Author Topic: A Minimal Architecture for Human Journeys to Mars (JPL)  (Read 73463 times)

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #60 on: 07/09/2015 05:15 pm »

Do you dispute my reasoning, or numbers?

The reasoning is sound. You pay more for an SEP vehicle. To make that worth it you have to reuse it. That's possible in Earth space where like a boomerang it comes back to you in 6 months or so. Then you get multiple reuses. When you send it to Mars, even if you can get it back, it will take so long that you only get a small number of reuses before its old.

Yes, my numbers dispute your numbers, because mine are based on actual research and quoted prices, rather then numbers that are hand-waved into existence.  I using the most obsolete Russian JUNK imaginable and your highly optimistic launch prices they show plenty of room for SEP to be cost effective.

Offline ClaytonBirchenough

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #61 on: 07/10/2015 12:50 am »
1) a regular hydrolox upper stage

2) The difference between a throw away falcon heavy and a fully reusable one is the cost halving you seek

3) See 2)

Do you dispute my reasoning, or numbers?

The reasoning is sound. You pay more for an SEP vehicle. To make that worth it you have to reuse it. That's possible in Earth space where like a boomerang it comes back to you in 6 months or so. Then you get multiple reuses. When you send it to Mars, even if you can get it back, it will take so long that you only get a small number of reuses before its old.

1) A regular hydrolox upper stage is "but a tin can with a modest engine strapped on"? I'd beg to differ.

2) Falcon Heavy has not even been flown successfully. SpaceX has not even recovered a first stage. I don't know how you could say matter-of-factly that a fully reusable Falcon Heavy will slash prices to $1,000/kg.

3) See 2 :)

I think your reasoning is sound. I think your reasoning for your numbers are not sound. I'm being hyper-rationale in pointing out that you assume a SEP stage of a magnitude that has not been built/proven, and then you go on to assume this is launched on a rocket that has not flown and is somehow fully reusable (years away from being demonstrated, and even more years away from being proven economical) for a price of $1,000 kg to orbit.

I also still can't get over the fact that you said a regular hydrolox upper stage is "but a tin can with a modest engine strapped on." Rocket stages are very much more than tin cans with engines on them. Hydrolox upper stages are rare. And hydrolox upper stages are not "a few million dollars worth", even without including development costs. Currently there is no hydrolox upper stage that would fit this architecture that would not need some upgrade/development money to be put into it.

I think you're being over optimistic and using numbers/assumptions that are not yet proven.


Yes, my numbers dispute your numbers, because mine are based on actual research and quoted prices, rather then numbers that are hand-waved into existence.  I using the most obsolete Russian JUNK imaginable and your highly optimistic launch prices they show plenty of room for SEP to be cost effective.

This^^^

And HEY! This "obsolete Russian JUNK" you talk of happens to be able to launch stuff into orbit. It's special junk at least. :)
Clayton Birchenough

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #62 on: 07/11/2015 01:03 pm »
Well I'm glad you had a giggle at the "tin can with a rocket strapped to it" because that is essentially what it is. I certainly got a giggle from the logic that says that this TV set costs $100 therefore I can't believe that in a few years it will only cost $50.

Also suspiciously absent is any attempt to argue why launch costs cannot fall given reusability or indeed why reusability cannot happen. To say it hasn't been done yet, is also to say the SLS hasn't been launched yet either. Soggy logic folks.

And my logic still applies. SEP isn't economic if it costs billions and you don't get enough reuse out of it. I've yet to see anyone even acknowledge that the number of times you reuse a SEP vehicle is what makes or breaks it economically. Instead you get the exact same arguments. It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.

Guys I work in electronics and mining. I see the law of volume production in front of me every day. A rocket is still a tin can. And an upper stage is a tiny fraction of the size of a booster. I even remember Elon Musk answering charges that he couldn't possibly build his rockets for the price. And the nay sayers merely responded with exactly the same anecdotal evidence without ever really questioning what is the fundamental "materials and energy" cost of building a rocket. It boils down to a few millions of dollars, with volume. That's all I have to say on the matter.

