Friday, October 31, 2014

STS-93: Yikes! We don't need any more of these.

I just found Wayne Hale's blog.  Be careful reading this thing, I just lost nearly an entire night of sleep.  The latest update, which covers the launch of STS-93, is just breathtaking.

Here's a video which documents the folks at mission control scrambling to figure out what is going on with their bird during the ascent.

Sunday, September 14, 2014

Quick trip to the Sierras

On Friday I took a quick trip to the Sierras to grab some Ponderosa pine forest images with a drone.  Initially, the logging road was just gorgeous.

Then I got to some bits that were less than gorgeous.  These roads don't see much use (I saw one other couple in a pickup during several hours on site), and I think these portions are probably just completely ignored until it's time for another logging operation, at which point they probably fill in the worst spots with gravel.  There were 18-inch-deep gullies in places, and nasty rocky bits that looked like a dry stream bed.  I walked several of these before trying them in the minivan.  There were a few uphill sections on which I was glad to have 4 wheel drive.

Eventually I got up to my target location.  That pile of wood is slash from a logging operation that probably happened in the last few years.

Target.  Life is good.

No crashes, nothing broke.  However, there are new noises coming from the minivan's power steering system now.  So, perhaps I did break something.  Overall it was a successful trip.

Tuesday, May 13, 2014

Happy Birthday to me

It's 5:13pm, and I'm sitting in the shade in my back yard, tweaking some really neat flexure mounts, while keeping an eye on two of my kids and two of their friends frolicking in the pool I built years ago. It's hot out, and there is steady traffic between the two hives near the back of the yard and the fountain to my right. A pair of ducks have been watching the kids too, and though they like the look of all that water they're leaving for someplace less noisy.  Lady Jane, our black Labrador, is lying in the grass, which is overdue for mowing, ripping up stems and chewing away. There are stains from fine droplets of sunscreen on the back of my laptop that won't be coming off. Martha will bring my youngest daughter back from gym class in an hour and then we'll head out for my birthday dinner.

At least once a day, at least one person helps me accomplish something I cannot achieve myself, things I am really happy to be working on.  I wonder if I manage to help someone else every day in the same way.

I have a lot to be thankful for.

Wednesday, April 23, 2014

Window 8.1 is unusable on a desktop

For the last two years I've been doing a lot of SolidWorks Simulation on my Lenovo W520 laptop.  This thing has been great.  But I've started doing fluid flow simulations, and it's time for more CPU than a 3.3 GHz (limited by heat load) dual core Sandy Bridge.

So I built a 6 core Ivy Bridge (i7 4930k) which I overclocked to 4.5 GHz.  Very nice.  However, I installed Windows 8.1 on it, which turns out to have been wrong.  This post is for people who, like me, figure that Windows 8 problems are old news and Microsoft must have fixed it by now.

Summary: Nope.

I figured that all those folks bellyaching about the new Windows were just whining about minor UI differences.  Windows 8 should benefit from 3 years of code development by thousands of serious engineers at Microsoft.  The drivers should be better, and it definitely starts up from sleep faster (and promptly serves me ads).   I figured I could deal with different menus or whatever.

