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Number 1 Shimbun

Exploring Other Exploring Other Worlds with JAXA’s Worlds with JAXA’s Deep Space Fleet

No1-2018-08 04

Exploring Other Exploring Other  Worlds with JAXA’s Worlds with JAXA’s Deep Space Fleet


Traveling more than three billion kilometers in order to grab a bunch of rocks from a small diamond-shaped asteroid and then returning home to complete a six-year round trip can only be described as one audacious adventure. That adventure, still in the making, began when Japan Space Exploration Agency (JAXA) launched the Hayabusa2 space probe on an H-2A rocket from Tanegashima Space Center in 2014.

After 1,302 days speeding through space, the probe arrived at the target asteroid, named Ryugu, on June 27. Currently, the spacecraft is slowly descending to observe Ryugu’s surface from as close as five kilometers. By the end of August JAXA will decide on a suitable place for the explorer to touch down and in September or October the delicate maneuver of landing Hayabusa2 on the dusty, boulder-strewn surface will begin.

What could go wrong? The asteroid’s weak gravity could see the craft bounce back into space. But if all goes according to plan, Hayabusa2 will land and take off up to three times on Ryugu during a period of 18 months. This will enable it to study conditions at different locations as the asteroid orbits around the Sun.

After the craft completes its long sojourn of picking, prodding and probing the asteroid’s surface, it will head back home. As it approaches Earth in late 2020, a capsule carrying its valuable crustaceous cargo will detach itself from the spacecraft and a parachute will deploy at an altitude of 10 kilometers to make a soft landing, perhaps in Australia if JAXA can negotiate permission. Meanwhile, Hayabusa2 will swing by our planet and continue traveling in space, possibly for eternity.

But why go to all this trouble, not to mention US$300 million in travel expenses, for only a handful of rocks? The answer is that asteroids happen to be some of the most primitive objects in our neck of the universe. So the samples brought back could tell us a lot about how our solar system was formed. Even more enticing, Ryugu is a Type C asteroid apparently packed with carbon and other organic materials containing water; consequently, this bunch of rocks might also help us learn how life on Earth came into existence.

The Hayabusa2 mission began four years after the first probe, Hayabusa (Japanese for peregrine falcon) returned to Earth in 2010. Hayabusa made two landings on another asteroid named Itokawa — this despite experiencing a series of equipment glitches, including problems with all four of the spacecraft’s engines; the failure of two of its three reaction wheels used to orientate the spacecraft; and a disappointing malfunction of the sampling mechanism, which limited the collecting of samples to mere grains rather than rocks.

Nevertheless, despite these issues, JAXA deemed Hayabusa an impressive achievement, for it was still able to limp back with 1,500 particles from Itokawa — the first time asteroid samples had been captured and brought back to earth for analysis.

According to Hitoshi Kuninaka, vice president and director general of JAXA’s Institute of Space and Astronautical Science, the agency learned much from that first operation. After Hayabusa2 rendezvoused with Ryugu, Kuninaka came to the Foreign Correspondents’ Club of Japan in July to brief the press on the new mission and to describe some forthcoming expeditions JAXA is planning. He was joined by Makoto Yoshikawa, mission manager of the Hayabusa2 project.

To strengthen the reliability of the craft and hopefully score even greater success than achieved by the first expedition, JAXA has modified several parts of Hayabusa2 and added new equipment. As a result, Hayabusa2 tips the scales at 609 kilograms, about 100 kilos heavier than its predecessor, though its 1 x 1.6 x 1.25-meter dimensions are not much larger than those of the first probe.

While chemically fueled rockets have tra- ditionally powered spacecraft, they require extravagant amounts of propellant. Given the small sizes of the Hayabusa and Hayabusa2, such a means was unfeasible from the start. Instead, JAXA has developed its own electric propulsion ion engine. Microwaves are used to generate ions (charged atoms) from xenon gas. The ions are then accelerated using an electric field and expelled at high speed to pro- vide the thrust that propels the craft forward.

