Mars Global Surveyor intercepted Mars on September 12, 1997 at 01:31 GMT (September 11, 9:31 p.m. EDT). It will now spend six months aerobraking through the thin Martian atmosphere to achieve a low-altitude mapping orbit. Mapping and science operations will begin on March 15, 1998.
Office of the Flight Operations Manager
Mars Surveyor Operations Project
Today marked Surveyor's third full day of operations in orbit around the red planet. As of 11:59 p.m. PDT, the spacecraft has just passed the halfway point of its second revolution around Mars and is now falling back toward the low point of its orbit. Surveyor will reach this point at 12:28 p.m. on Monday.
Currently, the spacecraft's velocity relative to the surface of Mars measures 1,271 m.p.h. (568 meters per second). By the time Surveyor reaches the bottom on Monday afternoon to start its third orbit, the velocity will have accelerated to nearly 10,515 m.p.h. (4,700 meters per second).
Most of the day's activities were devoted toward configuring the spacecraft for orbital operations. The first of these occurred early in the morning when the onboard flight computer was commanded to switch its internal navigation system from an Earth-based coordinate frame to a Mars-based frame. Later in the afternoon, the computer loaded critical parameters into the software for the aerobraking phase of the mission that will begin Wednesday morning.
Tomorrow afternoon, Surveyor will perform a rotation to point the science instruments directly at Mars during a 20-minute period centered on the point of closest approach of the third orbit. This opportunity will allow the laser altimeter and camera to collect science for the first time at Mars. The laser is currently powered off and will be activated about six hours prior to the start of orbit number 3.
In addition, the Thermal Emission Spectrometer and Magnetometer science instruments will also utilize Monday's 20-minute opportunity to scan the red planet. However, these instruments have been collecting data on a continuous basis because they do not need to be pointed directly at Mars in order to operate.
After a mission elapsed time of 311 days from launch, Surveyor is 159.49 million miles (256.67 million kilometers) from the Earth and in an orbit around Mars with a period of 45 hours. The spacecraft is currently executing the T2 command sequence, and all systems continue to be in excellent condition.
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
NASA's Mars Global Surveyor, the first in a series of orbiters and landers to explore Mars in the next decade, performed a critical engine burn this evening and successfully entered orbit around the red planet.
The spacecraft executed a 22-minute engine burn at 01:17 Universal Time (6:17 p.m. Pacific Daylight Time) and slowed its speed by more than 3,200 kilometers per hour (2,000 miles per hour) to be captured in Martian orbit. (Because radio signals traveling at the speed of light take 14 minutes, 6 seconds to reach Earth from Mars, the start of the engine burn was detected by ground controllers at 6:31 p.m. PDT.) Doppler data after the burn indicated that the spacecraft is now in a highly elliptical orbit which takes it within about 250 kilometers (155 miles) of Mars at its closest point and about 56,000 kilometers (34,800 miles) at the most distant.
Global Surveyor is the first U.S. spacecraft to orbit Mars in more than 20 years and the first to use aerobraking rather than propulsive maneuvers to adjust its orbit upon arrival. The technique was demonstrated during the final months of the Magellan mission to Venus in the summer of 1993, and found to be a plausible design for circularizing a spacecraft's orbit while saving fuel.
Preparations for this evening's orbit insertion burn began two days ago, on September 9, when Global Surveyor pressurized its propellant tanks. Pressurization occurred at 9:15 a.m. PDT and was nearly instantaneous. The propellant tanks reached the required value of 18.6 bars (270 pounds per square inch), which was necessary to perform the capture burn tonight.
Today's activities began about 17 minutes before the orbit insertion burn, when Mars Global Surveyor powered up its small 2.3-kilogram (5-pound) thrusters and prepared to turn its main engine in the direction of the spacecraft's motion, or toward Mars. After this reorientation, and at an altitude of 1,490 kilometers (926 miles) above Mars, the spacecraft fired its 660-newton main engine for approximately 22 minutes, 39 seconds.
