Earth Simulator (with Airplanes)

I've resuscitated this blog to write occasionally on my continuing infatuation with Microsoft Flight Simulator 2020. If you've read any of my earlier posts, you will know that I am a lifelong "airplane nut" and that MSFS does a very good job of simulating the experience of flying an airplane, as well as any simulator I have tried that doesn't move. It's actually better in most ways than the few I've tried that did toss me around in a small capsule with a screen in front (I have not yet tried a full motion simulator with VR, which could be great or sickening or possibly both). 

Even after hundreds of hours in the simulator, I am still finding new and wondrous things in the experience, and especially in the beautiful visual world as modeled within the simulator. As I have noted elsewhere, it is the combination of cloud computing, fast internet connections, fast computers, and advanced graphics processing that makes it all possible. Modeling the entire planet requires petabytes of data that can be selected and streamed "on demand" to your PC or XBox. There it is combined with flight modeling, weather modeling, sound modeling, and more to create the 25-60 high-res images per second needed to fool you into believing that you are in control of an airplane moving at extreme speed. One for each eye if you are in VR. 

I sometimes like to fly amphibious planes so I can land in water or on a runway. If I'm using Live Weather or if I decide to crank up some wind at ground level, water operations can be challenging. 

I devoted an earlier post to my amazement at the way light and weather are modeled in the sim, but sometimes I find new surprises. as when I was flying a silver PT-17 Stearman biplane near the Phare de Gatteville on the north coast of France, just after sunset. As I circled low around the lighthouse, the rotating beacon illuminated my wing, and the reflection was blinding! 

Even as I have started to take some real-life refresher lessons in a Cessna 172, I continue to be fascinated by what is really more of a dynamic "Earth simulator" than a "mere" flight simulator. 

The Joys of Virtual Travel

Is this thing on? This blog I mean. Since I haven’t written a post since 2018, I thought maybe the whole blog thing was over and nobody told me. We certainly seem to have passed the heyday of blogs if there ever was one. It was sort of cool back in 2005 when I was excited about Orbiter, a new space flight simulator I had discovered, and I decided to share my fascination with real and virtual space flight with anyone who cared to read those early posts. Cool to me anyway. I met a few other space bloggers and Orbiter fans and there was even a small online community of sorts for a while. Woo-hoo! If there are still any blog readers or old space blog colleagues around, welcome! Leave a comment! All my old posts seem to still be out there and we’ll soon see if this one joins them.

Of course, now it’s late 2021 and things have changed. You know what many of them are, but in addition, I retired from my job a few months ago, and between that and COVID, my travel has been sharply curtailed. But things have come full circle in a way. Last year I rediscovered an old interest, non-space flight simulators, and specifically Microsoft Flight Simulator 2020 (MSFS). I had played with various flight sims from 1994 to 2004, and between 1999 and 2004, I got my real private pilot’s license (2001). I didn’t fly as much as I hoped I would, but I feel lucky that I got to fly at all. For more information on that, please visit my other moribund blog, Flight SchoolRetrojournal.

When I say I didn’t fly much, I meant only as a pilot. As a passenger I flew constantly from 1983 until late 2019, just before COVID started. Hundreds of international business trips and a few cool vacations. I do miss that part of my working life, going places, seeing things, meeting people, doing things. It was great. In retirement, my wife and I plan to do some fun domestic and international travel once things settle down with COVID and a few other issues. Maybe next year.

In the meantime, MSFS allows me to experience some of the joys of flying and “virtual travel” from the comfort of my own office chair, with or without a VR headset. I’ll spare you the details you can learn from any number of websites or YouTube videos, but MSFS takes full advantage of the power of fast PC’s, graphical accelerators, and cloud computing to create a highly detailed simulation of the entire world, complete with “Live Weather” and stunning depictions of terrain, human-built structures, many different airplanes, and even other simulator pilots sharing the skies with you over the internet. It’s an amazing experience with a large high-res monitor, but even better with a modern virtual reality headset. I have the Hewlett-Packard Reverb G2 which works great with MSFS.

Where Have I Been?

