The thread for space cadets!

[Thorgalaeg]

ESA Vega rocket carrying important Spanish satellite (and another French one) lost in space. Electrical failure at fourth stage suspected.

https://spacenews.com/human-error-blamed-for-vega-launch-failure/

 

[Samson]

The 737 Max is back!

https://www.cnn.com/2020/11/18/business/boeing-737-max-approval/index.html

Took about 20 months.


I'm sure the FAA wouldn't have certified it again if it was still a death trap.

The reports I have read have said nothing about what they have actually changed. I wonder if that is because it would be too hard for the readers, too hard for the journo's or if it is secret info and we just have to believe them.

 

[Samson]

A broken cable has damaged the huge main dish at the iconic Arecibo Observatory in Puerto Rico. It’s not clear why the cable broke in the middle of Monday night, said a statement from the University of Central Florida, which manages the observatory. Arecibo has been weathering hurricanes and other challenges since 1963, and staff will focus on “restoring the facility to full operations as soon as possible,” says observatory director Francisco Cordova.

Gutted:

Legendary Arecibo telescope will close forever — scientists are reeling
One of astronomy’s most renowned telescopes — the 305-metre-wide radio telescope at Arecibo, Puerto Rico — is permanently closing. Engineers cannot find a safe way to repair it after two cables supporting the structure suddenly and catastrophically broke, one in August and one in early November.​

A high-resolution satellite image of the Arecibo dish shows gashes in the main dish through which green vegetation below is peeping through.Credit: Planet Labs, Inc.

 

[r16]

the 737 declaration is a corollary of Trump losing the elections .

 

[red_elk]

Gutted:

Legendary Arecibo telescope will close forever — scientists are reeling
One of astronomy’s most renowned telescopes — the 305-metre-wide radio telescope at Arecibo, Puerto Rico — is permanently closing. Engineers cannot find a safe way to repair it after two cables supporting the structure suddenly and catastrophically broke, one in August and one in early November.​

A high-resolution satellite image of the Arecibo dish shows gashes in the main dish through which green vegetation below is peeping through.Credit: Planet Labs, Inc.

That's sad.
The pictures remind of the Aperture Science lab

Spoiler :

 

[hobbsyoyo]

I thought that was not an absolute ban the US tried to foist on some of their allies.
IIRC, some German engineers and (potential) astronauts were learning Mandarin in order to be able to
continue several projects that the US were deliberately not involving themselves in.
EDIT: Found the link...
https://www.bbc.com/future/article/20180626-why-europes-astronauts-are-learning-chinese

Has something changed since 2018 that would have caused that German-Chinese co-operation to collapse?

There is nothing stopping any other country from having bilateral missions with the Chinese so long as they don't buy any American components to use in the resulting project. This is actually a very high bar to clear as the US is one of the biggest aerospace component supply sources for the worldwide industry and is very quick to sanction those that violate its anti-Chinese rule. But if Germany and China work on a project that they can prove has 0 ties (right down to the individual part level) back to the US, they can have at it.

These rules are very tough, and there is also a formal prohibition for NASA to have any meaningful collaboration with the Chinese. The most they can do is have very high level discussions with the Chinese, or to make requests of them to do or not do certain things which the Chinese are free to ignore.

ESA Vega rocket carrying important Spanish satellite (and another French one) lost in space. Electrical failure at fourth stage suspected.

https://spacenews.com/human-error-blamed-for-vega-launch-failure/

This is super bad for Arianespace, the rocket manufacturer. This makes for 2 failures out of the last 3 flights for a vehicle which had a perfect record prior to this rash of failures.

They do think they have traced the issue back to two cables which swapped places when they were plugged into the fourth stage so the fix should be straightforward. Still, it's an incredible embarrassment.

The reports I have read have said nothing about what they have actually changed. I wonder if that is because it would be too hard for the readers, too hard for the journo's or if it is secret info and we just have to believe them.

All of the changes were made in the software and they also installed an extra sensor.

That's sad.
The pictures remind of the Aperture Science lab

Spoiler :

It makes me feel like the US in a national decline that we first removed funding for this telescope such that it deteriorated so rapidly (funding was cut only 2 years ago I think) and we have no plans to replace it.

 

[r16]

yeah , Matt Damon is so dead when nobody talks to the Chinese !

 

[uppi]

It makes me feel like the US in a national decline that we first removed funding for this telescope such that it deteriorated so rapidly (funding was cut only 2 years ago I think) and we have no plans to replace it.

There certainly is symbolism here, but these days the Arecibo telescope falls into the category "awesome, but impractical". It does not really make sense to continue with this design.

 

[red_elk]

It makes me feel like the US in a national decline that we first removed funding for this telescope such that it deteriorated so rapidly (funding was cut only 2 years ago I think) and we have no plans to replace it.

Decline is not a catastrophe though. I remember lots of hi-tech projects in USSR stayed rotting in the 90-s.
One of crazy expensive hangars built for Buran in Kazakhstan just collapsed under its own weight.

