Mars Barges

One of the incredible mentions in the Elon Mars concept was a thousand spacecraft in orbit ready for the Mars launch window to open. I’m not sure how many launch windows down the road this would be, I assume several decades. Whether it is next decade or next century though, an expensive asset like a spacecraft that is only capable of being used once every other launch window is a massive investment that is mostly idle.

I suggest an alternate concept for having a thousand vehicles heading toward Mars during one launch window. Each vehicle is an inert barge with a homing beacon and barely enough structure to house the cargo during thrust and coast. No engines, electricity, shielding, or other frills.  These barges carry only items that store well. Machinery, provisions, propellant, clothing, etc.

The orbital gathering place for these barges is a high Earth orbit above the radiation belts but below Lunar orbit. The storage orbit keeps however many barges are heading out during each launch window in  parking lot adjacent to a refueling facility that is stocked up between launch windows. The third item is skeletal booster tugs with no frills like ability to reenter or handle gravity.

There is a certain limited amount of time in a Mars launch window when the Hohman transfer orbit uses minimum propellant. There are periods of time on both sides of the ideal window that still get you to Mars, just at the expense of additional propellant. Total available time in the window can be a few months depending on available propulsion.

At the first opportunity, a tug with a dry mass of perhaps ten tons, a propellant load of two hundred tons, and a hundred ton barge, does a short burn to drop its’ perigee to just outside noticeable atmospheric drag. At perigee it is at nearly escape velocity when it does a strong (~4km/sec)Oberth effect burn to place the whole assembly on a Mars trajectory. Immediately after reaching the required velocity, the tug separates and a short retro burn to place the light tug back into an eccentric orbit with an apogee equal to the barge parking lot. The orbital equivalent to the F9 boostback.

Back at the parking lot, the tug does a short burn to match velocities and goes for docking. Refuel, clamp onto another barge, and go again on intervals of one to four days. Depending on assumptions, each tug could send as many as a hundred barges per window to be caught on the other end.

So I can see the possibility of a hundred thousand tons of vessels heading to Mars during one launch window. The main hardware investments being launch vehicles, depots, and tugs that are kept employed at other tasks in the meantime between windows. People launch separately in vehicles suitable.

The main strength I would see in a scenario such as this is that the expensive hardware would be constantly available for use for other tasks. This is important for those of us that don’t see that much value in Mars as the next step out. The same equipment would be useful for asteroid missions or sending a Pluto lander. A heavyweight to Europa or a close solar corona  investigation. Or more immediately useful support for Lunar and NEO missions.

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johnhare

johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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17 Responses to Mars Barges

  1. Pingback: Mars Barges – MeasurementDataBases for Industry & Science

  2. Amusingly enough, there was a similar concept in the old tabletop wargame BattleFleet Mars

    https://www.boardgamegeek.com/boardgame/3662/battlefleet-mars

    Shown on the cover is a “catapult”, basically your skeletal booster tug. They launch cargoes of minerals mined in the asteroid belt into Trans-Earth trajectories. At Earth, other catapults intercept the cargoes and decelerate them into orbit.

  3. johnhare johnhare says:

    I have noticed inert inbound cargo vessels in some science fiction from time to time. I was unaware of board game usage of the concept. This post was basically F9 launch procedure in orbit. Retroburn equaling hold down, major burn equaling launch, boostback is boostback, circularization equaling landing.

    There are of course several improvements available. Most notable being the potential market for megatons of Lunar propellants.

  4. DougSpace says:

    I would hope that we wouldn’t be shipping material that we could fairly easily produce on Mars. For example, I hope that “provisions” wouldn’t include water. Fairly early, we ought to produce most types of food. Fibers for clothing could be produced on Mars although it would be a question of whether the cost of producing clothing on Mars would cost more or less than shipping them in bulk from Earth. The components of equipment come in two types: simple and difficult-to-produce. We should try to produce the simple items on Mars ASAP and so only be shipping those components which cannot be easily manufactured in Mars. And then, some assembly would be required.

    So, in the final analysis, most of the vehicles departing Earth would include: difficult-to-produce components, the passengers, their in-flight provisions, and the propellant necessary for TMI.

  5. Peter M says:

    You might be interested in this Delta-V analysis for transfers taking advantage of the Oberth effect:

    http://hopsblog-hop.blogspot.com/2015/05/eml2.html

  6. johnhare john hare says:

    Doug,
    The cheaper the shipping, the more the balance changes towards bringing stuff from Earth. The trades are very different at $200.00 a pound into TMI and the $100,000.00 plus for the earlier missions of the last century. While almost everything can eventually be produced on Mars, it will be far faster to have a lot of things ready to go. I could think of a million tons of useful materials for starting if a serious development efforts was intended. The early settlers may have more than they can do getting the first towns built without making shoes and tractors from scratch.

    Peter,
    Good information there at Hops blog. My thoughts on this post were that an orbit much lower than EML2 would allow faster turnaround of the tug fleet although obviously at the expense of more propellant. I also assumed most of the launches would be from less than optimum windows. For a single launch in the window, what I am suggesting wouldn’t make sense. You would use the optimum time to save fuel, and probably launch from LEO without all the complexity I suggest here.

