Magellan Mission: Radar Sensing and Image Interpretation - Essay Example

Magellan Mission: Radar Sensing and Image Interpretation Introduction The Magellan Mission was the first U.S. mission to study in detail the surfaceof Planet Venus. It was launched to Venus from Cape Canaveral, Florida on May 4, 1989 aboard Space Shuttle Atlantis. After fifteen months of interplanetary cruise the spacecraft arrived at Venus on August 10, 1990 and started mapping operations on September 15, 1990. The Magellan Mission was a follow - up mission of the previous Pioneer Venus Mission which mapped only 25 percent of the Venusian Surface near the north pole of the planet. The Magellan Mission's primary objectives were to map at least seventy percent of the surface at a resolution better than 300 m and to determine the global relief at a horizontal resolution of about 10 km and vertical accuracy of 80 km or better (Ford 1). The Mission was named after Ferdinand Magellan, a Portuguese-born explorer in the sixteenth century, who led an expedition that first circumnavigated the Earth. Scientific Objectives The earlier radar missions to Venus provided planetary scientist a global map of the surface of the planet and were very valuable in understanding the geological structure of the planet. However it further revealed a need for "global radar data coverage" of the planet's surface in "orders-of magnitude higher resolution" (Ford 1). This need facilitated and provided motivation to determine the design and objectives of the Magellan mission. The main purposes of the Magellan Mission were to create a global radar map of the surface of Venus at higher resolution using the synthetic aperture radar (SAR) and to determine the topographic relief of the planet. The scientific objectives of the Magellan Mission were to: (1) Obtain near-global radar images of Venus' surface, with resolution equivalent to optical imaging of 1 km per line pair. (2) Obtain a near-global topographic map with 50km spatial and 100m vertical resolution. (3) Obtain near-global gravity field data with 700km resolution and 2-3 milligals accuracy. (4) Develop an understanding of the geological structure of the planet, including its density distribution and dynamics. The end product of these four objectives shall be the classification of geographic and tectonic features of the surface like mountains, ridges, valleys, hills, and planes. Impact processes, lava flows, and other chemical processes will be explained and the internal density distribution of the planet will be modeled. The Magellan Spacecraft The spacecraft design was economical and simple in relation to other spacecraft missions. In fact, the key components of the spacecraft were acquired from the spare hardware from other space programs including Voyager, Galileo, Viking, and Mariner. The spacecraft was 6.4 m long and with a mass of 3,449 kilograms. Included in the spacecraft were a single radar sensor, a large 3.7-m diameter parabolic High-Gain Antenna dish used for communication with Earth and a science instrument for radar imaging, solar panels about 9.2 m across to collect solar energy for charging the spacecraft's nickel-cadmium batteries and to power the spacecraft, three orthogonal reaction wheels used for pointing control, monopropellant hydrazine thruster system used to make adjustments of large scale orbital corrections. Subsystems included a medium-gain antenna, star scanner, on-board computer, coherent X- and S- band radio subsystem used for communication and gravity field experiments, and two tape recorders. Fig. 1. Labeled drawing of Magellan Spacecraft Key features of the Magellan spacecraft. Shown here are the different hardware and electronic subsystems of the spacecraft. (NASA) The Magellan spacecraft in the payload bay of the Space Shuttle Atlantis before its scheduled launch (Magellan Probe). Fig. 2. Magellan Spacecraft The Magellan Radar Sensor The radar sensor is a single science instrument in the spacecraft capable of acquiring data in three different modes or functions: SAR imaging mode, altimeter mode, and radiometer mode. In the imaging mode, Magellan used the synthetic aperture radar (SAR) to obtain high resolution images of the surface. The SAR will use the high-gain antenna to transmit 150 to 800 burst of pulses in a fraction of a second and then will receive the SAR echoes. The signals acquired from SAR will be processed by a computer on Earth so that it will synthesize the behavior of a large antenna. Through this process, the 3.7-m diameter radar sensor will operate as if it has a huge antenna and therefore will produce high quality images. After the last SAR echo is received, the sensor shall then switch to altimeter mode which will acquire data on altitudes and elevations of the surface of the planet. The system is connected to a smaller altimeter horn antenna which shall transmit a burst of 17 pulses to the surface directly below the spacecraft. After the last altimeter echo is received, the sensor will then change to radiometer mode. Using the high-gain antenna, the sensor shall measure the natural thermal emissions from the surface. Sample Image Results from Magellan Surface of Venus obtained from the global radar mapping of Magellan mission. The surface has a uniform distribution of impact craters across the entire surface of the planet. (Venus) Fig. 3. Venusian Surface A radar image of a volcano named Grimke in Aphrodite Terra taken from the Magellan spacecraft (Grimke). Fig. 4. Sample Radar Image Computer-generated image of the volcano Maat Mons. Shown in the foreground are lava flows from fractured planes towards the base of the volcano (Maat Mons). Fig. 5. Maat Mons Dome - shaped volcanic features located in the Eastern edge of Alpha Regio are common features in Venusian surface which is covered about 85 percent of volcanic rocks. Lava flows extending several hundred kilometers flooded the lowlands creating immense plains (Terrestrial). Fig. 6. Volcanic Features Impact craters in Venus, as shown, are few compared to volcanic features suggesting that the planet is geologically young (Terrestrial). Fig. 7. Impact craters Important Scientific Results The high-resolution images provided by Magellan pointed to the existence of many volcanic features and volcanic materials that covered most of the Venusian surface. The study of this high quality images supplied pertinent details to understand better the formation of surface structures and provided evidence to the contribution of impacts, volcanic formation, and the faulting or deformation of the planet's lithosphere to the development of Venusian geology. Vast plains of lava, large - shield volcanoes, small lava domes scattered over a small area, and dome-shaped hills are common geological features of the planet. The surface of the planet is still geologically young in its formation as evidenced by the few impact craters. Volcanic activity is possibly regular because lava flows covered the surface to a large extent. The data revealed no evidence of terrestrial plate movements and sizeable wind erosion though it has a thick atmosphere. Conclusion To date, the Magellan mission has the best high quality, high resolution global mapping of the surface of the planet. The unprecedented radar data taken from Magellan facilitated the first geological understanding of planet Venus. Before it began its final descent to the planet, Magellan had mapped over 99 percent of the Venusian surface with a resolution of approximately 100 m, ten times better than that obtained by the previous Soviet Venera missions. On October 12, 1994, Magellan spacecraft lost radio contact and presumed to be burned up in the atmosphere on October 13 or 14, 1994. The overall cost for the operation and analysis through the entire mission was about USD 680 million. Works Cited Magellan Mission to Venus. 28 February 2005. NASA. 28 November 2007. http://nssdc.gsfc.nasa.gov/planetary/magellan.html Magellan.. National Space Science Data Center. 27 November 2007. 28 November 2007 Ford, John P. Chapter 1. Magellan: The Mission and the System. Guide to Magellan Image Interpretation. 28 November 2007. Magellan Fact Sheet. 30 December 2004. Magellan Mission to Venus. 28 November 2007. Magellan Probe. Wikipedia: The Free Encyclopedia. 28 October 2007. 28 November 2007. Labeled Drawing of Magellan Spacecraft. National Space Science Data Center. 29 November 2007. Grimke. Introduction to the Solar System. 03 October 2005. 29 November 2007. Venus. Tiverton and Mid Devon Astronomy Society. 29 November 2007. Maat Mons. NASA. 21 November 2006. 29 November 2007. Terrestrial Planets. University of Oregon. 29 November 2007. Read More