There are many exisiting launch sites, but Sea-Launch is the only existing equatorial launch site. It is also the only private launch site. It seems about $500 mil was invested in developing Sea-Launch. This is a mobile system, and it is for bigger rockets than we envision needing, so a cheaper launch platform could be developed. As a new venture we would not want to develop something this expensive if it could be avoided by renting. So it would be easier on investors if a deal could be worked out where early launches were from Sea-Launch.
After we are making money we could develop our own launch site. If we build something similar to Sea Launch the platform could be smaller as our rocket would be like 1/5th the mass. Also, the support ship could be much smaller if our vehicle does not require so many people to launch it. If we use a land based site it could be cheaper to operate. A land based site would require considering government issues and the safety of tourist traveling to the site.
The rocket probably needs a place to land downrange from the launch site. >From here it could be brought back by boat, plane, or even launched empty to return to the original launch site. There have been proposals for "flyback boosters" that had jet engines on them and flew back to their launch site. This might work as well.
The rocket could launch aimed West and just fly back the way it came. This would be much faster than a boat and a plane might not be practical if the launch site is a platform out in the ocean. Launching backwards also provides more test launches to verify the rockets reliability.
One way to solve the return problem is to have the rocket hold onto the tether and go around the Earth once, releasing so that it can land back at the launch site. If we had several launch sites around the globe the rocket could fly on forward. But this is a large number of launch sites and so probably not practical anytime soon.
So, depending on the design, a second site where the rocket lands may be required. This landing site may also be a launch site.
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