"The SPHEREx mission <snip> will map the entire sky four times over two years, offering scientists a chance to study how galaxies form and evolve, and providing a window into how the universe came to be."
So each object will be scanned ~6 months from the previous scan. How much evolving within the universe will be noticeable within that 2 year run? My gut response is not much, but that's why we do the science to see the changes.
"designed to map the celestial sky in 102 infrared colors "
So I'm guessing the coolant used to make IR scanning possible will be the limiting factor on operational time span. This article didn't say where this satellite will be parked either, but wikipedia[0] shows it to be a geosync orbit. Would have been interesting to be able to design a replaceable coolant module to extend the observations to really make seeing the evolution possible. Obviously complexity adds to cost and design time, so of course they didn't. Just dreaming
As an example, the study of the stars orbiting around SagA* are very revealing, but have required > 10 years of observations.
- It is passively cooled rather than using an expendable coolant- "SPHEREx relies on an entirely passive cooling system — no electricity or coolants are used, simplifying the spacecraft’s design and operational needs."
- It is a Medium-Class Explorers (MIDEX) mission - Investigations characterized by definition, development, mission operations, and data analysis costs not to exceed $180 to $200 million total cost to NASA.
I think the cost of ground support eats into the budget length. The original estimate for project was $241M, so it was a large MIDEX
- It is in a Polar orbit around Earth at the day-night (terminator) line
Possibly stupid question: how does this polar orbit stay over the terminator? And how is the terminator defined for a polar orbit here, since both the north and south poles are on the terminator only at the equinoxes?
ah, I misread the Orbital Parameters on the wiki. that day-night orbit is also a LEO which makes it even more possible to do a manned mission for upgrades. Oh, wait, we no longer have a shuttle for those types of missions.
A nearby (excellent) comment (https://news.ycombinator.com/item?id=43338459) gives further context, but: the 6-month revisit period is just an artifact of the Earth-orbit-based sky scanning strategy. In 6 months the satellite, precessing at 1 degree/day, and facing away from the sun during data collection, will scan the sky completely. (See Fig 1 of the paper [0]).
So in particular, the 6-month period is not to revisit these distant galaxies more than once to observe spectral changes. The strategy, indeed, is to “stack” the multiple exposures to beat down noise. (Fig.6 of [0], top left).
It is possible that they have designed the system so that it could produce “just good enough” results in 6 months, with one complete scan. This is called a “threshold mission” and it would only be described in the full proposal.
I looked through the rest of the science cases (which are secondary to the driving case of this mission), and none of them seem to be reliant on revisits. (But open to correction on this.)
Any chance there will be enough "parallax" in the 6-month period to get a stereo-distancing map for the galaxies? Or do we already have that from red-shift, relative luminance or some other means?
They're talking about galaxy evolution in the early universe, over timescales of millions of years. Statistics measured across the (large) sample group, not within one galaxy. Scroll down to "It will classify galaxies according to redshift accuracy..."
Most things astronomers observe do not change much over the course of 6 months. For comparison, it takes the Sun about 200 million years to orbit around the center of the Milky Way once, so a galaxy like the Milky Way would hardly change in 6 months.
However, there is an entire field of astronomy, called "time-domain astronomy," that deals with things that do change on human timescales. There are pulsating stars, supernovae, galaxies with rapidly accreting central black holes, and many other types of objects. Surveys that focus on the "time domain" have survey strategies that are tailored to whatever type of object they're looking at. For example, if you're looking for planets that transit in front of their host stars, you should look every ~30 minutes or so, because planet transits only last around that amount of time.
- "The telescope is passively cooled to below 80 K in low-Earth orbit by three nested V-groove radiators. An additional radiator cools the long wavelength focal plane temperature below 60 K to reduce detector dark current."