Now, explain to me how you can make SEP vehicles cheap without first making dozens of them. And explain to me why sending SEP vehicles off on years-long missions where they will only get reused a few times if at all, makes economic sense.
« Last Edit: 07/11/2015 01:04 pm by Russel »

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #63 on: 07/11/2015 03:14 pm »
I certainly got a giggle from the logic that says that this TV set costs $100 therefore I can't believe that in a few years it will only cost $50.

Also suspiciously absent is any attempt to argue why launch costs cannot fall given reusability or indeed why reusability cannot happen.

It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.

And the nay sayers merely responded with exactly the same anecdotal evidence without ever really questioning what is the fundamental "materials and energy" cost of building a rocket. It boils down to a few millions of dollars, with volume. That's all I have to say on the matter.

And explain to me why sending SEP vehicles off on years-long missions where they will only get reused a few times if at all, makes economic sense.

- I got a giggle from you comparing rockets to TV sets.

- Reusability will at best only marginally reduce cost. Anything else would be illogical, since otherwise it would have been done a long time ago.

- Chemical rockets have more or less reached their technological limits. You can make manufacturing more efficient, but that's about it. SEP however is only getting started.

- "Materials and energy" only make up a small fraction of GDP in any modern economy, so deriving the cost of a high-tech product from it is completely silly.

- If SEP requires little to none refurbishment it certainly could make sense to reuse it. The reusable SEP hybrid concept for example combines SEP with a pressure-fed hypergolics, both have proven to be very reliable. In fact it uses the orbital maneuvering engine of the shuttle (same as the Orion main engine), which never failed and never required replacement during the life of the shuttle program.
« Last Edit: 07/11/2015 03:16 pm by Oli »

Offline A_M_Swallow

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #64 on: 07/11/2015 11:07 pm »
Within a SEP tug the solar panels decay in the high radiation environment of space.  So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means  the SEP could make approximately
15 /  (2 + 2) = 3.75 trips

A 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.

The tug would need refuelling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #65 on: 07/11/2015 11:25 pm »

And my logic still applies. SEP isn't economic if it costs billions and you don't get enough reuse out of it. I've yet to see anyone even acknowledge that the number of times you reuse a SEP vehicle is what makes or breaks it economically. Instead you get the exact same arguments. It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.


When you just pull "Billions" out of the air as a price for what your opposing you can claim anything is too expensive.  But I've done the actual MATH that shows your cross-over is at 3.8 Billion using present launch costs and is still half a billion at best case future launch costs.

And that is with disposable usage, reuse would raise the cross-over point even higher.

What makes your argument bogus is that your assuming EVERY possible technology advancement, volume production improvement and new vehicle development in launch vehicles while assuming nothing for SEP.  The anticipated launch cost reductions are going to come from SpaceX, but we KNOW they are about to become a manufacturer of satellites (using SEP) using assembly line production, so it makes no sense to claim incredible cost saving will come ONLY in launch costs when SpaceX is clearly going to be trying to drive both costs down.

You don't have any idea what a large volume production of SEP vehicles would cost, no one here can do anything other then estimate.  Half of a SEP stage would generally be propellents, Xe is going to be phased out rapidly in preference for Kr which is $300 kg.  The rest of the SEP stage is solar-panels, electronic and thrusters which is basically the same kind of stuff a modern satellite is made of.  So based on the earlier comparison we would be looking at 62 mT each of propellents and hardware, the propellents would come to $18.75 Million, the hardware I'll compare with a well produced satellite Iridium which uses an assembly line process to get their costs down to 5 million each, the mass is 1500 pounds.  This would yield a hardware cost of ~460 million.  And thus a total cost of approximately 490 million, right at the cut off price of the optimistic launch cost estimate.

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #66 on: 07/12/2015 11:50 am »
Within a SEP tug the solar panels decay in the high radiation environment of space.  So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means  the SEP could make approximately
15 /  (2 + 2) = 3.75 trips

A 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.

The tug would need refuelling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.

Thanks for writing this. What it says is that the SEP vehicle has to be no more than 3 times the cost of the equivalent tonnage of EUSs that it would replace.

