There’s a couple iconic photographs from space that everyone is familiar with. The most recognizable is probably this one I used a couple years ago during the 40th anniversary celebration of the Apollo missions showing Buzz Aldrin standing on the dusty surface of the moon. A few other notables are ones like Earthrise, The Pale Blue Dot and the STS-1 mission liftoff (note the white external fuel tank, one of only 2 to have it) but above them all stands the Blue Marble, an incredibly breath taking view of our earth as seen by the Apollo 17 crew on their mission to the moon.
It’s a beautiful photo and one that changed my, and certainly many others, view of the world. I don’t know why I used to think this but before seeing this picture I imagined the world being mostly cloudless, not covered in the swaths of thick cloud that you see in the picture above. It also puts your entire life in perspective, much like the Pale Blue Dot does, knowing that in the end we’re all clinging to this giant water covered rock shooting through space.
Over the years NASA has set about recreating the Blue Marble as technology progressed, mostly just as an aside to one of their many Earth sensing programs. The big difference between the original and these subsequent releases is that the newer ones are composite images, I.E. they’re not a single photograph. You can see this quite clearly in the 2005 version which shows how the Earth would look like if there was no cloud cover, something that’s simply impossible to photograph. The most recent addition to this lineage of whole Earth pictures is the Blue Marble 2012 and it’s quite spectacular:
The original picture is some 8000 x 8000 pixels large (64 megapixels) and gives you an incredible amount of detail. The resolution is high enough for you to be able to pick out topographical details with relative ease and you can even see the shadows that some of the clouds are casting on the ground below them. The original article that was linked to me had a lot of interesting comments (a lot on how the Americas appear to be somewhat distorted) but one that caught my attention was a question about one of the differences between the two pictures.
Why, they asked, is there no thin blue halo in the original picture?
The halo they were referring to is clearly visible if you view the larger version of the new Blue Marble picture and seems distinctly absent in the original. The planet hasn’t radically changed (geologically, at least) in the time between the pictures so the question is a curious one. To figure this out we have to understand the differences in how both these images came to be and in there is where our answer lies.
The original Blue Marble was taken by a single 70mm Hasselblad camera with a 80mm lens at a distance of approximately 45,000KM away from the Earth. The newer version is a composite reconstruction from several images taken by the Suomi NPP satellite which orbits at around 500KM above the Earth’s surface. Disregarding the imaging technology used and the reconstruction techniques on the modern version it becomes apparent that there’s a massive difference in the distance that these pictures were taken. Looking at the halo you’ll notice that it’s quite small in comparison to the size of the Earth so as your distance from Earth increases the smaller that halo will appear. So for the original Blue Marble the halo is pretty much invisible because the resolution of the camera is insufficient to capture it. The newer picture, being much closer and having a higher effective resolution, is able to capture it.
These kinds of images are always fascinating to me, not just for their beauty but also for the story behind what went into creating them. The number of man hours that went into creating something like this that appears so simple is staggering and demonstrates that we, as a species, are capable of great things if we put our minds to it. The Blue Marble 2012 might not become the icon that its predecessor was but its still an awe inspiring image to look at and even more interesting one to contemplate.
The USA has always been wary of China’s ambitions in space and I believe it’s mostly for all the wrong reasons. Sure I can understand that the fact that China’s space division is basically a wing of its military might be cause for concern, but the same could be said for the fact that the USA’s Department of Defense’s budget for space exploration exceeds that of NASA’s. Indeed the USA is worried enough about China’s growing power in space and other industries that there’s already been speculation that it could spark another space race. Whilst this would be amazing for a space nut like myself I really wouldn’t wish that kind of tension on the world, especially when the USA is struggling as much as it is right now.
Of course that tension is enough to spark all sorts of other speculation, like for instance the true nature of the mysterious X-37B’s mission. It’s payload bay suggested that it was capable of satellite capture, an attribute shared by it’s bigger cousin the Shuttle, but its previous orbits didn’t put it near anything and it didn’t really have enough delta-v capability to be able to intersect with anything outside a few degrees of its own orbit. However since then there’s been a couple launches and one of them is smack bang in the X-37B’s territory.
The craft in question is none other than China’s Tiangong-1.
Yesterday the BBC ran an article that speculated that the USA was using the X-37B to spy on Tiangong-1. Now initially I dismissed this as pure speculation, there are far easier ways for the USA to spy on a satellite (like using one of their numerous other satellites or ground based dish arrays) than throwing their still experimental craft up in a chase orbit. However checking the orbital information for both Tiangong-1 and the X-37B shows that they do indeed share very similar orbits, varying by only 0.3 of a degree in inclination and having pretty similar apogees and perigees. Figuring this is the future and everything should be a few Google searches away from certainty I set about finding out just how far apart these two satellites actually are to see if there was some possibility of it being used to spy on China.
To do this I used 2 different tools, the first being n2yo.com a satellite tracking website. This site allows you to input the satellites you want to track and then displays them on a Google map. Once I have that I can then use another tool, this time from findpostcode.com.au which shows me the distance between two points (which thankfully also takes into account the fact the earth isn’t flat). So firstly here’s a picture of the two orbits overlapped:
So as you can see they do indeed share very similar orbits but there does seem to be an awful lot of distance between them. Just how much distance? Well the second picture tells the full story:
Just over 14,000KM which is greater than the diameter of the earth. What this means is that if the X-37B was being used to spy on Tiangong-1 it would have to peer through the earth in order to see it, something which I’m pretty sure it isn’t capable of. Also if you look at the first picture you’ll also notice that Tiangong-1 actually passes over the USA as part of its normal orbital rotation, putting it well within the purview of all the ground observations that they have control of. I’ll note that the distance between Tiangong-1 and the X-37B won’t remain constant, but they will spend a good portion of their lives apart. Enough so that I don’t believe it would be particularly useful for reconnaissance. Additionally unless the USA knew which orbit that Tiangong-1 was going to use (possible, but we’re getting deeper into conspiracy territory here) then technically Tiangong-1 launched onto the X-37B’s orbit and not the other way around (it has not changed its orbit since the second launch, unlike it did the first time).
Honestly the idea that the USA was using the X-37B was definitely an interesting prospect but in reality there’s really no justification apart from conspiracy theory-esque hand waving. The USA has far better tools at their disposal to spy on China’s fledgling space industry than a single run experimental craft that’s only on its second flight. The orbits also put them at a fair distance apart for a good chunk of the time (as far as I can tell, at least) as well making it even less likely that the X-37B is being used for spying. Still it was an interesting idea to investigate, as is most things to do with the ever mysterious X-37B.