- 2812 - TELESCOPES - around the world. In 2020 a white paper was published that points out the potential benefits of coordinating ground, orbital and in “situ” based observations of objects. It suggests a different path forward where all of the space science community can benefit from the type of coordinated output that can only come from a cohesive team on the same objective.
--------------- 2812 - TELESCOPES - around the world.
- The Hubble Space Telescope was launched April 24, 1990. This review is about the effort to surpass Hubble with multiple telescopes around the world working together. The James Webb telescope will see first light in 2021. First lets review Hubble’s accomplishments.
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- The Hubble telescope is 12 tons, 14 feet in diameter, 43 feet long, about the size of a large school bus, not counting its two 25 foot solar panels. It was carried into orbit by the Shuttle and released traveling 17,500 miles per hour, 375 miles above the Earth.
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- Construction was started in 1978 and by 1990 they had spent $2,000,000,000 on the project.
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- The original Hubble was to have a 3 meter primary mirror but NASA cutbacks reduced it to 2.4 meters saving $61,000,000 out of a projected cost of $273,000,000. Other cutbacks caused an error in the mirror construction.
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- The first images from Hubble had spherical aberrations making the images blurry. The primary mirror weighing 1,825 pounds ,and, was built with the wrong shape. Not by much, but, the accuracies demanded by the telescope could not tolerate the problem caused by the reflective null corrector that made measurements while being 1.3 millimeters out of position. As a result the mirror was too flat at its edges by 2 microns, 2 millionths of a meter, 1/50th the thickness of a piece of paper.
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- In December, 1993, the Endeavor Space Shuttle took a 7 astronaut repair crew up to fix the Hubble. The primary mirror needed corrective glasses to restore the optics for well focused images. The repair mission worked perfectly.
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- The Hubble telescope was designed to have resolving power of 1/30,000th the size of a full moon. The full moon has an angular size of 1,800 arc seconds and Hubble has to hold steady to within 0.012 arc seconds. With that the Hubble could resolve left and right headlights of a car in California with the telescope in New York.
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- Resolution power: 3000 miles between New York and California = 4,828,000 meters. 2 meters between headlights. Ratio is 2,400,000 million to one.
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- The Hubble is orbiting at 17,500 miles per hour but its tracking system could be the equivalent of training a laser on a dime on top of the Lincoln Monument in Washington D.C. from the laser mounting on top of the Empire State building in New York, and hold it there.
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----------------------- Tracking Ability: Dime = 1 centimeter = 0.01 meters.
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---------------------- DC to New York = 400 miles = 6.4*1065 meters.
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---------------------- Ratio is 64,000,000 to one.
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- Another analogy is the width of a human hair viewed at one mile.
--------------------- Human hair is .001 inches.
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--------------------- One mile is 63,400 inches.
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--------------------- Ratio is 63,400,000 to one.
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- Hubble’s tracking works using a sensor pointing on a guiding star to measure its position and correct Hubble’s pointing direction.
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- There have been 4 service missions to Hubble, Dec. 93, Feb. 97, Dec. 99, and Feb. 02. By 2002 all the instruments had been replaced and upgraded to the latest technologies.
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- Hubble uses 2800 watts of electricity each orbit. That is the same as 28, 100 watt light bulbs. The Solar panels generate the needed electricity but they only work while pointing at the Sun. 6 nickel-hydrogen batteries store the electricity, they are equivalent to 20 car batteries.
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- Hubble has many discoveries to its credit. It passes over us ever 97 minutes traveling at 5 miles per second. Each week it transmits 120,000,000,000 bytes of data, equivalent to a shelf of books 3,600 feet long, each week. Hubble was designed to be in service for 20 years. It is soon due a replacement. It will be a tough act to follow.
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- One way to outdo Hubble is to coordinate many telescopes on the same image and create a picture across the electromagnetic spectrum from infrared to X-rays. The reason why such coordination is important comes down to how imaging systems interact with different wavelengths of light. The electromagnetic spectrum is extremely large. It includes all types of light, such as radio, infrared, x-rays, ultraviolet and visible light.
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- There is no one single sensor that can collect data in all of those different wavelengths at the same time. Therefore, scientists have developed a plethora of instruments that are extremely good at collecting data in one specific spectrum, such as radio (ALMA), or mid-range infrared (James Webb Telescope).
