DAVID F. WEBB's PROJECTS
Solar Mass Ejection Imager (SMEI)
The Solar Mass Ejection Imager (SMEI) is an all-sky camera experiment capable
of imaging coronal mass ejections (CMEs) as they propagate from the Sun through
the solar wind or inner heliosphere. Successful operation of the SMEI will
significantly improve space weather forecasting. Detection of potentially
damaging Earth-bound CMEs will help to protect space assets and maintain
stable communications, capabilities important to both the military and civilians.
SMEI’s all-sky images may also help astrophysicists in understanding solar
processes and detecting astronomical phenomena. SMEI is part of the Space
Test Program's Coriolis Mission which was launched into an 840 km circular,
sun-synchronous orbit on 6 January 2003.
A main goal of SMEI is to obtain 1-3 day forecasts of magnetic storms at
Earth by tracking CMEs from the Sun to near-Earth space. SMEI has already
accomplished this major milestone by observing its first Earth-directed
("halo") CME in late May 2003. This fast (1000 km/s) event was detected
in the all-sky SMEI images ~15 hours before it passed over the Earth on
May 29-30 causing a major geomagnetic storm. The CME erupted from the Sun
following two X-class flares from an active region near Sun center. The
two ejections likely merged to become a single halo, which was seen moving
outward near the Sun by the SoHO/LASCO coronagraphs. Since launch,
SMEI has also observed several dozen CMEs viewed in projection coming off
the solar limb heading out into space.
I have been working with SMEI team members since the mid-1980s on advocating
and developing the concept. I wrote the original proposal sent to NASA and
helped with the many SMEI briefings by Air Force personnel and others. I
helped analyze the background readiation environment for various SMEI orbits,
and am a liason for other researchers and spacecraft experiments with which
SMEI might be complementary. Some details of the experiment can be found here.
A cadcam drawing of the SMEI instrument is shown below, and a photo of one
of the flight units below that. Each of the three triangular baffles, shown
with their outer doors opened, are mounted to a strongbox containing the
optics and CCD cameras. These in turn are connected to the main electronics
box. The vertical plates cool the CCDs by radiating heat to deep space.
Next is a photo of one of the actual flight baffles attached to the strongbox
with a flat cold plate. This was during recent vibration testing at the
University of Birmingham, UK.
When indivdual frames from each camera are stitched together and mapped
into ecliptic coordinates, a complete sky map can be built up over an orbit,
except for small areas centered on the Sun and in the anti-Solar direction.
One such map, an equal-area Hammer-Aitoff projection, produced in March 2003
is shown below. It is centered on the Sun with the North and South
ecliptic poles at the top and bottom, resp. The dark circle is a zone of
exclusion 20 deg. in radius centered on the Sun. Some features of interest
include the Zodiacal light on either side of the disk, Venus to the right,
the Milky Way, Orion to the left, and the Magellanic Clouds at the bottom.
One of the brightest of the limb CMEs seen by SMEI is shown in the panels
below. It erupted from the Sun on May 31, 2003 with a high speed of
nearly 2000 km/sec. The + sign marks the location of the Sun
within the exclusion zone; the CME loop is imaged by SMEI when it is about
30 deg. elongation from the Sun.
The SECCHI Experiment on the STEREO Mission
I am a Co-Investigator on the SECCHI experiment that is being developed
for launch on the twin STEREO missions in 2005 (hopefully). SECCHI is
a suite of remote sensing instruments consisting of two white light coronagraphs
(COR1 and COR2) and an EUV imager (EUVI), collectively referred to as the
Sun Centered Imaging Package (SCIP), and a two Heliospheric Imagers (HI).
SECCHI will follow in three-dimensions Coronal Mass Ejections (CMEs) from
their origin at the Sun, through the corona and interplanetary medium, to
impact at Earth. We anticipate major breakthroughs in understanding the
origin and consequences of CMEs, in determining their three-dimensional
structure, in identifying the magnetic configurations and evolutionary paths
leading to CMEs, in determining the key factors controlling their trajectories,
and in achieving the national goal of predicting space weather. Details about
SECCHI can be found here. Here is a view of
the SECCHI instrument. The COR 1 and COR2 instruments are on the bottom and
the EUVI is on the top.
And here is a mockup of the HI instrument, which actually consists of two
subsystems, one for viewing the sky near the Sun and the other out to beyond
the Earth. Details can be found at the HI PI's home site in England.
I am also a Co-I on the HI experiments and, as a SMEI team member, act
as liason between SMEI and SECCHI. And I am the Space Weather Coordinator
for SECCHI and, mostly by default, for the rest of STEREO. More details
on that can be found on our STEREO Space