[rbanffy]

Unless you extract fuel from the environment on your stop, it's a very bad idea to make a stop when you are shipping cargo to space. Any change in trajectory spends fuel. If you absolutely have to send the vehicle in pieces, you'd better send them to the lowest energy orbit, assemble them there and blast off. The ISS is not on a particularly useful orbit for this and the only reason I imagine to stop by would be to use the extra helping hands of the resident crew to do the required assembly.

And shipping cargo to Mars doesn't need to be very expensive if you are patient - you send the cargo towards a low-perihelion trajectory and deploy a solar sail closest to the Sun. It may take a good couple years for the shipment to get to Mars, but the delta-V on the way up will be free. If you send the shipments well ahead of the landing crews, they'll have lots of toys when they arrive.

But I agree with the SpaceX folks. Nuclear is the way to go if we are to even go back to the Moon.

[ceejayoz]

> The ISS is not on a particularly useful orbit for this and the only reason I imagine to stop by would be to use the extra helping hands of the resident crew to do the required assembly.

That, and the living quarters. If it's going to take a couple months to put stuff together and test, you don't want to be living out of an Apollo-sized capsule.

[bugsy]

I didn't mean to suggest the ISS in any way. I am talking about the various plans such as von Braun's Das Marsprojekt, where you assemble a fleet of (for example) 3720 ton Mars ships in orbit: http://www.thelivingmoon.com/41pegasus/01archives/Von_Braun_...

It's not possible to launch a 3720 ton ship to Mars from the surface in one shot, it has to be assembled in space from parts and fuel shipped up in multiple launches.

[rbanffy]

Von Braun's plan, while spectacular, was never particularly feasible - it's more like colonizing Mars on the first trip than anything else. You don't need to send your crew in a 3000+ ton spacecraft towards Mars - you can send the crew on a smaller craft and send habitats, vehicles, supplies and all other stuff in advance in low-energy orbits (because food is less sensitive to radiation than astronauts). Von Braun's plan did not rely on automation (we can land a robot on Mars) and thus required every supply ship to be manned.

[bugsy]

Yeah I'm aware of that. Above I pointed out that the XX was possibly coming and would have Saturn V level payload capability. The Saturn V is a giant rocket and needed to be that big to ship a bunch of stuff in one launch in order to beat the Russians rather than longer term plans involving using smaller rockets with smaller payloads and assembling things in orbit. Right now there is less point to going to the moon again rather than Mars but there is still the issue of assemble a big payload in orbit from small parts sent in modest ships or send a medium payload in one big giant freaking rocket. The Mars rovers and such were very tiny lightweight payloads compared to sending a human contingent to Mars, and even with the XX's payload, it is still barely enough to send a Mars crew and ship. So the issue remains. I only mentioned "without a space station stop" because I thought that people were going to otherwise jump on me with commentary about "yes but what about a space station stop then you can have smaller rockets". By mentioning "without" I had hoped to avoid needed to have that debate. I was not expecting to have the opposite debate and sorely wish I had said nothing at all and kept the link to the XX to myself now.

But now that we are having to have this talk, personally I think multiple ships assembled are still the way to go. A one-shot XX launch means not enough weight for proper radiation shielding, and enough food and spare parts to make it all the way there is a problem, and enough space to prevent the astronauts from killing each other is also an issue. We still have to have enough fuel to get there and land even if there is a bunch of fuel on site waiting in pods both in orbit and on the surface. The Dragon capsule is not really big enough to prevent mission failure from mass homicide en route, something considerable larger, and larger than the XX can lift in one go with fuel and food and water is needed to avoid this.

The space assembly step doesn't have to be something done in a giant station over a period of months. It can be send 4 modules up one after another, dock them together and go. We assembled two space ships together en route to Luna using this method on the Apollo mission. Adding a few more modules isn't a big deal, if we could assemble (not build from scratch) stuff in space 40 years ago, we can do it again now.