I have learned that Windows 8.1 is unusable for a workstation.
  • Metro apps are full screen.  Catastrophe.
    • When I click on a datasheet PDF in Windows 7, it pops up in a window and I stick it next to the Word doc and Excel doc that I'm working on.  In Windows 8, the PDF is full screen, with no way to minimize.  I can no longer cut and paste numbers into Skype.  I can no longer close open documents so that DropBox will avoid cache contention problems.
    • Full screen is fine for a tablet, but obliterates the entire value of a 39 inch 4K monitor.  I spent $500 on that monitor so I could see datasheets, spreadsheet, Word doc, and SolidWorks at the same time.
    • Basically, this is a step back to the Mac that I had 20 years ago, which ran one application, full screen, at a time.
  • Shortly after the build, I cut power to the computer while it was on.  Windows 8 cheerfully told me I had to reinstall the O/S from scratch, and blow away all the data on the machine.  I don't keep important data on single machines, but I still lost two hours of setup work.  That's not nice.  I have not had that problem with Windows 7.
  • I plugged the 4k monitor into my W520 running Windows 7.  It just worked.  My Windows 8 box wants to run different font sizes on it, which look terrible.
  • Windows 8 + Chome + 4k monitor = display problems.  It appears Chrome is rendering at half resolution and then upscaling.  WTF?  This has pushed me to use Internet Explorer, which I dislike.  Chrome works fine on the 4k on Windows 7.
  • Windows 8 + SolidWorks = unreadable fonts in dialog boxes.  I mean two-thirds of the character height is overwritten and not visible.  So actually unreadable.  The SolidWorks folks know they have a problem, and are working on it.  And, I found a workaround.  But it still looks unnecessarily ugly.
  • Windows 8 + SolidWorks + 4k monitor = display problems.  Not quite the same look as upscaling, but something terrible is clearly happening.  Interestingly, if more than half of the SW window is on my 30" monitor, lines drawn on the 39" look okay.  But when more than half of the SW window is on my 39" monitor, lines look like crap... even the ones on the smaller half of the window still on the 30".
  • Windows 7, to find an application: browse through the list on the start button.  Window 8: start by knowing the name of the application.  Go to the upper right corner of the screen, then search, then type in the name.
  • Finally, that upper right corner thing.  I have two screens.  That spot isn't a corner, it's between my two screens.  I keep triggering that thing when moving windows, and can't trigger it easily when I want to.  Microsoft clearly designed this interface for tablets, and was not concerned with how multi-screen desktop users would use it.
And here's the kicker: Microsoft won't swap the Windows 8.1 Pro license I got for a Windows 7 license.  I have to buy Windows 7.

Excel 2013 has one thing I like: multiple spreadsheets open in separate windows, like Word 2010 and like you'd expect.

Word 2013 has two things I dislike: Saving my notes file takes 20 seconds rather than being nearly instant (bug was reported for a year before Microsoft acknowledged it recently), and entering "┬Ám" now takes two more clicks than it used to -- and nothing else has gotten better in exchange.  Lame.

I suggest not upgrading, folks.  No real benefit and significant pain.

You have (another) angry customer, Microsoft.

Here's the difference in SolidWorks rendering, on the SAME MONITOR, running in Windows 8, as I shift the window from being 60% on the 30 inch monitor to 40% on the 30 inch monitor (and 60% on the 39 inch):

30 inch mode: Note that lines are rendered one pixel wide, text is crisp.

39 inch mode: Lines are fatter, antialiasing attempted but wrongly

Wednesday, January 15, 2014

Sensors, Survey and Surveillance from Space

The SkyBox satellites are the first to use area array rather than pushbroom sensors for survey work, but they certainly aren't the first to use area array sensors.  I think the first satellites to do that were the KH-11 surveillance satellites, versions of which are still the principle US optical spysats in use today.  The first KH-11s sported area array sensors of about the same resolution as a standard definition TV.  The most recent KH-11s probably have a focal plane similar to this tiled 18,000 x 18,000, 10 micron focal plane (shown below, that circle is a foot in diameter).

Optical spysats have two missions; call them surveillance and survey.  When you already know where the thing is, that's surveillance.  Response time matters, but throughput is usually not a big deal.  When you don't know where your thing is, or you don't even know what it is yet, you are doing survey.  Throughput is king in survey work, and if response time matters, you have a problem.  Coast Guard aerial search and rescue, for example, has this problem.  You can read about the difficulties of search at sea in this NY Times article on rescue of a fisherman last July.

