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Comment by beders | Hacker News Reader

It was heartbreaking to see the control room during the first few minutes after the landing.

Imagine a project you've worked on for years going kaput and you won't even know why. None of these engineers will find sleep tonight.

I hope some moon orbiter can take pics of the landing site soon.

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> you won't even know why

Not necessarily. We've frequently been able to determine the cause of unmanned spacecraft failures via telemetry and/or post-failure investigation. For example, https://en.wikipedia.org/wiki/Mars_Climate_Orbiter famously failed because NASA used metric and a vendor did not.

Foot pound second is such a weird unit. How did that pass the quality controls?

I also don’t understand how one team of educated engineers could decide to use imperial units instead of metric units.

As a former mechanical engineer, any calculations involving pounds in any form I pretty much always converted to metric and then back at the end if need-be. The trinity of pound-mass, pound-force, and slugs is incredibly easy to screw up--at least as a student.

Smh, Americans will literally convert into metric and back to keep using their bald eagles per shotgun squared units.

Admittedly, engineers are pretty much the only people making calculations with those kind of units and they generally use metric as far as I know. I went to school a long time ago and there were probably enough legacy imperial units hanging around that it seemed worthwhile to at least be exposed to examples you wouldn't have encountered in day to day living.

Since the 60s, America has literally been officially a conversion of standard SI units. A yard is defined as most of a meter (exactly 0.9144 meters) and an inch is derived from that.

Since the 60s? The yard measurement dates to sometime before the Norman invasion of England. And it's not even used that widely in the US outside of some specific contexts like sports. A gallon, from which a quart is derived is of a similar vintage. Without digging into history, I assume some SI volume and length measurements roughly mirrored existing Imperial units as opposed to the other way round.

The point is that the American units are now defined relative to metric units.

As recently as the 1800s, the yard was defined as:

"the Straight Line or Distance between the Centres of the Two Points in the Gold Studs of the Straight Brass Rod now in the Custody of the Clerk of the House of Commons whereon the Words and Figures "Standard Yard 1760" are engraved"

... That standard yard was destroyed in a fire in 1834, and a new standard yard was made using several copies of the original standard yard as reference.

But now, it's just defined as an exact fraction of a meter. First as 36/39.370113 m, now as exactly 0.9144 meters.

It's how literally all engineering in this country was done a single generation ago. When I studied mechanical engineering it was all units like slugs and foot-pound-second.

> A slug is defined as the mass that is accelerated by 1 ft/s2 when a net force of one pound (lbf) is exerted on it.[2] One slug is a mass equal to 32.1740 lb

this is like if you tried to explain the difference between a newton and a kilogram to an alien an they didn't quite get it

It's not that complicated. A slug is the Imperial unit of mass, like the kilogram. It's just that while in metric the unit of mass is primary and the unit of force (Newton) is derived, in foot-pound-second it is the reverse. Pounds is a fundamental unit of force and the slug is derived.

Pound force is the unit for force. Pound mass is the unit for mass. Colloquially people say pound.for both of them

This is true colloquially. In engineering (or at least aerospace engineering, which is what I was studying) we more generally used slugs for mass in our calculations. Gravity/weight isn’t always constant after all, even on earth.

Not universally. We still talked about a rocket’s “pounds of thrust.” But for things like angular momentum, center of gravity, etc. those were usually calculated with slugs.

Aerospace engineering is still a mix of both units. Especially on the aeronautics side, imperial is still widely used. Part of the reason for this is that past reference materials and tooling at many manufacturers still using imperial tooling. A team of good engineers is expected to be proficient with both unit systems --- its not really a big deal to use imperial on projects.

> its not really a big deal to use imperial on projects

but it does look pretty embarassing when it destroys a project

I guess an engineer should handle a imperial screw but deciding to use imperial units to exchange data in a software project seems so wrong.

Im American but have heard it’s common for 2-by imperial lumber units be used in Canada and uk for example. But metric would be used for cuts (which i think is easier often too)

Many years ago, probably about 40 years or so, I remember my dad pointing out plasterboard in the building supplies store that was marked as 1200mm x 8'6", because standard UK ceilings are 8'6" but everything else (kitchen units and appliances for example) are in multiples of 600mm...

