The Moon is a harsh mistress [Beresheet failure]

[Tim_T-Bonham.net]

@DPRK

Why would a single accelerometer be critical? Weren’t there at least a couple more?

Well, my guess is that there are 2 factors:

1. every bit of excess mass must be eliminated in space, and
2. they were doing it as cheap as possible.

If it turns out that a 2nd one would have saved the mission, then it is NOT excess, and that not including it was a very expensive wrong decision. But that often happens when doing things for the first time.

[Northern_Piper]

@Alessan

Thanks. It was not a fun experience, watching it live last night with my family. My son - who’s into space - was crying a bit, and I needed a few shots of bourbon myself to avoid joining him. Oh well.

We’ll do better next time.

I’m sorry it happened, but you’re right: there will be a next time!

Alessan, you might want to share this quotation with your son:

@John F Kennedy

We choose to go to the moon in this decade and do the other things, not because they are easy, **but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept… **

[N9IWP]

More info:

Software Command to Fix Faulty Sensor Doomed Beresheet

The command to fix the faulty IMU somehow caused a cascading failure.

Brian

[DPRK]

Thanks for the update. We’ll have to wait for the promised report, but it sure sounds like software or programming error. Interesting that they also felt the need to remotely reboot various subsystems in the middle of landing while also subject to spotty comms (and that there was no backup to withstand a “cascading failure”).

Now, apparently a bunch of NASA space probes and Mars missions have used VxWorks as a computer operating system for their platform. What hardware and software do SpaceIL use? How about SpaceX? What are the various “industry standards”, if any?

ETA: This discussion suggests that SpaceX has adopted some form of Linux

[swampspruce]

Linux. Because BSOD in Space is a bad thing…

[DPRK]

Some info on the (SpaceX) hardware:

SpaceX uses an Actor-Judge system to provide triple redundancy to its rockets and spacecraft. The Falcon 9 has 3 dual core x86 processors running an instance of linux on each core. The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the “flight string” compares the results from both cores. If there is a inconsistency, the string is bad and doesn’t send any commands. If both cores return the same response, the string sends the command to the various microcontrollers on the rocket that control things like the engines and grid fins.

The microcontrollers, running on PowerPC processors, received three commands from the three flight strings. They act as a judge to choose the correct course of actions. If all three strings are in agreement the microcontroller executes the command, but if 1 of the 3 is bad, it will go with the strings that have previously been correct. The Falcon 9 can successfully complete its mission with a single flight string.

The triple redundancy gives the system radiation tolerance without the need for expensive rad hardened components. SpaceX tests all flight software on what can be called a table rocket. They lay out all the computers and flight controllers on the Falcon 9 on a table and connect them like they would be on the actual rocket. They then run a complete simulated flight on the components, monitoring performance and potential failures.

SpaceX engineers perform what they call “Cutting the strings” where they randomly shut off a flight computer mid simulation, to see how it responds.

Dragon uses a similar triple redundant system for its flight computers.

[Darren_Garrison]

The splatting site has been found.