The view that the X-37B is a reconnaissance platform is strengthened by observations from amateur satellite watchers, who track the vehicles’ orbits, and noticed that it has similar orbits to spy satellites and scientific remote sensing craft. In addition, they noticed the craft changing its orbital path several times during its test flights.
This is to be expected, says Joan Johnson-Freese, professor of national security studies at the US Naval War College in Newport. “The upcoming launch will continue just to see what the vehicle can do,” she says. “One of the things they are testing is maneuverability. The problem with satellites in orbit is they are very predictably in certain orbits at certain times, and thus vulnerable to anti-satellite weapons (ASAT).”
Johnson-Freese says the military has long been interested in the ability of a spacecraft that has “the ability to evade, to maneuver, to not be in a predicable place at a predicable time.”
She expects the Air Force will be “pressing the envelope for manoeuvrability and duration” during the X-37B’s next flight. “That will give them the idea of potential missions where avoidance of ASATs comes into play.”
Although its orbits may be difficult to predict in advance, its tracks show where the X-37B has been and its likely purpose, says Brian Weeden, a technical advisor at the Secure World Foundation, a Washington-based foundation that focuses on space issues.
For example, he says, the X-37B flew at inclination of 42.79 degrees, which tells you how far north and south in latitude the spacecraft can see. “The tradeoff is that something at a 90 degree polar orbit covers the whole world, but its frequency is less; it may arrive only every couple of days,” he says. “If something is 40 or 45 degrees, it would be covering a smaller portion [of the earth], but more often. “
At a 42.79 degree inclination, the X-37B would be useful for looking at a geographic region such as the Middle East, says Weeden, pouring cold water on one theory that that it was used to spy on China’s spacelab, Tiangong-1. And given the current political context, he says, the Middle East “makes sense”.
Weeden also suggests the X-37B’s orbit may indicate that the military is trying out a new sensor system, such as radar imaging or hyperspectral sensors, which collect information across different wavelengths. He suggests this could be the case, because unlike satellites collecting light in the visible wavelength, the X-37B’s orbits are not synchronized with the sun, a trick used to maintain a predictable angle between the sun, satellite and ground.
But, like with many of the theories surrounding the X-37B, he warns, “it is just speculation.”
For its part, the Air Force itself is silent about the plane’s use, only speaking to allay fears that it was a weapon. "I don't know how this could be called weaponisation of space. It's just an updated version of the space shuttle type of activities in space," said Gary Payton, the Air Force's deputy undersecretary for space programmes, in 2010. "We, the Air Force, have a suite of military missions in space and this new vehicle could potentially help us do those missions better."
Whatever its purpose; the X-37B is perhaps one of the few bright spots among the Pentagon’s hypersonic test vehicle programs. The Air Force’s X-51A Waverider, a scramjet powered hypersonic missile, suffered a fatal mishap earlier this year on a test flight, and never reached hypersonic speeds. Separately, another hypersonic prototype, known as the Falcon Hypersonic Test Vehicle-2, suffered mishaps in both flight tests, plunging into the ocean.
Those other efforts, which are focused on creating missiles, are still in early testing phase, while the X-37B is clearly further along.
“I think the one interesting question is whether this is just test and evaluation, or is it being used to be support real world operations,” says Weeden. But like most questions about the plane, it is one that is currently impossible to answer.