IEEE - Aerospace and Electronic Systems - September 2019 - 21

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for radio landmarks for human exploration missions. The
Japanese word "omotenashi" means hospitality, and the technologies developed by the project will welcome newcomers
and help them to participate in exploration.
To realize a spacecraft within 14 kg and of 6U CubeSat
size, various new technologies had to be developed. A notable challenge is that the smaller the spacecraft, the more
dominant the mass of the structure and bus components. For
example, a propulsion system that would allow an entire
14-kg spacecraft to land on the lunar surface could not be
realized within 6U size; therefore, it is essential to minimize
the landing mass. The current mass allocation for a surface
probe (i.e., the landing part) is 715 g. Considering the specific impulse ðIsp Þ and dry mass of the propulsion system, a
solid rocket motor is used to decelerate from an orbital
velocity of roughly 2.5 km/s. Moreover, even the ignitor of
the solid rocket motor should separate just after ignition to
reduce the deceleration mass, and a laser ignitor is introduced to realize this concept.
Since the thrust magnitude of a solid rocket motor cannot
be controlled after its fabrication, an error of a few tens of
meters per second at impact on the lunar surface should be
considered. To withstand a high-speed impact, shock absorption mechanisms are needed, for which we employ three
types of technology, namely, an airbag, a crushable material,
and epoxy filling. The airbag uses the same material and
inflation mechanism as did the EGG Project, an inflatable
aeroshell for reentry, the deployment of which was demonstrated from the International Space Station in 2017 [5].
Microminiaturization of the telecommunication system is another important development. A radiation power
of 1 W is required for the Earth-Moon link, but nevertheless the size, mass, and power consumption should be
minimized. Based on the transponder for the PROCYON
SEPTEMBER 2019

Spacecraft (launched in 2014) [6]-[8], a new X-band
transponder has been developed that has a mass of a 100 g
and will consume roughly 10 W. A small and smart
onboard computer system has been developed based on
the MINERVA2 asteroid landing probe that was deployed
from the HAYABUSA2 spacecraft in 2018 [9].
This paper presents the mission objectives, mission
sequence, spacecraft configuration, and some technologies
newly developed for OMOTENASHI.

MISSION OBJECTIVES
As described in INTRODUCTION section, the main mission of OMOTENASHI is to show that a CubeSat can
make a semihard landing, after which future missions can
use not only the spacecraft system but also some of the
newly developed technologies, such as the small solid
rocket motor, the telecommunication system, the airbag,
and the crushable material. Because the semihard landing
itself has a relatively low probability of success, full
success of the mission is defined in relation to whether the
landing sequence is executed normally; landing safely on
the surface is defined as extra success.
The proposed scientific mission is to measure the
radiation environment of the cislunar region. Strategic
Knowledge Gaps (SKGs), that is, the knowledge needed to
reduce the risk of human exploration, have been discussed
internationally and are summarized in the Global Exploration Roadmap (GER) ver. 2 [10] of the International Space
Exploration Coordination Group (ISECG). Table 1 lists the
SKG for lunar exploration. It is essential to measure the
radiation environment beyond low Earth orbit to support
radiation risk assessments for astronauts and establish a
benchmark for space radiation models for human space
activities on the Moon and in the nearby region.

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IEEE - Aerospace and Electronic Systems - September 2019

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