Tuesday, 3 December 2019

An interesting CRS-19 Falcon upper stage deorbit area (UPDATED)

click map to enlarge
The Maritime Broadcast Warnings with the hazard areas for the upcoming December 4 SpaceX DRAGON CRS-19 supply mission to the ISS have appeared a few days ago.

These include a Broadcast Warning for the Falcon 9 upper stage deorbit area. And that deorbit area (depicted in red in the map above) has an odd position and timeframe:

HYDROPAC 3933/19

DNC 02, DNC 03, DNC 04.
042302Z TO 042344Z DEC, ALTERNATE
052240Z TO 052322Z DEC
58-52S 050-29E, 55-59S 052-23E,
55-26S 059-28E, 54-58S 065-18E,
54-08S 073-22E, 52-46S 083-57E,
51-25S 091-09E, 49-01S 100-13E,
46-34S 108-49E, 44-49S 113-54E,
46-47S 116-19E, 52-02S 109-55E,
52-57S 108-32E, 56-09S 102-10E,
59-05S 092-54E, 61-08S 081-09E,
61-48S 071-27E, 61-08S 060-26E.
2. CANCEL THIS MSG 060022Z DEC 19.//

Authority: PACMISRANFAC 250217Z NOV 19.

Date: 290929Z NOV 19
Cancel: 06002200 Dec 19

With DRAGON CRS launches, the Falcon 9 upper stage deorbit usually happens in the second part of the first revolution, south of Australia or in the southern Pacific. See e.g. the deorbit area for the Falcon 9 upper stage of CRS-17 from May this year, depicted in blue in the map above.

But not this time. The Maritime Broadcast Warning above suggests that the CRS-19 upper stage deorbit happens much later, about 5.5 hours or 3.5 revolutions after launch. In addition, the area is shifted southwards compared to the CRS-19 ground track, indicating a deorbit from an orbital inclination clearly higher than the 51.6 degrees orbital inclination of the DRAGON. In fact, it fits an orbital inclination in the order of of 57-58 degrees, i.e. some 5 degrees higher in inclination.

So that is odd.

The prolonged on-orbit time might be a coasting test with an eye on future missions that require coasting over several revolutions. The indicated inclination change might likewise be a test for a future mission requirement.

I have been entertaining the possibility of an undisclosed cubesat rideshare, to a ~58 degree inclination orbit. But that remains pure speculation and is perhaps not very likely.

Note: in the map in top of this post, the dashed white line is the DRAGON CRS-19 trajectory up to 23:45 UT (Dec 4), the end of the timewindow given by the Maritime Broadcast Warning for the Falcon upper stage deorbit.

UPDATE 4 Dec 2019 10:15 UT:

During the CRS-19 pre-launch press conference yesterday, the SpaceX Director of Dragon Mission Management, Jessica Jensen, said the Falcon 9 upper stage is doing a "thermal demonstration" after the CRS-19 orbit insertion, that amounts to a six-hour coasting phase:

In reply to reporter questions she provided slightly more details somewhat later in the press conference, adding that the test is done at the request of a customer for future missions that require a long coast. During the long coast phase, they will a.o. measure the thermal environment in the fuel tanks. The apparent ~5 degree orbital inclination change was not mentioned:


jim oberg said...

Can we estimate a deorbit burn location and lighting conditions with the goal of anticipating visual observation from the ground?

jim oberg said...

Can we compare delta-V for a plane change of this magnitude [440 ft/sec per degree of inclination] , combined with the deorbit burn, versus GTO burn to circular GEO at apogee?