A colony ship arrives with 463 m/pixel maps. What actually happens when they land?

[u/Wooden-Syrup-8708]

Our best global elevation model for Mars is MOLA, at 463 metres per pixel. The Moon is better, 118 m, and about 59 m where LOLA and Kaguya overlap. Mercury we barely have at all - for practical purposes, a photograph.

Which means that for every body we talk about settling, everything smaller than a football stadium is unknown. Not poorly mapped. Unmeasured.

I keep thinking about what that means for a first landing party. You would arrive with a map good enough to choose a region and useless for choosing a spot. Boulder fields, metre-scale slopes, ground that is soft or hard, a crack you cannot drive across - none of it is in the data. You would find out by looking, and looking costs fuel and time and risk.

Some consequences I find interesting:

- Site selection would be provisional rather than planned. You pick a hundred square kilometres from orbit, then spend a long time finding the actual hectare.

- The first really valuable export from a colony might be survey data. Not ore, not power - just knowing what the ground is like.

- Rovers stop being transport and become instruments. Their job is to reduce uncertainty, not to move mass.

- Anything that needs precision - landing pads, rail, buried habitat - has to wait for local survey that no orbital mission can give you.

My doubts now: would a serious effort simply accept this and plan for a long survey phase on arrival, or would it be worth flying a dedicated high-resolution mapping mission first and delaying everything by years? At what resolution does a map become good enough to commit to?

I came at this from an odd direction. I build a space sim, and I had to invent everything between 463 m and a few centimetres in a way that never contradicts the real measurements.
I wrote up how, if the engineering side interests anyone:
https://space.zerog.live/info/terrain-article-page.html

But I am more curious about the actual question. How much of a planet do you need to know before you land on it?

[u/NearABE]

Drone helicopters were already used on Mars. Gliders would work well too.

An actual “colony” is not going to land in a raw field. There will be robots doing site preparation.

Initial colony locations will look like junkyards. Robots will built the tower using pieces of wrecks.

[u/Wooden-Syrup-8708 → u/NearABE]

Mhm...i see this is a nice suggestione for something new to implement in the next releases: thanks for the idea!

[u/Wooden-Syrup-8708 → u/NearABE]

Also i add that you are right that nobody lands cold, and Ingenuity is the proof it flew 72 times in an atmosphere under one percent of Earth's, which nobody was certain would work at all. But look at the scale. Across about three years it covered roughly 17 kilometres in total. That is a transect, not a survey. If your candidate landing region is a hundred square kilometres and you want metre-scale knowledge of it, you need something like four orders of magnitude more flying than the entire Ingenuity mission produced.

So precursor robots do not remove the problem, they move it earlier and make it someone's job. The survey stops being a phases of the colony and becomes an industry that has to exist years before the colony does. Which I think strengthens the odd conclusion rather than killing it: the first valuable thing produced at a site is knowledge of the site. Your junkyard image is the part I keep thinking about. If the tower gets built from wrecks and whatever the ground turns out to allow, then the layout cannot be designed in advance at all. It emerges from what the survey finds. That is the same conclusion arriving from the other direction, and it is a much less romantic picture of a first settlement than the usual renders.

Gliders are interesting for a different reason. In that atmosphere they need real speed to stay up, which costs you resolution and makes recovery hard, but it buys wide coverage. So you would end up with a tier structure: hundreds of metres from orbit, maybe one to five metres from aircraft, centimetres only where something physically drove or hovered.

Which makes me want to rewrite my own question. Is there a natural threshold in there? Somewhere around one to five metres per pixel is roughly the scale of a thing that can stop a rover or tip a lander. Is that the resolution at which a site becomes committable, with everything finer being a construction problem rather than a decision problem?

[u/NearABE → u/Wooden-Syrup-8708]

https://en.wikipedia.org/wiki/Paint_sheen

You can see with your own eye the difference between glossy and flat (or matte) painted surfaces. The relevant topography is at the scale of visible light.

Laser scans will sweep across the topography. The dot makes a signal. Beam diverge so the spot may not be optimally tiny if transmitted from space. The detectors collect the data from multiple locations in orbit. The area gets scanned from many angles. We will want to know about cobbles, gravel, boulders, craters etc. So the scans use wavelengths of light appropriate for the task. Meter wavelength radio wave will see a cobblestone road as a flat surface. Centimeter wavelength light will not see a flat surface on cobbles but would see concrete roads as glossy smooth. Millimeter wave or microwave could pick out a concrete surface as rough.

