[dudeonthenet]

What i'm wondering is why is it that when the Inertial Measurement Unit erroneous information was fed into the navigation system, and resulted in a negative estimated altitude, didn't the mars lander also have an accelerometer that could tell "hey, we're still accelerating, we're not stationary" and thus attempt some form of recovery of the navigation system.. perhaps reset the IMU or something? Reread data from the IMU after a certain delay?

I'm also quite confident that even before commencing entry, they had some idea from simulations as to how much the descent should take. Surely there's something wrong f you read negative altitude after just half the time required for landing.

[fghgfdfg]

But you don't know which IMU is misreporting. Now, given the nature of the situation you could probably say it's best to err on the side of acceleration. If you've stopped accelerating and haven't initiated landing procedures you're either wrong or somehow already landed and can afford to wait.

It's also not clear to me that this was an issue of erroneous data. All they said so far was that a rotational sensor maxed out for about a second. I don't think a simple delay-and-retry would have sufficed here. When attempting to land a second seems like a pretty long wait.

[programmer_dude]

What's the difference between an IMU and an accelerometer?

[planteen]

IMU means gyro, that is, it measures rotational rates. Accelerometers measure translational rates.

[votingprawn]

> IMU means gyro

In aerospace the phrase IMU typically refers to the combination of accelerometers and gyroscopes.

[dudeonthenet]

Sorry, what I meant to say was a redundant IMU that could be read in specific cases like this one.