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In this video recording of Orion's reentry, you can hear and see the RCS thrusters firing during the communication blackout phase.

enter image description here

During the communication blackout, I would assume that GPS would not be able to receive signals. Do capsules implement some kind of inertial navigation, or do they just forgo using real-time position information during the reentry phase?

Either way, is the navigational error during the communication blackout phase small enough that capsules can course-correct after the blackout ends using GPS, and then touch down at a precise location?

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  • $\begingroup$ I don't think the capsule is steering for a ground target at that point, it's more likely using RCS thrusters to maintain its orientation against the airflow. $\endgroup$ Commented Mar 18 at 22:21
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    $\begingroup$ Not an answer to the question, but Ballistic missiles would pretty much be exemplars of inertial only space travel and even early ones could get at least the right city. $\endgroup$ Commented Mar 19 at 13:35

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The Orion capsule uses inertial guidance.

Honeywell provides Orion’s Inertial Measurement Unit that includes a three-axis gyro system to accurately track spacecraft attitude and body rates throughout the mission from liftoff to splashdown. The OIMU uses radiation hardened components and is internally redundant to ensure proper functionality throughout all mission phases. IMU data is augmented by GPS data that is used to determine the spacecraft’s position in near-Earth space.

Source

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    $\begingroup$ It is possibly worth noting for those born after GPS became a thing that the current crop of vehicles are the first to use GPS at all and all prior space missions happily did their thing using inertial navigation with occasional ground fixes. How regularly did Shuttle get fix updates? Where there any mission rules on initiating a return if fixes had been unavailable for X hours due navigational uncertainty? $\endgroup$ Commented Mar 19 at 13:29
  • $\begingroup$ @GremlinWranger that would be a good question! $\endgroup$ Commented Mar 19 at 18:35
  • $\begingroup$ @GremlinWranger BTW, shuttle used GPS. Late in the program. $\endgroup$ Commented Mar 20 at 2:48
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In supplement to Organic Marble's answer for position and using their source from a different question.

Along with knowing WHERE the vehicle is during the re-entry blackout phase the onboard navigation system also needs to know orientation if it is to do any active control of trajectory.

For the STS, mission rule A8-110 rationale indicates that a worse case IMU would still maintain the needed angular accuracy for 25 hours from last star alignment, giving plenty of time to achieve a re-entry that one way or another will be over in an hour.

Orion and similar capsule type vehicles are probable more tolerant of sub-optimal orientation during re-entry than the winged STS and presumably able to meaningfully navigate with longer periods between angular update and re-entry.

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  • $\begingroup$ Did you mean "winged Space Shuttle"? BTW, interesting source! $\endgroup$
    – phil1008
    Commented Mar 21 at 9:39
  • $\begingroup$ @phil1008 oops, mixed up my abbreviations, was trying to differentiate 'The Space Shuttle' from Buran, X37 and future winged things and made it MORE confusing. $\endgroup$ Commented Mar 21 at 10:18

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