[HN Gopher] Why it's so challenging to land upright on the moon
___________________________________________________________________
Why it's so challenging to land upright on the moon
Author : Brajeshwar
Score : 86 points
Date : 2024-03-04 15:46 UTC (7 hours ago)
(HTM) web link (www.nytimes.com)
(TXT) w3m dump (www.nytimes.com)
| huytersd wrote:
| I don't even think it should be called a successful landing
| unless you're upright on the moon.
| ck2 wrote:
| Airbag crash/roll would be valid as long as the lander self-
| corrects and uprights itself afterwards?
|
| Seems like that would save a lot of fuel too if you don't care
| how you come down, just not too incredibly fast.
|
| (wasn't there a Mars landing like that)
| huytersd wrote:
| Let's just say unless the intended thing happens, it's a
| failure.
| stevage wrote:
| Quite a few mars missions like that. They used aerobraking
| first though.
| 0_____0 wrote:
| The aviators might say - a good landing is one you walk away
| from.
|
| How exactly do you define a successful landing? What if you're
| upright but all four legs collapsed and the spacecraft crushed
| your primary science payload?
| electroly wrote:
| A _great_ landing is when you can use the plane again
| afterwards.
| ta1243 wrote:
| "Walk away from" would be "Primary payload can function (or
| at least not fail because of an action of the lander)"
| luxuryballs wrote:
| true all you did was crash into the moon
| neonate wrote:
| https://archive.ph/Nkucd
| amelius wrote:
| Waiting for a HNer to post a JavaScript based simulation game
| illustrating the difficulty.
| handedness wrote:
| https://ehmorris.com/lander/
| hathawsh wrote:
| Oh my goodness this is gold. I've never had so much fun
| failing.
| ViewTrick1002 wrote:
| Felt completely intuitive. All hours playing Kerbal Space
| Program re-loading the last save after crashing into the
| surface paying off....
| blharr wrote:
| If it's too easy, try doing a couple flips for more points
| hoten wrote:
| If it's too hard, just do many dozens of flips as you try
| to race away from the surface.
| super256 wrote:
| There is this experiment in OpenAI Gym to land a spacecraft
| via reinforcement learning. Is reinforcement learning
| actually working for this, and are such models deployed to
| real rockets, instead of "hardcoded" math?
|
| https://gymnasium.farama.org/environments/box2d/lunar_lander.
| ..
| nickthegreek wrote:
| I was thinking, I dunno.. I use to set that lander down on the
| time as a kid!
| ck2 wrote:
| Maybe before sending lots of landers we should build a moon GPS
| system for guiding to a precise safe landing spot?
|
| But it also occurs to me and therefore probably the actual
| engineers they should be throwing these landers out of an
| airplane over a rough, rocky earth desert many times before
| trying the moon?
| mecsred wrote:
| If they could get the budget to build a few extra multi million
| dollar spacecraft and throw them in the sand they absolutely
| would. Unfortunately all management gave us were these
| cardboard boxes with a lander drawn on them in sharpie so we'll
| have to use our imagination.
| thsksbd wrote:
| Is that really necessary? The moon has no atmosphere so
| "celestial" navigation is unhindered by weather, and can be
| done during the day.
| tintor wrote:
| What precision can be achieved using celestial navigation,
| and it is good enough for lunar landing?
| kube-system wrote:
| Well, the moon has never had a GPS system in the past, and
| there have been moon landings. Apollo used celestial
| navigation, so yes, it is good enough.
|
| https://www.youtube.com/watch?v=hVCNS2jQQ6g
| Firaxus wrote:
| Keeping satellites in orbit around the moon is very expensive.
| The moons gravity is lumpy, and if you try to orbit far enough
| that it balances out, then perturbations from the earth and sun
| still end up destabilizing it. This means it takes a lot of
| station keeping (firing thrusters, using limited propellant) to
| maintain an orbit.
|
| I think there are plans for better relays situated around the
| moon, but a lunar gps system is not likely given the costs and
| engineering difficulties.
| stevage wrote:
| It seems both of these landers fell over due to instrument
| failures. So o solution that relies on building different
| instruments is not obviously the right one.
| dsjoerg wrote:
| Would it be easier to have it land in any old position, with a
| mechanism to push itself into upright posture when needed?
| Tagbert wrote:
| I saw a diagram of a lander, maybe just a prototype, that was
| constructed like a truncated tetrahedron. It would end up on
| either the bottom, or one of three sides. Once it landed the
| three sides would open up. no matter which orientation, that
| would push it to an upright position.
| lpribis wrote:
| Maybe thinking of Spirit and Opportunity rovers which had a
| truncated tetrahedron shape of airbags (kinda) and unfolded
| to the upright position?
|
| https://en.wikipedia.org/wiki/Mars_Exploration_Rover
| 0_____0 wrote:
| That's how the earlier Mars rovers arrived, totally valid
| concept. But it's expensive to get mass to the Moon, and if you
| think you can likely land upright with thrusters, why bother
| with something more complex/massive?
| imglorp wrote:
| This is why the Dynetics lander makes so much sense: less to go
| wrong plus no elevators or long ladders needed:
| https://huntsvillebusinessjournal.com/wp-content/uploads/202...
|
| For that matter, the Space 1999 "Eagle" for the same reason, just
| good design. https://news.ycombinator.com/item?id=39484015
|
| If a human lander tips over for any reason, that could be
| disastrous.
