[meteorite-list] Cornell Researchers Turn To Telemetry And Geometry To Capture Distant Asteroid

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:06 2004
Message-ID: <200102052243.OAA20838_at_zagami.jpl.nasa.gov>

http://www.news.cornell.edu/releases/Feb01/NEAR.control.bpf.html

Images from outer space: Cornell researchers turn to telemetry and geometry
to capture distant asteroid

FOR RELEASE: Feb. 5, 2001

Cornell University News Service
Contact: Blaine P. Friedlander, Jr.
Office: 607-255-3290
E-mail: bpf2_at_cornell.edu

ITHACA, N.Y. -- Will this be the gang that could shoot straight? For the
past year, engineers and computer programmers from Johns Hopkins
University's Applied Physics Laboratory (APL), assisted by NASA's Jet
Propulsion Laboratory (JPL) and the imaging team at Cornell University,
have been figuring out how to slew a spacecraft precisely and aim its
camera perfectly for the final act of its mission: alighting on an asteroid.

On Feb. 12 the Near Earth Asteroid Rendezvous spacecraft, known as NEAR
Shoemaker, will attempt to land on Eros, an Earth-crossing asteroid about
196 million miles from Earth. In mid-descent, an onboard camera will point
toward the surface and hopefully send back the best images ever from a
small, solar-system body. The navigational prowess of APL and JPL will be
complemented by the imaging expertise of the Cornell research team.

"It's not like this craft is landing on a sphere. It's descending on a
potato-shaped rock that is 22 miles long, and the rock has a large,
saddle-shaped hole on one side. The rock continuously spins end-over-end.
Geometry is forcing us to land there -- where there is more motion than at
the poles -- so that NEAR's solar panels face the sun, its antenna points
to Earth and its camera faces the asteroid," says Cornell space sciences
researcher Ann Harch. "Other than that, it's easy."

Use of the navigation team's telemetry, geometry and other calculations --
for this never-before-attempted maneuver -- required unique software to
point the camera, and it took more than a year to perfect. Harch and her
Cornell research colleagues Maureen Bell and Colin Peterson and programmer
Brian Carcich worked with APL (which built the spacecraft and is managing
the mission) to develop special computer software that, with great
precision, displays the shape of Eros and how it will look from the
camera's point of view. First an exact model of the asteroid's shape had
to be determined. This shape-model software, called POINTS, developed by
Cornell's Jonathan Joseph, programmer analyst, and Peter Thomas, senior
research associate, correlates feature in thousands of images and plots the
asteroid's trajectory and orientation. From that information, the program
calculates a detailed three-dimensional asteroid model.

Harch, Bell and Peterson then used Orbit, a computer program developed at
Cornell by Carcich, to design pointing commands for the multispectral
imaging camera. Orbit reads input data on the asteroid's location and spin
orientation, then shows where the craft and camera will point. The program
also displays how the asteroid will look to the camera at each instant.

This information allowed Harch, Bell and Peterson to cobble together
command sequences that were uploaded to NEAR Shoemaker throughout the
mission. The comands take about 17 minutes for the information to be
received by the distant spacecraft and the same amount of time for the
craft to send back confirmation that the data was received.

If all goes as planned, at 10:31 a.m. Eastern time on Feb. 12, the
spacecraft will commence firing a series of burns -- firing thrusters away
from the asteroid -- to brake the craft for an anticipated 7 mph landing.
Control commands to the onboard, multispectral camera will be uploaded to
the spacecraft. However, if NEAR goes faster or slower than anticipated,
mission controllers at APL will be able to adjust the craft's onboard clock
to delay or advance the final photo sequence. "The spacecraft literally
has to be in the right place at the right time" for the camera to function
as planned, says Harch.

Reflecting on the five-year mission, Harch says: "This final week has been
such an emotional one. It was an extraordinary experience working with
these people to produce such a fabulous result, and all of us feel that
way."

Adds Bell, "Getting this altogether has meant many, many late nights."
Received on Mon 05 Feb 2001 05:43:06 PM PST