Japan has finally launched its small satellite launcher Epsilon to deliver nine satellites to orbit. Notably, this includes the RAISE-2 technology demonstrator.
Previously delayed due to weather and a scrub, the launch from Uchinoura Space Center occurred at 00:55 UTC on Nov. 9.
The Japan Aerospace Exploration Agency’s (JAXA’s) RAISE-2 was the primary payload aboard the Epsilon rocket for this launch. It was joined by eight small satellites – four microsatellites and four CubeSats – on its ride to space. Now in orbit, the nine satellites will carry out an array of scientific and technology demonstration missions.
The launch, designated Epsilon 5, targeted a near-polar sun-synchronous orbit, at an inclination of 97.6 degrees to the equator. The final operational orbit for the RAISE-2 satellite is planned to be at an altitude of around 560 kilometers, although the initial deployment orbits for Epsilon’s payloads are expected to be a few kilometers higher than this.
Rapid Innovative Payload Demonstration Satellite No. 2, or RAISE-2, is the second in a series of small satellite missions that JAXA is sponsoring to research and develop systems and technologies for future missions. It follows the RAPIS-1 satellite, which launched aboard Epsilon in early 2019, with additional RAISE satellites planned to fly over the coming years.
Weighing in at 110 kilograms, RAISE-2 has a cuboidal shape measuring one meter along two axes and 0.75 meters along the third. Surface-mounted solar cells provide electrical power to the spacecraft, generating around 215 watts at the beginning of its mission. The satellite was constructed by the Mitsubishi Electric Corporation and has been designed to operate for about one year.
RAISE-2 carries six experiments that were selected from proposals by educational and commercial organizations.
SPR is based on Sony’s off-the-shelf SPRSENSE computer board – a compact, low-power board designed for Internet of Things (IoT) devices. During the RAISE-2 mission, its performance in the environment of space will be assessed. In the future, this may lead to using the board for automated positioning and control of satellites.
I-FOG, the In-orbit Demonstration of Closed-Loop Fiber Optic Gyro, was proposed by the Tamagawa Seiki Company. It will test a fiber-optic gyroscope, which looks for interference in light passed through a fiber-optic coil to determine changes in the satellite’s orientation, instead of relying on a conventional mechanical gyroscope. It is hoped that I-FOG will pave the way for low-cost, high-precision attitude inertial monitoring systems on future missions.
Likewise, the Amanogi Corporation’s ASC is a miniaturized star tracker designed to be mass-produced for attitude determination on CubeSats.
Mitsubishi Electric’s 3D-ANT will test a lightweight, low-cost 3D-printed metal antenna for telemetry and uplink of commands to the satellite. ATCD, developed by Tohoku University, is an unpowered thermal control device, designed to help regulate the temperature of satellites as they are exposed to extreme conditions in the vacuum of space.
Finally, JAXA’s MARIN inertial measuring unit is intended to be a lightweight, low-cost system to monitor the position, orientation, and movement of the satellite using microelectromechanical systems (MEMS). Its inclusion in the RAISE-2 mission is aimed at validating its performance when exposed to the space environment – particularly radiation.
Data gathered by the RAISE-2 mission will help to validate these experimental systems in space so they can be used on future missions. In doing so, JAXA aims to bring down the cost of small satellites, opening new opportunities for researchers.
Joining RAISE-2 for the journey to orbit aboard Epsilon are four microsatellites and four CubeSats, which were deployed from Epsilon’s upper stage after the primary payload has separated.
The largest of these is the Debris Removal Unprecedented Micro Satellite (DRUMS), a 62-kilogram spacecraft that will test techniques for capturing pieces of space debris to remove them from the space environment. DRUMS will deploy a small target subsatellite, which it will then move away from before returning to rendezvous using automated visual navigation systems. After maneuvering to a position two meters away from the subsatellite, DRUMS will deploy a boom to reach out and touch it – as a precursor to a tool that might be able to capture a piece of debris on a subsequent satellite.
