米企業の無人宇宙船ドラゴン、ＩＳＳとドッキング [朝日]
国際宇宙ステーション（ＩＳＳ）に物資を補給する米宇宙企業スペースＸ社の無人宇宙船ドラゴンが米東部時間３日朝（日本時間３日夜）、ＩＳＳとのドッキングに成功した。１日に打ち上げられた後、燃料を噴射して姿勢を制御するスラスターに故障が生じ、２日に予定されていたドッキングを延期していた。
1日遅れですが無事到着したようです。
■ Resilient CRS-2 Dragon successfully berthed on the ISS [NASAspaceflight.com]
Meanwhile, controllers continued to evaluate the propulsion system, concluding it was was being caused by either a blockage in the helium line, or a sticky check valve. The solution was to “jack-hammer” the valves in the system by commanding them to cycle on and off several times in succession. This proved to be successful.
“Troubleshooting involved cycling the helium isolation valves between the He and Ox tanks 2-4. This allowed “slugs” of pressure to flow through the regulators and downstream to in-series check valves that were suspected to be the cause of the blockage,” added the notes. “After several cycles, the Quad 4 Ox tank suddenly rose to its expected pressure, indicating the blockage had cleared.”
“Troubleshooting involved cycling the helium isolation valves between the He and Ox tanks 2-4. This allowed “slugs” of pressure to flow through the regulators and downstream to in-series check valves that were suspected to be the cause of the blockage,” added the notes. “After several cycles, the Quad 4 Ox tank suddenly rose to its expected pressure, indicating the blockage had cleared.”
タンクを加圧するヘリウム供給系かチェックバルブの閉塞が疑われたため、並列チェックバルブを連続して開閉し「掘削機」のように押し出すことで圧力が回復したそうです。その後ISSへの接近、カナダアームによる把持はどうやら問題なく完了した模様。
ちょっと気になるのは、復路で再発しないかどうかということです。どういう条件で閉塞が発生したのかにもよりますが。
