You know...speaking from experience (my own and many many others I know)...
It's actually a lot easier to travel with an infant then it is with an older child.
Especially now that you can bring their car seat on the plane. Babies tend to eat and sleep a great deal. Which is a great blessing on the road. Older children need to run around, and they get bored and tired a lot faster then babies do.
Although....a fifteen hour flight from Seattle could be dropping you in any number of hotspots, unstable areas, or places with limited water and or health care(I started listing them and gave up for an unfortunate wealth of data). OR You could be flying to Rome with a couple hour layover in London.
If you're not flying into an area where you and your son would be considered for danger or hardship pay, you might consider taking him with you. If you don't have a nanny already it's possible to hire one specifically for the trip (so you can keep your mind on your business). Or bring a family member/friend on a working vacation. At the very least asking for the extra tickets/accommodations from your work gives you a bargaining chip. In any event, it's something to think over.
If you decide to be gone for a week you can pump (I'd personally recommend renting the professional type from the hospital), or use a milk bank, or even check into the possibility of a wet nurse. As long as you pump while you're gone (god I hate pouring all that work down the drain!), you'll still have a supply when you get back...and just because your son will have taken a bottle for a week doesn't mean he's going to decide to wean. I'd also look into what your work can do for you in this area.
Regardless, you've got a ton of options....AND a lot of companies not only offer childcare subsidies, but also have relocation teams. If yours has either you can take advantage of both: the childcare subsidies can be put toward the extra two tickets (for your son and a caregiver) if your company isn't willing to spring for them and you decide to take him, and the relocation specialist for finding temporary resources both where you're traveling to, and here. (I just love relocation specialists...they're like walking phone books who tell you what you want before you know you want it.)
For legal rights to being able to refuse the trip and keep your job I'd talk to an attorney...just not one employed by your company. ;)