TeikyoSat-4, also known as Ooruri, is a 52-kilogram scientific satellite built by Teikyo University. It is primarily designed as a technology demonstrator to validate its own systems as a bus for future scientific satellites and to carry out high-frequency communications experiments. The satellite carries a life sciences experiment aimed at growing a slime mold, known as Dictyostelium discoideum, in orbit to observe its progress and provide data to downlink.
The Tokyo Institute of Technology’s 55-kilogram HIBARI satellite will test a variable-shape attitude control (VASC) system. This relies on reaction torque generated when the satellite’s four solar array paddles are rotated. This is expected to allow the satellite to be reoriented more rapidly than would be possible with reaction wheels or control moment gyroscopes while retaining a high level of precision.
The mission aims to demonstrate an ability to rotate the satellite by 40 degrees in 20 seconds, although more ambitious extended goals call for a rotation rate of 40 degrees in 10 seconds. Onboard cameras will be used to verify the deployment and movement of the paddles, as well as the stability of the satellite by observing the position of stars.
To take advantage of this capability, HIBARI has a secondary mission to contribute to the research of gravitational waves once the initial demonstration objectives have been completed. When a ground-based observatory detects a potential source of gravitational waves, an alert will be uplinked to HIBARI via a communications satellite network. The spacecraft will then orient itself towards the detected source and image it with an ultraviolet camera system.
Mitsubishi Heavy Industries’ Z-SAT carries an experimental infrared imaging system that is intended to help detect heat sources on the planet’s surface. The 46-kilogram satellite carries near- and far-infrared cameras which will take observations at multiple wavelengths. These can then be combined to build a more complete picture of temperature distributions. The satellite is a precursor to a planned constellation of spacecraft that will provide continuous monitoring.
Four of the secondary payloads are CubeSats, built to a common standard size factor used for very small satellites. A single CubeSat unit (U) measures 10 centimeters along all three axes. Typical CubeSats are built to the size of one to three units of length, and one unit of width/depth, with a mass of a few kilograms. Larger CubeSats, such as the six-unit and twelve-unit layouts, expand along their width/depth axes. However, these form factors are less common. The standard form factors allow CubeSats to use standardized deployment mechanisms instead of each requiring their own systems to separate from the rocket.
ASTERISC, built by the Planetary Exploration Research Center at the Chiba Institute of Technology, is a three-unit CubeSat that will be used to study debris and cosmic dust particles in the low Earth orbit environment. The satellite will use piezoelectric sensors to detect dust particles as they impact a thin sheet of film deployed from the satellite.
KOSEN-1 is a two-unit CubeSat built by the Kochi National College of Technology. In orbit, it will deploy a seven-meter long antenna intended to observe radio waves emitted by the planet Jupiter. For launch, it is paired in the same dispenser as the mission’s smallest satellite, the single-unit ARICA. Produced by Aoyama Gakuin University, ARICA will test the relay of communications to the ground through the Globalstar and Iridium networks, while also carrying a sensor to detect gamma rays.
NanoDragon is the only non-Japanese satellite aboard Epsilon. It was built and operated by the Vietnam National Space Center (VNSC), although its inclusion on the Epsilon 5 mission is through a collaboration with Japan’s Meisei Electric Company. A three-unit CubeSat, with a mass of 3.8 kilograms, it carries a technology demonstration payload to help Vietnamese engineers develop systems for future small satellites. As part of its mission, it will use Automatic Identification System (AIS) signals to identify and track ships at sea.
This mission marks the fifth flight of the Epsilon rocket, which first flew in September 2013. Epsilon currently has a relatively low flight rate, with its last launch having taken place in January 2019. It is a three-stage solid-fueled rocket designed for launching smaller spacecraft, complimenting Japan’s larger H-IIA rocket with which it shares some components.
The first stage consists of an SRB-A3 solid rocket motor, two or four of which are used as boosters on the H-IIA to provide additional thrust at liftoff. Epsilon’s second stage, the M35, was developed from the third stage of the earlier M-V rocket, while its third stage – KM-V2c – is based on a kick motor that was flown as a fourth stage on some M-V missions. All three stages burn hydroxyl-terminated polybutadiene (HTPB), a common solid propellant compound used in rockets.
