Saturday, 19 September 2015

Waves in Space and Time: LIGO reopens UPDATED

Back in September I made the post below about LIGO reopening. Well, almost immediately after reopening, they made a discovery! The news made headlines and rightly so, they simultaneously confirmed that gravitational waves exist, added further credence to General Relativity, and made the first observation of a binary black hole system and merger.

It's worth pausing to consider what they have achieved here. Something that was first predicted in 1916 has been discovered 100 years later. The signal detected caused the length of LIGO's 4km long arms to change by a fraction of a protons width, the waves themselves originated from the merger of 2 black holes, each of about 30 times the mass of the Sun, which occurred 1.3 billion years ago. The event liberated something like 3 times the mass of the Sun in pure energy as gravitational waves, and the black holes reached velocities of ~ 60% of the speed of light immediately before their event horizons merged.

The next step is to carry on making observations - there are several sources that could be detected in theory, from compact object collisions, to the cosmological background thought to originate from quantum fluctuations during inflation!


LIGO (Laser-Interferometer-Gravitational-Wave-Observatory) in Louisiana has restarted after a 5 year hiatus. It is now around 10 times more sensitive. But what does LIGO do?

LIGO is an experiment to detect gravitational waves (GWs), ripples in space-time predicted by General Relativity. They have never been directly detected, although their existence has been strongly inferred from the mechanics of systems such as binary neutron stars. Essentially, GWs are though to be emitted from accelerating masses in much the same way electromagnetic waves are radiated from accelerating charges. The problem is, GWs are weak and the most powerful sources (e.g. black hole mergers) are so far away, the signal here on Earth is tiny.

LIGO aims to measure the stretching and compression of space caused by a GW passing through the experiment. It consists of two 4 km long evacuated tunnels, orientated at right angles and meeting at one end. From the corner they meet, laser beams from the same source are fired along the tunnels at right angles. The two beams are bounced off mirrors at the far ends. They come back along the tunnels and recombine very near to where they started. If the experimental set up is perfect (ie perfect vacuum, no vibrations, exact distances), each beam will travel exactly the same distance and thus when they recombine, they will be perfectly in phase still. Another way of thinking of it is to say that the time of flight of the photons is identical for each beam. The diagram below shows the set up, which is very similar to a Michelson-Morley interferometer.

If one beam is shortened/ lengthened (an interference pattern produced), we can determine that a GW has passed along one of the beams. The ideal situation is a GW parallel to one tunnel and perpendicular to the other.

LIGO should now be capable of detecting GWs of frequency ~100Hz, which is similar to the lower end of human hearing (hence 'listening to the comos'). For different frequencies, and more sensitivity, the next experiment will be LISA (Laser-Interferometer-Space-Antenna), now eLISA (e for evolved). This will involve 2 spacecraft separated by millions of km. The same principle will be used, but now the 'arm length' is millions of km, not 4 km. Hence greater sensitivity can be achieved. The first prototype of this experiment, LISA pathfinder, is in construction and will be launched later this year. 

It's an exciting time: we are on the eve of testing one of the final predictions of General Relativity, and opening up a whole new type of astronomy.

Concorde to the Sky?

Apparently, a 'group of British enthusiasts'  have raised £120 million, enough to purchase and restore to airworthy condition, one of the Concordes! If so, it will be certainly be a popular airshow attraction and a nice Vulcan replacement! The issue will likely be finding suppliers of parts.

Monday, 14 September 2015

Farewell XH558

On Sunday 13th September, the last flying Avro Vulcan made a final flypast of Coventry airport.

The Vulcan is a long range delta wing aircraft of 1950's vintage, built primarily as a nuclear bomber. It thankfully never saw action in this capacity of course, but it was used during the 1980's Falklands conflict.

The last flying example, XH558 (G-VLCN) has been kept flying for the last decade or so by the Vulcan to the Sky trust, which has relied on charitable support and private funding. 2015 is its last flying season, with suppliers of parts needed to maintain the aircraft withdrawing their support.