| bnralt wrote:
| Dynetics' proposal was the most expensive, and they also
| couldn't figure out a way to make it work at the time when the
| choice was made[1]:
|
| > Of particular concern is the significant weakness within
| Dynetics' proposal under Technical Area of Focus 1, Technical
| Design Concept, due to the SEP's finding that Dynetics' current
| mass estimate for its DAE far exceeds its current mass
| allocation; plainly stated, Dynetics' proposal evidences a
| substantial negative mass allocation. This negative value, as
| opposed to positive reserves that could protect against mass
| increases at this phase of Dynetics' development cycle, is
| disconcerting insofar as it calls into question the feasibility
| of Dynetics' mission architecture and its ability to
| successfully close its mission as proposed.
|
| You can read NASA's full thoughts on that link. But the basics
| are, they thought there were good ideas, but they weren't
| comfortable picking a lander that went far above the allotted
| budget, while the team who made the lander wasn't able to come
| up with a way that it would work yet.
|
| [1]
| https://www3.nasa.gov/sites/default/files/atoms/files/option...
| bryanlarsen wrote:
| IIRC the original Dynetics proposal had a positive mass
| allocation, but it relied on refueling at the Artemis Lunar
| Gateway. NASA then changed the requirements so that the
| Artemis Lunar Gateway would not be fully available for the
| first moon landing, and Dynetics was unable to adapt their
| proposal.
| recursivedoubts wrote:
| a flawless six for six using 1960's tech:
| https://www.history.com/news/us-moon-landings-apollo
|
| the past is a foreign country
| AnimalMuppet wrote:
| And humans at the controls. Having a program at the controls is
| rather a different problem...
| lupire wrote:
| I thought Elon Musk's robots are better drivers than humans.
| toast0 wrote:
| When traveling at highways speeds, they ignore stationary
| objects, such as parked emergency vehicles and presumably,
| the Moon.
| luxuryballs wrote:
| still bummed they never performed any impressive feats of
| agility made possible by the gravity
| saalweachter wrote:
| What gravity giveth, space suits taketh away.
|
| The jumps (4 feet) and bounds (15 feet) are pretty good by
| everyday standards, but like half of the Earth-bound records.
| luxuryballs wrote:
| they could have tossed something at least, somehow they
| managed to do all that footage without anything I can use
| to combat the conspiracy theorists who just say the footage
| is slowed down
| bagels wrote:
| Pretty risky to get injured or to get a puncture goofing off
| on the moon.
| gyrovagueGeist wrote:
| All the more reason to build a proper moon base with an
| indoor court
| mlsu wrote:
| I would give just about anything to watch an NBA game played
| on the moon. Make the court 4x bigger, the hoops 3x taller.
|
| The revenue for this would pay for several Starships.
| lupyro wrote:
| In this vein I've always thought it would be cool to see
| what kind of sports we could have in a zero gravity stadium
| in orbit. Something like the training facilities in Ender's
| game.
|
| Maybe a sport like Quidditch could become a reality
| knodi123 wrote:
| > the past is a foreign country
|
| It's a nice place to visit, but I wouldn't want to live there.
| thsksbd wrote:
| You wouldn't want to live in, say 1960s Portland Maine? Say
| as a professor of English literature?
|
| Seems pretty sweet to me.
| josefresco wrote:
| Stating the obvious but it probably depends on your gender,
| sexual orientation, and skin color (to a name just a few).
| knodi123 wrote:
| Yeah, I can't remember the show, but it was some time
| travel thing, and one of the tech guys isn't as excited
| as everyone else at the prospect of visiting great
| moments in history. They ask him why, and he says, "well,
| I'm black, so...."
| mnw21cam wrote:
| There's probably several different shows that match this
| description, but you're probably thinking of Star Trek
| DS9, Season 6, Episode 13, "Far Beyond the Stars".
| thsksbd wrote:
| Which peoples is this not true for?
| thsksbd wrote:
| Of course. 1960s Maine college campuses were one of the
| darkest, most depraved, periods of human history.
| knodi123 wrote:
| > Say as a professor of English literature?
|
| I'd probably be fired when they found out I hadn't read
| anything written since the 70s....
| serf wrote:
| I wouldn't want to give up my toys. I don't have enough
| brain cells left to accommodate to 1960s style programming,
| let alone the outward appearance needed to convince someone
| to let me use their mainframe back then.
| thsksbd wrote:
| https://en.m.wikipedia.org/wiki/Luna_programme
|
| The Soviet Union is even more foreign with 50's tech and no
| human to aid primitive computers.
|
| Better failure rate than the last 12 months of international
| moon landings.
| stevage wrote:
| And cold war budgets...
| isopede wrote:
| I like to solve this problem in Kerbal Space Program simply by
| avoiding it:
|
| My landers are designed to land sideways.
| sjducb wrote:
| Also solves the problem that starship's door is so far away
| from the ground.
| onethought wrote:
| It can carry 100 tons. I'm sure they can pack a ladder... or
| elevator... heck a smaller propulsive landing platform
| sjducb wrote:
| But what if the elevator doesn't work? The backup plan is a
| 25 meter ladder that you have to climb in a spacesuit.
| bloopernova wrote:
| That sideways drift was the bane of my existence. I could never
| quite kill all of my horizontal velocity, and tipping over was
| common. (Just as the article said)
|
| I wonder how SpaceX will solve this reliably for Starship?
| stevage wrote:
| Using SAS and RCS pointed retrograde to surface pretty much
| auto solves that problem.
| Zondartul wrote:
| Some Moon ideas: 1) have a small robot bulldozer flatten a
| landing pad/polygon so there is loads of safe landing area. 2)
| use same dozer to make a moon highway to other sites of interest
| around the moon. 3) Moon GPS or laser-based local navigation
| beacons, so the spacecraft can rely on those if instruments fail.
