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An Asteroid Deflection Investigation

Yesterday’s post on what we’re learning about Rosetta’s comet (67P/Churyumov–Gerasimenko) briefly touched on the issue of changing the orbit of such bodies for use in resource extraction. Moving the comet Grigg-Skjellerup is part of the plot of Neal Stephenson’s novel Seveneves, where the idea is to support a growing human population in space with the comet’s huge reserves of water. Just how hard it would be to move a comet is made clear by how a proposed near-term mission approaches the question of deflecting a small asteroid.

The mission, discussed at the ongoing European Planetary Science Congress in Nantes, is called AIDA, for Asteroid Impact and Deflection Assessment. A joint mission being developed by the European Space Agency and NASA, AIDA is actually a two-pronged affair. ESA is leading the Asteroid Impact Mission (AIM), while NASA is behind the Double Asteroid Redirection Test (DART). The plan is to rendezvous with the asteroid (65803) Didymos and its tiny satellite (known informally as ‘Didymoon’) for scientific study and a deflection test.

Think about this comparison: Comet Grigg-Skjellerup (studied by the Giotto probe in 1992, though from a considerable distance) is approximately 2.6 kilometers in diameter. Didymos is about 750 meters in diameter, and the Didymoon about 160 meters across. It’s the Didymoon that ESA and NASA plan on deflecting, driving the DART spacecraft into it as AIM observes and analyzes the plume of ejected material. With AIM remaining on the job, further mapping and monitoring will study the impact area and reveal any changes in Didymoon’s orbit.


Image: Arrival of AIM at Didymos and Didymoon. Credit: ESA.

Thus the spread between a near-future science fiction story (the acquisition of Grigg-Skjellerup for resources in Seveneves) and present-day technology — we can assume that Stephenson’s comet-catcher has some powerful propulsive assets compared to what we can deploy today. But the novel explains all this on its own terms and I’ll say no more about it. As to AIDA, the words of Patrick Michel give us the gist. Michel is lead on the AIM Investigation team:

“To protect Earth from potentially hazardous impacts, we need to understand asteroids much better – what they are made of, their structure, origins and how they respond to collisions. AIDA will be the first mission to study an asteroid binary system, as well as the first to test whether we can deflect an asteroid through an impact with a spacecraft. The European part of the mission, AIM, will study the structure of Didymoon and the orbit and rotation of the binary system, providing clues to its origin and evolution. Asteroids represent different stages in the rocky road to planetary formation, so offer fascinating snapshots into the Solar System’s history.”


Image: Impact on Didymoon, as observed by AIM and its deployed CubeSats. Credit: ESA.

AIM would launch in October of 2020, with rendezvous at (65803) Didymos in May of 2022. Didymos rotates rapidly, about once every 2.26 hours, and is considered the most accessible asteroid of its size from Earth. Didymoon orbits Didymos every 11.9 hours at an altitude of 1.1 kilometers — the name Didymos (Greek for ‘twin’) was chosen by astronomer Joe Montani, who discovered the objects, when light-curve analysis revealed the binary nature of the asteroid. While Didymos is thought to be a ‘chondrite’ (stony) asteroid, we know nothing about the mass and density of Didymoon, a lack that AIM and DART would be able to correct in short order.

The AIM mission has echoes of Rosetta, for like the latter, it carries a lander. MASCOT-2, built by the German aeronautics and space research center (DLR) will probe the internal structure of Didymoon, emitting low-frequency radar waves that will pass through the object, allowing AIM to chart the deep structure of the asteroid even as it measures Didymoon’s density and maps the surface at visible and infrared wavelengths. DART’s impact with Didymoon is scheduled for October of 2022. I also notice that AIM is scheduled to deploy three CubeSats to assist with impact observations and to test communication links between satellites in deep space.

