Transcript The Great Observatories - Center for STEM Education

The “Great Observatories”
(The Engineering Side)
Randy Moore
RE-SEED Volunteer
http://www.bostonreseedcenter.org/
Mechanical Engineer (Ret)
Electromagnetic Spectrum
Why Telescopes in Space???
Image of Altair as seen from a
ground based telescope
distorted by the layers of
atmosphere
Same star as seen from a
space based telescope
Refraction
The Earth’s Atmosphere acts very much like a prism or bent
window
BUT.. The atmosphere is not stationary.. So, the distortions move
like waves on a pond
The Primary Space Telescopes
HUBBLE and THE BIG BANG
Edwin Hubble is noted as the
“father” of the “Big Bang Theory”
though it was first conceived
years before. Observations from
the Hubble telescope and other
observatories have made
astounding discoveries which
support the theory.
Hubble in Flight
Launch date — 24 April 1990 - Orbital Period 96 minutes
HYPERBOLIC
SECONDARY
MIRROR
PARABOLIC
PRIMARY
MIRROR
Off Axis Cassegrain Telescope Configuration
A design considered for Spitzer
The Mathematics of Telescopes
Cartesian equation: y = ax2 + bx + c
Spitzer Infrared Space Telescope
launched on August 25, 2003 – Orbital Period 1 year (helicentric)
Within about a week of May 12, 2009 the telescope was expected to run out of
the liquid helium needed to chill some of its instruments to operating
temperatures. This would end its primary mission
Compton Gamma Ray Observatory
Launched in 1991 – Orbital Period 90 minutes (deorbited in June of 2000)
deployed in low earth orbit at 450 km (280 miles) to avoid the Van Allen
Radiation Belts
The Chandra X-Ray Astrophysics Facility
Launched from, Kennedy Space Center 23 July 1999.
Orbital Period 65 hours
http://chandra.harvard.edu/
Chandra in the Shuttle Bay just before its
deployment with the robot arm
Chandra and the upper stage
booster deployed from the
Shuttle and ready for orbit
insertion
Chandra’s Wolter Mirrors
“Grazing incidence” imagery for X-Rays with
nested cylindrical mirrors
Imaging x-rays is a lot like skipping stone on a pond..
A schematic side view of Chandra's orbit,
showing the inner and outer radiation belts
This elliptical orbit 10,000 km perigee, 100,000 km apogee,
yields 55hr observing time per orbit
Design considerations for a space based telescope
Launch (extreme random vibration, acoustic loads & g-loads)
Thermal
Unbalanced moments (stability) Newton Lives! F=Ma
Kinematic mountings
Weight (and to lesser extent, volume) $10,000 per lb to launch!!!!
Periodic calibration & telemetry
Effects of “out gassing”
Lubrication of mechanisms
Effects of monatomic gasses
Radiation effects =materials and single event upsets in electronics
SpaceCraft ‘Charging”
Micrometeriorites & small “junk”
Redundancy
Most mechanical designs are stress based.. telescopes are deflection based
Design considerations for a space based telescope
Part 2
What do I do with it at mission’s end??
Allow it to “de-orbit” and fall to earth
Design it for “burn up” on re-entry
Design in an engine to send it off into deep space
Design it to be serviced / re-fitted
May the “M x a” be with you
Space Junk
Debris Plot by NASA
The graphics are computer generated images of objects in Earth orbit that
are currently being tracked. Approximately 95% of the objects in this
illustration are orbital debris, i.e., not functional satellites
Random Vibration Testing
The “land of broken dreams”
Typical Momentum wheel for Space Craft Attitude Control
One for Each Axis to be Controlled
These would also have to compensate for “unbalanced” forces from the focal plane
instruments
Detector Vacuum Housing
Shows the Titanium Housing with a “50%” lightweighting
The Hubble primary mirror in the clean room waiting for
assembly into the telescope structure
HRC’s Microchannel Plate Based
Detector
Cesium Iodide coating
Grid of fine gold wires
Schematic view of the HRC
Chandra’s Picture of Cassiopeia
Why are these images actually looking back
in time??
The objects that are being looked at are so far away
that the light took may years to get here - so long, in
fact that the object may even no longer exist, or exist
in a different state of evolution by the time we “see”
it!!
The Nature of Light
AN OBSERVOR
TRAVELS MUCH
LIKE RIPPLES ON A
POND
How do astronomers measure the distance to stars? Is
it accurate?
In order to calculate how far away a star is, astronomers use a method called
parallax. During Earth's orbit, near stars seem to shift their position against the
farther stars. This is called parallax shift. By observing the distance of the shift
and knowing the diameter of the Earth's orbit, astronomers are able to calculate
the parallax angle across the sky.
If you follow the line on the diagram from the Earth in January to the appearance
of the star in January, then the line from the Earth in July to the appearance of
the star in July, you will see that they intersect in the middle. This is the true
location of the star. The distance of the star can then be measured using
trigonometry.
The smaller the parallax shift, the farther away from earth the star is. This
method is only accurate for stars within a few hundred light-years of Earth, since
when the stars are very far away, the parallax shift is too small to measure.
The method of measuring distance to stars beyond 100 light-years is to use
Cepheid variable stars. These stars change in brightness over time, with a regular
period. This period is directly related to the luminosity of the star--brighter stars
have a longer period of light variation. Comparing the apparent brightness of the
star to the true brightness allows the astronomer to calculate the distance to the
star. This method was discovered by American astronomer Henrietta Leavitt in
1912 and used in the early part of the century to find distances to many globular
clusters.
The NASA-led Swift mission has measured the
distance to two gamma-ray bursts -- back to back,
from opposite parts of the sky -- and both were
from over nine billion light years away, unleashed
billions of years before the Sun and Earth formed.
These represent the mission's first direct distance,
or redshift, measurements, its latest milestone
since being launched in November 2004. The
distances were attained with Swift's
Ultraviolet/OpticalTelescope (UVOT).
Large Advanced Mirror Program (LAMP)
To demonstrate the ability to fabricate the large mirror required by an SBL, the
Large Advanced Mirror Program (LAMP) built a lightweight, segmented 4 m
diameter mirror on which testing was completed in 1989
This program and its predecessor (HALO) also served as “proof of concept” for
large active segmented mirrors for both space based & ground based telescope
applications
Future telescopes (James Webb) will use segmented,
lightweighted mirrors based in part on the technologies
developed on HALO & LAMP and used on the Keck
projects
Active segmented mirror including a plurality of
piezoelectric drivers (atmospheric compensation)
See also: Advanced Technology Large-Aperture Space Telescope (ATLAST)
The Kepler Telescope
A Search for Habitable Planets
http://kepler.nasa.gov/
The Galaxy Evolution Explorer (GALEX) is an orbiting space telescope observing galaxies in ultraviolet light across
10 billion years of cosmic history. A Pegasus rocket launched GALEX into orbit at 8 a.m. EDT on April 28th, 2003.
Led by the California Institute of Technology, GALEX is conducting several first-of-a-kind sky surveys,
including an extra-galactic (beyond our galaxy) ultraviolet all-sky survey
Other Optical System Projects
Viking 1976
Atmospheric
Compensation
System for
AMOS (Maui)
(First photos on the
“Corona” Reconnaissance Satellite
(Photos of Cuban Missile Silos)
surface of another
planet)
ALOT Telescope & Zenith Star
Part of Anti-Ballistic Defense
The Keck Telescopes
U-2 Seyers
Airborne Photos