How to photograph shock waves ?

fyfd:

This week NASA released the first-ever image of shock waves interacting between two supersonic aircraft. It’s a stunning effort, requiring a cutting-edge version of a century-old photographic technique and perfect coordination between three airplanes – the two supersonic Air Force T-38s and the NASA B-200 King Air that captured the image. The T-38s are flying in formation, roughly 30 ft apart, and the interaction of their shock waves is distinctly visible. The otherwise straight lines curve sharply near their intersections. 

Fully capturing this kind of behavior in ground-based tests or in computer simulation is incredibly difficult, and engineers will no doubt be studying and comparing every one of these images with those smaller-scale counterparts. NASA developed this system as part of their ongoing project for commercial supersonic technologies. (Image credit: NASA Armstrong; submitted by multiple readers)

How do these images get captured?

It may not obvious as to how this image was generated because if you have heard about Schlieren imaging what you have in your head is a setup that looks something like:

image

But how does Schelerin photography scale up to capturing moving objects in the sky?

Heat Haze

When viewing objects through the exhaust gases emanating from the nozzle of aircrafts, one can observe the image to be distorted.

image

Hot air is less dense than cold air.

And this creates a gradient in the refractive index of the air

Light gets bent/distorted

image

Method-01 : BOSCO ( Background-Oriented Schlieren using Celestial Objects )

You make the aircraft whose shock-wave that you would like to analyze pass across the sun in the sky.

You place a hydrogen alpha filter on your ground based telescope and observe this:

image

                  Notice the ripples that pass through the sunspots

The different air density caused by the aircraft bends the specific wavelength of light from the sun. This allows us to see the density gradient like the case of our heat wave above.

We can now calculate how far each “speckle” on the sun moved, and that gives us the following Schlieren image.

Method-02: Airborne Background Oriented Schlieren Technique

In the previous technique how far each speckle of the sun moved was used for imaging. BUT you can also use any textured background pattern in general.

An aircraft with camera flies above the flight like so:

image

The patterned ground now plays the role of the sun. Some versions of textures that are commonly are:

image

The difficulty in this method is the Image processing that follows after the images have been taken. 

And one of the main reasons why the image that NASA has released is spectacular because NASA seems to have nailed the underlying processing involved.

Have a great day!

* More on Heat hazes

** More on BOSCO

*** Images from the following paper : Airborne Application of the Background Oriented Schlieren Technique to a Helicopter in Forward Flight

**** This post obviously oversimplifies the technique. A lot of research goes into the processing of these images. But the motive of the post was to give you an idea of the method used to capture the image, the underlying science goes much deeper than this post.

There are the Sketches of the four moons of Jupiter (Io, Europa, Ganymede and Callisto), as seen by Galileo
through his telescope.

image

                                                 Source

The drawing depicts observations from the time period January 7 to 24, 1610.

image

The above is the sequence of photographs taken by JunoCam aboard the Juno
spacecraft, in June 2016, of Jupiter and the motion of the four Galilean
moons, as the spacecraft approached the planet.

* There are 79 known moons of Jupiter.

** Jupiter has 4 rings.

Astronomy From 45,000 Feet

nasa:

What is the Stratospheric
Observatory for Infrared Astronomy, or SOFIA, up to?

image

SOFIA, the
Stratospheric Observatory for Infrared Astronomy, as our flying telescope is called, is a Boeing 747SP aircraft
that carries a 2.5-meter telescope to altitudes as high as 45,000 feet.
Researchers use SOFIA to study the solar system and beyond using infrared
light. This type of light does not reach the ground, but does reach the
altitudes where SOFIA flies.

image

 Recently, we used SOFIA to study water on Venus, hoping to
learn more about how
that planet lost its oceans
. Our researchers used a powerful instrument on
SOFIA, called a spectrograph,
to detect water in its normal form and “heavy water,” which has an extra
neutron. The heavy water takes longer to evaporate and builds up over time. By
measuring how much heavy water is on Venus’ surface now, our team will be able
to estimate how much water Venus had when the planet formed.

