PlanetSpace Comp.

NASA established the Commercial Orbital Transportation Services (COTS) program to develop a competitive market for crew and cargo flights to the International Space Station (ISS). The program breaks from the traditional government contracting approach by allowing the private sector to develop, own, and operate its own launch vehicles in service of NASA's ISS delivery needs. Unlike today's Space Shuttle, the reusable launch vehicles (RLV's) developed under COTS will also be able to serve commercial customers.
The original COTS announcement listed several capability requirements. These included the ability to lift a combined total of "up to" 16 tonnes of cargo per year to ISS using two to eight flights per year. Thus, the minimum launch vehicle/cargo carrier would need to be able to haul at least 2 tonnes of cargo per flight.

In August 2006, NASA announced its competitive selection of Space Exploration Technologies (SpaceX) and Rocketplane-Kistler (RpK) as partners in the COTS program.

In November 2007, PlanetSpace company, announced that it had teamed with aerospace giants Lockheed Martin and ATK to submit a proposal response for NASA's COTS (Commercial Orbital Transportation Services) program. The proposal was triggered by NASA's October 18, 2007 decision to cancel Rocketplane-Kistler's original COTS contract.

Meanwhile, it can be contemplated alongside other proposed launch vehicles like Orbital Sciences Taurus II and SpaceX Falcon 9.

The PlanetSpace Athena-III rocket would stand somewhere in the 52 meter height range, including 10 meter long payload fairing, would weigh 439 tonnes at lift-off.
The first stage would be based on ATK's Space Shuttle Reusable Solid Rocket Motor (RSRM). It would use 2.5 motor segments.
The second stage would be an ATK Castor 120 motor.
The third stage would use a new ATK Castor 30 motor. Castor 30 should be loaded with 13,000 kg of propellant at launch. ATK has been developing Castor 30.  Castor 30 appears to match the reported second stage requirements of Orbital Sciences Taurus-II COTS launch vehicle proposal.
The launch vehicle would be topped by an Orbit Adjust Module (OAM) of the type previously flown on Lockheed Martin's Athena-I and -II launch vehicles. OAM was a pressure-fed monomethylhydrazine (MMH) propulsion system that provided on-orbit maneuvering and trim.
The new launch vehicle would be able to lift about 6 metric tons (tonnes) to low earth orbit (LEO), using existing Shuttle SRB-style steel motor casings. New composite first stage motor casings would improve LEO performance to 6.71 tonnes. ATK said that the launch vehicle (presumably the composite case version) would be able to boost 2.79 tonnes to geosynchronous transfer orbit, 1.88 tonnes to a trans-lunar trajectory, and 1.36 tonnes toward Mars.