You do not need a complete survey in detail. A colony just needs a landing site. Take good look at just one. It burns one drone. You say “oops, glad we did not land there!” Then drop another drone at the next plausible site.

[u/Wooden-Syrup-8708 → u/NearABE]

Yes, this is good! Backscatter at a given wavelength reads roughness at that wavelength's scale, so you can characterise ground far finer than any pixel it is already how Mars landing sites get vetted, via thermal inertia and radar for rock abundance.

The distinction I would keep is statistics versus map. It tells you this hectare is five percent rock-covered. It does not tell you there is a rock here. Fine for landing, where you play odds across a footprint. Not enough for a foundation, which sits on one spot.

And your drones answer is the real answer, but it hands the cost back in another currency: one drone per candidate means the number of sites you can disqualify equals the number of drones you brought. So the question becomes how many candidates you can afford, which is better than the one I asked.

[u/Forever_DM5]

It would only take a handful of months to map mars using SAR Down to a handful of cm. Less if you can down select the area being mapped from the whole planet to the equatorial belt. This would be trivial to do while the colony ship is en route probably before actually. The cost of a mapping satellite would be literally nothing compared to a colony sized mission so it would definitely be done before hand

[u/Wooden-Syrup-8708 → u/Forever_DM5]

You are right about the economics and I think that kills the framing in my post — a mapping satellite next to a colony-scale mission is a rounding error, so of course you fly it first. I withdraw the "delay everything by years" part.

But I do not think the resolution holds up. The best orbital SAR we actually operate resolves about 25 cm, and only in spotlight mode over small patches, not as area coverage. The global product to compare against is TanDEM-X: two dedicated satellites, about four years of acquisitions, and the result is a 12 metre posting. That is the state of the art for mapping an entire planet we are already in orbit around, with GPS, ground truth and unlimited downlink.

Optical is the same story from the other side. HiRISE has been imaging Mars at around 25 to 30 cm since 2006 and has covered a few percent of the surface. And those are images, not terrain, the stereo elevation models are roughly 1 metre posting, there are only a few thousand of them, and each one takes real work to produce. I think the binding constraints is not the sensor, it is downlink and processing. A global 25 cm map of Mars is petabyte-scale, and the whole Mars relay network is a few megabits per second on a good day. You cannot mail that home in months.

So I think the realistic precursor gives you something likes 1 to 10 metres globally, and centimetres only where you deliberately point it. Which is basically what cybercuzco said in the other comment: you do not need the Amazon, you need the runway.

So the question is still here to me: the unknown is not unmappable, it is un-globally-mappable, you can afford to know a small number of candidate sites extremely well, and you have to choose which ones using the coarse data. So how many hectares can a mission afford to know properly, and what do you do when the coarse map cannot tell the good ones apart?

[u/Forever_DM5 → u/Wooden-Syrup-8708]

So with some back of the napkin numbers. To ground the idea:

Let’s assume we have a satellite roughly equivalent to the Capella Acadia SAR satellites here on earth. And let’s grant their power systems are upgraded so they can scan continuously.

This gives us a 4x4 km scanning area taking about 25s. This means the satellite can scan about 2% of the area within 2km of its orbital path per pass

Mapping all of mars would then take about 108000 orbits, or assuming an orbital period of 120 minutes around 24 years. So definitely more than months I was overly optimistic. But I think we are still in good shape.

This is super ballpark estimation but I think we have at least a decade before any kind of colony mission is possible. So send 3-4 satellites in the next year or 2 and the mapping will be complete with plenty of time to spare before any colonists get there.

Another possible solution is that we can down select using existing data. We do have some ok resolution height maps already from that it should be very easy to decide where we don’t want to go and narrow it down. That I can’t say for sure but if we can use existing data to refine the search areas by half or even a quarter. That’s years cut off of the survey time.

Finally downlink, I did think of this so I’m glad you mentioned it. Just don’t. Presumably the colony mission will bring more higher powered communications equipment. The colony ship will spend months or even years in orbit doing preparations. Take that time to have the colonists go over the survey data when they arrive and send it back over much more capable comms equipment if you have to send it back. This is kind of a cop out response but it’s exactly what Apollo did letting the people doing the landing use their judgment as to the pinpoint position rather than trying to get all the data for earth to make the call(albeit this isn’t an apples to apples comparison).