DART itself is a 300 kg impactor that is designed to carry no scientific payload other than a 20-cm aperture CCD camera to support guidance during the impact approach phase. Launch is currently proposed for July of 2021. The impact at 6.25 kilometers per second is expected to produce a velocity change in the range of 0.4 mm/s, which should change the relative orbit of Didymos and Didymoon but create only a slight change in the binary’s heliocentric orbit.

Related: NASA has funded a concept design study and analysis for a mission called Psyche, which would investigate the interesting asteroid of the same name. Psyche is thought to be the survivor of a collision with another object that stripped off the outer layers of a protoplanet. About 200 kilometers in diameter, it is thought to be the most massive M-type asteroid, with a surface that is 90 percent iron. The Psyche mission, led by Linda Elkins-Tanton (Arizona State) would be an orbiter that would launch in 2020 and arrive in 2026.


Comments on this entry are closed.

  • ljk October 1, 2015, 13:23

    The Planetary Society blog post on the Discovery class mission to Psyche:


    Anyone who is not excited about this planetoid on multiple levels appreciates neither planetary science nor the possibilities it offers for colonizing the Sol system.

    Details on the five proposed missions – two of them to Venus:


    Yet still no mission plans for this enigmatic world that looks like an egg!


  • Hop David October 1, 2015, 14:38

    I’m excited that there seems to be a growing interest in water. Living at the bottom of a gravity well covered with water, it’s easy to discard the value of H2O.

    Extra-terrestrial propellent sources could do away 16 or 20 km/s delta V budgets. The present delta V budgets mandate extremely difficult dry mass ratios. When Tsiolkovsky says you need to be 96% propellent and 4% dry mass, structure is scaled back to gossamer and moon beams. One way to achieve difficult fraction that is to throw away dry mass enroute — disposable spaceships is a major factor driving up the cost of spaceflight.

    In my opinion there are 3 possible extra terrestrial propellent sources.

    1) Cometary. Comets could well have massive deposit of volatile ices. But they’re hard to reach. A comet’s high aphelion means it’s moving very fast when in earth’s neighborhood. A comet with a 5.2 A.U. aphelion will be moving at least 38 km/s wrt sun when it’s 1 A.U. from the sun. Earth is moving about 30 km/s wrt sun

    2) Lunar. There may be massive deposits of volatile deposits in the lunar cold traps at the poles. This is still an open question. If so, these would be 2.5 km/s from EML2. In terms of delta V, EML2 is close to many destinations. See http://hopsblog-hop.blogspot.com/2015/05/eml2.html

    3) NEAs. There are many Near Earth Asteroids very close to the earth moon neighborhood in terms of delta V. Many of these accessible asteroids are carbonaceous ivunas with can be up to 40% water by mass. But this water is in the form of hydrated clays, more difficult to extract than water in the form of ice. Another problem with the accessible NEAs is rarity of launch windows. Let’s say it takes 10 missions to establish a propellent mine on an NEA. If launch windows occur each 10 years, it would take a century to establish the mine. However parking a small NEA in lunar orbit is doable. Then launch windows would be very frequent. Trip time from earth less than a week. Light lag latency about 3 seconds. And proximity to earth gives a much higher bandwidth than an object in heliocentric orbit since signal strength falls with inverse square of distance.

    At the moment I’m most enthused about water from NEAs but also excited about the possibility of lunar ice. Comets? Not so much, at least near term.

  • Hop David October 1, 2015, 16:34

    ijk, of those 5 missions, I’m enthused about NEOcam. Getting a better inventory of near earth asteroids is good for planetary defense as well as future efforts to mine asteroids.

    I’m also excited about Lucy. Science fiction writer William Barton has described the Sun Jupiter l4 and l5 regions as the solar system’s Sargasso. I expect there’s a lot of interesting stuff in these regions. I am wondering if Lucy would orbit bodies at the L4 and/or L5 or just fly by.

    Marshal Eubanks was also enthused about a Psyche mission to a metallic asteroid. Something that is evidently a fragment of a differentiated body is of scientific interest, I’d agree. So far as colonizing the solar system, I would say water rich asteroids are of greater interest.

