Module 3 - What is SIR-C/X-SAR?

D) SIR-C/X-SAR Missions

Objectives

Students will be introduced to SIR-C/X-SAR science mission planning.
Students will learn the names of the two astronaut crews for the SIR-C/X-SAR missions.
Students will learn how a Mission Timeline is prepared and executed.

Launch and Orbit Insertion

As part of NASA's Mission to Planet Earth, the SIR-C/X-SAR radar instrument was launched on board the space shuttle Endeavour in April and October 1994. In addition, MAPS, a NASA-Langley instrument to Measure Air Pollution from Space was flown as a joint payload with SIR-C/X-SAR. These payloads formed the Spaceborne Radar Laboratory (SRL); the two flights in 1994 were designated SRL-1 and SRL-2 and a third flight (SRL-3) may take place in 1996.

After the space shuttle launch and insertion into a stable earth orbit, the payload bay doors were opened and the antenna deployed to start collecting data. The orbit for the first mission was at an altitude of 215 km above the earth's surface, and at an inclination of 57deg. allowing data to be collected between + 57deg. and -57deg. latitude. The orbit drifted slightly from day to day, so the same site could be imaged at different incidence angles during the mission. The second flight repeated observations of many sites from the first flight to study any changes that may have occurred between flights. In addition, for a portion of the second mission, a series of shuttle maneuvers were used to keep the shuttle in a exact repeat orbit. This allowed the same site to be imaged at the same angle during the mission; scientists will use these data to study daily changes at each site and for radar interferometry.

Astronaut Crew

Six astronauts flew on each of the first two SIR-C/X-SAR missions. Although the astronauts did not actually operate the radar antenna, which is commanded from the ground, they made important observations of the sites (including Hand-held photographs) and were also be responsible for changing tapes for data recording. The crew for each mission divided into two shifts of three people each, permitting 24-hour observations for the mission. Both crews participated in pre-mission training to familiarize them with the purpose of the SIR-C/X-SAR mission and the sites that were to be imaged. The crews of both missions were able to achieve unprecedented stability of the Endeavour by very fine adjustment of the shuttle's thrusters. This was a big plus for the radar observations and meant that it was much easier to compare results from orbit to orbit and between missions than was previously thought.

STS-59/SRL-1 Astronaut Crew

USAF Colonel Sidney M. Gutierrez - Commander of the SRL-1 mission. Gutierrez, age 41, was a Pilot on the Spacelab Life Sciences flight in June 1991. Born in Albuquerque, New Mexico. Received a B.S. degree in aeronautical engineering from the US Air Force Academy in 1973 and an M.A. in management from Webster College in 1977.

USAF Colonel Kevin P. Chilton - Pilot on the SRL-1 mission. Chilton, age 38, was Pilot on STS-49, Endeavour's maiden flight in May 1992. Born in Los Angeles, California, received a B.S. degree in engineering sciences in 1976 and a masters degree from Columbia University on a Guggenheim Fellowship in 1977.

Linda M. Godwin, Ph.D. - Payload Commander for the SRL-1 mission. Godwin, age 40, was a crew member to deploy the Gamma Ray Observatory in April 1991. Received a B.S. degree in mathematics and physics from Southeast Missouri State University in 1974, followed by an M.S. and Ph.D. in physics from the University of Missouri in 1976 and 1980.

Thomas D. Jones, Ph.D., - Mission Specialist for the SRL-1 mission. This was Tom's first space shuttle flight. Tom, age 39, received a B.S. degree from the US Air Force Academy in 1977 and a Ph.D. in planetary science from the University of Arizona in 1988.

US Army Lieutenant Colonel Michael R. "RICH" Clifford - Mission Specialist for the SRL-1 mission. Clifford, 40, flew as a mission specialist on a Department of Defense space shuttle flight in December 1992. Born in San Bernardino, California, he considers Ogden, Utah his hometown. Received a B.S. degree from US Military Academy in 1974 and M.S. degree in aerospace eng. from Georgia Institute of Technology in 1982.

Jay Apt, Ph.D. - Mission Specialist on the SRL-1 mission. Apt, age 43, was a mission specialist and a spacewalking crew member of an April 1991 mission to deploy the Gamma Ray Observatory and also a flight engineer on a September 1992 SpaceLab flight. He was born in Springfield, Massachusetts, but considers Pittsburgh, Pennsylvania his hometown. Graduated with a B.A. degree in physics from Harvard College in 1971 and a Ph.D. in physics from the Massachusetts Institute of Technology in 1976.

STS-68/SRL-2 Astronaut Crew

US Navy Captain Michael A. Baker - Commander on the SRL-2 mission. Mike, age 41, was born in Memphis, Tennessee, but considers Lemoore, California his hometown. Received a B.S. degree in aerospace engineering from the University of Texas in 1975 and graduated from the US Naval Test Pilot School in 1981.

US Marine Corps Major Terry W. Wilcutt - Pilot on the SRL-2 mission. This was his first shuttle flight. Age 45, born in Russellville, Kentucky, he was the first astronaut from this state to go into space. Received B.A. in math from Western Kentucky University in 1974, taught high school math for 2 years and then entered the Marine Corps. He attended the Naval Fighter Weapons School and the US Naval Test Pilot School.

Thomas D. Jones, Ph.D. - Payload Commander on the SRL-2 mission. Previously was Mission Specialist on STS-59. Tom, age 39, received a B.S. degree from the US Air Force Academy in 1977 and a Ph.D. in planetary science from the University of Arizona in 1988. He is from Baltimore, Maryland.

