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OTV/X-37B


Tyneside, UK
2020 Jul 14
Tuesday, Day 196

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The X-37B and Tiangong 1 (!?)

2012 - early January, the Brirish Interplanetary Society (BIS) Twitter feed heralded an upcoming story in its magazine "Spaceflight" that the USAF/Boeing X-37B joint venture spaceplane, performing the OTV-2 mission, was being used to spy on China's Tiangong 1 developmental space laboratory.


Whoops!

The item was picked up almost immediately by the BBC News web site and turned into an even bigger story. The thing was...... it simply was not true. It's author, Jonathan Amos, was forced to point out that his own story was wrong. Equally embarrasingly, the BIS had to do the same.

The uncredited Spaceflight author (subsequently revealed as the magazine's editor, David Baker) had noticed the similarity between apogee, perigee and orbital inclination of the two craft and jumped to the conclusion that they were were effectively orbiting side by side! He concluded that the spaceplane must, by definition, be checking out Tiangong 1. Had the idea been run past anyone with a knowledge of orbital mechanics and access to the actual orbital parameters of the two vehicles, an embarrassing story would never have seen the light of day.


Reality

The story did not question how the US could have launched the X-37B early in 2011. with full knowledge of exactly when, and into what orbit, Tiangong 1 was to be injected six months later. There is a secondary question of how the USAF could have known in advance that Tiangong 1 would fly at a subtly different inclination from its Shenzhou predecessors.

The whole assumption was flawed. because, although the heights and inclination were similar, the two orbits were hugely different. The difference related to their relative orientation in space - they actually cross each other at quite a large angle. The author had simply assumed that the orbits were 'nested' within each other - rather like the rings of Saturn. The article describes a 0°.1 change in orbital inclination by the X-37B as being sufficient to make them co-planar. This can only be true if the two orbits had a second parameter in common, namely the Right ascension of the Ascending Node (RAAN). In reality, the two RAANs were 100° apart so the two orbits intersect each other at an angle of 62°.

The diagram shows the ground tracks of both vehicles around the middle of the day 2012 January 5. Positions are as they were at 11:53 UTC. Tiangong 1 was above the mid-Pacific, in darkness near midnight local time, heading south-east towards the tip of South America. It crossed the X-37B orbit on the way. The only thing was, 55 minutes had elapsed since the X-37B was there - equivalent to about half a circuit of the Earth. At the same time, the X-37B was approaching Gibraltar on a north-easterly heading that took it across the Middle East at around noon local time.

The relative locations of the orbits were largely unchanged since Tiangong 1 entered space. Any 'spying' could only be done if the two vehicles got to the intersection point at the same time. That would have happened naturally at intervals because of the orbital periods being slightly different, but at a relative speed of over 15,000 kilometres per hour and the 62° closing angle, there would not be much time for the X-37B to train its sensors.

Unfortunately for the item's author, Spaceflight magazine, the British Interplanetary Society and BBC News, the story is clearly nonsense. Interestingly, the 'Tweet' that first drew attention to the story was quietly deleted and no longer appears in the BIS Twitter history.

TG-1 & OTV-2 intersection


Page Date: 2012 Jan 17

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