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Successful landings on the Moon happened 50 years ago. Technology (satellites, computer, ML) has come a long way during this time, so why did Israel and India fail recently to land a probe there?

Is the chance of successfully landing a manned mission higher than for a non-manned mission?

Does the US have some secret insight into landing on the Moon?

George W.
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    They, and Russia, have had more practice –  Oct 01 '19 at 21:00
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    We spent more.... – Organic Marble Oct 01 '19 at 21:01
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    NASA software engineers don't come from an Agile "fear of failure is a bad thing" background? –  Oct 01 '19 at 22:54
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    There's also the very small sample size. Even with a good survival rate, 2/2 failures is not statistically remarkable. (and why does the sample not include the Chinese landings?) – SE - stop firing the good guys Oct 01 '19 at 23:48
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    I'd be happy to see the straightforward answer of (# of successes) / (# of attempts) -- but not so much that I'm going to crunch the numbers myself. Surely someone here will! – Roger Oct 02 '19 at 14:16
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    @JCRM NASA did plenty of fail fast and early In fact, I expect they did far more - and still they ran into some... lets say "interesting" software faults. – Baldrickk Oct 02 '19 at 14:49
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    Landing is extremely easy. It's the nanosecond afterwards that usually presents the problem. – Richard Oct 02 '19 at 21:43
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    Because there are lots of things that can go wrong; and because there is no way of testing everything in a controlled environment. The fact that technology has advanced doesn't alter either of those factors. – Michael Kay Oct 02 '19 at 23:16
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    Because you can't quicksave in real life. – Vikki Oct 02 '19 at 23:24
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    It is possible to commit no mistakes and still lose. That is not a weakness; that is life. – Magic Octopus Urn Oct 03 '19 at 19:10
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    Did the US have some secret? Yes. His name was Wernher von Braun, whose singular goal in life was to do so. – Mazura Oct 04 '19 at 00:39
  • @Richard I am by no means an expert on this issue, but I suspect that crashing an object into the moon is also difficult. – emory Oct 04 '19 at 17:57
  • @Richard: Or as Arthur Dent said (to Ford Prefect?): "It's not a question of whose habitat it is; it's a question of how hard you hit it." (when he fell from a 25-km-high marble statue of himself on the planet Brontitall (the statue defies the laws of physics, because it is artistically right), built by the bird people after the event Shoe Event Horizon) – Peter Mortensen Oct 04 '19 at 18:27
  • @Emory - I don't confess to be a rocket scientist but I'm pretty sure from playing a couple of games of kerbal that hitting the moon at a gazillion miles an hour is a hell of a lot easier than landing on it. Heck, you only need to get halfway and it's essentially a certainty – Richard Oct 04 '19 at 18:31
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    @Mazura - Von Braun was really only involved in the getting the LM to the moon part - not the software / hardware of landing the thing which is what the latest attempts that prompted this question have had trouble with. They've all demonstrated enough lifting capability to get to the the moon and near the surface. A non-destructive touchdown seems to the be the sticking point... – NKCampbell Oct 04 '19 at 19:19
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    @Richard, it took NASA four tries to hit the Moon with a spacecraft. It took the Soviets six tries. And yes, both programs had a flight that got halfway there and still missed. Combining the Luna, Ranger, and Surveyor programs and ignoring launch failures, there's only a historic success rate of 83% at hitting the Moon. – Mark Oct 04 '19 at 22:13
  • @Richard - in reality you only have to get halfway. In KSP, it's more like 7/8ths, and you're a gazillion times more likely to find yourself lost in orbit of the sun - if you can bullseye the mun w/o MechJeb or the maneuver planner, my hat's off to ya. – Mazura Oct 16 '19 at 03:08

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Does the US have some secret insight into landing on the moon?

Yes: fail early and often.

The US developed experience with uncrewed landings first, before attempting crewed landings in the Apollo program; those earlier programs had a very high failure rate.

The first US lunar spacecraft were in the Ranger program, which was simply attempting to hit the moon while taking photographs all the way down, and didn't achieve that goal until Ranger 7. The first two Rangers didn't even leave Earth orbit. Ranger 4 was completely inert after separation from its launcher, but it at least hit the moon.

Following Ranger was the Surveyor program, which attempted soft landings. Two out of seven of the US Surveyor missions crashed (#2 and #4).

By comparison, the ISRO lunar program has been very successful; the Chandrayaan-1 and Chandrayaan-2 missions both put spacecraft into lunar orbit, and the landing attempt of the latter came very close to succeeding. I haven't seen a thorough explanation of the landing failure, but my guess is that the root cause was a hardware fault.

Israel's Beresheet was likewise nearly successful, and this was the first spacecraft developed by that team. The failure in this case appears to have been a gyroscope sensor malfunction, which could happen to any spacecraft at any time, but in this case happened at a crucial moment in descent when there wasn't enough time to recover. There's nothing fundamentally wrong with the design, and the team didn't do anything wrong.