Twelve minutes after the start of the engine burn, the spacecraft passed behind Mars as seen from Earth and was temporarily blocked from communications with Earth. This occultation lasted 12 minutes. The spacecraft emerged from behind Mars nearly four minutes after the engine burn had been completed. Two of NASA's Deep Space Network tracking facilities at Goldstone, CA and Canberra, Australia, were monitoring the spacecraft's orbit insertion burn and reacquired Mars Global Surveyor's signal within seconds of its reappearance from the back side of Mars at 6:57 p.m. PDT.
Global Surveyor has arrived at Mars during fall in the northern hemisphere and spring in the southern hemisphere, which usually coincides with the start of the dust storm season. Although dust storms are a concern for the navigation team, the spacecraft will be able to raise its orbit and fly over these storms if it becomes necessary. Data from the surface of Mars, furnished by the highly successful Mars Pathfinder lander and rover mission, in addition to data from the orbiting Hubble Space Telescope and the National Radio Astronomy Observatory microwave antenna in Boulder, CO, will assist the Mars Global Surveyor team as they begin to dive into the upper atmosphere and understand the dynamics of the Martian environment.
Mars Global Surveyor will complete three revolutions around Mars in its initial, highly elliptical orbit, and gather some science data. On September 17, the spacecraft will perform its first aerobraking maneuver. Each time the spacecraft reaches the farthest point in its orbit around Mars –- known as the apoapsis –- it will perform an engine burn to trim the orbit. After four engine burns at apoapsis -- on September 17, 20, 22 and 24 –- Global Surveyor's orbit will be reduced to about three hours, meaning the spacecraft will be completing one revolution around Mars about every three hours.
During the next three months, the navigation team will continue to fine-tune the spacecraft's apoapsis and periapsis, or farthest and closest points over Mars, respectively. In January 1998, the navigation team will begin three weeks of final orbital adjustments. Then the science instruments will be turned on around March 10 and the mapping mission will begin on March 15, 1998.
Additional information and periodic updates at:
http://www.jpl.nasa.gov/marsnews
The Mars Global Surveyor mission is managed by the Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology, Pasadena, CA.
Astronomy Picture of the Day: Mars Global Surveyor - Aerobraking
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
April 30, 1997
No special maneuvers will be conducted to attempt to force the array to latch, and the focus of the Surveyor engineering team now will turn to minor modifications to the critical aerobraking phase that will circularize the spacecraft's orbit for the beginning of two years of science operations.
"After careful analysis of the situation, we've determined that the solar panel on Mars Global Surveyor that is not fully deployed presents very little risk to the mission," said Glenn E. Cunningham, Mars Global Surveyor project manager at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
The decision by NASA's flight team at JPL and its partners at Lockheed Martin Astronautics, Denver, CO, was reached after several months of extensive analysis of spacecraft data, ground-based computer simulations and a series of very slight spacecraft maneuvers that were carried out in January and February to characterize the situation.
"Thanks to an early launch that gave us an advantageous trajectory, we will not have to aerobrake into the Martian atmosphere as fast as we had originally planned to reach the mapping orbit, and that will reduce the amount of heating that the solar panels undergo during this gradual descent," Cunningham explained.
"We will rotate the solar-cell side of the panel that is not fully deployed by 180 degrees, so that it faces into the direction of the air flow that exerts drag force on the spacecraft as it dips repeatedly into the atmosphere," he said. "This way, the unlatched panel will not be in danger of folding up onto the spacecraft's main structure, nor will the panel be at any greater risk of heating up too much."
The solar panel in question is one of two 11-foot wings that were unfolded shortly after Surveyor's Nov. 7, 1996, launch from Cape Canaveral Air Station, FL. Data suggest that a piece of metal called the "damper arm," which is part of the solar array deployment mechanism located at the "elbow" joint where the entire panel is attached to the spacecraft body, probably was sheared off during deployment in the first day of flight. The lever that turns the shaft became wedged in a two-inch space between the shoulder joint and the edge of the solar panel, leaving the panel tilted at 20.5 degrees from its fully deployed and latched position.
Although the situation was never considered a serious threat to accomplishing the science objectives of the mission, the tilted array caused the JPL/Lockheed Martin flight team to re-evaluate the aerobraking phase, in which the spacecraft must rely almost solely on its solar panels for the drag needed to lower it into a nearly circular mapping orbit over the poles of the planet. This phase of the mission will begin a week after Mars Global Surveyor is captured in orbit around Mars on Sept. 11, and will last approximately four months.
