NEC played a leading role in the development and manufacture of the Hayabusa2 asteroid explorer, not only designing the system, integrating equipment, conducting tests, and providing operational support, but also coordinating the development of the subsystems for the spacecraft’s structure, thermal, power supply, telecommunications, data handling, attitude/orbit control, ion engine, electric instrumentation, and sampling systems. NEC supplied some of the components for these subsystems as well as several of the observation devices. This paper discusses the role NEC played in the Hayabusa2 project and discusses operational scenarios and results in the vicinity of asteroid Ryugu as well as the factors that contributed to the mission’s success.

1. Introduction

As it did with the first Hayabusa, NEC supplied many subsystems and devices to the Hayabusa2 asteroid explorer and took responsibility for much of the project’s system design, integration, testing, and operational support. More reliable and more functional than the first Hayabusa, Hayabusa2 was launched in December 2014, arriving at the asteroid Ryugu in 2018. From June 2018 to December 2019, it conducted asteroid proximity operations and brought back a re-entry capsule to Earth in December 2020. This paper introduces Hayabusa2’s system, operational results, and factors that contributed to the success of the mission.

2. Structure of the Spacecraft

An external view of the Hayabusa2 is shown in Fig. 1 and Fig. 2. All devices marked with a black circle (•) were the responsibility of NEC. The main differences from the first Hayabusa are that the high gain antenna was changed from parabola to a radial line slot array antenna and that a Ka band antenna (down link bit rate increased by a factor of 4) was provided in addition to the X band antenna.

Based on the assumption that Haybusa2 approach the asteroid from Earth’s direction (nearly equal to the Sun’s direction), the solar array paddles and high gain antennas were installed on the top, whereas the sensors to observe the asteroid and the other devices that would be released and deployed on the asteroid as well as the sampler horn were installed on the bottom.

Also assuming that the change in velocity (delta-v) would take place perpendicular to the sun, the thrust direction of the ion engine system (IES) was set in an almost perpendicular direction to the sun. The IES’s thrusters were mounted on two-axis gimbals. By changing the thrust axis around the center of gravity of the spacecraft, two-axis torque control by the IES was made possible. This was also used in the unloading (rotation speed adjustment) of the reaction wheel for attitude control.

NEC supplied almost all of the devices installed inside the spacecraft in addition to those mentioned earlier. The subsystems that NEC was responsible for are listed here.

In addition to these, we also conducted the overall system design, integration, and testing, as well as operations support including the devices made by other companies such as science payloads, the reaction control system (RCS) and the Xe supply system.

3. Planned Touchdown Scenario

The touchdown scenario we had originally planned before Hayabusa2 arrived at asteroid Ryugu was as follows.

4. Shape of Asteroid Ryugu

An external view of asteroid Ryugu is shown in Photo 1. The entire surface was covered with rugged boulders. Nowhere could we find a flat area measuring 100 m in dimeter that we had assumed would be found.

Other features of Ryugu are as follows.

5. Proactive Measures for the First Touchdown

We took the following measures proactively to deal with any unforeseen situations.

The dropped TM and its environs are shown in Photo 2.

6. The First Touchdown

Our proactive measures were effective and the Hayabusa2 successfully touched down on Ryugu at 7:29 JST on February 22, 2019. The asteroid’s surface was nothing like we anticipated. The surface was very friable, and fragments flew up like swirling confetti. These fragments were very black and dirtied the lenses of the optical sensors. The LRF was especially affected. Subsequent checks showed that its distance measurement range had been reduced and that the distance measurement characteristics also changed.

7. Proactive Measures for the Second Touchdown

After creating an artificial crater with the SCI, Hayabusa2 made a second touchdown in a location where subsurface material was likely present. A view of the artificial crater is shown in Photo 3 and Photo 4.

We took the following proactive measures to support the second touchdown.

8. Results of the Second Touchdown

The second touchdown was successfully completed at 10:06 JST on July 11, 2019. This resulted in two achievements unprecedented in space exploration: sampling from two locations and access to underground material.

9. The Elements of Success 1: Careful Preparation

A lot more work went into preparing the Hayabusa2 for landing than was the case with the original Hayabusa.

10. The Elements of Success 2: Teamwork That Produced Results

Teamwork is critical to success and in this case everyone was involved in the operations.

11. Conclusion

Hayabusa2’s re-entry capsule returned safely to Earth on December 6, 2020, bringing with it a rich collection of material samples and gasses (5.4 g). The spacecraft is now on its way to asteroid 1998KY26 (with a diameter of 30 m and a rotation period of 10.7 minutes) where it is scheduled to arrive in July 2031. Prior to that, it is planned to fly by asteroid 2001CC21. Building on the experience gained in the development and operation of Hayabusa and Hayabusa2, NEC will continue to develop systems for deep space exploration and asteroid exploration.

Finally, we would like to express our gratitude to JAXA who has guided and supported NEC throughout the development process and the actual mission operations.

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