Then of course, there's also China's lunar exploration program, with three successful robotic landings (Chang'e 3, Chang'e 4, Chang'e 5), along with rovers and (as of December 3, 2020) a sample-return launch, and apparently no major failures.

Is the chance of successfully landing a manned mission higher than for a non-manned mission?

I would say so, for three major reasons.

  • The US went from uncrewed impact programs to uncrewed landing programs to crewed landing, and incorporated many hard lessons learned in the earlier programs. Anyone else contemplating a crewed lunar landing is very likely to take a similar path.

  • Crewed spacecraft and launchers are held to higher safety standards and provided with more redundant backup options in virtually all spacecraft systems.

  • Automatic systems plus humans can solve many more critical problems than either automatics alone or humans alone; this finding was one of the most important results of the X-15 spaceplane program.

Russell Borogove
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    You could add that the Soviet programme also had plenty of failures. – gerrit Oct 02 '19 at 10:56
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    But the Indian space program isn't starting from scratch, couldn't they learn from the history of the US, Soviet, and European space programs? – Barmar Oct 02 '19 at 18:27
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    @Barmar They have. Chandrayaan-1 was a near total success on the first try at a cost of ~US$56 million. The orbiter portion of Chandrayaan-2 was also successful. Between just those two missions they achieved more than the entire Ranger program did at a cost of ~US1B in today's money (albeit with US instead of Indian labor costs). Despite the disappointment of failing to successfully soft-land, the ISRO's lunar program has been extremely successful so far. – Russell Borogove Oct 02 '19 at 19:53
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    I just think it's inappropriate to compare any program from the 60's with a 21st century program. Everything was new technology then, failure was expected. I'm not saying that it's easy now, but you're comparing apples and oranges to some extent. – Barmar Oct 02 '19 at 20:19
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    In addition, pretty much everyone involved in the US Apollo program is retired or dead now, and none of the parts or equipment it used are being made for any purpose anymore. Lots of it nobody knows how to make anymore. So even the US at this point would likely require the same amount of time (or more) if they wanted to do it again. – T.E.D. Oct 03 '19 at 02:16
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    @Barmar Being twenty times as money efficient isn't good enough for you? And it's not like the US is going to give everyone all of that knowledge just like that. Don't forget that the Space race was as much about showing off your ability to build rockets (delivery platforms for nuclear weapons) as anything else. This was, and still is, extremely high-tech, with very few chances of recovery. There's no repair shops in Moon's orbit. – Luaan Oct 03 '19 at 08:25
  • @Luaan The Cold War is over, there's no space race now, we're in an era of international cooperation. Russia is America's political enemy, yet we still fly to the ISS on their rockets. – Barmar Oct 03 '19 at 15:55
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    @Barmar Remember that even SpaceX failed the first three Falcon 1 launches and blew up a Falcon 9 with payload on the launch pad. They've gone over budget and behind schedule like everyone else does in space. Space is hard, and even with the world's experience behind you, your own team has to develop their own experience, and their own technology can fail in unexpected ways. Anyone who puts something into orbit has still done something amazing. – Greg Oct 03 '19 at 17:07
  • @Greg Perhaps we should flip the question on its head: Why are some aerospace organizations so much better? – Barmar Oct 03 '19 at 17:45
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    @Barmar "Everything was new technology then, failure was expected." Exactly. If Armstrong and Aldrin had crashed into the moon, people would have said they were heroes who died advancing the frontiers of humanity. If astronauts died on the moon today, people would say, "FFS, we did that 50 years ago." – David Richerby Oct 03 '19 at 20:25
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    And don't forget that part of the planning for a manned mission is that it has to make it back to earth again in one piece... – Rufus L Oct 03 '19 at 22:32
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    @Barmar We were in an era of international cooperation even during the Cold War. What does that have to do with anything? Last time I checked, the US wasn't happily providing Iran with all of their nuclear secrets. Why do you think rocket technology is any different? – Luaan Oct 04 '19 at 07:42
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While engineering and available technologies have greatly advanced since the 50's and 60's, safely landing something on the moon is still a highly technical feat with a critically long list of potential failure points.

After a quick look at a list of moon missions, it appears that the US alone has had more launch failures than India and Israel's combined attempts.

When all a mission failure takes is to have a valve's response time in space being a handful of percentage out of spec, it becomes easy to see how a limited number of attempts might not add up to all that many successful missions...

The more launches you have, the more direct data you can gather, and the more collective knowledge and experience an organization has to draw on for future missions, which translates into fewer issues leading to critical mission losses.

