Artist’s impression of NASA’s Double Asteroid Redirection Test (DART) spacecraft speeding toward the smaller of the two bodies in the Didymos asteroid system.
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.
The Double Asteroid Redirection Test (DART), 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 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.
To assess and formulate capabilities to address potential asteroid threats, NASA established its Planetary Defense Coordination Office in 2016, which is responsible for finding, tracking and characterizing potentially hazardous asteroids and comets coming near Earth, issuing warnings about possible impacts, and assisting plans for and coordination of a U.S. government response to an actual impact threat.
APL manages DART for NASA’s Planetary Missions Program Office at Marshall Space Flight Center in Huntsville, Alabama. DART also is supported by teams from Goddard Space Flight Center, Greenbelt, Maryland; Johnson Space Center, Houston; Glenn Research Center, Cleveland; Langley Research Center, Hampton, Virginia; the Jet Propulsion Laboratory, Pasadena, California; the University of Maryland, College Park; University of Colorado, Boulder; Lawrence Livermore National Laboratory, Livermore, California; and Aerojet Rocketdyne, Arlington, Virginia.
Quelle: The Johns Hopkins University
DART Mission Set to Launch on SpaceX Falcon 9
DART will target the smaller of the two objects (left) that make up the binary asteroid Didymos, which will be about 7 million miles (11 million kilometers) from Earth at the time of impact, scheduled for October 2022.
Credit: NASA/Johns Hopkins APL
NASA’s first planetary defense mission, the Double Asteroid Redirection Test (DART), has been slated for a June 2021 launch aboard a SpaceX Falcon 9 rocket from Vandenberg Air Force Base, California. The mission, led by the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, will be the first to demonstrate the kinetic impactor technique, which involves slamming a spacecraft into an asteroid at high speed to shift it off course.
“We’re excited that NASA has selected the vehicle to launch DART on its important planetary defense mission,” said DART Mission Systems Engineer Elena Adams, of APL. “The DART team is eager to move ahead with our spacecraft and mission designs and demonstrate, for the first time in space, a method to keep potentially hazardous bodies from reaching Earth.”
DART will target the smaller of the two objects that make up the binary asteroid Didymos, which will be about 7 million miles (11 million kilometers) from Earth at the time of impact, scheduled for October 2022.
APL will build and operate the DART spacecraft and manages the mission for the Planetary Missions Program Office at Marshall Space Flight Center in Huntsville, Alabama. DART also is supported by teams from the Goddard Space Flight Center, Greenbelt, Maryland; Johnson Space Center, Houston, Texas; and the Jet Propulsion Laboratory, Pasadena, California.
Quelle: THE JOHNS HOPKINS UNIVERSITY
SpaceX’s Falcon 9 wins launch of an asteroid-attacking NASA spacecraft
Just minutes before SpaceX began fueling Falcon Heavy for its commercial launch debut, NASA announced that the company had won a contract for its Double Asteroid Redirection Test (DART) mission, to be launched by Falcon 9 for the low cost of $69M.
Designed to cost less than $250M total, the DART mission will aim to be as light and fast as possible, using a dedicated Falcon 9 to send the ~600 kg (~1300 lb) spacecraft and its Italian companion cubesat on an ~11 million kilometer (~7M mi) journey to the binary asteroid Didymos. The ultimate purpose of DART is to effectively prove out both technologies and physics that could be used in the future to defend Earth from asteroids known to be on a collision course.
If all goes as planned during DART’s imminent design review milestones and hardware integration, Falcon 9 could launch the spacecraft towards the Didymos asteroid system in June 2021 for an October 2022 arrival. That “arrival” would involve DART impacting Didymos-B – the smaller of the pair at 163 m (535 ft) across – at a relative velocity of more than 6 km/s (3.7 mi/s). Nicknamed Didymoon, Didymos-B effectively orbits Didymos-A. At that speed, the ~600 kg probe will create an impact with the equivalent explosive force of nearly two and a half tons of TNT, the purpose of which is to determine just how much the sheer kinetic energy of impact can modify a small body’s orbit around the main asteroid.
