Have you ever watched a space shuttle take off on TV and remembered hearing or seeing the final countdown?
If so, you may have wondered what kind of time-telling device they used. Rest assured that they don’t use a cheap plastic stopwatch. Yes, they do have a precise time-telling method. OnlineClock.net thought it would be fun to research the subject further. What we found was even more interesting than you may think. NASA’s procedure for these countdowns involves much more than the 10 to zero verbal count – so read on to find out what we discovered!
Although the first space craft wouldn’t be launched for decades after the event, the release of a 1929 silent movie called “The Woman in the Moon” is thought to be responsible for the reason why counting down instead of forward was chosen for launches. According to a science fiction history compilation by East Tennessee State University, in “The Woman in the Moon,” German film creator Fritz Lang depicts an eerily realistic version of a later V-2 rocket and makes clear the final countdown to the launch.
As time is being counted toward the takeoff of a spacecraft, the amount of time between the current time and the launch is stated in respect to takeoff, or “T.” So, if the spacecraft were set to take off in 12 hours, the NASA officials would say “T minus 12 hours.” Quite oppositely, once the spacecraft has been launched, the time is referred to as “T plus” instead of “T minus.” The countdown clock itself is located at the Kennedy Space Center in Cape Canaveral, Florida. It stands in a field a safe distance from the shuttle launch pad and has counted down the time of launches since the Apollo mission.
When you think about NASA clocks, you might picture a futuristic clear glass clock with a crystal-clear digital display. However, NASA’s countdown clock is far from this! While it is extremely precise, it doesn’t look as high-tech or attractive as many people who aren’t familiar with it may think. According to Matt Kaplan in an article published by the Planetary Society, the famed clock’s display digits are powered via 40-watt incandescent bulbs. Kaplan is the host and producer of Planetary Radio. For those of you who aren’t familiar with lighting devices, incandescent bulbs are the old-style bulbs that are not very energy-efficient. Although 40 watts isn’t bright for a house, the clock does seem to light up well at night since it sits in an expansive field with few other lights surrounding it.
NASA's Countdown Clock - this photo is from the wonderful blog at Planetary.org !
On NASA’s official site, there is an interesting article titled “Countdown 101.” They don’t give us all the details of the inner workings of the famous countdown clock, but they do note that there are “hold” capabilities built in to this device, which allow the launch team to program a specific time cushion for various procedural tasks without affecting the original launch schedule. These holds are programmed at the hourly intervals of T-27, T-19, T-11, T-6, T-3 and the minute intervals of T-20 and T-9. Now, you’re probably wondering what the launch team does at these points, right?
At T-43 hours, the Shuttle Test Director makes calls to the stations to activate the clock. Flight software, the backup flight systems and preliminary flight deck inspections are reviewed. The backup software is installed in the orbiter’s general purpose computers and several other preparatory procedures are performed. At T-27, there is a four-hour hold in which the launch pad is cleared of all workers who are not essential. After this, the cryogenic propellants are loaded into the orbiter’s power reactant storage and distribution system, also called the PRSD. When T-27 is counting, the operations to load the cryogenic reactants in the orbiter’s fuel storage are begun. Another four-hour hold happens at T-19 hours. The crew module is vacuumed and cleaned, the external tank nosecone purge is performed and the umbilical unit of the orbiter is demated. When T-19 is counting, final preparations begin in the orbiter’s three main engines, in addition to a few other preparatory items. When T-11 is holding, the time lapse is about 13 or 14 hours. Inspections, closeouts and briefings regarding engineering and weather occur during this time.