  • Andrew Palfreyman October 1, 2015, 17:02

    Manufacturing fuel outside our gravity well sounds like a useful proposition, and a natural candidate is a lunar base. So it makes sense to get asteroids into the vicinity.

    However, none of this is going to take off without cheap launches. For this we need something like StarTram and/or Skylon. And then we need to establish a web of DE-STAR style bidirectional beams between Earth, Moon, Mars and the Asteroid Belt to get it all moving out there with a much reduced dependence on fuel.

    It is just rather frustrating that these necessary developments are taking so long to come to fruition.

  • Alex Tolley October 2, 2015, 11:48

    There are a number of NEO that are [suspected] comets.
    If those delta-v’s are small enough, they would be good sources of water.

    However, we should also consider that water resources mining and supply infrastructure will become like that of the oil industry – mining, refining and moving the commodity to suitable locations using the lowest cost transport mechanism.

  • ljk October 2, 2015, 13:17

    The article makes it seem like NASA is being the villain here, but it would appear that the B612 Foundation is the one who stalled and failed to communicate during the process:

    Nasa pulls the plug on killer asteroid hunter: Sentinel mission set up to search for dangerous space rocks loses $30 million support

    Sentinel space telescope is being built by the private B612 Foundation

    It is intended to search for large asteroids from an orbit around the sun

    Nasa had pledged to provide analytical and data support worth $30 million

    But Nasa says it has terminated the agreement due to missed deadlines


    PUBLISHED: 11:18 EST, 30 September 2015 | UPDATED: 12:45 EST, 30 September 2015

    Full article here:


  • Michael October 3, 2015, 6:44

    I am wondering if a lot of small impactors would be better than one big hit i.e. shotgun style. Although a large dense mass would cause a deep crater it may not be the best idea in terms of moving an asteroid. Cracking the surface in multiple places to expose the volatiles below the surface would create a improved effect and if a chemical such as hydrogen peroxide is used instead potentially an explosive effect could be added to the energy budget.

  • Colorado October 6, 2015, 18:43

    I had some unpleasant dealings with B612 several years ago- I asked them about using hydrogen bombs and they flipped out on me. I was willing to invest personal time and money into their cause but they turned out to be not so much concerned with getting the job done as how to go about it. The main guy I talked to was downright rude. They have an agenda centered on a “gravity tug” and I had the impression they were completely closed to anything except the technology already decided upon. Ed Lu has taken over since then and I have read some of his releases and he seems focused on whatever works. But if they have people in the organization following a very narrow mission statement as they appeared to have had before- I can see how there would be problems.

  • Michael October 9, 2015, 10:02

    At some point in the future a nuclear device, fusion, will have to be used to determine the effectiveness of moving an asteroid. Chemical, gravity tugs etc. simply can’t match the power of these devices.

  • ljk October 9, 2015, 12:53
  • Michael October 10, 2015, 1:58

    @ljk October 9, 2015 at 12:53

    ‘Good article on the Psyche mission:


    Is there any way Dawn could be rerouted to Psyche? I am not sure of the amount of fuel left on Dawn.

    • ljk February 17, 2016, 10:39

      I do not think so. The plan is to hopefully “soft” land Dawn on Ceres at mission end, just like with NEAR on Eros in 2001.

  • Michael October 11, 2015, 1:18

    Here is a current map of the solar system, the number of objects out there is staggering! If you run the movie you can see how the objects move through the system. The asteroid belt offers a wealth of material to be had.


  • Michael October 11, 2015, 1:22

    A live site where you can see asteroid positions and other celestial objects.


  • ljk February 17, 2016, 10:43

    Twenty years ago today, NEAR was launched to become the first space probe to orbit a planetoid and eventually soft-land on it:


  • ljk February 17, 2016, 10:56

    Russia wants to use Cold War era weapons technology to deflect Apophis when it gets near Earth in 2036: