Last Full Day on Orbit
Dispatch #10 (Sunday, December 26)
The time on orbit has
gone so fast. It is hard to believe that in the last week we have
captured the Hubble Space Telescope, performed three space walks
to repair and service it, and deployed it back into space to observe
the cosmos. Today was mostly a day of cleaning, stowing all the
tools we took out to service Hubble, and putting the space suits
away for the last time on this flight.
We also did an orbit
adjust burn to bring us down to a slightly lower orbit than Hubble.
Orbital mechanics has caused us to advance far above the telescope
in only a few hours, so that we can no longer see it. Earlier
we could see Hubble at sunrise as a bright star on the horizon,
set in front of a sea of stars. I am so pleased that we have returned
Hubble to the heavens to again be a bright star in astronomical
Once the cabin was put
in order we had time to spend doing some of our favorite things
in space. Of course, going up to the flight deck with all the
lights out and gazing at the Earth and stars at night is high
on that list.
From our vantage point
some 300 miles above the planet, the Earth at night is all but
a dark orb. Flying over the Gulf of Mexico we could see city lights
dominating the coastline of California, cities down to Mexico
City, up through Houston, St. Louis, even to Chicago, and east
to Atlanta and Florida down to Miami and the Florida Keys. Once
over Florida, we could see the entire East Coast of the United
States up to Washington, D.C. and New York. At night it would
seem that the United States is an interconnected system of cities
and interstates in a kind of national nervous system.
Once out over the Atlantic
heading south the surface darkens, and with some dark adaptation
the horizon fills with a layer of light. This feature of the 'dark'
Earth is called the air glow layer. It is caused by the delayed
emission of light from nitrogen and oxygen atoms energized by
the Sun during the daytime. Most of the light is emitted at altitudes
of about 95 kilometers, and even at that height the atmosphere
looks perilously thin. Of course most of the habitable atmosphere
occurs in the first five kilometers, with the highest flying airplanes
only able to achieve about 30 kilometers.
As we circle the Earth
at 8 kilometers per second stars slowly rise through this green
and red thin veil of light. The Milky Way cuts across the sky
like a cloud let loose from the Earth rising across our windows.
A pleasure for the astronomers on board was to see the Southern
Cross, the Magellenic Clouds, and all the southern hemisphere
constellations that we can't see from Houston.
With ethereal constancy
stars continued to rise through the mist, piercing the visible
horizon, reminding us that the horizon we see is just the top
of the air glow. At one point after the moon rose we saw a kind
of strange cloud 10 or 15 degrees above the horizon, looking like
a higher layer, at perhaps 200 kilometers. We speculated about
whether the layer was real or a reflection. It had a relative
motion to us and slowly passed out of view. What strange physical
phenomena caused it we may likely never know.
There are still many
mysteries in the Earth's atmosphere that we are just beginning
to observe and study. The Compton Gamma-Ray Observatory has observed
high energy x-rays being emitted from upward going lightning in
energetic thunderstorms, called sprites.
From space we observe
thunderstorms at night as localized flashes of lightning in a
sea of grayish cloud tops, illuminated by a half-moon. Lightning
seems to go off in one place creating a cascade of bolts that
can go on for hundreds of miles before stopping as quickly as
it started. Then, from some other spot it starts all over again
with the staccato events traveling off in a different direction.
Occasionally you can see a precise bolt, going in a random circuit
cloud to cloud, and other times a single cloud just lights up
in a strange pattern of diffuse light.
After traveling across
the Atlantic observing the stars, Venus cast her bright image
in our direction. At first we were slightly confused by her presence
because she seemed so bright. Almost in Scorpio's pincers, there
could be no real ambiguity or confusion, only to be confirmed
by the signal of the impending sunrise.
Sunrise occurs over a
period of about three or four minutes, with the sky going from
a starlit wonderland to a painfully bright sun. In the transition
is the most beautiful spectrum of hues from a deep red, changing
to fire orange, with many layers and the silhouette of clouds
on the horizon, with an edge of bright yellow near the limb. The
colors continue to brighten and expand, until the Sun asserts
itself over the horizon, and with a brief presence of a red-orange
sphere, turns into our familiar bright Sun surrounded by the blackness
Tomorrow we leave this
magical world of weightlessness, stellar tours, space walks, and
earth views. The world we return to is dominated by gravity, which
at least for a few days will seem like a weight hung around our
necks and our psyche. But for the crew here aboard Discovery,
at least we trade our most excellent adventure for the warmth
of our families in this holiday season. And of course we bring
back the great satisfaction of returning the Hubble Space Telescope
to operation, and memories of a great expedition. For myself,
I also found that I have a new relationship with the Hubble, and
when I go out to view the transit of the observatory over Houston
at dusk or dawn, I will smile and think of the first space walk
when I reached out for the first time to touch the telescope.