Talk:HTV-X: Difference between revisions – Wikipedia

The pressurised volume is given here as 78m³, however the article says HTV-X reuses the pressurised module of its predecessor HTV which provides only 14m³ of pressurised volume.
Also the module is 3.5m long with an outside diameter of 4.4m, which is a cylinder of about 53m³.
And last but not least, in the comparison diagram the volume is quite obviously smaller then the one of the ATV which did provide 48m³ of pressurised space. 2.241.200.230 (talk) 18:42, 21 October 2025 (UTC)[reply]

That comes from this source: https://www.jaxa.jp/press/2017/12/files/20171206_HTV-X.pdf (Page 1.2.1).

• Increased Cargo Capacity
  • Mass: 4 tons→5.82 tons (45% increase)
  • Volume: 49m³→78m³ (60% increase)

I think that it’s saying the TOTAL cargo capacity is 78m³. But there are plenty of sources that say HTV-X reuses the pressurized module. I think all of that gain came with loading the unpressurised cargo outside the spacecraft where its only limited by the launch vehicle fairing. RickyCourtney (talk) 19:15, 21 October 2025 (UTC)[reply]

Note that the available volume of the pressurized section is different from the (actual) volume of the pressurized cargo it carries, as it excludes racks and unused space. According to this paper, for the HTV-1 mission, the internal volume of the pressurized section was 39.6 m³, while the pressurised cargo occupied 27.8% of it, or 11.0 m³ of volume. From HTV-2 and onward the percentage of cargo increased to 34.0% (which is 13.46 m³, close to the 14 m³ written in the HTV page?)

The HTV-X uses a new rack with a higher volume efficiency[1] and the pressurized cargo capacity increased from 3.25 tons (HTV) to 4.1 tons (HTV-X). While JAXA hasn’t published the pressurized cargo volume of the HTV-X, as the weight has increaed it’s likely not 14 m³ but somewhere closer to 39.6 m³ now. Kind regards, Hms1103 (talk) 06:08, 23 October 2025 (UTC)[reply]

I’m not sure what you mean here. As per JAXA’s own documents, the pressurized section of the HTV-X is identical to and reused from the original HTV. We don’t measure the used volume or mass; we only measure the available internal volume. RickyCourtney (talk) 16:42, 23 October 2025 (UTC)[reply]