Universe Today : Shuttle Launch Decision on Tap

Written by Nancy Atkinson

NASA engineers continue to repair a faulty electrical connector on Space Shuttle Atlantis’ external fuel tank which has delayed the launch of the STS-122 mission to the International Space Station. An update of the progress on that work will be presented at a mission management team meeting scheduled for Thursday, January 3 and mission managers will perhaps then be prepared to announce a proposed launch date for Atlantis.

The repairs could take several days or even weeks. At a press briefing last week, shuttle program manager Wayne Hale declined to offer a probable launch date. “We’re in the middle of troubleshooting and repair,” he said. “Until that gets a little bit further along, I actually have no valid dates to give you… To avoid what I think would be a totally misleading headline along the lines of ‘NASA Delays the Space Shuttle Again’ we’re just not going to give you a launch date because that, in fact, would not be accurate.”

The engine cutoff (ECO) fuel sensor system transmitted false readings during two launch countdowns for Atlantis earlier in December. A fueling test performed on December 18 isolated the problem to a 1 ½ -by 3 inch connector called a pass-through connector, located both inside and outside the tank. The wires for all four ECO sensors pass through the same connector. From the data of that test, engineers believe the problem lies in gaps between pins and sockets on the external side of the pass-through connector when the system is chilled to cryogenic temperatures, as when the tank is filled with liquid hydrogen and oxygen.

Engineers have removed the connector and are bench-testing the components in similar cryogenic conditions to try to duplicate the failure. Meanwhile, new hardware is being installed on the tank as the shuttle sits on launchpad 39A at the Kennedy Space Center.

“We have allowed the team that did the troubleshooting to very thoroughly go through all the data,” said Hale. “They have told us they are sure the problems that we’re seeing reside in that series of connectors. Where exactly in that series of connectors is a little bit open to interpretation.”

The connectors on the inside of the tank are being visually inspected. “It is a possibility that the internal connector is involved,” Hale said. “However, all the physics based discussion of the kinds of things that can happen point to something happening on the external connector.” Problems with the internal connector would involve “more invasive” work, Hale said, that could possibly damage the tank.

A similar repair was done to the Atlas rockets several years ago to fix problems with circuitry in the Centaur stage. ECO sensors protect the shuttle's main engines by triggering engine shut down if fuel runs unexpectedly low. The Space shuttle main engines running without fuel would likely result in an explosion.

The STS-112 mission will deliver the European Space Agency’s Columbus science module to the station along with a new crew member Leopold Eyharts from France who will take over for Dan Tani. Tani, whose mother was killed in a car accident on December 19, will return to Earth on Atlantis.

“These repairs and troubleshooting activities will determine when we will launch,” said Hale. “The plan to go forward will take as long as it takes, but we don’t think this will be a long-term thing. Probably something that will take a couple of weeks.”

Universe Today : Controversial NASA Aviation Report Released

Written by Nancy Atkinson

NASA released the results on Dec. 31 from an $11.3 million federal air safety study. The agency previously withheld the report, and came under fire from Congress and news organizations for doing so. Earlier reports said NASA was concerned the data in the report would upset travelers and hurt airline profits. But today NASA administrator Mike Griffin and the head of NASA’s Office of Safety and Mission Assurance Bryan O’Connor said the release of the report was delayed to protect both pilot confidentiality and classified commercial aviation information.

“We came across instances in looking at the raw data where information was contained that could have compromised one of those two things,” said Administrator Griffin. “We determined that an independent review of that data was necessary in order to prevent such compromise.”

A panel led by O’Connor reviewed the 16,000 page report and data such as pilots’ names and other confidential information was redacted.

Also, Griffin said there are questions as to the validity of the data in the report, which has not been peer-reviewed.

“We consider the study was not properly organized and not properly reviewed, and that makes the results very difficult to interpret and to use,” he said. The study was conducted by the Battelle Memorial Institute for NASA.

An independant review of the data will be done in the future by the National Academy of Sciences.

Griffin said the original press release highlighting the refusal to release the data used “inappropriate language” to explain the rationale for not releasing the report.

NASA's survey, the National Aviation Operations Monitoring System (NAOMS), interviewed about 8,000 pilots per year from 2001 until the end of 2004. The program was terminated before moving on to interview flight attendants and air traffic controllers, as originally proposed.

Approximately one million dollars a year was put into this study. Griffin said it is a small fraction of NASA’s overall work, and in retrospect, the study did not receive the attention that it should have.

The report can be found on NASA's website. Its length makes it difficult to wade through the data. Additionally, some portions of the report that have not yet been edited for confidential information have been left out. NASA will release the remainder of the report as soon as possible.

The original plan for the survey never called for NASA to interpret and analyze the data. The study’s purpose was to develop new methodologies for collecting aviation safety data, and then the data would be transitioned to the aviation safety community. “NASA conducts research, and this was one element of such research,” said Griffin. “NASA extended the research, which was originally to be concluded in 2004 in order to properly fund the transition of the data and its review. We’ve gone the extra mile with this data and we’ve gone well beyond our original intentions, which is why we’ve brought it to an end.”