Estimates from the spacecraft’s mission managers expect Didymoon’s orbit to be shifted by about 1% as measured by the time it takes to orbit Didymos-A, from ~11.9 hours to ~11.8 to 12.0 hours. This is a very small change but one that should – in theory – be easily measurable by telescopes on Earth, despite the fact that Didymoon has been estimated to have a mass of approximately 3.5 million metric tons (7.6 billion pounds), approximately seven million times heavier than DART. In short, NASA is going to functionally bomb an asteroid moon to see if humans might be able to use kinetic impactors to gently ‘boop’ threatening space objects off of the offending trajectory years or even decades in advance.
Despite the inherently destructive, single-use nature that DART’s impactor status bestows, current plans thankfully include an Italian cubesat known as LICIACube. The small copassenger will deploy two days before impact to fully exploit the scientific value of DART’s demise with high-quality photos of the event and aftermath. LICIACube will be traveling the same speed and thus won’t be able to enter orbit around the asteroid system, but a European Space Agency (ESA) mission known as Hera plans to do just that in the mid-2020s to better characterize Didymos and the crater (hopefully) made by DART.
Aside from the mission itself, DART serves as a technology demonstration platform for NASA. It will mark the first in-space use of the NASA-built NEXT-C ion thruster and powerpack, as well as the first standalone use of Roll-Out Solar Array (ROSA) deployment mechanism (shown above being tested on the ISS). Even more intriguing is a proposed transformational solar array planned at one point for DART, a flexible combination of advanced solar cells (~33% efficient) and mirror concentrators that could feed a spacecraft five times as much power for a given solar array area and distance from the sun. It’s unclear whether this will make it into DART’s final design but it still appears to be on the table as of January 2019. According to the contracted manufacturer, DART’s solar array will produce ~6.6 kW, while rough estimates suggest that the solar array will have an area of 16 m^2 (170 ft^2). Relative to the simplicity of the deployment mechanism and small size of DART (~600 kg total), this is an incredible amount of accessible power.
GETTING TO ORBIT
For NASA’s SpaceX launch contract, the agency will pay just $69M, barely 10% above Falcon 9’s bare-minimum list price of $62M. It’s safe to assume that the timing of the contract award – days after SpaceX abruptly dropped an official protest of ULA winning a ~$150M NASA contract – might not be coincidence. Regardless, SpaceX’s decision to bid so low for a NASA launch does lend some serious credence to the company’s protest that ULA’s contract for the mission – NASA’s LUCY asteroid explorer – was “vastly more [expensive]” than the bid SpaceX submitted.
Weighing just ~600 kg (~1300 lb) wet, DART could end up launching with additional copassengers on Falcon 9, although there is a precedent set by NASA’s ~360 kg TESS and Taiwan’s Formosat-5 for SpaceX giving tiny spacecraft dedicated launches. Additionally, it’s possible that DART will launch on a flight-proven Falcon 9 Block 5 rocket, given the likelihood that NASA will have certified flight-proven SpaceX vehicles for almost any launch by 2021.
NASA’s First Planetary Defense Technology Demonstration to Collide with Asteroid in 2022
The Double Asteroid Redirection Test (DART) – NASA’s first mission to demonstrate a planetary defense technique – will get one chance to hit its target, the small moonlet in the binary asteroid system Didymos. The asteroid poses no threat to Earth and is an ideal test target: measuring the change in how the smaller asteroid orbits about the larger asteroid in a binary system is much easier than observing the change in a single asteroid's orbit around the Sun. Work is ramping up at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and other locations across the country, as the mission heads toward its summer 2021 launch – and attempts to pull off a feat so far seen only in science fiction films.
To navigate the DART spacecraft to its intended target – a binary asteroid that consists of a small moon (Didymos B) orbiting a larger body (Didymos A) – scientists need to understand how the system behaves. Scientists have been making efforts to observe Didymos from Earth since 2015, and now, an international campaign coordinated by Northern Arizona University’s Cristina Thomas, DART’s Observing Working Group Lead, is making critical observations using powerful telescopes worldwide to understand the state of the asteroid system before DART reaches it. Current observations will help researchers to better understand the extent of the impact made when DART slams into its target – Didymos B – in September 2022.