It was announced (although very badly advertised I must say!) that the Vulcan was due to do a small display at Coventry on Sunday 13th. On the day, the expected time of fly past was announced as 15:45, and we were over there like a shot!

Special parking had been made available (a field opposite the airport) and there were alot of people there - remarkable, since as far as I can tell, the only advertising done was in a local paper and on Facebook & twitter. We walked down to get a good view, ending up outside the Coventry flying club, where we got a surprise:

Apologies for not zooming but those 2 dots are a Meteor and Venom, operated by Classic Air Force and flying in formation (callsign: Vintage Formation!). With so many people turning up to see the Vulcan, I suppose Airbase thought it a good day to give some of the other jets a run!

On schedule, I heard 'Vulcan' on the scanner and we caught a glimpse of smokey-trailed triangle in the distance! A few minutes later...

I think most of us expected a fly by and nothing more, but we were treated to something like 5 or 6 fly pasts, it was a properly planned display:

A fantastic view of XH558 turning base leg for another low fly past along rwy23...

And, after one final flypast along rwy05, she climbed out on full power, up and away back to Doncaster, her home base. I can honestly say that standing below a Vulcan on full power, climbing out, is the best sound I have ever heard! And the loudest too!

I had the privilege of watching the same aircraft 5 years ago, from air-side:

So it was a bitter sweet experience really, sad to see the vintage jets (which are going up for sale) and the Vulcan airborne for the last time, but of course a pleasure to see them while we can! I have to conclude by saying how much of commercial opportunity operating these aircraft could be, and I can't help but think that if advertised and developed into a tourist attraction, Airbase and the Vulcan could have bright futures. Donations alone have kept them going this long, after all.

Thursday, 10 September 2015

3 Museums - 2 Coventrys and a Cosford

So I haven't posted in an age, largely because I haven't had very much to say! But over the last few weeks I've been to 3 local (ish) air musuems: Midland Air Museum, Classic Air Force Airbase, and RAF Cosford, so I thought I'd do a review of sorts.

Midland Air Museum (Coventry Airport) 

Although fairly small, this place packs in as much as it can with the space and is really worth a visit. It houses a variety of aircraft, from fighters to bombers to civilian aircraft. What I particularly like about this place, is that you can have a look inside a few of the aircraft, including a Vulcan. This sets it apart from other aviation museums I've been to as it makes a bit more interactive, clambering up ladders into cockpits!

Classic Air Force Airbase (Coventry Airport) 

This is a fantastic collection of old aircraft, a lot of which are not only airworthy, but still operating pleasure flights! I previously had a flight on their DeHavilland Dragon Rapide in 2012, here's a post about it. I've also been to airbase before, back in 2011, again here's a post. The museum is now free, everyone there is a volunteer, working to keep the aircraft airworthy or at least in good condition! Unfortunately though, the museum has moved out of the building it was in and is now in a cabin on the apron, and sadly it seem as though the museum may be shutting down (although this will be a slow process it will be around for while yet!). Round the corner from Airbase is restaurant, converted from a DC-6, which I visited here. Like I said at the end of that post, with the 2 museums (both nice set ups!), the diner and even pleasure flights, Coventry airport could be a real tourist and enthusiast attraction.

A nice scene from Airbase a few years back!
A nice bonus of Airbase is that you get a great view airside - here are a couple of BAe ATP's and in the background, a visiting Yak!
RAF Museum (RAF Cosford)

The RAF museum at Cosford is a huge site spanning 4 hangars, containing aircraft from WW1 through to modern fighters. Although you can't go inside any aircraft, it's great museum for people more interested in the historical side of aviation, with exhibits themed around the world wars and the cold war. They also have a few unique treats, such as a TSR2 prototype and the 1:1 scale Airfix model of a Spitfire made for James May's toy stories! Here's a few pics:

A Vulcan, suspended from the roof!

The Airfix Spitfire

A Comet in BOAC colours
So this another air museum absolutely worth visiting!