.5-meter antenna in New Norcia, Western Australia, will capture its very first words – the ‘acquisition of signal’.
- This smaller, more agile radio dish was specifically designed for moments like this. With a wide ‘beamwidth’ it offers a wider field of view than the nearby 35 m antenna, as well as the ability to quickly tilt and point to target swiftly moving objects in the sky.
Cruisin’ for a bruisin’
- DART’s cruise phase will last about 11 months as it homes in on Dimorphos, before impacting the orbiting asteroid at a speed of 6.6 km/s in October 2022. During this period, additional ESA ground stations will support the mission.
- ESA’s ‘big iron’ – the 35m dish antenna at Malargüe, Argentina, together with the almost-identical dish at New Norcia – will help conduct vital ‘Delta-DOR’ measurements, an ultra-precise navigation technique that allows mission controllers to know the position of spacecraft hundreds of millions of kilometers away, to within just a few hundred meters.
DART’s final days
- The last ten days before impact in 2022 are super-critical. As Dimorphos comes into view, essential, non-stop footage of the arrival, collision and subsequent plume of materials will be streamed home via the LICIACube, a hand-sized CubeSat from the Italian Space Agency, ASI, that will be deployed before impact.
- In this terminal phase, observations of the target are needed 24 hours per day, something which NASA’s Deep Space Network cannot provide on its own due to the geometry of the spacecraft’s trajectory.
- ESA’s Malargüe station will help to fill the DSN visibility gaps, ensuring radio links to DART every moment until impact.
Next comes Hera
- After the deflection impact, ESA’s Hera mission will head towards the Didymos binary system in November 2024, commencing its detailed ‘crime scene investigation’ of the asteroids in late 2026.
- By gathering data close-up, Hera will help turn DART’s grand-scale impact experiment into a well-understood and repeatable deflection technique – ready to be deployed if an asteroid should ever be spotted heading Earthward.
• August 12, 2021: Perched atop a stand in the middle of a high-ceilinged clean room, DART is beginning to look like the intrepid spacecraft that will aim itself directly into an asteroid next fall. With the addition of its compact Roll-Out Solar Arrays (ROSA) coiled into two gold cylinders that flank the sides of the spacecraft, and its less visible but still integral imager, the Didymos Reconnaissance and Asteroid Camera for Optical (DRACO) navigation tucked safely beneath its panels, the spacecraft is close to fully integrated. 17)
- This mix of current and new technologies, some of which it will demonstrate for the first time, will see DART through its 10-month journey toward its asteroid target.
- NASA's DART is a carefully planned demonstration that will help determine if kinetic impactor technology — flying a spacecraft directly into a small Solar System body at speeds of about 15,000 miles per hour with the intention of changing its course — can serve as a reliable method of asteroid deflection in the event that such a hazard ever heads for the Earth. NASA is constantly monitoring the skies and has already identified nearly 40% of potentially hazardous asteroids larger than 140 meters (459 feet) in size, none of which are slated to impact our planet, including the binary system selected for this first-ever deflection test.
- But to prove that our planet can expect the unexpected, the DART mission will set out to push an asteroid and safely change its motion in space. For the last two years, the spacecraft destined for this undertaking has been developed and built at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. APL, which leads the mission for NASA, is now putting the finishing touches on the spacecraft.
- The recently installed ROSA and DRACO are two critical technologies that will enable the spacecraft to navigate through space and reach the Didymos asteroid system. The flexible and rollable modular “wings” are lighter, more compact and stiffer than traditional solar arrays despite their size; in space, each array will slowly unfurl to reach 28 feet in length—about the size of a bus. The technology was first successfully tested in 2017 on the International Space Station (ISS), and newer versions were installed this past June for full-time use on the ISS. DART will be the first spacecraft to fly the new arrays, paving the way for their use on future missions. Redwire developed the technology at their Goleta, California facility and delivered ROSA to APL in May and worked closely with the APL team in the following weeks to carefully install them onto the spacecraft.
