By Duncan Steel 27/06/2019


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With so many thousand satellites now in orbit, and tens of thousands of other tracked items, one might think that it is difficult keeping tabs on them, simply as an interested person. In fact it is quite straightforward, with long lists of orbital elements freely available for all except the few satellites deemed by the US Government to require secrecy, and of course one might find information about those in other ways. There are also many applications available to peruse what might be passing overhead at any time, plus sophisticated software tools that are free and make use of the very best algorithms for following how the various orbits alter over weeks and months. 

In a press release issued yesterday the NZ Space Agency has announced that it has partnered with US company LeoLabs on a “project which allows officials to see real-time information on the orbital position of satellites launched from New Zealand.” This is a vitally important thing for the NZSA to be able to do. LeoLabs had earlier posted a two-minute video on YouTube showing what is involved.

It sounds fairly complex, but actually it is quite straightforward. In a blog post in early April I discussed and displayed the orbit of the R3D2 satellite, which had been launched from the Mahia Peninsula by Rocket Lab a few days previously. Today I have spent a couple of hours extending this to all 28 satellites that Rocket Lab has put into geocentric orbit, plus the three Electron rocket bodies/kick motors* also left up there, making 31 objects in total.

(*Actually there is a fourth kick motor still in orbit, utilised in the launch last November and attached to the NABEO-1 module, the intent of which is a test of a drag mechanism for causing a more-rapid fall from orbit, thus limiting the amount of junk circuiting Earth and posing a hazard to other satellites.)

Just below is a still frame showing where those orbiters will be at precisely 3:23 pm (NZST) on Friday June 28th; admittedly you can only see those on one side of the globe. If you would like to see them all, I have made a 36-second movie that displays the motion of each of the 31 objects over the three hours starting at noon on Friday June 28th, again NZST (or, twelve hours earlier on Universal Time, UTC). The movie file occupies 22 MB, and can be downloaded from here. Please feel free to use it for educational or other purposes. Note that the downloaded movie is far clearer than the version you see if you merely run it online.

Where the various satellites launched so far by Rocket Lab will be at 3:23 pm on Friday June 28th. The colour coding indicates which launch placed that object into orbit, as indicated by the display at upper left.

In the graphic above one might note that there is a bewildering array of names; I will explain their formats now. The first thing to look at is perhaps the five-digit number at the end of each name (e.g. 43164). This is the Satellite Catalog Number, which is often termed the NORAD Number or some variant. It is a sequential listing that starts with the initial space launches in the late 1950s though the system was not introduced until a few years later.

The earlier part in each satellite label comes in one of two types. Most of these are either formal or informal identifiers, which may contain multiple aspects. For example Electron_Rocket_Body_44227 in red is the kick motor that placed three functioning satellites into near-circular orbits on May 5th this year. Irvine-01_43693 in green is a 1U (one-unit) CubeSat built by pupils from five high schools in Irvine, California, supported by the Irvine Public School Foundation and launched last November 11th. (Wouldn’t it be wonderful to see something like that happening in NZ schools?)

Other labels are a bit more long-winded. For example: TOMSat-EagleScout-AeroCube-11A_43861, in white (launched on Beethoven’s birthday last year). TOMSat stands for Testbed for Optical Missions Satellite. EagleScout differentiates this satellite from TOMSat-R3, both of which shot aloft on the same launch on December 16th as Irvine-01 and ten other CubeSats. Providing extra redundancy in naming, the two TOMSats are also called AeroCube-11A and -11B, being twin 3U CubeSats that carry multispectral push-broom sensors having the same wavelength band coverage as the far-larger Landsat-8 satellite’s Operational Land Imager (OLI), which was launched by NASA in 2013 and is operated by the US Geological Survey. Phew!


Of the 31 orbiters, six have labels that look something like this: COSPAR-2018-104K_43858. You know (from the above) what the five digits on the end mean. The six have such numbers running 43851, 43853, 43854, 43858, 43859 and 43862. All contain the string 2018-104 (which as we will see, implies that they were all launched by the same rocket). The letter following that string is C, E, F, K, L and P respectively.

So, what is this about? The COSPAR I inserted myself, to indicate that the labels are based in part on the COommittee on SPAce Research designations (otherwise known as the International Designator). As for all such appellations, the first four digits indicate the year of launch (2018), the next three show the chronological launch sequence during the year (i.e. the December 16th launch by Rocket Lab was the 104th globally during last year), and the subsequent letter is used to label all the satellites, boosters and fragments that result from that launch. In the case of a satellite disintegration some time (months or years) post-launch, the lettering can get highly complicated with hundreds or even thousands of debris pieces being identified and tracked from the ground.

So, why do this six not have allocated names, instead merely alphanumeric designations? A good question. By comparing the list of satellite names apparently launched together one can deduce that the six are ALBus, CeReS, NMTSat, RSat-P (the preceding four all being 3U CubeSats), CubeSail-A and CubeSail-B (though the final two are tethered together by that ‘sail’). As to which of those five/six should be associated with each of the six letters C, E, F, K, L and P, however, is not clear. All five/six are owned/operated by institutions in the USA. Possible assignations are given in this rather nice list of objects in orbit: C=NMTSat; E=CeReS; F=RSat-P; K=CubeSail-A and -B (i.e. conjoined); L=ALBus; and P is debris from the Electron rocket/kick stage. (That last link I gave was a page on the excellent website of Jonathan McDowell, which is called www.planet4589.org. Why 4589? Because that’s the number of ‘his’ minor planet; go to this list and search for (4589) McDowell.)

