What happens if an asteroid hits Earth?
Bruce Willis might have saved the world by blowing up a nuclear device on an asteroid in the film Armageddon. In the movie, Bruce Willis heroically sacrifices his life, breaking the killer Asteroid in two. But this time, NASA isn’t calling on Bruce Willis’s character Harry Stamper to save the world. NASA called Aerojet Rocketdyne and Johns Hopkins Applied Physics Laboratory (APL).
NASA has a plan, not to blow up an asteroid, but redirect one. The mission: The Double Asteroid Redirection Test (DART) led by NASA’s Planetary Defense Coordination Office and the Science Mission Directorate’s Planetary Science Division. NASA also enrolled the Applied Physics Laboratory (APL) with support from several NASA centers:
- 1. The Jet Propulsion Laboratory (JPL)
- 2. Goddard Space Flight Center (GSFC)
- 3. Johnson Space Center (JSC)
- 4. Glenn Research Center (GRC)
- 5. Langley Research Center (LRC).
Finding a target asteroid:
Many factors play in the ease of asteroid detection. The Albedo of the asteroid relates to the amount of light reflectivity. Think about Elon Musk’s Starlink satellites. Astronomers complain about the high reflectivity of these satellites ruining the night sky. Unlike Starlink, the Albedo of most asteroids pales in comparison. This makes asteroids more difficult to spot. Astronomers leverage more than just visible light to detect and track asteroids.
Size matters for the detection of asteroids. Larger asteroids absorb more light and potentially reflect more light. Sometimes that release of absorbed light ends up in a different wavelength than the original, but still detectable. Many times this light is emitted as infrared light.
NASA’s WISE (Wide-field Infrared Survey Explorer) spacecraft mission ended in 2011 after completing an infrared-wavelength astronomical survey between December 2009 to February 2011. The space telescope ran out of cooling fluids to operate certain instruments. NASA repurposed this satellite In September 2013 and assigned the spacecraft a new mission as NEOWISE to help find near-Earth asteroids and comets.
Along with NEOWISE, Earth-based observation telescopes and some other missions continue to scan and monitor the space around Earth for Near-Earth Objects. Earth-based telescope’s ability to spot larger asteroids makes larger asteroids make them ideal for tracking. A downside of the larger asteroids is the increased mass. More mass makes these asteroids harder to deflect.
NASA and JAXA sent spacecraft to visit certain asteroids over the last twenty years. As a result, our knowledge of asteroids increased greatly. Is there a cause for concern? Yes.
The DART spacecraft mission:
DART represents a first of a kind planetary defense-driven test to prove technologies for preventing an impact of Earth by a hazardous asteroid. The DART demonstration includes a kinetic impactor technique to change the motion of an asteroid in space. If successful, DART intends on redirecting an asteroid to a different orbit.
Credits: NASA/Johns Hopkins Applied Physics Lab
The spacecraft shall deliberately strike an asteroid at high velocity to change the asteroid’s orbit. Which unsuspecting asteroid did NASA choose? The binary asteroid Didymos(65803) includes Didymos A and a smaller asteroid orbiting it called Didymos B. Didymos primary body measures approximately 780 meters across. The secondary body (or “moonlet”) about 160-meters in size.
At 780 meters, the 2000 Report Of The Task Force On Potentially Hazardous Near-Earth Objects estimated Didymos A would produce Tsunamis reaching hemispheric scales of a water impact. In the event of a land impact, absolute destruction of 100,000 km^2 area. For reference, think the country of South Korea or the state of Virginia wiped out of existence leaving a 12 km wide crater. Also, scientists predict the impact of 10,000-100,000 mega tonnes like this once every 63,000 years (or so). If on an intercept course with Earth, Didymos-A sized asteroids pose a threat. How does that compare to a nuclear bomb?
How big was the biggest nuclear bomb ever detonated?
The most powerful nuclear weapon ever detonated, the Tsar Bomba device only yielded about 50 megatons, (50 million tons of TNT). The USSR developed the bomb and then detonated one on October 30th 1961 at 11:32, Moscow time. This bomb created a fireball estimated to be five miles wide and a mushroom cloud 40 miles high(64km). The mushroom cloud top extended roughly 63 miles(100km) from end to end. Reports of the flash from the explosion came in from 1,000km (630 miles) away.
The tiny village of Severny 34 miles(55km) away ended the day with no houses left standing. Settlements hundreds of miles from the blast zone experienced houses collapsing, roofs caving in, doors damaged, broken glass. Radio communications disrupted, sustained for more than an hour.
What kind of damage would a smaller asteroid do to Earth?
