Author Topic: Mars "domestic" launcher  (Read 7081 times)

Offline RonM

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Re: Mars "domestic" launcher
« Reply #40 on: 01/19/2018 04:05 PM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

Offline Lar

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Re: Mars "domestic" launcher
« Reply #41 on: 01/19/2018 04:24 PM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

My take? There isn't a need for one immediately. BFS can do it all. But in the long run, one size fits all isn't the optimal cost. intially? when you have limited development resources? absolutely it is.

But as Mars and the rest of our system see a robust industrial and transport infrastructure develop? Yes of course there will be specialty vehicles. Including this one. Because that's the lowest cost approach. The American West was settled initially with a lot of Conestogas but eventually there were lots and lots of specialty vehicles.

That's my take. The question is not if, but when.. .when is it time to do this? I'd say when transport is cash flow positive at the earliest, and there's enough traffic that specialization  will have significant use.
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #42 on: 01/20/2018 12:34 AM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.

CO/O2 may be very much better geared for Mars orbit - if it is substantially easier to produce.
It requires no water, though the efficiency I'm unsure of - I've never found decent estimates for CH4/O2 in large plants.

kWh/kg to LMO might be considerably better.

Might it be better enough than CH4/O2 to make things like lifting propellant for topping off BFS in orbit is worth it?
Or better enough so you can get BFS to mars with 250 tons of cargo and no landing propellant and add that on orbit, or even ferry stuff down?

If it costs half (kWh/kg) what BFS costs to launch a kilo to orbit, you might be able to top up BFS in orbit after a minimal fuel launch to more than the normal fill, and get 150, not 50 tons back to earth.

I guess for further computation, you'd need some figure on the relative costs of CH4/CO production. If it's cheap enough, it can be an enabler.
If it's not substantially cheaper, losing the commonality of methane all around isn't worth it.

I guess an aside might be if Raptor can run on CO, or a CO/CH4 mix.

Offline gin455res

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Re: Mars "domestic" launcher
« Reply #43 on: 01/20/2018 12:47 AM »
So, with all this discussion about aerocapture, are you guys saying there is no need for a Mars "domestic" launcher. That's what the thread is about.


CO/O2 may be very much better geared for Mars orbit - if it is substantially easier to produce.
It requires no water, though the efficiency I'm unsure of - I've never found decent estimates for CH4/O2 in large plants.

kWh/kg to LMO might be considerably better.

Might it be better enough than CH4/O2 to make things like lifting propellant for topping off BFS in orbit is worth it?
Or better enough so you can get BFS to mars with 250 tons of cargo and no landing propellant and add that on orbit, or even ferry stuff down?

If it costs half (kWh/kg) what BFS costs to launch a kilo to orbit, you might be able to top up BFS in orbit after a minimal fuel launch to more than the normal fill, and get 150, not 50 tons back to earth.

I guess for further computation, you'd need some figure on the relative costs of CH4/CO production. If it's cheap enough, it can be an enabler.
If it's not substantially cheaper, losing the commonality of methane all around isn't worth it.

I guess an aside might be if Raptor can run on CO, or a CO/CH4 mix.


If there was access to water, could h2o2/co also work?

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #44 on: 01/20/2018 01:14 AM »
If there was access to water, could h2o2/co also work?
There are lots of potential propellants on Mars from H2O2/CO, H2O2 monopropellant, Mg/O2, CH4/O2, H2/O2, Fe/O2, Al/O2, ...

All of them have their own issues, but I think it's safe to say of all of them that there is no nicely published efficiency of (at specific sites on Mars surface) for kWh/kg to LMO (for example), or more relevant metrics like (kg/year to LMO)/kg-landed.

Storage power varies - for example, CH4 is going to take a lot less power to keep cold than H2 but you can just stick H2O2 in an uninsulated tank. Sites access to resources (solar, water, minerals, secure flat spots) varies. ISP varies.

It's a huge pile of complicated trades.

An approach at such a table, or best guess at whole system efficiencies of fuel generation would be great.

« Last Edit: 01/20/2018 01:16 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #45 on: 01/20/2018 02:49 AM »
If there was access to water, could h2o2/co also work?
There are lots of potential propellants on Mars from H2O2/CO, H2O2 monopropellant, Mg/O2, CH4/O2, H2/O2, Fe/O2, Al/O2, ...

All of them have their own issues, but I think it's safe to say of all of them that there is no nicely published efficiency of (at specific sites on Mars surface) for kWh/kg to LMO (for example), or more relevant metrics like (kg/year to LMO)/kg-landed.

Storage power varies - for example, CH4 is going to take a lot less power to keep cold than H2 but you can just stick H2O2 in an uninsulated tank. Sites access to resources (solar, water, minerals, secure flat spots) varies. ISP varies.

It's a huge pile of complicated trades.

An approach at such a table, or best guess at whole system efficiencies of fuel generation would be great.
Not that hard to back out how much energy needed to reach LMO for various propellants as long as you keep it simple. I've done it several times already in this discussion to back up my intuition.
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #46 on: 01/20/2018 03:25 AM »
Not that hard to back out how much energy needed to reach LMO for various propellants as long as you keep it simple. I've done it several times already in this discussion to back up my intuition.

That is the almost trivial part.

How does the total landed mass trade with the total mass you can orbit, counting everything from trucks scraping up propellant, to the on/off cycling penalty of the ISRU due to solar for each days effort is where it gets hard, to storage losses differing, to ...

It is very unclear that the simple metric of kg of propellant used per kg of payload is useful other than as a first cut to eliminate  options like H2O2 monopropellant for SSTO to LMO.
« Last Edit: 01/20/2018 03:27 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #47 on: 01/20/2018 07:25 PM »
Energy scales much of the surface infrastructure needs. I didn't say propellant mass, I said energy.
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Offline RonM

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Re: Mars "domestic" launcher
« Reply #48 on: 01/20/2018 10:18 PM »
In addition to type of propellant, another important design consideration is where does the spacecraft come from?

I see three basic options:

1) Bought in parts on BFS and assembled on Mars (could be an issue if depending on how big the parts can be)
2) Complete smaller vehicle launched from Earth (something like the Lockheed Martin reusable lander design)
3) Built on Mars (requires extensive industrial capacity).

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