| 4) Just stupid-wide landing legs that let the craft ski around
| the moon even when landing at an angle and with horizontal
| velocity.
| wongarsu wrote:
| The reason Odysseus's legs are so narrow is that they wanted
| fixed legs, so there's no leg deployment that could go wrong.
| But payload fairings are only so wide. The legs are the widest
| that fit a Falcon 9 payload fairing.
|
| I really like the idea of a mission to build infrastructure
| though.
| bigyikes wrote:
| Building infrastructure is the only way this stuff will get
| cheaper and easier
| krasin wrote:
| Just like Canadarm ([1]) on ISS considerably simplified
| docking, I can see a similar approach working for lunar
| landing: slow down to below 5 m/s, get caught by a robotic
| arm and gently put into a good spot.
|
| 1. https://en.wikipedia.org/wiki/Canadarm
| ramses0 wrote:
| https://en.wikipedia.org/wiki/Catcher_pouch
| stevage wrote:
| Building infrastructure doesn't make sense for exploratory
| missions that each want to land somewhere new though.
| saalweachter wrote:
| You know, we're probably capable of landing on a landing pad on
| the moon, now.
|
| Apollo 11/Eagle landed something like 4 miles off from their
| target site, but SpaceX nowadays routinely lands on target.
| onethought wrote:
| A launch and return to the same rotating body is surely a
| simpler maneuver than orbital transfer to a different
| spinning body and landing. No doubt we are better at it but
| I'm not sure earth landings are an accurate analog.
| stevage wrote:
| Nah, you can't really compare them like that. And landing
| on a planet with an atmosphere is completely different from
| a moon without one.
|
| Landing on the moon is easier. It just looks hard because
| it's so expensive to get there that you don't get many
| attempts.
| bluGill wrote:
| That depends on how much atmosphere. Mars has enough
| atmosphere to be annoying, but not really enough to be
| useful. Winds can throw you off target, but you can't use
| a parachute for a soft landing.
| stevage wrote:
| That's not true. Many (most?) Mars missions with Landers
| have used parachutes, though they are not sufficient for
| a true soft landing.
|
| I'm not an expert but I think landing on Mars with no
| atmosphere would be harder, because you'd need so much
| more fuel for a controlled descent.
| dylan604 wrote:
| Apollo 11/Eagle was deliberately piloted away from the
| initial landing site because the pilot did not think the
| original location was safe. So until a perfectly placed
| target for a robot to land on like SpaceX does (which seems
| only likely if establishing a sort of base), the robots will
| need to be made smarter about landing or built to be more
| agile on landing on less than ideal sites.
| josefresco wrote:
| > SpaceX nowadays routinely lands on target
|
| On the moon?
| lupire wrote:
| The article mentions that SpaceX has landed on the moon once,
| and tipped over. The moon is harder to land on then the Earth
| - less gravity and atmosphere.
| Firaxus wrote:
| I haven't read the article (paywall) so I can't be sure,
| but I believe the article is referring to the Intuitive
| Machines lunar landing.
|
| SpaceX has not yet attempted to land anything on the moon.
| dblohm7 wrote:
| Apollo 11 isn't really the proper comparison to make, though;
| more precise landings were goals of later missions.
| saalweachter wrote:
| Fair enough; Apollo 12 landed within walking distance of
| the Surveyor probe, but I don't have enough information to
| know whether 535 feet from the probe was exactly on target,
| or hundreds of feet off target. So maybe we could have
| landed on a pad 50 years ago, too?
| kube-system wrote:
| Probably, but do we want to keep going back to the same spot?
| rst wrote:
| ... and then Apollo 12 targeted one of the earlier Surveyor
| probes (which had successfully done its own automated moon
| landing in the mid-1960s!), and the guidance system had it
| coming down very close to the earlier probe -- astronaut Pete
| Conrad manually overrode it to make sure they stayed a safe
| distance away.
|
| There had been upgrades to software and procedures since
| Apollo 11 -- most notably, a new guidance parameter the
| astronauts could enter ("noun 69") to correct for deviations
| between the planned lunar orbit and the one in which the
| spacecraft actually was, before descent.
|
| https://www.forbes.com/sites/davidmindell/2019/11/19/apollo-.
| ..
| georgecmu wrote:
| I had an interesting experience a few years back as a reviewer
| for proposals to NASA LuSTR program:
| https://www.nasa.gov/directorates/stmd/space-tech-research-g...
|
| The topic was exactly that: landing pad preparation solutions.
| Here's a summary slide for one of the winning proposals:
| https://www.nasa.gov/wp-content/uploads/2022/03/lustr2021_qu...
|
| _The Autonomous Site Preparation: Excavation, Compaction, and
| Testing (ASPECT) Project will develop tools and methods to
| clear, level, and compact the lunar surface. ASPECT is a fully
| autonomous rover with equipment for regolith excavation,
| boulder moving, and surface compaction._
| ChuckMcM wrote:
| There are a number of well fleshed out plans for doing
| essentially this. One of the more interesting ones for me was
| that microwaves can be used to fuse lunar regolith into a
| solid. One plan had a solar powered rover that sat there and
| microwaved the ground until is was solid far enough down, then
| would move forward on to that patch and start with the next
| patch. As I recall it would take about a month to make an acre
| sized "pad" which would support landing.
| hinkley wrote:
| You know how the martian landers now use a crane to lower the
| lander to the ground so the retro rockets are outside of the
| ground effects range?
|
| Someone proposed doing something similar with a lander, where a
| landing-site-prep robot gets dropped first. But that sounded
| like a lot of hovering to me, and a solution that would be very
| specific to lunar landing. I can't see that being successful on
| anything with higher gravity.
