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The NASA DART spacecraft will ram into asteroid moonlet Dimorphos tonight - Details and Liveblog [1]

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Date: 2022-09-26

As most you are aware of, the NASA DART (Double Asteroid Redirection Test) spacecraft will ram into Dimorphos, a moonlet of asteroid Didymos, and change its trajectory a bit, this evening at 7:14 p.m. EDT. This is just a test mission of the “kinetic impact” technique of deflecting hazardous asteroids; earth is in no danger from Didymos. Someday, we may have to use this technology to defend earth from an asteroid headed towards us. There will be a livecast on NASA TV and the NASA YouTube channel, starting at 5:30 p.m. EDT, which will include real-time observations from the DART spacecraft as it approaches and crashes into Dimorphos. We wrote a diary on the subject when DART was launched on Nov 24, 2021. This diary draws heavily from that diary and takes a deep dive into the DART mission and its significance. x 🛰️ This is only a test – of planetary defense. Today, our #DARTMission is set to crash into a non-hazardous asteroid to test deflection technology, should we ever discover a threat.



Impact: 7:14pm ET (23:14 UTC). Watch our LIVE broadcast at 6pm ET: https://t.co/VAfF5ZXcYB pic.twitter.com/czGqnYJIGJ — NASA (@NASA) September 26, 2022 Here is the location of Didymos in the solar system at the time of impact — ssd.jpl.nasa.gov/…

Tonight, Jupiter will be closest to earth in many decades The DART mission and its effects will be observed by a long list of telescopes around the world and in space, include the Webb and Hubble space telescopes. dart.jhuapl.edu/... The Lucy spacecraft, on its journey to the Trojan Asteroids, is approaching earth for a gravity assist maneuver on Oct 16. It will will use its 'LORRI Instrument, to observe the event. x Lucy is now about 6.5 million miles from Earth, and #DARTMission is only a bit over half a million miles from Didymos and Dimorphos! Go DART! pic.twitter.com/drBmLD6Enj — Lucy Mission (@LucyMission) September 24, 2022 The Double Asteroid Redirection Test (DART) Double Asteroid Redirection Test (DART) will visit the binary asteroid Didymos and demonstrate the kinetic effects of crashing an impactor spacecraft into an asteroid for planetary defense purposes. Its target is the binary near-Earth asteroid 65803 Didymos, which consists of a primary body approximately 780 meters across, and a secondary 160m “moonlet” Dimorphos. Due to its binary nature, the asteroid is named "Didymos", the Greek word for twin. Dimorphos is informally known as Didymoon. The DART spacecraft will achieve the kinetic impact by deliberately crashing itself into the moonlet at a speed of approximately 21,600 km/hour. 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. By targeting the small moonlet in a binary system, the DART mission plan makes these precise measurements possible and ensures that there is no chance the impact could inadvertently create a hazard to Earth. Here are a couple of videos on the DART mission — x YouTube Video x YouTube Video Originally, DART was part of a joint mission with the European Space Agency (ESA) called AIDA. ESA would launch the AIM spacecraft, which would have orbited the larger asteroid to study its composition and that of its moon, as well as measure the effect on the asteroid moon's orbit around the larger asteroid. The AIM mission was cancelled. Instead, DART will be accompanied by LICIACube (Light Italian CubeSat for Imaging of Asteroids), a small 6-unit CubeSat being developed by the Italian Space Agency (ASI). LICIACube separated from the DART spacecraft on Sep 12 and will acquire images of the impact and ejecta as it drifts past the asteroid. In addition, ESA will launch the Hera spacecraft to Didymos in 2024, which will arrive in Dec 2026 — 4 years after DART's impact — to do a detailed reconnaissance and assessment. The Journey The diagram below shows the approximate trajectory of the 10 month journey to Didymos. It was originally scheduled to impact on Oct 5. The original diagram is based on a launch date of June 15, 2021

TCM = Trajectory Correction Maneuver

The NASA Evolutionary Xenon Thruster Commercial (NEXT-C) electric propulsion system provides low impulse but sustained propulsion along the orange thrust arcs.

trs.jpl.nasa.gov/... The Collision The 550 kg DART spacecraft will collide with the 4 billion kg 160 meter diameter Dimorphos moonlet at a speed of 6.6 km per second. It will thereby slow down Dimorphos’ orbital speed, causing its orbit to decrease in radius a bit and shorten the orbital period by about 10 minutes. There will be no noticeable effect on the orbit of the Didymos system around the Sun. The info-graphic below shows the before and after orbit of Dimorphos (not to scale). The impact is expected to create a crater and a plume of dust and debris. That assumes that Dimorphos is a relatively solid object. Recent close observations of small asteroids have shown that they are more like a pile of rubble loosely held together by gravity. In that case, the moonlet the debris field might be larger or the moonlet might break up into pieces. x “This could drastically change the outcome of the collision of #DART and Dimorphos, which is scheduled to take place in the coming September”, says Sabina Raducan, planetary scientist and NEO-MAPP member.

