Narrative:

I had come in for the [late night] shift only 15 minutes or so before the event. All domestic sectors were combined and the ocean sectors were moved to the domestic side of the room (normal ops) for the midnight shift. Aircraft X was at FL400 and I wanted to begin his descent as he got closer to the houston area so I issued; 'descend now to FL300 then descend via the BAYYY2 arrival' because I recognized converging traffic at 31000 feet - aircraft Y.a couple of minutes later I saw that aircraft X was descending too slowly so I amended his altitude. I meant to say 'amend altitude; maintain FL320'; but instead I amended him to FL300. I also issued aircraft X a vector to the southwest (heading 210) to provide room for his descent when he was clear of traffic. There was weather to the north; so I had to vector him to the south. After a couple of minutes I realized I had not updated aircraft X's data block with the amended altitude and I wanted to confirm it with him so I stated; 'aircraft X maintain FL320.' at this point he responded that he was through 31700 feet so I told him to expedite to 30000 feet. I recognized that I needed to keep his descent going fast so I told him to expedite through 30000 feet down to 24000 feet and 'report leaving FL300'. I then issued an aggressive vector to aircraft Y; even stating to 'turn right immediately heading 300.' I realize this was a very sharp turn but I wanted to create as much space as I could as quickly as I could. However; he never seemed to take the heading. I also instructed aircraft Y to climb and maintain 33000 feet; again to begin speeding up vertical separation between the two aircraft; but he never acknowledged the climb and at that point I had vertical separation. There was an urgency in my voice as I was scrambling to create separation. Aircraft X did report that he was responding to an RA descending. When both aircraft were vertically separated I cleared them both on course. After the event; I had [a cpc] take over the domestics as well and I reported the incident to the mid-watch supervisor. He listened to the audio and watched the falcon. He said that aircraft X was trying to report leaving 30000 feet at or just before the computer reported a loss of separation; but aircraft Y was broadcasting during his report.there was not a failure of the system or a procedure that led to this event. I made the classic 'think one thing; say another' mistake. In over 17 years of ATC this is my first event like this. I simply misspoke. I'll be vigilant about saying what I mean going forward.

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Original NASA ASRS Text

Title: ZHU Controller reported mistakenly assigning an altitude 2000 feet below intended. This placed the aircraft into confliction with converging traffic. Both aircraft responded to RAs.

Narrative: I had come in for the [late night] shift only 15 minutes or so before the event. All Domestic Sectors were combined and the Ocean Sectors were moved to the domestic side of the room (normal ops) for the midnight shift. Aircraft X was at FL400 and I wanted to begin his descent as he got closer to the Houston area so I issued; 'descend now to FL300 then descend via the BAYYY2 Arrival' because I recognized converging traffic at 31000 feet - Aircraft Y.A couple of minutes later I saw that Aircraft X was descending too slowly so I amended his altitude. I meant to say 'amend altitude; maintain FL320'; but instead I amended him to FL300. I also issued Aircraft X a vector to the southwest (Heading 210) to provide room for his descent when he was clear of traffic. There was weather to the north; so I had to vector him to the south. After a couple of minutes I realized I had not updated Aircraft X's data block with the amended altitude and I wanted to confirm it with him so I stated; 'Aircraft X maintain FL320.' At this point he responded that he was through 31700 feet so I told him to expedite to 30000 feet. I recognized that I needed to keep his descent going fast so I told him to expedite through 30000 feet down to 24000 feet and 'report leaving FL300'. I then issued an aggressive vector to Aircraft Y; even stating to 'turn right immediately heading 300.' I realize this was a very sharp turn but I wanted to create as much space as I could as quickly as I could. However; he never seemed to take the heading. I also instructed Aircraft Y to climb and maintain 33000 feet; again to begin speeding up vertical separation between the two aircraft; but he never acknowledged the climb and at that point I had vertical separation. There was an urgency in my voice as I was scrambling to create separation. Aircraft X did report that he was responding to an RA descending. When both aircraft were vertically separated I cleared them both on course. After the event; I had [a CPC] take over the domestics as well and I reported the incident to the mid-watch supervisor. He listened to the audio and watched the falcon. He said that Aircraft X was trying to report leaving 30000 feet at or just before the computer reported a loss of separation; but Aircraft Y was broadcasting during his report.There was not a failure of the system or a procedure that led to this event. I made the classic 'think one thing; say another' mistake. In over 17 years of ATC this is my first event like this. I simply misspoke. I'll be vigilant about saying what I mean going forward.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.