Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)
11Successful Demonstration for Upper Stage Controlled
Re-entry Experiment by H-IIB Launch Vehicle

KAZUO TAKASE*1

MASANORI TSUBOI*2

SHIGERU MORI*3

KIYOSHI KOBAYASHI*3

The space debris created by launch vehicles after orbital injections can be hazardous. Apiece of debris can collide with artificial satellites or cause a casualty when it falls back to earth,which is an ongoing problem among countries that utilize outer space. This paper reports on aJapanese controlled re-entry disposal method that brings the upper stage of a launch vehicle down
in a safe ocean area after the mission has been completed. The method was successfully
demonstrated on the H-IIB launch vehicle during Flight No. 2, and provides a means of reducing
the amount of space debris and the risk of ground casualty.

|1. Introduction
The H-IIB launch vehicle was jointly developed by the Japan Aerospace Exploration Agency(JAXA) and Mitsubishi Heavy Industries, Ltd., to launch the Kounotori (‘Stork’) H-II TransferVehicle (HTV), which carries supply goods to the International Space Station (ISS). The H-IIBlaunch vehicle has the largest launch capability of the H-IIA launch vehicle family: it can inject a
16.5-ton HTV into a low earth orbit (ISS transfer orbit). Figure 1 shows an overview of the H-IIBlaunch vehicle.

Figure 1 Overview of the H-IIB launch vehicle

The changes introduced in the H-IIB launch vehicle are as follows:・ Enhanced first stage relative to the H-IIA: tank diameter extension, cluster system fortwo main engines, and four solid rocket boosters (SRB-A)・ Reinforced upper stage (second stage) relative to the H-IIA to launch the HTV・ 5S-H fairing (newly developed to launch the HTV)H-IIB Test Flight No. 1 was successfully launched from the Tanegashima Space Center on
September 11, 2009, and the launch vehicle inserted the HTV to its desired orbit. The second-stage
remained in a geocentric orbit after orbiting the HTV. This orbit had the following characteristics:*1

Space Systems Engineering Department, Space Systems Division, Aerospace Systems*2Manager, Space Systems Engineering Department, Space Systems Division, Aerospace Systems*3

Japan Aerospace Exploration Agency

Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)12(1) An inclination of 51.65º, passing over most of the inhabited area on earth.
(2) A low altitude of 200 km, causing it to fall to earth within several days.
Based on this orbit, the second stage is expected to fall randomly in an area between 51
north latitude and 51º south latitude after flying around the earth several times in a geocentric orbit.
The second stage is disintegrated by aerodynamic heating and dynamic pressure during re-entry,
and most of the fragments will burn out. As a result, the level of risk on the ground is very low.
However, considering the planned regular HTV launches, it is desirable to develop a controlled
re-entry method to bring the second stage to a safe ocean area to minimize the risk of a casualty asmuch as possible.1
H-IIB Test Flight No. 1 verified that the vehicle has sufficient launch capability as planned.
The flight results confirmed that some propellant remained after the HTV separation, so anadditional development project was undertaken to achieve controlled re-entry during H-IIB Flight
No. 2. Controlled re-entry of the upper stage of a launch vehicle is an advanced technology that has
only been attempted on a few actual missions worldwide, such as the Ariane 5 EPS/ATV andDELTA-IV/DMSP-17. This paper describes the development and flight results of the controlled
re-entry experiment on H-IIB Flight No. 2.2|2. De-orbit Scenario and Development Items
2.1

De-orbit Scenario

The development target of the H-IIB controlled re-entry project was the utilization of extra
onboard propellant to de-orbit the second stage while maintaining HTV launch capability
requirements. The development had to be completed within a year after Test Flight No. 1, andvehicle modifications were restricted to a minimum.
The requirements of the de-orbiting procedure were to ensure that the vehicle would fall
down in a safe ocean area, to allow a decision to be made to start de-orbit burn, and to monitor
de-orbit burn for safe flight control.
The South Pacific Ocean was selected as the target impact area as it provided the largest safearea over which the second stage orbited after the HTV separation. Two plans were compared toconsider trade-offs for the de-orbiting procedure (Figure 2).