As another comment mentions, SPHEREx is passively cooled. But fwiw, plenty of infrared space telescopes use consumable coolant:
> Notable infrared missions that carried consumable cryogen include IRAS (1983), ISO (1995–1998), Spitzer (2003–2009 in cryo mode), Herschel (2009–2013), WISE (2009–2011 in cryo mode), and Planck (2009–2013). Each relied on a finite liquid helium (or solid hydrogen) supply to keep detectors cold and reverted to a warmer operating mode or ended once their coolant was depleted.
Every system I'm familiar with that used liquid nitrogen to cool the IR instruments has had a operational lifespan based on the coolant. JWST is one such. "The coolant will slowly vaporize, limiting the lifetime of the instrument from as short as a few months to a few years at most."[0]
It always surprises me how my enthusiasm for scientific discovery is affected by fears of a dystopian future. My understanding is that with red shift calibration here we'll get a much better idea of the 'when' in terms of various galactic structures emerged, that might give us an interesting idea of where we are in the life-cycle of the Milky Way. But the observation of water signatures will be the most interesting to me. Presumably there is a lot of water tied up in comets and such, but will SPHERE be able to detect those signatures near planets?
The galactic and extragalactic science cases (meaning, “stuff in the Milky Way” vs “everything inside the Milky Way”) are actually pretty unrelated here.
We actually have quite a good idea about the history of the Milky Way and all the smaller galaxies that it’s eaten (and will eat, such as our main current satellites the Small and Large Magellanic Clouds). We’re even pretty sure that the MW merged with another large galaxy about 11bil year ago, sometimes called “Kraken”
https://en.wikipedia.org/wiki/Kraken_galaxy?wprov=sfti1. SPHEREx is not interested in any of that, and it looks like it’s galactic science will mostly be mapping out where clouds of ice crystals are in the Milky Way. SPHEREx has very low spatial resolution (about 6 arcsec), so it’s certainly not observing any exoplanets, but that’s the trade off with an all-sky mission like this.
One of the big drivers of the extragalactic science, though, is looking for signatures of cosmic inflation in the distribution of galaxies on large scales. IMO this is by far the most interesting science case, and will be genuinely exciting and novel. Its survey design doesn’t give it great resolution, but it’s amazing IR spectrophometry will let it map the rough distribution of galaxies at redshifts we haven’t been able to survey before. This is called intensity mapping
Hard for me to parse as well — but I think OP is talking broadly about humans being able to keep our shit together long enough to be able to reach other solar systems before we outgrow our own.
And to think I assumed Astronomy was a stagnant field some decades ago. I have no idea why I thought that. Maybe that optical resolution from ground-based telescopes was not going to advance orders of magnitudes? Maybe I didn't think the sciences would continue to get money for space telescopes?
Astronomy has been in a golden age for the last 35 years, based on:
1. Digital cameras, and the computers to analyze images.
2. Space telescopes (Hubble Space Telescope, the first large space telescope, only launched in 1990).
3. The building of massive ground-based telescopes. Before 1990, the largest telescope had a mirror diameter of 6 meters. Now, multiple 30-meter telescopes are under construction. Collecting power goes with the square of the diameter, so this is an increase of 25 times in collecting power!
4. Very recently, the development of gravitational-wave interferometers, which allow astronomers to observe a totally new type of radiation.
It's pretty wild how much astronomy has progressed, especially with advancements in adaptive optics, interferometry, and space telescopes. Even ground-based observatories have improved way beyond what most people would've expected a few decades ago
Yeah, same here. It's a humbling feeling... realizing how tiny we are in the grand scheme of things. But also kind of amazing that, despite our smallness, we've figured out how to explore and understand the universe at this scale
450M is somewhere between .1% and 0 % of the total number of galaxies in the observable universe, so I am laying claim to 50, galaxies, which is hopefully a full set of galaxie types, but with a little haggling and trading, buying and selling galaxies I can figure that out later.
My Mom says as a child she sent away and got title to one sqare inch of the moon, but it was a much smaller universe then, especialy before inflation.
