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Sunday, February 19, 2012

Size Matters


In our celestial navigation classes, I always stress that the inherent flaw of utilizing spherical trigonometry on a body which is not actually a sphere introduces navigation errors many times larger than those introduced by imperfections in our instruments, or rounding errors in our logarithmic tables. This happens to be true, but I had never bothered to actually quantify this until yesterday. One of my coworkers recently sat for his 500 ton Master's license, and one of the questions he was asked was the great-circle circumference of the earth. Presumably the answer the USCG was looking for was 21,600 nautical miles, which is just 360° x 60' of arc. Which would be true, if the earth happened to be a sphere. Which, of course, it isn't.

Along any of earth's meridians, the circumference is about 21,603 nm, which is pretty close to the abstract spherical circumference. Along the equator, however, the earth's circumference is about 21,639 nm. 39 nautical miles is about 45 statute miles, or 72 kilometers. A navigation error of this magnitude is far from trivial.

Fortunately, by the nature of the way celestial navigation is performed, the greatest distance we ever have to worry about is 1/4 of the circumference of the earth, and this in turn limits our possible position error to 1/4 of that distance.

So, here's the very worst case imaginable. You are somewhere on the equator, and you take sights of the stars Mintaka and Polaris at the moment that both of these objects are just touching the horizon. Let's ignore all of the other reasons why this is a really bad idea, and also ignore the very large error in atmospheric refraction which would also occur in this case. We see that the actual geographic position of Polaris is only six tenths of a mile further away than our standard sight reduction would tell us, but Mintaka is nearly ten miles further away. Yes, ten. And even if we shoot Mintaka at the more reasonable altitude of 45°, the error is still in the neighborhood of 5 nautical miles.

By extension, if we are in the tropics, all celestial bodies on the equinoctial will be in error by as much as ten nautical miles, and if we are in temperate latitudes they may still be in error by as much as five nautical miles. From the standpoint of ocean navigation this isn't horrible. But it does give some perspective on the relative importance of precision in celestial navigation, as opposed to accuracy.

Monday, February 13, 2012

To rocks and the red planet: the NASA FY 2013 Budget Estimate

Here we are, again.

NASA's 2013 budget looks, well, an awful lot like the 2012 budget. But at least now we have some more specifics, and something a bit sexier than the ISS as a centerpiece.

Looking at what is on the docket, to quote John Mellencamp, "it ain't love, but it ain't bad".


In no particular order--

Space X and other commercial operators will begin regular crew and cargo flights to the ISS and other low earth orbit destinations.

The SLS/Orion project will continue, with uncrewed missions beginning in 2017 and crewed missions beginning in 2021. The only destinations mentioned (repeatedly) were near-earth asteroids and Mars. No mention of the moon or the earth-moon L1 or L2 Langrangian orbits. Back in November there had been discussion of building a semipermanent space station at the Earth-Moon L2 orbit, that seems to have been tabled. Lunar landing is apparently completely out of the question, or at least completely out of the budget, so it looks like NASA is opting to bypass the moon entirely. For the asteroid and Mars missions, much emphasis was placed on the integrated roles of humans and robots. The missions of Mars Science Laboratory and the rover Curiosity appear to be especially focused on research and preparation for crewed missions to Mars.

Research satellites for astronomy, atmospherics, space-weather and asteroid tracking continue to be a priority, as does research in advanced aviation technology.

The James Webb Space Telescope continues to be funded, now looking to launch in late 2018. I consider the JWST to be the single most important project NASA has ever been involved in, but Congress does not share my enthusiasm; I'm very glad it made the cut, again.

Given the current austerity of the federal budget a a whole, this is probably the best we could hope for at this point. Here is the 2013 budget estimate in its entirety:

http://www.nasa.gov/pdf/622655main_FY13_NASA_Budget_Estimates.pdf

Saturday, February 11, 2012

One small step for woman...

NASA is finding that some male astronauts, subsequent to a six month mission on the International Space Station, are suffering debilitating and possibly permanent vision loss due to papilledema.

I am not an opthamologist, I have no idea what papilledema is, or what that means. Here is the link to a pdf from NASA which gives good medical information for those inclined and capable to decipher such.
http://ston.jsc.nasa.gov/collections/TRS/_techrep/TM-2010-216114.pdf

I don't know why it seems to affect only men and not women. I don't especially care. It simply happens to be.

The relevant point is, six months is about the minimum amount of time we could get astronauts to Mars from Earth, using the technology of the SLS rockets and Orion spacecraft. Astronaut Mike Barratt, who is one of the individuals experiencing papilledema, believes that the solution is to wait for better and faster technology to shorten the length of time in space. This is not unreasonable for a crewed mission to Mars, but as we venture further afield to Ceres and the icy moons of Jupiter and Saturn, barring building the real (atomic pulse) Orion we probably are going to need to exist in space for greater than six months time.

The first step, obviously, is to extend the missions on the ISS to see if other health issues arise with longer stays in space. ISS is close; if somebody starts to exhibit serious health problems it's pretty easy to get them back to earth quickly. This will not be true for Mars.

The second, as Barratt proposed, is to continue R&D on better propulsion systems, such as the ion engines being used by the Dawn spacecraft, and solar sail technology.