I have spent some simulator time in a Cessna 152 flying around Central Massachusetts as I did in real life 15-22 years ago, and it’s fun to see how well Asobo has done recreating airports, towns, and terrain familiar to me (Asobo are the French makers of Microsoft’s current flight simulator). It is detailed enough to navigate “VFR” using familiar landmarks. You can usually even find your house! But with the whole world at my fingertips, and with a stable full of airplanes from ultralights to business jets to a Boeing 747, I’m not usually so close to home. When not flying a Beech Bonanza G36 or a tail-wheel XCub, I tend to favor an old Stearman biplane or the Aermacchi MB-339, an Italian-built jet trainer, both bought from third-party developers. 

Human and Robot Tour Guides

One thing I have enjoyed is a weekly group flight organized by Jules Altis, who happens to be an active private pilot as well as a simulator enthusiast. For months he focused on US National Parks of which there are many worth touring from the air. He would research the history and special features of each park and share those presentations and videos along with the flight plan for all of us to follow in the simulator and on Twitch or Discord. Olympia National Park, Washington, was my personal favorite. More recently he switched to a more informal format with international destinations like the Amalfi Coast of Italy, the Great Rift Valley of Africa, and the Tokaido Road in Japan. He makes use of a great free add-on developed by others called Bushtalk Radio which provides computer-narrated tours within the simulator of over twelve-thousand points of interest around the world. I’ve helped in small ways with Bushtalk Radio, especially with this brief trailer video that introduces it in the same synthetic “English lady” voice used for the actual tours (the music is mine).

Favorite Places

In addition to the “standards” like the Grand Canyon, Mount Fuji, and New York City, there are so many lesser-known mountains, lakes, cities, bridges, and dams, not to mention so many great airports. If you love airplanes you’ve got to love airports! Many of these sights are beautiful right out of the box, but there is also a facility for “add-ons,” both free and paid. In addition to an expanded air fleet (fancy a Spitfire or F-14 Tomcat?), you can find hundreds of airports with added details. Duxford Airfield, England is a current (free) favorite of mine. Scenery enhancements are also popular, many free, but many great commercial ones that are well worth a few dollars, like this improved version of Seoul, Korea which reminds me of my many visits there over the years.

I have created many videos which are usually short flights in some cool area I’ve discovered. I’ve experimented with adding my own music to a few, like this one of a Spitfire (White Cliffs of Dover, of course) or this flight around Tokyo. One of my favorite videos is this one (not mine) of many beauty spots, set to an instrumental version of “What a Wonderful World.”

This is already a long post so I will end here. I’ll probably write another one talking about what it is that makes the Microsoft Flight Simulator experience so engaging for me.

MSFS screenshots above, from the top (* add-on aircraft):

1. Stearman* over north Australia; 2. Dorand AR.1* (WWI) over Minnesota; 3. Stearman* passing through Tower Bridge, London; 4. Diamond DA-40NG over Sphinx Observatory, Jungfrau, Switzerland; 5. Cubcrafters XCub, Milford Sound, New Zealand; 6. Cessna 208 on a group flight in Iceland; 7. XCub on floats, Nahuel Huapi National Park, Argentina; 8. Beechcraft G36 near Lotte World Tower, Seoul, Korea; 9. Nieuport 17* (WWI) over Duxford Airfield, England; 10. Aermacchi MB-339* somewhere over Ireland

Here's a link to a shared Google Photos album with a few other screenshots from Microsoft Flight Simulator.

Perspective

My heart goes out to the many people who have been injured or lost loved ones in terrorist actions around the world, most recently the horrific Bastille Day truck attack in Nice, France. These actions are unconscionable and the people who perpetrate or support such acts must be brought to justice.  Terrorism is obviously intended to terrorize, and these attacks are certainly scary, with the scariness amplified by instant and repetitive news coverage that makes Nice or Paris seem as close as Orlando or Boston (and for my friends in France, recent attacks have been all too close). It is a small world thanks to global communication and the internet, and we know that terrorism, like other types of crime, can happen anywhere, so we shouldn’t be complacent. But we shouldn’t panic either.

