NASA to launch space observatory that will map 450M galaxies
79 comments
·March 8, 2025ChuckMcM
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
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dylan604
"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.
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.)
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.
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.
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]
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!
layer8
The Wikipedia article has more useful information: https://en.wikipedia.org/wiki/SPHEREx
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.)
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.
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alfiedotwtf
To be honest, I was expecting Elon and DOGE to have completely gutted NASA by now, while at the same time allocating more contracts to SpaceX.
dakr
They're working on it. NASA HQ has already cut their "Office of the Chief Scientist" (among others) and the current proposal is to cut 50% of the science budget (which would effectively kill it, it's already been squeezed).
dylan604
I'd imagine he's currently more focused on FAA to get them off his back about Starship issues.
Awarding new contracts doesn't require gutting NASA first, so he can get to it later once the FAA has bent the knee
temptemptemp111
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shmageggy
This is so cool, but I did not see a key piece of info in the article: does the ongoing operation of this mission fall under NASA's science budget and therefore at risk of cuts and defunding under Trump [1]?
[1] https://arstechnica.com/space/2025/03/white-house-may-seek-t...
connicpu
This one is planned to launch on Falcon so I wouldn't be too surprised if it's one project the administration spares.
kelnos
Sure, the launch will go through, but SpaceX doesn't see any recurring revenue from later operations, and I wouldn't put it past the current administration to cut NASA's budget such that continuing operations are affected.
indoordin0saur
Everything launches on a Falcon these days. No one else can catch up in terms of safety cost or speed.
gibolt
SpaceX is going to pass whatever company is launching Falcon in short order, leaving them in the dust
ddon
Yep, it looks like it will be cut and closed, which is truly unfortunate. It’s disappointing to see that science nor innovation are not a priority for this administration. And this doge cutting of funding or even shutting down important projects will have long-term consequences, impacting research, education, and technological advancements that benefit everyone.
bpodgursky
This is a proposal (not final) budget to be sent to congress. What congress eventually allocates is what matters.
jeffgreco
Not according to the current presidential administration. Impoundment is their stated goal.
ImJamal
Trump created the Space Force so he will presumably want some amount of funding for rockets and what not. If Space Force fails it would make him look bad after all.
andsoitis
Notwithstanding what you said, it is worth noting that the US Space Force has been a long time in the making: https://en.wikipedia.org/wiki/United_States_Space_Force
ImJamal
Trump is the one who actually decided to go through with the creation of a distinct branch rather than having it as a command. I think it is fair to say he created it.
There are all sorts of politicians and military members who advocate for a distinct Cyber branch of the military instead of Cyber Command. If a politician ends up doing that, then he should get credit for creating it even though it has been a long time coming.
kelnos
That really has nothing to do with whether or not operations for this project will be funded over the next several years.
rickandmortyy
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FirmwareBurner
> four suitcase-sized satellites
Americans will use anything else but the metric system :)
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malfist
Wait, is this carry on sized or checked size?
Is it delta's size limits, or are we following united or American Airlines? Or heaven forbid, alligent?
schainks
Hey! I know exactly how many Stanley cups fit in four suitcases, you don't have to tell me twice.
</s>
niwtsol
The PUNCH mission features four 140-pound small satellites, each about 1-by-2-by-3 feet in size.
Or
The PUNCH mission features four 63.5 kg small satellites, each about 0.3048 m × 0.6096 m × 0.9144 m in size.
https://blogs.nasa.gov/spherex/2025/03/04/nasas-spherex-punc...
Ao7bei3s
About 30x60x90cm in size.
xyst
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dang
Could you please stop taking HN threads on generic flamewar tangents? You've been doing it repeatedly, unfortunately. It's not what this site is for, and destroys what it is for.
fernandopj
Unfounded, IMHO:
Musk is obviously a factor in space exploration.
Trump founded the https://en.wikipedia.org/wiki/United_States_Space_Force
Also, as soon as China starts to put people on the Moon before Artemis can, I doubt POTUS would let that slide...
dakr
Trump 1 mostly targeted climate and Earth science (when it came to NASA funding). Trump 2/Musk is going after everything. They've just shut down the Office of the Chief Scientist at NASA and are planning to cut fully half of the remaining science budget.
Me1000
This administration under through Elon is pushing to cut 50% of NASA's science funding. Mapping galaxies we'll never visit is a purely scientific endeavor. Trump seems to care more about military expansion or for lack of a better term more "masculine" expansion of space. The science stuff is not interesting to him, and I'm honestly not sure I think Musk cares about it that much anymore either.
kelnos
I don't think it's unfounded. This mission is purely about science, in the pursuit of understanding our universe, and is unlikely to lead to any military applications (and even if it might, I doubt Trump et al. would have the foresight to see it).
From the Musk perspective, he wants to go to Mars. Anything that doesn't contribute to that goal could easily go on the chopping block.
Regarding China and the moon, this particular science experiment has nothing to do with that.
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?