From: NASA Flight Research Center

To: NASA Headquarters Code S

Dr. Charles H. Roadman

Acting Director

Office of Life Science Programs

Subject: Visual Observations During Flight 2-14-28 March 30, 1961

Reference: NASA letter dated April 21, 1961

1. In accordance with the request of Congressman A. C. Pucinski, attached is a resume of Joe Walker's impressions of the horizon, haze, clouds, etc. as experienced in his recent X-15 flight.

It is hoped that this information will be helpful in meeting his requirements.

Paul F. Bikle

Attachment 1

Subject: Visual Observations During Flight 2-14-28 March 30, 1961

I had plenty of time at the peak of the trajectory to make outside observations. The most impressive observation initially was the aspect of the sky overhead. The color I would describe as being a very deep violet blue, not indicative of a black shading, but an extremely dark bluish cast. I looked to the left and to the right and upward and outward to the horizon. Our flight path course was south southwest and hence I felt that the best chance, if it were possible, to observe stars in the daytime would be out the right hand side towards the northwest away from the sun. However, careful scanning as far as I could look to the side and upward did not reveal any points of light shining through the blue canopy overhead. This overhead sky was impressive in that it did not change shade from horizon to horizon, the color was almost uniform.

The next thing is that you have no doubt from external visual cues that you're really high up. The horizon is depressed far below the level line or plain of level about the aircraft. At the perimeter of vision, about the demarcation line between the sky and earth, there is a bright diffused band, caused I think, by looking through the atmosphere from overhead and across the tangent to the earth at the horizon and then back out through the atmosphere. This bright band is very sharply cut off at the top. However the blue from the sky can be observed through it as well as the shape and coloring connected with the earth's surface. I would say that you get the impression that this band extends above and below the apparent horizon, probably a little more above than below.

No difficulty is experienced in observing and identifying geographical features on the surface of the earth particularly in areas with which one is familiar. An outstanding aspect of this is the appreciation of relative heights or elevations; different levels of the surface. Mountains still stand out as mountains and looking down into the Los Angeles Basin, I could tell the smog as distinct from some low stratocumulus clouds along the seacoast. Areas which are heavily forested or under agricultural development, could be separated from those areas where nothing was growing, and once again, if one were familiar with the territory, this is even easier to pick out. I think anywhere if one had plenty of time to observe he could make these distinctions. Looking down vertically or near vertically features are very distinct. As one's gaze swings further and further out toward the horizon, of course, features become more blurred. It was a disappointment to me that there seemed to be an almost continuous string of low stratus along the coast all the way from left to right so that my efforts to identify prominent coastal features in order to arrive at an estimate of how far I could see to the side, were frustrated, however judging a little from the apparent angle towards San Diego, it was obvious that I was looking well down the coast of Baja, California and I could see equal distance up northerly along the coast. The curvature of the earth was very apparent.

The time of the flight was just after 10:00 am, hence the sun was shining at a near vertical to the plane of the surface over which I was flying. Under these conditions, features ranging down to medium size were easily identified. Cities, small lakes, and the features I mentioned before, could be distinguished. Also it was obvious to me that things had a sort of brightness about them which was above and beyond that lighting enabling the surface features to be seen, apparently once again some diffusion of sunlight due to passing through the atmosphere. Also the exceptional clarity of vision for long distances is easily appreciated. The texture and associated visual cues of the ocean are easily identified and in fact, this was so apparent that I didn't spend much time looking at it, however the general aspect looking away from the sun was of a dark satiny appearance. It was a bright sheen even though the water was of a dark color. As to land color in this area, the majority are shades of grays and browns, some tinges toward mild reddish cast, but generally sandy aspect. Vegetation is no longer a rich green color, it goes to a dark gray black.

Joseph A. Walker

Aeronautical Research Pilot