NEAR Shoemaker’s Historic Landing on Eros Exceeds Science, Engineering Expectations
The NEAR Shoemaker spacecraft’s historic soft landing on asteroid 433 Eros
Feb. 12 turned out to be a mission planner’s dream – providing NEAR team
members with more scientific and engineering information than they ever
expected from the carefully designed series of descent maneuvers.
“We put the first priority on getting high-resolution images of the surface
and the second on putting the spacecraft down safely – and we got both,”
says NEAR Mission Director Dr. Robert Farquhar of the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md., which manages the Near
Earth Asteroid Rendezvous (NEAR) mission for NASA. “This could not have
worked out better.”
Two days after a set of five de-orbit and braking maneuvers brought it to
the surface of Eros, NEAR Shoemaker is still communicating with the NEAR
team at the Applied Physics Lab. The spacecraft gently touched down at
3:01:52 p.m. EST on Monday, ending a journey of more than 2 billion miles
(3.2 billion kilometers) and a full year in orbit around the large space
rock.
Yesterday the NEAR mission operations team disabled a redundant engine
firing that would have been activated had it been necessary to adjust the
spacecraft’s orientation in order to receive telemetry from it. But because
NEAR Shoemaker landed with such a favorable orientation, and telemetry has
already been received, it was no longer necessary to move the spacecraft
from its resting place.
Mission operators say the touchdown speed of less than 4 miles per hour
(between 1.5 and 1.8 meters per second) may have been one of the slowest
planetary landings in history. They also have a better picture of what
happened in the moments after the landing: What they originally thought was
the spacecraft bouncing may have been little more than short hop or “jiggle”
on the surface; the thrusters were still firing when the craft hit the
surface, but cut off on impact; and NEAR Shoemaker came down only about 650
feet (200 meters) from the projected landing site.
“It essentially confirmed that all the mathematical models we proposed for a
controlled descent would work,” says Dr. Bobby Williams, NEAR navigation
team leader at NASA’s Jet Propulsion Laboratory. “You never know if they’ll
work until you test them, and this was like our laboratory. The spacecraft
did what we expected it to do, and everyone’s real happy about that.”
NEAR Shoemaker snapped 69 detailed pictures during the final three miles
(five kilometers) of its descent, the highest resolution images ever
obtained of an asteroid. The camera delivered clear pictures from as close
as 394 feet (120 meters) showing features as small as one centimeter across.
The images also included several things that piqued the curiosity of NEAR
scientists, such as fractured boulders, a football-field sized crater filled
with dust, and a mysterious area where the surface appears to have
collapsed.
“These spectacular images have started to answer the many questions we had
about Eros,” says Dr. Joseph Veverka, NEAR imaging team leader from Cornell
University in Ithaca, N.Y., “but they also revealed new mysteries that we
will explore for years to come.”
NEAR Shoemaker launched on Feb. 17, 1996 – the first in NASA’s Discovery
Program of low-cost, scientifically focused planetary missions – and became
the first spacecraft to orbit an asteroid on Feb. 14, 2000. The car-sized
spacecraft gathered 10 times more data during its orbit than originally
planned, and completed all the mission’s science goals before Monday’s
controlled descent.
“NEAR has raised the bar,” says Dr. Stamatios M. Krimigis, head of the
Applied Physics Laboratory’s Space Department. “The Laboratory is very proud
to manage such a successful mission and work with such a strong team of
partners from industry, government and other universities. This team had no
weak links – not only did we deliver a spacecraft in 26 months, we were
ready to launch a month early, and that efficiency continued through five
years of operations. This is what the Discovery Program is designed to do.”
