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Thread: Mercury: A Case For Settlement

  1. #1 Mercury: A Case For Settlement 
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    This posting is aimed at answering the fundamental question: Why settle Mercury?
    Mercury is not a paradise planet. You can die a number of unpleasant ways there if you are not careful or properly prepared. In a later post I will talk about the cost – with real numbers! – of going to Mercury, for now, just know it is expensive. So why go? NASA has three mandates that are of most concern here. . . 1) Exploring the universe. 2) Exploring the Solar System with spacecraft. 3) Applying space technologies to meet human needs. Currently, NASA is spending around $18 Billion per year to meet these objectives. It should be noted that nothing in any of these ‘mandates’ requires NASA to exclusively use people to accomplish goals.
    1) Over the next decades NASA will need to replace every orbiting astronomical instrument with either a new (and improved?) model, or find an alternative way to do astronomy in space. Mercury offers a way to expand our space-based astronomy while reducing its costs. Mercury’s slow rotation and rapid orbital motion combine to provide up to 88 continuous days of dark sky for all forms of observing. Up to 44 days can be devoted to observing specific objects of interest. This is 3.14 times what an instrument relying on the Moon’s dark sky would have. Essentially airless, Mercury’s surface is available to all wavelengths. Mercury has the energy and raw materials to build 90-95% of an instrument’s total design mass. This tremendously reduces the mass to be launched from Earth to perform an astronomy mission.
    2) Exploring the Solar System is severely constrained by the need to accommodate Earth-centered synodic periods in mission planning. In the important case of missions to Mars, this is ~780 days. Another constraint is the transportation systems in use now are based on chemical fuels which severely limit payload capacity to any given destination. Mercury can decisively break these constraints. The orbital position of Mercury can allow many more launch opportunities to all Solar System objects. In the case of Mars, Mercury presents seven launch opportunities to every one Earth presents. This dramatically alters exploration strategies by allowing far more options in mission planning, hardware design and ultimate return. Solar sails, combined with Mercury’s launch window advantage, provide for very economical access to all Solar System destinations, despite the generally higher delta-V’s involved.
    3) An important potential application of space technologies is power transmission to Earth’s surface. The design of powersats continues to evolve and has many more technologies to utilize than was the case at the concept’s inception. Mercury can provide space structures of almost any size and configuration. Very large structures can be provided in modular elements with each ‘module’ in the100 metric ton mass category. Strange and counterintuitive as it may seem, it may prove more economical to produce such units at Mercury and transport them to Earth than produce them on the Moon.
    In all of the above examples, Mercury either saves billions of dollars in potential expense or actually generates revenue through provision of products or services.
    To accommodate the operations outlined above will require a facility on Mercury’s surface that will have a total mass in the thousands of tons; an ultimate population of at least 1700 people and require many Megawatts of power. This, at the very least, defines a village or small town. Following posts will expand on the above points and many others not mentioned here. . .


    Last edited by moonguy; September 6th, 2013 at 01:24 PM.
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  3. #2  
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    "Mercury's surface experiences the greatest temperature variation of all the planets, ranging from 100 K (−173 C; −280 F) at night to 700 K (427 C; 800 F) during the day at some equatorial regions. The poles are constantly below 180 K (−93 C; −136 F)."
    Mercury (planet) - Wikipedia, the free encyclopedia

    I think I'll visit a different planet.


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    Quote Originally Posted by RedPanda View Post
    "Mercury's surface experiences the greatest temperature variation of all the planets, ranging from 100 K (−173 C; −280 F) at night to 700 K (427 C; 800 F) during the day at some equatorial regions. The poles are constantly below 180 K (−93 C; −136 F)."
    Mercury (planet) - Wikipedia, the free encyclopedia

    I think I'll visit a different planet.
    Venus is sounding kind of cold comparatively.
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    Quote Originally Posted by TheUnknowable View Post
    Quote Originally Posted by RedPanda View Post
    "Mercury's surface experiences the greatest temperature variation of all the planets, ranging from 100 K (−173 C; −280 F) at night to 700 K (427 C; 800 F) during the day at some equatorial regions. The poles are constantly below 180 K (−93 C; −136 F)."
    Mercury (planet) - Wikipedia, the free encyclopedia