|
| Better perhaps to send a separate stage or a scouting mission
| to do the work, then land later.
| blackbear_ wrote:
| Why can't you make a spherical lander? With some moving masses on
| the inside to roll around? (Clearly I'm not an engineer)
| theultdev wrote:
| That's basically the SLIM's LEV-2. Not a lander itself, but a
| small rover.
|
| https://www.space.com/jaxa-slim-moon-lander-lev-2-ball-robot
|
| There's also the method of dropping a ball of airbags that
| deflate and detach, so you aren't limited to being a ball.
|
| I assume it's more efficient and versatile (lots of tools on
| these things) to not be a ball.
|
| You basically want a small truck loaded with equipment and a
| solar panel on top.
| knodi123 wrote:
| isn't regolith microscopic and sharp? A sealed ball that
| rolls around is one thing, but wouldn't a non-sealed ball
| just get its motor shredded pretty quickly?
| serf wrote:
| I remember reading before that given the consistency and
| weight of moon dust that electrostatic protection of assets
| is viable.
|
| I guess the concept would be to surround the motors in a
| electrostatic force that results in propulsive removal of
| particulates away from the drivetrain.
|
| I don't know if it has been practically used.
| cstross wrote:
| Worth noting is that because Starship HLS carries astronauts, it
| has to be capable of abort-to-orbit -- that is, to cancel the
| landing at _any_ point and return to Lunar orbit. The Apollo LEM
| would have done this by shutting down and dumping the descent
| stage then lighting the ascent motor: Starship is a single stage
| that should have enough fuel and oxidizer left after a successful
| landing to lift off and return to orbit with a minimal payload.
|
| I expect if astronauts aboard HLS lose their altimeter they'd
| have to abort the landing immediately -- to proceed without it
| would be the height of recklessness. But Odysseus had no abort-
| to-orbit capability so was committed to landing.
| facialwipe wrote:
| I'm a huge space nerd. It takes up most of my free time.
|
| I have never once read about abort-to-orbit capability as a
| concept, let alone a requirement for Artemis HLS.
|
| Here's a 4 year old video detailing past abort systems and why
| Starship won't have one:
| https://m.youtube.com/watch?v=v6lPMFgZU5Q
| dabluecaboose wrote:
| >I have never once read about abort-to-orbit capability as a
| concept
|
| ATO was an abort mode [1] on the Shuttle program and is
| notably the only abort mode that was successfully used in the
| entire program, on STS-51f [2] . _Challenger_ suffered an
| engine anomaly on liftoff that resulted in a lower orbit than
| was intended, but otherwise the mission went off without a
| hitch.
|
| [1] https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#A
| bor... [2] https://en.wikipedia.org/wiki/STS-51-F
| mrexroad wrote:
| Thanks! I'd seen about the bailout capability mentioned in
| passing, but had always wondered what it would be in
| practice (spoiler: a pole!). Also, I didn't realize a
| second engine almost shut down on STS-51-F .
|
| Per the links: "A particularly significant enhancement was
| bailout capability. Unlike the ejection seat in a fighter
| plane, the shuttle had an inflight crew escape system[12]
| (ICES). The vehicle was put in a stable glide on autopilot,
| the hatch was blown, and the crew slid out a pole to clear
| the orbiter's left wing. They would then parachute to earth
| or the sea. [...] Before the Challenger disaster, this
| almost happened on STS-51-F, when a single SSME failed at
| about T+345 seconds. [...] A second SSME almost failed
| because of a spurious temperature reading; however, the
| engine shutdown was inhibited by a quick-thinking flight
| controller. If the second SSME had failed within about 69
| seconds of the first, there would have been insufficient
| energy to cross the Atlantic. Without bailout capability,
| the entire crew would have been killed."
| whycome wrote:
| > STS-51-F
|
| Why is the naming scheme of shuttle launches so bad
| dsr_ wrote:
| https://www.nasa.gov/missions/space-shuttle/behind-the-
| space...
| dabluecaboose wrote:
| It's doubly confusing that STS-51-F, with the
| _Challenger_ , is the only exercised launch abort; while
| STS-51-L is the famous launch disaster for which
| _Challenger_ is most well known.
| Isamu wrote:
| The video is about launch abort I believe. As opposed to
| aborting a lunar landing.
| loa_in_ wrote:
| Apollo Lunar Module had an abort-to-orbit that was also used
| to lift off the surface of the Moon after successfully
| completing the mission. It used explosive charges to throw
| the lander frame away and involved Apollo Guidance Computer
| manuevering into orbit at any point of the mission up until
| the landing.
| grouchomarx wrote:
| the four year old video you linked to has nothing to do with
| aborting a landing on the moon
| MPSimmons wrote:
| Dragon 2 has abort to orbit capabilities, too. The abort
| zones they call out as the rocket's IIP advances up the east
| coast continue until Ireland, and then after that, it's abort
| to orbit, where the superdracos will carry the ship to orbit
| without the second stage.
| mandeepj wrote:
| > Starship is a single stage
|
| I'm no expert, so this is a question to confirm my
| understanding: Starship does have a booster. So, doesn't that
| make it a dual stage?
|
| https://www.zenger.news/2023/11/27/elon-musk-reveals-simple-...
| dabluecaboose wrote:
| I think GP was saying that the _lander_ is single-stage. By
| the time of a presumptive lunar landing, there 's no lower
| stage to drop as with the Apollo LEM.
| justrealist wrote:
| The part that's landing on the moon is just the second stage.
