Ask the Astronaut: Why not build and launch spacecraft from the ISS?, Tom Jones, Air & Space
"We won't use the ISS as a departure point for cost reasons. First, the ISS today is a microgravity research lab, not a spacecraft assembly hangar. Modifying it for assembly, checkout, and propellant storage would cost billions of dollars NASA does not have. A second, more serious problem is that the ISS orbit is inclined to the equator at 51.6 degrees, as opposed to a 28.5-degree orbit reached by launching straight east from Kennedy Space Center. (We chose the ISS orbit so the Russians could reach it from their launch sites farther north.) To haul spacecraft parts and propellant to ISS for assembly in that high-inclination orbit, we would lose about 20 percent of each rocket's payload capacity, since we can't use as much of the Earth's eastward rotation to give us a free boost to orbital velocity. That payload penalty would add billions to the costs of any deep space expedition assembled at ISS (e.g., a Mars expedition will need many hundreds of tons of propellant for Earth departure)."
Keith's note: This is a classic example of the old way of thinking. Tom Jones apparently cannot imagine an alternate future where things change.
1. He assumes that everything that we do in the future will be done by NASA - the way that NASA always does things - and that it will be equally as expensive as NASA stuff always is. Narrow thinking.
2. The penalty for launching to 51.6 degrees - yea its real. Launching to 28.5 degrees like the Shuttle did had a penalty when compared to launching from the equator. So we moved the station to make it easier for the Russians - and harder for ourselves. As NASA did at the time, you just factor launch capabilities into the overall equation - one wherein you factor in the counterbalancing benefit of being able to assemble large things in space and test them out from an existing location that has the benefit of generous resources already in place. That's how we built the space station, Tom - remember? Oh yes: NASA also still "hauls spacecraft parts and propellant" to ISS routinely - and a lof the stuff is launched from Virginia and Florida not Kazakhstan. If NASA plans hold up we'll be doing even more of that - with crew too. But that's inefficient, right? So why are we doing it?
3. The inclination issue as it relates to where you want to send things - yea, if you want to use big rockets all the time and get everywhere in a hurry. But if you simply exercise a little advanced planning, be patient, and plan longer delivery times using solar- or nuclear-electric propulsion then time will solve these problems - and you can factor the lower costs of such systems into your overall cost equation.
4. ISS is a microgravity lab - this is something I had to deal with every day when I worked on space station at NASA in the 90s. I had experts telling me that anything the astronauts did would ruin everything that the scientists wanted to do - and vice versa. So NASA came up with rack level vibroacoustic isolation and used scheduling to manage noisy activities. Problem solved. BTW, Tom you have seen the video of how the entire space station flexes when its exercise time for the crew, yes? I do not hear scientists screaming how this makes their research impossible. Crew and cargo vehicles arrive and depart on a regular basis. How is that any different than "launching" a spacecraft from ISS? But wait: Nanoracks is actually launching cubesats from the ISS on a regular basis. Again, no complaints.
I remember back in the 90s when the orbit was shifted to 51.6 - and the implications that had for Shuttle launch windows. I sat in meetings where experts emphatically stated that NASA could never work with 5 minute launch windows. Well, they did. Now SpaceX has managed to design hardware and operations such that they can recycle multiple times within a single launch window. I remember people saying that you could not dock a Soyuz to the space station due to the somewhat brutal way it docks and how fragile the U.S. structure was. So they docked to the Russian segment instead. Problem solved. I remember asking why we couldn't leave logistics modules on the ISS permanently for simple storage. Everyone said "no" because of super high costs to make them meet requirement. Now they do - because they decided to - with only minimal mods. NASA wanted a reusable Space Shuttle that would fly like an airline. It never actually happened. Now Blue Origin and SpaceX are on the cusp of doing it. Just because the same group of experts says that something is not possible or practical doesn't mean that you can't go out and find other experts who can make it work.
Who knows, maybe we will just shift the future role of ISS at some point to focus on on-orbit assembly of larger expeditionary vessels and do the science stuff on the next generation of space stations built by the private sector. Look at Antarctica - there are bases there that have been operating continuously for more than half a century. They are constantly being readjusted to do new things and not do other things. Some are decommissioned. Some are disassembled. New ones now move or raise their height when conditions warrant. Some are rebuilt using parts from older facilities. Fragile cargo and people fly in on planes. Other supplies arrive on slow-moving ships that depart weeks or months in advance of when their cargoes are actually needed. One would hope that we try and instill similar flexibility in what we build in low Earth orbit and beyond. If we don't adopt expeditionary thinking and pragmatism then none of this commercial LEO stuff NASA is praying for is going to happen since no commercial effort will ever be able to afford things that are mired down with outmoded NASA costing and operational mindsets.
Oh yes: then there's Mark Watney and "The Martian". What better way to make sure a Mars ship works than to run it for a year or two in LEO after being assembled from smaller subunits launched by a variety of existing ISS cargo carrier. If we do not promote flexibility and long-term thinking in LEO and cis-lunar space so as to guide the whole #JourneyToMars thing we'll just be begging for something bad to happen because no one thought to equip our Mars crews with the ability (and experience) to fix things that are not supposed to break.
Just because we've done things a certain way in space doesn't mean that this is the only way to do things.