Learn more in our latest blog post!https://t.co/798vJA10l7 — NEO-Mapp (@neo_mapp) August 11, 2022 About Didymos, Dimorphos and DART Here are a few vital stats about Didymos and its moonlet Dimorphos. Parameter Didymos Dimorphos DART Diameter 780 m 160 m About 2 m (excluding 8.5 m solar arrays) Mass Approx. 5x1011 kg 500,000,000,000 kg* Approx. 4x109 kg 4,000,000,000 kg 550 kg Distance From Sun — 1.0141 AU to 2.2755 AU 1 AU is mean Sun-Earth distance = 150 million km From Didymos — 1.18 km From earth at impact — 11 million km (36.7 light-seconds) Orbital period 2.11 years 11.92 hours 10 minutes shorter after impact Rotation period 2.26 hours 11.92 hours Speed ~22 km per second around the Sun ~22 km per second around the Sun 17 cm per second around Didymos in opposite direction ~29 km/s 104,400 km/h 6.6 km/s relative to Dimorphos * Assuming density = 2 gram/cm3 The DART Spacecraft Unlike spacecraft for other inter-planetary missions, DART is a relatively simple spacecraft with a single primary instrument — an onboard camera called DRACO which will provide visuals and autonomous guidance before impact. Here is an image of the spacecraft during test and assembly. The striped rolls are the roll-out solar arrays (ROSA), similar to the ones installed at the ISS. DRACO DRACO (Didymos Reconnaissance and Asteroid Camera for OpNav) is a narrow-angle telescope with a 208-millimeter aperture and field of view of 0.29 degrees. DRACO with real-time imaging and autonomous guidance software will guide the spacecraft towards the tiny target during the final hour of the mission. The visuals below show how large each asteroid will likely appear to DRACO in the final hour. DRACO’s images are fed to a series of guidance algorithms, called SMART Nav, which can identify the asteroids and tell the spacecraft how to maneuver toward them. This autonomous process begins four hours before impact — 87,000 to 98,000 km from the asteroid system — and can isolate Dimorphos from Didymos once the asteroids come into view. SMART Nav will continue to guide DART until two and a half minutes before impact. The images acquired by DRACO before the kinetic impact will be streamed back to Earth in real time. Expected views of Didymos and Dimorphos from DRACO Note that Dimorphos is nothing more than a few pixels in ground based observations; we do not have detailed info on its shape and terrain. The SMART Nav algorithms will need to figure everything out on its own in less than an hour. LICIACube

A small CubeSat, contributed by the Italian Space Agency and designed, built and operated by Argotec, is accompanying DART, to help image the impact and to take measurements after the impact. LICIACube was deployed from the DART spacecraft on Sep 12. It will use its onboard propulsion system to alter its trajectory, offsetting so that it flies past Dimorphos approximately three minutes after the DART impact. This gives it the opportunity to image the kinetic impact itself, the resultant ejecta plume, possibly the impact crater and the departure (back-side) hemispheres of both Didymos and Dimorphos. These images, in addition to ground-based telescope observations, can help confirm impact. More importantly, LICIACube’s images of the ejecta plume and crater can complement the DRACO images, helping to better characterize the momentum exchange and the effectiveness of the kinetic impact deflection. dart.jhuapl.edu/… x YouTube Video NEXT-C Ion Propulsion DART is also demonstrating the NEXT-C (NASA Evolutionary Xenon Thruster – Commercial) ion propulsion system developed by NASA’s Glenn Research Center and Aerojet Rocketdyne. NEXT-C is a solar-powered electric propulsion system that produces thrust by electrostatic acceleration of Xenon ions. Similar, but lower performance systems have flown on NASA’s Dawn and Deep Space 1 spacecraft. What are asteroids and why should we be concerned?

Asteroids are small, airless rocky worlds leftover from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today.

There are millions of asteroids; the large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans). However, other orbital families exist with significant populations, including the near-Earth asteroids.

Occasional collisions and gravitational tugs perturb the orbits of asteroids into elliptical ones, some of which cross the orbits of Earth.

