countdown
The countdown (rare: Countdown) ( engl. "Count down", "the countdown") is (in shortly before the end of the timed intervals of one second ) Announcement of up to occurrence of a specific event z (B. launch of a missile or of the year. ) still missing period. The time of the event in the case of rocket launches is formally specified. B. with T (test), the remaining time with t (e.g. 10 min), so that announcements like " T minus 10 minutes" are made. As a rule, the countdown is carried out silently and only announced aloud during the last few seconds before the start.
Emergence
The countdown was first staged in the science fiction silent film Frau im Mond ( 1929 ) by Fritz Lang ; it is about the attempt to fly a rocket to the moon in order to develop raw materials there. Lang was faced with the question of how one could depict the tension before the moon rocket "Peace" took off without special effects and without noises in this silent film.
“When I turned the take-off of the rocket, I said: If I count one, two, three, four, ten, fifty, one hundred, the audience doesn't know when it's going to start. But when I count backwards: ten, nine, eight, seven, six, five, four, three, two, one, ZERO! - then you understand. "
Because of his film, Fritz Lang was invited by NASA to a space science seminar in the rocket test center in Huntsville (USA) in 1964. In a letter to Lotte Eisner in December 1968, he reports on this event as follows:
“The scholars, engineers, etc. gathered there in Huntsville explained to me that they regard me in a way as 'the father of the rocket science'. I was there for a few days, they showed me all the hush-hush-secret inventions, the different stages of the rockets built there, and they all believed that what I had done with the help of Professor Oberth and Willy Ley , had become almost absolute reality. Like, for example, throwing off the burned-out first missile, as is common practice today. But the most important thing was, and a lot has been written about it and was only mentioned again on TV a few weeks ago , that I invented the countdown . "
Countdown to space starts
The countdown almost always occurs with rocket launches , where before the launch process - especially with liquid missiles - numerous controls have to be carried out according to a fixed schedule within a tight time window . The critical tests must be completed positively at a certain point in time before the rocket lifts off, otherwise this leads to the countdown being stopped or aborted.
Depending on the complexity of the start of the countdown starts a few minutes (start small ballistic missiles) to 7 days ( manned starts ) before the scheduled start time T .
If a more serious problem occurs, the countdown is interrupted until it is resolved. If the problem cannot be resolved within the specified time (start window ), the countdown is canceled and the start is postponed. When the space shuttles started , there were set times at which the countdown was stopped in order to be able to complete work that had taken longer than planned. Only when this work was completed was it continued, or if this was not possible by the end of the start window, it was canceled. The last scheduled stop before take-off was at T -9 minutes.
The last seconds of the countdown are often counted down loudly: 10 - 9 - 8… 3 - 2 - 1 - Zero (also Go or (Ignition ... and) Lift-off ). This has also become common for television broadcasts from control centers. When taking off from the Kourou space center , the countdown will be announced in French (“… trois - deux - unité or un - top or feu”) , as Kourou is in French Guiana . Here, the zero point does not mean lift-off, as is the case with US take-offs, but the ignition of the engines.
The countdown is only typical of the western world, Russian missiles launch without a loud countdown.
Other uses
One of the most popular uses for counting down a time is the short-term alarm clock found in almost every household. However, their origins can be found in early forms of time measurement, e.g. B. the hourglass .
Before major social events such as B. the football world championship or the beginning of a new year on New Year's Eve, there are also numerous countdown counters on the Internet that count down the time until the beginning. Countdown counters that count down the time to a personal event can be set up on various pages on the Internet.
In many countries, e.g. B. in Denmark, the United States of America, Canada and China, traffic lights are equipped with countdown counters that show the remaining duration of the red or green phase. Such traffic lights are currently being tested in Hamburg and Berlin. The countdown traffic lights are to be tested in Bern from December 2019 as the first city in Switzerland. [outdated]
Some watches, especially digital watches , contain a zero count alarm . An alarm is triggered after the set period has elapsed.
Web links
Individual evidence
- ↑ What does space travel owe to the silent film "Die Frau im Mond" (1929) by Fritz Lang? Spectrum of Science, accessed October 28, 2009 .
- ↑ Audi Magazin, 04/2015, p. 39
- ↑ Cornelius Schnauber: Fritz Lang in Hollywood (1986), p. 68
- ↑ Countdown 101. NASA, accessed October 28, 2009 .
- ^ Ariane 5 - Launch operations. Arianespace, accessed October 30, 2009 .
- ↑ Berlin is testing "countdown" traffic lights. Berlin. In: Der Tagesspiegel. September 20, 2013, accessed June 24, 2015 .
- ^ Mathias Streit: The city of Bern dares to try countdown lights. In: derbund.ch . October 2, 2019, accessed October 2, 2019 .