Every day asteroids collide with Earth. Most of these wayward space rocks do not pose a threat to inhabitants of Earth. Smaller objects waste away during the last moments of their existence. Smaller objects remain a risk for spacecraft in orbit, but not to the inhabitants below(for the most part).
On February 15, 2013, a house-sized meteor entered Earth’s atmosphere at over 40,000 mph. The Asteroid exploded 14 miles above Chelyabinsk, Russia. The blast from the exploding asteroid was more than 30 times the energy of the Hiroshima atom bomb. It generated a shock wave that shattered windows and damaged buildings in several Russian cities, injuring over 1600 people. No reported fatalities from this silent celestial killer, but the next one might be bigger than a house. Bigger Asteroids lurk in our solar system.
Although Didymos A is a dangerous size of an asteroid for Earth, most asteroids are much smaller. The Didymos B provides a good reference for typical asteroids posing the most significant threat to Earth. The smaller the asteroid, the more difficult to detect. Didymos B sized asteroids still can inflict a lot of damage.
Estimates place this size asteroid between 100-1000 megatons. Asteroids like this rank more than twice the power of the Tsar Bomba detonated by the USSR. Imagine an entire metropolitan area like New York, Shanghai, or Tokyo removed from the face of the Earth. Luckily, events like these happen only about once every 4,000 years. Dire news. It could happen at any time. NASA’s planetary asteroid redirect mission, therefore, focusses on a large enough celestial body to prove the concept.
NASA’s Plan to save the Earth:
NASA plans to launch a spacecraft to impact an asteroid causing its orbit to be shifted. After the late July 2021 launch from Vandenberg Air Force Base, California, DART’s onboard targeting system will aim at Didymos. The spacecraft arrives at Didymos’ secondary body in late September 2022 and the spacecraft impacts itself on Didymos B. Released just before impact, a shoebox-sized LICIACube (provided by NASA’s International partner) would document DART’s impact and its aftermath from close up. The CubeSat will tag along during the ride until the last moment.
The Didymos binary asteroids will be observed using telescopes on Earth. These observations establish a baseline by precisely measuring the properties before DART arrives. Those Earth-based telescopes can easily spot Didymos A and track the relative position of Didymos B. Earth-based telescopes measurements can show the change in the orbit of Didymos B around Didymos A. The measurement of before and after DART’s impact allows scientists to calculate the amount of deflection.
From this demonstration, NASA can learn how effective the impact method is to defect these potentially hazardous asteroids. Future missions can make adjustments in technique, mass or velocity.
Aerojet Rocketdyne provided the DART spacecraft’s propulsion systems.
DART spacecraft includes not one, but multiple propulsion systems. The spacecraft’s chemical propulsion system includes 12 MR-103G hydrazine thrusters, each with 0.2 pounds of thrust. The DART spacecraft will fire its chemical propulsion system during the final approach to the asteroid and conduct last-minute direction changes to ensure an accurate collision with its target.
Aerojet Rocketdyne’s NEXT-C (NASA Evolutionary Xenon Thruster–Commercial) system also installed on the spacecraft will demonstrate the next-generation solar electric propulsion system. NEXT-C technology stems from mission-proven technology developed at NASA’s Glenn Research Center.
APL subcontracted the dual chemical and electric propulsion to Aerojet Rocketdyne. The propulsion systems underwent assembly, integration at Aerojet Rocketdyne’s facility in Redmond, Washington, since August 2019.
Eileen Drake, president and CEO of Aerojet Rocketdyne in a press release.
“DART plays an important role in understanding if it is possible to deflect asteroids and change their orbits. 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.”
Aerojet delivered APL in Laurel, Maryland. APL now starts the balance of the subsystems and test of the spacecraft ahead of the 2021 launch.
NASA selected Elon Musk’s SpaceX to launch the mission. The DART mission currently is slated to launch in June 2021 on a Falcon 9 rocket from Space Launch Complex 4E at Vandenberg Air Force Base in California. By using solar electric propulsion, DART will intercept the asteroid Didymos’ small moon in October 2022 after 14 months journey. At that time, the asteroid will be within 11 million kilometers of Earth providing a safe viewing distance.
About The Author
Bill D’Zio
Co-Founder at WestEastSpace.com
Bill founded WestEastSpace.com after returning to China in 2019 to be supportive of his wife’s career. Moving to China meant leaving the US rocket/launch industry behind, as the USA and China don’t see eye to eye on cooperation in space. Bill has an engineering degree and is an experienced leader of international cross-functional teams with experience in evaluating, optimizing and awarding sub-contracts for complex systems. Bill has worked with ASME Components, Instrumentation and Controls (I&C) for use in launch vehicles, satellites, aerospace nuclear, and industrial applications.
Bill provides consulting services for engineering, supply chain, and project management.
