Johns Hopkins Gazette: January 9, 1995

Holland Ford's Team Gets Nod Over JPL, Goddard

By Emil Venere

     NASA has selected a team of scientists headed by Hopkins
astronomer Holland Ford to design a new camera that may enable
the Hubble Space Telescope to bring the very edge of the universe
into focus.
     The Hubble Advanced Camera for Exploration will be eight
times more sensitive than the present camera, promising to yield
new insights into cosmology, while also providing important
details about the solar system. It is scheduled to be installed
by astronauts during a servicing mission in 1999. HACE will make
the space telescope 16 times more efficient at finding galaxies
and clusters of galaxies forming in the early universe, and it
will give cosmologists a precise tool for probing the mysterious
"dark matter."
     Astronomers plan to photograph the deepest possible reaches
of space, surveying nearly a square degree of the sky--a region
about the size of four full moons. The survey will take hundreds
of hours of observing time. But when it is finished, scientists
hope to see literally all the galaxies that emit optical light
within that region, said Dr. Ford, a professor in the Department
of Physics and Astronomy.
     "That's a very exciting possibility, the idea that we may be
able to photograph an area of the sky and in those directions see
virtually all of the galaxies in the universe," he said.
     The design was one of three proposals, facing stiff
competition from the Jet Propulsion Laboratory and the Goddard
Space Flight Center. JPL was considered a favorite, having
designed both of the space telescope's previous cameras, Dr. Ford
     But his team had an advantage. Many of the scientists,
himself included, were involved in the design of COSTAR, a device
installed in December 1993 that corrected the blurred vision for
three of the space telescope's instruments, impaired by a flaw in
the primary mirror. 
     "My own belief is that we have a very strong science team,"
said Dr. Ford, principal investigator for the HACE project, who
has a dual appointment at Space Telescope Science Institute.
Scientists and engineers developing HACE are from Hopkins, STScI,
the University of Arizona, the University of California, Santa
Cruz, and the University of Leiden in the Netherlands.
     Collectively, they've had "hundreds of years of experience"
using the space telescope, which was launched in April 1990, said
Jim Crocker, the HACE systems engineer.
     "They knew not only the science but they knew what the
telescope was capable of," he said.  "I think, for the first
time, with this instrument we will be able to fully exploit the
capabilities of the space telescope."
     Crocker conceived COSTAR's design while director of STScI's
advanced programs office. He presently is on a one-year leave of
absence at the European Southern Observatory, in Germany.
     HACE will be built by Ball Aerospace Corp., in Boulder,
Colo., which also built COSTAR.
     The new camera's design includes a "solar blind channel"
that blocks out all but certain ultraviolet light, enabling
scientists to make detailed atmospheric studies of other planets
in the solar system, said Paul Feldman, a Hopkins professor in
the Department of Physics and Astronomy. HACE's superb
sensitivity will enable much shorter exposures than those
required by the present camera, called the Wide Field Planetary
Camera-2. Long exposures of objects such as Jupiter cause smeared
images of features in the Jovian atmosphere, since the planet
rotates in the time it takes to capture the image. The new camera
will snap pictures in 15 to 30 seconds, making much sharper
images, said Dr. Feldman, a member of the science team.
     He wants to use HACE to study how solar radiation and solar
winds interact with the upper atmosphere of Jupiter and other
planets in the solar system. Another possible use will be to
study the inner structure of comets. 
     Because the space telescope is above Earth's image-
distorting atmosphere, it is ideal for precisely measuring the
distances of galaxies. By carefully measuring the way that light
from a distant galaxy fluctuates, astronomers can calculate
precisely how far away it is. WFPC-2 isn't efficient enough to
make the measurements for a large sample of distant galaxies--it
takes too much observing time to collect enough light. A large
sample is needed in order to map the large-scale distribution of
matter. The new camera's increased efficiency will make those
measurements possible, said Marc Postman, an astrophysicist at
     HACE will feature a novel design that has the fewest
possible number of reflecting surfaces, so that fewer photons are
lost. Other advanced features making the camera more efficient
include highly reflective coatings and a larger and more
sensitive imaging chip, made up of imaging sensors called
charge-coupled devices. The CCDs will form an array containing
4,096-by-4,096 pixels, compared with the current camera's
1,600-by-1,600 pixels. 
     The new camera won't actually replace WFPC-2, which was
installed with COSTAR in 1993. HACE is an axial instrument,
meaning it is located perpendicular to the focal plane. It will
replace one of HST's four axial instruments, depending on which
one is least needed by the time of the servicing mission, Crocker
said. WFPC-2 is a radial instrument, the only such instrument on
HST, and is located parallel to the focal plane.
     George Hartig, an astrophysicist at STScI, is project
scientist for HACE. One other Hopkins scientist, postdoctoral
fellow Tom Broadhurst, is working on the project. 

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