| thereisnospork wrote:
| Assuming the landing is soft enough to survive, shouldn't it be
| fairly trivial for the astronauts to disembark and right the
| lander? To the extent anything in space is trivial.
|
| Even if it's a bit more than doable by hand a ratchet jack
| should make short work of it.
| jethro_tell wrote:
| Assuming you have jack points in the right place based on the
| way it tipped over.
| toss1 wrote:
| Yup, jack points in the right place, jacking equipment with
| sufficient range of motion, _AND_ solid lunar soil in the
| right place under the jack points.
|
| Plus, you've got to get the whole jacking operation done
| without damaging any of your main or control thruster
| rockets, and without tipping past the upright point over to
| the other side, or just effectively rolling onto an
| adjacent side.
|
| I wouldn't want to go on a craft where [jacking it back
| upright] was in the top ten on the list of recovery options
| to get home.
| thereisnospork wrote:
| >I wouldn't want to go on a craft where [jacking it back
| upright] was in the top ten on the list of recovery
| options to get home.
|
| For a counter, I wouldn't want to be on a lander so
| fragile[0] that being manipulated upright is infeasible.
| Something will go wrong, maybe not on that lander, but
| when it does go wrong it'll have to get duct taped
| together.
|
| [0]Not just mechanically, but in terms of operation
| scope. Planning that everything must go perfectly or
| people die is a recipe for the latter.
| ghufran_syed wrote:
| agree - which is probably why Elon Musk is so obsessive
| about increasing the efficiency and thrust of the merlin
| and raptor rocket engines, a huge amount of downstream
| capability can be achieved by increasing that number (all
| other things being equal)
| hinkley wrote:
| So if the lander falls over because two of the feet land
| on regolith, odds are good you don't have a solid point
| on that side of the craft to put the jack...
| cpgxiii wrote:
| The Apollo LEM, only craft that has ever taken humans to the
| moon's surface, weighted somewhere around 20,000 kg after
| landing. Since it only ever operated in space and lunar
| gravity, it could be built with a much higher mass fraction
| than a rocket launched from earth requires - greater than
| 30%, where a Falcon 9 in comparison has a mass fraction below
| 5%. Even then, the LEM structure had to be built incredibly
| lightly. While the LEM structure could obviously be lifted by
| crane and survive launch and docking stresses, those were are
| at designed points in the structure. Without the presence of
| a crane capable of lifting the whole LEM, righting an LEM
| that had landed on its side would have been effectively
| impossible. Basically all of the modern proposed manned lunar
| landers are considerably larger than the LEM, and thus
| considerably heavier.
|
| For comparison, a craft built for earth launch mass fractions
| probably wouldn't survive falling over in the first place -
| when that happened to a Falcon 9, the whole rocket simply
| exploded.
| ooterness wrote:
| If it's good enough for Jebediah Kerman, it's good enough for
| me, but maybe not NASA.
|
| https://xkcd.com/1244/
| stonemetal12 wrote:
| >shouldn't it be fairly trivial for the astronauts to
| disembark and right the lander?
|
| I don't think that is an assumption you can make. In the
| worst case scenario the lander lands on the door. In which
| case the only way to disembark is to lift the lander.
| narag wrote:
| _I expect if astronauts aboard HLS lose their altimeter they 'd
| have to abort the landing immediately -- to proceed without it
| would be the height of recklessness._
|
| In addition to the obvious, it should be taken into account
| that the absence of atmosphere makes _very_ difficult to assess
| distance and scale. Videos of approach seem like a fractal
| browser.
| abledon wrote:
| are they going to send a 'test run' HLS first? like, completely
| computer controlled, to stick the landing?
| bryanlarsen wrote:
| Yes, that is a condition in NASA's contract with SpaceX. It
| is currently scheduled for 2025.
| josefresco wrote:
| The suggestions here:
|
| flatten a landing pad
|
| make a moon highway
|
| Moon GPS (2 votes)
|
| stupid-wide landing legs
|
| Dynetics lander
|
| spherical lander
|
| mechanism to push itself into upright
|
| land sideways (ok this was a joke right?)
|
| I couldn't find the relevant XKCD but I remember one along the
| lines of "why did they just do Y?". I say all of this in jest, as
| this is what we do here at HN: give our opinion on areas outside
| our expertise.
| blowski wrote:
| It's easy to say what they should do when there's absolutely no
| accountability for your recommendation.
| eatbitseveryday wrote:
| A spacecraft perhaps could inflate lots of impact balloons that
| would cushion impact, allowing landing in any orientation. Then
| on landing, rotate with gyros or something until the legs are
| underneath and that way end upright?
| sadhorse wrote:
| Humans did it manually in the 60's. How hard can it be to do it
| with computers and radar? I don't want to sound like that guy
| but... how hard can it be?
|
| Edit: My point being: spacex is already doing it on earth,
| dealing with stronger gravity and air non linearity.
| adamredwoods wrote:
| This would be a cool simulation / programming game.
| NoraCodes wrote:
| I highly recommend taking a look at Kerbal Space Program
| plus k/OS. I've done a few Kerbal hackathons with friends
| where we all get the same spacecraft, in the same scenario,
| and have to write k/OS scripts to perform some mission.
| Difficult, but fun and often hilarious!
| NoraCodes wrote:
| I mean, it's not like it's rocket science!
|
| More seriously, the humans in question were very skilled
| pilots with huge amounts of general flight experience and
| specific lunar training; they also had access to hardware
| that had already been expensively tested in the lunar
| environment. Neither of those were available to this project.
