This illustration shows a high-altitude balloon rising to the upper atmosphere. When fully inflated, these balloons are 400 feet (150 meters) wide, or approximately the size of a soccer stadium, and reach an altitude of 130,000 feet (24.6 miles or 40 kilometers). Credit: NASA Goddard Space Flight Center Concept Image Laboratory / Michael Lentz
Transported by a balloon the size of a football stadium, ASTHROS will use a state-of-the-art telescope to observe wavelengths of light that are not visible from the ground.
Work has begun on an ambitious new mission that will bring an advanced 8.4-foot (2.5-meter) telescope to the stratosphere in a balloon. Tentatively planned to launch in December 2023 from Antarctica, ASTHROS (short for Astrophysics Stratospheric Telescope for high-resolution spectral observations at sub-millimeter wavelengths) will drift about three weeks in air currents over the icy southern continent and It will accomplish several firsts along the way.
Managed by POTIn the Jet Propulsion Laboratory, ASTHROS observes far infrared light or light with much longer wavelengths than is visible to the human eye. To do that, ASTHROS will need to reach an altitude of approximately 130,000 feet (24.6 miles or 40 kilometers), approximately four times higher than the commercial aircraft they fly. Although it is still well below the limit of space (approximately 62 miles, or 100 kilometers, above Earth’s surface), it will be high enough to observe wavelengths of light blocked by Earth’s atmosphere.
The mission team recently put the finishing touches on the observatory’s payload design, which includes its telescope (which captures light), its scientific instrument, and subsystems such as cooling and electronic systems. In early August, engineers at JPL integration and testing of those subsystems will begin to verify that they function as expected.
While balloons may seem like outdated technology, they offer NASA’s unique advantages over space or ground missions. NASA’s Balloon Science Program has been operating for 30 years at the Wallops Flight Facility in Virginia. It launches 10 to 15 missions a year from locations around the world in support of experiments in all of NASA’s scientific disciplines, as well as for technological development and educational purposes. Globe missions not only have lower costs compared to space missions, but also have shorter times between early planning and deployment, which means they can accept the higher risks associated with using new technologies or avant-garde not but flown in space. These risks can come in the form of unknown technical or operational challenges that can affect the scientific output of a mission. By overcoming these challenges, balloon missions can set the stage for future missions to reap the benefits of these new technologies.
“Balloon missions like ASTHROS are more risky than space missions, but they produce high rewards at a modest cost,” said JPL engineer José Siles, project manager for ASTHROS. “With ASTHROS, our goal is to make astrophysical observations that have never been attempted before. The mission will pave the way for future space missions by testing new technologies and providing training for the next generation of engineers and scientists. “
Infrared eyes in the sky
ASTHROS will carry an instrument to measure the movement and velocity of the gas around the newly formed stars. During the flight, the mission will study four main targets, including two star-forming regions in the Milky Way galaxy. It will also detect and map for the first time the presence of two specific types of nitrogen ions (atoms that have lost some electrons). These nitrogen ions can reveal places where massive star winds and supernova explosions have reshaped gas clouds within these star-forming regions.
In a process known as stellar feedback, such violent outbursts can, over millions of years, disperse surrounding material and prevent or stop stars from forming. But stellar feedback can also cause material to clump together, speeding up star formation. Without this process, all the gas and dust available in galaxies like ours would have fused into stars long ago.
ASTHROS will make the first detailed 3D maps of gas density, velocity, and movement in these regions to see how newborn giants influence their placental material. In doing so, the team hopes to gain insight into how stellar feedback works and provide new information to refine computer simulations of the evolution of galaxies.
The Carina Nebula, a star-forming region in the Milky Way galaxy, is among the four scientific targets that scientists plan to observe with the ASTHROS high-altitude balloon mission. ASTHROS will study stellar feedback in this region, the process by which stars influence the formation of more stars in their environment. Image credit: NASA, ESA, N. Smith (University of California, Berkeley) et al., The Hubble Heritage Team (STScI / AURA)
A third target for ASTHROS will be the Messier 83 galaxy. Observing signs of stellar feedback will allow the ASTHROS team to gain a deeper insight into its effect on different types of galaxies. “I think stellar feedback is understood to be the main regulator of star formation throughout the history of the universe,” said JPL scientist Jorge Pineda, ASTHROS principal investigator. “Computer simulations of the evolution of galaxies still cannot replicate the reality we see in the cosmos. The nitrogen mapping we’ll be doing with ASTHROS has never been done before, and it will be exciting to see how that information helps make those models more accurate. “
Finally, as its fourth target, ASTHROS will observe TW Hydrae, a young star surrounded by a wide disk of dust and gas where planets may be forming. With its unique capabilities, ASTHROS will measure the total mass of this protoplanetary disk and show how this mass is distributed everywhere. These observations could reveal places where dust is gathering to form planets. Learning more about protoplanetary disks could help astronomers understand how different types of planets form in young solar systems.
A high focus
To do all of this, ASTHROS will need a large balloon – when fully inflated with helium, it will be approximately 400 feet (150 meters) wide, or approximately the size of a soccer stadium. A gondola under the balloon will carry the instrument and the lightweight telescope, which consists of an 8.4-foot (2.5-meter) satellite dish, as well as a series of mirrors, lenses, and detectors designed and optimized to capture far infrared light. Thanks to the dish, ASTHROS tied for the largest telescope that has ever flown in a balloon at high altitude. During the flight, scientists will be able to precisely control the direction the telescope is pointing and download the data in real time using satellite links.
This time-lapse video shows the launch of the Terahertz II Stratospheric Observatory (STO-2), a NASA astrophysics mission, from Antarctica in 2016. Such high-altitude balloon missions provide an opportunity to observe wavelengths of light that are blocked by Earth’s atmosphere. Credit: NASA / JPL-Caltech
Because far-infrared instruments must be kept very cold, many missions carry liquid helium to cool them down. ASTHROS will instead rely on a cryogenic cooler, which uses electricity (supplied by ASTHROS solar panels) to keep superconducting detectors close to minus 451.3 degrees. Fahrenheit (minus 268.5 degrees Celsius) – a little higher Absolute zero, the coldest temperature that matter can reach. The cryocooler weighs much less than the large container of liquid helium that ASTHROS would need to keep its instrument cool throughout the mission. That means the payload is considerably lighter, and the life of the mission is no longer limited by the amount of liquid helium on board.
The team expects the balloon to complete two or three laps around the South Pole in approximately 21 to 28 days, carried by prevailing stratospheric winds. Once the scientific mission is complete, operators will send flight termination commands that separate the gondola, which is connected to a parachute, from the balloon. The parachute returns the gondola to the ground so that the telescope can recover and recondition to fly again.
“We will launch ASTHROS at the edge of space from the most remote and hard part of our planet,” said Siles. “If you stop to think about it, it’s really challenging, which makes it so exciting at the same time.”
A division of Caltech in Pasadena, JPL manages the ASTHROS mission for the Astrophysics Division of NASA’s Scientific Mission Directorate. JPL is also building the mission payload. The Johns Hopkins Applied Physics Laboratory in Maryland is developing the gondola and signaling systems. The 2.5 meter antenna unit is being built by Media Lario Srl in Lecco, Italy. The payload cryocooler was developed by Lockheed Martin under NASA’s Advanced Cryocooler Technology Development Program. NASA’s Scientific Balloon program and its Columbia Science Balloon facility will facilitate the balloon and launch services. ASTHROS is scheduled to launch from McMurdo Station in Antarctica, which is administered by the National Science Foundation through the United States Antarctic Program. Other key partners include Arizona State University and the University of Miami.