Figure 2De-orbit scenarios【Plan A】 Start the de-orbit burn immediately after the HTV separation to bring the vehicle
down in the South Pacific Ocean.
【Plan B】 Allow the flight once around the earth after the HTV separation and then start thede-orbit burn within visible range of the Tanegashima ground station to bring thevehicle down in the South Pacific Ocean.
Plan A required considerable deceleration from the de-orbit burn to allow the vehicle to fall
into the South Pacific Ocean after orbiting the HTV above or near the equator. This plan was not
adopted as it would reduce the launch capability of the H-IIB launch vehicle. Development
proceeded with Plan B because it could satisfy the launch capability requirements with one-sixth
the deceleration required for Plan A by de-orbiting above or near the Tanegashima ground station.
Plan B also permitted the use of existing ground stations.

Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)132.2(1)Development Items
Application of idle mode burn
During de-orbit burn, dispersion of the impact point must be reduced by guidance
calculation with an onboard computer. Plan B required minimal deceleration from the de-orbit
burn, as well as a low thrust level burn (thrust force: 4 kN) designated ‘idle-mode burn,’because the normal thrust level burn of the second-stage engine (thrust force: 137 kN) was toolarge to allow enough time for guidance calculation. Idle-mode burn does not operate theturbo-pump, and is unique to the second stage engine (LE-5B-2). Figure 3 shows thesecond-stage engine, and Figure 4 presents the system diagrams for normal thrust level burnand idle-mode burn.

Figure 3
Second-stageengine(LE-5B-2)

Figure 4 LB-5B-2 engine system diagrams for the normal thrust level
burn and idle-mode burnIdle-mode burn was used for only a short period to re-ignite the H-IIA second stageengine. Therefore, to acquire detailed performance data of idle-mode burn, additional engine
qualification tests and flight experiments by the post-mission second stage of H-IIA Flight
No.17 were executed.
(2) Development of the ground control system for de-orbit
The ground control system used to activate or deactivate de-orbit maneuver wasdeveloped by JAXA. The health status and trajectory of the second stage are evaluated after theflight once around the earth, to ensure safe de-orbit maneuver as planned. The developed
system automatically evaluates whether the health status data from each part of the second
stage satisfy predetermined criteria, and ensures that the trajectory data before de-orbit burnindicate that the vehicle can be brought down to the targeted impact area. The commandallowing de-orbit burn is sent from the ground station after de-orbit is estimated possible. Only
when the command is received by the second stage does de-orbit burn begin. Figure 5 presents
an operational image of the ground control system.

Figure 5

Operational image of the ground control system1

Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)14|3. Vehicle Modifications
The main mission of Test Flight No. 1 was completed in approximately 1,000 seconds, as theHTV was separated approximately 910 seconds after liftoff. In the case of Flight No. 2, the flying
time was approximately 6,000 seconds, as de-orbit maneuver was to execute after the flight oncearound the earth. The following vehicle modifications were required for the prolonged flight timeand de-orbit burn:・ Application of thermal protection tape to the onboard equipment to reduce thermaleffects during the long ballistic phase.
・ Addition of functions to receive the de-orbit approval command from the ground station
and begin idle-mode burn.
・ Addition of a helium bottle to pressurize the hydrogen tank prior to de-orbit burn.
The amount of hydrazine propellant required for the attitude control system and batteriescapacity required to manage the prolonged flight time were evaluated, and additional hydrazine
propellant and batteries were estimated unnecessary. H-IIB Flight No. 2 was eventually confirmed
to have the required launch capability considering the additional weight of the above modifications
and the controlled re-entry was conducted.

|4. Flight Plan
Figure 6 shows the trajectory profile of H-IIB Flight No. 2. The H-IIB launch vehicle was tobe launched from the Tanegashima Space Center, flying southeast. The vehicle was to separate theHTV within sight of the Guam ground station, 300 km above the Pacific Ocean, approximately 910
seconds after liftoff.