- “Traditional navigation techniques would only get DART somewhere within about 9 miles of the target asteroid,” said APL’s Zach Fletcher, DRACO lead engineer. “To achieve our mission objectives, we need to remove the rest of that error via on-board optical navigation. DRACO starts supplying images to DART's on-board autonomous navigation system more than 50,000 miles from its target, four hours before the impact and is key to DART achieving a kinetic impact on Dimorphos."
- The images DRACO returns of the target asteroid Dimorphos, including the last-second glimpse of its own impact site on the asteroid, will be crucial toward analyzing the results of the DART test and understanding how the asteroid was affected.
- DART has been through its paces in the last several months, enduring a battery of environmental testing and analysis as the final pieces of the craft started coming together. Likewise, the SMART Nav software has seen its fair share of testing so the team can confidently relinquish the reins on DART in the final hours before it collides into Dimorphos. With DRACO and ROSA on board, the DART spacecraft completed vibration testing in late July to ensure that all of its hardware is secure and ready for the rigors of launch.
- The LICIACube (Light Italian CubeSat for Imaging of Asteroids) contributed by the Italian Space Agency, will be one of the final components to hitch a ride on DART before it is delivered to the launch site this October. LICIACube will deploy roughly five days prior to the DART impact and capture images of the spacecraft's final moments, the resulting ejecta plume, and the back side of the asteroid that DRACO will never see.
- "DART is the result of years of work by a dedicated team and partners who have overcome unique challenges to accomplish firsts in both technology development and planetary defense," said DART mechanical engineer Betsy Congdon, who led the team during the installation. “With the successful installation and testing of two critical technologies, DRACO and ROSA, we're very confident that DART is ready to complete its final system testing and reviews before shipping to the launch site."
- This November, the spacecraft will launch on a SpaceX Falcon 9 rocket from Vandenberg Space Force Base near Lompoc, California. In the fall of 2022, DART will have its sights set for Dimorphos, the smaller moonlet orbiting the larger Didymos asteroid. Its collision with Dimorphos will change the speed of the moonlet’s orbit around the main body by several minutes. And despite being approximately 6.8 million miles away from Earth at the time of impact, the asteroid system will be visible to ground-based telescopes, which scientists will use to determine the exact change in the orbital period.
- DART is directed by NASA's Planetary Defense Coordination Office to APL with support from several NASA centers: the Jet Propulsion Laboratory, Goddard Space Flight Center, Johnson Space Center, Glenn Research Center and Langley Research Center.
• February 17, 2021: DART (Double Asteroid Redirection Test), NASA's first flight demonstration for planetary defense, seeks to test and validate a method to protect Earth in case of an asteroid impact threat. The mission aims to shift an asteroid's orbit through kinetic impact – specifically, by impacting a spacecraft into the smaller member of the binary asteroid system Didymos to change its orbital speed. — At the request of Science Mission Directorate (SMD) senior leadership, a risk assessment was performed on the DART project schedule to determine the viability of the primary (July 21, 2021 to August 24, 2021) and secondary (November 24, 2021 to February 15, 2022) launch periods. Based on the results of this assessment, SMD determined the primary launch period is no longer viable and has directed the DART project pursue their secondary launch window. The DART project is currently working with SpaceX and NASA’s Launch Services Program (LSP) to identify the earliest possible launch opportunity within this secondary window. 18)
- This decision, in part, stems from technical challenges associated with two mission critical components: the Didymos Reconnaissance and Asteroid Camera for Optical-navigation (DRACO) imager, which needs to be reinforced to ensure it withstands the stress of launch, and the roll-out solar arrays (ROSA), which are delayed due to supply chain impacts resulting from, but not limited to, the COVID-19 pandemic.
- “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 the Science Mission Directorate at NASA Headquarters in Washington. “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.”
- This change reflects NASA’s priority for both mission success and personnel health and safety, which are paramount for all NASA missions. While COVID-19 was not the sole factor for this delay, it has been a significant and critically contributing factor for multiple issues. Testing equipment before launch is a crucial step in all missions to ensure mission success, and project teams build time into processing schedules to accommodate for potential delays.