| gene-h wrote:
| The IM-1 Lander was supposed to land using a LIDAR altimeter,
| but they forgot to remove the safety before launch. They
| tried to make a last minute software change to use an
| experimental navigation system from NASA to get altimetry,
| but this didn't work. So the lander landed using visual
| navigation and IMU data only for the last 15km to the
| surface.
|
| It probably would have landed upright if the LIDAR worked. It
| is impressive that it landed as intact as it did
|
| [0] https://arstechnica.com/space/2024/02/it-turns-out-that-
| odys...
| 4silvertooth wrote:
| Humans have been driving cars since decades, how hard would
| it be to make a self-driving, well it seems it is difficult.
| pvg wrote:
| Pathfinder landed on Mars using that design:
|
| https://en.wikipedia.org/wiki/Mars_Pathfinder#/media/File:Pa...
|
| Having an atmosphere helps, though and that's not available on
| the Moon.
| stevage wrote:
| That's how they used to land on Mars.
| SilverBirch wrote:
| What you do is descend very slowly, as you descend your thrusters
| will slowly melt a smooth landing pad beneath you. The only
| problem is you have to sacrifice part of the landing legs when
| you take off because obviously the melted cheese will bind to
| them once you touch down.
| toast0 wrote:
| If you get a good crust on the cheese, it shouldn't bind with
| your legs.
| jvm___ wrote:
| Explain like I'm Grommit
| photochemsyn wrote:
| I'm all for the US space program returning to the Moon and the
| NASA public-private approach seems fairly reasonable.
|
| It is very odd however to see no mention of the fact that China
| is about a decade ahead, having completed the Chang'e 3, 4 and 5
| missions. which included a successful return of Moon rocks to the
| Earth. Two more missions are in the works.
|
| The article mentions a Japanese effort, but the omission of
| China's successes seems fairly deliberate. I wonder what the
| motivation was?
|
| https://www.space.com/china-new-moon-rover-change-7-mission
| HarHarVeryFunny wrote:
| The USSR also had successful robotic sample return missions,
| and rovers, in the 1970s.
| ThisIsMyAltAcct wrote:
| Because the article is about recent difficulties landing on the
| moon and China has not had recent difficulties landing on the
| moon?
| api_or_ipa wrote:
| I feel an overwhelming itch to fire up KSP and show them how it's
| done!
| kelseyfrog wrote:
| More power to you, but I've had multiple munar landing attempts
| turn into munar rescue missions precisely because the first
| mission lander tipped over :D
| HarHarVeryFunny wrote:
| Maybe for a small lander, an alternative to landing upright would
| be to avoid having an upright in the first place. Have a
| spherical/polyhedral design with legs on all faces and redundant
| solar panels/cameras on each face.
| jethro_tell wrote:
| Or even a design that allows for self righting. You can find
| many of these in highschool robotics club battle bots.
|
| Obviously much more complex, but probably cheaper than
| redundant everything.
| invalidator wrote:
| Mars Pathfinder did exactly this. It was a tetrahedron which
| could land in any orientation. As it happened they rolled a
| 4, but if it was on one of the other 3 sides it would have
| pushed itself upright as the sides folded open.
|
| https://en.wikipedia.org/wiki/Mars_Pathfinder
| johnwalkr wrote:
| Very easy solution until you realize you need solar panels
| facing the sun[1], radiators facing deep space[2], antennas
| facing earth, payloads facing x, y, and z, deployable payloads
| facing x, y, and z plus the lunar surface. And all of those
| things are fragile, at least in terms of mounting them on the
| outside of a bowling ball rolling across sharp gravel/sand. And
| of course multiply difficulty by the number of all
| configurations^2 for both design and testing. [1] and [2] are
| especially huge drivers, you need power and therefore heat
| input, but you also need radiators to expel heat. Depending on
| complexity, solar panels in shade act as passive radiators
| leaking heat at best, and at worst as heaters, actively taking
| battery power to heat up and become even better radiators. And
| radiators act, to some extent, less effectively or even as
| heaters if they are facing the sun, sunlit earth, or sunlit
| lunar surface instead of deep space.
|
| It's not only a matter of adding complexity, mass, money, etc.
| This kind of solution is simple on its face, but it is akin to
| being ignorant of why a car has windows (for the driver to
| see), doors (for the passengers to enter/exit) or a cooling
| system (to not overheat), and then reading that Jeeps (or to be
| more fair, a new Jeep prototype) are prone to tipping over on a
| trail after driving 1000km on a highway to a trailhead, and
| then commenting on how Chrysler should just make a dodecahedron
| Jeep with 20 wheels instead of 4.
|
| These spacecraft also made it past 99% of the hurdles, the next
| try will probably make it and overcome the final 1% without
| starting from scratch and adding all kinds of complexity that
| are far more likely to add failure.
|
| I work in the industry and opinions are mine and not of my
| employer.
| whycome wrote:
| Or have the singular versions and just roll the thing after
| landing.
| HarHarVeryFunny wrote:
| I think the economics of a one-off lunar lander are a bit
| different to those of Jeep! The cost of the lander hardware
| is only a small part of overall cost of the mission, and
| adding some (or even a lot) of redundancy would seem a small
| price to pay if that provides a high likelihood of mission
| success. Of course this needs to be compared to cost and
| reliability of alternate solutions. This is a lot different
| to adding a lot of redundancy and cost and compromised design
| to a mass-produced vehicle where you can iterate and test in
| deployed environment as many times as you like.
|
| Obviously N-way redundancy isn't optimal, but it would seem
| potentially simple if you had a modular design with multiple
| instances of the same "omniface" component. Perhaps use 1/2
| of each redundant face for radiator and 1/2 for solar panel?