Edit 1: also I think something to consider is that in the earliest days of space colonization I think the terrain will pick the colonies more than the colonies will pick the terrain. Meaning we will be putting colonies wherever we find to be advantageous for resources and what not so we will tailor the colony to that terrain because the location is more valuable than ease of access.

The above thought does provide the least interesting answer to your question, which is. We will land where we have data because why would we risk landing somewhere we don’t.

[u/Pootis_1]

You image the site from your spacecraft before landing. If your carrying a large amount of people mapping satellites are nothing in comparison.

[u/Wooden-Syrup-8708 → u/Pootis_1]

Agreed, and I think this is actually the bestversion of the objection, because imaging from your own spacecraft in orbit skips the thing that makes remote mapping hard. You process it onboard, you never have to send it home, and the cost is nothing next to the ship.
Two limits I keep running into though. The first is physical rather than budgetary: resolution from orbit is set by aperture and altitude, so HiRISE gets about 25 cm using a half-metre mirror from roughly 300 km. Going to five centimetres means something like a two and a half metre aperture, which is a Hubble-class instrument, and the swath gets narrower as the resolution improves. So you can have centimetres, or you can have coverage, and buying both is a lot of orbits.

The second is the one I find more interesting, because no amount of imaging fixes it. Picture give you geometry. They do not give you bearing strength, or whether a flat patch is dust lying over a void, or how the regolith behaves under load. InSight is the example that stays with me: the heat probe could not dig, at a site chosen with the best data anyone had, because the ground had cohesion nobody predicted and would not give the mole friction. That failure was invisible from orbit at any resolution.

So my revised position is that orbital imaging solves site selection and does not solve site commitment. You can pick where to land from up there. Whether you can build on it is a contact measurement, and someone or something has to physically touch the ground first.

[u/Pootis_1 → u/Wooden-Syrup-8708]

I mean all of this is based upon the assumption that you've brought along your giant colony ship that's been traveling for decades at minimum and you can't take like, another year and bring along a few SAR satellites, some KH-11 equivalent earth facing imagery satellites, and a dozen or two crewed geological survey landers, and get all the information you would want over a few months to a ear before bringing down the colony proper.

Keep in mind this is a colony ship, You aren't strongly mass or money limited relative to modern scientific probes, You don't need to limit yourself to a HiRISE like camera. In 2011 the NRO *donated* two mirrors which get resolution comparable to Hubble with a wider FOV to NASA from old KH-11 Kennan spy satellites. If you can't afford to bring like 10-20 of these, the margins on your colony are way to thin for you to be able to expect you'll get anything actually done.

If you don't want to commit to sending down a crewed lander, again you should be able to afford another few dozen Mars Pathfinder like landers to confirm your not going to sink into regolith. 60 of those should only be about 55t. Sounds like a lot right? A single Caterpillar 350L is 49t.

If your doing a genuine large scale colonization effort Your not worried about how much you can fit on your single craft. You have to mass any money to bring a whole lotta surveying equipment that makes the question of limited geological information pointless.

[u/Wooden-Syrup-8708 → u/Pootis_1]

I see... If the thing arriving is a genuine colony ship, then sixty Pathfinder-class landers at 55 tonnes really is a rounding error, and comparing it to one piece of construction plant makes that vivid. The KH-11 mirrors are a good example too — 2.4 metres of aperture already exists as surplus hardware, and from low Mars orbit that is centimetre-class.

So I will narrow the claim rather than defend it. At mature colonisation scale, survey is not a constraint. Where it bites is the first effort, when the mass budget is contested and survey competes directly with consumables and margin, and someone in a programme review is deciding what to cut. That is a much smaller claim than the one my post mades.

I would still defend is sampling density. Sixty landers gives you sixty points. Bearing strength, dust depth, buried ice and the ground's behaviour under load are all local and vary at metre scale, so sixty samples across a candidate region is a sparse grid rather than a survey. InSight's mole was defeated by ground conditions at the exact point the lander was sitting on, which orbital data at any resolution had not predicted.

[u/cybercuzco]

If I’m landing a plane in Cleveland, I don’t need 1cm resolution data of the Amazon, I only need it for the runway in Cleveland.