 

[Cutlass]

Decline is not a catastrophe though. I remember lots of hi-tech projects in USSR stayed rotting in the 90-s.
One of crazy expensive hangars built for Buran in Kazakhstan just collapsed under its own weight.

The difference though is that the Soviet government, and nation, came apart. And the successor states simply did not have the resources to continue a lot of programs. The Soviet space program accomplished a number of very impressive things. But paid a steep price for doing so. The Russian space program accomplished less, but did so despite far more limited resources.

Us Americans, we just largely can no longer be bothered to care to get it done. It is entirely a self-inflicted failure.

 

[hobbsyoyo]

Decline is not a catastrophe though. I remember lots of hi-tech projects in USSR stayed rotting in the 90-s.
One of crazy expensive hangars built for Buran in Kazakhstan just collapsed under its own weight.

I remember that and it was very sad.

Speaking of rotting projects from the 90's -

The Cosmonauts on the ISS just completed a spacewalk to prepare to jettison one of the old Russian docking modules. It will be replaced next year by a new Russian science module that was originally built in the 80s/90s and has recently be fully refurbished and prepared for flight! Very exciting.

Also, the ISS has its first 7 person crew in a very long time now that SpaceX's Crew Dragon is fully operational. This crew also includes the first black astronaut to stay on the station long-duration (there have been previous black astronauts at the station but for only short trips).

 

[hobbsyoyo]

There certainly is symbolism here, but these days the Arecibo telescope falls into the category "awesome, but impractical". It does not really make sense to continue with this design.

Cool, then we should build a newer, better dish. AFAIK, Arecibo still had some radar capabilities that are unmatched outside of China. Unfortunately, we can't even agree to spend more money to help the 10% of Americans that are going hungry at the moment, so there will be no American Arecibo replacement for the foreseeable future - maybe never.

 

[hobbsyoyo]

SpaceX launched out of Vandenberg, California yesterday. It was the first orbital launch out of that facility in about a year and a half. Earlier this year, SpaceX began launching to polar inclinations out of Florida using a trajectory that overflies Cuba. The last time that happened (in the 1960's or so), the rocket actually crashed on Cuba, and they picked up the pieces and gave them to the USSR or China or something. That led to a ban on flying polar trajectories out of Florida until today, and only SpaceX is allowed to do them now because the first stage lands on a barge or back at the coast rather than actually flying over Cuba. (The second stage is so high by the time it overflies that even if it came down, it would disintegrate before landfall)

Vandy has stayed busy with ICBM test launches, but some people were worried about the future of the facility and are glad to see SpaceX using it again.

Firefly will launch their very first rocket out of Vandy in the coming weeks (it's already in the hangar there) and ULA will have a launch sometime soon as well.
Here's a cool picture that I can't figure out how to embed because of Twitter: https://twitter.com/Firefly_Space/status/1328369575046619136/photo/1



Rocket Lab was able to have a soft-landing of their first stage in the water after their recent launch. Next they will try and catch it mid-air by snagging its parachutes with a helicopter.

 

[Samson]

Is dark energy really the aether?

Cosmologists say that they have uncovered hints of an intriguing twisting in the way that ancient light moves across the Universe, which could offer clues about the nature of dark energy — the mysterious force that seems to be pushing the cosmos to expand ever-faster.
They suggest that the twisting of light, which they identified in data on the cosmic microwave background (CMB) collected by the Planck space telescope, and the acceleration of the Universe could be produced by a cosmic ‘quintessence’, an exotic substance that pervades the cosmos. Such a discovery would require a major revision of current theories, and physicists warn that the evidence is tentative — it does not meet the ‘5 sigma’ threshold used to determine whether a signal is a discovery. But it underscores the fact that modern cosmology still has an incomplete picture of the Universe’s contents.
If dark energy is a quintessence, its push on the expansion could slowly wither or disappear, or could even reverse to become an attractive force, causing the Universe to collapse into a ‘big crunch’, says Sean Carroll, a theoretical physicist at the California Institute of Technology in Pasadena. “We’re back to a situation where we have zero idea about how the Universe is going to end.” The work was reported on 23 November in Physical Review Letters.
The first direct evidence that an unknown force was pushing cosmic expansion to accelerate emerged in 1998, from two separate surveys of supernovae. A host of other studies have since confirmed the presence of this force, dubbed dark energy, but have provided precious little information about its nature.
Researchers’ first guess — which remains the leading theory — was that dark energy is an intrinsic property of space, which would mean that the amount of dark energy per unit volume of space is fixed as a ‘cosmological constant’. But some cosmologists theorized that dark energy is made of something else entirely. They call this a quintessence field, after the fifth element, or aether — the name that ancient Greek philosophers gave to an invisible material thought to fill all the empty space in the Universe.
​

I do not understand this at all, in fact I have never understood what polarization of light really means in a physical sense. I find it a little interesting how the world of science is coming round full circle back to aether.

 

[hobbsyoyo]

Light rays can be oriented any which way as they travel through space. Polarization is a fancy way of saying that they have all been made to line up such that they are all aligned with each other. This diagram shows how light rays are oriented in all directions until they pass through a filter which blocks all the rays that are not aligned with the filter, thus polarizing the light.