    I think I'll visit a different planet.
    Venus is sounding kind of cold comparatively.
    Surprisingly (to me), Venus is hotter than Mercury.
    And the clouds of sulphuric acid would prevent us getting a decent tan...
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  6. #5  
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    Venus is also a one way trip. Too much gravity to realistically hope to get back out into space after you land. (~0.9 of Earth's gravity, so you'd need a full launch setup)


    Mercury would be fun to set up a colony just to prove we can. But we might want to set one up on the (comparatively much easier) Moon first.
    Some clocks are only right twice a day, but they are still right when they are right.
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    Quote Originally Posted by kojax View Post
    Venus is also a one way trip. Too much gravity to realistically hope to get back out into space after you land. (~0.9 of Earth's gravity, so you'd need a full launch setup)


    Mercury would be fun to set up a colony just to prove we can. But we might want to set one up on the (comparatively much easier) Moon first.
    Agreed! That is the operating plan of the Mercury Project so far. The first manned mission would launch sometime in the 2030's. By then a lunar base should be operational for about ten years and matured to a point where it can provide propellants to the out-going manned vehicle. The actual launch point is from an orbit around the Earth-Moon L2 point. Thanks for your post!
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    Mentioning Mercury everyone automatically thinks of the ungodly heat there. This is reasonable, but lets not forget a couple of things: 1) Heat is energy we can use to do a LOT of things. In Mercury's case, the solar flux ranges between 6.2 - 11.0 times the flux at 1 AU. At perihelion, a staggering 15,000 watts per square meter are available. At aphelion it chills to 8,400 watts. We can do things with that much power. . . 2) Mercury does rotate, Therefore, it has a night. A very long, dark night. 88 days of night. So you actually have an equal chance of freezing to death as broiling. The temperatures drop to around -100c after only a few hours after sunset. These temperatures are near cryogenic levels and the prospects of a cryogenics production capacity are just as good on Mercury as on the Moon. The much longer night (88 days vs. 14 for the Moon) would likely be decisive for this. 3) For habitats, it only takes about 70 centimeters of regolith to balance temperatures underground at a comfortable range. We will need several meters of regolith to protect against particle radiations, so the thermal management problem becomes one of removing excess heat form inside the habitat. 4) We have had a number of spacecraft operating in that region of space for extended periods. Not just MESSENGER, but solar probes. We know how to build spacecraft that survive in that region and perform excellently. This experience should be applicable to mining equipment, people movers, manned flight vehicles and other equipment.
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  9. #8  
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    Quote Originally Posted by moonguy View Post
    Quote Originally Posted by kojax View Post
    Venus is also a one way trip. Too much gravity to realistically hope to get back out into space after you land. (~0.9 of Earth's gravity, so you'd need a full launch setup)


    Mercury would be fun to set up a colony just to prove we can. But we might want to set one up on the (comparatively much easier) Moon first.
    Agreed! That is the operating plan of the Mercury Project so far. The first manned mission would launch sometime in the 2030's. By then a lunar base should be operational for about ten years and matured to a point where it can provide propellants to the out-going manned vehicle. The actual launch point is from an orbit around the Earth-Moon L2 point. Thanks for your post!
    Surely the problem is how to get there without being fried on the way? You can dig a shady shelter and hide in it once you are there, but there's no way to do this for the spacecraft en route. You can spin it I suppose, to even out the stress, but whatever you do it will be intercepting a hell of a lot of heat and radiation as you get close. How would this be dealt with?
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    Surely the problem is how to get there without being fried on the way? You can dig a shady shelter and hide in it once you are there, but there's no way to do this for the spacecraft en route. You can spin it I suppose, to even out the stress, but whatever you do it will be intercepting a hell of a lot of heat and radiation as you get close. How would this be dealt with? Hydrogen is probably the single best radiation shield material. The current spacecraft design has the crew module inside a cylinder which is mounted inside the forward end of an SLS upper stage. When full of LH2 the crew module is surrounded by at least two meters of LH2. The crew module itself has a layered radiation shielding that includes the water used for life support, Hydrogenated Polyethylene (HPE) and a thermal insulation foam. Demron fabric ids also through the module as well. The module is also all non-metallic composite for lightness and reduced 'Brehmstrahling' effect. For thermal protection, the vehicle carries a Sun shade that has at least 85% reflectivity. This sunshade is not a solar sail, but it is utilized near Mercury for orienting and stabilization. This helps reduce the mass of the Reaction Control System. Between the Mercury Orbit Insertion maneuver and docking to an orbiting Orbiting Transfer Station (OTS) the crew is confined to command/navigation section of the crew module which is much more robustly shielded from radiation, mostly with greater amounts of HPE. This phase of the mission only lasts about two or three days at most. The real tricky maneuver is the landing. This has to get the crew on the surface just before the sunset terminator. That means descent over the dayside of the planet. Heat from the Sun above. . . Heat from the planet below. . . The landers (there are two) have their own sunshades somewhat similar to what MESSENGER carries.
    Last edited by moonguy; September 7th, 2013 at 06:29 PM.
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    Sounds like you'd want to build a geothermal loop to utilize the intense surface temps. CPV cells would be necessary (some can handle up to 500 or more suns of light on earth at 40% or greater efficiency). So you'd build an underground shelter and load everyone and everything into it before day gets there, then build things remotely with robots?
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    You can dig a shady shelter and hide in it once you are there, but there's no way to do this for the spacecraft en route.


