Sensors from space

Written by: Tom Shelley | Published:

Tom Shelley reports on some very useful, down-to-earth technologies that have come to us from space.

Lighter weight and more precise torque sensing bolts, infra red sensing that targets the delivery of fertilisers and herbicides and hand-held micro defect detection are useful sensing technologies that have all come out of space research.

Bolts with ultrasonic transducers mounted in the bolt heads, developed for the International Space Station's Material Science Laboratory, have been taken up by ZF Lemförder for use in automotive applications. The bolts have been developed by the German company, Intellifast, and as well as the ISS, they have also been used on NASA's Pathfinder Mars Rover. The big advantage they offer is more reliable measurement of bolt tension. The traditional approach has in the past been to use a torque wrench, which ensures the imposition of correct torque, from which bolt tension can only be implied.

There is always a certain amount of error in this assumption, so more recently, the trend has been to measure bolt tension directly using ultrasound. According to Intellifast engineer, Frank Scheuch, "If you want to do an ultrasound scan on your pregnant wife, you have to put glycerine on her belly. If you want to an ultrasound on a bolt, you have to put a coupling liquid on the bolt and use a hand held sensor", but, "If you measure five times with the same person, you get five different readings." In fact, bolt tightening tension using conventional methods can be wrong by as much as 30%, which risks either failure or use of larger and heavier bolts than are really needed, tightened to less than optimum tension.

The system developed by Intellifast, called, PMTS (Permanent Mounted Transducer System), on the other hand, gives reliable values every time. A technician only has to attach a meter to perform an ultrasound sweep in order to measure the strain in the bolt. The meter can also be attached to a torque wrench so that the bolt's condition can be tracked as it is screwed into place. With the new system, the company says bolt tension can be measured to an accuracy of 3%.

Apart from other applications in aerospace, bolts in wind turbines need to be tightened with considerable precision, and ZF Lemförder engineer Ferry Oude Kotte says that this also applies to cars. "In some cases, we really do have to know the exact clamp load. The really good thing about Intellifast's solution is we don't have to alter the connection itself to conduct tests.

The result is better, safer cars made possible with bolt technology developed for space." One of the technologies that is heavily used by both ESA and NASA is infra red mapping to determine the state of vegetation and the environment. Infra red sensing comes completely from the military aerospace arena, starting in the Second World War. A US company, NTech Industries, based in Ukiah, California, has for some years being applying this methodology to assess the health of crops in order to spray exactly the right amount of nitrogen-containing fertilisers on individual plants, and also detecting individual weeds and spraying weed killer on just the weeds and not the crop in general.

The two technologies are called, 'GreenSeeker' and 'WeedSeeker', and they not only result in huge savings in not spraying unnecessary amounts of chemicals but also greatly reduce the load on the environment. The GreenSeeker RT200 system shines down light at two different wavelengths and measures reflectances, so the sensors can distinguish plants from soil and plants that need lots of nitrogen from ones that need less, based on what the company terms the Normalized Difference Vegetative Index. The WeedSeeker uses a single light wavelength and identifies chlorophyll associated with weeds as opposed to plants.

The systems control the spraying in real time using microcomputers and CANbus technology although a GPS system is used to record historical data, which helps in general plant and farm management. The technology was developed in conjunction with Oklahoma State University. Similar ideas were researched and demonstrated some years ago at the Silsoe Research Centre in Bedfordshire in the days before GPS, using data obtained from photographs taken from model aircraft and dead reckoning navigation. Nothing came of the work in the UK at the time and the Centre was closed down.

Both NASA and ESA continue to develop more and more sophisticated satellite based crop and vegetation mapping techniques. Kiri Wagstaff at Caltech and Terran Lane at the University of New Mexico, working for NASA's Jet Propulsion Laboratory have recently announced that they have perfected an alternating projection technique that applies weighting to individual pixels of visual data so analysing computers can automatically establish which pixels contain which crop. Reliable early estimates of likely volumes of products can significantly affect crop prices.

The same kind of technique could be applied to most kinds of vision system process monitoring. Mark Pestana at NASA's Dryden Flight Research Center (DFRC) working with the NASA Ames Research Center has perfected and demonstrated a system for the location of wildfires using infrared cameras on Unmanned Aerial Vehicles – UAVs, and delivering the data to fire fighters in real time. An Ames developed Autonomous Modular Scanner (AMS), mounted beneath a wing of DFRC's MQ-9 Ikhana, a version of the military Predator B, contains an infrared sensor capable of discriminating temperatures within 0.3 °C up to 540 °C.

The AMS operates as a digital camera with filters to detect light at visible, infrared, and thermal wavelengths. By placing the AMS aboard unmanned aircraft, one can gather information and imaging over thousands of square miles, and provide critical information about the location, size, and terrain around fires to commanders in the field through the satellite linked command and control system.

Slighty more down to earth, Curtis Ihlefeld and Adam Dokos at the Kennedy Space Center and Bradley Burns of ASRC Aerospace have developed a device that enables the field inspection of damage defects in aircraft windows in order to assess whether they need to be replaced without having to take them out to be examined in a lab.The Portable Handheld Optical Window Inspection Device (PHOWID) attaches to a smooth surface with suction cups and conducts a raster scan of a 25mm square area with an optical pen to produce a three dimensional image of the defect.

The system consists of a scanning head, motor control board, graphical user interface and supporting electronics and weighs 2.3kg. The head has a camera and LCD screen that allows the user to position it over the defect and describe the area of interest to be scanned at various speeds and resolutions. Once the scan is completed, software determines the defect length, width and depth and stores the information in a file. Depth range is 0.25mm. Noise floor is better than 1.5µm. Smallest resolution in the X-Y direction is 7.6µm.

Last but not least, and not from space but from the Woods Hole Oceanographic Institution, Scott Gallager, an associate scientist in the biology department has developed a technology that observes single celled organisms called protozoa, and can at once tell from their movements, whether there is something toxic in the water they are swimming in. The device is called a Swimming Behavioural Spectrophotometer. A camera records the protozoa's swimming patterns, which are analysed using software developed by Gallager and his colleagues to deliver red (dangerous), yellow (check) or green (safe) signals.

It is much faster than observing the behaviour of fish or larger creatures, and can quickly establish the presence of unknown hazards whereas chemical sensors can only detect known hazards, or factors such as biological oxygen demand.

Design Pointers
• Present motors deliver 2Nm of torque to assist the movement of heavy luggage. They are 36mm wide and 191 mm in diameter, with built-in drives
• Power is delivered by 10 AA nickel metal hydride batteries
• Cost in large-volume quantities is in terms of tens of pounds
• The wheel motors can easily be scaled up to deliver more torque or higher speed
• Present motors deliver 2Nm of torque to assist the movement of heavy luggage. They are 36mm wide and 191 mm in diameter, with built-in drives
• Power is delivered by 10 AA nickel metal hydride batteries
• Cost in large-volume quantities is in terms of tens of pounds


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