image

We are also using SOFIA to create a detailed map of the Whirlpool
Galaxy
by making multiple observations of the galaxy. This map will help us
understand how stars form from clouds in that galaxy. In particular, it will
help us to know if the spiral arms in the galaxy trigger clouds to collapse
into stars, or if the arms just show up where stars have already formed.

image

We can also use SOFIA to study methane on Mars. The Curiosity rover
has detected methane
on the surface of Mars. But the total amount of methane on Mars is unknown and
evidence so far indicates that its levels change significantly over time and
location. We are using SOFIA to search for evidence of this gas by mapping the Red
Planet with an instrument specially tuned to sniff out methane.

image

Next our team will use SOFIA to study Jupiter’s icy moon Europa, searching for evidence of possible water plumes detected by the Hubble Space Telescope. The plumes, illustrated in the artist’s concept above, were previously seen in images as extensions from the edge of the moon. Using SOFIA, we will search for water and determine if the plumes are eruptions of water from the surface. If the plumes are coming from the surface, they may be erupting through cracks in the ice that covers Europa’s oceans. Members of our SOFIA team recently discussed studying Europa on the NASA in Silicon Valley Podcast.

image

This is the view of Jupiter and its moons taken with SOFIA’s
visible
light guide camera that is used to position the telescope.  

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

In addition to conventional means of space observation like from space telescopes(like Hubble)

image

and telescopes on the ground (like the Keck Observatory)

image

SOFIA (or the flying telescope) is yet another tool that Astronomers use on a regular basis to study our universe.

image

Resource: 
Inside NASA’s SOFIA Airborne Astronomical Observatory
 

Saturn’s rotational axis is tilted, just like Earth. While Earth’s
axis is tilted at an angle of 23.4°, Saturn’s tilt is 26.7°, which is
pretty close. 

In these pictures [1-2] you can witness the
dramatic shadows on Saturn that are cast by its rings. And in [3-4] the
shadows that are cast by Saturn on its rings. Truly epic!


Image Credit: NASA/JPL-Caltech/Space Science Institute
     

        

JunoCam : Processing | Mission Juno | Mission Juno

image

                     A processed image of Jupiter from JunoCam

JunoCam
is a visible-light camera/telescope placed on the Juno Jupiter Orbiter.
But the cool part about this is that it was primarily put on board the
orbiter primarily for public science and outreach.

If you are
an amateur astronomer and also interested in image processing, you have
full access to all the raw images taken by the orbiter (check link).

Have fun!

JunoCam : Processing | Mission Juno
| Mission Juno

Well.. Now you know!

Image Source Gif Source

coolthingoftheday:

Saturn’s hexagon is a hexagonal cloud pattern that has persisted at the North Pole of Saturn since its discovery in 1981. At the time, Cassini was only able to take infrared photographs of the phenomenon until it passed into sunlight in 2009, at which point amateur photographers managed to be able to photograph it from Earth. 

The structure is roughly 20,000 miles (32,000 km) wide, which is larger than Earth; and thermal images show that it reaches roughly 60 miles (100 km) down into Saturn’s interior.

Read an explanation of how Saturn’s hexagon works here: [x]

Saturn’s fascinating geometry

From the images produced from Voyager and Cassini, scientists were able to develop models that commensurated with the data obtained. Here’s what they found :

image
  1. The Hexagon is associated with an eastward zonal jet moving at more than 200 mph.
    The cause of the Hexagon is believed to be a jet stream, similar to the
    ones that we experience on Earth. The path of the jet itself appears to
    follow the hexagon’s outline.
  2. The Hexagon rotates at roughly the same rate as Saturn’s overall rotation.
    While we observe individual storms and cloud patterns moving at
    different speeds within the Hexagon, the vertices of the Hexagon move at
    almost exactly the same rotational speed as that of Saturn itself.

How do we know this ?

We know this because we can experimentally reproduce the Saturn’s hexagon on earth in a laboratory. ( If you are interested in the technical details of the experiment – click here and here)

The setup is simple :

Researchers placed a 30-liter cylinder of water on a slowly spinning table. ( The water representing the Saturn’s atmosphere )

Inside this tank, they placed a small ring that spun more
rapidly than the cylinder. This created a miniature artificial “jet
stream” that the researchers tracked with a green dye.