The asteroid belt (white) and Jupiter's trojan asteroids (green)

Trojans share an orbit with a larger planet or moon, but do not collide with it because they orbit in one of the two Lagrangian points of stability L4 and L5, which lie 60° ahead of and behind the larger body.

As of today and according to statistics maintained by CNEOS, 29,867 near-Earth asteroids (NEAs) have been discovered. ranging in size from 1 meter up to 32 km. The number of near-Earth asteroids over 1 km in diameter is estimated to be about 856, of which over 90% have been discovered. 2,270 of the NEAs are classified as potentially hazardous asteroids (PHAs).

Asteroids smaller than about 25 meters generally burn up as they enter the Earth's atmosphere and cause little or no damage.

The Tunguska event was caused by a stony asteroid estimated to be 50–60 metres wide. The airburst at 6–10 km above the Earth's surface flattened an estimated 80 million trees over an area of 2,150 square km. No impact crater was found.

Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the impacted area.

Only once every few million years, an object large enough to threaten life on Earth comes along. Impact craters on Earth, the moon and other planetary bodies are evidence of these occurrences. According to abundant geological evidence, an asteroid roughly 10 km in size hit Earth about 65 million years ago. This impact made a huge explosion and a crater about 180 km across. Debris from the explosion was thrown into the atmosphere, severely altering the climate, and leading to the extinction of roughly 3/4 of species that existed at that time, including the dinosaurs.

433 Eros is a near-Earth asteroid approximately 34.4×11.2×11.2 km

A reminder from the Nobel Prize committee about the most infamous asteroid that collided with earth -

x Luis Alvarez, received the 1968 Nobel Prize in Physics for his research in elementary particle physics. However he is probably more famous for publishing the theory that the dinosaurs became extinct after an asteroid collided with Earth 65 million years ago.#AsteroidDay pic.twitter.com/9i6o7eRiPs — The Nobel Prize (@NobelPrize) June 30, 2021

Searching for and cataloging Asteroids and Comets

The Center for Near-Earth Object Studies (CNEOS) is the Jet Propulsion Laboratory (JPL) center for computing asteroid and comet orbits and their probability of Earth impact.

Since NASA's initiation of the NEO Observations program in 1998, Near-Earth Object (NEO) surveys have been extremely successful finding more than 90% of the Near-Earth Asteroids (NEAs) larger than one km and a good fraction of the NEOs larger than 140 meters.

While no known asteroid larger than 140 meters in size has a significant chance to hit Earth for the next 100 years, only about 40 percent of those asteroids have been found as of October 2021.

NEA Discovery Stats — cneos.jpl.nasa.gov/...

The vast majority of NEO discoveries have been made by NASA-supported ground-based telescopic surveys. Note that the NEO survey includes comets.

NEO SURVEY PROGRAM LOcation Status LINEAR (Lincoln Near-Earth Asteroid Research) Socorro New Mexico PAN-STARRS ( Panoramic Survey Telescope and Rapid Response System) Haleakala, Maui, Hawaii CATALINA SKY SURVEY (CSS) Tucson Arizona SPACEWATCH Tucson Arizona Follow-up missions only LONEOS Flagstaff Arizona Discontinued NEAT NASA/JPL Discontinued NEOWISE Earth polar orbit ATLAS Haleakala and Mauna Loa, Hawaii

Here is one of the techniques used to detect asteroids.

x How are asteroids discovered? We take several images of the same region of the sky and make a sequence (a short movie). Asteroids move, whereas stars are stationary. It is the motion of asteroids that allows us to discover them! Here is the discovery sequence of an asteroid. pic.twitter.com/nKqK6Xzn5g — Catalina Sky Survey (@catalina_sky) November 23, 2021

Typically, this is followed by imaging using ground based radar. The now destroyed Arecibo Observatory was the premier source of Radar astronomy. The following radar images of Didymos and Dimorphos were taken by Arecibo.

Fourteen sequential Arecibo radar images of the near-Earth asteroid (65803) Didymos and its moonlet, taken on 23, 24 and 26 November 2003. NASA’s planetary radar capabilities enable scientists to resolve shape, concavities, and possible large boulders on the surfaces of these small worlds. Photometric lightcurve data indicated that Didymos is a binary system, and radar imagery distinctly shows the secondary body. www.nasa.gov/...

A new space based NEO Surveyor telescope is planned for launch in 2026 -

x .@NASA approved the Near-Earth Object Surveyor space telescope (NEO Surveyor) to move to the next phase of mission development.