- DART will still arrive at the Didymos binary asteroid system within a few days of the originally scheduled impact date of September 30, 2022 and will carry out its kinetic impact test on the moonlet Dimorphos as planned.
• May 19, 2020: The dual chemical and electric propulsion systems for NASA’s Double Asteroid Redirection Test (DART) were recently delivered by Aerojet Rocketdyne to the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. The chemical propulsion system and the electric propulsion Xenon feed system have been undergoing assembly and integration onto the spacecraft structure at Aerojet Rocketdyne’s facility in Redmond, Washington, since August 2019. APL – designing, building and managing the mission for NASA– will now begin integration of the rest of the subsystems and final test of the spacecraft ahead of next year’s launch for the mission. 19)
- Propelled by Aerojet Rocketdyne propulsion, the DART spacecraft will be the first demonstration of a kinetic impactor: a spacecraft deliberately targeted to strike an asteroid at high speed in order to change the asteroid’s motion in space. The asteroid target is Didymos, a binary near-Earth asteroid that consists of Didymos A and a smaller asteroid orbiting it called Didymos B. After launch, DART will fly to Didymos and use an onboard targeting system to aim and impact itself on Didymos B. Earth-based telescopes will then measure the change in orbit of Didymos B around Didymos A.
- DART is set to launch in late July 2021 from Vandenberg Air Force Base, California, intercepting Didymos’ secondary body in late September 2022.The spacecraft’s chemical propulsion system is comprised of 12 MR-103G hydrazine thrusters, each with 0.2 pounds of thrust. The system will conduct a number of trajectory correction maneuvers during the spacecraft’s roughly 14-month cruise to Didymos, controlling its speed and direction. As the DART spacecraft closes in on the asteroid, its chemical propulsion system will conduct last minute direction changes to ensure it accurately impacts its target.
- In addition to providing the chemical propulsion system for the spacecraft, Aerojet Rocketdyne’s NEXT-C (NASA Evolutionary Xenon Thruster –Commercial) system will also be demonstrated on the mission. NEXT-C is a next-generation solar electric propulsion system designed and built by Aerojet Rocketdyne based on mission-proven technology developed at NASA’s Glenn Research Center.
- “DART plays an important role in understanding if it is possible to deflect asteroids and change their orbits,” said Eileen Drake, president and CEO of Aerojet Rocketdyne. “Our chemical propulsion system will help the spacecraft reach its destination and impact its target, while our electric propulsion system will demonstrate its capability for future applications.”
- The NEXT-C system completed acceptance and integration testing at NASA Glenn in February. With a successful in-flight test of this next generation of ion engine technology, DART will demonstrate its potential for application to future NASA missions and may make use of NEXT-C for two of the planned spacecraft trajectory correction maneuvers.
- The DART mission is an effort led by NASA’s Planetary Defense Coordination Office (https://www.nasa.gov/planetarydefense/overview) and managed by APL with support from other industry partners (https://dart.jhuapl.edu/).
• March 17, 2020: After undergoing a series of performance and environmental tests, NASA’s Evolutionary Xenon Thruster - Commercial (NEXT-C) is being prepared for the DART (Double Asteroid Redirection Test) Mission, which will launch next year. 20)
- In the past few months, the thruster, developed at NASA’s Glenn Research Center in Cleveland and designed and built by Aerojet Rocketdyne, was put through vibration, thermal vacuum and performance tests and then integrated with its power processing unit. The environmental testing verified that NEXT-C could withstand the extreme launch vibrations and temperatures of spaceflight.
- DART will be the first space mission to demonstrate asteroid deflection by kinetic impact, a technique that could prevent a hazardous asteroid from impacting Earth by changing the motion of the asteroid in space. NEXT-C’s propulsion system will be tested on that mission, along with several other technologies.
- When the propulsion system is successfully demonstrated on DART, NEXT-C will be considered on a variety of 10 to 15 year-long, uncrewed missions that could include going to other asteroids, comets or planets such as Venus.