Terrorism is a real problem, but it is not the end of the world, which is currently home to some 7.2 billion humans and countless other species. For perspective, note that in the US, something like 100 people die in car accidents each day. Worldwide, over a million people die annually in car accidents, and there are over half a million “intentional homicides” each year. So many lives tragically cut short every day, yet we hear nothing about most of these millions of deaths. Commercial plane crashes are rare, and when one does occur, many people may die, so it’s big news. The same with terrorist attacks, which have become more common worldwide, though nations like Iraq, Afghanistan, and Nigeria continue to bear the brunt of those attacks, even though attacks in Western countries get much more news coverage.  

You can Google for statistics as well as I can and find that you are more likely to be killed by falling furniture than by terrorism. My wife has recently told me she’s getting more concerned about my business travel, especially to Europe. But I am far safer on a business trip to anywhere in Europe, Japan, or Korea than I am driving my car to work. I’m not saying we shouldn’t be concerned about terrorism. It’s an awful thing if this is the “new normal,” and we shouldn’t simply accept that. We can and should come together worldwide to make progress against this threat, though it is certainly not the greatest threat to civilization that we face (that would be climate change).

Steven Pinker and others have pointed to extensive data to show that even as terrorism and crime fill the headlines, the world is not falling apart, and on an overall basis, violence in the world has greatly decreased, and not only because there are fewer wars.  Other forms of violence and cruelty are also greatly in decline, though they have not reached zero and probably never will. I’m optimistic that we can still build a better world for my grandchildren -- and for everyone else. We should not be complacent about terrorism, but we shouldn’t freak out, change our way of life, or start another war over it. 

The image above has nothing to do with it except that this is the planet we all happen to share (a screen shot from the free Orbiter space flight simulator, and one of my most popular pictures on Flickr). 

No Explanation Needed

One definition of a tautology is the needless repetition of an idea, statement, or word. It strikes me that some of the "big questions" that are often discussed about the universe and life are little more than tautologies. They may be interesting to discuss, and if you believe in God or another cosmic consciousness or creator, they might even seem to have meaning. But based on what is actually observable, there is a big and complex physical universe that has been chugging along for billions of years, much longer than there have been human brains to do things like wonder why. And for a few thousand years, there have been human brains, some with enough security and free time to do the wondering. That's it!

The "anthropic principle" is the one that bugs me the most. This is the idea that since physical constants and conditions are suitable for stable matter, life, and intelligence, and since we can conceive of these things having been otherwise, someone or something must have set them that way so matter, life and intelligence can exist. But this is a tautology, since we wouldn't even be around if this were not true. If the conditions were wrong, or if there are multiple universes and some don't have these conditions, there would be no "we" around to wonder about this. It clearly assumes some purpose for the universe or a god or creator that could make decisions about this. And if that is the case, who or what created that creator, and in what universe, with what physical constants, defined by whom or what? It's an infinite regress.

Why not stick with what's observable? As far as I'm concerned, the universe simply is. That doesn't mean I can't be awed by its beauty or impressed with its intricacy, or that I can't be curious about its many parts and try to understand how some of them work (that's why I majored in physics). It just means I accept the universe as the natural state of things and that I don't believe it was created for the benefit of humans. We are simply one of the complex manifestations of its properties. Life with a cherry on top (more like cherry Jello).

There's a related question that is often asked about the universe: Why is there something rather than nothing? Again it's a tautology -- if there were nothing, nothing would exist to even think about this. There is no why there.

Sometimes people talk about "the will to live." I have often marveled myself at the enormous efforts that animals (including humans) will make to survive or even just carry on their normal life cycles. Things like certain migrating birds that fly thousands of miles twice a year to feed and reproduce. But the will to live is "baked into" life itself because natural selection eliminates those without it. So it's one of those things that is both amazing and commonplace, even inevitable. Of course it has some side-effects that we and some of our fellow creatures may perceive as happiness or contentment. When my dog and I are well-rested and well-fed and are enjoying the sights and smells of a walk on a sunny fall morning, that feeling came from evolution too. It's still pretty awesome.

And what about "are we alone in the universe?" This is a different kind of question, not a tautology. It's worth thinking about, and even doing some research, although it is not as exact question as some people may believe it to be. Clearly there is insufficient data now to evaluate this, though this may not always be so. Humans are certainly expending some effort to find information related to this question through space exploration and other means, and as we have identified thousands of exoplanets, we know at least that there are other places where life similar to ours could exist.