Peter "JEFF" Wisoff, Ph.D. - Mission Specialist on the SRL-2 mission. Previously was Mission Specialist and spacewalking crew member on a June 1993 flight to retrieve the European Retrievable Carrier satellite. Jeff, age 36, was born in Norfolk, Virginia. He received a B.S. degree in physics in 1980 from the University of Virginia, and an M.S. degree in 1982 and Ph.D. in 1986 in applied physics from Stanford University.

US Navy Commander Daniel W. Bursch - Mission Specialist on the SRL-2 mission. Previously, Dan was a Mission Specialist on a July 1993 flight to deploy an Advanced Communications Technology Satellite and deploy and later retrieve the Shuttle Pallet Satellite. Dan, age 37, was born in Bristol, Pennsylvania, but considers Vestal, New York, his hometown. Received a B.S. in physics from the US Naval Academy in 1979 and an M.S. in engineering science from the Naval Postgraduate School in 1991.

Steven L. Smith - Mission Specialist on the SRL-2 mission. This was Steve's first shuttle flight. Steve, age 36, was born in Phoenix, Arizona, but considers San Jose, California his hometown. Received a B.S. in electrical engineering in 1981, an M.S. in electrical engineering in 1982, and an M.A. in business administration in 1987 all from Stanford University. Steve worked for IBM on their semiconductor, voice and telephony products before joining the astronaut corps.

Mission Timeline

Before each mission, planners from both the SIR-C and X-SAR projects prepared a detailed plan known as the pre-mission timeline. The pre-mission timeline was a list of sites to be imaged during the mission and the times during which data were to be collected over each site. This timeline was based on a pre-mission orbit model which placed the shuttle (and its payload passengers) at a certain position orbiting the earth. The exact orbital path could not be known until the actual shuttle launch and orbit insertion, after which adjustments were made to the pre-mission plan.

In order to make the pre-mission plan, the SIR-C/X-SAR Science Team gave a list of their site locations to the mission planners. In many cases, these were sites where scientists have been working for many years to characterize an area. Using a computer program, planners compared the site list with the modeled orbital path to determine which sites could be imaged during the mission and to calculate the angle at which the radar beam needed to be aimed to hit each site. Since each mission lasted just 11 days, the timeline was designed to maximize the amount of radar data that was collected.

Since SIR-C/X-SAR is an international mission involving scientists and sites from all over the world, a great many compromises had to be made in order to optimize the mission timeline. Choices had to be made between sites that are geographically close together. For example, the Chesapeake Bay and the Appalachian mountains could not be imaged at the same time although the shuttle passed over both at the same time. Since the shuttle is a complicated manned spacecraft, planners also had to consider the amount of power that the timeline requires, and shuttle maintenance activities and maneuvers.

As changes in the position of the orbit or problems with the equipment occurred during the mission, the timeline was changed to ensure that good data were collected over as many sites as possible. During the second mission, for example, the timeline was adjusted to ensure that radar data was collected over a volcano that erupted while the shuttle was in orbit on the Kamchatka peninsula in Eastern Russia, Mt. Kliuchevskoi.

Plot showing datatakes collected on the April 1994 SIR-C/X-SAR mission.

Mission Control

NASA's space shuttle operations are controlled by Johnson Space Center in Houston, Texas. The SIR-C/X-SAR radar antenna was commanded from a Payload Operations Control Center (POCC) also located at Johnson Space Center. The SIR-C/X-SAR POCC was actually operated by SIR-C and X-SAR personnel during each mission.

POCC personnel were responsible for operating the radar antenna and ensuring that radar data were recorded onboard the shuttle. This was done by sending commands from the POCC to the radar antenna hardware. The commands were sent through the TDRSS (Tracking Data Relay Satellite System) satellites which are a series of communication satellites used by NASA and the US Government. Each command contained information that should tell the antenna when to turn on and in which operational mode data are to be collected. The SIR-C/X-SAR equipment onboard the shuttle has the ability to store 128 commands in case the communication between the POCC and the shuttle is lost for a period of time.

To help determine if the radar antenna was operating properly, some data collected were transmitted to the POCC for analysis during the missions. This transmission occurred over the same TDRSS link that was used to command the radar antenna. (See the section on real time processing below.)

In addition to ensuring that data were collected and are of good quality, POCC personnel also discussed site observations with the astronaut crew. The crew identified particular sites that should be added to the mission timeline, such as the Mt. Kliuchevskoi eruption. Crew communication was also useful for trouble-shooting minor problems with the antenna and the tape recorders on board the Shuttle.

Aside from the radar antenna responsibilities, the SIR-C/X-SAR POCC team worked closely with shuttle flight design people at JSC. JSC had to approve any proposed change to the orbital path of the shuttle.

Real Time Data Processing

All of the radar data collected during the SIR-C/X-SAR missions was recorded on-board the shuttle on digital tape recorders. These tape recorders look similar to the ones in your VCR at home, but are capable of recording much more data. The tapes were taken off the shuttle following it's return to Earth and the data sent to JPL and Germany and Italy for processing. In addition, during the mission some data were transmitted ("DOWNLINKED") to the POCC for processing and analysis. These data were used to make sure the radar was working as expected, and also to produce images for press releases.

Teacher's Guide - Table of Contents

Converted to the IBM-PC by Al Wong, sirced03@southport.jpl.nasa.gov

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