NEO Surveyor would help #planetarydefense experts expedite the search for near-Earth Objects (#NEOs) and #asteroids.



More: https://t.co/3exgwNU8L3 pic.twitter.com/ccqddh4GTA — NASA Asteroid Watch (@AsteroidWatch) June 11, 2021

The following animation represents a map of the increased count of all known asteroids in the solar system between Jan. 1, 1999, and Jan. 31, 2018. Blue represents near-Earth asteroids. Orange represents main-belt asteroids between the orbits of Mars and Jupiter.

x YouTube Video

Asteroid Impact Avoidance

So, if we detected an asteroid on a collision course with earth, how would we stop it?

The following tables (from cneos.jpl.nasa.gov/...) summarize various deflection techniques being explored by NASA and other space agencies. PHO stands for Potentially Hazardous Object.

Impulsive Technique Description Kinetic Impact High velocity impact. DART is an example of this technique. Conventional Explosive (surface) Detonate on impact Conventional Explosive (subsurface) Drive explosive device into PHO, detonate Nuclear Explosive (standoff) Detonate on flyby via proximity fuse Nuclear Explosive (surface) Impact, detonate via contact fuse Nuclear Explosive (delayed) Land on surface, detonate at optimal time Nuclear Explosive (subsurface) Drive explosive device into PHO, detonate

Slow Push Technique Description Focused Solar Use large mirror to focus solar energy on a spot, heat surface, “boil off” material Pulsed Laser Rendezvous, position spacecraft near PHO and focus laser on surface, material “boiled off” surface provides small force Mass Driver Rendezvous, land, attach, mine material and eject material from PHO at high velocity Gravity Tractor Rendezvous with PHO and fly in close proximity for extended period, gravitational attraction provides small force Asteroid Tug Rendezvous with PHO, attach to PHO, push Enhanced Yarkovsky Effect Change albedo of a rotating PHO; radiation from sun-heated material will provide small force as body rotates

Key Findings for Diverting a Potentially Hazardous Object (PHO)

A study report from 2007 provides the following assessment of the various PHO deflection techniques —

Nuclear standoff explosions are assessed to be 10-100 times more effective than the non-nuclear alternatives. Because of international treaties, use of a nuclear device would likely require prior international coordination. Conventional explosives were found to be ineffective against most threats.

are assessed to be 10-100 times more than the non-nuclear alternatives. Because of international treaties, use of a nuclear device would likely require prior international coordination. Conventional explosives were found to be ineffective against most threats. Non-nuclear kinetic impactors are the most mature approach and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body.

are the and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body. "Slow push" mitigation techniques are the most expensive, have the lowest level of technical readiness, and their ability to both travel to and divert a threatening NEO would be limited unless mission durations of many years to decades are possible.

Next we look at a few interesting past and canceled missions for Asteroid Deflection.

Deep Impact

Deep Impact was a NASA space probe launched in January 2005. It was designed to study the interior composition of the comet Tempel 1, by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the impactor successfully collided with the comet's nucleus.

The 370 kg impactor included a 100 kg copper cratering mass. Since copper was not expected to be found on a comet, scientists could ignore copper's signature in any spectrometer readings. At its closing velocity of 10.2 km/s, the impactor's kinetic energy was equivalent to 4.8 metric tons of TNT.

Although the primary goal of the mission was to study the comet and its composition, it provided some insights into kinetic impact based deflection. The impactor generated a predicted small 0.0001 mm/s velocity change in the comet's orbital motion and decreased its perihelion distance a tad by 10 meters. Note that Tempel 1 is a relatively large comet at 7.6 km × 4.9 km.

So, DART is not the first mission to deflect an asteroid.

The Deep Impact collision encounter with comet Tempel 1 (8 x 5 km in dimensions)

Asteroid Redirect Mission (ARM)

ARM was an ambitious NASA robotic mission to visit a large near-Earth asteroid, collect a multi-ton boulder from its surface, deflect the asteroid and transport the boulder into a stable orbit around the moon. The project was cancelled in 2017. Here is a description of the exciting mission nevertheless; hopefully, something like this might get funded in the future.

The ARM consisted of two mission segments: 1) the ARRM, which would be the first robotic mission to visit a large (greater than ~100 m diameter) near-Earth asteroid (NEA), collect a multi-ton boulder and regolith from its surface, use the boulder to perform an enhanced gravity tractor asteroid deflection demonstration, and then transport the asteroidal material to a stable orbit around the Moon; and 2) the Asteroid Redirect Crewed Mission (ARCM), in which astronauts would explore the boulder and return samples to Earth. The ARRM was planned to launch at the end of 2020 and the ARCM was planned for late 2025.