The results of which follow below

image

                                                    Source

image

                                                    Source

These models however are still unable to dictate the exact phenomenon that is happening on Saturn, but surely they offer insight into the bizarre phenomenon that dwells in the celestial.

Bonus – Color Change

image

These images from the NASA’s Cassini spacecraft show the changing appearance of Saturn’s north polar region between 2012 and 2016.

The change is thought to be an effect of Saturn’s season ( Yes! Saturn has seasons ). Scientists are still probing into the causes for this change.

image

The universe is a beautiful place.

Have a great day!

Aerodynamic Flutter

The wings of aircraft swaying as if dancing to the music of the winds is a fascinating spectacle indeed. This phenomenon in the engineering vernacular is known as Aerodynamic Flutter.

Flutter is an unstable oscillation which can lead to destruction.
Flutter can occur on fixed surfaces, such as the wing or the stabilizer,
as well as on control surfaces such as the aileron or the elevator for
instance.

Wings are sort of like springs

Wings are very flexible. Well if the wings were rigid ( as you can guess ), it would snap at the slightest turbulent load; But since gusts are just a part and parcel of the flying experience, it is impertinent to address them.

If flutter does not occur:

The vertical vibrations of the wings are damped i.e the amplitude of the vibrations die out and as a result do not necessarily do much harm.

image

If flutter occurs :

However if flutter occurs, the periodic vibration of the gust has a frequency similar to the natural structural frequency of the wing, the vibrations are amplified.

The amplification of these vibrations eventually leads to its destruction.

image

                                          PC: Jkrieger

Prolonged oscillation and Fatigue

image

The number of oscillations and the amplitude with which you make the oscillation has a huge impact of the life of any object.

In fact there is something known as the Fatigue-curve that denotes the behavior.

image

Have a great day!

Sources and more:

Flutter at a glance – NASA

Airbus A380 Flutter test

The tale of the “Gallopin Gertie” – Tacoma Narrows ( detailed account )

**

Maybe @missaerospaceblog can dedicate a post on the impact of flutter on Rockets and spaceflight ?

The best things come in small packages (#2)

In part one of the series, we looked at how the ball plays a crucial role in the functioning of the ball point pen. In this post, we shall articulate how space pens work.

Space Pens

Unlike most ballpoint pens, the Fisher’s space pen* does not rely on gravity to get the ink flowing. Instead, the ingenuity lied in pressurizing the cartridge with nitrogen at 35 psi( 240 kpa )

image

                                                         PC: Vat19

This pressure pushes the ink towards the tungsten carbide ball at the pen’s tip.

How can it write in any orientation?

As the force of the pressurized gas doesn’t depend on the orientation of the pen (unlike gravity based ones ) the pen can write at any angle even upside down, in any fluid, adverse climatic conditions, and well, space!

image

Thixotropic Ink

The ink is a special type of semisolid thixotropic ink which liquefies
only when necessary, thus avoiding leaking and lasting longer.

It’s a lot like ketchup where you go to pour your ketchup and nothing happens, but suddenly you are left with a large quantity of ketchup on your plate. Only upon the application of the force does the ketchup liquefy and at all other times it remains as thick gel.

image

                                         Why is ketchup so hard to pour?                                      

Another advantage of using pressurized nitrogen is that it prevents air from mixing with the ink so it cannot evaporate or oxidize,

Did NASA actually invest millions on developing the pen?

image

NASA invested millions (sometimes stated as billions) into developing
a pen that would work in orbit. However, when the Russians went into
space they just took pencils.

It’s a famous story that is mostly false.

Although Soviet cosmonauts did use pencils in space for a time, so
did the Americans.  However, it quickly became clear that pencils were  a
very bad idea since they had a habit of breaking and sending tiny
eye-seeking fragments of pencil lead and wood bits into the air.

image

There
were also some concerns over these fragments potentially damaging
equipment, even perhaps causing a fire..

Hope you guys enjoyed this post. Have a great day!!

* Fischer was the guy who came up with the idea of a space pen and sold it to the government for $6.