Sunday Seismometer #12

Rocard (1958)

From last week's prototype, let's move on to a more useful set of instruments, designed specifically to detect nuclear explosions in the context of Comprehensive Test Ban Treaty monitoring.



They are named after Professor Yves Rocard, the physicist who started to develop detection seismology in France in the 1960s, and who founded the division of the French Atomic Energy Commission (CEA) that is in charge of geophysical studies and activities associated with monitoring and the environment (LDG).



The Rocard is a classical electromagnetic seismometer, with a 1s natural period and electronic amplification. Rocard instruments were in operation at the Welschbruch station not far from Strasbourg.

Sunday Seismometer #11

Peterschmitt (1950)

Continuing our mini-series on electromagnetic seismometers (see the Galitzine and Press-Ewing posts), here is a seismometer you are unlikely to see anywhere else. The Peterschmitt was designed and built in Strasbourg in 1950, where it was in use until 1975.



This admittedly ugly looking beast is a prototype classical electromagnetic seismometer (you can see its coils on the near side, very similar to those on the Galitzine instrument) combined with a galvanometer. It has a natural period of 1s, and its amplification is provided by a resistance bridge. The most interesting feature of this instrument is its original inbuilt calibration system.

The design of this instrument is attributed to Elie Peterschmitt, who was recruited by Strasbourg in 1937, took charge of the Strasbourg historical seismological station as well as the stations of Besançon and Bagnères de Bigorre, and later helped develop the European-Mediterranean Seismological Center (EMSC).

On batteries and aeroplanes

Earlier this week I wrote about space-crafts with thermostatic skins, implying this kind of technology could prove to be useful for temperature control in low-power autonomous seismic stations in the Antarctic. Here is another technological achievement that may be of some use.

The BBC reported over the weekend that a UK-built solar-powered and unmanned plane, the Zephyr-6, had stayed aloft for more than three days, running though the night on batteries it had recharged during the day.

The Zephyr weighs 30kg and flies at an altitude of over 60,000 feet. Its power derives from solar power generated by paper-thin amorphous silicon solar arrays glued over the aircraft's wings. This power is stored in a new type of lithium-sulphur battery.

A lot of effort has gone into power storage and light-weighting the systems. Lithium sulphur is more than double the energy density of the best alternative technology which is lithium polymer batteries. Mr Kelleher, Qinetiq (UK defense and research firm)

These batteries are made by the Sion Corporation:

The custom built Li-S battery pack was designed and assembled by SION Power and consisted of 576 cells built into a battery configuration of 12 cells in series and 48 in parallel. The battery utilized SION’s unique, high specific energy Li-S cells (350 Wh/kg). At ~10 kg, the Li-S battery pack was carefully engineered to minimize total pack weight.
In addition to providing flight power, the battery pack supplied power to a special
internal pack heating system to maintain the batteries at 0oC throughout the cold nights. Sion press release.

The Sion battery data-sheet is available here: sion_product_spec.pdf.

The usefulness of this kind of battery for our stations in Antarctica would depend on its adaptability to long-duration low-power applications, and on its performance at low temperatures. Yet another thing to look into this fall!

Funky thermostat film for spacecrafts

You may remember that keeping our antarctic instrumentation at a constant and not-too low operating temperatures is a major challenge. Some time ago I posted about the heating / insulation strategy we implemented in last year's prototype stations. I'm planning to write a short piece on how that strategy worked out in the next couple of weeks.

The subject of today's post is an innovation in thermostat technology that has just been presented at the 236th American Chemical Society' National Meeting in Philadelphia, and that was brought to my attention by the BBC News website.

Spacecraft have a serious problem with temperature regulation, as they operate in blazing sunlight, in the cold shadow of the Earth, or in even more extreme conditions closer or further away from the Sun. As operating conditions vary, so does the amount of heat generated by the onboard electronics.

For large spacecraft, [temperature control] is done with mechanical louvers—basically glorified window blinds—that open and close to allow in or reflect heat. But as satellites get smaller, these systems get too heavy and bulky. - Prasanna Chandrasekhar of Ashwin-Ushas, an American tehnology firm

Chadrasekhar and his team have developed a "skin" that can be placed on a spacecraft to actively control the amount of heat that it radiate by controlling its emissivity.

Polymers in the skin change their emissivity when electricity is applied to them, retaining heat in cold conditions and radiating it away in hot ones. That leads to an active temperature control that can be maintained with very little power.

The skin is just a few tenths of a millimetre thick, has been tested to withstand the rigours of the vacuum and temperature extremes of space, and can be bent and cut to fit craft of any shape without losing its properties.

Would such material be useful in Antarctic conditions, which are much less extreme than those experienced in outer space ? The answer will depend on the amount of energy required to power the emissivity-regulating skin.

Energy is a serious problem in Antarctica given the duration of the winter night. Should the new skin system be as low power and low-cost as announced at the conference, then its use in Antarctica may well be possible. We shall be keeping a lookout for updates on this product!

Sunday Seismometer #10

Press-Ewing (1953)

Some 40 years after the Galitzine electromagnetic innovation, the same principles of operation are put to work in the Ewing-Press seismograph, built at the Lamont Geological Observatory of Columbia (now the Lamont-Doherty Earth Observatory) by Maurice Ewing and Frank Press.

In the photo below you can see the vertical Press-Ewing instrument on display at the Strasbourg Seismological Museum. It was in use in Strasbourg from 1963 to 1975.



It is an electromagnetic seismograph, coupled with a galvanometer, and has a natural period that can be selected and fixed up to 30s. Recording was optical, on photographic paper. The glass ball you can see on the near side of the instrument reduces the effect of variations in atmospheric pressure on the seismograph recordings, using the Archimedes principle.

This seismograph and its horizontal counterparts are very well adapted for the recording of surface waves. In 1957-58, Press-Ewing instruments were deployed in 125 locations around the globe to establish the World-Wide Standardized Seismograph Network, the first global earthquake monitoring system.