Artists’ conception of ARM spacecraft with boulder

The gravity tractor method uses the gravitational force of a large spacecraft to deflect the asteroid slowly over a time. The boulder effectively increases the mass of the spacecraft, thereby increasing the gravitational force and reducing the total time needed to achieve deflection to a few months. The spacecraft and the asteroid mutually attract one another; if the spacecraft counters the force towards the asteroid by, e.g., an ion thruster, the net effect is that the asteroid is accelerated towards the spacecraft and thus slightly deflected from its orbit. While slow, this method has the advantage of working irrespective of the asteroid composition, structure or spin rate.

The gravity tractor method leverages the mass of the spacecraft to impart a gravitational force on the asteroid, slowly altering the asteroid's trajectory. A circular (helical) orbit located in front of the asteroid, prevents the exhaust from the spacecraft from hitting the asteroid, which would negate the forward pull of the spacecraft.

The crew segment of the mission ARCM would have included spacewalk activities for sample selection, extraction, containment and return; and mission operations of integrated robotic and crewed vehicle stack - all key components of future in-space operations for human missions to the Mars system.

Robotic sampling arm and capture mechanism to collect a multi-ton boulder from an asteroid are under development at NASA Goddard and other agency centers. Credit: Ken Kremer/kenkremer.com

The concept animation video below opens with a rendering of the mission's spacecraft trajectory, rendezvous, and approach to asteroid 2008 EV5. The animation concludes with the notional crew operations that would have taken place after the asteroid boulder was placed in lunar orbit.

x YouTube Video

In 2016-17, the House Appropriations Committee decided to block funding for NASA’s Asteroid Redirect Mission (ARM). The sub-committee explained that decision by saying “The Committee believes that neither a robotic nor a crewed mission to an asteroid appreciably contribute to the overarching mission to Mars.”

Mars over civilization-destroying asteroids?

Epilogue

From en.wikipedia.org/… — While the chances of a major collision are low in the near term, it is a near-certainty that one will happen eventually unless defensive measures are taken. In April 2018, the B612 Foundation reported "It's 100 percent certain we'll be hit by a devastating asteroid, but we're not 100 percent sure when." Also in 2018, physicist Stephen Hawking, in his final book, Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet.

That’s not much the average person can do for planetary defense against marauding asteroids, but it helps to be aware and knowledgeable about asteroids, comets and the science of our solar system. Let’s support our scientists and various R&D efforts in this area and let’s impress upon our lawmakers that a few billion dollars spent on planetary defense will do lot more for humanity than the trillions we spend on the military and on high-tech weapon systems.

Please join us tonight as we view the culmination of this historical and exciting mission. Please feel free to post additional info, your opinion and your questions on this mission and its underlying objectives.

References

Double Asteroid Redirection Test (DART) Mission — www.nasa.gov/... Double Asteroid Redirection Test (DART) — en.wikipedia.org/… DART at APL — dart.jhuapl.edu Double Asteroid Redirection Test (DART) Mission Design and Navigation for Low Energy Escape — trs.jpl.nasa.gov/… The Double Asteroid Redirection Test (DART): Planetary Defense Investigations and Requirements — iopscience.iop.org/... 65803 Didymos (1996 GT) — ssd.jpl.nasa.gov/... Center for NEO Studies (CNEOS) — cneos.jpl.nasa.gov NEO Earth Close Approaches — cneos.jpl.nasa.gov/… (database of NEOs, default view shows upcoming NEOs) Near-Earth Object Survey and Deflection Analysis of Alternatives — Report to Congress (2007) — cneos.jpl.nasa.gov/… National Near-Earth Object Preparedness Strategy and Action Plan (2018) — www.nasa.gov/... Asteroid impact avoidance — en.wikipedia.org/... Enhanced Gravity Tractor Technique for Planetary Defense — ntrs.nasa.gov/… 5 Planetary Defense Systems That Could Keep Us Safe From Asteroids — interestingengineering.com/… Asteroids and Planetary Defense — www.dailykos.com/… NASA launches DART, the planetary defense test mission, which will ram into an asteroid in 2022 — www.dailykos.com/… It's Asteriod Day 2021. Let's talk and learn about Asteroids, Comets and Planetary Defense — www.dailykos.com/...

Link to webcast starting at 6:00 p.m. EDT —

This feed shows just the images from DART without commentary, starting at 5:30 p.m. EDT. Updated very second.

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