When T-11 is counting, the blast danger area is cleared, the purge air is switched to nitrogen and the orbiter’s fuel cells are activated. The T-6 hour hold last about two hours. The weather update is received. Verifications of vital criteria must be made at this time and several final preparations for the space shuttle are performed. The external tank is loaded with about 500,000 gallons of cryogenic propellants. When T-6 is counting, they finish the filling of the tank. At the T-3 hold, there is a two and a half hour time lapse. The crew is briefed about weather and the report is televised. More final inspections and preparations are performed. When counting, the T-3 segment is the time when the space crew heads to the launch pad and enters through the White Room. The craft is checked for leaks and properly sealed. At the T-20 minute hold, there is a 10 minute time lapse in which briefings are completed. When time is counting in this segment, final preparations for takeoff are made. At T-9 and holding, flight recorders are activated and final launch prep is completed. During counting, the complex procedures involved in creating liftoff are performed. At approximately T-6.6 seconds, the main engine is started and liftoff finally occurs at T-0!
Although the large countdown timer is an attraction and point of interest, there are more timing mechanisms used by NASA.
In an informative article by NASA regarding the Space Shuttle Main Engine Controller, the time-telling method is described. Aboard the shuttle, the computer’s input and output interface is comprised of several different components, as well as a real-time clock and watch-dog timer, or WDT. The WDT is dual-redundant and is put in every DCU channel to communicate the performance of each one. One part of the dual timer is connected to the real-time clock for incrementation and the other is connected to output electronics. If not re-triggered by the DCU, the WDT times out in 18+3 milliseconds. The skew and frequency variations are calculated and considered in order to maintain failsafe periodic testing and switching. If you’re wondering what kind of clocks are used by NASA in general, they’re radio-controlled or atomic. As of today, they’re some of the most reliable and precise time-telling devices.
These clocks all sound very precise, but never think that NASA is done with timekeeping research.
According to “Tick Tock Atomic Clock” by NASA Science News, the NIST-F1 laser-cooled atomic clock is the country’s main time and frequency standard. It is located in Boulder, Colorado. They have tested atomic clocks in space and continue to do so, researching whether or not they maintain their abilities at the International Space Station, which is free-falling around the Earth.
The “Tick Tock Atomic Clock” article explains that much like the NIST-F1, the particles are cooled in a weightless environment, which is optimal for movement and observation. In doing this, they’re also testing Einstein’s theory of general relativity. Clocks in space or on board space shuttles that are in orbit gain an extra second for every 10,000 years compared to clocks on Earth. NASA expects that unraveling this phenomenon will only be the beginning of understanding the complexities of time and space.
If you want to see the launch timer during the next big event, visit NASA’s official online timer found on their countdown page. If you plan to open this page at the T-9 and counting interval, be sure to download Java in advance, as the page requires a Java plugin to function correctly.
An exciting peek inside NASA's control room...
To cap it all off, we’ve got a pretty amusing anecdote on the subject of NASA and countdowns. It was back in May, 2007 and we were checking out some server logs for OnlineClock.net when we found several hits coming from NASA.gov as a the referring website. Curious and excited that perhaps NASA was linking to our countdown, we entered the referring URL into our web browser…and what did we see on NASA.gov? A carbon copy of Online Clock’s famous Countdown Timer. 
Now, what would you do in a situation like this? First of all, we were very flattered. But after several days the idea of having a copy of our timer on the NASA site just didn’t seem right. We weren’t given credit for it, after all. Soooo, we somehow found an email address for someone connected with the website, and we wrote them an email explaining that our countdown clock had apparently been copied onto their web servers. (The web page it was on wasn’t even protected by a login.) Anyway, to make a long story short, a webmaster associated with the website wrote us back that they’d taken the copy of our countdown down from the NASA web servers (which was true)…and that it wouldn’t be used in any final version of any countdown on the NASA website.
We even have a screenshot of our countdown as it appeared on NASA’s web server here, just as a curiosity. And heck, we love NASA and are totally flattered by the experience…we just like to tell this story occasionally as an amusing anecdote – it’s part of the five+ year history of the world’s original Online Alarm Clock website!
So, we hope you’ve enjoyed OnlineClock.net‘s special look at countdowns and NASA!
We’re out of here in 5…4…3…2…1…LIFT OFF !
Countdowns Used By NASA is a post from: Alarm Clock Blog, the official blog of the original Online Alarm Clock.
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