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #67 on: 07/12/2015 11:59 am »

And my logic still applies. SEP isn't economic if it costs billions and you don't get enough reuse out of it. I've yet to see anyone even acknowledge that the number of times you reuse a SEP vehicle is what makes or breaks it economically. Instead you get the exact same arguments. It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.


When you just pull "Billions" out of the air as a price for what your opposing you can claim anything is too expensive.  But I've done the actual MATH that shows your cross-over is at 3.8 Billion using present launch costs and is still half a billion at best case future launch costs.

And that is with disposable usage, reuse would raise the cross-over point even higher.

What makes your argument bogus is that your assuming EVERY possible technology advancement, volume production improvement and new vehicle development in launch vehicles while assuming nothing for SEP.  The anticipated launch cost reductions are going to come from SpaceX, but we KNOW they are about to become a manufacturer of satellites (using SEP) using assembly line production, so it makes no sense to claim incredible cost saving will come ONLY in launch costs when SpaceX is clearly going to be trying to drive both costs down.

You don't have any idea what a large volume production of SEP vehicles would cost, no one here can do anything other then estimate.  Half of a SEP stage would generally be propellents, Xe is going to be phased out rapidly in preference for Kr which is $300 kg.  The rest of the SEP stage is solar-panels, electronic and thrusters which is basically the same kind of stuff a modern satellite is made of.  So based on the earlier comparison we would be looking at 62 mT each of propellents and hardware, the propellents would come to $18.75 Million, the hardware I'll compare with a well produced satellite Iridium which uses an assembly line process to get their costs down to 5 million each, the mass is 1500 pounds.  This would yield a hardware cost of ~460 million.  And thus a total cost of approximately 490 million, right at the cut off price of the optimistic launch cost estimate.

I am absolutely NOT assuming that the cost of SEP won't come down. What proponents of SEP need to do is to explain how the cost of SEP will come down ENOUGH given the high development costs and the low volume production. You will never get to the Iridium level of volume production.

Satellites can afford to fail because they are unmanned. The moment you consider using SEP for manned flights it has to go through the same level of assurance and testing as any chemical stage. There's your billions of dollars of development folks.

I would also like to reiterate that there is a very big difference between the economics of SEP for Earth-space use which can be reused many times, and doing the same thing on round trips to Mars.

I am considering SEP but only for Earth space and only for unmanned flights.

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #68 on: 07/12/2015 01:39 pm »
I would also like to reiterate that there is a very big difference between the economics of SEP for Earth-space use which can be reused many times, and doing the same thing on round trips to Mars.

Why? SEP thrusts almost permanently in both cases. If the inbound trajectory takes approx. the same time as the outboud trajectory, it will transport a payload half of the time, similar to SEP used in "Earth-space".
« Last Edit: 07/12/2015 02:00 pm by Oli »

Offline A_M_Swallow

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #69 on: 07/12/2015 02:40 pm »
Within a SEP tug the solar panels decay in the high radiation environment of space.  So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means  the SEP could make approximately
15 /  (2 + 2) = 3.75 trips

A 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.

The tug would need refuelling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.

Thanks for writing this. What it says is that the SEP vehicle has to be no more than 3 times the cost of the equivalent tonnage of EUSs that it would replace.

At the mission design level the cost of launch vehicles needs including.

The SEP will probably require a Falcon Heavy to launch it. With ~4 trips to Mars 4 Falcon Heavies will be needed to lift the cargo.

The whole cost of the SLS needs including, not just the EUS. So for the tax payer this becomes
cost of SEP + 5 off Falcon Heavies Vs. 5 off SLS

Offline Coastal Ron

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #70 on: 07/12/2015 03:12 pm »
Satellites can afford to fail because they are unmanned.

Tell that to the satellite owners, and the investors too.  They would disagree.

Quote
The moment you consider using SEP for manned flights it has to go through the same level of assurance and testing as any chemical stage. There's your billions of dollars of development folks.

Maybe it does have to go through the same level of assurance as a chemical stage, but since Solar Electric Propulsion does not use combustion there will be far less concern about the propulsion part of the SEP vehicle.  And as for an human occupied part, that would be the same as with chemical propulsion systems.