It remains uncertain whether any data from the report will ever be used by the aviation safety community. Griffin said it was his understanding that the FAA has “simply moved on from NAOMS,” and that the FAA has over 150 different programs to provide survey data from individuals involved in all areas of air flight.

While NASA didn’t analyze the data, Griffin offered his opinion of what the report surmises: “What the flying public should understand is that they have approximately the same risk of dying from a lightning strike as they do dying from an air transport accident in the United States, which means to say that this is one of the safest forms of travel that human beings have ever invented, and that no one should think otherwise.”

In testimony to congress earlier this year, Griffin characterized the data in the report as not as valid as he would prefer to have for a NASA report. Griffin said that he still feels that way, and that his concern is that this research work was not properly peer reviewed and the data that was extracted from the survey was not properly vailidated at its conclusion.

The survey purportedly unearthed approximately four times as many engine failures than the FAA has documentation for. “It calls into question the reporting mechanisms rather than the underlying rate of engine failures, which we believe we understand,” Griffin said, adding there are other inconsistencies, as well. “Those kinds of inconsistencies, when we looked at the data, gave us pause for thought, and still do.”

“The value of this will need to be determined by the larger aviation community, which I remind you, does not reside within NASA,”Griffin continued. “All that we at NASA have said is that this survey was not peer reviewed and the data was not validated at its conclusion….its up to others whether or not they believe this research has value.”

Griffin had promised to release the report before the end of 2007, and he did so without compromising confidential information that, by law, NASA is prohibited from releasing.

Griffin said this survey doesn’t cast any doubt in his mind about the safety of aviation in the United States. “I did not, having looked at a snapshot of the data, see anything that the flying public would care about or ought to care about,” he said. “But it’s not for me to prescribe what others may care about. We were asked to release the data and we did that.”

The report can be found on the NASA website.

Original News Source: NASA News Audio

Bad Astronomy : Repost: Happy New Year!

I don’t usually repost blog entries, but it’s the end of the year, and my post at this time last year took me forever to research and write, and I like it so much I’m gonna just plop it down here to end 2007. Enjoy.

Yay! Tonight at midnight it’s New Year!

But what does that mean, exactly?

The year, of course, is the time it takes for the Earth to orbit the Sun, right? Well, not exactly. It depends on what you mean by "year", and how you measure it. This takes a wee bit of explaining, so put down the champagne, take the lampshade off your head, and hang on.

First, I will ignore a few things. For example, time zones. These were invented by a sadistic watchmaker, who only wanted to keep people in thrall of his devious plans. So for now, let’s just ignore them, and assume that for these purposes you spend a whole year (whatever length of time that turns out to be) planted in one spot (though I’ll note that as I write this, it’s already 2007 in Australia and other points west of the international date line).

However, I will not ignore the rotation of the Earth. That turns (haha) out to be important.

Let’s take a look at the Earth from a distance. From our imaginary point in space, we look down and see the Earth and the Sun. The Earth is moving, orbiting the Sun. Of course it is, you think to yourself. But how do you measure that? For something to be moving, it has to be moving relative to something else. What can we use as a yardstick against which to measure the Earth’s motion?

Well, we might notice as we float in space that we are surrounded by zillions of pretty stars. We can use them! So we mark the position of the Earth and Sun using the stars as benchmarks, and then watch and wait. Some time later, the Earth has moved in a big circle and is back to where it started in reference to those stars. That’s called a "sidereal year" (sidus is the Latin word for star). How long did that take?

Let’s say we used a stopwatch to measure the elapsed time. We’ll see that it took the Earth 31,558,149 seconds (some people like to approximate that as pi x 10 million (31,415,926) seconds, which is an easy way to be pretty close). But how many days is that?

Well, that’s a second complication. A "day" is how long it takes the Earth to rotate once, but we’re back to that measurement problem again. But hey, we used the stars once, let’s do it again! You stand on the Earth, and define a day as the time it takes for a star to go from directly overhead to directly overhead again: a sidereal day. That takes 23 hours 56 minutes 4 seconds = 86,164 seconds. But wait a second (a sidereal second?) — why isn’t that exactly equal to 24 hours?

I was afraid you’d ask that — but this turns out to be important.

It’s because the 24 hour day is based on the motion of the Sun in the sky, and not the stars. During the course of that almost-but-not-quite 24 hours, the Earth was busily orbiting the Sun, so it moved a little bit of the way around its orbit (about a degree). If you measure the time it takes the Sun to go around the sky once — a solar day — that takes 24 hours, or 86,400 seconds. It’s longer than a sidereal day because the Earth has moved a bit around the Sun during that day, and it takes a few extra minutes for the Earth to spin a little bit more to "catch up" to the Sun’s position in the sky.

Here is a diagram from Nick Strobel’s fine site Astronomy Notes that will help explain this:

See how the Earth has to spin a little bit longer to get the Sun in the same part of the sky? That extra 4 minutes (really 3 m 56 s) is the difference between a solar and sidereal day.

