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SpaceX CRS-20 Launch

Tyneside, UK
2024 Jul 24
Wednesday, Day 206

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SpaceX CRS-20 - Falcon 9 Re-entry

For the third time recently, SpaceX is planning a major manoeuvre by a Falcon 9 upper stage after it has delivered its payload into orbit. A Navigation Warning for re-entry of the rocket that will deliver the Dragon CRS-20 mission to space defines an area that is not in keeping with the 51°.6 inclination orbit for a spacecraft heading for rendezvous with the ISS.

The rockets for two other, previous, missions also exhibited major changes to the orbit after releasing their payloads. One was the vehicle that carried a Dragon on the CRS-19 mission in 2019 where the orbit inclination was raised by 6-7 degrees before the deorbit burn.

The other was the Falcon 9 used for an X-37B space plane on the OTV-5 mission back in 2017. It seems to have deposited the X-37B into an orbit at 54°.5 then shifted its own inclination to 63° before disposal.

There may be other similar events that were not documented at the time.

Why the Manoeuvres?

SpaceX has many missions planned for the next few years. These orbit changes may be tests relating to re-starts of the Falcon 9 upper stage engine after a few hours in space, simulating launch missions involving a long coasting period between engine firings.

Dragon CRS-20

The re-entry zone for the Falcon 9 has already been published in the form of a maritime navigation warning for an area of the south Pacific Ocean. In the cases of the the CRS-19 and X-37B launches, the manoeuvre and re-entry occurred a small number of hours and multiple Earth circuits after lift-off. For the CRS-20 mission, it will occur during the very first circuit of the Earth.

The plan seems to be for the Dragon spacecraft to be released 9-10 minutes after lift-off, presumably into a ‘standard’ 200 x 380 km orbit at 51°.6 inclination. From there it will chase-down the ISS.

After that, when it is a safe distance from Dragon, and at about L+25 minutes, the Falcon 9 will re-start its engine to change its inclination to 47°.8 and lower perigee sufficiently to cause re-entry. It will enter the atmosphere shortly after the orbit’s southern apex at about L+65 minutes. Surviving debris will start to fall through the atmosphere a couple of minutes later and the event will continue for several minutes as lighter items of surviving debris will glide or float rather than plunge through the air.

The zone lies on an orbit arc between 163° west and 143° west that extends from 41° south up to 28° south.

Where the previous examples involved the Falcon 9 dwelling on orbit, the CRS-20 re-entry is planned for at the earliest opportunity. As it does not involve a long ‘coast’ it is always possible that the purpose of this particular burn is to deplete residual propellant before re-entry as a simple retro-fire event might not use it all.

Page Date: 2020 Mar 1

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