|
| I'm not suggesting a rolling design - just one with legs on
| every side such that if it did tip over (or worst case tumble
| if landing on an incline) from preferred engine-down
| orientation then it would not make any difference.
|
| Seeing as Intuitive Machines wanted to avoid deployable
| (spreadable) legs as a way to achieve a more stable low
| center of gravity, another alternative would seem to be to
| shrink the design (lose the height) to better work within the
| width of the faring, although I don't know how viable that
| would be given amount of propellant needed for the landing.
| hinkley wrote:
| You're just trying to ruin our zorbing fun.
| demondemidi wrote:
| The first mars lander was in a tetraheadron in an airbag. There
| was no way for it to land in the wrong orientation because the
| tetraheadron always unfolded in the correct orientation. And
| that was almost 30 years ago.
| HarHarVeryFunny wrote:
| Yes - that was a great design. I've seen some people suggest
| that it wouldn't work on the moon due to lack of atmosphere
| and less gravity, but not obvious why that would prevent it.
|
| Of course it's a more complex design in a way given that you
| deploy this airbag at low altitude - something else to go
| wrong. It's interesting though that NASA has used that and
| the even more complex air-crane technique on Mars both
| successful first attempt. Even though they seem complex I'd
| assume NASA determined they were the least-complex approaches
| that had a high likelihood of success.
|
| Maybe the economics of doing this on the moon, and with a
| cheaper lander, are different - better to have a simpler
| system with higher chance of failure, and redo the mission if
| it fails ?
| tintor wrote:
| Is there a geometrical shape, that will always settle in the same
| orientation?
| isopede wrote:
| In fact there is! It's called a Gomboc:
|
| https://en.wikipedia.org/wiki/G%C3%B6mb%C3%B6c
| solardev wrote:
| My d20 needs this
| lapetitejort wrote:
| You could create a d1 with this shape! Much better are more
| stable than Jorge Luis Borges':
| https://biblioklept.org/2019/04/02/the-disk-a-very-short-
| sto...
| bradley13 wrote:
| Wow, that's unintuitive, but cool.
|
| Doesn't help on the moon, though, where the surface is soft,
| and may contain boulders.
| koliber wrote:
| With a lunar lander you can play with the weight
| distribution. You can make it more dense on one side. This,
| together with a self-righting shape, could increase the
| chances of settling in the desired orientation.
| giantrobot wrote:
| While it was settling it would destroy all/most of the
| external fixtures including antennae, engine nozzles, and
| sensor housings. Bonus the rocking action during settling
| could puncture the hull or break a windows on a sharp
| boulder.
| rolph wrote:
| https://en.wikipedia.org/wiki/Weebles#Design_principle
| Bengalilol wrote:
| I clearly understood this while playing Lunar Flight
| https://store.steampowered.com/app/208600/Lunar_Flight/
| ubermonkey wrote:
| "Because they don't teach Lunar Lander in schools anymore."
| Julesman wrote:
| Radical suggestion. Don't make your lander taller than wide. I'm
| the first to assume that the science nerds have thought of
| everything and that my uneducated self has nothing to say about
| it. But then I saw the lander. It looks very tippable.
|
| So then here's my luddite take. Can't they just unfurl wider
| stabilizers from the legs that increase their footprint? At slow
| speeds in low gravity it seems like they wouldn't need to be
| heavy or strong.
| stavros wrote:
| In general, when it seems to my uneducated opinion that a bunch
| of experts have missed something obvious to me, it's almost
| always the case that the one who has missed something is me.
| foobarian wrote:
| I feel exactly the same and this is the reason why I would
| absolutely love to read an expert article titled "Why super-
| wide Moon landing gear is not a good idea"
| db48x wrote:
| Stabilizers are made of matter, and matter has mass. Lifting
| mass off of the Earth and on to the Moon takes fuel. Fuel is
| made of matter too, and has mass. Lifting the fuel to lift the
| fuel to lift the mass is expensive.
|
| So much cheaper just to have an altimeter and no extra
| stabilizers. Sadly, their altimeter didn't work. They forgot to
| turn it on correctly.
|
| Honestly, they're lucky that it got so close to landing
| correctly; if it had been going faster the damage would have
| been even worse than just a crumpled landing leg.
| wolfendin wrote:
| If you have legs that unfurl, now you have minimum three more
| more systems that fail and cause the same problem
| unethical_ban wrote:
| TIL the lunar lander for Artemis is 100 TONS! My goodness! I
| didn't think it'd be the Mylar balloon of the Apollo LM, but I
| did not really think it was going to be the entire first stage of
| Starship. I guess I need to read more.
| russellbeattie wrote:
| The spacecraft failed long before it tipped over. With the
| altitude laser system out of action, it wasn't going to land
| correctly unless they got lucky, which they didn't.
|
| Like the article said in the last line, the margin of error is
| only manageable if all the systems are functioning correctly. The
| argument over the height of the lander is as nonsensical as
| arguing over any of the thousands of other design decisions.
| Second guessing literal rocket scientists is silly.
|
| The lander was designed as a whole, any single change - redundant
| systems, extendible legs, etc., etc. - would have required other
| changes due to weight or space constraints, requiring other
| changes, ad nauseum.
|
| The specific thing that killed this landing is a failure in
| quality control/checklists which if done better would have
| ensured all the systems operated correctly and a successful
| landing.
| rolph wrote:
| https://en.wikipedia.org/wiki/Weebles#Design_principle
| demondemidi wrote:
| Everything about landing on the moon is challenging. Seems oddly
| specific to pick this challenge? Weird.
| whartung wrote:
| The past few failed missions certainly highlights how amazing
| the successes the US had back in the day.