OK, so we have a year of 31,558,149 seconds. If we divide that by 86,164 seconds/day we get 366.256 days per year.

Wait, that doesn’t sound right. You’ve always read it’s 365.25 days per year, right? But that first number, 366.256, is a year in sidereal days. In solar days, you divide the seconds in a year by 86,400 to get 365.256 days.

Phew! That number sounds right. But really, both numbers are right. It just depends on what unit you use. It’s like saying something is 1 inch long, and it’s also 2.54 centimeters long. Both are correct.

Having said all that, I have to admit that the 365.25 number this is not really correct. It’s a cheat. That’s really using a mean or average solar day. The Sun is not a point source, it’s a disk, so you have to measure a solar day using the center of the Sun, correcting for the differences in Earth’s motion as it orbits the Sun (because it’s not really a circle, it’s an ellipse) and and and. In the end, the solar day is really just an average version of the day, because the actual length of the day changes every, um, day.

Confused yet? Yeah, me too. It’s hard to keep all this straight. But back to the year: that year we measured was a sidereal year. It turns out that’s not the only way to measure a year.

You could, for example, measure it from the exact moment of the vernal equinox in one year to the next. That’s called a tropical year. But why the heck would you want to use that? Ah, because of an interesting problem! Here’s a hint:

The Earth precesses! That means as it spins, it wobbles very slightly, like a top does as it slows down. The Earth’s wobble means the direction the Earth’s axis points in the sky changes over time. It makes a big circle, taking over 20,000 years to complete one wobble. Right now, the Earth’s axis points pretty close to the star Polaris, but in a few hundred years it’ll be noticeably off from Polaris.

Remember too, that our seasons depend on the Earth’s tilt. Because of this slow wobble, the tropical year (from season to season) does not precisely match the sidereal year (using stars). The tropical year is a wee bit shorter, 21 minutes or so. If we don’t account for this, then every year the seasons come 21 minutes earlier. Eventually we’ll have winter in August, and summer in December! That’s fine if you’re in Australia, but in the northern hemisphere this would cause, panic, rioting, bloggers blaming each other, etc.

So how do you account for it? Easy: you adopt the tropical year as your standard year. Done! You have to pick some way to measure a year, so why not the one that keeps the seasons more or less where they are now? This means that the apparent times of the rising and setting of stars changes over time, but really, astronomers are the only ones who care about that, and they’re a smart bunch. They know how to compensate.

Okay, so where were we? Oh yeah– our standard year (also called a Gregorian year) is the tropical year, and it’s made up of 365.24 mean solar days, each of which is 86,400 seconds long, pretty much just as you’ve always been taught. And this way, the vernal equinox always happens on or around March 21 every year.

But there are other "years", too. The Earth orbits the Sun in an ellipse, remember. When it’s closest to the Sun we call that perihelion. If you measure the year from perihelion to perihelion (an anomalistic year) you get yet a different number! That’s because the orientation of the Earth’s orbital ellipse changes due to the tugs of gravity from the other planets. It takes about 100,000 years for the ellipse to rotate once relative to the stars! Also, it’s not a smooth effect, since the positions of the planets change, sometimes tugging on us harder, sometimes not as hard. The average length of the anomalistic year is 346.6 solar days, or 29,947,974 seconds 365.26 days, or 31,558,432 seconds. What is that in sidereal days, you may ask? The answer is: I don’t really care. Do the math yourself.

Let’s see, what else? Well, there’s a pile of years based on the Moon, too, and the Sun’s position relative to it. There are ideal years, using pure math with simplified inputs (like a massless planet with no other planets in the solar system prodding it). There’s also the Julian year, which is a defined year of 365.25 days (those would be the 86,400 seconds-long solar days). Astronomers actually use this because it makes it easier to calculate the times between two events separated by many years. I used them in my PhD research because I was watching an object fade away over several years, and it made life a lot easier.

So there you go. As usual, astronomers have taken a simple concept like "years" and turned it into a horrifying nightmare of nerdy details. But really, it’s not like we made all this stuff up. The fault literally lies in the stars, and not ourselves.

Now if you’re still curious about all this even after reading my lengthy oratory, and you want to know more about some of these less well-known years, then check out Wikipedia. They have lots of info, but curiously I found it rather incomplete. I may submit something to them as an update (like how many seconds are in each kind of year; they only list how many days, which is useful but could be better).

I have to add one more bit of geekiness. While researching this entry, I learned a new word! It’s nychthemeron, which is the complete cycle of day and night. You and I, in general, would call this a "day". Personally, if someone dropped that word into casual conversation, I’d beat them with my orrery and astrolabe.

Incidentally, after all this talk of durations and lengths, you might be curious to know just when the Earth reaches perihelion, or when the exact moment of the vernal equinox occurs. If you do, check out the U.S. Naval Observatory website. They have tons of gory details about this stuff.

Hmmmm, anything else? (counting on fingers) Years, days, seconds, yeah, got those. Nychthemeron, yeah, Gregorian, tropical, anomalistic… oh wait! I know something I forgot to say!

Happy New Year.