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Comment by zymhan | Hacker News Reader

> On the way down, the main engine cut out. The engine was successfully restarted, but then communications were cut off, and no more information was sent back.

Definitely a terrible time to have an engine failure :/

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Based on the telemetry from the broadcast it seems that there was a failure at 13km that resulted in both telemetry and engine loss. When telemetry connection came back vertical speed has already doubled and it kept going up until spacecraft hit the ground. Engine was probably never restarted.

Edit1: Telemetry came back at 10k. For the next minute and a half there was uncertainty about the main engine even though telemetry clearly showed vertical speed going up fast. More then a minute later, at 5k a reset request was made.

Edit2: A minute goes by and at about 500m controller asked if there is a confirmation to send rest to JPL, another, announced that engine is on. Crash happens at that moment. 149m, 134.3ms vertical.

>900m/s horizontal.

Was the request to restart the engine made from Earth?

It seems like the landing program would want to have a feature in place that automatically restarted the engine in a situation like this.

From the NY Times story “We are resetting the spacecraft to try to enable the engine.”

I can't tell from that if normally an engine outage would automatically restart but didn't or if the condition would always require manual intervention. I hope we get more details soon. The moon seems close enough (a few seconds), but accidents always happen closest to your destination. More automation is more complexity but it will be valuable for longer trips.

When they said the engine had a problem the altitude was 678m and vertical velocity was 130.1m/s. After restart it was 149m at 134.3m/s. They never had a chance. Assuming those numbers were correct. A few minutes before they had lost the intertial measurement unit.

then communications were cut off, and no more information was sent back.

Have any of these moon landings been done at night where people have been able to watch it happening through a telescope? Or are things so small at the moon's distance that there'd be nothing to see?

It might be a stretch to call it a landing, but the LCROSS mission maneuvered a Centaur upper stage to a controlled crash on the moon. IIRC it was done at night so that telescopes on Earth could see it, but none actually did.

Actual landers tend to try to land during lunar day, to take advantage of the warmer temperatures and to have sunlight to recharge batteries.

Just watched the ted talk from the woman who came up with the algorithm to photograph the black hole and she had a slide of the best picture we can get of the moon from earth and she said each pixel on that picture could fit something like 600,000 oranges. don't think it's possible that we can see a spacecraft landing on the moon with what we have.

The resolution a 10 meter telescope on Earth can make out of the moon is about 22 meters per pixel. We can yet make out the moon landing site with earth based telescope.

Making a 23 metre mark on the moon seems like a natural project for some country, then. Perhaps easier than orchestrating a soft landing.

There are lunar retroreflectors about a metre across [0] that are detectable with optical equipment, for some definition of optical. But to leave a mark that can be seen from earth - to leave your tag, or an X, or a crude drawing of a penis and testes - surely that's an urge as old as art itself.

[0]https://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/...

When is it not a terrible time to have an engine failure?

When you're floating along on a stable orbit not about to impact the surface.

Or with more time to recover from the outage before landing. If it happens within the last minute (wild estimation) then you have little time to recover the lost velocity.

When you are floating along on a stable orbit the engines are off, so it's quite hard to have a failure in this context.

Maybe the failure occurs as you are initiating acceleration burn, while you are in stable orbit.

They could fail to ignite if you were attempting a burn from a stable orbit into another orbit.

But you're still having an engine failure when the engine is far away from anyone that could potentially start mending it.

Not an engine failure, but: "Debugging a program running on a $100M piece of hardware that is 100 million miles away is an interesting experience." http://www.flownet.com/gat/jpl-lisp.html

"failure" does not necessarily imply it is permanently disabled. It just means the engine stopped working as expected at some point.

Obviously they restarted it after this failure so it was not a complete breakdown of the engine.

When you have redundant engines??

I was on a plane that had one engine fail. It was fine.

While parked on the surface.

Gotta be a terrible "oh man we're back up---- nope" moment :(

It was. Some people in the audience were clapping when the announcement came that the engine was back on, but quite a few other people were shaking their heads and shushing them.

There was mention there about IMU issues - losing track of where you're pointing, then trying to recover could mean you're pointing the wrong way (while still running the main engine ....)

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