Aerospace and Electronic Systems - April 2019 - 3

MISSION ANALYSIS FOR THE EM-1 CUBESATS EQUULEUS AND OMOTENASHI
EQUULEUS is a Lunar L2 orbiter and a 6-Unit CubeSat by JAXA and the University of Tokyo. OMOTENASHI is a 6Unit CubeSat by JAXA, the world's smallest Lunar lander. EQUULEUS and OMOTENASHI are among the 13 secondary payloads selected by NASA to be launched with Exploration Mission-1 in 2019. Despite their limited size and cost,
EQUULEUS and OMOTENASHI are challenging missions, especially in terms of trajectory design and control. EQUULEUS exploits the Earth-Sun-Moon chaotic dynamics and enters a libration point orbit around the L2 of the Earth-
Moon system, using a new water propulsion system with low thrust and little propellant. This "Orbit Control
Experiment" is one of the main objectives of the mission. OMOTENASHI executes a semihard landing that requires
breaking the spacecraft to a stop just a few hundred meters above the Moon's surface. Both missions present new and
unique challenges, where the design of the nominal trajectory is mainly driven by the constraints on orbital control capabilities, and operational and robustness considerations. This paper presents the current notional trajectories, and gives an
overview of the new techniques developed for their design.

DEEP SPACE NETWORK IN THE CUBESAT ERA
As the CubeSat era moves from low Earth operations to beyond geostationary orbit into Deep Space, many changes to
NASA's Deep Space Network's (DSN's) operating paradigm will be required. The DSN is made up of three communication complexes spaced approximately 120 degrees apart around the world that have a set of high-performance antennas
which track (providing uplink and downlink services) spacecraft from geostationary orbit to beyond the edge of the solar
system. CubeSats will usually start their missions as secondary payloads in a launch, generally with multiple CubeSats
being released from a launch vehicle over a short period of time; this a time period when the majority of the DSN assets
(e.g., antennas) will likely be supporting the primary spacecraft that will accompany the CubeSats on the launch vehicle,
leaving a limited number of assets for use for the CubeSats. When the CubeSats are initially released, they will all be in
the beamwidth of the ground antenna assigned by the DSN to track them. To allow a single antenna to track several
CubeSats simultaneously, frequency diversity in the CubeSat downlinks can be employed; however, only one spacecraft
at a time will be able to get an uplink. Enhancing the existing techniques that the DSN currently uses daily for Mars missions to provide greater flexibility in the CubeSat era, is one of the changes that the DSN is presently addressing. Additionally, future changes in the CubeSat transponders may allow further enhancement of initial acquisition challenge, as
may other changes that could be done in the DSN. As the CubeSats transition to nominal operations, other challenges
will need to be addressed, such as minimizing the resource scheduling overhead for the missions and maximizing the
CubeSats' usage of the limited DSN resources. This paper will discuss the challenges in the DSN support for CubeSats
and the planned and potential changes to both the DSN and CubeSats to increase the CubeSat data return.

APRIL 2019

IEEE A&E SYSTEMS MAGAZINE

Aerospace and Electronic Systems - April 2019

Table of Contents for the Digital Edition of Aerospace and Electronic Systems - April 2019