Do these missions ever build back-up hardware? What if the probe is lost because of a lunch mishap, or there is a malfunction during the deploy (see Viasat VS3 antenna deploy failure).
It is an added cost, but it cannot be that much compared to the overall R&D/tooling/launch/ect cost.
Into the 1970's, NASA did that. That was why there was Viking 1 and 2, Voyager 1 and 2, Pioneer 10 and 11, etc. Since then, however, NASA has stopped doing that. It became a balancing act- yes, 0 to 1 is much more expensive than 1 to 2, (1 to n is not quite as cheap as it is with software but it's still much cheaper than 0->1), but NASA Science is in the business of answering questions. The question is, will building, launching, and operating (the expensive part) two Parker Solar Probe's and two Juno's answer more questions than building one Parker Solar Probe, one Juno, and one OSIRIS-Rex? Almost certainly the three different probes answers more questions than two copies of two different probes. So once launch vehicle reliability got to be good enough that the fear of total mission failure went down low enough (1), duplicate missions basically went away.
1: Edited to add: this is actually tied into the Space Shuttle in interesting ways. See T.A. Heppenheimer, _The Space Shuttle Decision_ for why the STS became the sole space launch system for all of the US Government. Of course if it's manned it's reliability has to be so high that you don't have to worry about loss of payload, so building two copies of it was no longer necessary.
> Of course if it's manned it's reliability has to be so high that you don't have to worry about loss of payload, so building two copies of it was no longer necessary.
I wasn't expecting a space shuttle tie in, but of course there would be. They sure had to promise a lot to get that thing off the ground.
Readit News
So each object will be scanned ~6 months from the previous scan. How much evolving within the universe will be noticeable within that 2 year run? My gut response is not much, but that's why we do the science to see the changes.
"designed to map the celestial sky in 102 infrared colors "
So I'm guessing the coolant used to make IR scanning possible will be the limiting factor on operational time span. This article didn't say where this satellite will be parked either, but wikipedia[0] shows it to be a geosync orbit. Would have been interesting to be able to design a replaceable coolant module to extend the observations to really make seeing the evolution possible. Obviously complexity adds to cost and design time, so of course they didn't. Just dreaming
As an example, the study of the stars orbiting around SagA* are very revealing, but have required > 10 years of observations.
[0] https://en.wikipedia.org/wiki/SPHEREx
- It is passively cooled rather than using an expendable coolant- "SPHEREx relies on an entirely passive cooling system — no electricity or coolants are used, simplifying the spacecraft’s design and operational needs."
- It is a Medium-Class Explorers (MIDEX) mission - Investigations characterized by definition, development, mission operations, and data analysis costs not to exceed $180 to $200 million total cost to NASA. I think the cost of ground support eats into the budget length. The original estimate for project was $241M, so it was a large MIDEX
- It is in a Polar orbit around Earth at the day-night (terminator) line
https://www.jpl.nasa.gov/press-kits/spherex/
https://explorers.gsfc.nasa.gov/missions.html
https://spaceflightnow.com/2019/02/14/nasa-selects-mission-t...
So in particular, the 6-month period is not to revisit these distant galaxies more than once to observe spectral changes. The strategy, indeed, is to “stack” the multiple exposures to beat down noise. (Fig.6 of [0], top left).
It is possible that they have designed the system so that it could produce “just good enough” results in 6 months, with one complete scan. This is called a “threshold mission” and it would only be described in the full proposal.
I looked through the rest of the science cases (which are secondary to the driving case of this mission), and none of them seem to be reliant on revisits. (But open to correction on this.)
