What do Y, Yb, Tb, Er, Gd, Tm, Sc, Ho, Dy and Lu have in common?

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What do the following ten elements have in common?

  • Yttrium
  • Ytterbium
  • Terbium
  • Erbium
  • Gadolinium
  • Thulium
  • Scandium
  • Holmium
  • Dysprosium
  • Lutetium

The answer (and there is a tiny clue in some of the names) is that all ten elements were isolated from one sample, taken from a mine in the small village of Ytterby in Sweden. All of the elements are rare earth metals which occur in similar locations and have similar properties. This makes their extraction and isolation very difficult and this is where the “rare” in their name comes from.

In 1787 one of the students of Lieutenant Carl Axel Arrhenius found a dark-coloured ore that was much too heavy to be coal. Arrhenius took this ore, which he named “ytterbite”, and sent samples to various chemists for analysis. One of these chemists, Johan Gadolin, determined that ytterbite did indeed contain a previously unknown element and called this element yttrium.

In 1843 Carl Gustav Mosander demonstrated that ytterbite was actually made of three metal oxides, not one as Gadolin had thought. The original name was kept for one of these three parts and the other two elements named terbium and erbium, both after the village of Ytterby where they were found.

Terbium was later demonstrated to be a mixture of terbium and a new element which was named gadolinium in honour of Gadolin. Erbium was demonstrated to be a mixture of erbium and and a new element which was named ytterbium, again after the village of Ytterby.

Erbium was then itself demonstrated to a mixture of three elements: erbium; thulium, named after Thule, a term used by early map makers for the far north where Sweden is located; and holmium, named after the Swedish capital Stockholm. Holmium was then later demonstrated to be a mixture of holmium and dysprosium, which takes its name from the Greek word dysprositos meaning “difficult to get”, reflecting the difficulty found in isolating it.

Ytterbium was demonstrated to be composed of ytterbium and a new element which was named scandium after Scandanavia, and finally ytterbium was split again to yield ytterbium and lutetium.

A diagram showing the order in which the ten elements were isolated.

Why is Quincy, Washington so popular with tech companies?

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Quincy, WA is a small town (population 6750) in the north-west of the US. So why have technology giants Microsoft, Yahoo!, Dell, Vantage Data Centers, Sabey and Intuit all chosen to build huge data centres there? Quincy is now home to nearly 190 000 square metres (more than two million square feet) of data centre.

The answer is very simple: electrical power.

The town of Quincy is close to the Columbia river, the fourth largest (by volume) river in the US. There are fourteen hydroelectric dams on the Columbia river, two of which, the Priest Rapids Dam and Wanapum Dam, provide electricity to Quincy.

The Priest Rapids Dam

The Wanapum Dam

Hydroelectric power is cheap,* but more importantly from the point of view of data centre operators, it is very reliable. The reliability of the electricity supply to Quincy is better than 99.99% which is very important for “mission-critical” always-on services like cloud computing. Using renewable non-polluting hydroelectric power also helps service providers demonstrate their green credentials. Server farms consume a huge amount of electricity – more for cooling than for processing – and using hydroelectric power helps to reduce their associated carbon footprints.

* The local utility company, Grant County Public Utility District, offered electricity at a discount rate to attract users to the area.

Why putting missiles on roofs in London isn’t as dumb as it sounds.

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The UK government has recently announced that it will be placing Starstreak HVM surface-to-air missiles on some roofs in London as a security measure during the 2012 Olympics. This has caused a bit of a kerfuffle.

Below are some thoughts on the issue from a physicist’s point of view.

What are Starstreak missiles and how do they work?

The Starstreak is a short-range laser-guided surface-to-air missile. When launched it very quickly accelerates to Mach 3.5 (1200 metres per second) and is then guided onto its target by a pair of laser beams projected from its ground-based aiming unit. Being laser-guided means that unlike heat-seaking or radar-seeking missiles the Starstreak cannot be avoided through the use of chaff or flares; however unlike those missiles it does not have fire-and-forget capabilities.

The Starstreak Light Multiple Launcher showing three Starstreak missiles and the guidance unit.

Once the Starstreak approaches its target it releases three 900 gram tungsten-coated beam-riding submunitions. Once one of the submunitions (or all three) impacts the target a short delay fuse is activated and the 450g of explosive inside the submunition explodes inside the target, throwing out tungsten alloy shrapnel and tearing it to pieces.

What scenario is the deployment of Starstreak missiles designed to prevent?

My guess is that the government is trying to defend against suicide bombers using aircraft as weapons. A heavy aircraft moving at high speed has a large amount of kinetic energy and this, coupled with the chemical potential energy in the fuel, makes it a formidable weapon.* The Olympics will concentrate a large number of people in a small space which makes the Olympic sites attractive targets.

If a plane is shot down, won’t it kill people when the wreckage lands?

It depends on the size of the aircraft involved. A light aircraft at high altitude wouldn’t produce much dangerous wreckage, a low-flying jumbo jet would. But falling wreckage will kill far fewer people than an aeroplane striking one of the Olympic sites would.