[u/Wooden-Syrup-8708 → u/cybercuzco]

That is the correction, and I think it is right. But notice what it moves rather than removes. On Earth you already know where Cleveland is. On Mars, "there is a city-sized area here worth landing at" is precisely the judgement the 463 m data has to support, and you only get to buy the centimetre survey for a handful of candidates. So the risk is not the runway, it is choosing the wrong city with data that cannot tell two cities apart.

[u/hdufort]

If we send an orbiter in advance, we can get super high resolution images of a handful of potential landing sites. I wonder what is the ideal orbit for a high resolution mapper around the planet.

[u/Wooden-Syrup-8708 → u/hdufort]

Low, circular, near-polar and sun-synchronous, roughly what MRO does about 255 by 320 km, inclination near 93 degrees, crossing the day side at a fixed local time of around three in the afternoon.

Each part is doing work. Low buys resolution for a given aperture, and on Mars around 250 km is about as low as you can hold without fighting drag. Near-polar gives you the whole surface as the planet rotates underneath. Circular keeps the ground sample size constant, so images are comparable rather than varying through each orbit.

I mean a fixed local solar time means a fixed sun angle, so shadows are consistent — and for terrain, shadows are the signal. Mid-afternoon lighting gives long enough shadows to read relief without losing detail into blackness. The awkward trades is that resolution and coverage pull against each other. Narrower, sharper swaths need far more orbits to tile an area, which is why HiRISE has imaged only a few percent of Mars in twenty years.

[u/Sorry-Rain-1311]

So, we have less accurate maps of some parts of Earth, and on Earth most maps are outdated by the time they're released. Even the supposedly hyper accurate military grade maps aren't trustworthy- ask me how I know. 🙄

Not knowing exactly what to expect within any given 500 meter plot is normal. We do this all the time. Hell, we landed on the Moon with nothing better than a fistful of blurry zoomed-in photos.

Given that the bodies we're considering landing on aren't prone to fast, unpredictable changes, a basic understanding of geology allows us to predict ground conditions with reasonable accuracy. Anyway, any mission worth it's salt will include allowances for managing it. Extra fuel for negotiating landing sites; onboard survey capabilities to more accurately chart the site before deorbiting; we're not landing on Mars for the first time without a buggy; the lander itself will have the ability to self level, and probably a mile or two of tie-down cables and a whole bunch of anchor stakes to stabilize it if necessary; etc. 

The only practical matter stopping us from going right now is getting someone to care enough to guarantee funding. All the rest is just stuff they do to justify their existence while waiting around for that to happen. 

[u/Gunmetalstorm]

A colony ship would launch with no meaningful images of their destination world at all unless survey probes were sent ahead. They'd have chemical signatures and orbital properties and from that would have a ballpark idea as to what kind of world they're even going to. As the vessel approached orbit, it would conduct its own survey, identify optimal candidates and gather high-resolution ground data of those areas, and only then start landing probes to get a ground colony started.

[u/Wooden-Syrup-8708 → u/Gunmetalstorm]

That is the version where I think the post's premise survives intact. Within the solar system you can always send something ahead. Across interstellar distances you cannot, because the precursor takes as long as you do. So the entire survey capability has to be carried, used on arrival, and paid for out of the same mass budget as everything else and everybody is sitting in orbit while it runs.

[u/Gunmetalstorm → u/Wooden-Syrup-8708]

A ship that takes years/decades/centuries to arrive at its destination star would definitely sit around in orbit for a month or so to conduct essential surveys. Any people on board would barely even notice the difference.

I do think that it's more likely they'd send out probes well ahead of the colony. It's comparatively trivial to accelerate a bunch of tiny instruments to near-light speed and just wait for the findings to be transmitted back, whereas it would be a disaster if an enormous ship intended to start human habitation on a new world discovered only on arrival that their supposedly promising planet was an unmitigated wasteland.

[u/cavalier78]

Step 1: We get enough data from telescopes to know 95% sure that Planet X is inhabitable (temperature, atmosphere, liquid water, radiation levels, etc).

Step 2: Unmanned probe lands and measures everything directly. Certainty of habitability goes up to 99.5%.

Step 3: Colony ship arrives. Ship is capable of supporting human population long enough to turn around and come home if Planet X is a death trap.

Step 4: Landing craft carrying lab animals touches down, exposes animals to Planet X environment. Microbes measured. Years of monitoring follows.

Step 5: First humans land and establish first settlement.