The most recent observation campaign took place on Cerro Paranal in northern Chile, where scientists viewed Didymos using the Very Large Telescope, which is run by the European Southern Observatory. The “VLT” comprises four telescopes, each with 8.2-meter mirrors; two of them were used in the recent observations.
“The Didymos system is too small and too far to be seen as anything more than a point of light, but we can get the data we need by measuring the brightness of that point of light, which changes as Didymos A rotates and Didymos B orbits,” said APL’s Andy Rivkin, DART investigation team co-lead, who participated in the observations. The brightness changes indicate when the smaller moon, Didymos B, passes in front of or is hidden behind Didymos A from our point of view. These observations will help scientists determine the location of Didymos B about Didymos A and inform the exact timing of DART’s impact to maximize the deflection.
The investigation team will observe Didymos again from late 2020 into the spring of 2021. Final ground-based observations will occur as the spacecraft travels toward the asteroid, as well as after impact occurs.
Research with Impact
The telescope observations are key to understanding Didymos, but they’re not quite enough to fully understand Didymos B, DART’s target.
“Even though we are performing ground-based observations, we don’t know much about Didymos B in terms of composition and structure,” said Angela Stickle, DART’s Impact Simulation Working Group Lead from APL. “We need to anticipate a wide range of possibilities and predict their outcomes, so that after DART slams into Didymos B we’ll know what our measurements are telling us.”
Structure is essential to the equation; in Didymos, researchers aren’t sure whether DART will impact an asteroid composed of solid rock, loose rubble or something “softer,” more akin to sand. A softer surface would absorb more of DART’s force and may not be pushed as drastically as if DART hit a harder surface.
Extensive modeling and simulation, part of a large international campaign that started in 2014, is being done in conjunction with Lawrence Livermore National Laboratory and other members of the investigation team to help researchers predict what will happen to DART’s target after impact. They’ve considered these various factors—along with the added momentum from DART’s impact and the resulting debris ejected from the crater it creates – as they’ve run various simulations. These simulations help the team shape its expectations for impact.
Eyes on DART and Didymos
Researchers will have the ability to eventually see the Didymos asteroid system close-up – albeit briefly – thanks to DART’s onboard DRACO imager and a planned ride-along CubeSat, the Italian Space Agency’s LICIACube.
Released just before impact, the shoebox-sized LICIACube would document DART’s impact and its aftermath. The CubeSat recently passed its preliminary design review and has moved into the next phase of development.
DRACO – the Didymos Reconnaissance and Asteroid Camera for Op-nav – is DART’s only onboard instrument. It will serve primarily as DART’s optical navigation system, capturing images that help the spacecraft reach its target.
DRACO will feed its images into the APL-developed Small-body Maneuvering Autonomous Real-Time Navigation (SMART Nav) algorithm – the system that, in the spacecraft’s final hours, will precisely and automatically guide DART into Didymos B. SMART Nav is preparing to undergo a series of tests on simulated spacecraft avionics, which will boost engineers’ confidence that the system will be ready to operate successfully when the mission will be relying on it.
Wired for Success
While much of the work on DART so far has been modeling and simulation, many parts of the spacecraft have started to take shape. A full-scale mock-up of DART now serves as a placeholder for the assembly of cables and connectors that will eventually make up the wiring harness. The mission has signed off on the manufacturing of several flight hardware components, specifically the spacecraft’s solar arrays—which passed the critical design review stage—as well as the radio and power system electronics.
In a recent design change, DART will now be able to complete its mission by relying on small hydrazine thrusters in addition to having the ability to utilize the electric propulsion system, NASA’s Evolutionary Xenon Thruster Commercial (NEXT-C) ion engine, which will also push the start of the primary launch window to July of 2021, shortening the mission flight time. “For a mission that relies on one chance, it’s a move that will provide DART with more options to ensure it hits its mark,” said Ed Reynolds, DART project manager at APL.