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PART 1: WebChat with weather technologist
and more WEBCHAT WITH WEATHER TECHNOLOGIST AND MORE
Upcoming events in the Shuttle Team Online chat room include: Wednesday, July 16, 1000 a.m.-1100 a.m. Pacific: Frank Merceret is part of a team that provides systems for forecasting weather conditions for space shuttle launches, landings or ground operations. At times his team advances the state-of-the-art by developing new weather equipment. Thursday, July 24, 1000 a.m.-1100 a.m. Pacific: John Horack is the Science Communications Coordinator for the STS-94 Mission Scientist Team. These chats will let you interact with the enthusiastic folks who make the shuttle program go. To participate, all you need is a modern Web browser. If you want to ask questions (instead of just observing), you will need to RSVP ahead of time by sending a note to ocox@mail.arc.nasa.gov For all of the details, visit http://quest.arc.nasa.gov/space/events/interact.html [Editor's note: Paul is an electronics engineer in the Contamination Monitoring Laboratory at the Kennedy Space Center. Paul's group develops instruments for monitoring the clean rooms where payloads are processed, improving the ability to measure contamination.] MAKING AIR-SNIFFING MACHINES
Paul Mogan http://quest.arc.nasa.gov/space/team/mogan.html June 25, l997 One of the projects we're doing is putting together some ammonia detection carts. They have instruments in them that detect ammonia vapor concentration. We are designing these because the space station elements use ammonia as a refrigerant instead of freon. Concentrations of ammonia that are too high can be toxic at one level, and flammable at higher levels. So when processing is being done at Kennedy Space Center's Space Station Processing Facility with ammonia, we want to be able to detect ammonia vapors in case there is a leak. My role in these projects is to get others started on the work, defining the requirements, doing conceptual design, and working with the people in the lab to implement the designs. What we first did on the ammonia detecting project was to produce a prototype, which was used by the Operations people. They liked it, so we enhanced the design and are producing final units that are going to be fully up to our design standards. We made smaller parts; changed the type of computer that is used on it; rewrote the software, and made it more functional. We are now converting the prototype of the ammonia detection cart into a hydrocarbon detection cart for use with the AXAF payload, since our customers want a hydrocarbon detection cart. We "trained" the instrument to detect hydrocarbons instead of ammonia compounds. One of the reasons we had to use a more sophisticated instrument is because we do many different things in our processing area. A lot of different chemicals may be used in one area, and so the instruments can be fooled. An alarm may sound which indicates a hazardous situation when, in fact, only harmless vapors are present. Another project we're working on is developing a real-time monitor for particulate fallout. We've invented it, it's been patented, we've worked with it a lot, and now we're redesigning the electronics and enhancing it to make it cheaper to build and more sensitive so that smaller amounts of contamination could be detected. At this time, we think a company is going to commercialize our product. When we work on something and someone else thinks it's a good idea and sees a market for it and will manufacture it, that's a real feeling of success. [Editor's note: Stokes is a manager in the Mission Evaluation Room, or MER. The MER is a large room where several engineers monitor data from the Shuttle during missions. If the data does not look the way it should, they to figure out why. Stokes is the lead MER manager for the STS-94 mission.] THE MYSTERY OF THREE MASTER ALARMS
Stokes McMillan http://quest.arc.nasa.gov/space/team/mcmillan.html July 3, l997 The MER's first detective task of the mission involved something that happened right after ascent when the pilot, Eileen Collins, called down that she received three Master Alarms when she shut down APU #3. There are three auxiliary power units (APUs) on each Orbiter that pressurize the three hydraulic fluid systems. Hydraulic fluid at 3100 psi moves the main engine nozzles to provide ascent steering (called thrust vector control) along with many other uses. The APUs, controlled by switches on the pilot's right, are started about 4 minutes prior to launch and shut down roughly 5 to 10 minutes after main engine cut-off. When an APU is shut down, it is normal to get two caution and warning Master Alarms as the hydraulic pressure drops off. The caution and warning system (C&W) is the alarm system that alerts the crew when some Orbiter parameter (pressure, temperature, voltage, etc.) goes out of limits. Additionally, a parameter may have two different limits, called "hardware" and "software" limits. Hardware limits on a critical parameter sound a Master Alarm and produce a light on the 40-light C&W panel matrix located in front of the commander and pilot. This light generally tells what Orbiter system had the problem. Software limits also sound a Master Alarm and produce a fault message on the crew's CRT display. A Master Alarm is called this because, along with a loud alert tone to the crew, a red "Master Alarm" button is lit in several places throughout the Orbiter, including in front of both the commander and pilot. By depressing this button, the Master Alarm light goes out and the alert tone is silenced. In each of the three hydraulic systems, the hydraulic pressure that we're interested in has two different pressure sensing devices, transducers, located at slightly different places on the hydraulic lines. One transducer is used for hardware C&W limit detection, and the other for software C&W limit detection. Although both C&W limits are 2400 psi (in other words, if the hydraulic pressure decreases to 2400 psi, alarms go off) the hardware and software alarms may not occur simultaneously due to transducer biases, position differences, and timing differences. So when the pilot shuts down each APU, she expects to get two Master Alarms, separated by a second or so, as the controlling APU's hydraulic pressure decreases below 2400 psi. They train for this event hundreds of times in simulators and get used to quickly depressing