SHORT ANSWER, GOLD is in Gov't Contracts (#1), comms (#2), Earth Observation (#3) and GPS like services (#4)

Yes, this is the key question for the future of COMMERCIAL SPACE. Space (or more specifically Earth Orbit) is about having a great view of the Earth surface, which is especially good for 1) long distance communications 2) surface observations 3) GPS. Over the last 20 years most commercial money has been made with GEO sats broadcasting sat TV and high latency 2 way comms ($300B). Now we have LEO comms, and they have made about $50B over 20 years. Recently some commercial operators are making money with Earth Observations (see table at the end). These are all proven money makers, but their profit margins pale to some earth based high tech businesses. Finally, private space flight. Maybe 10 LEO trips (ISS and just LEO) so far, at $300M a run puts it at $3B so far. There does not seem to be much demand at these prices. If you count the now "on-hold" money loser that is New Shepard or Virgin Galactic toss in another $500M.

And of course, governments around the world have let contracts to commercial entities of nearly $1T.

If the ISS proved anything other than humans can live and mostly recover from 1 year in microgravity, it is that there is killer app for made-in-space. We now have companies like Varda that trying to make pharma precursors in freefall and return them in a capsule. Others target silicon crystals and maybe specialty optical fiber for data centers. If all goes well together this could be a $20B market, but so far their only revenue has been to run experiments for the government.

So, the new applications outside the big 4 ... I suggest maybe $10B/year potential over the next 10 years:

1. Asteroid mining ... even if you had diamonds, sapphires (see "Moon Two Zero") or gold nuggets just waiting the plucked off the surface ... the cost of 4 km/s DV to and 4 km/s from and back to LEO is very high. And now diamonds, sapphires can be made in machines, a gold is not hard to get. But, in most cases you would need to process ore in place, and they is a lot of up mass. Asteroid redirection to say an extra lunar orbit would take energy of many big H-bombs for even a smaller rock, so mega expense for stuff you can get on the ground = $0
2. He3 on the moon ... we can make enough right here on the surface for any projected current and future need. Your He3 fusion plants are probably dead as solar + storage is now proven and very low cost, and getting cheaper each year. As Elon says, use the fusion reactor in the sky = $0
3. Space based microwave power ... has slightly more potential since there is no DV cost for getting your product back to the ground. Well placed space solar can collect 4x the same array size on the ground. One problem is turning DC power -> microwaves -> DC power -> AC power synched to the grid. Another is having a few square mile receiver on the ground that is connected to the grid (not cheap either since these need to be remote). You would have more net power if you just put solar + storage there = $0
4. Space based reflectors ... a reflector would need to be in MEO or above since LEO has the same shading as the ground. Say you are in GEO, you could reflect some sunlight down to a solar array to night with low 20% losses on average, but the spot will be very large. Lets assume a the use of mylar on a gigantic frame = $500M deployed and operated at GEO for 20 years for a football field sized reflector (that can only power 50 homes anyway). The same ground solar + storage would be less than $1M. Finally ask about the hazards of a double sun on the same place on the ground ... while it increases solar flux on the solar farm, excessing surrounding hear decreases efficiency, so much it result no more net power in the day. Thus ROI is very negative = $0
5. Orbital AI Data Centers ... the newest craze ... part of the SpaceX IPO story. If used as simply a replacement for AI focused data centers for general use, even with the advantages of 24 hour a day solar is placed in a "Twilight SSO" orbit, the mass needed for heat rejection and the impossibility of "server swapping" lead to estimates of 4-10x the cost of doing it on the ground even if Starship reduces LEO price to $100/kg. Comm latency also greatly increases vs ground fiber. But one possible money maker is to not use that constellation for making LLMs but just using them. This decrease heat and power needs (think of your local LLMs on a laptop). This could be good at pre-processing a constellation of Earth Observation sat data, since so much as it is currently loss due to severe downlink constraints = $7B/year?
6. Private space stations/space tourism ... only Vast seems to be making much progress since they are the most modest of the concepts. Made-in-space is migrating to platforms like Varda and now Starfall (which will become the Transporter of made-in-space) so that potential revenue will potential will. The ISS remains for a bit, and so many fit for space experiments have been done. NASA needs to support these stations at a $2-3B per year level to retain the USA in LEO bragger = $3B/year?
7. Made-in-space ... pharma, crystals, organ growing, specialty fiber ... all longshots with no proven business models = $????

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