The M-V, which was retired in 2006, was Japan’s previous small satellite launcher and the final evolution of the Mu family of rockets. M-V had a relatively high cost for its capabilities, and one of the key objectives of the Epsilon project was to provide lower-cost access to space for small satellite missions.
While the basic Epsilon vehicle has three stages, it usually flies in a four-stage configuration with an additional post-boost stage (PBS), the hydrazine-fueled Compact Liquid Propulsion System (CLPS). This can be restarted multiple times during the mission to inject a satellite into a precise orbit or to deliver multiple payloads into different orbits. This configuration was used for Epsilon 5, with a short orbit adjustment made between the separation of the third and fourth payloads.
All four of Epsilon’s previous launches were also completed successfully. After the first three flights each deployed a single satellite, the January 2019 mission carried a cluster of seven payloads. The primary payload for that launch was RAPIS-1, the predecessor to the RAISE-2 satellite.
Epsilon launches take place from the former M-V launch pad at the Uchinoura Space Center in Japan’s Kagoshima Prefecture. Known as the Mu Center, this complex was originally built for the Mu-3 series and has been modified several times as Japan’s rockets have evolved. Mu rockets were rail-launched, with the former launch rail now serving as an umbilical tower for the vertically-launched Epsilon.
The pad structure includes an assembly building where the rocket was integrated vertically atop its launch platform. This was then swung into position ready for liftoff. Epsilon 5 was the 37th from the Mu launch pad.
The launch begins with the ignition of Epsilon’s first stage at the zero mark in the countdown. Lifting off, Epsilon climbs away from Uchinoura on a south-southwesterly track to target its planned near-polar sun-synchronous orbit. The first stage fires for the first 108 seconds of flight before depleting its propellant and burning out. After burnout, the flight enters a short coast phase as Epsilon continues to climb out of the Earth’s atmosphere.
About 43 seconds after burnout, with the rocket now at an altitude of 121 kilometers, the payload fairing separates. The fairing protects Epsilon’s upper stages and payload during the early stages of the ascent, but once the rocket reaches space it is no longer needed. 10 seconds later the spent first stage is also jettisoned, with the second stage igniting after a further four seconds to begin its own 129-second burn.
Epsilon coasts for another 96 seconds after second stage burnout before staging and third stage ignition occur. The third stage ignites four seconds after separation and burns for 88 seconds. About 112 seconds later, the post-boost stage is deployed to continue the mission.
The CLPS post-boost stage makes three burns to deploy Epsilon’s payloads into their designated orbits. The first of these began about 16 minutes and 13 seconds after liftoff – or six minutes and 19 seconds after CLPS separated from the third stage of the rocket. This first burn lasted about 110 seconds, with a longer second burn beginning 24 minutes and 14 seconds later. This eight-minute, 37-second firing of the upper stage engine circularized the orbit in preparation for the first round of spacecraft deployments.
RAISE-2 was the first spacecraft to separate from the rocket, at 52 minutes and 35 seconds mission elapsed time. TeikyoSat-4 was released at the 66-minute, 30-second mark in the flight, with ASTERISC following 23 seconds later.
With the first three payloads deployed, the CLPS performed a short third burn to put some distance between itself and the satellites. This began 101 seconds after ASTERISC separates, and lasted just thirteen seconds. Deployment of the remaining payloads began with Z-Sat, 79 seconds after the end of the burn. The other satellites then followed at 23-second intervals: DRUMS, HIBARI, KOSEN-1 and ARICA, and finally NanoDragon. Because the KOSEN-1 and ARICA satellites shared a dispenser, they separated simultaneously.
Epsilon’s next launch is expected to carry the RAISE-3 satellite, due for liftoff in the 2022 Japanese financial year, which runs from 1 April 2022 to 31 March 2023.
(Lead image credit: JAXA)