The NROL-15 payload which Delta 360 was carrying is classified, and there has been much speculation as to what type of satellite it may be. The launch hazard areas for Delta 360 show that the rocket was heading due east from Cape Canaveral, presumably towards a geosynchronous orbit. Its payload is most likely to be a geosynchronous electronic intelligence (ELINT) satellite, of the same type as NROL-26 and NROL-32. These satellites are rumoured to be named Mentor, however it is not known whether this is true, and if it is the NRO has probably already changed the programme name. They are also known as Advanced Orion.
An alternative theory is that NROL-15 is carrying a Misty imaging satellite. The Misty programme was reported to have been discontinued around 2007, however it could have since been revived, or if a spacecraft was already under construction, the NRO may still have proceeded with it. Misty, which is believed to be one of the largest and most expensive satellites ever developed is a stealth imaging satellite reportedly derived from the KH-11. Two have been launched to date; USA-53 and USA-144.
USA-53 was deployed by space Shuttle Atalntis in March 1990, during STS-36 into an orbit with an inclination of 62 degrees, and an altitude of around 254 kilometres (158 statute miles, 137 nautical miles). Four days after deployment from Atlantis, the spacecraft was reported to have disintegrated, with five pieces of debris being catalogued. It remains unclear whether the debris was a deliberate decoy, or whether it served a purpose, such as lens covers.
USA-144 was launched in May 1999, atop a Titan IV(404)B. Like USA-53, it shed debris, then it appeared to manoeuvre into a higher orbit, with a perigee of 2,705 kilometres (1,681 statute miles, 1,461 nautical miles), an apogee of 3,129 kilometres (1,944 statute miles, 1,670 nautical miles), and 63.4 degrees of inclination. This unusual orbit confused observers, leading to it being identified as a technology demonstration satellite, part of the apparently-cancelled Enhanced Imaging System or 8X programme, or even an SDS satellite which had failed to inject itself into Molniya orbit. It was later discovered from its orbital perturbations that it had a very low density, suggesting that it was actually a decoy. The real payload has never been observed, and is widely believed to have been a second Misty satellite. Its status is unknown.
Delta 360′s launch azimuth is not consistent with a Misty launch; imaging satellites typically require high-inclination orbits; the previous Misty satellites operated at around 65 degrees, and NROL-15 is launching to an orbit with an inclination of no more 28.5 degrees. Some observers believe that after leaving the launch hazard area, the rocket will manoeuvre to increase its orbit’s inclination, allowing a Misty satellite to be deployed while giving the impression the rocket is heading for a geosynchronous orbit.
Another theory is that Misty would be deployed into a 28.5 degree orbit and use its own propulsion system to increase its inclination, while Delta 360′s upper stage continues to geosynchronous orbit with a decoy payload.