The force of the missile’s explosion will tear any aircraft into pieces, and once the structural integrity of the aircraft is ruined the force of the wind will tear it into further smaller pieces. Each of those falling pieces will reach terminal velocity relatively quickly and will therefore strike the ground at a lower speed than if it were flown into the ground under power. The video that has been going around showing a helicopter shot down by a Starstreak missile crash into the ground in a fireball is of a guidance test – the missile in the video was not carrying an explosive payload.

What about burning jet fuel hitting the ground?

This is much less of a problem. An explosion inside an aircraft, combined with the high-speeds involved would aerosolise the fuel, causing it to burn up very quickly in mid air. Again, this is a much lower risk than if a plane full of jet fuel were to crash into one of the Olympic stadia.

Won’t the missile launches damage the buildings they’re launched from?

No. The Starstreak missile is ejected from its launch tube by a low power first stage rocket motor that is extinguished before the missile leaves the tube. The powerful second stage motor doesn’t kick in until the missile is safely away from the launcher, meaning that there is almost no recoil at all. The launch of a Starstreak missile produces no significant overpressure so there is no danger to windows or walls. The missiles have to be launched from roofs or open spaces because the rocket requires a certain amount of space to accelerate to attack velocity.

* It was the chemical energy in the tens of thousands of litres of fuel that were responsible for the collapse of the Twin Towers in the 9/11 attacks. Had the planes had no fuel aboard the Towers would have survived.

The classified Space Shuttle missions

The Space Shuttle flew a total of 135 missions in its lifetime. Of these 135 missions, seven were classified Department of Defense missions whose purposes were never officially announced.*

  • STS-51-C (15th mission, January 1985) deployed a Magnum satellite designed to intercept communications, mainly from the Soviet Union and China.
  • STS-51-J (21st mission, October 1985) deployed two satellites that form part of the Defense Satellite Communications System that allows the military to communicate with units all across the globe.
  • STS-27 (27th mission, December 1988) deployed the first Lacrosse radar imaging reconnaissance satellite. It is alleged (on Wikipedia) that one of the uses of the Lacrosse system would have been to provide real-time targetting data to the B-2 Spirit stealth bomber.
  • STS-28 (30th mission, August 1989) deployed one of the satellites that forms part of the second generation of the Satellite Data System (SDS2) which relays data from low-orbit reconnaissance satellites.
  • STS-33 (32nd mission, November 1989) deployed another Magnum satellite.
  • STS-36 (34th mission, February 1990) deployed a MISTY photographic reconnaissance satellite and the PROWLER satellite. MISTY satellites are alleged to have both optical and radar stealth capabilities to make them difficult to track. The purpose of PROWLER is uncertain, but it is probably designed to inspect other satellites and intercept signals; it has been tracked from Earth approaching close to Russian communication satellites.
  • STS-38 (37th mission, November 1990) deployed the second of the SDS2 satellites.

There was also one partially classified mission:

  • STS-53 (52nd mission, December 1992) deployed the third SDS2 satellite along with a number of unclassified experiments.

The National Reconnaissance Office, one of the seventeen “elements” of the US Intelligence Community, actually influenced the design of the Space Shuttle, having its payload bay size increased so that it could accommodate the KH-9 HEXAGON spy satellite. In the end all of the KH-9 satellites were actually launched by third generation Titan rockets.

* Everything in this post should be heavily prefaced with “allegedly”.

Where is the best place to launch a rocket from?

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NASA has quite often had to “scrub” (cancel) launches from the Kennedy Space Center (KSC) in Florida because of inclement weather. But why build a Space Centre in Florida in the first place? It’s location makes it particularly vulnerable to hurricanes and other weather “events” so there must be a significant advantage to its location.

The paths of the eighty-three Florida hurricanes that occurred between 1975 and 1999.

Florida is a good location for rocket launches because it is both on the east coast of the US and because it is close to the equator.

Launching from the east coast of the US means that the rocket can take advantage of the Earth’s west-to-east spin. If a rocket were launched from the west coast it would either have to fly right across the continental US, which would be dangerous if it malfunctioned; or it would have to take off east-to-west, flying against the spin of the Earth.

At the North or South pole the speed at which you are moving, relative to a stationary observer not on Earth, is zero. As you move closer to the equator this speed increases, until at the equator you are travelling at a speed of 465 metres per second (1040 mph). At KSC, which is at a latitude of 28°N, this speed boost is reduced slightly, to about 410 m/s (916 mph). This is the best possible location in the continental USA, presumably more suitable (i.e. more southern) locations in Hawaii, Puerto Rico or one of the US’s other territories were discounted because of their remoteness.

The closer to the equator you can get, the greater the speed boost you receive. This reduces the amount of energy required to get into space and means that less fuel is required. The European Space Agency makes its launches from the Guiana Space Centre in French Guiana which is only 5° north of the equator. The commercial space launch service Sea Launch uses a mobile launch platform that sails nearly 5000 kilometres from Long Beach in Los Angeles where the rockets are assembled, to a location actually on the equator where the launches take place.