The Japanese H-II Transfer Vehicle-5 (HTV-5) resupply spacecraft successfully arrived at the International Space Station (ISS) on Monday. Following its launch into space from the Tanegashima space center Wednesday. HTV-5 arrived at the orbital outpost for capture at 6:28 AM EDT, ahead of an berthing at 10:02 AM EDT – marking a welcome delivery of critical supplies and research cargo to the orbital outpost.
HTV-5 rendezvous, capture and berthing operations:
HTV-5 has brought 4.5 tons of essential cargo to the ISS during a period the orbital outpost is still evaluating the impacts from the loss of three resupply missions.
The loss of the CRS-3/OrB-3 Cygnus in October of last year was followed by the failure of the Russian Progress M-27M spacecraft and the destruction of the CRS-7 Dragon when SpaceX’s Falcon 9 v1.1 failed during ascent.
While Progress has returned to nominal operations, Cygnus and Dragon are yet to return to flight.
With Europe’s ATV now retired from ISS missions, Japan’s HTV-5 launch needed to go smoothly, which proved to be the case as the spacecraft was successfully injected into a roughly 200km x 300km orbit by the H-IIB booster on Wednesday.
Safely into its initial orbit, HTV-5 conducted a series of burns to prepare for the rendezvous and berthing events on Monday.
The rendezvous burns involved a Phasing Maneuver-1 (PM-1), followed by Height Adjustment Maneuver-1 (HAM-1), followed by PM-2, which leads into Co-elliptic Maneuver-1 (CM-1) and CM-2, and then HAM-0, CM-3, HAM-2.
The key events ahead of arrival took place inside the Communication Zone (CZ) with the ISS, ahead of “Approach Initiation (AI)”.
Once inside the CZ, HTV-5 began to use the Proximity Operations (PROX) system – located in the Japanese Experiment Module (JEM) on the ISS – to communicate with the station.
Using PROX, HTV-5 performed an AI burn and once it reached a desired point below the station, make an R-bar Injection (RI) burn.
The R-bar – a term commonly heard during Space Shuttle dockings to the ISS – stands for Radius bar, and is effectively an imaginary line drawn between the center of the ISS and the center of the Earth, thus ensuring that any vehicle which approaches “up” the R-bar is directly below the ISS.
Once HTV-5 performed the RI burn, it entered the ISS Keep Out Sphere (KOS) – which is a three-dimensional “back yard” for the Station involving a number of additional procedures to ensure no misbehaving Visiting Vehicle proves to be risk to the Station. All such vehicles hold the ability to abort their closure on the orbital outpost.
With the two vehicles enjoying a “Tally Ho”, HTV-5 proceeded to a point 30 meters below the station, following which it will then proceeded to the capture point – thus concluding the rendezvous phase of the mission, and beginning the capture phase.
Following HTV-5’s arrival at the capture point, the spacecraft was put into free drift, inhibiting any thruster activity from occurring during this time.
The free drift command was sent to HTV-5 via the Hardware Command Panel (HCP), which sends commands between the ISS and HTV via the PROX link, in the same way that the Crew Command Panel (CCP) sends commands between the ISS and Dragon spacecraft via the COTS UHF Communication Unit (CUCU).
The HCP previously stood for HTV Command Panel, but the “HTV” has since been replaced with “Hardware” since the Cygnus spacecraft also uses the HCP, utilizing the PROX link to communicate with the ISS, as the HTV does.
The HCP, located in the Cupola module on the ISS, allows the crew to control the Space Station Remote Manipulator System (SSRMS) via the Cupola Robotics Workstation (RWS), with the RWS in the US Lab in “hot backup” standby mode.
The Cupola RWS offers increased situational awareness over the Lab RWS due to its seven windows.
The SSRMS was translated over the Flight Releasable Grapple Fixture (FRGF) on HTV-5, and “fired” the snares on the SSRMS to close over the grapple pin, following which rigidization of the SSRMS was completed. The FRGF/HTV was “pulled tight” against the SSRMS, thus securing the HTV-5 firmly in the station’s grip.
Following HTV capture – marked at 6:28 AM EDT – the SSRMS translated the spacecraft to the Ready To Latch (RTL) position below the Node 2 Nadir Active Common Berthing Mechanism (ACBM) port –the same port used by SpaceX’s Dragon – and the process to attach the HTV to the ISS began via the Node 2 Nadir ACBM extending hooks to pull the HTV’s Passive CBM (PCBM) into the ACBM.
Four sets of four bolts (16 in total) drove to secure the HTV to the ISS.
HTV-5 hatch opening – including pressurization of the CBM vestibule, opening of the Node 2 Nadir hatch, removal of the Center Disk Cover (CDC) and four Controller Panel Assemblies (CPAs), connection of vestibule jumpers including Inter-Module Ventilation (IMV) ducts, installation of the Vestibule Barrier Assembly (VBA), and finally opening of the HTV-5 hatch – is scheduled to be completed later in the day, depending on how fast the ISS crew can work.
The HTVs consist of two cargo-carrying sections: The Pressurized Logistics Carrier (PLC) to carry internal cargo, and the Unpressurized Logistics Carrier (ULC) to carry external cargo.
The PLC has space for eight ISS racks in total, however the four aft racks in the PLC are fixed and can only be of the HTV Resupply Rack (HRR) type, whereas the four forward racks can be either HRRs or any other type of International Standard Payload Rack (ISPR).
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HTV-5’s eight rack bays, all of which are filled with HTV Resupply Racks (HRRs), are packed with food, water, hygiene items, clothing, spare parts, personal items, and scientific experiments for the ISS crew.
Included in HTV-5’s manifest is 600 liters of potable water as well as food, crew commodities, system components, and science experiments – totalling 1 ton of unpressurized cargo.
HTV-5’s the primary external piece of equipment for this mission is the CALorimetric Electron Telescope (CALET).
(Images via L2 artist Nathan Koga, L2 HTV, JAXA and NASA).
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