The Hayabusa 2 ion engine fired up today, May 12, at 7:00 JST (onboard time). Aboard the spacecraft, samples collected from the asteroid Ryugu which orbits the sun between the planet Mars and Jupiter. The collection of samples that may contain the evidence of life took exhaustive work to obtain. Scientists think asteroids like Ryugu hold secrets about how the early solar system developed and life took hold on Earth.
The spacecraft arrived at the asteroid Hayabusa 2 launched December 3rd, 2014 and arrived at asteroid Ryugu on 27 June 2018 and remained at a distance of about 20 km to study and map the asteroid. Hayabusa 2 probe deployed several hopping devices on the surface allowing collection of rare pictures from the surface of an asteroid. The smaller spacecraft identified a rock-strewn surface, potentially hazardous for close approach.
In 2019, after much deliberation, the team located a site for collecting samples from the asteroid. During the daring approach, the Hayabusa 2 mission shot a bullet at the asteroid. The bullet penetrated the surface of the asteroid and the probe collected ejected material from the impact region.
Asteroids crash course
Most asteroids fall in the main asteroid belt and cluster together by the immense pull of the Planet Jupiter. As the planet Jupiter orbits the sun at a distance of roughly 5 AU or about 5 times further than Earth. The main asteroid belt sits with the orbit of Jupiter, closer to the sun. The clusters group together in a ratio of the orbit of Jupiter. Over the billions of years for our solar system, the gravity of Jupiter pulled at the asteroids. The strength of that pull relates to the mass of Jupiter and the mass of the asteroid along with the square of the distance. Voids between the clusters of asteroids occur at the 2:1, 3:1, 5:2, and 7:3 orbital resonances, otherwise known as the Kirkwood Gaps.
Scientists also classify asteroids by what materials they contain. Keep in mind that the classification of asteroids keeps evolving as our understanding of asteroids improves. Scientists developed several classifications schemes over the years group the asteroids by composition and albedo. The three broad composition classes of asteroids include:
The C-type: carbonaceous or chondrite asteroids are most common. Based on limited data collected, scientists believe the C-types probably include large amounts of clay and silicate rocks. These asteroids also reflect little light since the dark appearance tends to low albedo. Indications suggest their age ranks them among the most ancient objects in the solar system. Ryugu falls in this classification.
The S-types (“stony”) consist of silicate materials and nickel-iron.
The M-types are metallic (nickel-iron). Scientists hypothesize some experienced high temperatures after they formed. The high temperatures resulted in partial melting of the asteroids, allowing the iron to sink and forcing basaltic (volcanic) lava to the surface.
Japan’s focus of this mission isn’t one of these asteroids that make up the main asteroid belt. Rather, the mission explored a different classification of asteroid called Near-Earth Objects. Ryugu’s orbit brings it closer to Earth than many other asteroids and therefore atypical of common asteroids that sit between the Kirkwood gaps. Ryugu’s C-type makeup makes it an interesting target for science since the proximity to Earth makes accessing it easier. Typically, C-type asteroids are about 3.5 AU from the sun. Ryugu, by comparison, is between 1.4 and 1.2 AU. That means the asteroid can be within 2/10th AU of the Earth.
JAXA discovered the asteroid has a spinning top look to it rather than a round look.
The spacecraft long burn
JAXA confirmed the spacecraft’s condition as normal as it set course back to Earth. The Hayabusa 2 collects power from the Sun using its twin solar panels. The engine fired up and started spewing charged ions out the rear of the spacecraft.
Ion thrusters differ from chemical thrusters as only one propellent rather than an oxidizer and propellent. The process works by adding or removing electrons to produce ions. Thrusters typically ionize propellant through electron bombardment. The plasma produced keeps some properties of a gas, but it is affected by electric and magnetic fields. The engine produces the field and shoots the charged gas out the back creating thrust.
Although highly efficient, Ion engines produce relativity low thrust when compared to chemical engines. This high efficiency allows the engine to run for prolonged periods of time, slowly producing thrust to speed up the spacecraft. Missions like Hayabusa 2 are suited well for ion drives since the engine can operate for long periods of time and reduce the overall cost. The reduction in cost predominantly stems from less propellent required to be launched from Earth. Chemical rockets still shine when the high thrust requirements of launching from Earth are considered.
The 2nd phase of the ion engine operation continues until around September 2020. Hayabusa 2 at that point can deliver the sample capsule to Earth. Until the sample touches down, scientists will wait and hope that none of a million potential issues prevent the spacecraft from returning to Earth.
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.