• June 27, 2019: There are models and simulations, but nobody knows exactly what is going to happen after NASA’s DART impactor crashes into the smaller of the two Didymos asteroids at 6.6 km/s – humankind’s first full-scale deflection test for planetary defense. 21)
- It will take detailed telescope and radar observations from Earth to find out, complemented by a close-up survey to be performed by ESA’s Hera mission.
- The collision itself takes place in late 2022. Meanwhile, PhD student Harrison Agrusa from the University of Maryland – as part of a larger team studying the dynamics of the Didymos system – is among the most qualified people to make an educated guess.
- Harrison has been simulating the interaction between the fridge-sized DART spacecraft and smaller 160-m diameter Didymos asteroid hundreds of times, run on his university’s powerful computing cluster.
- His simulations recreate the 780-m diameter main Didymos asteroid and its orbiting ‘Didymoon’ as a collection of small spheres – like the rubble piles that researchers believe these bodies to resemble – then apply the equivalent force of the DART impact.
- “The interesting thing, depending on where DART hits and how hard, is that we can see a pronounced wobble triggered as a result,” explains Harrison.
- “We’ve compared four different simulation codes to study this post-impact swinging back and forth and seen the same effect recur in all of them, even with conservative estimates of DART’s momentum transfer.”
- In asteroid researcher terms this effect is known as ‘libration’ – the same term used for the wobble of the Moon as seen from Earth, which means that different parts of the lunar surface can be observed over time.
- Like the Moon, the smaller ‘Didymoon’ is expected to be tidally locked to its parent at the present time, although it has not yet been confirmed with ground-based observations. Long-range measurements of distant lightcurves – gradual patterns of light shifting over time – or radar imagery do not give enough detail.
- In the same way, any wobble imparted to the asteroid by DART’s collision will not be visible from Earth. It will take close-up observations after Hera’s arrival to be sure.
- Harrison has shown that this induced libration is closely related to the momentum transfer efficiency – in other words, Hera’s measuring of the libration can be used to constrain the asteroid’s deflection. Such a measurement is crucial to developing a usable, repeatable planetary defence technique.
- In addition, Harrison notes that the ability to measure any libration in the post-impact asteroid will also open up a valuable scientific opportunity: “The fundamental frequency of the libration will depend on the mass of the secondary, and how that mass is distributed throughout its interior – in the same way that the frequency of a pendulum's swing depends on its mass.
- “So measuring this effect will give researchers an important insight into the nature of Didymoon’s interior, constraining our models. However, it is essential to have a spacecraft on location to make such a measurement.”
- Harrison is part of the DART Dynamics Working Group, led by his PhD adviser Prof. Derek Richardson, tasked with performing dynamic modelling of the Didymos system before and after DART’s impact.
- “As an undergraduate I interned at LLNL (Lawrence Livermore National Laboratory) in northern California, where I encountered some researchers working on planetary defence,” explains Harrison. “I never even knew this was a field until then, but after that I decided I wanted to get involved.”
- This summer Harrison returns to LLNL, where he will take advantage of their supercomputer facilities to perform full-scale impact simulations, modelling the ejecta material thrown off of the asteroid by the DART impact.
- “Overall, it’s great timing for me,” says Harrison. “When the DART mission ends with its impact in 2022, then my PhD does too. We’ll get a first glimpse of the actual shape of Didymoon from DART and the LICIA CubeSat – provided by ASI, the Italian Space Agency – it will deploy before colliding. Then, within a few years Hera will be providing its data, so we can rigorously compare our models to reality.”
- The Hera mission will be presented to ESA’s Space19+ meeting this November, where Europe’s space ministers will take a final decision on flying the mission.
