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In Space SE I've asked Would it have been cheaper and faster to put a James Webb-like Space Telescope on a balloon instead of a rocket?

I linked there to a few news items:

Question: But here I'd like to ask about the ASTHROS instrument and how it compares in capability and range of instrumentation compared to the JWST. I know that they both have infrared capabilities and cryogenically cooled instrumentation, but I don't know how their instrumentation or spectral ranges compare. I'm pretty confident that ASTHROS will not have the same aperture as JWST, but I don't know how much smaller it will be

update: The JPL/NASA News article above intriguingly says:

A gondola beneath the balloon will carry the instrument and the lightweight telescope, which consists of an 8.4-foot (2.5-meter) dish antenna 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 to ever fly on a high-altitude balloon. During flight, scientists will be able to precisely control the direction that the telescope points and download the data in real-time using satellite links.

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I found this link that might seem interesting : https://www.nasa.gov/feature/jpl/nasa-mission-will-study-the-cosmos-with-a-stratospheric-balloon

The article in the link doesn't clearly specify the actual instruments or their functionality, but as this is an official article, I thought it might be useful.

The only info that NASA has officially released about ASTHROS is the cooling systems :

Because far-infrared instruments need to be kept very cold, many missions carry liquid helium to cool them. ASTHROS will instead rely on a cryocooler, which uses electricity (supplied by ASTHROS' solar panels) to keep the superconducting detectors close to minus 451.3 degrees Fahrenheit (minus 268.5 degrees Celsius) — a little above absolute zero, the coldest temperature matter can reach. The cryocooler weighs much less than the large liquid helium container that ASTHROS would need to keep its instrument cold for the entire mission. That means the payload is considerably lighter and the mission's lifetime is no longer limited by how much liquid helium is on board.

Here is a link about the JWST : https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

This link also does not specify the difference between JWST and ASTHROS, but it compares the JWST with the Hubble Space Telescope. Here are some comparions:-

The JWST has an expected mass about half of Hubble Space Telescope's, but its primary mirror, a 6.5 meter diameter gold-coated beryllium reflector will have a collecting area over six times as large, 25.4 square metres (273 sq ft), using 18 hexagon mirrors with 0.9 square metres (9.7 sq ft) obscuration for the secondary support struts.[22]

The JWST is oriented toward near-infrared astronomy, but can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument. The design emphasizes the near to mid-infrared for three main reasons: high-redshift objects have their visible emissions shifted into the infrared, cold objects such as debris disks and planets emit most strongly in the infrared, and this band is difficult to study from the ground or by existing space telescopes such as Hubble. Ground-based telescopes must look through the atmosphere, which is opaque in many infrared bands (see figure of atmospheric absorption). Even where the atmosphere is transparent, many of the target chemical compounds, such as water, carbon dioxide, and methane, also exist in the Earth's atmosphere, vastly complicating analysis. Existing space telescopes such as Hubble cannot study these bands since their mirrors are insufficiently cool (the Hubble mirror is maintained at about 15 °C or 288 K) thus the telescope itself radiates strongly in the infrared bands.

The article goes on to compare the JWST with other telescopes (mainly the cooling systems, aperture and wavelengths) so you can compare the currently being planned JWST telescope with other already launched ones like IRT, ISO and Spitzer.

The above WIKI article is amazingly detailed and may help.

The article linked above contains the wavelength range of ASTHROS as follows :

Managed by NASA's Jet Propulsion Laboratory, ASTHROS observes far-infrared light, or light with wavelengths much longer than what is visible to the human eye. To do that, ASTHROS will need to reach an altitude of about 130,000 feet (24.6 miles, or 40 kilometers) – roughly four times higher than commercial airliners fly. Though still well below the boundary of space (about 62 miles, or 100 kilometers, above Earth's surface), it will be high enough to observe light wavelengths blocked by Earth's atmosphere.

It also defines the targets for ASTHROS, listed as follows :

ASTHROS will make the first detailed 3D maps of the density, speed, and motion of gas in these regions to see how the newborn giants influence their placental material. By doing so, the team hopes to gain insight into how stellar feedback works and to provide new information to refine computer simulations of galaxy evolution.

It will also for the first time detect and map the presence of two specific types of nitrogen ions

A third target for ASTHROS will be the galaxy Messier 83. Observing signs of stellar feedback there will enable the ASTHROS team to gain deeper insight into its effect on different types of galaxies. "I think it's understood that stellar feedback is the main regulator of star formation throughout the universe's history," said JPL scientist Jorge Pineda, principal investigator of ASTHROS. "Computer simulations of galaxy evolution still can't quite replicate the reality that we see out in the cosmos. The nitrogen mapping that we'll do 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 throughout. These observations could potentially reveal places where the dust is clumping together to form planets. Learning more about protoplanetary disks could help astronomers understand how different types of planets form in young solar systems.

Wavelength Range of JWST explained as :

The JWST will observe in a lower frequency range, from long-wavelength visible light through mid-infrared (0.6 to 28.3 μm), which will allow it to observe high redshift objects that are too old and too distant for the Hubble to observe.[8][9] The telescope must be kept very cold in order to observe in the infrared without interference, so it will be deployed in space near the Earth–Sun L2 Lagrangian point, and a large sunshield made of silicon-coated and aluminium-coated Kapton will keep its mirror and instruments below 50 K (−220 °C; −370 °F).

Also, here are some targets of the JWST : https://www.nasa.gov/feature/goddard/2017/icy-moons-galaxy-clusters-and-distant-worlds-among-selected-targets-for-james-webb-space

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  • $\begingroup$ Thank you for your answer! It turns out that your first link and my third link are the same articles but placed on different NASA web sites. Searching scholar.google.com found this which may be of some help. This is the principle investigator (PI) for ASTHROS. $\endgroup$
    – uhoh
    Sep 13 '20 at 5:13
  • $\begingroup$ You might at least add a comparison of the wavelength ranges of JWST and ASTHROS to your answer if possible. $\endgroup$
    – uhoh
    Sep 13 '20 at 5:16
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    $\begingroup$ This is just verbatim reproduction of material in a link given in the question. $\endgroup$
    – ProfRob
    Sep 13 '20 at 8:11
  • $\begingroup$ @RobJeffries, I intended originally only to provide the links and the cautions, but instead of opening the link, I have added convenience by simply posting the important parts in the answer itself. The links are provided only as an external reference. But if you feel that I should only have presented the things I knew, then please know that I already knew all that is in the links, I only wanted to make things easier by sharing the links and saving people the trouble of having to look up and verify all I said in the answer. $\endgroup$ Sep 13 '20 at 8:54
  • $\begingroup$ I'm just commenting that I don't think it adds much information to what was implicitly available in the question. And at least some of the information is incorrect (e.g. the wavelength range of HST). $\endgroup$
    – ProfRob
    Sep 13 '20 at 9:47

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