Many years ago, astronomer Frank Drake defined an equation that aims to estimate the number of intelligent civilizations in the universe. It identified some of the relevant parameters of this question, and defined them as probabilities, although some of them are not well enough defined to plausibly consider as a probability. Things like "the probability that an intelligent life form will develop a technological civilization." This is almost like asking "what is the probability that my karma is purple?" How to you define "karma?" Do karmas come in colors? How to you even define "intelligent life?" Does that mean "capable of developing technology?" Isn't that a tautology?

I just read an article describing a similar equation that considers the probability of detectable life. The "Seager Equation" is geared to our current knowledge of (many) exoplanets and how likely it is we could detect some planetary biosignatures. It is a bit more physical than Drake's equation, and does not consider intelligence or technology. A planet hosting only blue-green algae might have an oxygen-rich atmosphere detectable by spectroscopic methods if conditions like distance, star type, exoplanets in the habitable zone of the star, and others are right. The answer to this question? Her best estimate is 2. Not 42. Not millions. But not zero or .0005. That suggests it is worth looking.

I hope we are not alone in the universe. I hope there is simple life and intelligent life in abundance and that someday we can find it. But if we are alone, that's OK too. We will keep busy and maybe even survive to a ripe old age. We aren't here for any particular reason, but it's a great party, and I'm glad we crashed it.

-----

Nick Bostrom has a book on anthropic bias that apparently goes much more deeply into this subject. I haven't read it, but his web site has a lot of helpful information.

The picture here is by Slovak graphic designer Martin Vargic. It's a chart showing his artist's impressions of 500 of the some 2000 confirmed exoplanets arranged by mean temperature (x) vs. density (y). Although these planets have not been directly observed, the depictions are not completely  fictional, as they are based on temperature, density, metal content, and other factors (the rings are purely for looks -- they are pretty common in our solar system, but only prominent on Saturn).

Plain or Peanut?

I watched a very interesting short video from Worldviews Network today, "A Global Water Story." I learned a lot about fresh water and how it's in increasing demand around the world, even as climate change makes dry areas drier and wet areas wetter and ancient underground aquifers sink rapidly. To set the scene, the video uses a clever analogy to show how little of our planet's water is fresh water. 

Imagine that all the water in the world is represented by a one gallon (3.8 liter) pitcher. All of this would be salt water except for three shot glasses of fresh water (a shot glass holds about 1.5 fl. oz. or 44 ml). The contents of two of the three shot glasses would be frozen polar ice. Of the fresh liquid water in the third glass, most of it would be underground. The drinkable amount available on the Earth's surface would be the volume of a single M&M candy (a volume of about 0.64 cm^3 or 0.64 ml):

Happy Earth Day!

Before it slips away and becomes belated as so many occasions seem to do, here's wishing everyone a very happy Earth Day!

The picture above is a screen shot from the Orbiter space flight simulator, which I keep wanting to return to playing with, but never seem to have time. This is a nice, big-picture graphic, but as a celebration of the Earth, it pales in comparison to the daily stream of fascinating Earth images beamed down from the International Space Station by its commander, Col. Chris Hadfield. Just amazing stuff. Follow him on Twitter or Facebook (or on Tumblr) if you really want to get to know the face of this wonderful planet! He also does great science demonstrations (thanks to Astropixie for this tip).

Beautiful Earth Views from ISS!

Some space advocates decry the fact that humans are currently "stuck in low Earth orbit." While I too would love to see humans branch out to the Moon, Mars, the asteroids, and perhaps further, I have to say that low Earth orbit is still a pretty cool place to be. Case in point: I recently learned that the current ISS commander, Canadian astronaut Col. Chris Hadfield, frequently posts pictures from the ISS on Twitter and Facebook. So I "liked" Col. Hadfield on Facebook, and I now receive daily reports and photos from the ISS. Pretty amazing stuff (you can also see his pictures on Tumblr).

I also found a wonderful video compiled from ISS photography, including time-lapse views of auroras and other beautiful images of Earth. Christoph Malin's "Making the invisible visible" is a 15 minute video that is described as "a tribute to the International Space Station Program as well as Dr. Don Pettit, NASA Astronaut and ISS Astrophotographer." The screen shot below is from the video, looking north over New England (notice the hook of Cape Cod in the lower center). Also note the green aurora along the limb of the Earth. You should watch this video, preferably in HD.  