Figure 23: Hera surveying Didymos. ESA’s Hera mission concept, currently under study, would be humanity’s first mission to a binary asteroid: the 780 m-diameter Didymos is accompanied by a 160 m-diameter secondary body. Hera will study the aftermath of the impact caused by the NASA spacecraft DART on the smaller body (image credit: ESA–ScienceOffice.org)
• April 29, 2019: There are so many important components involved in getting the Double Asteroid Redirection Test (DART) to Didymos. As a ground-based observer, I am particularly excited that telescopes are high up on that list of critical elements. I lead the DART observing working group and we have been hard at work for the past several months trying to obtain more information about the Didymos binary system and the orbit of "Didymoon" in particular, the DART spacecraft's target. This information is so critical to the mission because our job as observers is to note the change in the orbit of Didymoon after the impact of DART. We need to have a very firm understanding of the pre-impact orbit to understand how much we've changed the orbit. 22)
• August 30, 2018: The first-ever mission to demonstrate an asteroid deflection technique for planetary defense has moved into the final design and assembly phase, following NASA’s approval on Aug. 16. 23)
- DART (Double Asteroid Redirection Test), being designed, built and managed by the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, will test what’s known as the kinetic impactor technique — striking an asteroid to shift its orbit — and take a critical step in demonstrating how to protect our planet from a potential impact.
- DART’s target is the asteroid Didymos, a binary system that consists of Didymos A, about one-half mile in size, and a smaller asteroid orbiting it called Didymos B, about 530 feet (~160 m) across. After launch — scheduled for spring/summer 2021 — DART will fly to Didymos (Greek for “twin”) and use an APL-developed onboard targeting system to aim itself at Didymos B. Then the spacecraft, about the size of a small car, would strike the smaller body at approximately 3.7 miles per second.
- “With DART, we want to understand the nature of asteroids by seeing how a representative body reacts when impacted, with an eye toward applying that knowledge if we are faced with the need to deflect an incoming object,” said APL’s Andrew Rivkin, who co-leads the DART investigation with APL’s Andrew Cheng. “In addition, DART will be the first planned visit to a binary asteroid system, which is an important subset of near-Earth asteroids and one we have yet to fully understand.”
- The kinetic impact technique works by making a very small change in the orbital speed of the target asteroid. DART will demonstrate the kinetic impact technique and will measure the effect of the DART impact. Observatories on Earth will determine the resulting change in the orbit of Didymos B around Didymos A, allowing scientists around the world to better determine the capabilities of kinetic impact as an asteroid mitigation strategy.
A SpaceX Falcon 9 successfully launched a NASA mission that will deliberately collide with a near Earth asteroid to test a technique that could be used to deflect the trajectory of any future asteroid on a collision course with the Earth. 24) 25)
The Falcon 9 lifted off on schedule at 1:21 a.m. EST Nov. 24 (06:21 UTC) 2021 from Space Launch Complex 4E at Vandenberg Space Force Base in California. The rocket’s upper stage deployed NASA’s Double Asteroid Redirection Test (DART) spacecraft about 55 minutes later, after two burns of that stage. NASA later confirmed that the spacecraft was in good health and had deployed its solar arrays.
The rocket’s first stage landed on a droneship in the Pacific Ocean downrange from Vandenberg. The stage was on its third flight, having previously launched the Sentinel-6 Michael Freilich ocean science satellite a year ago and a batch of Starlink satellites in May. This was the first SpaceX launch for NASA’s Launch Services Program, which handles spacecraft missions like DART, to use a previously flown booster, although such boosters have been used extensively for NASA commercial cargo and crew missions.
DART is NASA’s first mission devoted to planetary defense. In September 2022 the spacecraft will collide with Dimorphos, a moon orbiting the near Earth asteroid Didymos, at more than 24,000 kilometers per hour. The impact will change the orbit of Dimorphos slightly, demonstrating how such a “kinetic impactor” could be used to change the trajectory of a threatening asteroid.
“We definitely have a reason to want to be able to see, by ramming this asteroid,” said NASA Administrator Bill Nelson in a Nov. 23 interview, “can you slightly move the trajectory. And if so, then we have a template for the future.”
DART is the first mission devoted primarily to planetary defense at NASA. “The DART project is part of a larger portfolio that we have for the planetary defense program at NASA,” said Lindley Johnson, NASA’s planetary defense officer and head of the Planetary Defense Coordination Office at the agency, during a Nov. 22 briefing.
That effort includes funding of ground-based observations and coordination with other agencies for planning in the event an asteroid on a collision course is detected. No known asteroid poses an impact threat to the Earth for the next century, but only about 40% percent of the estimated population of large near Earth asteroids has been discovered.
