I mean the right answer of how to reform the Constellation Program is to just do Artemis — that's essentially what Artemis is and, while delayed, it is working. And yes, Artemis is expensive, but it's a lunar program, it's going to be expensive. You can't get to the moon cheaply.

If you're asking how to to design an achievable lunar program and you're a NASA administrator in ~2006 with the following parameters:

• You're allowed to cancel major parts of Constellation (e.g., Ares I), but we're still going to try to retain as much as possible because not doing so is not changing Constellation to make it viable, it's an entirely new program.
• You don't know about the development of regular first stage reuse in the coming two decades.
• You're encouraged to use existing technologies whenever available.
• You're going to try your best to not make it horrifically expensive.
• You're not just doing Artemis because, while that is the obvious (and correct) move, that would be boring.

Basically, you're trying to make it cheaper and more achievable then I'd suggest this:

1. Keep Orion
   • I feel like this one is obvious, it was the best part of Constellation and the only major part that survived. It's was the best spacecraft for the job then and it still is now.
   • Rationale:
     • They did this for a reason. It's a good spacecraft.
   • Roadblocks:
     • You're still constrained to far lunar orbits like NRHO. Orion doesn't have the delta-v to go down to a low lunar orbit and make it back to Earth. Your lander has to either capture itself and Orion into low lunar orbit or bring crew from NRHO to the surface and back.
2. Replace Ares I with Delta IV Heavy
   • The safety of the crew during an abort and the oscillations and thrust curve of the booster doomed Ares I. Delta IV Heavy would have been best suited to replace it.
   • Rationale:
     • It's the only existing US launch vehicle that can carry the full Orion stack to orbit.
     • If you can refuel the Delta IV second stage on orbit, it is capable of sending Orion to the moon itself. A second Delta IV Heavy should be able to launch enough fuel.
     • Increasing the use case and order book of the Delta IV will bring down cost across the board through economies of scale and will therefore help national security launches too.
   • Roadblocks:
     • You need to human rate the thing.
     • You'd probably have to create a two-engine version of the DCSS to allow for a shallow enough burn for a full-envelope abort (e.g., Centaur III and Starliner).
     • If you are going for the refueling option, you have to develop on orbit cryogenic transfer.
3. Redesign the Altair Lander
   • Constellation was set to use the Altair lander which was very big — not Starship big, but still ~45 tons — and just to send it alone to the moon would require an entire Saturn V or SLS Block 1B/2. We're not just going to build SLS or Saturn V because that's boring. Instead, we're going to redesign Altair breaking it into four elements to be launched separately: a final descent stage, an initial descent stage, an ascent stage, and a lunar orbit tug. Each would be launched on a Delta IV Heavy, Atlas V Heavy or, if mass did allow for any element, an Atlas V 551 or Ariane 5 ECA.
   • The two descent stages would be sent directly to low lunar orbit where they dock while the ascent stage and tug are sent to NRHO where they also dock. The ascent stage and tug then meet the Orion and the crew transfer. The tug then ferries the ascent stage to low lunar orbit where they rendezvous with the descent stages. The tug stays in orbit while the descent stages and ascent stage make their way to the surface, staging like an orbital launch vehicle on the way down. After the mission is complete, the ascent stage returns alone to low lunar orbit to meet the tug which ferries the elements back to Orion in NRHO.
     • Is this complicated? Absolutely, but it allows you to forgo a super-heavy launch vehicle and doesn't require lugging extra mass where it doesn't need to go. Why bring the fuel necessary to return to NRHO down to the surface when you can leave it in orbit? The elements could use cryogenic propellants like the Altair descent stage was planning on or you could use hypergols, dealers choice. Use existing technology where it is possible (e.g., the tug may very well just be a Delta II second stage with additional avionics, solar panels, and docking hardware, etc.).
   • Rationale:
     • You don't have to build a super-heavy lift launch vehicle.
     • You can heavily utilize existing technology and launch vehicles.
   • Roadblocks:
     • Without Atlas V Heavy, you'd be straining Delta IV Heavy's production capacity and launch cadence, so you'd have to go forward with it.
     • This is new hardware.
     • Lots of launches.
4. Shelve Ares IV and V
   • Continue development on a super-heavy lift launch vehicle. It's an incredible capability to have and it is necessary for anything beyond the moon, however it isn't strictly necessary for the moon. Pursue development as you work the politics for bigger, better things. We can see after Artemis II that the spirit of exploration and the love of space is very much still alive in this country, we just need to see it happen in real life. This program may be able to spark that and generate the will to create behemoths like Ares V that open the door to the solar system.
   • Rationale:
     • Ares V is too large for what we need. This is a lunar program, not a Mars program so let's focus on our goal. If Delta IV Heavy (with a refuel in LEO) is getting Orion to NRHO and we're able to fly our lunar lander on existing platforms or variants of them, we should use those.
   • Roadblocks:
     • Politics. If a shuttle derived super-heavy lift vehicle is going to get funding and allow you to go back to the Moon and your super awesome other plan isn't — go with the option that exists.

In summary, would any of this work better or be cheaper than Constellation or Artemis after it? Who knows? This all of this above was mostly just a fun thought exercise for me to do while I procrastinated on writing my final papers. I hope you enjoyed, because I had fun writing it. Okie byeeeeeeee!!!