Sundancer vs. Orion

You have to deal with the rocket equation. More mass means more cost. Bigelow says the BA330 makes the Orion unnecessary but it has some disadvantages compared to the Orion. But those disadvantages completely disappear if you compare it to a modified Sundancer instead. I came to this realization here.

The BA330 has life support for six. The Sundancer could be given that as well. Both Orion and Sundancer require a propulsion module. The BA330 at 23mt is just slightly too big for existing launch vehicles, but either the Orion or Sundancer could be fully integrated on the ground and launched using existing rockets. Total mass of the Orion is 21,250 kg. The Sundancer is 8,618.4 kg which means it even wins the all important rocket equation match up! This means one launch to orbit, after which either would need fuel transferred to it. The Sundancer would just need less fuel resulting in a lower cost mission. An additional launch would be required to transfer crew to the Sundancer but for any meaningful mission BEO that's not a big deal.

Then the Orion just loses in the comparison being unsuited to take 6 crew for anything more than a short trip (which then loses in comparison to the Dragon for the intent of going to and from orbit.) The problem is that the 9m3 of the Orion simply isn't enough when you need about 5m3 per crew for supplies on a six to nine month mission such as going to mars. The Sundancer gives you 60m3 per crew  (but 30m3 each if upgraded for six crew) providing both living space and storage space that just isn't found on the Orion but is pretty darn important for a journey that takes most of a year.

Neither is a lander for the destinations they may go to (and generally a reusable general purpose orbit to orbit ship shouldn't be.) Either would be required to meet a prepositioned lander for such a mission which could be sent ahead on a low energy, slower, lower cost transfer.

I hear the Orion has a toilet. How hard would it be to include one on the Sundancer (and with more privacy!)

The Orion is obsolete before it's even completed. I don't have the heart to tell Jason. Update: ok, I just did.

Update: Even more Sundancer advantages...

It has better ballistic protection from all the small objects that might hit it at high speed from time to time. Leaving LEO it should burn all of it's fuel because it would be kept outside the hull in a less protected state than the crew and you don't want to depend on fuel being there after many months of trip. Then midcourse corrections and mars capture, for example, Hall ion thrusters could be used having it's fuel inside the protection of the hull... because they can with the Sundancer's internal volume.

Because of the internal volume, Sundancer can have the extra supplies that are required for a free return should they not be able to meet their landers at their destination.

It has better radiation protection and could also have a central storm shelter if solar flares endanger the crew.

Stuffing too much crew in too little space in an Orion is just a bad idea. With the Sundancer having less mass, you can't even make an economic argument for the Orion as you might against a BA330 or larger. Related discussions here.

Send twelve to mars for $1b in less than ten years.

Better yet. Twelve in four years for $800m.