Scientists
are hoping for a literal slam dunk with NASA's upcoming Lunar Crater Observation
and Sensing Satellite, or LCROSS mission — an event to be observed by a
coordinated network of Earth and space-based equipment.
LCROSS will
search for water
ice on the moon on Friday morning by crashing its spent upper-stage Centaur
rocket into Cabeus, a permanently sunlight-shy crater within the lunar south
pole region. The impact is set for 7:30 a.m. EDT (1130 GMT).
That
Centaur will serve as a heavy impactor on the moon, with scientists hoping a
resulting debris plume will ascend above the moon's landscape. The intent is to
toss tons of debris and potentially water ice and vapor high above the lunar
surface.
As part of
the LCROSS mission, along with the upper stage's "bang-up" job, a Shepherding
Spacecraft will follow a similar trajectory of the Centaur, flying through and
studying the Centaur impact plume before it too speeds into the lunar terrain.
Ground-based
professionals and amateur sky watchers are anxiously awaiting
the impact day, ready to observe the dust and water vapor cloud caused by
the impacts into the lunar surface.
A best
guess is that the larger of the two, the Centaur impact plume, could become
about 12 miles (20 km) wide and reach some 5 to 9 miles (8-15 km) in altitude
above the moon for the brightest part of the event — which is what amateur
observers might expect to be able to see.
The cloud
of lunar material is expected to be bright at first, as soon as it rises into
sunlight, but will fade in brightness quickly as it grows in altitude.
Citizen
science
"This may
be the
largest event that's been observed for a NASA mission in recent memory,"
said Jennifer Heldmann, lead for the LCROSS Observation Campaign at NASA's Ames
Research Center at Moffett Field, California.
Ames is
overseeing the development of the LCROSS mission with its spacecraft builder
and integration partner, Northrop Grumman of Redondo Beach, California.
Heldmann's
job includes coordinating not only amateur programs, but also those being
planned at professional observatories.
"From west
of the Mississippi all the way out to Hawaii is in prime viewing conditions.
You only need a ten to 12-inch telescope. So it's a really good opportunity for
a lot of people to be involved," Heldmann told SPACE.com.
"We're
asking anyone who observes the impact to upload their data to us," said
Heldmann. The public can contribute via the LCROSS Citizen Science Web site by clicking here. NASA will broadcast the
impact live on NASA
TV beginning at 6:30 a.m. EDT (1030 GMT).
The pick of
the Cabeus crater is a good one, Heldmann noted. "There's a shadow that is cast
behind where the impact plume will be. So there's a nice contrast between where
the plume will be coming up...and then the background of this dark shadow."
That final
resting site for the LCROSS mission hardware was driven by data.
Information
from NASA's now on-the-job Lunar Reconnaissance Orbiter (LRO) — as well as
older data from the space agency's Lunar Prospector that circled the moon in 1998-1999
— have been correlated, showing that there's a "significant concentration" of
hydrogen in Cabeus, Heldmann said.
LRO radar
data — not all yet publicly released — played into the LCROSS
impact site selection, Heldmann said. That choice was also bolstered by
science output from other lunar orbiters: India's Chandrayaan-1 and Japan's Kaguya.
"All in
all...it seemed to be the place to go," Heldmann explained.
Ring side
seat
A fleet of
Earth-orbiting satellites is at the ready to take a distant look at the
collision, including the Hubble Space Telescope; Odin, an international
astronomy and aeronomy mission led by Sweden, with Canada, France, and Finland
as partners; the U.S. Missile Defense Agency's Near Field Infrared Experiment
(NFIRE) satellite; NASA's Earth Observing-1 satellite; as well as the
commercial Ikonos and GeoEye-1 remote sensing satellites.
Heldmann
said that the Earth-watching spacecraft regularly use the moon for calibration
purposes.
"So since
they look at the moon anyway, they're able to collect some data. We've been
helping them plan out their observations...when they should time their exposures.
