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Janus: Twin Spacecraft to Study Binary Asteroids

When we looked earlier this week at the Solaris mission, a concept designed to study the Sun’s polar regions, I commented on another early concept called the Auroral Reconstruction CubeSwarm (ARCS). The mission intrigued me because it consisted of CubeSats in swarm formation, working together with numerous ground observatories, to study the Earth’s auroras. The paradigm of miniaturization, low cost and creative design surfaces yet again in Janus, a proposal out of the University of Colorado at Boulder and Lockheed Martin that would involve twin spacecraft studying twin targets, the binary asteroids 1996 FG3 and 1991 VH.

Daniel Scheeres (CU-Boulder) is principal investigator for Janus, the plan being for the university to handle the analysis of data and images from the mission, with Lockheed Martin building and operating the two spacecraft. It should be a familiar role for both entities, as Lockheed Martin supports operations for OSIRIS-REx at asteroid Bennu, while Scheeres leads the radio science team for that mission. Each Janus spacecraft is roughly the size of a suitcase, a carry-on at that, echoing the theme of keeping spacecraft small and straightforward.

Lockheed Martin’s Josh Wood is project manager for Janus:

“We see an advantage to be able to shrink our spacecraft. With technology advancements, we can now explore our solar system and address important science questions with smaller spacecraft… We see this evolution to smaller and more capable spacecraft being a key market in the future for scientific missions. Now, we want to execute and show that we can do it.”

Lowering costs and preparation time by using off-the-shelf components is all part of the same parameter space that supports the movement toward CubeSats and so-called SmallSats. The mission will be part of NASA’s SIMPLEx program, which focuses on small spacecraft and satellites, and is projected to cost less than $55 million.

The twin Janus spacecraft have a long journey ahead, with a gravity assist at Earth following an initial solar orbit and a subsequent trajectory that takes them beyond the orbit of Mars. The craft are to use VACCO MiPS (Micro-Propulsion System), a low-cost, cold gas propulsion option designed for CubeSats consisting of five thrusters for pitch, yaw, roll and delta-v.

Malin Space Science Systems is to provide the instrument suite including visible and infrared cameras, with power delivered by three deployable solar arrays and batteries. Launch is to be in 2022, with the twin craft lofted as secondary payloads on a Falcon-Heavy (Block 5) in the same launch that will carry the Psyche and EscaPADE missions.

From a short summary presented at the 51st Lunar and Planetary Science Conference (2020):

Janus science will combine flyby observations of the target binary asteroids with ground-based observations, enabling the high resolution imaging and thermal data to be placed into a global context and leveraging all available data to construct an accurate topographical and morphological model of these bodies. Based on these measurements, the formation and evolutionary implications for small rubble pile asteroids will be studied.

Image: Rendering of the orbital pattern of the binary asteroid 1999 KW4. We have much to learn about binary asteroids. (Credit: NASA/JPL).

Binary asteroids have yet to be studied up close, but this is a configuration that represents about 15 percent of the asteroids in the Solar System. Says Scheeres:

“We think that binary asteroids form when you have a single asteroid that gets spun up so fast that the whole thing splits in two and goes through this crazy dance… Once we see them up close, there will be a lot of questions we can answer, but these will raise new questions as well. We think Janus will motivate additional missions to binary asteroids.”


Comments on this entry are closed.

  • Alex Tolley September 11, 2020, 17:19

    “We think that binary asteroids form when you have a single asteroid that gets spun up so fast that the whole thing splits in two and goes through this crazy dance…”

    When the split happens, doesn’t the primary lose angular velocity? Then gravitational attraction can pull the ejected piece back, and the whole process can repeat?

    When we saw the Kuiper belt object Arrokoth, it looked like 2 pieces joined, with circular marks perhaps suggesting previous joins. Could they indicate the multiple ejection and rejoining of a binary?

    It makes one wonder that had conditions been very different, that the Earth-Moon system could possibly have become such a contact binary, periodically separating and joining. Has anyone ever seen such a thing in computer simulations of planetary formation? If nothing else, it would make an interesting and novel scenario for a scifi plot background.

    • Bruce D Mayfield September 12, 2020, 11:39

      A solid contact binary can only form if there is insufficient mass for both bodies to achieve hydrostatic equilibrium. The Earth would have pulled the Moon into itself if they had ever come in contact with each other, since the Earth’s crust and mantle couldn’t have supported the Moon’s weight. The same would be the case even for the much less massive “double planet” pair of Pluto-Charon.

      • Alex Tolley September 13, 2020, 17:48

        Thanks Bruce. I did try to come up with a condition that would allow the Earth and Moon to be a contact binary, literarlly gently kissing each each other, but you are quite right, it cannot be done. Glad to be corrected on that speculation.

  • Geoffrey Hillend September 12, 2020, 16:26

    Your correct about the angular momentum and torque increasing causing a single asteroid to separate due to the heat from sunshine, and the moon of the asteroid could in potential crash back onto the larger body and the process could start over. The same thing doesn’t apply to larger bodies and certainly not as large as the Moon and Earth because the gravity holds these to together, but bodies smaller than asteroids and maybe planetesimals have low gravity compared to the torque and centrifugal force during spinning.

    • Jeff Wright September 13, 2020, 1:04

      Binaries might allow artificial gravity if they are wrapped and cable bound one to another and the tether tightened, right?

      I think you will need this for mining

    • charlie September 13, 2020, 21:05

      Now I’m not positively, absolutely certain about this following statement – but I believe that if two bodies fracture in which there is a rotational angular momentum associated with the initial primary, upon separation the larger spinning body will actually LOSE angular momentum when the smaller secondary body fractures away from it.

      Wouldn’t that be correct for the simple reason that the secondary body would carry away some of the angular momentum from the original un-fractured primary?

  • Wojciech J September 12, 2020, 21:41

    Heads up. There is a lot of chatter about supposedly significant astrobiology related discovery being announced this Monday by Royal Astronomical Society. The press release is embargoed, but I managed to dig out that it is not Mars related, and most likely concerns possible microbial life in clouds of Venus. We will see.


  • Michael September 14, 2020, 9:46

    I don’t really buy the spin up theory, could it not be micro meteors impacting the main body ejecting material that forms a stable object in orbit over time instead.