Awesome (Truly!) Video

Overview by the Planetary Collective. See also this website.

Sitting On Top of the World

This has to be one of my absolute favorite space photos, a picture of astronaut Tracy Caldwell Dyson looking at the Earth through the recently added cupola windows on the ISS. Reminds me of the old blues/Cream song "Sitting on Top of the World." I would love to experience that view someday. This was NASA's Astronomy Picture of the Day on November 15.

Fall Day in New England

Wachusett Reservoir, October 25, 2009.

Getting Hyper(spectral)

As an optical engineer, I have a professional interest in all sorts of optical systems. I currently don't do optical design on a regular basis myself, but sometimes I have to dig into some particular aspect of optical design to develop a presentation or prepare for a customer visit. It is such a circumstance that is leading me to dig a bit into hyperspectral imaging systems. These are cool optical systems that also connect nicely with my interest in space exploration. The picture above is the spectrometer part of a sample system I've been playing with today (designed by a colleague for demonstration purposes).

Spectrometers are pretty well known in astronomy and other technical fields (e.g., chemistry). A spectrometer uses a prism, or more commonly a diffraction grating, to spread incoming light into its component wavelengths (corresponding to colors for visible light). Spectra can be collected from the sun, from stars, from flames, light bulbs, etc. and when properly captured, recorded, and analyzed, they can reveal information about materials present in the light source (and possibly also of a medium in between the source and the instrument, e.g., the Earth's atmosphere, which selectively passes or absorbs certain wavelengths emitted by the sun). Spectrometers can also look at reflected or scattered light, and if the properties of the source are known, changes in the spectrum recorded from the reflected light can provide information on what chemical substances must have been present in the object that reflected or scattered the light.

Imaging spectrometers also do this, but they do it in a way that captures both an image of the source ("spatial data") and spectral data from specific parts of the image. So instead of recording a spectrum of the whole scene or object (which would have to be some sort of average of everything in the scene), an imaging spectrometer records a separate "rainbow" for each pixel in the image.
If you scale this up to where you are collecting such pixel-by-pixel spectra for many narrow wavelength bands across a wide range of wavelengths (maybe ultraviolet to infrared), you are now in the hyperspectral imaging domain, and this is especially exciting for remote sensing of the Earth and other planets. Instruments of this type are carried on the Mars Reconnaissance Orbiter (CRISM) and on various Earth remote sensing satellites (and aircraft) to help map the locations and types of minerals and also vegetation (at least on Earth). The amount of data that is collected can be huge if you have high spatial resolution (many megapixels) and high spectral resolution (many wavelength channels). This data can be depicted visually as a "datacube," as in the AVIRIS example at left (the 224 contiguous wavelength bands form the "depth" of this cube). This article is a good brief overview of hyperspectral imaging for remote sensing.

Staying Ten Years Old

Here's a cool TED talk from 2006 by scientist Penelope Boston. She has specialized in searching for life in extreme places, from the Antarctic to high deserts to caves to Mars. She talks about the importance of "staying ten years old" (and curious) and the idea that "perspective is everything" (looking at Earth as an "exoplanet"). Some of the caves she has explored are incredibly hostile to human life, full of sulfuric acid and lethal levels of poisonous gases - but various non-human life thrives in these nasty places. Based on the surface discoveries of the Mars rovers and high-resolution images from Mars orbit, she believes there is a good chance (25 to 50 percent) that there is life on Mars now, most likely in caves, and quite likely very different in chemistry and biology from life on Earth. She even gets into how caves on other planets may help future humans to survive there.

Update: For a fictional (hard SF) view of life in caves on Mars, The Martian Race by Gregory Benford is really good. One of my favorite Mars exploration novels.

The Good Earth

Apollo 8, December 24, 1968.

SSP at Change.gov

One of the great things about the Obama transition is that the public is invited to participate, to have "a seat at the table," as they put it on the change.gov web site. They have invited proposals from outside groups (37 pages of links so far) with the provision that all documents submitted will become public (they are PDF files on the web site). You can read them and then join in the discussion through forums associated with these proposals. Open government!