Aerobraking was first tested in the final days of the Magellan mission to Venus in October 1994. The technique is an innovative method of braking which allows a spacecraft to carry less fuel to a planet and take advantage of the planet's atmospheric drag to descend into a low-altitude orbit.
Mars Global Surveyor will use an aerobraking phase much like that used to circularize Magellan's orbit. The solar wings -- which feature a Kapton flap at the tip of each wing for added drag -- supply most of the surface area that will slow the spacecraft by a total of more than 2,684 miles per hour during the four-month phase. Surveyor's orbit around Mars will shrink during this phase from an initial, highly elliptical orbit of 45 hours to a nearly circular orbit taking less than two hours to complete.
Engineers determined that the deployment springs currently holding the tilted solar panel in its nearly deployed position will not be strong enough to withstand the forces of aerobraking. To solve that problem, they designed a new configuration in which the tilted solar panel, along with the deployment springs, will be rotated 180 degrees, using a motor- driven inner gimbal actuator, and held in position with force applied by an outer gimbal actuator. Sequencing software will be modified to turn the gimbal actuators on before each closest approach to the planet and off at the conclusion of each drag pass.
As a consequence of the new aerobraking configuration, the more sensitive cell-side of the unlatched wing will be exposed directly to the wind flow of atmospheric entry, requiring that aerobraking be done in a more gradual, gentle manner. Ground tests have demonstrated that the unlatched solar panel will have more than adequate thermal margin to withstand additional heating as the spacecraft circularizes its orbit for the beginning of science mapping in March 1998.
Meanwhile, Mars Global Surveyor continues to perform very well on its arcing flight path toward the red planet and its arrival in orbit. A third, very minor trajectory correction maneuver, planned for April 21, was deemed unnecessary and canceled. In addition, science instrument calibrations continue to go well, and plans are being prepared to take an approach image of Mars a few days before the July 4 landing of Mars Pathfinder, which passed Mars Global Surveyor enroute to Mars on March 14, 1997.
Mars Global Surveyor is the first mission in a sustained program of robotic exploration of Mars, managed by JPL for NASA's Office of Space Science, Washington, DC.
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
November 27, 1996
The solar panel under analysis is one of two 11-foot (3.5-meter) wings that were unfolded shortly after the Nov. 7 launch and are used to power Global Surveyor. Currently, the so-called -Y direction array is tilted 20.5 degrees away from its fully deployed and latched position.
"After extensive investigation with our industry partner, Lockheed Martin Astronautics, using a variety of computer-simulated models and engineering tests, we believe the tilted array poses no extreme threat to the mission," said Glenn Cunningham, Mars Global Surveyor project manager at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "We plan to carry out some activities in the next couple of months using the spacecraft's electrically driven solar array positioning actuators to try to gently manipulate the array so that it drops into place. Even if we are not able to fully deploy the array, we can orient it during aerobraking so that the panel will not be a significant problem."
Diagnosis of the solar array position emerged from two weeks of spacecraft telemetry and Global Surveyor's picture- perfect performance during the first trajectory maneuver, which was conducted on Nov. 21. The 43-second burn achieved a change in spacecraft velocity of about 60 miles per hour (27 meters per second), just as expected. The burn was performed to move the spacecraft on a track more directly aimed toward Mars, since it was launched at a slight angle to prevent its Delta third-stage booster from following a trajectory that would collide with the planet.
Both the telemetry data and ground-based computer models indicate that a piece of metal called the "damper arm," which is part of the solar array deployment mechanism at the joint where the entire panel is attached to the spacecraft, probably broke during the panel's initial rotation and was trapped in the two inch space between the shoulder joint and the edge of the solar panel, Cunningham said.
Engineers at JPL and Lockheed Martin Astronautics, Denver, CO, are working to develop a process to clear the obstruction by gently moving the solar panel. The damper arm connects the panel to a device called the "rate damper," which functions in much the same way as the hydraulic closer on a screen door acts to limit the speed at which the door closes. In Global Surveyor's case, the rate damper was used to slow the motion of the solar panel as it unfolded from its stowed position.
