By Randy Siniard Aviation and Missile. Research, Development, and Engineering CenterSeptember 7, 2010
Redstone Arsenal, Ala. - Your family is on vacation, travelling through the mountains, and suddenly your car's navigation system loses connectivity with is Global Positioning System satellite signal. You're lost, misoriented, and basically out of luck until the signal is regained.
Physicists from the Aviation and Missile Research, Development and Engineering Center, and the Marshall Space Flight Center are co-leading a collaborative effort along with Alabama A&M University, the University of Alabama at Huntsville, and the University of Nebraska at Lincoln to demonstrate the enhancement in sensitivity and improvement in performance of optical gyroscopes-being able to navigate without the use of GPS.
Krishna Myneni, a Research Physicist in the AMRDEC's Weapons Sciences Directorate and Dr. David Smith, Optical Physicist, in NASA's Marshall Space Flight Center's Sensors Branch are conducting the research they believe will improve the navigation of military air and ground vehicles and missiles and also have commercial uses.
Helping them this summer was Alexandra Toftul, NASA Marshall Space Grant Research Intern Program University of Nebraska-Lincoln student.
"I supported the research using various methods of stabilizing the laser used in the experiment. Also, I simplified the data collection process by building control hardware using my major in electrical engineering and knowledge on electronic circuits," Toftul said.
The collaborative effort has allowed for students to obtain invaluable experience on the cutting edge of scientific research and development, while allowing them to contribute directly to the team's effort.
"I was able to learn a great deal from the team with whom I worked this summer; I arrived with little previous experience in this field. This has been a rare opportunity," Toftul said.
Chris Roberts, Division Chief, Navigation Control and Technology, Weapons Development and Integration Directorate is charged to provide central Army oversight of research and development in inertial systems and components for missiles, aircraft and drones; land navigation; and other applications such as inertial land surveying and inertial fuzing.
"In general, an inertial measurement unit consists of 3 accelerometers and 3 gyroscopes, and provides to the host platform, be it an aircraft, launcher or vehicle, submarine, spacecraft, or a guided missile, a data stream over time measuring the dynamical changes in attitude, rate and velocity, acceleration being experienced by the host platform. If the sensors are very accurate, the IMU can be coupled with a computer to make an inertial navigation system," said Roberts.
"The INS output provides the host platform with an accurate solution to its location relative to its initial starting location as it moves over time," said Roberts.
For example, current inertial guidance systems guide missiles from their launch point to their targets because they "know" where they fired from and where the target is located. However, this type of guidance doesn't last long enough to engage most targets and so other guidance methods, such as GPS, are employed.
"In the absence of a GPS signal an IMU can keep track of changes in position for a vehicle; however as time grows so does the non-dependency rate of the IMU," said Myneni,
One way to improve a missile's capabilities is to improve its guidance system so it doesn't rely solely on a single means of navigation. The AMRDEC - NASA team is trying to develop a guidance system that works in areas with limited or no connectivity with GPS Satellite signals.
Myneni and Smith's work is done in Optical Cavities. Optical cavities are an arrangement of mirrors which allow light to make multiple trips inside the cavity by bouncing off the mirrors.
When there is a medium introduced to the cavity, it becomes the ring laser gyroscope, which is used on many commercial and military vehicles as part of an overall inertial measurement package to provide position, heading, and attitude information.
In part of their collaborative effort they are using atoms at room temperature to provide desired optical properties for enhancing the performance of ring cavity gyroscopes.
Through experimentation we discovered that by using a second pumping beam the sensitivity of the optical cavity could be changed or tuned. Practically, that meant that we could adaptively change the sensitivity of an optical gyroscope, increasing it for low rotation rates and decreasing it for large ones, so that the gyroscope could operate well over a wide range of rates, said Myneni.
The team is also working to establish a laser cooling and trapping facility at the Weapons Science Directorate to support the development of inertial sensors that use very cold atoms; temperatures about ten millionths of a degree above absolute zero.
Once these trapped atoms are released, the acceleration of the atoms relative to lasers situated on a moving platform, an Army vehicle perhaps, is measured through an indirect technique known as atom interferometry, said Myneni.
These measurements allow the computation of the acceleration experienced by an object.
Atom interferometry with cold atoms provides exquisite sensitivity owing to the fact that the measurement can be made simultaneously on a large number, billions, of nearly identical particles. The lasers used to encode the position in the atom's quantum state act as a high precision ruler on the microscopic level, and precise timing can be accomplished, said Myneni.
Myneni and Smith's experimentation in navigational control technology is vital for the development of future Army weapons systems.
"This research needs to be done to keep striving for better performance, smaller, and lower cost break-through technology," said Roberts.