Figure 6

Trajectory profile of H-IIB Flight No. 2

After separating the HTV, the second stage was to change its attitude and move away fromthe HTV to avoid collision. Once the second stage was sufficiently far from the HTV, it was toadjust its attitude in preparation for de-orbit burn. It was then to begin a ballistic phase making theflight once around the earth; during this ballistic phase, the vehicle was to continue to roll about its
axle line (barbecue roll) to maintain appropriate thermal conditions.

Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)15

Approximately 100 minutes after liftoff, the second stage was to complete the flight oncearound the earth, and to be visible from the Tanegashima ground station. Idle-mode burn was tostart after the de-orbit operation was confirmed by the Tanegashima ground station and theapproval command was received. The guidance calculations were to be performed duringidle-mode burn to minimize the dispersion of the impact footprint and the burn was to shut off at an
appropriate time. The remaining propellants (liquid hydrogen, liquid oxygen, and hydrazine) were
to be discharged from the tank, and the ground stations (Tanegashima and Guam) were to continue
monitoring the vehicle health status and its trajectory until the vehicle went beyond the horizon.
Tumbling rotation (random rotation to place the vehicle’s front/rear ends and side faces alternately
in the forward position) was to be applied before reentering the atmosphere to cancel any
aerodynamic lift.
The first disintegration of the vehicle was assumed to occur at an altitude near 80 km, after
re-entry, and almost all of the fragments were to burn out. The remaining small fragments were tofall down in the ocean.
Figure 7 shows the predicted impact area of the second stage, based on the results offragment impact footprint computation. This area was determined to alert the international shipping
and air carrier communities of the potential debris impact hazard.

Figure 7

Second-stage predicted impact area

Figure 8 Launching ofH-IIB flight No.2
(Courtesy of JAXA)

Figure 9Controlled re-entry result of H-IIB Flight No.2

|5. Flight Results
H-IIB Flight No. 2 was launched on January 22, 2011 (Figure 8). The flight profile wasconsistent with the pre-flight calculations, and the HTV was launched into the desired orbit. The
second stage was monitored from the Tanegashima ground station after the flight once around theearth, and the de-orbit maneuver was executed as planned. The idle-mode burn performance of thesecond stage engine was close to the pre-flight calculations, and the main event timeline, such asthe burn duration were very close to the analysis predictions. Figure 9 shows the pre-calculated
impact point and the actual impact points based on descent trajectory information after de-orbit
maneuver. The impact footprint trace was very consistent with pre-flight calculations, and thehealth status data acquired from each part of the vehicle were normal. Consequently, all acquired
flight data suggested that the controlled re-entry of the second stage was conducted successfully.

Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)16|6. Conclusions
The development of controlled re-entry with H-IIB Flight No. 2 was undertaken after thecompletion of Test Flight No. 1. The development was completed in a short period of one year byutilizing H-IIA launch vehicle technologies, as in the case of Test Flight No. 1, and thedemonstration flight was successful. One reason for the successful achievement of the project
within such a short development period was the good utilization of engineers’ skills after thecompletion of Test Flight No. 1.
The increasing amount of space debris is becoming an international problem, and regulations
concerning the upper stage of used launch vehicles which are the source of much space debris, arebecoming increasingly stringent. The success of our controlled re-entry demonstrates Japan’sleading-edge approach to mitigating space debris.
Controlled re-entry is an innovative technology that can dispose of the launch vehicle safely
and quickly from orbit at the end of its mission. The acquisition of this technology illustrates theadvanced launching technology in Japan, and also reduces the risk presented by HTV missions
launched into low earth orbit, which are expected to continue regularly.
We will continue to improve the technology, for the development of the H-IIA upgradesystem, which ignites a third time after a five-hour coasting, as well as the orbit change techniqueof the next flagship launch system to reduce the amount of space debris.

References
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Makoto, A. et al., H-IIB Launch Vehicle Result of Test Flight and Plan of 2nd Flight, Aeronautical andSpace Sciences Japan, Vol. 59, No. 684 (2011) p. 24-27
Kazuo, T. et al., Upper Stage Controlled Re-entry Experiment by H-IIB Launch Vehicle, 28th ISTS Paper,
2011-g-16