[0] https://arxiv.org/pdf/1412.4872
Anton Petrov had a recent episode about rapid transformations in large supergiant stars, so there are some parts of space that can rapidly evolve.
https://www.youtube.com/watch?v=gHvV9ewPY7s
However, there is an entire field of astronomy, called "time-domain astronomy," that deals with things that do change on human timescales. There are pulsating stars, supernovae, galaxies with rapidly accreting central black holes, and many other types of objects. Surveys that focus on the "time domain" have survey strategies that are tailored to whatever type of object they're looking at. For example, if you're looking for planets that transit in front of their host stars, you should look every ~30 minutes or so, because planet transits only last around that amount of time.
- "SPHEREx relies on an entirely passive cooling system — no electricity or coolants are used during normal operations"
https://www.jpl.nasa.gov/news/6-things-to-know-about-spherex...
edit to add:
- "The telescope is passively cooled to below 80 K in low-Earth orbit by three nested V-groove radiators. An additional radiator cools the long wavelength focal plane temperature below 60 K to reduce detector dark current."
https://arxiv.org/abs/2404.11017v1
> Notable infrared missions that carried consumable cryogen include IRAS (1983), ISO (1995–1998), Spitzer (2003–2009 in cryo mode), Herschel (2009–2013), WISE (2009–2011 in cryo mode), and Planck (2009–2013). Each relied on a finite liquid helium (or solid hydrogen) supply to keep detectors cold and reverted to a warmer operating mode or ended once their coolant was depleted.
[0]https://en.wikipedia.org/wiki/James_Webb_Space_Telescope
We actually have quite a good idea about the history of the Milky Way and all the smaller galaxies that it’s eaten (and will eat, such as our main current satellites the Small and Large Magellanic Clouds). We’re even pretty sure that the MW merged with another large galaxy about 11bil year ago, sometimes called “Kraken” https://en.wikipedia.org/wiki/Kraken_galaxy?wprov=sfti1. SPHEREx is not interested in any of that, and it looks like it’s galactic science will mostly be mapping out where clouds of ice crystals are in the Milky Way. SPHEREx has very low spatial resolution (about 6 arcsec), so it’s certainly not observing any exoplanets, but that’s the trade off with an all-sky mission like this.
One of the big drivers of the extragalactic science, though, is looking for signatures of cosmic inflation in the distribution of galaxies on large scales. IMO this is by far the most interesting science case, and will be genuinely exciting and novel. Its survey design doesn’t give it great resolution, but it’s amazing IR spectrophometry will let it map the rough distribution of galaxies at redshifts we haven’t been able to survey before. This is called intensity mapping
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But there are many more galaxies in the observable universe … somewhere between 2 and 20 trillion
A bit less officially, need to remove one zero [1]
[1] https://en.wikipedia.org/wiki/Galaxy#:~:text=It%20is%20estim...
1. Digital cameras, and the computers to analyze images.
2. Space telescopes (Hubble Space Telescope, the first large space telescope, only launched in 1990).
3. The building of massive ground-based telescopes. Before 1990, the largest telescope had a mirror diameter of 6 meters. Now, multiple 30-meter telescopes are under construction. Collecting power goes with the square of the diameter, so this is an increase of 25 times in collecting power!
4. Very recently, the development of gravitational-wave interferometers, which allow astronomers to observe a totally new type of radiation.
Success!
It is an added cost, but it cannot be that much compared to the overall R&D/tooling/launch/ect cost.
1: Edited to add: this is actually tied into the Space Shuttle in interesting ways. See T.A. Heppenheimer, _The Space Shuttle Decision_ for why the STS became the sole space launch system for all of the US Government. Of course if it's manned it's reliability has to be so high that you don't have to worry about loss of payload, so building two copies of it was no longer necessary.
> Of course if it's manned it's reliability has to be so high that you don't have to worry about loss of payload, so building two copies of it was no longer necessary.
I wasn't expecting a space shuttle tie in, but of course there would be. They sure had to promise a lot to get that thing off the ground.
Well, hopefully the people who are building the probe aren't eating their lunches on top of it.
(Yes, I know. Fun typo nonetheless.)
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