Kuninaka noted that although this type of propulsion provides less raw power than standard chemical propulsion — each probe required a rocket to launch it into space — it is highly efficient and can maintain acceleration for a long time on relatively little propellant. Following JAXA’s improvement of Hayabusa2’s engine and durability, “the system can now achieve a velocity of over 30 kilometers a second compared to five kilometers a second for conventional chemical propulsion,” says Kuninaka. “So Hayabusa2 is able to reach the asteroid Ryugu and return to earth on just 60 kilograms of propellant — one-tenth the weight of the craft.”

Concerning the craft’s communications with Earth, mission manager Yoshikawa notes that the first space probe employed a large, bulky parabolic X-band antenna. This has been replaced with two smaller but equally powerful planar antennas that use different wavelengths that are better tailored for the different kinds of data being transmitted back to Earth. What’s more, this new set-up has the advantage of providing Hayabusa2 with a communications fallback should one of the systems fail.

Other important equipment packed on board includes a suite of cameras, a near-infrared spectrometer, a laser altimeter to measure the distance between probe and asteroid, asteroid sampling devices, and three small rover robots — compared with one rover on the first probe that was never deployed.

Two new additions are a novel impactor and a small lander containing several scientific instruments.

The impactor will release a high-speed projectile composed of an explosive copper plate to smash into the surface of Ryugu and form an artificial crater. JAXA then hopes to land the Hayabusa in the crater or close to it and pick up samples of the asteroid’s internal makeup – an enterprising experiment worthy of high praise if it succeeds.

The small lander was created jointly by the German Aerospace Center and the French National Center for Space Studies. Dubbed the Mobile Asteroid Surface Scout (MASCOT), it will change location once by jumping. It carries a wide-angle camera, spectroscopic microscope, thermal radiometer and a magnetometer to study composition of the aster- oid’s surface.

The craft’s electric power is generated by a two-winged solar array paddle system con- sisting of three panels per wing. This produces 1,460 watts to charge eleven inline-mounted 13.2 Ah lithium-ion batteries that supply power to onboard equipment as needed.

JAXA aims to have three traveling robots explore Ryugu’s surface: Rover-1A, Rover-1B, and Rover-2. They will be deployed via a MINERVA-ll minilander. Each of the first two concentric robots weighs approximately 1.1 kilograms with dimensions of 18 x 7 centime- ters. Each contains a wide-angle and a stereo camera; a temperature sensor and photodiode; and an accelerometer and gyro. Power is supplied by solar cells, movement by means of internal flywheels.

The optional Rover-2 is some 45 percent taller than its two counterparts and contains similar equipment but also incorporates four types of mobility systems: two kinds of bucking mechanisms, an eccentric motor micro-hop mechanism, and a permanent magnet-type impact generation mechanism.

While all this is going on, JAXA is planning to launch several more space expeditions. On October 19, JAXA and the European Space Agency (ESA) will jointly launch two spacecraft — JAXA’s Mercury Magnetospheric Orbiter (MIO) and ESA’s Mercury Planetary Orbiter (MPO) — from French Guinea on an Ariane 5 rocket. The two agencies will cooperate to learn more about Mercury. MIO will study the planet’s mysterious magnetic field and how it interacts with harsh solar winds, given its proximity to the Sun, as well as study the planet’s magnetosphere. MPO will observe the planet’s surface and internal composition.

Then around 2020, just as Hayabusa is on its way home, JAXA will send its Smart Lander for Investigating the Moon (SLIM) to the moon. With SLIM, JAXA hopes to demonstrate pinpoint lunar landing techniques to pave the wave for future exploration missions on the moon and on other planets.

And possibly in 2024, we will see the launch of the Martian Moon Exploration Mission (MMX). JAXA aims to have MMX visit the two Martian moons, Phobos and Deimos, land on one of them, collect samples and return to Earth in 2029. Such samples could help astrophysicists understand how these moons originated.

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John Boyd covers the SciTechBiz scene in Japan as well as current events.

Published in: August 2018

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