A second planetary defense mission, the Near Earth Object (NEO) Surveyor, is in development to fill those gaps. It is a space-based infrared telescope designed to accelerate the discovery of near Earth asteroids to help achieve a congressionally mandated goal of finding at least 90 percent of all NEOs at least 140 meters across. NEO Surveyor is scheduled for launch in 2026.
“It’s a whole program,” Nelson said of those planetary defense efforts, one that also includes international cooperation with organizations like the European Space Agency, which will send the Hera mission to Didymos and Dimorphos later this decade to observe the after effects of DART’s collision. “Everybody on Earth ought to, in their space agencies, have an interest in doing this.”
LICIACube (Light Italian CubeSat for Imaging of Asteroids), a 6U CubeSat (14 kg) made by Italian Space Agency (ASI). LICIACube is a part of Double Asteroid Redirection Test mission and is built to carry out observational analysis of the Didymos asteroid binary system after DART's impact. It will communicate directly with Earth, sending back images of the ejecta and plume of DART's impact as well as do an asteroidal study during its flyby of the Didymos system, 3 days after the Dart's impact. 26)
ESA’s Hera mission seen with its CubeSats in orbit around its target asteroid. Now NASA’s Double Asteroid Redirection Test, DART, is on its way to test the kinetic impact technique of asteroid deflection, ESA’s Hera will be Earth’s next planetary defense mission, scheduled to fly to the same body that DART will impact next year. 27)
• June 29, 2022: NASA’s Double Asteroid Redirection Test (DART) mission is the world’s first full-scale planetary defense test against potential asteroid impacts on Earth. Researchers of the University of Bern and the National Centre of Competence in Research (NCCR) PlanetS now show that instead of leaving behind a relatively small crater, the impact of the DART spacecraft on its target could leave the asteroid near unrecognizable. 28)
- 66 million years ago, a giant asteroid impact on the Earth likely caused the extinction of the dinosaurs. Currently no known asteroid poses an immediate threat. But if one day a large asteroid were to be discovered on a collision course with Earth, it might have to be deflected from its trajectory to prevent catastrophic consequences.
- Last November, the DART space probe of the US space agency NASA was launched as a first full-scale experiment of such a manoeuvre: Its mission is to collide with an asteroid and to deflect it from its orbit, in order to provide valuable information for the development of such a planetary defense system.
- In a new study published in The Planetary Science Journal, researchers of the University of Bern and the National Centre of Competence in Research (NCCR) PlanetS have simulated this impact with a new method. Their results indicate that it may deform its target far more severely than previously thought (see Infographic of Figure 9). 29)
Rubble Instead of Solid Rock
- “Contrary to what one might imagine when picturing an asteroid, direct evidence from space missions like the Japanese space agency’s (JAXA) Hayabusa2 probe demonstrate that asteroid can have a very loose internal structure – similar to a pile of rubble – that is held together by gravitational interactions and small cohesive forces”, says study lead-author Sabina Raducan from the Institute of Physics and the National Centre of Competence in Research PlanetS at the University of Bern.
- Yet, previous simulations of the DART mission impact mostly assumed a much more solid interior of its asteroid target Dimorphos. “This could drastically change the outcome the collision of DART and Dimorphos, which is scheduled to take place in the coming September”, Raducan points out. Instead of leaving a relatively small crater on the 160 meter wide asteroid, DART’s impact at a speed of around 24,000 km/h could completely deform Dimorphos. The asteroid could also be deflected much more strongly and larger amounts of material could be ejected from the impact than the previous estimates predicted.
A prize winning new approach
- “One of the reasons that this scenario of a loose internal structure has so far not been thoroughly studied is that the necessary methods were not available”, study lead-author Sabina Raducan says.
- “Such impact conditions cannot be recreated in laboratory experiments and the relatively long and complex process of crater formation following such an impact – a matter of hours in the case of DART – made it impossible to realistically simulate these impact processes up to now”, according to the researcher.
