SpaceX Tuesday...
Discussion
I'm pretty sure they haven't got that kind of data yet. They would need to do a full topographic radar coverage of the proposed landing sites. That hasn't been done yet and as far as I know, no such missions are planned.
As has been pointed out, the tall nature of Starship makes it much more vulnerable to tipping than the relatively squat Lunar Module. That's one of the reasons why I think Bezos' "Universal Lander" concept will get the nod over using a Starship "Destination Moon" type lander.
As has been pointed out, the tall nature of Starship makes it much more vulnerable to tipping than the relatively squat Lunar Module. That's one of the reasons why I think Bezos' "Universal Lander" concept will get the nod over using a Starship "Destination Moon" type lander.
CraigyMc said:
Fully fuelled, the "lander"/"top" part of Starship -- ie. boosterless - is ~1400 tons (it would be ~5000 with the booster).
The landing weight might be (assuming zero fuel, and 20 tons of gubbins) in the region of 160 tons, which is equivalent to 60 tons on Earth -- so even on initial landing there will need to be something capable of dealing with those forces.
On the way back up it's much harder.
Given the lack of gravity/pressure on Mars, I think Starship will be SSTO from the Martian surface so lets ignore the booster. Lets take 1.4 million kg as the takeoff mass. Martian gravity is about 38% that of Earth, so that 1.4Mkg will exert a force equivalent to 532 tons on Earth.
Mesh won't do; a trampoline won't work; what I'm saying is, the launch platform is going to have to be solid.
Tough problem. Do they have dry lakes on Mars?
*yes I know.
edited to add: I know the target is 100 tons to Mars surface. I don't see that being what happens with the first landing though!
Interesting thought experiment. Thoughts:The landing weight might be (assuming zero fuel, and 20 tons of gubbins) in the region of 160 tons, which is equivalent to 60 tons on Earth -- so even on initial landing there will need to be something capable of dealing with those forces.
On the way back up it's much harder.
Given the lack of gravity/pressure on Mars, I think Starship will be SSTO from the Martian surface so lets ignore the booster. Lets take 1.4 million kg as the takeoff mass. Martian gravity is about 38% that of Earth, so that 1.4Mkg will exert a force equivalent to 532 tons on Earth.
Mesh won't do; a trampoline won't work; what I'm saying is, the launch platform is going to have to be solid.
Tough problem. Do they have dry lakes on Mars?
*yes I know.
edited to add: I know the target is 100 tons to Mars surface. I don't see that being what happens with the first landing though!
Edited by CraigyMc on Tuesday 16th February 14:50
The landing pad needed on Earth does not seem to be tremendously thick (based on what we have seen them lay it doesn't seem to be more than a foot deep - there's a photo of a guy on the ground next to it with the pad only seeming to come halfway up his calf). It's also not tremendously large either, all things considered. Assuming the same width and length but only a third the depth (as forces will be a third less, presumably) you would not need much in the way of construction equipment to build a pad for the first landing. They mostly seem to be doing it here the old fashioned way - using bits of wood! Is laying a pad amenable to automation? The rovers that are already on Mars can certainly drill and scrape, albeit more like a kid's toy than heavy duty construction equipment. Not sure how you'd mix up concrete in the Martian atmosphere but I guess it's possible to work something out, if you can deliver sufficient supplies. It's not like most building sites rely on a bloke with a shovel to mix the concrete after all.
So, assuming a pad can be constructed with relatively minimal equipment (dropped off from orbit and landing the old fashioned way under parachute/bouncing bubble thingies) that's the first issue solved. Doing the first deliveries that way would also mean the first Starships sent to Mars don't need to have the fuel to make a landing - not sure what payload (if any) could be lobbed on a direct ascent profile versus the planned refuel in orbit approach but it might simplify the first missions.
Then we come to takeoff. The existing Starship test stand - that has already launched two ships to 12km altitude - is hilariously primitive compared with almost everything we've seen in the past. But it probably only contains what, a couple of missions worth of steel? If that? You'd need a crane (and robot welder, robot arms) to construct it from the raw girders, but again I think it's probably within the realms of automation. The existing landers have arms and grabbers, so some things along those lines have been done already. With the ship only weighing a third as much as on Earth, even if the ones already launched weren't fully fuelled a Mars stand as strong as the Earth stand would likely be sufficient.
However, the elephant in the room is from where does the fuel come from? The fuel production infrastructure is going to make building a launch and landing pad look easy ...
Eric Mc said:
I'm pretty sure they haven't got that kind of data yet. They would need to do a full topographic radar coverage of the proposed landing sites. That hasn't been done yet and as far as I know, no such missions are planned.
As has been pointed out, the tall nature of Starship makes it much more vulnerable to tipping than the relatively squat Lunar Module. That's one of the reasons why I think Bezos' "Universal Lander" concept will get the nod over using a Starship "Destination Moon" type lander.
Fitting suitable legs to Starship is a relatively minor engineering issue. I don’t think SpaceX will get the contract for political reasons though. As has been pointed out, the tall nature of Starship makes it much more vulnerable to tipping than the relatively squat Lunar Module. That's one of the reasons why I think Bezos' "Universal Lander" concept will get the nod over using a Starship "Destination Moon" type lander.
