Japan’s H-IIA rocket is gearing up for its sixth and final launch of the year, set for a Saturday liftoff from the picturesque Tanegashima Space Center to send a pair of very different satellites into orbit, one to study changes of our planet over a long time scale while the other will descend and complete a mission orbiting on the edge of the atmosphere to help develop previously unused orbital real estate.
H-IIA is targeting a 22-minute launch window opening at 1:26:22 UTC on Saturday and will first be tasked with a direct ascent into an 800-Kilometer orbit from where the GCOM-C satellite will operate, joining Japan’s Global Change Observation Mission that aims to study Earth’s water, energy and carbon cycles over a period of over ten years to deliver relevant data for long-term climate assessments. The rocket’s second stage will then show off its new multi-orbit mission capability by performing an additional two engine burns to descend in altitude before sending SLATS, the Super-Low Altitude Test Satellite, on its way to demonstrate the feasibility of operating a satellite between 200 and 300 Kilometers in altitude.
Saturday’s H-IIA launch window opens just 61 seconds before the instantaneous launch opportunity comes for a Falcon 9 rocket launching out of California’s Vandenberg Air Force Base with the next ten satellites joining the Iridium-NEXT communications constellation. Provided H-IIA launches at the top of its window and Falcon 9 makes its instantaneous window, these two missions are contenders for a new record for the shortest time ever between two orbital launches.
The current record goes all the way back to the dawn of the Space Age when, on August 18, 1960 a Thor-Agena and a Thor-Ablestar lifted off from Vandenberg and Florida’s Cape Canaveral at 19:57:08 and 19:58 UTC. Unfortunately, the launch time for the latter is only known to the minute, leaving an uncertainty in the all-time record between 52 and 111 seconds. Nevertheless, avid space fans will be in need for dual screen viewing Friday night if these two launches occur just over a minute apart – a page with both webcasts is provided by Spaceflight101 here.
For H-IIA, this mission will close the rocket’s busiest year to date, having already broken its previous record of four flights in a calendar year. Half of H-IIA’s missions in 2017 were dedicated to lifting three Quasi-Zenith Satellites to complete the QZS System designed to improve GPS navigation in Japan’s urban canyons and enabling high-accuracy GPS exploitation in a number of areas including aviation and mapping. The other H-IIA missions performed so far this year lifted the DSN-2 communications satellite for the Japanese government and armed forces and the IGS-Radar 5 reconnaissance satellite.
Saturday’s mission will be headed to Low Earth Orbit and demonstrate a new multi-orbit capability as the GCOM-C1 and SLATS satellites target two different orbital regimes.
GCOM-C1, the Global Change Observation Mission for Climate, is part of the GCOM project operated by the Japan Aerospace Exploration Agency to collect surface and atmospheric parameters over an extended observation period to contribute to climate research. GCOM-C, also known as Shikisai, joins the GCOM-W1 satellite (Shizuku) launched in 2012.
Under the two-satellite architecture, GCOM-W hosts a high-fidelity microwave radiometer to collect data on Earth’s water and energy cycles while GCOM-C contributes surface and atmospheric measurements of various parameters through the use of a 19-channel imaging payload, providing insight into Earth’s carbon cycle and radiation budget. Data from the GCOM project is employed in a twofold fashion – long-term records established by multiple generations of satellites will feed into numerical climate models while the constantly updated data from the satellites finds application in operational areas like weather forecasting and disaster mitigation.
The 1,950-Kilogram GCOM-C satellite hosts a single instrument known as the Second-Generation Global Imager (SGLI) – a multi-channel imaging instrument covering 19 spectral bands from the UV spectrum over the visible & near-infrared wavelengths to the thermal infrared spectrum with varying ground resolutions between 250 and 1,000 meters and polarization sensitivity.
Combining a pushbroom sensor for VNIR imaging and a whiskbroom scanning instrument for the infrared measurements, GCOM-C1 will deliver a complete picture of Earth every two to three days and its high image resolution will enable anthropogenic climate effects to be assessed over extended periods.
Riding shotgun underneath the GCOM-C1 satellite is the Super-Low Altitude Test Satellite SLATS, setting out on a mission orbiting on the edge of the atmosphere where the satellite will have to actively combat air resistance to avoid dropping out of orbit.
Orbital altitudes between 200 and 300 Kilometers are rarely used given the high-drag environment in the upper reaches of Earth’s atmosphere, but offer a number of advantages for scientific and operational missions arising from the close distance to Earth’s surface.
Orbiting closer to Earth will enhance the resolution of imaging instruments while radars or LIDARs would be able to accomplish their measurements at much lower transmit power. In addition to operational benefits, the Super-Low Earth Orbit regime is also of interest to the scientific community as a rarely explored atmospheric region.
In fact, the lower thermosphere, extending from 90 to 380 Kilometers, is the least explored layer of the atmosphere even though it plays an important role in energy-exchange processes between the dense gaseous atmosphere and the higher layers where energetic particles roam.
Exploration of this region is difficult since remote sensing instruments looking from the ground up or watching down from satellites in higher orbits are only sensitive enough to capture vertical profiles from the lower atmosphere up to around 100 Kilometers. This would mean that the only way of exploring this vital part of Earth’s atmosphere is through in-situ measurements – considered a difficult endeavor due to the atmospheric density at these altitudes which would bring a satellite to a fiery re-entry within a period of days if it can not actively counter drag to hold its altitude.