It's working out quite well with the Earth observing satellites and the LCROSS
mission," Heldmann said.
But for
on-the-spot viewing, you can't beat NASA's Lunar Reconnaissance Orbiter (LRO).
It's got a true ring-side seat of the LCROSS event.
Shadow
imaging
LRO is
ready for LCROSS, said Mark Robinson of Arizona State University's School of
Earth and Space Exploration in Tempe, Arizona. He is principal investigator of
the ultra-powerful Lunar Reconnaissance Orbiter Camera, or LROC for short.
Robinson
said that LRO will fly perpendicularly past the impact site about 60 seconds after
LCROSS hits.
That
post-impact look-see will allow LRO's Lyman-Alpha Mapping Project (LAMP) to
scrutinize the plume growth. LAMP, built and developed at the Southwest
Research Institute in San Antonio, is designed to search for surface ice and
frost in the polar regions of the moon and provide images of permanently
shadowed regions illuminated only by starlight and the glow of interplanetary
hydrogen emission.
LAMP will
attempt to measure spectra of the growing plume just after the impact.
The orbiter
won't fly directly over the impact, but off to the side, Robinson told SPACE.com.
LRO will slew a little over 80 degrees off to the side making sure the LAMP
gear is taking in a view just above the lunar horizon, thus able to see the
plume against the background of space.
Additionally,
LRO's Miniature Radio Frequency (Mini-RF) radar is to image the impact point
both before and after the impact, but not during.
Robinson
added that LROC will attempt shadow imaging with long exposures the day before
the impact as the spacecraft passes over the site. An attempt will also be made
after the impact.
If LCROSS impacts
in a single shadowed region, LROC might find the impact crater. "In a
double-shadowed region all bets are off," Robinson said.
The reason
is that single shadow areas receive sunlight bounced off a crater wall sticking
into the light. A double shadowed area only receives light from two bounces —
for example, the interior of a small crater that is entirely inside a larger
shadowed crater, Robinson added.
Going-in
plan
Could
LCROSS come up dry in the sense of running into lunar
water ice?
"Whatever
answer we get back, if we see ice or we don't, is going to be significant,"
said NASA's Heldmann. Seeing ice, she continued, will enable scientists to
start quantifying the material, to agree on how much is resident within the
crash zone.
Not
detecting the material means there's no ice in the impact spot?
"So either
it's not there...or there's some patchiness and spottiness to it...if it is indeed
there," Heldmann added. "We're going to learn a lot no matter what results are
obtained."
On impact
day, the science operations center at NASA's Ames Research Center will be a
busy hub, given the expected onslaught of incoming data. Within two-and-a-half hours
post-impact, a press conference at Ames Research Center will be held making use
of mostly ground-based observations. Accumulating the data gleaned by
moon-watching spacecraft will take longer.
The LCROSS
Shepherding Spacecraft is collecting data continuously during its plunge though
the plume and transmitting it back to Earth before its own demise.
Overall,
observations in the near infrared, such as those made by the Infrared Telescope
Facility and Keck telescope in Hawaii, are expected to provide quick look and
learn findings about any subliming water vapor in the LCROSS ejecta curtain.
There's a
large cadre of professional astronomers using many of the Earth's most capable
observatories is helping maximize the scientific return from the LCROSS impacts,
including the Magdalena Ridge and Apache Ridge Observatories in New Mexico and
the MMT Observatory in Arizona.
For
Heldmann, she's prepared for impact day...ready to scan and span the spectrum of
data to be gathered.
"It has been
a lot of work for four minutes of data...but it's a really important four minutes
of data," Heldmann said. "Hopefully, we'll have a variety of data sets that we
can combine and make a coherent story. That's the going-in plan."
Leonard
David has been reporting on the space industry for more than four decades. He
is past editor-in-chief of the National Space Society's Ad Astra and Space
World magazines and has written for SPACE.com since 1999.
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