Engineers have been re-evaluating the aerobraking phase of the Global Surveyor mission, which begins in September 1997 after the spacecraft is captured into an elongated orbit around the planet using its on-board rocket engine. The solar arrays are essential to the aerobraking technique and will be used to drag the spacecraft into its final, circular mapping orbit. First tested on the Magellan spacecraft at Venus, aerobraking allows the spacecraft to carry less fuel to a planet and take advantage of its atmospheric drag to gradually lower itself into the correct orbit.
"Since we launched early in our window of opportunity, we will not have to aerobrake as fast to reach the mapping orbit, and this reduces the amount of heating that the solar panels are exposed to," Cunningham said. "In the event that our efforts to latch the solar array properly in place are not successful, this reduced heating should allow us to tilt the array in such a way to prevent it from folding up and yet still provide enough useful aerobraking force." Additional analysis and testing will be performed over the next several months to verify this hypothesis.
Meanwhile, Mars Global Surveyor continues to perform very well as it completes its first two weeks in space, with on-going science instrument calibrations being performed this week. At the same time, the Mars Relay radio transmitter has been turned on for a post-launch checkout. Radio amateurs around the world are gearing up to participate in a radio tracking experiment in which they will become receiving stations for the low-power beacon signal transmitted by the Mars Relay radio system.
Mars Global Surveyor is approximately 3.4 million miles (5.5 million kilometers) from Earth today, traveling at a speed of about 74,000 miles per hour (119,000 kilometers per hour) with respect to the Sun.
Mars Global Surveyor is the first mission in a sustained program of robotic exploration of Mars, managed by JPL for NASA's Office of Space Science, Washington, DC.
November 7, 1996
The Mars Global Surveyor spacecraft was successfully launched today and is on its way to Mars. The Delta 2 first stage rocket with its nine strap-on solid rockets all ignited at 9:00:49.99 PST and leaped off the launch pad at Kennedy Space Center. Just 33 seconds later, the launch vehicle had reached Mach 1 (the speed of sound). In the following 90 seconds, the strap-on solid rockets burned out and fell away, as planned, and the main engine on the Delta 2 first stage continued to burn for another 2 minutes until it too, burned out and was jettisoned. The spacecraft was now 115 km above the Earth. At 4 minutes 14 minutes after liftoff (+4:14), the second stage ignited and burned for 5 minutes, and then was cutoff, as planned. The spacecraft was now out of view of the long range cameras on the ground, but tracking stations around the world would continue to monitor the status of the flight through the upper stage rockets. The Mars Global Surveyor spacecraft was placed in a circular Earth parking orbit 185 km above the Earth, where it would coast for the next 31 minutes.
Various tracking stations and a NASA ARIA plane achieved telemetry lock with the second stage at this point. After coasting for 31 minutes, the second stage reignited and burned for 2 minutes, raising the apogee, or the high point, of the Earth parking orbit. Small rockets were then fired to spinup the spacecraft to 60 rpm. After jettisoning the second stage, the third and final stage was ignited. The third stage, a Star 48B solid rocket, would burn for 87 seconds to send Mars Global Surveyor out of Earth orbit towards Mars. About 4.5 minutes after the third stage burnout, the spacecraft was despun by the deployment of a yo-yo cable device. The yo-yo cable device consists of two weights on wires which were uncoiled to slow the spin in the same way ice skaters slow their spins by extending their arms. The third stage was then jettisoned, and the separation was confirmed by the tracking stations in contact with the third stage. Mars Global Surveyor was now its way to Mars. About 2 minutes after separation from the third stage, the spacecraft automatically started to deploy its solar arrays, which would take about 5 minutes. After deploying its solar arrays, the spacecraft began configuring itself and finally turned on its X-band transmitter, and the X-band signal was acquired by the Deep Space Network station in Canberra, Australia. The spacecraft's health and status was then transmitted to Earth, and solar array deployment and spacecraft configuration was then confirmed. One slight anomaly was noted with one of the solar arrays. The solar arrays are fully deployed but one of the arrays was about 20 degrees off in the Y direction of where it was expected to be.
Mars Global Surveyor will go into orbit around Mars on September 12, 1997. It will then use aerobraking maneuvers in the upper atmosphere of Mars to reshape its orbit, and the spacecraft will then map the red planet for one full Martian year. Mars Global Surveyor's primary mission will end in January 2000.
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