I'm not seeing where the "billions of dollars" is supposed to come from.  In fact I haven't seen that high a quote for human rating any chemical rocket, which would arguably be far more complex and dangerous.  So I think you are far overestimating.

Quote
I would also like to reiterate that there is a very big difference between the economics of SEP for Earth-space use which can be reused many times, and doing the same thing on round trips to Mars.

I am considering SEP but only for Earth space and only for unmanned flights.

From what I understand SEP makes the most sense in local space when you aren't concerned with time.  So cargo trips from Earth to the Moon would be good candidates, assuming the cargo doesn't have radiation sensitive items.  But if you want to get through the radiation belts around Earth you would likely use chemical engines to transit quickly.

Clearly at the beginning any type of transportation system will not have a long lifetime, for a number of reasons.  For instance, since we'll be operating in environments where we don't have a lot of experience it doesn't make sense to over-build a system if you assume that you'll be iterating the design for a while to find the best combination of solutions.  In that case you'll want to swap out a system after a few cycles so the engineers can tear it apart and see what's working and what's not, and redesign accordingly.  So in the beginning getting a few trips will be enough.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #71 on: 07/12/2015 04:00 pm »
Within a SEP tug the solar panels decay in the high radiation environment of space.  So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means  the SEP could make approximately
15 /  (2 + 2) = 3.75 trips

A 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.

The tug would need refueling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.

Thanks for writing this. What it says is that the SEP vehicle has to be no more than 3 times the cost of the equivalent tonnage of EUSs that it would replace.

Completely obsolete assumptions.  Amorphous silicon solar panels (which are what we would use in thin-film type panels) do not suffer significant performance loss from radiation because of an annealing effect that essentially heals the damage from radiation.

Hall effect thrusters used to have limited lifespans but newer version are vastly improved, they would also be relatively simply to replace on orbit by EVA (about akin to a Hubble servicing mission).

Any lose in vehicle performance from these life-span based degradations is going to be smooth and we don't simply throw the vehicle away because it is at 80% performance, we would just put smaller cargoes on it or less time sensitive cargo for a longer trip.

Lastly the trip count math doesn't even take into account the 2.6 year synod which is what dictates all trips to and from Mars.  Your synods per round trip will be a whole number, either 1, 2 or 3 synods per round trip, nothing else makes any sense. 

And total lifespan is very hard to predict because the space environment is really not causing any decay, most commercial satellites run out of propellents and drift from their orbits still fully functional (but technologically obsolete).  A transportation system already on-orbit and able to be refilled with propellentswould only be obsolete when newer technology with higher ISP can be both launched and filled with propellents for less cost then re-filling the old system.  Much like how it is often cheaper to keep using a gas-guzzler then to buy a newer more efficient car.

Offline nadreck


Completely obsolete assumptions.  Amorphous silicon solar panels (which are what we would use in thin-film type panels) do not suffer significant performance loss from radiation because of an annealing effect that essentially heals the damage from radiation.



As well current manufacturing process for Amorphous slicon solar panels involve a deposition technology using silane something that could easily be workable on Mars.  After locally produced propellant, ISRU for as much of the mass of solar power arrays and batteries is the most important step IMNSHO BWTHFDIKIAMJAG.  While nitrates for a variety of purposes including food production are important too they will, at least early on, mass far less than what is needed for growing power needs.

So Argon could easily be produced on Mars, as could solar panels, lets presume that SEP craft can be refurbished at Mars.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #73 on: 07/12/2015 11:34 pm »

So Argon could easily be produced on Mars, as could solar panels, lets presume that SEP craft can be refurbished at Mars.

While Argon propellents are a viable means to re-fill a SEP vehicle when in Mars orbit, I see no need for manufactured components like solar-panels to be replaced at Mars.  The vehicle is constantly transiting between Earth and Mars so it can receive maintenance at Earth with the exact same impact on schedule.

If solar-panels could be manufactured on Mars (and I am highly skeptical of that), the proper use would be to employ them on Mars surface for power needs, not taking them to orbit to place on a vehicle going back to Earth.  The cost of sending anything to Mars and setting up manufacturing their are so high that all outputs need to serve local needs.

