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2.5 Space Astronomy [Astronomy: State of the Art]


Space astronomy is an important, but also expensive, and complex part of the astronomy enterprise. As you recall, most of the electromagnetic
waves that run from gamma rays to radio waves do not penetrate the earth’s atmosphere. The
only way we can observe these waves from celestial sources is in earth orbit or even beyond. So
space astronomy is an essential part of how we learn about the universe. The most iconic
space observatories are NASA’s missions called the Great Observatories, which includes the
Compton Gamma ray Observatory, now defunct, and three currently operating missions: the
Hubble Space Telescope, The Spitzer Space Telescope,and the Chandra Observatory, working
at x-ray wavelengths. These are NASA’s center pieces for space astronomy. Each of them having
cost multiple billion dollars. Space astronomy doesn’t come cheap. Square meter for square
meter it cost 10 to 20 times more to put a telescope in orbit than it does to operate
that same telescope from the ground so you have to have a good reason to go into space. The
strongest reason of all of course is the fact that you cannot detect those waves from the ground
but you also need an astronomical reason to be interested in those invisible wavelengths.
These missions are not only expensive but they’re difficult to get approved. If we look at NASA’s
manifests, over the last decade, we’ll see that the missions it has planned, due to limited
budgets, have often been delayed at close to a year per year. So missions that astronomers
have dreamed of ten or twenty years ago, are only just coming to fruition. Space astronomy
is a long game. The people involved in it have to have the patience to deliver almost
their whole career towards one telescope getting launched. The ultimate place for a
space observatory would actually be the far side of the moon. It’s incredibly dark, it’s
shielded from all artificial sources of light and it’s also shielded from sunlight. And
it’s geologically quiet. There’s almost no radio interference, or light contamination
of any kind; the perfect place for an optical or radio observatory. The far side of the moon is a place where
we could operate a robotic telescope using technologies that we’ve tested at ground based
observatories. And it wouldn’t be much more expensive than conducting moon landings for
other purposes. So astronomers still have a hankering, and they have well developed plans
for an observatory on the moon. At the moment it’s unfunded. NASA’s Great Observatories,
3 out of 4 of which are operating right now, mean this is a wonderful time for space astronomy.
One of those 3 observatories, the Spitzer Space Telescope, ran out of its primary cryogen
a year or so ago, but is continuing in what is called a warm mode and still doing exceptional
science at infrared wavelengths. The other 2 facilities, Hubble Space Telescope and Chandra
X-ray observatory are doing frontier science in all fields from comets to cosmology, and
are producing discoveries virtually weekly.These flagship missions are billion dollar plus
missions but NASA and other space agencies also have a portfolio that includes mid scale
missions, things that might cost a few hundred million dollars which sounds expensive, but
for space astronomy is actually quite cheap. These mission are different in concept. The
great observatories are like swiss army knives with a complex suite of 8-12 instruments,
and they’re able to do everything and they need to do everything well. These midscale
missions are different in concept, they’re designed to address one scientific issue,
with one instrument typically, and do it with exceptional precision. Excellent examples
of these instruments, which you’ll hear about later in the course, are W-MAP which looks
at the microwave background from the Big Bang and Kepler , which is designed to find earth
like planets. Both missions have succeeded exceptionally well for a price tag under half
a billion dollars. And finally, there are flagship missions still under concept and
not yet funded that are really out of the box because they go beyond the detection of
normal electromagnetic radiation. A good example of these is LISA, the Laser Interferometer
Space Antenna which is an interferometer that we’ve already talked about, in space, designed
to detect gravity waves. This is a frontier instrument that will do something that no
ground based telescope can do, and astronomer dream of being able to detect gravity waves
from space using this instrument, but it’s at least a decade off. Currently, there are
over a dozen space based observatories, some doing specialized missions and some, the Great
Observatories, doing a little bit of everything. It’s actually a wonderful time for space astronomy.
The engineering and the techniques involved are state of the art. Many of these missions
cannot be serviced or fixed if anything is wrong when they’re launched. Everything has
to be made just right on the ground. And most astronomers consider the scientific payoff
to be worth the high price tag. That’s the big and expensive end of the scale of astronomy.
What about the other end, accessible to all of us? In 2009 it the 400th anniversary of
Galileo’s first use of the telescope to study the night sky and in commemoration of that
event, very important for most astronomers, the Galileoscope was produced. The Galileoscope
is a modern version of Galileo’s best telescope using modern optical components, entirely
made out of plastic, in fact. This has found its way into the hands of hundreds of thousands
of people and has provided the best entree to the night sky for the average person. It’s
still a highly recommended way of learning about the sky but it’s always a good idea
to spend an extra $15 on a tripod. Galileo’s telescope has a very small field of view and
is a long device, so holding steady on the sky is difficult, a tripod makes that much
easier. If we were going to summarize the history of optical telescopes over 400 years
in one graph, it would be the improvement in sensitivity over the eye in factors of
ten. Galileo’s improvement with his best telescope was a factor of 100, then through the 17th,
18th and 19th century, larger and larger mirrors were produced to increase that to factors
of millions. With the development of electronic detectors and sensitive telescopes in space,
the fullness of four centuries of telescopic design is a factor of ten billion times fainter
than the eye can see; That’s the limit of the Hubble Space Telescope when it stares
at one region of the sky for a week. The improvement in resolving power is not the same enormous
factor relative to Galileo’s telescope or the naked eye. But it’s still several orders
of magnitude and with interferometry, several orders of magnitude more. So 400 years of
telescope has given us enormous differences in light grasp and sensitivity and resolution.
Space astronomy is an important way to learn about the universe; the missions are expensive
but they do things that cannot be done from the ground; often looking at invisible waves
that are extinguished by the Earth’s atmosphere. Astronomers currently have a portfolio ranging
from great observatories that cost multi billions of dollars to specialist missions doing particular
scientific experiments. All are important and together they’ve delivered a factor of
ten billion gain in depth over the night sky observed by the naked eye.

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