SEVEN MINUTES OF TERROR

SEVEN MINUTES OF TERROR FOR MARS ROVER CURIOSITY
by NASA

The entry, descent and landing (EDL) of the Mars rover is without doubt the most dramatic and violent part of the nuclear-powered robotic mission to Gale Crater. Like robotic missions before it, the time it takes for a surface mission to travel from the top of the Martian atmosphere to the surface is seven minutes. It is for that reason it is known as the "7 Minutes of Terror."

MPU-9150™ the world’s first 9-axis motion tracking device

Nine-Axis (Gyro + Accelerometer + Compass) MEMS MotionTracking™ Device
via  invensense.com





The MPU-9150™ is the world’s first 9-axis motion tracking device designed for the low power, low cost, and high performance requirements of consumer electronics equipment including smartphones, tablets and wearable sensors.

The MPU-9150 incorporates InvenSense’s MotionFusion™ and run-time calibration firmware that enables manufacturers to eliminate the costly and complex selection, qualification, and system level integration of discrete devices in motion-enabled products, and guarantees that sensor fusion algorithms and calibration procedures deliver optimal performance for consumers.

The MPU-9150 with MotionFusion and run-time calibration firmware enables consumer electronics manufacturers to rapidly commercialize cost effective motion-based functionality.

The MPU-9150 is a System in Package (SiP) that combines two chips: the MPU-6050, which contains a 3-axis gyroscope, 3-axis accelerometer, and an onboard Digital Motion Processor™ (DMP™) capable of processing complex 9-axis MotionFusion algorithms; and the AK8975, a 3-axis digital compass. The part’s integrated 9-axis MotionFusion algorithms access all internal sensors to gather a full set of sensor data. The part is offered in a 4x4x1mm LGA package and is upgrade-compatible with the MPU-6050™ integrated 6-axis MotionTracking device, providing a simple upgrade path and making it easy to fit on space constrained boards.

The InvenSense MotionApps™ Platform that comes with the MPU-9150 abstracts motion-based complexities, offloads sensor management from the operating system and provides a structured set of APIs for application development.

For precision tracking of both fast and slow motions, the parts feature a user-programmable gyro full-scale range of ±250, ±500, ±1000, and ±2000°/sec (dps), a user-programmable accelerometer full-scale range of ±2g, ±4g, ±8g, and ±16g, and compass with a full scale range of ±1200┬ÁT.

MPU-9150 System Diagram






NIST-F1 Cesium Fountain Atomic Clock

The Primary Time and Frequency Standard for the United States 

NIST-F1, the nation's primary time and frequency standard, is a cesium fountain atomic clock developed at the NIST laboratories in Boulder, Colorado. NIST-F1 contributes to the international group of atomic clocks that define Coordinated Universal Time (UTC), the official world time. Because NIST-F1 is among the most accurate clocks in the world, it makes UTC more accurate than ever before.

The uncertainty of NIST-F1 is continually improving. In 2000 the uncertainty was about 1 x 10-15, but as of the summer of 2010, the uncertainty has been reduced to about 3 x 10-16, which means it would neither gain nor lose a second in more than 100 million years! The graph below shows how NIST-F1 compares to previous atomic clocks built by NIST. It is now approximately ten times more accurate than NIST-7, a cesium beam atomic clock that served as the United State's primary time and frequency standard from 1993-1999.

Uncertainty of NIST Time and Frequency Standards

Technical Description

NIST-F1 is referred to as a fountain clock because it uses a fountain-like movement of atoms to measure frequency and time interval. First, a gas of cesium atoms is introduced into the clock's vacuum chamber. Six infrared laser beams then are directed at right angles to each other at the center of the chamber. The lasers gently push the cesium atoms together into a ball. In the process of creating this ball, the lasers slow down the movement of the atoms and cool them to temperatures near absolute zero.

Two vertical lasers are used to gently toss the ball upward (the "fountain" action), and then all of the lasers are turned off. This little push is just enough to loft the ball about a meter high through a microwave-filled cavity. Under the influence of gravity, the ball then falls back down through the microwave cavity.

NIST-F1 Cesium Fountain (Block Diagram)


The round trip up and down through the microwave cavity lasts for about 1 second. During the trip, the atomic states of the atoms might or might not be altered as they interact with the microwave signal. When their trip is finished, another laser is pointed at the atoms. Those atoms whose atomic state were altered by the microwave signal emit light (a state known as fluorescence). The photons, or the tiny packets of light that they emit, are measured by a detector.

This process is repeated many times while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the cesium atoms and maximizes their fluorescence. This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz), or the frequency used to define the second.

As you might guess, the longer observation times make it easier to tune the microwave frequency. The improved tuning of the microwave frequency leads to a better realization and control of the resonance frequency of cesium. And of course, the improved frequency control leads to what is one of the world's most accurate clocks.The combination of laser cooling and the fountain design allows NIST-F1 to observe cesium atoms for longer periods, and thus achieve its unprecedented accuracy. 

Traditional cesium clocks measure room-temperature atoms moving at several hundred meters per second. Since the atoms are moving so fast, the observation time is limited to a few milliseconds. NIST-F1 uses a different approach. Laser cooling drops the temperature of the atoms to a few millionths of a degree above absolute zero, and reduces their thermal velocity to a few centimeters per second. The laser cooled atoms are launched vertically and pass twice through a microwave cavity, once on the way up and once on the way down. The result is an observation time of about one second, which is limited only by the force of gravity pulling the atoms to the ground.


Bill ( The Engineering Guy) shows the world's smallest atomic clock and then describes how the first one made in the 1950s worked. He describes in detail the use of cesium vapor to create a feedback or control loop to control a quartz oscillator. He highlights the importance of atomic team by describing briefly how a GPS receiver uses four satellites to find its position. You can learn more about atomic clocks and the GPS system in the EngineerGuy team's new book Eight Amazing Engineering Stories http://www.engineerguy.com/elements

Credits

NIST-F1 was developed by Steve Jefferts and Dawn Meekhof of the Time and Frequency Division of NIST's Physical Measurement Laboratory in Boulder, Colorado. It was constructed and tested in less than four years. The current NIST-F1 team includes physicists Steve Jefferts and Tom Heavner.

Google-Blockly – A visual programming language


via Google Blocky by neil.fraser@gmail.com
Blockly is a web-based, graphical programming language. Users can drag blocks together to build an application. No typing required.

Check out the demos:
  • Maze - Use Blockly to solve a maze.
  • Code - Export a Blockly program into JavaScript, Dart, Python or XML.
  • RTL - See what Blockly looks like in right-to-left mode (for Arabic and Hebrew).
Blockly is currently a technology preview. We want developers to be able to play with Blockly, give feedback, and think of novel uses for it. All the code is free and open source. Join the mailing list and let us know what you think.