Offline nadreck


So Argon could easily be produced on Mars, as could solar panels, lets presume that SEP craft can be refurbished at Mars.

While Argon propellents are a viable means to re-fill a SEP vehicle when in Mars orbit, I see no need for manufactured components like solar-panels to be replaced at Mars.  The vehicle is constantly transiting between Earth and Mars so it can receive maintenance at Earth with the exact same impact on schedule.

If solar-panels could be manufactured on Mars (and I am highly skeptical of that), the proper use would be to employ them on Mars surface for power needs, not taking them to orbit to place on a vehicle going back to Earth.  The cost of sending anything to Mars and setting up manufacturing their are so high that all outputs need to serve local needs.

I expect that the cost of solar panels made on Mars would be much cheaper in Mars orbit than ones made on Earth in Earth orbit.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #75 on: 07/13/2015 05:56 am »

I expect that the cost of solar panels made on Mars would be much cheaper in Mars orbit than ones made on Earth in Earth orbit.

This is quite impossible.  If you have some notion that the lower DeltaV to Mars orbit some how compensates for incredible difficulty of manufacturing on the surface you are off by orders of magnitude.

This is not going to BE any manufacturing on Mars until Earth launch costs are on the scale of $100 kg, nothing on Mars could compete with that because manufacturing requires massive infrastructure, solar panels on Earth are only the cost they are now because this giant factory called ASIA is being used to make them.

Offline nadreck


I expect that the cost of solar panels made on Mars would be much cheaper in Mars orbit than ones made on Earth in Earth orbit.

This is quite impossible.  If you have some notion that the lower DeltaV to Mars orbit some how compensates for incredible difficulty of manufacturing on the surface you are off by orders of magnitude.

This is not going to BE any manufacturing on Mars until Earth launch costs are on the scale of $100 kg, nothing on Mars could compete with that because manufacturing requires massive infrastructure, solar panels on Earth are only the cost they are now because this giant factory called ASIA is being used to make them.
They are still going to be cheaper to make on Mars than to import in the volume needed, at that point the manufacturing facility to make them will be a sunk cost, so the incremental cost to make them and ship them to Earth will be what competes with Earth manufactured ones sent up from Earth. The craft have to come back from Mars virtually empty, why not have them carry a cargo that can be used in LEO. Argon and solar panels would be good candidate exports.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Online guckyfan

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #77 on: 07/13/2015 07:40 am »
Producing solar panels on Mars for surface use is one thing, I agree that this should be done as early as possible and appropriate designs will be developed. Building SEP tugs in orbit is another. I don't see that happen on Mars for a very long time.

Offline R7

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #78 on: 07/13/2015 03:10 pm »
I reckon Martian solar panel factory is a clear marker for domain outside minimal architecture for human journeys to Mars.  ;)
AD·ASTRA·ASTRORVM·GRATIA

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #79 on: 07/13/2015 09:50 pm »

They are still going to be cheaper to make on Mars than to import in the volume needed, at that point the manufacturing facility to make them will be a sunk cost, so the incremental cost to make them and ship them to Earth will be what competes with Earth manufactured ones sent up from Earth. The craft have to come back from Mars virtually empty, why not have them carry a cargo that can be used in LEO. Argon and solar panels would be good candidate exports.

Your trying to apply the logic of the trucking/shipping industry which hates to dead-head.  But this is completely inappropriate for two reason.

First Mars is a effectively a wilderness location without infrastructure or exports, not like two cities on Earth which both have plenty of gasoline and a mix of imports and exports.  Our supply ships sent to Antarctica do not load up on ICE to bring back to sell at convenience stores.

Second a SEP propellent consumption and or trip duration is DIRECTLY proportional to mass being carried, unlike a truck or plane or a boat which use mostly the same fuel regardless of if they are carrying cargo.  Returning without cargo saves HUGE propellent, even if we had propellent available at Mars the more we try to carry back to Earth the more propellent would be needed.  Even if the return cargo and propellents was magically placed into Mars orbit for each vehicle that carried return cargo rather then dead-head we would likely have to give up one INCOMING shipment because we would lack the propellent to return it to Earth.

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