On the night of May 23rd, I was on a job down in a friendly south Texas town called Cuero. It was a hazy night, with high-altitude fast-moving cirrus clouds coming and going every 20-30 minutes. Not particularly ideal conditions for astrophotography, but excellent for showing off the interesting light patterns that a small town casts off. Unlike a big city, the light pollution of a small town comes from very concentrated sources, and each of them is often monochromatic. For instance, an oil services depot in the countryside may use sodium vapor lamps, while the city itself may use mercury vapor lamps. Various farming and oil operations across the landscape all use different lighting sources, which makes for a beautiful array of colors in a long exposure.
I spent 30-40 minutes filming a few short scenes from an overlook south of town (a popular spot among the locals). Being pretty busy with other projects and processing cityscape scenes of Cuero, I didn't actually have time to review this footage until last night. What I discovered was at first a curiosity to me as a photographer, but turned into something I would find fascinating as an aerospace engineer.
Early in one of my first image sequences there was a 5 frame series of streaks in the sky, all seemingly connected. Sure enough, the streaks lined up perfectly, and after stacking the frames in Photoshop and doing a little minor touching-up, I was rewarded with the following image:
If one looks closely at the top-center of the image, the two streaks can be seen. A detail shot is shown below:
Once I realized this wasn't an aircraft, I knew it was most likely an orbiting object, and even more interesting was that this orbiting object had apparently flared twice in a single pass.
(Aside: A satellite flare is a highly specular reflection of the sun off of solar panels or other glossy surfaces on an orbiting spacecraft. The spacecraft must have a very special alignment to direct the rays of the sun to an observer on the dark side of the Earth, so seeing one flare, let alone two distinct flares in a row is quite rare.)
The aerospace engineer in me took over and I set about doing some back-of-the-envelope orbit determination to be sure I was looking at a satellite. I looked up the nearby stars on my trusty star chart and estimated the observed angular distance traveled during the 50 second flare interval. I then applied some trigonometry and the definition of mean motion, and I was able to ascertain that the body was indeed moving at the correct angular rate to be in low-Earth orbit. Just by observing the direction the flares pointed in, I knew it was a highly inclined orbit also. My coarse calculations alone didn't help me identify the specific object, but they at least confirmed that what I had captured could most likely be attributed to an orbiting body.
Exactly identifying the body by continuing in this manner seemed daunting . At best, my calculations would perhaps narrow the list of potential objects down to a few hundred. I knew estimating the other orbital elements based on my crude observations would be difficult to impossible. To make matters worse, the internal clock on my camera was significantly off (and had since been corrected), so the image timestamps were useless for finding any absolute timing information. I quickly realized this could turn into a rather laborious exercise of parsing and sorting Space Track data.
Fortunately, I remembered that my favorite planetarium software, Stellarium, was bundled with a plugin that seamlessly pulls two-line elements from Celestrak to display satellites passing overhead. I knew approximately when I was out shooting that night (based on when I sent some text messages as I was packing up), and sure enough, I was able to quickly find a spacecraft that exactly fit the observed trajectory:
What I had captured was the Advanced Land Observation Satellite (ALOS), otherwise known as Daichi. ALOS is a Japanese Earth-observing satellite that was launched in 2006. At 4,000kg, ALOS is a fairly large vehicle (hence the name -- Daichi can be roughly translated from Japanese as "big"). Here's what ALOS looks like:
In 2011, after only five years, the ALOS mission was cut short by an unknown technical fault. It has been speculated that the vehicle sustained damage from a meteoroid impact causing the spacecraft to enter a power saving mode and become unresponsive. Despite this, ALOS is considered to be a success in that it exceeded its three year design life and collected a vast amount of high resolution imagery of the earth. This imagery is being used to construct a high-resolution global digital map which will have broad applications in mapping, natural disaster damage analysis, and water resource research [link].
ALOS has been derelict in a 700km altitude sun-synchronous orbit for the past 5 years. With no active attitude control systems, the vehicle is undoubtedly in a tumbling state, which increases the possibility for multiple flares as I was able to observe two weeks ago. At such a high altitude, ALOS will likely be in orbit for decades (or more) to come.
In yet another amazing coincidence, the successor to ALOS, ALOS-2, aka Daichi-2 was launched by JAXA at almost the SAME TIME I photographed ALOS (May 24th, 2014 at 03:05 UTC, or May 23rd, 2014 at 10:05PM CST)!
ALOS-2 also has an Earth-observing mission, but, unlike ALOS, has no optical cameras, and relies solely on radar for its imaging duties.
This wound up being a long post, but it's not often that I get a direct connection between my photography work and my aerospace engineering background. This string of coincidences was quite a treat!