A new launch attempt for ZUMA

Probable launch trajectory of ZUMA
(click map to enlarge)

 UPDATE 4 Jan 2018 22:00 UT: The launch has again been postponed by one day, to January 7th (January 6 local time)

If it isn’t delayed again, SpaceX will finally launch the secretive classified ZUMA satellite for the US Government on January 6th (January 5th local time in the USA) from Kennedy Space Center pad 40 in Florida. The launch already has slipped one day from the initial January 5 aim.

The satellite was originally to be launched last November (see an earlier post) from Kennedy Space Center pad 39A but was postponed because of  issues with the payload fairing.

The launch hazard zones and the Falcon 9 upper stage de-orbit zone as gleaned from the Maritime Broadcast Warnings are virtually the same as in November, as was to be expected (there is a very small lateral shift in the launch hazard zone, which is probably related to the change in launch pad, but the direction of the area is the same). They are depicted on the map above.

From the launch azimuth (as gleaned from the launch hazard zones) and the location, extent and time window of the Falcon 9 upper stage de-orbit area, ZUMA will be launched into an approximately 50 degree inclined Low Earth Orbit. In the map above, a trajectory has been plotted for launch into a 50 degree inclined, approximately 400 km orbital altitude orbit. The orbital altitude is a bit uncertain and the eventual real orbit might be higher.

The launch window runs from 1:00 UT to 3:30 UT (January 6th). The de-orbit of the Falcon 9 Upper stage happens some 2 hours after launch over the southern Indian Ocean north of Kerguelen, halfway during the 2nd orbital revolution.

As remarked in my earlier post from November, the launch hazard area and the apparent orbit aimed for as decuced from these hazard zones seem to be very similar to that of USA 276, the classified SpaceX launch for the US government from May 2017 which went into a 50 degree inclined, 400 km altitude orbit (see my article in The Space Review of July 2017). Compare the launch hazard zones of these two launches, they are very similar:

Launch hazard area of ZUMA (red) compared to that of USA 276 (blue)
(click map to enlarge)

Back in November there was some speculation that ZUMA might target the ISS orbital plane, just like the odd classified satellite USA 276 appears to have done last year (see my article in The Space Review of July 2017).

For the initial launch date and window in November 2017, the orbital planes of the ISS (and USA 276) would have passed over the launch site during the launch window, allowing a launch into the same orbital plane.

The new launch window for January 6th is the same as it was in November: 1:00 UT to 3:30 UT. This excludes a launch (exactly) into either the ISS or USA 276 orbital planes, as the latter only pass over the Florida launch site after the launch window has ended.

This would seem to suggest that the coincidence in time of the launch window and orbital plane passages in November was indeed coincidence (but there is a “but”: see below…).

On January 6th, the orbital plane of USA 276 passes over the launch site around 4:27 UT, an hour after the end of the launch window. The orbital plane of the ISS passes over the launch site around 7:04 UT, some 3.5 hours after the end of the launch window.

The image below shows the spatial separation of the orbital planes for launch on January 6th.  For ZUMA, two planes are given (in red), one for launch at 1:00 UT and one for launch at 3:30 UT, representing the start and end of the launch window:

Relative positions of orbital planes of ZUMA (red), USA 276 (blue) and ISS (white)
(click map to enlarge)

The USA 276 orbital plane is actually not too far from the ZUMA orbital plane if launch occurs near the end of the launch window.

The launch already has slipped one day, and a few days further delay would slip the passage of the USA 276 orbital plane back into the launch window, as the moment of orbital plane passage shifts about 24 minutes earlier in time each day. This would happen already with a 3-day delay in launch. And a further delay eventually would do the same for the ISS orbital plane passage after several more days.

[UPDATE 4 Jan 2018 22:00 UT: indeed a further delay is happening: launch has been postponed again by one day to January 7th. – end of update]

At any rate: if launch is near the end of the launch window (i.e. near 3:30 UT), the ZUMA and USA 276 orbits could end up relatively close, albeit not being exactly the same.

Like we pressume USA 276 to be, ZUMA probably is a technology demonstrator, i.e. an experimental satellite to show that a particular technology is feasible.

I could speculate that perhaps ZUMA and USA 276 are part of the same experimental program. As these two spacecraft were built by two different companies (Northrop-Grumman and Ball Aerospace), perhaps they are technology demonstrators in competition for a follow-up contract. But this is pure speculation.

Exactly how (if at all) the two satellites are related to each other remains murky. Maybe future orbital behaviour will shed some light on what ZUMA is doing.

For a further discussion of the ZUMA mission, see my earlier post from November 2017. Some TLE estimates for the orbit are here.Source sattrackcam.blogspot.com