|
| 50-60 years of history, crazy advances in technology from
| materials to computers to everything else, yet its still
| objectively a difficult, "unsolved" problem.
| ge96 wrote:
| Idk how starship will do it since it is tall af
| hinkley wrote:
| The landing and take off tanks would have to be ballast tanks I
| suspect. Meaning at the bottom, center of the craft, where the
| moment arm is the most favorable.
|
| If Flight 3 explodes again, my completely armchair prediction
| is that stage 1 will get something similar, but to stop
| sloshing on boostback.
| GMoromisato wrote:
| Almost all challenges are caused by tight mass budgets--the
| maximum mass that we can get to the lunar surface. Symmetrically,
| almost all problems can be solved by increasing the mass budget:
| more fuel to loiter longer, redundant systems, etc.
|
| The advantage of SpaceX's Starship--and the reason NASA chose it
| for the first HLS--is that it has an insane mass budget. It's
| literally designed to land 100 people on the surface of Mars (TBD
| whether it will ever meet that goal, but that's the design
| point).
|
| Starship is so hilariously large that there's enough mass budget
| to solve almost any problem.
| LarsDu88 wrote:
| What if it tips over?
| Workaccount2 wrote:
| Didn't the Saturn 5 have a similar mass budget as the Starship?
| I am guessing there is some major caveat to it.
| bryanlarsen wrote:
| They might be comparable without refueling, but Starship
| utilizes refueling to massively increase it's deep space mass
| budget.
| pavon wrote:
| This is the huge difference. Apollo missions used two
| launches of the Saturn V - one for the crew capsule and one
| for the lunar lander, which rendezvoused in orbit. Artemis
| is planning on using one SLS launch for the crew capsule,
| and an estimated 8-16 Starship launches for the lunar
| lander and refueling.
| saratogacx wrote:
| That isn't how the Apollo missions worked. They put the
| command module, service module and the LEM on a single
| Saturn 5[1]. Once in space, the command+service module
| would need to turn around and dock with the LEM before
| heading off to the moon.
|
| https://www.nasa.gov/history/diagrams/apollo.html
|
| 1: https://www.nasa.gov/wp-
| content/uploads/static/history/diagr...
| nativeit wrote:
| Starship _might_ utilize refueling. So far it hasn't done
| anything of the sort.
| GMoromisato wrote:
| No, it did not.
|
| Starship gets refueled in orbit (by a fleet of Saturn V-class
| rockets). A Saturn V could put about 8 metric tons on the
| lunar surface. With refueling, Starship can land 100 metric
| tons on the moon.
| giantrobot wrote:
| The Saturn V could get a lot of mass to LEO but most of that
| mass was fuel to get from LEO to the surface of the Moon. A
| design caveat of SpaceX Starship (a design feature that's yet
| to be demonstrated/proven) is refueling in LEO. So the
| Starship gets a bunch of payload mass to LEO, refuels, and
| then heads to the Moon. For Mars it would need to refuel _on
| Mars_ to get back to Earth.
|
| It's the refueling that potentially gets a huge usable
| payload to the Moon. A second Starship whose only payload is
| fuel would launch with the first and they'd rendezvous and
| transfer fuel. Ostensibly if something went wrong with the
| refuel rendezvous the payload (or personnel) carrier would
| still be able to abort back to Earth.
| kunai wrote:
| That's incorrect -- the reason NASA chose Starship is because
| it was the most capable lander for the lowest possible
| projected upfront cost. Government contracts always attempt to
| maximize economic utility while meeting objectives -- any other
| advantages are ancillary to this.
|
| > Symmetrically, almost all problems can be solved by
| increasing the mass budget: more fuel to loiter longer,
| redundant systems, etc...Starship is so hilariously large that
| there's enough mass budget to solve almost any problem.
|
| Also incorrect. Mass budget does not change fundamental
| Newtonian physics, nor does it alter the issue of instability
| caused by a high center of mass. The engineers at SpaceX are
| very smart and I'm sure they're hard at work trying to engineer
| out this solution, but it's a bit like saying that you can
| prevent a car from rolling over if you make it heavy and
| powerful enough. Sure, but that causes problems and challenges
| of its own. It would have been easier to engineer the car to
| have a lower center of mass, i.e. it would be easier to land on
| the moon with a lander that had its mass spread out over a
| larger surface area and didn't have an angular moment of
| inertia significant enough to where topple was a concern --
| like the Dynetics or BO proposals.
| mr_toad wrote:
| > Also incorrect. Mass budget does not change fundamental
| Newtonian physics, nor does it alter the issue of instability
| caused by a high center of mass.
|
| The size of the ship solves some problems. Illustrations
| depict landing gear taller than a person, which means small
| rocks and holes are less of an issue.
| jojobas wrote:
| This high mass budget comes with some insane quantity of
| refueling launches (nobody can tell precisely how many, but
| more than 5 per mission).
| Dagger2 wrote:
| "Why is there a sudden epidemic of spacecraft rolling on the moon
| like Olympic gymnasts performing floor routines?"
|
| That's not how statistics work. We don't have a "sudden
| epidemic", we just happened to get unlucky a few times in a short
| period.
|
| The exact same underlying risks and chances of success could have
| led to a long period of everything working fine, or (the least
| likely outcome) a perfectly spaced series of accidents occurring
| at whatever the mean rate is.
|
| Not understanding this is part of how we let people get away with
| lax safety standards. Nothing gets mass attention until enough
| people get unlucky in a short period, despite the safety
| standards being lax the whole time. (I think many people reading
| this could name a company this has happened to recently -- but
| will attention stay on them for long when random chance gives us
| a period of no problems?)
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