NASA to launch space observatory that will map 450M galaxies
133 comments
·March 8, 2025dylan604
niwtsol
To answer three of your questions:
- 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...
pklausler
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?
sbierwagen
>how does this polar orbit stay over the terminator?
Because it's launched at a angle greater than a straight north-south 90 degree orbit, so orbital precession will correctly follow the terminator. Depending on the orbital altitude this can be more than 140 degrees: https://en.wikipedia.org/wiki/Sun-synchronous_orbit
dylan604
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.
mturmon
Remember, it is passively cooled (a major design plus and, I assume, part of why it was able to achieve the cost it did). So there would be no need for a manned mission. And in fact, at that cost, it wouldn’t make sense anyway.
nine_k
Even a Dragon could bring enough hardware and a crew for a small upgrade or repair (to say nothing of the upcoming Starship).
mturmon
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.)
JKCalhoun
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?
perihelions
Andromeda (the nearest) is 2e19 km away and has a relative motion of 300 km/s in the radial direction. If we assume the tangential motion is similar, that's 5e9 km of tangential displacement over 6 months, for a total angular displacement of 5e-5 arcseconds (50 microarcseconds).
That's well below the precision of every telescope. (Admittedly GAIA, the one designed for parallax measurements, comes close, but its techniques only work on very bright point-source objects).
I think these articles answer your question:
https://en.wikipedia.org/wiki/Cosmic_distance_ladder
https://news.ycombinator.com/item?id=43151943 ("Part two of Grant Sanderson's video with Terry Tao on the cosmic distance ladder (mathstodon.xyz)", 99 comments)
perihelions
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..."
nashashmi
Right, at that scale, For a galaxy to move a fraction of a centimeter will take a thousand years. So not much will be missed in a gap of 6 months.
queuebert
This is nonsensical. Do you mean a tiny movement in the field of view, which should be measured in angular distance?
Or do you mean actual motion through the universe, in which case the galaxies are moving at hundreds of kms per second, which means they would move billions of kms in 6 mos.
pixl97
>How much evolving within the universe will be noticeable within that 2 year run?
Anton Petrov had a recent episode about rapid transformations in large supergiant stars, so there are some parts of space that can rapidly evolve.
DiogenesKynikos
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.
Sanzig
Why would coolant be a consumable? These things are usually cooled with Stirling cryocoolers which are closed systems.
perihelions
I did a quick search and it seems there is neither?
- "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."
dylan604
The Spitzer used passive cooling, but only as a method to reduce the amount of coolant required. It still needed a coolant.
"One of the most important advances of this redesign was an Earth-trailing orbit.[1] Cryogenic satellites that require liquid helium (LHe, T ≈ 4 K) temperatures in near-Earth orbit are typically exposed to a large heat load from Earth, and consequently require large amounts of LHe coolant, which then tends to dominate the total payload mass and limits mission life. Placing the satellite in solar orbit far from Earth allowed innovative passive cooling. The sun shield protected the rest of the spacecraft from the Sun's heat, the far side of the spacecraft was painted black to enhance passive radiation of heat, and the spacecraft bus was thermally isolated from the telescope. All of these design choices combined to drastically reduce the total mass of helium needed, resulting in an overall smaller and lighter payload, resulting in major cost savings, but with a mirror the same diameter as originally designed. This orbit also simplified telescope pointing, but did require the NASA Deep Space Network for communications"[0]
perihelions
I found an explanation of the "v-groove" radiator geometry, if anyone else was curious about it:
(.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...
jessriedel
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.
perihelions
Notably those were all far-infrared telescopes, which need even lower temperatures (liquid helium) to escape thermal noise.
dylan604
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]
perihelions
You've misread your source article—what you've quoted is not a description of Webb.
computerex
Thank you for awesome information!
ChuckMcM
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?
turtletontine
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
tiborsaas
I can't really get what you meant by "dystopian future" in this context. In my understanding that is a human caused concept.
JKCalhoun
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.
eleveriven
As for water detection, I'd imagine SPHEREx will be better suited for large-scale mapping rather than pinpointing water on specific planets
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eleveriven
It's pretty incredible to think that we're at a point in human history where we can map 450 million galaxies and probe the origins of the universe
Tepix
The Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey has recorded more than one billion galaxies.
But there are many more galaxies in the observable universe … somewhere between 2 and 20 trillion
jajko
> 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...
Tepix
There are more recent estimates going from 6-20 trillion now: https://bigthink.com/starts-with-a-bang/galaxies-in-universe...
eleveriven
Yeah, the scale of it is absolutely mind-blowing
JKCalhoun
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?
DiogenesKynikos
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.
nuccy
To add to the list (the order is arbitrary):
5. Advances in the multi-messenger observations, where apart of photons and gravitational waves, astronomers can detects also neutrinos with specialized neutrino detectors, e.g.: IceCube [a], though there are many more of those [b].
6. Advances in very-long-baseline interferometry [c] using a globe-sized array of radio-telescopes, like Event Horizon Telescope [d]
[a] https://en.wikipedia.org/wiki/IceCube_Neutrino_Observatory
[b] https://en.wikipedia.org/wiki/Neutrino_detector or here https://en.wikipedia.org/wiki/List_of_neutrino_experiments
[c] https://en.wikipedia.org/wiki/Very-long-baseline_interferome...
eleveriven
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
jimkleiber
I feel infinitesimally small.
eleveriven
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
igleria
me too, but big things have small beginnings!
layer8
The Wikipedia article has more useful information: https://en.wikipedia.org/wiki/SPHEREx
metalman
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.
eleveriven
Imagine the value after cosmic inflation kicks in
perihelions
https://blogs.nasa.gov/spherex/2025/03/12/signal-acquired-na... ("Signal Acquired: NASA’s SPHEREx Begins Science Mission")
Success!
dj_gitmo
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.
mandevil
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.
dj_gitmo
Great answer.
> 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.
kelnos
> What if the probe is lost because of a lunch mishap
Well, hopefully the people who are building the probe aren't eating their lunches on top of it.
(Yes, I know. Fun typo nonetheless.)
ourmandave
Like the myth Inuit have 100 words for snow, how many words do astronomers have for big?
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foobarbecue
aquisition of signal! https://www.nasa.gov/news-release/nasa-launches-missions-to-...
nicholasbraker
“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's long way down the road to the chemist's, but that's just peanuts to space.”
arisAlexis
I call it here, Musk will cut it before they do it
keepsweet
I highly doubt it, but is that plausible?
lobsterthief
It’s possible. But if he thinks his company will benefit (like by launching the things into Space) then he probably won’t. Sad that this is where we are. Absolute power corrupts absolutely.
"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.
[0] https://en.wikipedia.org/wiki/SPHEREx