  7. You still need about 670 m/s to capture into an eccentric Mars orbit, don’t you? So it can’t be a completely inert barge.

    Figure a 100 tonne barge with an AJ10-like engine (Isp=319 s), and you get a mass ratio of 1.24. That’s about 24 tonnes of propellant.

    From there, presumably you can use the same trick in reverse: Tugs in LMO can rendezvous and reduce the orbit to the point where cargo can be transferred to something that can enter the atmosphere.

  8. Hop David says:

    In terms of delta V EML2 is closer than EML1 (3.5 km/s vs 3.8 km/s from LEO).
    It is about 8 or 9 days away from LEO.

    Not sure what parking orbit you have in mind. Reaching GEO from LEO takes about 4 km/s. Dropping from GEO you don’t get a perigee speed just under escape. Dropping from GEO, perigee speed would be around 10.2 km/s.

  9. ken anthony says:

    Always enjoy your posts that inspire thought (which is all of them actually.) Good job.

  10. DougSpace says:

    John, The options are not $100,000/lb vs $200/lb. Both of those are unrealistic. We live in the age of Falcon 9 and nearly Falcon Heavy and partially reusable at that. So a bit over $2,000/kg to LEO. The BFR age of $400/kg is pretty theoretical right now and even when the BFR launches it will probably take a while until flight rate gets the cost that low. So, what I am saying is that, if we go with what we will likely have in the near future (i.e. FH) and then do the other things which are the equivalent of reducing launch costs (e.g. extend crew stay, recycle, produce ISRU propellant, water, & oxygen, grow food, etc) then, fairly early on, it won’t cost so much to sustain a permanent base. If we start at the Moon then, relatively cheap Earth labor could work on the Moon via telerobotics so that we are not dependent upon the crew to do all of the setting up.

  11. johnhare john hare says:

    Doug, $100,000.00 a pound or more was the cost of some missions of the last century. $200.00 a pound or less is realistic in the timeline implied by the Elon concept and this post. I didn’t think it was necessary to point out that this was well into the future when it contained a thousand spaceships going anywhere. I have a fairly good imagination, and I cannot imagine anything Mars is likely to have that would make it worth sending a thousand ships at $2,000.00 a kilogram. Until there is a viable economic reason, sending a thousand ship at any cost wouldn’t make sense. It is my opinion that true space development will start in the cislunar volume of space and spread to asteroids with Mars just one of the destinations.

    As for shipping costs, I’m sure that Columbus would have been astonished at the sea traffic today including supertankers and Panamax container ships, which have crews comparable to his in size. A single container carries more cargo than his fleet at a fraction of the cost. Nobody has to persuade the crown to finance shipping today. Nobody will have to persuade governments to finance shipping in space by the time 1,000 ship fleets are viable.

  12. AlanSE says:

    I wrote a response to this, but I put it in my own blog:

    https://medium.com/@AlanSE/a-response-to-mars-barges-567b23dcfe21

    One thought that I just now remembered is that I believe that Zubrin had discussed this same general idea of a reusable Mars departure stage. He might have been assuming some EML point or even LEO staging orbit in the start. Not quite sure.

  13. johnhare johnhare says:

    I just saw Alans’ comment Sunday morning in the spam bucket. He has a good description and critique of the concept on his blog. I couldn’t easily comment over there.

  14. James Walker says:

    Why trap people on pokey little barges for months at a time? The advantage of space is that size limits go away; microgravity can handle huge projects and vaccuum plus slingshot orbits means never slowing down.

    Now, remember that 1 in 3 humans are Christian, and Christian prophecy talks about a New Jerusalem that is a cube with dimensions of 1,500 KM: announce plans to hollow out Ceres, name it New Jerusalem and use it as a constant trade city, moving between the inner planets, and you get an extra reason for a third of the planet’s population to invest in the scheme, *and* travelling on it becomes a religious pilgrimage (which is seriously big money). A settlement the size of a nation avoids cabin fever; spend the trip acquiring a degree at one of the universities means you don’t waste years of your life in travel.

    Note that the real wealth during the age of sail was made in the trade ports, from the Hanseatic League, London etc in Europe to Shanghai, Hong Kong and Macao in China – a trade port that moves from planet to planet would become the economic hub of the solar system.

  15. Brock says:

    It’s a good plan; especially not having useful engines idling for years at a time. The size of the fuel depots necessary is mind-boggling though.

    Another thought (this isn’t an insurmountable problem, just a thought) is that the whole Solar economy will have to plan around having nearly zero propulsion capability for 2-4 months once every two years, as I expect this would effectively absorb 100% of the space tug supply while the window is open. Either that or pay a considerable premium to have dedicated resources.

  16. Bob Steinke says:

    @Brock

    The size of oil supertankers is also mind-boggling.

    There are probably some parallels on Earth for needing lots of specialized vehicles for short periods of time. Alaskan fishing vessels maybe?

  17. James Walker says:

    Parallels could include:
    – the tea clippers, especially for the economic side of things.
    – the return of whaling ships.
    – major military landings, such as D-Day, for the admin/infrastructure overload side of things.
    – migrations of prey species for the social side of things.

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