Given a 2x4 is 1.75 by 3.75 inches, it sure doesn't make using Imperial measure any easier than metric. It's more that certain demographics are oppositional-defiant when it comes to change and they tend to make up the "base" of a powerful political parry.

Or another example, ESA's ExoMars lander cut its parachute and deployed itself 3.7 km above ground due to IMU saturation, thinking it was already landed.

https://www.esa.int/Science_Exploration/Human_and_Robotic_Ex...

Can confirm it was hard to sleep last night. I knew there was a high chance of failure but still, not the best evening.

Wow, so you worked on this project? That's awesome! Congratulations on making it to the moon!

According to the doppler telemetry analysis on Twitter, it entered free fall 90 seconds before loss of signal. So presumably the engine cut out and they have telemetry data to determine why. Most likely explanation: insufficient fuel.

> ispace engineers monitored the estimated remaining propellant reached at the lower threshold and shortly afterward the descent speed rapidly increased

https://ispace-inc.com/news-en/?p=4655

There's an unconfirmed supposition that they didn't cut over to the aux boosters from the main.

This was a commercial landing though. I guess its not there to do science or improve the human race.

What was behind it?

It was a commercial craft carrying a payload from a few sources, including a rover from JAXA, the Japanese space agency, and a second rover built by the UAE.

Do the rovers at least still work?

Things tend to stop working after a crash landing

But, even if they did separate, find themselves on the ground, undamaged, still powered, they rely on the lander as a radio relay.

A commercial endeavor being able to land on the moon is an accomplishment in itself. That’s how you go from proof of concept to economic viability

> That’s how you go from proof of concept to economic viability

I don't think this is particularly coherent in this case. It's commercial, but there is no private sector customer.

All of the customers are government scientific agencies. It's all still very much science and/or nation-state prestige-driven. What's more, it's unclear what the commercial case for lunar landing would be in the near term, where "near term" means "any reasonable expectation of return on capital that doesn't come from taxpayers".

That’s a fair criticism, but one important distinction is that this develops infrastructure and expertise for purely economically/recreationally motivated projects down the line.

As for economic motivations in the near term, a lot I can think of are indeed still based on public funds, but one important thing about commercial landing being viable is that those publically funded endeavors don’t need to work the bureaucracy engine to get a government launch/can span governmental boundaries. If some US or UAE entity wants a telescope array on the moon, if they have the money for it, they could just pay for a commercial lunar lander. If the DOE wants to test he-3 mining they don’t need to go through congress to get NASA to deliver their payload.

Most of the things that have improved the human race have been done commercially, and those motivated by profit have done a hundredfold more for humanity than those who were motivated by idealism.

Weird considering idealism got us things like free insulin[1] when none existed, Linux, important things like human rights, democracy etc.

[1] https://www.vox.com/2019/4/3/18293950/why-is-insulin-so-expe...

What if I told you that both can be true at the same time? A free market is one of the only vehicles that has allowed people to be lifted out of poverty, self determination and the freedom to decide one’s own destiny is a very profound idea that we take for granted when talking about different forms of governance that are fundamentally incompatible with that. On the other hand, we need a balance of power for the benefit and health of a society. Social safety nets, publicly beneficial infrastructure, and sensible regulations must exist, not in spite of, but to complement and protect the freedom we enjoy.

> free insulin[1] when none existed

Um, your reference is about how far from being free insulin is in the US.

> Linux

You think Linus built Linux out of idealism? Or that Linux is maintained at the quality level it has out of idealism?

It is to laugh.

Idealism has brought us genocide, mass murder and war. Majority of the most awful people in human history have been idealists.

Most of the US fleet is now commercial as well, and they're doing plenty of science on NASA's behalf. This is the future. Or we'd be stuck with one SLS launch every decade instead.

Just because it’s a commercial endeavor does not make it useless, impactful, or suggest the people behind it genuinely care about the work they are doing. I’m willing to bet people working there right now watched in awe while humans first stepped foot on the moon, or watched the first space walk, or even witnessed some of the tragedies that happened during the shuttle program, all while dreaming to be part of them next team to do something even greater.

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