By Duncan Steel 02/07/2019


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On Saturday June 29th Rocket Lab launched another cluster of seven satellites into low-Earth orbit from the Mahia Peninsula in New Zealand’s North Island. In this blog post I illustrate the orbital paths of the ten resultant tracked items now in orbit. 

In a blog post last week (June 27th) I showed the orbits of the various satellites launched by Rocket Lab through to that date. Following the launch last Saturday I added a note to that post, as follows:

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).

The present post fulfills that promise (or maybe it was a threat…).


The June 29th launch was given the name Make It Rain. Information on the seven satellites involved is given on the Rocket Lab website here. The satellite operators doubtless know the orbits that their payloads are following, but quite independently the US DoD network of sensors tracks all detectable objects and make the orbits available. A list of the items lofted by this launch and now being tracked in orbit is as follows:

The orbital elements of the above are available from, for example, the CelesTrak website here.

The positions of the satellites as at 18:00 on Tuesday July 2nd NZST (about 30 minutes after I am writing these words) are as shown by the white dots in the header graphic of this post. Immediately below is a graphic also showing their locations, with a tilted viewing geometry (so as to make the labels a little clearer). It happens that at that time (or thereabouts) the satellites will be passing over Alexandra in Central Otago, where the headquarters of the Xerra Earth Observation Institute (for which I work) is located. I am not so far away at present, at a team meeting in Wanaka.


In my previous post I explained the rather convoluted labels/names attached to each of these objects.

The purple lines show the orbital paths of ten objects. They are moving in prograde orbits (from west to east) and tilted by about 45 degrees to the equatorial plane. Two items in slightly-lower orbits are apparently parts of the main Electron rocket body. Due to the fact that their orbits are lower, those two (labelled H and J) are substantially separated from the other eight items in higher orbits.

Those eight apparently comprise the seven functional satellites (labelled as A through G) plus one other object (K) which is, I would imagine, the apogee kick motor used to boost those seven into their intended orbits.

A movie that follows the paths of all ten objects over five hours from 17:30 until 22:30 today NZST (2019 July 2nd) is available for anyone to download from here. It is 200 seconds long, and occupies 110 MB.

Please feel free to use that movie plus the graphics above for any good purposes (such as for educational uses, or displaying on your own websites). The more that people know about New Zealand’s entries into space, the better.

 


 

Addendum, July 8th: It is now almost a week since my post above, and some things have changed regarding the objects placed in orbit by the Rocket Lab launch on June 29th.

All orbits alter in time, due to a variety of effects. In the blog post above I stated that there were two rocket body components left in orbit, which I labelled as Electron_RB_2019-037H_44372 and Electron_RB_2019-037J_44373, and I have explained just what those lines of characters imply. As shorthand, herein let’s just call them 037H and 037J.

It happens that 037J, having a low perigee and being subject to substantial atmospheric drag, re-entered and was destroyed in doing so, on July 3rd. If you want to take a look at past or forthcoming (i.e. predicted) re-entries, then a good web resource to access is that maintained by The Aerospace Corporation; take a look here, in particular.

This means that only component 037H of the Electron launcher (as opposed to the apogee kick motor, apparently 037K) is left in orbit. In the diagrams below the path of 037H is shown in red.

 

Locations of orbiting objects from the Rocket Lab launch on June 29th, as at 12 minutes to noon (NZST) on July 9th, and then at 22 minutes after noon. The red path is that followed by the remnant Electron rocket body; the green orbits are those of the seven satellites constituting the payload, plus the apogee kick motor.

Also shown in the diagrams above are the satellites placed into 45-degree inclination, near-circular orbits. In the left diagram the time was chosen so as to show how these are spread along the orbit. In the right diagram, for 34 minutes later, the Electron rocket body 037H is seen, apparently lagging behind the payload satellites; in fact, 037H being in a lower orbit, it is travelling faster than 037A, B, C, D, E, F, G and K, and so catching them up from behind (and below).

A movie (WMV format, 45 MB, 132 seconds long) showing all these objects orbiting the Earth is available by clicking here. The time-step in the movie is 10 seconds, making it a more-than-three-times-faster depiction than the movie linked in the post above. It follows the orbits for eleven hours from 06:22 on July 9th NZST (18:22 on July 8th, UTC).

One thing to note is as follows. The rocket body (red path) is in a lower orbit than the payload satellites (green paths, much the same as each other). Due to the differing altitudes, the precession rates (due mainly to the Earth’s gravitational field being non-spherical) are not the same. As a consequence, ten days after these objects were launch the red orbit has precessed/swivelled by a different amount to the higher green orbits, and a small angle is apparent between them.