Confusion still surrounds the cause of the intermittent failure of the LH2 Engine Cut Out sensor (number 2) during yesterday\u2019s countdown \u2013 leading to a scrub and subsequent delay to \u2018no sooner than\u2019 late next week for the Return to Flight of the Shuttle fleet. <\/p>\n
However, it is highly unlikely Discovery will launch anytime soon.\n<\/p>\n
Troubleshooting started in earnest following Discovery\u2019s scrub, although the length of time before another launch attempt will be undertaken depends of targeting what is still classed as an Unexplained Anomaly (UA).<\/font><\/p>\n Discovery is no stranger to an ECO sensor issue, following her double fault during the first tanking test. However, on that occurrence, LH2 ECO sensors 3 and 4 were at fault.<\/p>\n There are four LH2 sensors and four LOX sensors. They are checked like this: LH2 and LOX sensors number 1,2,3,4. The sensors kick in during the final seconds of the Shuttle\u2019s assent into orbit, checking the level of propellant remaining in the External Tank.<\/p>\n Should a failure occur where a sensors fail to correctly note how much LOX and LH2 is remaining, the Space Shuttle Main Engines (SSMEs) could potential run out of propellant, begin ingesting ullage gas, cavitation would the result in the turbines over-spin and rip the Orbiter apart.<\/p>\n Speaking on condition of anonymity, one of the launch operators gave the full outline to the issue arising, the troubleshooting that is on-going, and potential scenarios to solve the problem.<\/p>\n \u201cThe sensors are checked, the LH2 and LOX sensors are checked in pairs \u2013 #1 ECO LOX is checked along with #1 ECO LH2.<\/p>\n \u201c(During \u2018replenish\u2019) United Space Alliance (in control of the Shuttle pre-launch) did this with the #1 ECOs and both temporarily went \u2018DRY\u2019, then they switched them back on to read data. The input to the sensors for this check is provided by something called a \u2018SIM circuit\u2019.<\/p>\n \u201cThey did the test for ECO #1\u2019s and it passed since they both indicated DRY. Then they did this for the #2 ECOs, and only the LOX ECO indicated \u2018DRY\u2019 \u2013 the LH2 ECO (#2) indicated WET. They repeated this test several times, all with the same result. All other ECO sensors passed the test successfully.\u201d<\/p>\n \u201cThen they did a special form of this test where all eight ECOs (all four LH2 ECOs plus all four LOX ECOs) were tested simultaneously, and all eight indicated \u2018DRY\u2019.\u201d<\/p>\n \u201cBefore this test all four LH2 ECOs were working perfectly.\u201d<\/p>\n \u201cBear in mind that when they switched the test \u2018OFF\u2019, the LH2 ECO #2 sensor indicated \u2018WET\u2019, as it should. This seems to indicate that the sensor was working properly. We\u2019re thinking it was something about that test that failed.\u201d<\/p>\n \u201cThey decided to leave the #2 ECOs switched in the \u2018DRY\u2019 test position (which meant that LOX ECO was indicating \u2018DRY\u2019 and the LH2 ECO was errantly indicating \u2018WET\u2019, with both tanks completely full).<\/p>\n \u201cWhen the tanks were drained, they were hoping that LH2 ECO #2 would suddenly indicate \u2018DRY\u2019 as it should \u2013 then they could pinpoint the problem with the SIM circuit.<\/p>\n \u201cWell, we were hoping that this would happen \u2013 that LH2 ECO #2 would indicate \u2018DRY\u2019 when the other three did \u2013 but it stayed wet, eerily similar to the first tanking test.\u201d <\/font><\/p>\n Speaking today from the Kennedy Space Center, NASA manager Wayne Hale noted Engineers are discussing how the thermal environment of the avionics box affects its operation. If the box is at fault a replacement would take at least 10 days \u2013 most likely longer \u2013 to build.<\/font> <\/font> However, the issue has not yet been pinpointed.<\/p>\n \u201cLH2 ECO \u2018wet\u2019 indication is an indication that there\u2019s an \u2018open circuit\u2019,\u201d added the source. \u201cwhich could be anywhere from the sensor itself to the wiring in the Orbiter.\u201d<\/font><\/p>\n","protected":false},"excerpt":{"rendered":" Confusion still surrounds the cause of the intermittent failure of the LH2 Engine Cut Out sensor (number 2) during yesterday\u2019s countdown \u2013 leading to a scrub and subsequent delay to \u2018no sooner than\u2019 late next week for the Return to Flight of the Shuttle fleet. However, it is highly unlikely Discovery will launch anytime soon. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[],"class_list":["post-42348","post","type-post","status-publish","format-standard","hentry","category-news"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/42348"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=42348"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/42348\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=42348"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=42348"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=42348"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}