Astronauts in Spacewalks
On March 2, 2011, I took my second image of a spacewalking astronaut from the ground. Astronaut Stephen Bowen during the STS-133 mission. Bowen was riding the robotic arm Canadarm-2 on its way to the Columbus module. The used equipment of the images was similar as used for the first-ever from the ground captured images of a spacewalk in 2009. See the images and analyses below.
First ever Image - The Evidence
After several attempts to capture a sign of EVA activity during different opportunities, there was finally success on March 21, 2009 when 2 astronauts were outside during the STS-119 mission to the ISS. Steven Swanson and Joseph Acaba were deploying an Unpressurized Cargo Carrier Attachment System (UCCAS). The 2 astronauts appeared on the Earth-facing side of the ISS in front of one of the trusses. That evening, I tracked the spacewalk via NASA television to see where Swanson and Acaba were working. The location of the UCCAS was partially on the Earth-facing side so I was pretty sure that the spacewalkers could be captured in an image. I remember that it was a nothern pass of the ISS with the docked Space Shuttle Discovery and I remember that during the approach from the west, there was a flare, easily seen with the naked eye and recorded by other amateurs as it would appear later. It was a very exciting moment as I realised that eventual success could lead to something that was never done before at that time: An image of a human being in space, taken from the ground.
Analyses of the final image sequence, taken during the pass with a JVC color camcorder attached to my fully handtracked 10 inch Newtonian reflector, showed immediately a detail that I was not used to see in earlier ISS images taken with the same equipment during different passes and at a certain location. The images below show how the particular location on the truss looks during a normal pass and during a pass with a spacewalker in front of it. The difference is obvious. This image would really become the first-ever photo of a spacewalker during an extravehicular activity that has been taken from the ground. The main reason for this is that - although spacewalks are done already for decades, a good imaging technique for telescopic spacecraft photography has only just developed in the last years since the digital revolution. Another factor is that spacecraft imaging is - even today - done by just a limited number of astrophotographers.
Below: Comparison of the same location on the ISS truss without (left) and with (right) spacewalker in front of it.
Knowing that the astronauts were working on that particular location on the ISS, the difference is very clear:
There is an additional detail, which is elongated and brighter then the overall surroundings.
The final analyses of these images would cover several months and in january 15, 2010 I finally wrote:
my observation of spacewalk activity on March 21, 2009 during STS-119 EVA-2.
Because the point of orbital sunset was visible in both the helmet-cam
recordings and from my location (35° above horizon), it was very well
possible to calculate which was the exact point in the helmet cam recordings
at the moment of my captures, to see what they exactly were doing. Now I found
out: they were moving the diagonal and SARJ-braces out of its way in preparation
to deploy the nadir-UCCAS, as earlier mentioned. The braces were released at the
SARJ-side by Acaba, and Swanson moved them to mid-truss. This point is as seen
from Earth more at the truss-upper-edge. Acaba however was floating between the
SARJ and the mid-brace of the truss on the nadir-side. So this is exactly the
point which corresponds in my images as the bright dot and with earlier analyses'.
The picture-set below shows on the left the overview of the ISS starboard-side with the location of the spacewalkers and on the right a view from the helmet-cam from spacewalker Swanson - captured from NASA television - showing the approximate real-time view of the pass at the moment when I took the images with the telescope. Another version of this image was published on April 10, 2009 as NASA Astronomy Picture of the Day
Success Factors / Conclusion
With all the experience I gathered during telescopic imaging sessions of spacecraft where extravehicular activities were going on, I would conclude the following main factors for success for capturing an astronaut in Earth orbit with telescopes from the ground.
1 - There has to be a favorable pass of the spacecraft where the EVA occurs. This means that the altitude of the object (in this case the spacecraft with astronaut) above the horizon should be not too low. Otherwise, both the distance to the object would become too large, and the seeing conditions would be too poor to have a chance to capture something small as a person.
2 - The air (seeing) conditions should be steady in general. Because very small imaging scales are required to have a chance to capture a spacewalker, the seeing factors for success are equally important as in high resolution planetary imaging.
3 - The spacewalker must be located at a favorable location during the pass and well illuminated by sunlight. This means that the spacewalker should not be located in shadow or behind an element of the spacecraft. There are many shadows on an extensive structure as the ISS, but even a smaller spacecraft can cast huge shadows, such as the tail of the Space Shuttle. The shadows in space are very dark and contrasty. The high-reflective white color of the spacesuites used in EVA's however, helps to get a good illuminated view.
4 - A good knowledge about the structure of the spacestation/spacecraft is required to do good image analyses. A good analysis of the recorded data is very important because without knowing the location of different bigger and smaller elements, a person would hardly be recognizable at that discance considering the general resolution of even the best telescopes in the best seeing conditions.