General Schwarzkopf said after the first Gulf War that spysats (he must have been referring to the earlier KH-11s) could not provide useful, timely imagery.  He was comparing single pictures of targets after a hit to the target camera footage of his planes, which gave him continuous video snippets of the target before, during, and after a hit.  These videos were very popular at press conferences and with his upper management.
Satellites are excellent for getting access to denied airspace -- there is no other way to take pictures inside China and Russia.  But in Iraq, Afghanistan, and Pakistan they are completely outclassed by airplanes and now drones with long-range optics (like the MB-110 reconnaissance pod which I still haven't written up).  In a 20 year battle against irrelevancy, I suspect that getting near-real-time imagery, especially video, from orbit has been a major NRO focus.  I'm sure the Block IV KH-11 launches in 2005, 2011, and recently in August 2013 can all do real-time downlinks of their imagery through the SDS satellite constellation.  However, the second part of real-time is getting a satellite into position to take the picture quickly.  The three KH-11s in orbit often cannot get to a surprise target in less than 30 minutes, and cannot provide continuous video coverage.  Guaranteeing coverage within 30 minutes would require dozens of satellites.  Continuous coverage, if done with satellites 300 km up, would require around 1000.  The KH-11 series is expensive (they refer to them as "battleships") and the US will not be launching a big constellation of these.

The Next Generation Electro-Optical program, which started in 2008 or so, is probably looking at getting the cost of the satellites down into the sub-$500m range, while still using 2+ meter telescopes, so that a dozen or two can be launched over a decade within a budget that NRO can actually sell to Congress.  My guess is they won't launch one of these until 2018.  In the meantime, SkyBox Imaging and ExactEarth, who are both launching constellations of small imaging sats, will be trying to sell much lower-resolution images that can be had more quickly.  These civilian operators have 50-60 cm apertures and higher orbits, and so can't deliver the resolution that NRO and NGA customers are used to, and they can't or don't use the SDS or TDRS constellations to relay data in real time.  (SkyBox can do video, but then downlinks it 10 to 90 minutes later when they overfly one of their ground stations.)

The second spysat mission is survey: looking for a needle in a haystack.  From 1972 to 1986 we had this in the form of the KH-9 Hexagon, which shot the entire Soviet Union every 2 to 4 months at 1 to 2 foot resolution.  The intel community at the time could not search or inspect all that imagery, but the survey imagery was great once they'd found something surprising.  Surprise, a new site for making nuclear weapons!  Survey answers the question: What did it look like during construction?  Or, How many other things like this are there?  Nowadays, Big Data and computer vision have got some handle on finding needles in haystacks, but we no longer have the KH-9 or anything like it to supply the survey imagery to search.  We still use the U-2 for aerial survey imagery, but we haven't flown that into denied airspace (e.g. Russia and China) for many decades.

From 1999 to 2005 Boeing ran the Future Imagery Architecture program,which was intended to make a spy satellite that could do radar, survey, and surveillance.  The program took too long and ran way over budget, and was eventually salvaged by cancelling the optical portion and having the team design a synthetic aperture radar satellite, which did get launched.  (Apparently this was the successor to the Lacrosse radar satellite.)

As I wrote, SkyBox does survey with a low-resolution area array.  They would need about 16,000 orbits to cover the entire surface of the earth, which is 2.7 years with one satellite.  I'm sure they can optimize this down a bit by steering left/right when over the ocean.  But this is 70 cm GSD imagery.

Two of the telescopes designed for FIA were donated to NASA in 2012, and the few details that have emerged tell us about late 1990s spy satellites.  From 300 km up, they could deliver 7 cm imagery, and had a (circular) field of view of about 50,000 pixels.  This could have been used with a 48,000 x 16,000 pixel tiled focal plane array.  Using the simple expedient of shooting frames along the line of the ground track, the ground swath would have been 3.2 km wide, and could have surveyed the entire Earth in about 2.7 years (the same number is a coincidence -- spysats fly at half the altitude and this one had twice my presumed field of view for SkyBox).

