Elon Musk says he will put millions of people on Mars.

[HopDavid]

I think a moon base would be feasible for less than a couple of billion, including a fair amount of habitation. A lot of robotic construction, and sending machines to build machines to build machines and things though. Since the cost for getting to LEO dominates, especially for slower robotic/unmanned missions, a Mars base shouldn't cost too much more.

Building a lunar base with telerobots is plausible. Building a Mars base this way, much less so.

Light lag to the Moon: 3 seconds
Light lag to Mars: ten to fifty minutes.

Another thing you need for telerobots is lots of bandwidth. Since signal strength falls with inverse square of distance, high lunar bandwidth is less challenging than high band width to Mars telerobots.

It would take numerous missions to send the equipment to build infrastructure. 30 missions to the moon would be accomplished in a few years. Since Mars launch windows are each 2.14 years, 30 missions could take six decades.

[Betruger]

And the initial reply that Hop snipped above was in the context of the original discussion: millennial timeframe colonization/terraforming scenarios.

Um... no. Here is the original post in it's entirety:

I would not sit arround for millenia. The moon is close and we should be able to colonize it in the near term.

Or Mars. It's a toss up and frankly colonizing Mars is more inspiring. Unless it falls on its face for some reason (ie because it's too hard compared to e.g. the Moon).

So no, the discussion I entered was about near term development. I bolded the part you seemed to have missed.

Near term the moon is plausible. Mars is not.

Ok, if you say so.

[williatw]

It would take numerous missions to send the equipment to build infrastructure. 30 missions to the moon would be accomplished in a few years. Since Mars launch windows are each 2.14 years, 30 missions could take six decades.

Yes assuming one launch per launch window. If Musk succeeds in producing reusable chemical rockets he could launch multiple flights to earth parking orbit, in the months prior to launch window to mars opening up. The upper stage(s) that would send the payloads to mars could presumably be fueled/refueled as needed. When the launch window to mars opens up the equivalent of say many flights worth of payload could be sent to mars per launch window cycle(don't know how long a launch window stays open).

[HopDavid]

It would take numerous missions to send the equipment to build infrastructure. 30 missions to the moon would be accomplished in a few years. Since Mars launch windows are each 2.14 years, 30 missions could take six decades.

Yes assuming one launch per launch window. If Musk succeeds in producing reusable chemical rockets he could launch multiple flights to earth parking orbit, in the months prior to launch window to mars opening up. The upper stage(s) that would send the payloads to mars could presumably be fueled/refueled as needed. When the launch window to mars opens up the equivalent of say many flights worth of payload could be sent to mars per launch window cycle(don't know how long a launch window stays open).

In Wilson and Clarke's plan, the mission each 2.14 years requires 694 tonnes to LEO. The I.S.S. weighs 450 tonnes. A single mission each 2.14 years would be very ambitious.

If you look at Table 7, you will see 440 tonnes of that 694 tonnes is Trans-Mars Stages. These are to get the payloads out of low earth orbit and on their way to Mars. These four 110 tonne rockets are basically rocket engines and propellant. They would need to be launched close to the launch window, or the else the propellant they carry would suffer boil off losses.

But I believe Willson & Clarke's plan would be a suicide mission for the astronauts. The radiation shielding is likely inadequate for an 8 month trip. A Mars Transfer Vehicle (MTV) adequate to protect against galactic cosmic rays would be a lot more massive than Willson & Clarke's 130 tonne MTV.

[krenshala]

A launch window is determined by the capabilities of the vehicle compared to the optimal flight path. The more extra performance the vehicle is capable of, the "wider" the launch window can be and still successfully reach the intended target.

I see no reason why the plan of launching numerous rockets into earth orbit, and then firing them all off into a Mars Transfer Orbit during the launch window wouldn't work. Complex, but getting the rockets working in the first place is complex ...

[HopDavid]

I see no reason why the plan of launching numerous rockets into earth orbit, and then firing them all off into a Mars Transfer Orbit during the launch window wouldn't work.

Money's a finite resource.

[williatw]

I see no reason why the plan of launching numerous rockets into earth orbit, and then firing them all off into a Mars Transfer Orbit during the launch window wouldn't work.

Money's a finite resource.

Yes it is which is why I prefaced it by saying if Musk succeeds in developing reusable rockets. This would lower the cost of putting mass in orbit by at least one and probably two orders of magnitude. Instead of thousands of dollars per pound low hundreds or maybe even tens of dollars per pound. The more mass you can orbit, the more shielding you have available. If multiple launches to parking orbit are made in the months before the launch window to Mars opens, the crew containing modules could be surrounded by the cargo/propellant tanks and their modules on the trip to Mars.

[HopDavid]

I see no reason why the plan of launching numerous rockets into earth orbit, and then firing them all off into a Mars Transfer Orbit during the launch window wouldn't work.

Money's a finite resource.

