<font color="yellow">"I would guess that the side mount would be a perfect bridge between the shuttle and the in-line. "</font><br /><br />No -- then you're paying development costs twice. Not much of the development for the side-mount would transfer over to the in-line. Personally, I was leaning toward side-mount as well, but there are advantages and disadvantages to both routes:<br /><br />Side mount:<br />Pros:<br />- Faster/cheaper to develop. <br />- Uses more of the existing pad/etc. infrastructure.<br /><br />Cons:<br />- Less payload to orbit<br />- Corollary of payload -- larger cost/pound to orbit.<br />- Corollary of payload -- more on-orbit assembly required, increasing complexity, potential for failure, and redundant mass (i.e. module docking hardware, avionics, etc.)*<br /><br />The in-line is obviously the inverse of the above. The upshot is that the in-line will be more costly and time-consuming to <b>develop</b>, but should be cheaper (in theory at least) to <b>operate</b>. Considering the problem we have with the current system, which kept compromising on development costs... and ended up with an operational nightmare, I have a hard time thinking the in-line is a bad idea. Ultimately it will depend on how many flights it makes. The more flights, the more it pays for the increased development costs. If it makes only a dozen flights, then gets decommissioned, the side-mount would have been a better option. This is another reason to go with the in-line now or never (i.e. not making a pit-stop at side mount) -- we need to make as much use of it as possible to recoup the costs of development. <br /><br />Ultimately, we won't know if the decision was a good one until long after it's history. This of course pretty much describes <b>most</b> decisions. <br /><br /><br /><br />* Since there is less on-orbit assembly required, that means that any mission for which this assembly requirement has been eliminated now can be developed for less money. These s