The Blue Origin proposal has the right political ‘suction’, since they’re also partnered with Lockheed and Northrop Grumman. I don’t think NASA are too keen on the ridiculously long access ladder down the side of the lander, but they’ll do as their told like always.
Sierra Nevada/ Dynetics’”flying drum kit” lander looks more practical to me. Dynetics are based in Huntsville, Alabama so that’s not going to hurt them.
Flooble said:
However, the elephant in the room is from where does the fuel come from? The fuel production infrastructure is going to make building a launch and landing pad look easy ...
Land a starship with the generation equipment inside, generate and store the fuel in the tanks.Another launch carrying equipment to extract water.
The challenge is efficiency.
Eric Mc said:
Has anybody any idea what tonnage of material a Starship could land on Mars as cargo?
I *think* that they can ultimately land 100 tons of payload on Mars surface, but as I said before, I doubt that will be on mission #1. I think the early missions will have a greater amount of fuel+oxygen margin available.The Mars landing propellant load is obviously much smaller than the Mars takeoff propellant load, there's more than sufficient power available from all the engines. Consequently I think "landing heavy" is more about structural issues. A starship is expected to endure about 5G of decel on landing in Mars, coming in at a similar entry speed to an Earth LEO mission (~17000mph)
All the public data just talks about what they can get into orbit around Earth. Going to Mars requires on-orbit refuelling (around Earth) so that you can get the delta-V up to escape LEO and transit over there.
TL;DR If you assume Starship can get 100 tons into Mars Orbit, and it has fuel, then it's a question of the structure as to whether it can be landed on Mars (notes about landing pads aside). I think it's being built to take the lot to the surface.
The rocket fuel factory (O2 and Methane) will presumably be either in a Starship, or a Starship itself - it already has tanks and a lot of the valves/plumbing, with the obvious benefit that it can be built here.
An open question is -- where do you get the electricity to power the electrolysis/Sabatier process to produce that amount of propellant?
Solar power is an option but it comes with constraints. Mars is about half as good at Earth for sunlight; solar panels will need tracking to have much efficacy. Batteries don't like cold.
Assuming a source of water-ice can be mined (more energy), it'll have to be purified (more energy) and all this will have to happen in pretty cold temperatures so you're talking about a heated factory (more energy).
It's sort of interesting when you run through some of the numbers - liquifying and purifying the water (as feedstock for the propellant factory) will be the energy-intensive part of this. I would not be surprised to see an RTG going to Mars for this reason.
MartG said:
It would need to be aircooled for use on Mars
Define "air" It'd be primarily CO2 cooled on Mars and the pressure of that atmosphere is something like 0.6% of that on the surface of Earth, so to get a similar amount of cooling effect, you'd have to have a cooling system to cope with that lack of pressure.
You can't just run it 100x faster because you will run into mach effect problems when the flow rate goes supersonic. (Speed of sound at the Mars surface is around 550mph)
I'm not saying it's impossible, but the engineering of putting an actual reactor into that environment are probably more nontrivial than the whole rocketry thing.
rxe said:
MartG said:
It would need to be aircooled for use on Mars
Why could you not use a water circuit? Closed and pressurised. Water may not be the best fluid for that anyway -- en route to Mars it would have to cope with space temperatures and the pressure vessel would need to keep it contained, as well as obviously the fact that ice expands so you're into engineering vessels and pipework to cope with that.
Using something that doesn't expand when it solidifies would be a good start if you wanted a liquid cooled reactor at all.
Aren’t there bits of Mars that are very cold - surely you could bury a pipe network and use conductive cooling?
The challenge for them will be to get enough energy to establish an industrial capability - that can ideally make a s
t load of solar panels out of local materials rather than shipping them from Earth. Once you have that, you can make more panels and fuel to come home.
The challenge for them will be to get enough energy to establish an industrial capability - that can ideally make a s
t load of solar panels out of local materials rather than shipping them from Earth. Once you have that, you can make more panels and fuel to come home.CraigyMc said:
It's sort of interesting when you run through some of the numbers - liquifying and purifying the water (as feedstock for the propellant factory) will be the energy-intensive part of this. I would not be surprised to see an RTG going to Mars for this reason.
Would need to be a very big one and even then it'll be veeery slooow; an MSR would be a better bet, orders of magnitude higher power density. Just the small matter of funding someone to perfect a working example, NASA's SLS budget would comfortably pay for the development several times.
Eric Mc said:
As ever, the Russians did it first.They sent some turtles around the moon in 1968.
I like to think it ended happily for the turtles, after being fêted on their return, awarded the title Hero Turtles of the Soviet Union, photographed waving from the May Day parade reviewing stand next to Brezhnev, and finally retiring to a nice dacha on the Black Sea coast, spending the rest of their days blissfully frolicking about on the warm sandy beaches.As I say, I like to think that, which is why I'm not going to Google to find out what actually happened to them.
Gassing Station | Science! | Top of Page | What's New | My Stuff