[shiftpgdn]

Can someone smarter than me explain why astronmers can't stick something like this on the back of an existing geostationary platform (like what is used for the XM radio sattelites) and get amazing data out of them? Surely sticking something like this array 100km into space will yield better results without the overhead of a 20 year mission plan like James Webb or Hubble.

[ianburrell]

Cause it wouldn't give better results. The big advantage of putting telescope in space is that don't have to deal with the movement of the air distorting the image. That doesn't matter when taking pictures of diffuse objects.

The disadvantage is that it is in space, you have to spend 10x or 100x as much making something that can work in space, and you can't maintain it. I bet it would be much better to spend that money making dozens of these around the world, or iterating on the design.

The other advantage is that atmosphere is opaque for some wavelengths. The infrared wavelength that JWST looks in are absorbed. It also helps to be able to cool down the detectors to lower temps. One reason we aren't seeing direct replacement for Hubble is that the big ground telescopes with active optics are as good.

[gridspy]

The lenses are made of materials that will not resist the conditions in space (high temperature gradients, oxidizing environment, radiation).

Once in space they cannot tweak the array.

Launch weight and stresses would damage this array.

[lvspiff]

I've always wondered that myself - If the Russians could build and launch sputnik in 1957 and get it around the earth a few times why aren't we seeing a huge number of backyard dad+son duos building rockets to launch their own telescope array. Its amazing that its a 60 year old feat that is still only in the hands of governments and massive corps

[eichin]

The problem is the lack of a "backyard" ICBM program to piggyback off of... the R-7 that the sputnik launcher was based on "was designed with excess thrust since they were unsure how heavy the hydrogen bomb payload would be" (wikipedia.)

[FredPret]

1) You need more than just getting to space, you need to go really fast when you get there. So, lots of propellant and a big rocket is needed. So, it's really expensive.

2) Because you're setting fire to a big tube of propellant that then goes crazy fast, you need all sorts of permits and safety reviews to do it

3) Space is hard, so your rocket will almost certainly blow up / fail a couple of times.

All of this means: big budgets and state-level patience and persistence is needed

[Aspos]

But there are actually so so many startups and garage enthusiasts at various stages of readiness to put payloads into orbit

https://www.youtube.com/watch?v=SH3lR2GLgT0

[dylan604]

Rocket science ain't easy. Just because you can build a great telescope does not mean you can build a rocket. Also, I could only imagine the NIMBY revolt when you file your permit plans to build launchpad-38A in your backyard. I hope you don't spend too much time wondering before coming to obvious answers

[woopsn]

You might look up the sagas of Rocket Lab and other small launch providers if you're interested in what it takes to put ~200lb into LEO today. It's way beyond dad and son stuff, still incredibly hard, but not so much anymore that you need to be Boeing/Lockheed/SpaceX/etc if not a national agency. This is a recent achievement.

[KeplerBoy]

Just because it was possible for the soviets back then, doesn't mean it's trivial today.

Rocket fuel is also not exactly easy to come by.

[dekhn]

Projects like this have been done; see for example https://www.jpl.nasa.gov/missions/arcsecond-space-telescope-...

[sgt101]

I am no expert, but the things I would worry about:

- cost to get into geostationary orbit might dominate the value/saving of the cheap instrument, so it might be smart to spend more on that - managing and controlling it might be very challenging - need to get the data down from it - might create difficulties and costs that kill the value - heating and cooling in space might kill it - radiation in space might kill the hardware - acceleration during launch might kill the hardware - the payload needs to be stable during launch or there will be an accident - scientific value might be lower than other missions for similar spend

[VohuMana]

Not a professional so take this with a grain of salt but my guess would be weight first and foremost. From what I understand geostationary orbit isn’t cheap to get to and each added kilogram increases cost significantly. These lenses while not incredibly heavy are heavy enough to add a fair amount of cost.

[consp]

I also doubt these lenses will hold up in a very cold or very hot near-vacuum.