(ignore polarizer 2)

 

[Samson]

Light rays can be oriented any which way as they travel through space. Polarization is a fancy way of saying that they have all been made to line up such that they are all aligned with each other. This diagram shows how light rays are oriented in all directions until they pass through a filter which blocks all the rays that are not aligned with the filter, thus polarizing the light.

(ignore polarizer 2)

Does this actually mean that 1 photon of light can be meaningfully said to take up say 700 nm in the vertical dimension but only 100 nm in the perpendicular dimension? Does this also apply if we are modelling photons as particles rather than waves, in the the particles are actually shaped something like rugby balls?

And then comes the question what does that distance represent? If these were water waves, it would be the magnitude, but electromagnetic waves at a particular wavelength do not vary in magnitude, so what is this measure that varies in a particular dimension actually mean?

 

[hobbsyoyo]

Because light is both a particle and a wave, I have 0 idea how to interpret how much space a ray of light takes up. Paging @uppi

Sorry!

 

[uppi]

A "ray of light" isn't really something that has a meaningful definition, so I am going to focus on photons instead.

For those there is some sort of definition what a photon is, but it is still surprisingly complex to get it right and sometimes a matter of hot debate. Most of the time, it is not helpful to think of a photon as a particle. Instead you should think of a photon as the minimum (observable) amount of energy you can take out of a light field. So any time you measure a light field, you will always observe an integer number of photons.

You can easily estimate how small a photon can be: The wavelength sets a limit on how small a spot you can focus a light beam and a photon needs to be at least near one cycle of its frequency in length, so you will not be able to have a photon much smaller than the wavelength cubed (an exact number will depend on how exactly you make your definitions).

How large a photon can be is a much harder question: If you have a very stable photon source, you can distribute a photon over a very large area. For example, if your photon source is stable to 100 kHz, you can make photons with a duration of more than 1µs, which will have a length of more than 300m in space (and the lateral extent will depend on how big you make your beam). So there will be the energy of one photon distributed over all that space. And if you improve your system, there is no theoretical limit on how big you can make it. Practically, there will be limitations of course, like the stability of your system, the background noise of your system, and ultimately, the number of background photons because of the finite temperature of your system.

And you can have a vastly different extent in the three dimensions as well. For example, if oyu put a narrowband photon into an optical fiber, it will be confined to 10µm in the transverse directions, but could be hundreds of meters along the fiber. (As a side note: you can debate whether a photon in an optical fiber is still a photon, though).

Polarisation is nothing else than the direction of the electric (and magnetic field). If you have a dipole radio antenna, it will emit an electric field which has a certain direction. And if you turn the antenna by 90 degrees, the direction will change by 90 degrees as well. With light it is exactly the same, just on a much smaller scale.

 

[Samson]

you should think of a photon as the minimum (observable) amount of energy you can take out of a light field. So any time you measure a light field, you will always observe an integer number of photons.
...
Polarisation is nothing else than the direction of the electric (and magnetic field). If you have a dipole radio antenna, it will emit an electric field which has a certain direction. And if you turn the antenna by 90 degrees, the direction will change by 90 degrees as well. With light it is exactly the same, just on a much smaller scale.

So when they say:

They suggest that the twisting of light, which they identified in data on the cosmic microwave background (CMB) collected by the Planck space telescope

Or more formally:

evidence of parity-violating physics in the Planck 2018 polarization data and report on a new measurement of the cosmic birefringence angle β
...
observed cross-correlation of the E- and B-mode polarization of the cosmic microwave background and the Galactic foreground emission

They mean the orientation of the light field in which the photons of the CMB are detected? I am still not sure I understand, but I feel a bit closer somehow, thanks.

[EDIT]No, I really do not understand it. "polarization is a tensor or spin-2 object"? "spin tensor is a quantity used to describe the rotational motion of particles in spacetime"

 

[uppi]

So when they say:

Or more formally:

They mean the orientation of the light field in which the photons of the CMB are detected? I am still not sure I understand, but I feel a bit closer somehow, thanks.

[EDIT]No, I really do not understand it. "polarization is a tensor or spin-2 object"? "spin tensor is a quantity used to describe the rotational motion of particles in spacetime"

If you have an electromagnetic wave, it will have a direction and an amplitude for the electric and the magnetic field at every point in space. And this varies with time as well. If you would want to measure this exactly, you would need a huge amount of data. Fortunately, the directions and amplitudes are correlated to each other, because of physics - they need to follow Maxwell's equations. So the field at one point cannot be very different from the field at another, very close point. As it turns out, you can then reduce the direction of the field to just a handful of parameters which you need to measure.

But you need to have a mathematical model to describe how these parameters relate to each others and what happens if you rotate everything by a certain amount. There are only so many ways things can behave under rotation, so there are existing models to describe this, so you don't have to do all the mathematical legwork yourself.

But don't let the fancy names distract you from the simple physics that it is about the direction of the electromagnetic field. If the vacuum would be isotropic, it should not rotate. So a rotation of the polarization would mean that there is an anisotropy somewhere, which would be very interesting. But no reason to revive the aether just yet.