I just learned about a proposal on space solar power (SSP) that is under discussion there. I read the brief proposal and browsed many of the comments. Although there are some off-the-wall comments as in any public forum, the discussion is impressively multi-level and well informed. I rated a number of comments (thumbs up or down) and added a general comment to one of the most informative posts. If you care about this issue, you should go read, vote, and comment.

Of course there is no guarantee that SSP will be pursued by the Obama administration. It's one of hundreds of proposals. But the fact that these discussions are happening is in itself such a hopeful sign. This combined with the impressive cabinet and other appointments that have been announced shows that change is indeed coming. We will soon have leaders in Washington who don't have their heads in the sand! Or wherever the current administration's heads have been.

P.S. It's not very clear on change.gov, but the forums are run by IntenseDebate.com, and to register for the forums, you need to set up a free account there, even if you have registered at change.gov for other things (as I had done).

Terrible Beauty

Satellite weather imagery is one of the best applications of space technology, and a real life saver when it comes to tropical storms like Gustav, which tore into western Cuba and is now strengthening and heading for landfall somewhere on the U.S. Gulf coast. New Orleans is under mandatory evacuation. This recent satellite image is a frame of an animated GIF from wunderground.com - the animation has a terrible kaleidoscopic beauty. The interactive tracking map (static frame below) from the same web site shows Gustav strengthening to Cat 5 in the mid-Gulf at 11 pm Sunday night, then weakening to "only" Cat 4 the following day, with the projected path reaching New Orleans with 138-150 mph winds, gusting to 167-184 mph. Cross your fingers (this is about as effective as praying).

Don't Blame Canada...

...if an asteroid sneaks up on us and hits the Earth. At least they are trying to keep an eye on the neighborhood with a new microsatellite that's in development for launch in 2010.

The 65 kg NEOSSat (Near Earth Object Surveillance Satellite) will have a telescope with a very small (15 cm) primary mirror, but because it will be above the atmosphere, this small mirror will collect enough light to detect and track small NEO's and satellites. And as explained in the mission background notes, its design will allow it to orient itself very quickly and precisely and to take very quick exposures, using technology originally deployed to measure microvariability and oscillation of stars. A sunshade will allow it to look to within 45 degrees of the sun, a region that's almost impossible to observe from Earth's surface. Pretty amazing for a $12 million mission.

Thanks Canada! And thanks to Centauri Dreams for the tip.

NASA and Climate Change

Dr. James Hansen is well known as the NASA scientist who told Congress in 1988 that global warming was already here. This is often considered to be the point at which "global warming" started to receive more attention in the press and to become better known to the public. This week Dr. Hansen was back in Washington, telling Congress 20 years later that the Earth has "long passed" the dangerous level of greenhouse gases and that we need to take drastic action to lower these levels and avoid more serious consequences (still possible, he believes, if we act quickly).

There are still some climate change skeptics, but in the past 20 years, we have collected a lot more data and have seen a growing number of problems that can be linked to climate change. Much of the data on the changes the Earth is experiencing have come from satellites operated by NASA and other space agencies, and these satellites are continuing to add to our knowledge and to allow us to see the "big picture" as polar ice caps, clouds, the level of the sea, and other things are changing. You can explore the evidence on a new NASA/JPL web site, Global Climate Change. It's a nicely designed site with excellent graphics and a wide range of interactive features.

GeoEye-1 and TMA Notes

The other day I read a Technology Review article on GeoEye-1, a commercial Earth-imaging satellite that will be launched into a 684 km sun-synchronous polar orbit August 22 from Vandenberg AFB, California. This satellite will provide the highest ground resolution color imagery to date of any commercial satellite - able to distinguish objects as small as 0.17 square meters (about 0.41 m x 0.41 m, beach ball size) and to locate this imagery within 3 meters of "ground truth." This is made possible by GPS and by the use of star trackers, auxiliary optical systems which allow the spacecraft to determine its position and alignment from guide stars. This technology has been used extensively in NASA and military systems, but not in commercial Earth-imagery satellites. There's another good Geo-Eye article here.