[perihelions]

I don't think there's that big of an advantage for space-based astronomy here, for visible-wavelength light with large pixel scales, and relatively bright (total luminosity) objects. Because it's done in narrowband filters, it's particularly good at erasing sky noise.

/not an astrophotographer

[mapt]

There are... nine main limitations on telescope imagery that I can think of. In no particular order:

First is weather. We can't see through clouds. Most new astronomy is about sources too faint to have been analyzed a hundred years ago, and even clouds that are barely visible to the human eye will drown those out.

Second is various engineering difficulties resulting from differential temperatures in the air in close proximity to the telescope dome, defects in the mirror surface, and limitations to the optical design (you're projecting a spherical globe onto a flat surface).

Third is 'atmospheric seeing' - high-order distortions caused by thermal patterns in the air which change significantly on a tens of milliseconds timescale, ultimately leading to a gaussian blur of the light in long exposures. The lower your altitude, and the more disturbed the airmass, and the more humid this is, the worse this is.

Fourth is sky glow - light pollution from nearby upwards facing lightbulbs, from the full moon, and from the sun at twilight & in the daytime

Fifth is the diffraction limit. A perfectly engineered, spherical-cow-world telescope with a perfect sensor has fundamental optical limits to the resolution it can observe, and optical resolution in arc seconds scales with wavelength / aperture.

Sixth is bright-source confusion and the limitations of your background field. It's very difficult with CCD & CMOS sensors (and even with spherical-cow sensors, the optics present limitations) to image a faint thing next to a bright thing. This is why we have fewer galaxies mapped on the other side of the Milky Way,, and why it can be very difficult to pick up, say, a nebula right next to a bright nearby star

Seventh is light-gathering ability, thermal noise, and readout noise. If you're trying to capture a photon every second, it's going to be very difficult if your CCD is absorbing thousands of photons per second thermally from the surrounding blackbody radiation and the readout circuitry.

Eighth is differential focus. To make matters more complicated, optical resolution is not 'fixed' because focus is not identical in different parts of the iamger; Typically telescopes are optimized for nominal focus at the center of their field, but get a few arc-minutes off of the center and optical resolution goes down. Get a few degrees off and it can go down to un-usability. There are characteristic abberations that crop up, and every optical design that aims for wide fields is a compromise between these abberations.

Ninth is atmospheric windows. Atmosphere absorbs hard UV. And portions of infrared. And portions of radio. To get a full spectrograph of a source, to detect the exotic portions of the EM spectrum that we don't really deal with frequently, you can't do it through atmosphere.

Generally speaking, it's relatively easy with on Earth for professional observatories to reach a point where atmospheric seeing limits your observations more than diffraction or readout noise or field distortions or sky glow or ambient light. It's not easy to defeat bright-source confusion with a larger and larger telescope. Many astronomers have had to content themselves with knowing little about the sky right next to bright sources like nearby stars. The telescope in the article tries to probe this known unknown with numerous small low-res cameras.

Space observatories provide us a small amount (10x?) better surveys because of no sky glow, daytime observations, no weather, etc. They eliminate atmospheric windows and simplify some engineering issues (while complicating others).

Part of the big remaining purpose of space observatories, the thing it's very difficult to do on the ground (we've tried!) is to defeat the atmospheric seeing limit and allow us to use very large telescopes which are relatively simply designed. Light-gathering ability from a source scales with aperture^2, and light-concentrating ability scales with aperture^2, so ideally sensitivity to sources should scale with aperture^4. It rarely does on the ground, because we have to put up with atmospheric seeing. The technologies we've used on the ground to fight atmospheric seeing are extremely limiting, expensive, complex, the subject of an inane number of PhD theses, and only suitable for very small fields.

This goal of survey astronomy is at cross purposes to the telescopes in the article, which aim to get diffuse low resolution impressions of the light near bright objects, defeating problem number 6; They can do this with relatively short exposures over hundreds of sensors, so that none of the electron wells in the sensors ever saturate from being full of too much light and spill over into their neighboring electron wells