Third, continue developing SLS, and continue with the already planned Mars missions. For exploration missions, send crews of only women. For colonization missions, send crews of only women, with a sperm bank. This isn't rocket science.

Even without the papilledema issue, women are arguably better candidates for space flight than men. Simple gender dimorphism has provided women with bodies which are smaller, and consume less food, oxygen and water than their male counterparts. Their body-fat is also better distributed for thermal insulation, and women are less susceptible to trauma-induced shock. And all the worlds we're likely to explore and colonize have significantly less gravity than Earth, so it isn't as likely that upper-body strength would be a major hindrance.

Women are probably just better suited to boldly go, where no man has gone before.




======================================================


Astronaut feels space's toll on his body


(CNN)
It’s not really why he signed up to be an astronaut, but like it or not, Mike Barratt and his eyes have become a science project.

The eye charts he reads, the red drops that turn his eyes yellow and the ultrasounds being performed on him could determine whether he or any other astronaut ever journeys into deep space or sets foot on other worlds.

NASA’s new priority is how to protect astronauts from going blind on the years-long trip to get wherever they are going.

“I absolutely agree that this is our number one priority,” Barratt said.

Why?

Because when Barratt blasted off to the international space station, he needed eyeglasses for distance. When he returned to Earth, his distance vision was fine, but he needed reading glasses. That was more than two years ago. And he’s not getting better.

“We really need to understand this. This is a critical point for understanding how humans adapt to spaceflight,” he said.

In the past few years, about half of the astronauts aboard the international space station have developed an increasing pressure inside their heads, an intracranial pressure that reshapes their optic nerve, causing a significant shift in the eyesight of male astronauts. Doctors call it papilledema.

Female space travelers have not been affected.

Some of the astronauts slowly recover. Others have not.

Space station astronauts typically spend about six months in orbit.

Barratt is one of 10 male astronauts, all older than 45, who have not recovered. Barratt returned from a six-month stint aboard the station in October 2009 and has experienced a profound change in his sight.

He used to be nearsighted. But now, the space veteran says he’s eagle-eyed at long distance but needs glasses for reading. There is no treatment and no answers as to why female space flyers are not affected.

CNN spent part of a day with Barratt, watching as doctors monitored his progress with high-resolution testing as they try to understand how the weightless environment of space is causing half of all space station astronauts to have this vision change. Today, space station astronauts fly with specially designed variable focus glasses to help combat the vision shift.

“The big benefit of these is that they allow us to adjust for significant prescription changes,” said Dr. Robert Gibson, a senior vision consultant, who was brought in to help study the problem.

Doctors have found that Barratt’s retinas have microscopic folds or wrinkles on them, and the back of his eye, the optic nerve, is no longer round but has flattened.

“I think this is showing that there are physiologic aspects of adaption to spaceflight we weren’t seeing before,” said Barratt.

This raises a red flag for all of NASA’s plans for long-duration human space flight. The space station is supposed to be the test bed for how humans would learn to live in space, but it opens profound questions on whether humans will ever venture to Mars or to an asteroid if they are unable to figure out how the outer-space environment is affecting the eyes.

“This has all of our attention,” said Terry Taddeo, the acting chief of space medicine at Johnson Space Center in Houston.

“It is a serious problem and one we are going to have to understand more about before we would be able to send somebody into a long-duration mission away from Earth, where they would be away for years,” he said.

Right now, the only data that doctors have are from six-month tours of duty on the space station.

NASA has begun doing extensive preflight and postflight eye exams, including high-resolution MRIs of the eyes. There have been anecdotes from some space shuttle astronauts who also complained about vision change, but it does not appear they had long-lasting effects from the much shorter space flights that typically lasted up to about three weeks.

“What we’re seeing appears to occur within the first couple of months of flight and appears to level off, plateau after about four to five months,” Gibson said.

“If it’s just a matter of giving them a stronger prescription, we can live with that,” he said. “But if there is an elevated intracranial pressure as the cause of this, we have to be concerned about other neurologic effects."

That means there could be other effects on the body that haven’t become apparent.

This is why a three-year mission to Mars is in question.

It would be humans' next great leap, and NASA is spending almost $18 billion over the next five years to develop a heavy lift rocket that would take astronauts to the Red Planet or even to an asteroid. They would travel in a new spacecraft, Orion.

But right now, a trip to Mars is still more science fiction than fact. No one is calling this vision problem a showstopper, yet the program’s price tag begs for a solution to be found fast so NASA won’t be building the world’s largest, fastest rocket to nowhere.

Dr. Bruce Ehni, a neurosurgeon at the VA Medical Center at the Baylor College of Medicine in Houston, has consulted with NASA and is the only neurosurgeon on their panel.

“If they can’t predict who is at risk ... they put his health in jeopardy. They put, possibly, the mission in jeopardy if he can’t see or do his job effectively,” he said.

But Barratt thinks that any deep space venture to Mars is still 20 years away. He’s hoping that spacecraft will be a whole lot faster than anything the space agency can fly now.

“You fly fast, and you don’t worry,” he said, with a grin.

“I’m still hopeful that in 20 years, we’ll have advanced propulsion capabilities that can get us there in a matter of weeks to a few months. Then, a lot of these problems go away,” he said.