- “With our novel modelling approach, which takes into account the propagation of the shock waves, the compaction and the subsequent flow of material, we were for the first time able to model the entire cratering process resulting from impacts on small, asteroids like Dimorphos”, Raducan reports. For this achievement, she was awarded by ESA and by the mayor of Nice at a workshop on the DART follow-up mission HERA.
Widen horizon of expectations
- In 2024, the European Space Agency ESA will send a space probe to Dimorphos as part of the space mission HERA. The aim is to visually investigate the aftermath of the DART probe impact. “To get the most out of the HERA mission, we need to have a good understanding of potential outcomes of the DART impact”, says study co-author Martin Jutzi from the Institute of Physics and the National Centre of Competence in Research PlanetS. “Our work on the impact simulations adds an important potential scenario that requires us to widen our expectations in this regard. This is not only relevant in the context of planetary defense, but also adds an important piece to the puzzle of our understanding of asteroids in general”, Jutzi concludes.
DRACO (Didymos Reconnaissance and Asteroid Camera for OpNav)
The DART payload consists of a high-resolution visible imager to support the primary mission objective of impacting the Didymos secondary. The DART imager is required to support optical navigation on approach and autonomous navigation in the terminal phase. The imager is derived from the New Horizons LORRI instrument 30) and will use a 20 cm aperture Ritchey-Chretien telescope with 0.5 arcsec/pixel. The DART imager will determine the impact point within ~1 m, and it will characterize the pre-impact surface morphology and geology of the target asteroid and the primary to ≤50 cm/px. 31)
Observation Campaign Strategy
Telescopic measurements of the Didymos system are a critical piece of the DART mission. The DART impact is expected to create a several-minute change in the period of Didymos B’s orbit around Didymos A. Observing opportunities occur in spring 2019 and winter 2020-2021 prior to a 2022-2023 opportunity that runs for several months and includes the impact time itself. Observations prior to the impact will serve to establish as precise a baseline as possible for the undisturbed state of the Didymos system.
The observing campaign will focus on photometric lightcurve measurements. By precisely measuring the timing of Didymos B eclipsing and being occulted by Didymos A via these lightcurves, and the change in that timing, Δv imparted on Didymos B will be determined.
During the impact period Didymos will be at roughly V magnitude of 14-15 as viewed from Earth. At this brightness, telescopes as small as 1 meter in aperture can obtain useful data. Dozens of such telescopes exist, which mitigates the risk of bad weather or equipment failure at specific sites. Larger telescopes (4 meter apertures or larger, available on 5 continents) can be used to enable optical coverage by those facilities for 20 out of 24 hours per day near the impact date, weather permitting. The orbit period of Didymos B is 11.92 hours, so a little over two orbits occur per Earth day. The placement of the large telescopes is such that all orbit phases are covered by at least one telescope per 24 hours.
In addition to ground-based telescopes, spaceborne observatories will be used when possible. The Hubble Space Telescope is capable of observing during the impact period if it is still operating, and the limits on tracking rates for the James Webb Space Telescope allow observations 6 weeks before and after the nominal impact date.
Finally, the proximity of Didymos to Earth at the time of the 2022 impact will also allow the use of the Goldstone and Arecibo radars, perhaps in conjunction with the Green Bank radio telescope, to make measurements of the Didymos system. These measurements, along with potential optical studies of ejecta evolution, will provide a fuller understanding of the consequences of the DART impact.
3) Cheryl L. B. Reed, Elena Adams, Daniel O'Shoughnessy, Justin A. Atchison, Andrew F. Cheng, Andrew S. Rivkin, Nancy Cabot, ”Asteroid Impact & Deflection Assessment: Double Asteroid Redirection Test,” Proceedings of the 69th IAC (International Astronautical Congress) Bremen, Germany, 1-5 October 2018, paper: IAC-18.A3.4A.4, URL: https://iafastro.directory/iac/proceedings/IAC-18/IAC-18/A3/4A/manuscripts/IAC-18,A3,4A,4,x44689.pdf
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. Comments and corrections to this article are always welcome for further updates (email@example.com).
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