However, to keep up with the ground track pixel velocity, the sensors would have to read out at over 6 frames per second.  That's almost 5 gigapixels per second.  I don't believe area array sensors that big can yet read out that fast with low enough noise.  (The recent Aptina AR1411 reads out at 1.4 gigapixels per second, but it's much smaller, so the column lines have far less capacitance.)

The large number is not a result of the specifics of the telescope or sensor design -- it's fundamental to high resolution orbital survey.  It's just the rate at which the satellite flies over ground pixels.  Getting 5 billion tiny analog charge packets to A/D converters every second is hard.  Once there, getting 20 gigabits/second of digital data to the ground is even harder (I don't think it's been done yet either).  I'll defer that discussion to a later post.

Pushbroom sensors are more practical to arrange.
  • The satellite simply stares straight down at the ground.  Attitude corrections are very slow.
  • It's easy to get lots of A/D converters per sensor, you simply add multiple taps to the readout line.
  • It's easy to tile lots of sensors across the focal plane.  You stagger two rows of sensors, so that ground points that fall between the active areas of the first row are imaged by the second row, like this focal plane from ESA Sentinel-2.  Once stitched, the resulting imagery has no seams.

Tiled area array sensors are more difficult, but have the advantage of being able to shoot video, as well as a few long exposures on the night side of the Earth.
  • The image must be held steady while the field of view slides along the ground.  Although this can be done by rotating the whole satellite, survey work is going to require rapidly stepping the stabilized field forward along the optical path, several times a second.  Fast cycling requires a lightweight optical element, usually the secondary mirror, to have a fast and super precise tip/tilt mechanism to track out the motion.  Cycling this element back into position between shots can add vibration to the satellite.
  • While the secondary mirror is moving the image back into position, the pixel photodiodes must not accumulate charge that affects the values read out.  This typically means that either the cycling time can't be used for readout, or (as in the VisionMap A3) the sensor is an interline CCD with two capacitors per pixel, one of which is shielded.  With this choice comes a bunch of minor but annoying problems.
  • In one line time, charge is transferred from the pixels all the way across the array to the readout.  The bit lines can be long and capacitive and add noise.
  • Take another look at the first pic in this blog post, and note the seams between the active arrays.  These are annoying.  It's possible to take them out with clever combinations of sparse arrays and stepping patterns.
Lenses generally resolve a circular field of view, and pushbroom sensors take a rectangular stripe down the middle.  It's possible to put an area array sensor in the leftover upper or lower crescent around a pushbroom sensor.  This gives a smaller area sensor, but in the context of a 50,000 pixel diameter focal plane, a "smaller" area sensor might be 10,000 pixels on a side, with 50 times the pixel count of an HD video sensor.  This allows for a 10:1 "digital zoom" for context with no loss of display resolution.

If I were building a government spysat today, I'd want it to do survey work, and I'd make surveillance the secondary mission.  Airplanes and drones are better for most surveillance work.  I'd want to shoot the whole Earth each year, which can be done with three satellites at 300 km altitude.  I'd use a staggered pushbroom array as the primary sensor and a smaller area array for surveillance.

The step-stare approach that SkyBox is using makes sense when a big, fast area array sensor covering the whole field of view can be had at low risk.  Sensors are developing quickly, so this envelope is growing over time, but it's still an order of magnitude away from what large-aperture spysats can do.

Maybe I'm wrong about that order of magnitude.  In 2010 Canon announced a 205 mm square CMOS sensor that supposedly reads out 60 frames per second.  Here it is pictured next to a full-frame 35mm DSLR sensor -- it's slightly bigger than the tiled array at the top of this post.  Canon did not announce the resolution, but they did say the sensor had 100 times the sensitivity of a DSLR, which suggests a pixel size around 35 microns.  That's too big for a spysat focal plane, unless it's specifically for use at night.
No subsequent announcement was made suggesting a purpose for this sensor.  Canon claims it was a technology demonstration, and I believe that (they would not have been allowed to show a production part for a spysat to the press).  Who were they demonstrating that technology to?  Is this the focal plane for a Japanese spysat?