the Master Alarm button to stop the alarm and extinguish the light. So imagine Collins' surprise when she shuts down APU 3, gets the normal two Master Alarms, and then quickly gets a third! A glance at her instruments show what she would normally see (including the "HYD P" light on the C&W matrix and the "HYD PRESS" message on her CRT) so she pushes the Master Alarm button a third time, calls this strange occurrence down to the ground, and moves on to other post-ascent procedures. We start pulling data in the MER. Thanks to our advanced data collecting system we can plot data on anything and have it on our displays or paper in minutes. Yep, there are the three rapid Master Alarms. Then we plot hydraulic system 3 pressure on the same time scale as the Master Alarms. We see the hardware Master Alarm almost simultaneously with hydraulic pressure going below 2400 psi, followed soon by the software Master Alarm. But wait! These are the 2nd and 3rd Master Alarms - we got another one seconds ahead of these two that doesn't appear to be connected to hydraulic pressure. We look at the other CRT C&W messages that occurred during ascent and see none that correspond to this time. A Master Alarm with no CRT message means we had a hardware C&W limit exceeded. The lack of a message means a software C&W limit was not exceeded. Another thing about hardware C&Ws is that they are stored in the Orbiter's computer memory. In addition to the forward C&W light matrix, there is another normally unlit C&W matrix of 120 lights in the right rear of the flight deck where, when the crew throws a switch, lights come on producing numbers that represent all the hardware C&W limits that were exceeded since the crew last erased this C&W memory (in this case, prelaunch). It does not give an idea of when this limit was exceeded, however. As I said in an earlier journal explaining the MER, we in the MER often work with the Mission Control flight controllers to solve problems. After working on theories all the first night, we discussed this with flight controllers the next morning and soon Capcom asked the crew to activate the "MEMORY READ" switch. This produced 16 numbered lights coming on. The crew read down the numbers and we got to work evaluating them. The story started emerging. Each APU has many gears within it that require lubrication, just like the engine of a car. Lubrication oil circulates throughout these gears and gets very hot, around 270 deg. F. The lube oil is monitored so that it does not get too hot, and C&W alarms will sound if it does. For lube oil, however, there is a small difference between the hardware C&W limit (286.8 deg F) and the software C&W limit (290 deg. F). For each APU, the associated lube oil lines along with hydraulic fluid lines (also very hot) are routed into a large high-tech can where water is sprayed on them to cool off the two fluids. Lube oil is cooled to around 250 deg. F and returned to the APU. The resulting steam is vented overboard. This is the water spray boiler (WSB). Again, there are three of them - one for each APU/hydraulic system. Each WSB is normally shut off by the pilot approximately 20 to 30 seconds before its associated APU is shut down so that there will be no water left in the WSB can or steam vent line. This water could turn to ice and cause difficulty in the next WSB start. One of the 16 rear C&W lights the crew called down was #58, APU 3 OIL T (lube oil temperature high). We looked at the data and saw that there was a 23-second delay between WSB 1 and APU 1 shutdown, 27 sec. between WSB 2/APU 2, and a slightly long 45 sec. between WSB 3/APU 3. For 45 seconds the APU 3 lube oil heated up without being cooled. Right before APU 3 was shut down, the lube oil temperature broke through its hardware C&W limit of 286.8 deg. F. It peaked at 287.0 deg F. and then started cooling as the APU stopped running. This produced the first Master Alarm. There was no CRT message since the 290 deg. F software C&W limit was not reached. Seconds later the decreasing hydraulic pressure produced the second and third (normal) Master Alarms. Voila. There was no hardware damage, no one messed up. It was just one of those coincidences that occasionally pops up. Events like this are one reason why I like my job. STATUS OF STS-94
Below is some status of the STS-94 mission as it unfolds. This material comes directly from the Shuttle Web site at http://shuttle.nasa.gov With almost 11 full days on orbit under their belts, the astronauts on board the Space Shuttle Columbia are moving into the final phases of a 16-day agenda of microgravity science research that the mission scientists at the Spacelab mission operations control center report has returned more data than they had expected. Most of the activity today has been combustion experiments. Payload specialist Greg Linteris is the combustion specialist among the crew of Columbia. He notes that the results of these combustion experiments could lead to better use of fuels on Earth, with financial and environmental advantages. "The goal [of the combustion experiments], of course, is to try and learn things about the fundamental properties of combustion so we can make more efficient, cleaner-burning devices down there on Earth. . . . . the point of all this is that billions of dollars can be saved if we can save just a few percent [by burning fuel more efficiently], and so combustion research is an active area of research that's really benefiting from this microgravity science mission. . . . "One of the experiments is studying very, very lean flames that might be appropriate for very lean-burning engines of the future, and some of those mixtures are very weak and yet they can still burn in microgravity. Other flames look like tiny beads or droplets, and they are spherical. Because the buoyancy doesn't cause the gas to rise up here, everything propagates out spherically. It's really quite beautiful, and that's what allows us to study them in more detail, because without the buoyancy disrupting the flow we can learn a lot more about the reaction zone, which is what we're trying to study." Columbia is now flying about 185 miles above the Earth. Jim Halsell is videotaping experiment activities in the Spacelab module, where Don Thomas and Greg Linteris are working with two experiments investigating characteristics of the combustion of liquid droplets in microgravity.
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