The UN Convention on Registration of Objects Launched into Outer Space mandates that owner states should report certain pieces of information about each satellite inserted into orbit to the UN Office for Outer Space AffairsNew Zealand has registered one object: the Humanity Star, which was launched on January 21st 2018 and fell back into the atmosphere (its orbit ‘decayed’) a couple of months later, on March 22nd. In fact NZ’s accession to the Registration Convention only occurred two days after this launch. North Korea has registered two, having given them names.

The website of UNOOSA does not indicate any completed satellite registrations by the USA since October last year, although it seems that there is a long list of registration submissions from numerous countries being processed at the moment. Looks like someone is being a bit tardy. We will need to wait to discover for sure the full identities of those six miscreant CubeSats.

The reader might care to note that New Zealand is the most recent country to notify UNOOSA of the establishment of a space registry (on 27th November 2018), and the 41st overall.


Just to review the above: there can be (if the system works properly) multiple redundancies in the label put on any satellite; not by me, here, but in the tally sheet used for international information purposes. One is the Satellite Catalog Number (SCN) or NORAD Number (44074 and so on); the second is the International Designator (2018-104J and so on; note that letters I and O are not used); and the third is the name given to it. Thus the Hubble Space Telescope is both 20580 and 1990-037B.

How can one convert between different systems? That is, if you know part of the label, say the SCN, but want to know the rest, how can that be discovered? One simple solution is to go to the wonderful CelesTrak website, specifically this page. There, you can enter the Name, the International Designator, or the NORAD Catalog Number (i.e. SCN), and the lookup will – in most cases – quickly tell you the rest of the information pertaining to that space object.

CelesTrak is one place in which one can get the latest orbital elements available for most tracked objects in space. Another closely-related site is Space-Track. An alternative is at the Union of Concerned Scientists. Myself, I sometimes use one of those websites to look up a specific satellite, but generally I induct the latest available orbit for any object by using the facilities within the STK tool from Analytical Graphics, Inc. STK automatically accesses the listing at the Center for Space Standards and Innovation in Colorado, which operates the CelesTrak website.

In the first line of the preceding paragraph I wrote that the orbital elements are available for most tracked objects in space. What I meant was this. The above catalogues of orbiting objects are compiled at Air Force Space Command (currently undergoing some re-organisation as the US Department of Defense prepares to stand up a Space Force), using a range of US Government sensors. All detectable objects are listed therein – there is a limit to what any radar or optical system can pick up and track – except for a handful. Those are security-classified satellites of the US DoD or other intelligence-related agencies. However, even some satellites that were previously kept secret are now having information released via the Space-Track website. Examples of classified satellites include projects like Lacrosse, SBIRS, or Key Hole/Crystal, all of which have much information now openly available, as you can see from those Wikipedia pages.


Another question that might arise is this: given a sensor (a suitable radar, or optical telescope at night) located at a certain location in New Zealand, when might each of these orbiters be detectable? That is also a trivial question to answer, given suitable software and knowledge of the object’s orbit. In the diagram below I indicate the three satellites potentially detectable from Wellington at the displayed time on Friday afternoon.

Line-of-sight accesses to three satellites at the instant shown at the bottom of this graphic. A requirement input here was that each object had to be more than ten degrees above the horizon (zenith angle less than 80 degrees) from Wellington.

Just to show how dynamic the situation is, and how the line-of-sight accesses may be computed automatically, and in advance, I have made another brief movie (20 seconds long, data volume 12 MB) that can be downloaded from here (and, as previously, I suggest you download the movie so as to see it run most clearly). This clip covers just the half-hour between 3:15 and 3:45 pm NZST on Friday June 28th (i.e., tomorrow, as I write). Again, please feel free to make use of this movie, and/or the still frames in this blog post, for educational or other purposes.


Is it difficult to do the sort of things I have run through above, displaying the orbits of satellites circuiting Earth with the full accuracy feasible, given the orbital data available from the network of US Government sensors around the globe? No, not really.

The physics engine in the STK tool is really good; I have tested it out repeatedly over the past 15 years. The orbital parameters are the best available, usually based on the latest observations from the past two or three days, and in any case I run the SGP4 numerical integrator within STK (i.e. an algorithm which is best-in-class, allowing for orbital evolution due to the non-sphericity of our planet, the perturbations due to the Moon, the Sun, and so on). Indeed, in a poster I presented at the NZ Institute of Physics conference back in April, I argued that such work would be suitable for undergraduate student research projects.

My point here is that there is much we can do in New Zealand to encourage good students into studying suitable subjects preparing them for careers in space technology. Apparently Rocket Lab has a requirement for many skilled staff to be engaged, which is great for younger people here, who should be thinking now about what they could be doing a decade hence.

In the past adventurous types were told Go West, young man (please excuse the sexism, characteristic of the era). Nowadays one could argue that the direction to look to the future for young women and men is not at any of the cardinal points of the compass, but actually orthogonal to them. Look up, young people!

We are all in the gutter, but some of us are looking at the stars” — Oscar Wilde.

 


 

Update (June 30th): Congratulations to Rocket Lab on another successful launch yesterday. I will post here graphics and a movie of the orbits of the seven deployed satellites as soon as possible (perhaps a few days).