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- The down side of this specialization is that those instruments are blind in other spectral ranges. If a scientific team is only observing in one type of light, there is a chance that they could miss important aspects of a phenomena they are studying that are only visible in a different spectral band.
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- Infrared telescopes are particularly useful as there is a lot of physical data points that can be obtained in a single measurement, such as pressure, temperature, and molecular abundances.
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- Another advantage that earth-based observatories have over their in situ counterparts is their ability to image a whole planet at once. Many orbiter or fly by missions are only capable of measuring part of their subject at a single point in time.
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- This results in a loss of contextual understanding, as dynamic phenomena that might be observed in a single place by the in situ spacecraft might not be present over the entire surface of the planet or moon. Support from earth-based telescopes, whether on the ground or in space, could provide that larger context that the spacecraft itself lacks.
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- This sort of coordination to cover all of the spectral bases has already been accomplished with one in situ planetary mission, the “Juno Spacecraft” currently in orbit around Jupiter. The resulting coordination between the Juno spacecraft and a series of earth-based observatories resulted in over 40 papers that used data from more than one observational source of the Jupiter system during that time.
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- The orbiters around Mars provide excellent two-dimensional slices of spectral data as they are passing over a specific strip of the planet. However, observatories closer to Earth can provide data on the entire hemisphere of the planet that is facing them, and add a layer of depth that would allow scientists to piece together a three-dimensional picture that would be impossible using only data from the orbiters.
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- There are still some limitations to earth-based observations, such as the fact that methane is present in Earth’s atmosphere as well, which could skew the data when looking at Mars. To get around this problem, scientists came up with an ingenious method of only observing Mars while it is moving away from (or toward) Earth at more than 13 kilometers a second. This differential speed red, or blue, shifts the spectral signature of the Martian methane enough that it can be differentiated from that simply present in Earth’s atmosphere.
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- Another particularly interesting target of joint observations is Titan, which has been the subject of intense scrutiny in recent years due to its hydrocarbon lakes, and its methane/ethane based hydrological cycle.
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- This moon is so interesting it is about to receive it’s own in situ visitor in the form of the “Dragonfly” mission. Dragonfly lands on Titan in 2034. Dragonfly will be equipped a mass spectrometer, which allows the detection of molecules which are impossible to see remotely, and reveals the full composition of the atmosphere. Earth-based observation could in turn provide context for these measurements.
Dragonfly's lander will be the first to reach Titan's surface, and can provide local data to any coordinated observation program.
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- Those combined observations will focus on the organic chemistry that is taking place on Titan. ALMA is a series of radio telescopes, which are particularly good at observing organic compounds and making detailed maps of its observational subjects. Both capabilities would be particularly helpful in helping the Dragonfly mission, and ALMA’s operators are already very familiar with Titan.
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- The array actually used Titan as a calibration target for a number of years after it first launched, due to its brightness and seeming stability. The wealth of observations allowed researchers to study Titan and the evolution of its atmosphere, revealing dynamic processes, and leading to improved understanding of the moon.
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- Unfortunately, this new data also revealed Titan is actively changing, making it less suitable as a flux calibration target. The ALMA team then switched to using a pulsar for future calibrations.
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- Unless the data on a given object was collected simultaneously by more than one observatory, the benefits of coordination are lost as transient phenomena would not be present in both those sets of data. There might be some simultaneous data of an object collected by more than one observational platform buried in their data archives.
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- Coordinating future observational efforts is much more likely to result in new discoveries rather than trawling through old data. Concerted observations may reveal phenomena that wouldn’t be visible without combining the datasets, revealing new and exciting glimpses into foreign worlds.
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- Coordinating as many of those future observational efforts as possible is the main intent.
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------------------------------------ Other reviews available.
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- 2798 - TELESCOPES - James Webb launch in 2021? - The James Webb Space Telescope will be a large infrared telescope with a 6.5-meter primary mirror. The telescope will be launched from French Guiana.
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- 2789 - TELESCOPES - to do a 3D map of the Universe. Since 2005, scientists have been scanning the night sky to create a three-dimensional map of our universe with the purpose of shedding light on one of the biggest mysteries in physics. The quest is to learn the true nature and identity of dark energy and dark matter.
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- September 2, 2020 772 2812
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