TheLuckless
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    From another source, I get that smaller rockets imply longer trips, which implies longer cosmic radiation, which implies a higher risk of electronic failure. Sometimes you just have to pick chances and have a heap of funds to build a big rocket. – George W. Oct 01 '19 at 22:49
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    Hmm, a manned mission might have a higher chance of success because they can make more corrections in flight, if some part has a problem. (But more likely, no one is willing to do a manned mission without feeling at least a little sure of unmanned first.) – user3067860 Oct 02 '19 at 14:26
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    On the other hand, a manned mission has many more parts that might fail. – Camille Goudeseune Oct 02 '19 at 21:06
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    Manned missions have a higher rate of success because you don't risk putting a person in a spacecraft until you are sure you can get it right. – Seth R Oct 02 '19 at 22:09
  • "they can make more corrections in flight" - Those doing the manning? We know they've jury-rigged some CO2 scrubbers but isn't almost everything else "in flight" under full automation or the ground crew? – Beanluc Oct 02 '19 at 22:33
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    @Beanluc, the CO2 scrubber on Apollo 13 gets all the attention, but the crew jury-rigged a whole lot of other things (eg. a procedure for aligning the spacecraft without using the alignment computer). – Mark Oct 02 '19 at 23:03
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    @Beanluc not at all. For example, all US human spaceflight dockings to date have been flown manually. – Organic Marble Oct 03 '19 at 01:27
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You could also put it this way: The secret insight of the US was to use the following procedure:

  1. Be the richest country in the world.
  2. Over a 13 year period, spend an amount equal to 4.5% of your gross domestic product as of the year you started working.

The recent missions that didn't make it were operating on much lower budgets. The technological improvements were what allowed them to try at all.

Note: In 1960, the GDP was \$543 billion. The total cost of Apollo from 1960 to 1973 was \$25.4 billion, about 4.5% of $543 billion. Of course, the money was spent over time and the 1960 GDP is just used as a reference. Originally I said "Over 8 years" because I was going from 1961 to 1969, but the budget accounting goes from 1960 to 1973.

Mark Foskey
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"Technology (satellites, computer, ML) has come a long way during this time"

That may be true, but there's so much you can take with you! These modern rockets are nowhere close to the lifting capacity the Americans used. Which means you can't do the landing, stabilizing with so much brute force to keep your vehicle steady. The less weight is available to you, the less energy you can take with you. The less stabilizing you can do using sheer force, the more precise you have to control your landing. The more complicated routines needed, the more measurement and sensor technology to install. The more complex the programming, the more complex your systems, both hard- and software. The more complexity, the more can go wrong, etc.

Engineering with "unlimited" resources allowing you "a lot of energy" and "a lot of weight" allows the engineer to use more "raw" and "basic" solutions which is not comparable with high-tech engineering if you have only limited resources and limited power and limited weight-fuel.

To visualize this for those among you who are no engineers:

Imagine you have a water reservoir and the only task for the engineer and later operator is to either lock the reservoir or open it to drain the levels.

You basically just need one big switch: open or close.

Not much can go wrong there.

But now you add more tasks (only tasks to open up more or less without really interfering each other):

  • Opening % based on demand of farmers needs down the river
  • Open % based on demand of power production
  • Open % based on demand for fresh water down the river

And now you're going to add more tasks that actually interfere with each other: opening up more for farmers' needs, but the turbines produce more energy into the power grid, the energy into the power grid is based on voltage, current, and frequency, more water = higher frequency (a standard defines the boundaries between which frequencies it can variate). You're now getting to the maximum of that boundary, but farmers still need more water, so you have got to either limit the turbines or reroute water through different flows.

See what is going on here? The more complexity, the more switches needed, the more the engineer and operator have to consider.

And now I'm going to tell the engineer and operator additional tasks:

The original design the switch controlled a 1 meter radius water flow pipe with 1.5 cm stainless steel. But in the new design the engineer should limit the pipe to 0.3 meter and the thickness of the pipe to 0.4 cm and please below 350 kg per meter pipe. So steel is now out of the question, getting more complicated.

Also just opening one pipe for the operator might not do the trick. You need to handle a multitude of switches even for the same task based on the limits of weight, available flow, etc.

See how complex it is getting already with such an extreme simple comparison?

So just because the USA could do it with old technology and their extreme heavy lifting capacity doesn't mean you can copy it or do it easier just because you have more technology at hand, if at the same time you're going to do it with a lot more restrictions than US engineers had.

And the lifting weight for any space operation is the absolute most daunting restriction for any engineer in that field.

Peter Mortensen
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Vince
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  • As an example of substituting brute force for complexity, consider the Ascent Propulsion System from the Apollo landers: it had to work, because there was no abort mode possible if it failed. It's the closest thing you can get to a "single-switch" rocket engine: no gimbals, no throttle, no ignition system, no pumps, just a pair of valves and pressurized tanks of fuel and oxidizer that ignite on contact. Efficiency was about 70% that of a more advanced design. – Mark Oct 04 '19 at 22:35