As an optical engineering sort of guy, I wondered who made the optical systems and what the specs were. Turns out it was ITT Space Systems in Rochester, NY, which for many years was part of Kodak (in the 1970's, Kodak made a backup primary mirror for Hubble that was not used, which was too bad because unlike the mirror made and tested at Perkin-Elmer, its prescription was the correct one!). I found a data sheet (PDF) which says that the telescope is a TMA design (three mirror anastigmat) with a 1.1 meter primary mirror with a focal length of 13.3 meters. It also includes two fold mirrors, presumably for more compact packaging.

When I read this, I first assumed that it was an off-axis TMA, a design form that has no central obscuration but which can be difficult (expensive) to fabricate and align. But looking at a graphic of the spacecraft (above), I saw that there is a fairly large central obscuration - a three-leg "spider" for the center-mounted secondary mirror. So I looked up axial TMA designs and found this paper (PDF). I set up the second of two lens data prescriptions in my optical design software, and although the design shown here is not necessarily the one ITT used for GeoEye-1, it has two folds and a pretty compact form. So it's probably something like this. JWST is also a TMA design.

I also noted that it doesn't use a "staring" sensor (2D array like a digital camera, where X and Y directions are read all at once), but rather a "line scan imaging system with time delay integration." This means that there is a single row of detectors to cover (say) the X coordinate (with 4 color bands, blue, green, red, and near IR) and some means to scan this in the perpendicular (Y) direction to capture the full frame line by line. This scanning can be done with something like a rotating polygon mirror, or it could possibly use the satellite's own north-south motion (not too sure about this!).

While searching I also found a great PowerPoint presentation on telescope history and optics by Jim Burge at the University of Arizona (5 MB PDF, 62 slides).

P.S. Just to add a bit more optics, how might you estimate the ground resolution of such an orbiting telescope? You could do it roughly with a simple formula (explained here) for angular resolution in radians, which is 1.22*(wavelength)/(Lens Diameter). This shows that resolution gets better (smaller) for smaller wavelengths and bigger mirrors. GeoSat-1's primary mirror is 1.1 meters in diameter, and you can use a wavelength of 500 nanometers (10^-9 meters) for the approximate center of of the visible spectrum. The angular resolution works out to about 0.55 microradians (0.55E-06). If you multiply this tiny angle by the satellite's typical altitude of 684 kilometers to turn this into a linear number (the short side of a very long, skinny triangle), you get 0.38 meters, pretty close to the stated 0.41 meters (square root of 0.17 square meters). This ignores things like the central obscuration, atmospheric effects, and satellite motion, but it's a pretty darn good estimate.

I Want That Window

Actually not so much the window, just the view. The shuttle Discovery undocked from the ISS yesterday, but before they departed, the crew had some free time to take advantage of the spacious new Kibo module and its windows on the world. Astronaut Karen Nyberg seems to be enjoying the view.

Options in the Big, Bright Solar System

In a NYT op-ed piece titled "Running Out of Planet to Exploit," Paul Krugman wonders whether this time, with oil at $117 a barrel and Australia in its tenth year of drought, we might really be facing massive food and energy shortages that will hurt lots of people and trigger all sorts of bad side effects. It's a big world, but it's feeling noticeably finite, isn't it?

But as I and many others have written before, the sun is an immense source of energy, and the Moon and near-Earth asteroids hold immense stores of various materials. Not that we can use these next year or even in ten years, but if we can develop better access to space, we will have more options.

And speaking of more options, acclaimed physicist Stephen Hawking gave a speech on the occasion of NASA's fiftieth anniversary, calling for much greater investment in space development, leading to colonies on the Moon and Mars. He argues that the world should devote about 10 times as much as NASA's current budget to space development, around 0.25% of the world's financial resources - a lot of money but a tiny fraction of our available resources, and a true investment in the future. Not that this will be easy or quick, but it would represent a real insurance policy for humankind, and we can certainly afford to do this while still working to keep things under control here. He supports NASA's plans to return people to the Moon by 2020 and to get humans to Mars soon after that - first steps in permanent settlement.

Hawking has spoken before about his concern that natural or human-made disasters could wipe out life on Earth (or at least human life). He's not the only one worried about this, but I'm afraid things will have to get a lot worse before many people will start to take seriously the need for a backup plan for humanity. I hope we will act before things get really, really bad as in John Barnes' alternate near-future SF "Kaleidescope Century" series, but I'm only vaguely optimistic that we will. I like those books, but I wouldn't want to live there.