Mide, IMO- it's been stated that the STS-111 is the demo ship for L3 and others (maybe Home Land Security, etc.) The STS-111 has a stated ceiling of 20,000 feet and a payload of 25lbs. It's mission is tracking assets (GTC appliques), ISR and comm.
The SkySat has a different mission and a ceiling of 45,000 feet. I believe it's mission is missile defense and will be one huge radar platform. I think the SkySat is several months away before test flight.
The future Strat (STS-232) has a ceiling of 60,000 plus feet and a large payload (250 plus lbs?). It's mission is com and ISR. I think Rocky Mountain will be funding the development shortly.