Yes it is which is why I prefaced it by saying if Musk succeeds in developing reusable rockets. This would lower the cost of putting mass in orbit by at least one and probably two orders of magnitude. Instead of thousands of dollars per pound low hundreds or maybe even tens of dollars per pound.

Tens of dollars per pound is exceedingly optimistic even if Musk does achieve reusable rockets to LEO.

And my point on trans-mars stages remains ignored. These are mostly propellant, which doesn't store well in LEO. The Trans Mars stages would need to be launched close to the launch window.

How many pads do you have for the Trans Mars Stages? What sort of turnover do you expect at these pads?

The more mass you can orbit, the more shielding you have available. If multiple launches to parking orbit are made in the months before the launch window to Mars opens, the crew containing modules could be surrounded by the cargo/propellant tanks and their modules on the trip to Mars.

For the sake of argument let's say you have all the infrastructure to launch the trans mars stages just before launch window. We have reusable rockets that deliver mass to LEO for tens of dollars per pound.

Further, the payloads are dirt cheap.

These same assumptions would also bring down the expense of a lunar base.

Given many launch pads and extensive infra-structure, a lunar mission could be launched every two weeks. Trip time would be less than a week.

If initial lunar construction can be done by telerobots, mass to LEO would be a small fraction that needed for sending humans for an eight month interplanetary journey.

[williatw]

Just how quickly would boil off of propellant O2 & H2 occur? How long would it take to lose say 5-10% of your propellant while parked in earth orbit? How much time would there be to prior to the opening of a mars window to make multiple launches to earth orbit without worrying about significant boil off? We talking weeks? Days? Hours/minutes? The more time you have to make the launches before the launch window to mars opens, the less the strain on terrestrial launch facilities. Of course if Musk makes rockets re-usable, then the cheaper costs of launches would likely cause a greater increase in the no. of launches and inevitably more launch capacity would occur anyway, mars mission or naught. Also I seem to recall you championing the idea of propellant depots from lunar resources in low earth orbit and/or Lagrangian points. I assume they would have to deal with the issue of boil off as well. Would think there would likely be propellant depots in earth orbit launched from earth probably long before the lunar ones would be available.

[HopDavid]

Also I seem to recall you championing the idea of propellant depots from lunar resources in low earth orbit and/or Lagrangian points. I assume they would have to deal with the issue of boil off as well. Would think there would likely be propellant depots in earth orbit launched from earth probably long before the lunar ones would be available.

More frequent launch windows enables a higher through put. When a depot is used once a month rather then once a year, boil off is less of an issue. This is one of the reasons lunar architecture is more more amenable to propellant depots.

There would be less boil off in EML1 or EML2. These can be made colder than low earth orbit. These staging platforms not only have delta V advantages, but they're a better thermal environment for cryogenic propellant storage.

[Skipjack]

These are mostly propellant, which doesn't store well in LEO.

There are several studies that say otherwise. Also, there are propellants that are not cryogenic.

[HopDavid]

These are mostly propellant, which doesn't store well in LEO.

There are several studies that say otherwise.

Are they online? Could you give a url? I'm interested in that sort of stuff.

Also, there are propellants that are not cryogenic.

Hydrogen is one of the best chemical fuels. If you use other fuels, your mass fraction will be even more challenging.

Oxygen's cryogenic but not as difficult to store as hydrogen.

[KitemanSA]

Yes it is which is why I prefaced it by saying if Musk succeeds in developing reusable rockets. This would lower the cost of putting mass in orbit by at least one and probably two orders of magnitude. Instead of thousands of dollars per pound low hundreds or maybe even tens of dollars per pound.

Tens of dollars per pound is exceedingly optimistic even if Musk does achieve reusable rockets to LEO.
.

The energy used to get to Sydney from the States is greater than that needed to get to orbit. And most anyone can fly to Sydney for less than $10 per pound. Get the flight rate up and the same will apply to orbit.

[KitemanSA]

Just how quickly would boil off of propellant O2 & H2 occur?

Store it as solid water and I'd say "not quickly at all"!

[tomclarke]

Yes it is which is why I prefaced it by saying if Musk succeeds in developing reusable rockets. This would lower the cost of putting mass in orbit by at least one and probably two orders of magnitude. Instead of thousands of dollars per pound low hundreds or maybe even tens of dollars per pound.

Tens of dollars per pound is exceedingly optimistic even if Musk does achieve reusable rockets to LEO.
.

The energy used to get to Sydney from the States is greater than that needed to get to orbit. And most anyone can fly to Sydney for less than $10 per pound. Get the flight rate up and the same will apply to orbit.

10 hour 747 flight uses ~ 150,000 litres of fuel. And carries ~100,000kg load That is an FMR of ~ 1:1

Realistic FMR for LEO is 16:1.

Maybe Sydney/US needs two 10 hour flights? But even so it looks like LEO is 10X more expensive (in fuel weight) than travel to Sydney?

Add to this that rocket fuel is more expensive than jet fuel.

of course, fuel cost is still insignificant compared with other stuff.