A stratospheric balloon will lift NASA telescope over Antarctica

The telescope will study star dust from the stratosphere.
Ameya Paleja
The assembled primary mirror of ASTHROS Media Laro

As part of its Scientific Balloon Program, NASA launches 10-15 balloon missions into the Earth's atmosphere every year. For an upcoming mission, NASA is using a balloon that is the size of a football field, and its telescope has giant mirrors plated with nickel and gold, the space agency said in a press release

NASA's space telescopes might be grabbing all the headlines, but the space agency also relies on humble balloons to demonstrate new technology as well as carry out research about the Earth's atmosphere, study the Sun, or even the universe at large. A balloon based mission may not look swanky but typically costs less and moves faster from planning to deployment. 

If this has given you the impression that these missions are any less complex to put together, then you need to read further to know about Astrophysics Stratospheric Telescope for High Spectral Resolution Observations at Submillimeter-wavelengths or ASTHROS that is scheduled to be deployed in December 2023. 

What will the ASTHROS mission do? 

When launched, ASTHROS will rise to an altitude of 130,000 feet (40,000 m) above Antarctica to observe wavelengths in the far-infrared region blocked by the Earth's atmosphere. 

By looking at these wavelengths, scientists will attempt to understand how clouds of gas and dust which are dispersed in galaxies can also stop the formation of a star. The mission will look at distant galaxies containing millions of stars to understand how stardust and gas interact with other processes such as eruptions from living stars or deaths of massive stars. During the four-week mission, ASTHROS will create high-resolution 3D maps of the distribution and motion of the gas in our galaxy, the press release said. 

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A giant mirror critical to the mission

An 8.2 feet (2.5 m) wide mirror will help improve the ability of the mission telescope to observe fainter light sources and resolve the finer details. Since the telescope will proceed to its target destination on a balloon, the mirror needs to be as lightweight as possible. However, even at that altitude, the Earth's gravity continues to impact objects and could easily deform the mirror. Even a minuscule change to the parabolic shape, greater than 0.0001 inches (2.5 micrometers), could jeopardize the mission.

NASA contracted the difficult task of manufacturing the mirror to an Italian optics company, Media Laro, which has contributed to the building of the Atacama Large Millimeter Array, which has multiple discoveries to its credit.  

The primary mirror construction was recently completed by putting together nine panels. Using lightweight aluminum in a honeycomb structure has helped reduce the mass of the mirror. The surface panels are made from nickel and coated with gold since the latter increases the reflectivity at far-infrared wavelengths. 

Unlike space telescope missions, where mirror alignments can be remotely controlled, the mirror of the ASTHROS needs to remain secured in mission position from the moment the balloon lifts off, and carbon fiber is being used to achieve this. 

“I think this is probably the most complex telescope ever built for a high-altitude balloon mission,” said Jose Siles, the ASTHROS project manager at JPL in the press release. “We had specifications similar to a space telescope but on a tighter budget, schedule, and mass. We had to combine techniques from ground-based telescopes that observe in similar wavelengths with advanced manufacturing techniques used for professional racing sailboats."

With the primary mirror completed, Media Laro will deliver the telescope later in July, following which the ASTHROS team will put it together with other key components and the giant balloon, paving the way for flight testing. 

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