The 400-Kilogram SLATS satellite aims to demonstrate a platform that would enable extended operations at altitudes of 250 Kilometers and less for commercial and scientific exploitation. This will be possible through the use of a hybrid propulsion system featuring chemical thrusters and ion engines to be able to accomplish fast orbital changes using the traditional thrusters and long thrust phases for drag compensation with the ion engine.
After completing checkouts at a safe altitude, SLATS is planned to spiral down to 250 Kilometers and enter its orbit-keeping mode using the ion thruster. On a weekly basis, the satellite will reduce its altitude by another ten Kilometers until reaching 220 Kilometers where SLATS will operate for two months. An extended mission at 180 Kilometers will see the satellite use its ion thruster at full duty cycle and the chemical thrusters joining in to help keep it in orbit.
SLATS will demonstrate the increase in spatial resolution possible from Super Low Earth Orbit by using an inexpensive imaging system while a materials science payload will study the effects of atomic oxygen on different samples to inform designers of future satellites operating at altitudes of 300km and less.
To send GCOM-C1 and SLATS into different orbits, H-IIA will demonstrate its new multi-orbit injection capability that builds on upgrades inaugurated on the rocket’s second stage on H-IIA Flight 29 in 2015 that added modifications to allow for extended coast and multi-burn missions.
These features were first used for Geotransfer missions with extended coast phase but can also be applied for missions aiming for two or more distinct orbits, adding to H-IIA’s repertoire and opening the launcher for competing in the growing LEO launch business by offering ride-share missions to different orbits.
Gearing up for launch, the 53-meter tall H-IIA is expected emerge from its Vehicle Assembly Building at 11:30 UTC on Friday, covering the first 500 meters toward orbit to be centered on the sea-side launch pad for power-up and checkouts. Propellant loading is expected to pick up seven hours and 45 minutes before launch to fill the two-stage rocket with 120 metric tons of -183°C Liquid Oxygen and -253°C Liquid Hydrogen. Extensive testing continues once the vehicle is fueled to clear the way for the computer-controlled countdown sequence kicking in at X-4.5 minutes.
Once in the hands of ground and onboard computers, H-IIA will go through the final preparatory steps, notably the pressurization of its four tanks, the transition to internal power and the activation of the Flight Control System. H-IIA will begin breathing fire at X-5.2 seconds when the LE-7A engine will start its ignition sequence to soar to a thrust of nearly 100 metric ton force under close watch by the rocket’s flight computers.
Upon completion of engine monitoring, when clocks strike zero, H-IIA will fire up the twin boosters and leap off the pad with a total thrust of 600 metric-ton-force.
H-IIA will climb vertically for only a handful of seconds before initiating its pitch and roll program to enter a dogleg trajectory – initially flying south-east to depart Tanegashima and clear the Philippines to avoid frequented fishing areas so that its boosters and fairing drop into clear areas of the Pacific. In the later portion of the first stage burn, H-IIA will make a right hand turn to transition onto a heading to south-south-west in order to reach the desired orbital inclination of 98.7 degrees.
The twin boosters, each burning 65 metric tons of propellant, will burn out 91 seconds into the flight after helping accelerate the vehicle to 1.4 Kilometers per second. They will drop away 17 seconds later when H-IIA will have reached an altitude of 56 Kilometers.
With the 15-meter boosters swinging outward along their thrust struts, H-IIA will from then on rely on its LE-7A engine alone, burning 260 Kilograms of cryogenics per second to deliver 109,300-Kilogram force of thrust when heading into the upper reaches of Earth’s atmosphere. The protective payload fairing will split open and drop away four minutes and five seconds into the flight when H-IIA crosses 167 Kilometers in altitude where aerodynamic forces are no longer a danger to the delicate satellite structure.
Per the nominal mission plan, the first stage will shut down six minutes and 38 seconds into the flight, having boosted the vehicle to a speed of 3.6 Kilometers per second. Eight seconds later, the separation of the 37-meter long core stage will be commanded through loaded springs, expected some 380 Kilometers in altitude.
The second stage will fire up its LE-5B engine nine seconds after staging, generating 13,970kgf of thrust for a burn of eight minutes and 11 seconds – tasked with a direct ascent into an orbit of 788 by 806 Kilometers. Riding in the main passenger seat, GCOM-C1 is set for separation at X+16 minutes and 21 seconds upon which H-IIA will head into the second part of its mission to dispatch SLATS into a lower orbit.
The second stage will fire up for a retrograde burn of eight seconds 57 minutes and 46 seconds into the mission to hit the brakes and reduce the low point of the orbit to 470 Kilometers in altitude. 59 minutes and 55 seconds into the flight, Stage 2 will jettison the payload adapter that facilitated GCOM-C1 and reveal the SLATS satellite for another half lap of coasting before the second stage re-starts one hour, 45 minutes and 45 seconds into the flight to step on the brake again in order to set up an orbit of 450 by 643 Kilometers for the separation of SLATS one hour and 48 minutes after liftoff.