High on a mountain in the Atacama desert, Chile, the European Southern Observatory is building something immense.
It's called the Extremely Large Telescope, and here's a highlight reel of this beast's ultimate capabilities.
With a 39m main mirror it will be, by a long way, the biggest optical & infrared telescope in the world. It will transform study of planets around other stars, distant galaxies, the early universe, dark matter, black holes.
And it's an engineering miracle.
A telescope is limited, among other things, by the light it's main mirror can gather. The ELT will gather 100 million times more light than the human eye.
It will do this with an adaptive array of five mirrors, four of which can adaptively change shape.
M1:
The 39m primary mirror is made up of 798 interlocking hexagons which are all in active control: To adjust for thermal and wind variation each must be precisely positioned & shaped to within 10s of nanometres, 10,000 times thinner than human hair, across the entire radius!
Each M1 segment is supported at 27 locations, with warping harnesses. Each segment has 3 positioning actuators to control tip & tilt to within 2nm.
In total, M1 has 798 segments, 2500 actuators and 9000 edge sensors.
M2 & M3:
In any other telescope, the M2 & M3 mirrors would be huge even as primary mirrors.
After firing, the mirror blanks are cooled & annealed for 3 months for near perfect homogeneity to minimize internal stresses, then heat treated into glass ceramic for 6 months.
The 4.25 metre mirrors have a near zero coefficient of thermal expansion. They are ground, figured & polished to within nanometres accuracy, 20,000 times more precise than the width of a human hair: Figuring and polishing takes 2 years.
M4:
The world's largest deformable mirror: Designed to adjust for vision distortion produced by atmospheric turbulence or facility vibration, it is a thin shell sitting 90 microns away from a silicon carbide reference surface. 5000 actuators adjust it's shape up to 1,000 times/s
The M4 shell is measured to the nanometre range 70,000 times a second, and the primary input also includes 8 powerful lasers fired into the upper atmosphere, which are used as references to measure and correct for atmospheric turbulence hundreds of times a second.
Instruments:
The HARMONI 3D spectrograph.
MICADO high resolution near infrared camera.
METIS mid infrared spectrograph.
ANDES multi wavelength high resolution spectrograph.
MOSAIC multi object spectrograph.
The dome itself is built on a film of oil and shock absorbers on the foundations to guard it against seismic interference.
The ELT will be ready for first light around 2028, and is likely to quickly eclipse it's predecessor (the VLT) which is even now the most scientifically productive astromical telescope in the world.
European science & engineering has it's weaknesses, but also undoubted strengths. Projects like the ELT are absolutely one of them.
Follow the European Southern Observatory at @ESO
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Well a number of things, but one of the biggest is that the A330 on the left is mostly Aluminium, whereas the A350 on the right is mostly composite. This matters.
Find out why & how this happens...
In this thread we'll cover Carbon Fibre Reinforced Polymers (CFRP), what they are, what they're good for, how they're made and the increasing automation of CFRP assembly which has reduced costs and scaled-up applications for the aerospace world.
CFRP comprises a 'matrix' (thermoplastic/ epoxy etc) around a mesh of aligned high carbon 'reinforcer' fibers. This gives extremely good tensile strength in a single axis, and resistance to crack propagation perpendicular to the fibers.
As a little treat for us all, here's an appreciation thread for my favourite NASA X Planes.
From rocket powered spaceplanes through lifting bodies, darts, tailless aircraft, the world's fastest to the eerily quiet, here we go...
Starting at the start:
The Bell X1, built in 1945, was a high speed rocket plane that famously was the first to break the sound barrier in level flight in 1947, launched from a B29 and piloted by Chuck Yeager.
He nicknamed the plane Glamorous Glennis for his wife.
The Douglas X3 Stiletto.
Designed to test low aspect ratio wings and Titanium construction in sustained 2000mph flight, the underpowered X3 sadly didn't even manage Mach 1.
But it did validate the theory of intertia coupling...
Why is there a blended fan at the back of that aeroplane?
For fuel efficiency. Let's talk about the Propulsive Fuselage Concept, and wake energy loss...
Some 60%-70% of a commercial aircraft's total drag is viscous skin friction drag, from the creation of a boundary layer & resultant wake. This wake loses kinetic energy to the surrounding air.
Of this viscous drag, about half is from the fuselage, another half from the wings.
Most aircraft engines, for optimal propulsive efficiency, operate in the freestream, away from boundary layer wakes. Because their kinetic energy exchange must balance out aircraft drag, this creates an inverse wake and plenty of wasteful churn.
What is the link between this 90s beast from Russia, and an aerospace technology that is on the cusp of something revolutionary?
The NK93, counter-rotating turbofans, and the COBRA project. A thread.
Unique at the time, the core of the NK93 drove two huge counter-rotating fans through a 30,000hp planetary gearbox. The small core and huge fan stage gave a bypass ratio of 20, making it an 'Ultra High Bypass Ratio' engine.
But it was the contrarotating fans that were special.
The increasing bypass ratio of turbofans is driven by a truism: It's more efficient to accelerate a large volume of air slowly than a small volume quickly. So, bigger fans.
But UHBR fans are limited by geometry. Eventually they can't be any wider, and tip speed is a concern.
I've no catchy tagine for this thread: It's all about the basics. Here we go...
We'll explore wing sweep, tailplane position, dihedral, anhedral, high & low wing mounts, wing position and oddities like the flying wing and ground effect.
Static stability is the ability of an aircraft to return to. It's original orientation if disturbed. For us to talk about this we need to understand two concepts: Centre of lift and centre of mass.
Centre of mass/gravity (CoG) is obvious: It's the balancing point at rest.