    You build a reflective umbrella in front of the ship--or more precisely between the ship and the sun, comet like. Most of the solar radiation spectrum is very easy to avoid. The high energy x-ray and gamma, particularly if the ship is unlucky enough to intercept a solar flare, is the real problem.
    Last edited by Lynx_Fox; September 7th, 2013 at 08:56 PM.
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    Solar flares would be a big deal that close to the sun. Radiation shielding meant for normal solar energy levels might not be abole to handle them. At least on Mars you have a bit of an atmosphere to attenuate it.
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    Quote Originally Posted by TheUnknowable View Post
    Sounds like you'd want to build a geothermal loop to utilize the intense surface temps. CPV cells would be necessary (some can handle up to 500 or more suns of light on earth at 40% or greater efficiency). So you'd build an underground shelter and load everyone and everything into it before day gets there, then build things remotely with robots?
    It would be awesome to find a geothermal source right where we need it. Mercury does have a molten outer core and lots of volcanic vents. We have to investigate that further to have confidence in it for the initial operation. The first power system is a 'powersail' in a non-Keplerian orbit over Mercury's night side. It is equipped with a microwave power system. Ground equipment for that is a modular 'Surface Power Receiver' (SPR) that can be built up over time. CPV for daytime is preferred, but there are concerns about the longevity of cells under surface conditions. Not just the heat, but particle radiation too. It is the baseline at this point. Thanks for a good, if brief post!!
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    Quote Originally Posted by TheUnknowable View Post
    Solar flares would be a big deal that close to the sun. Radiation shielding meant for normal solar energy levels might not be abole to handle them. At least on Mars you have a bit of an atmosphere to attenuate it.
    There is actually a silver lining behind your observation. The current design for the Main Base incorporates a ten meter thick regolith shield for radiation protection. We are not sure that much shielding is warranted by conditions. We are erring on the side of caution. The silver lining is that, on Mercury, with its .38 gravity, ten meters of regolith will have a dead-load weight identical to the pressure of a 14.7 psi atmosphere. If the hydrocarbons food at the poles along with the water are cometary in origin, they are likely to contain more than enough Nitrogen to provide even a very large facility with a normal air pressure and gas mixture. The balance between that pressure and the weight of the regolith makes designing the Main Base structure a lot easier. One of the more important objectives for the Mercury settlement is to facilitate the construction of Mars settlements. Thanks for the post. . .I hope you'll be back soon!
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    Quote Originally Posted by Lynx_Fox View Post
    You can dig a shady shelter and hide in it once you are there, but there's no way to do this for the spacecraft en route.


    You build a reflective umbrella in front of the ship--or more precisely between the ship and the sun, comet like. Most of the solar radiation spectrum is very easy to avoid. The high energy x-ray and gamma, particularly if the ship is unlucky enough to intercept a solar flare, is the real problem.
    Yes, that more or less describes the Sun shade I noted in an earlier post here. It is mounted on a long, extensible boom and can be reoriented relative to the axis of the vehicle - just like an umbrella! The design is intended to keep the vehicle's temperature at or below those encountered at 1 AU.
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  17. #16  
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    Hell of a delta V.
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    Quote Originally Posted by moonguy View Post
    Quote Originally Posted by TheUnknowable View Post
    Sounds like you'd want to build a geothermal loop to utilize the intense surface temps. CPV cells would be necessary (some can handle up to 500 or more suns of light on earth at 40% or greater efficiency). So you'd build an underground shelter and load everyone and everything into it before day gets there, then build things remotely with robots?
    It would be awesome to find a geothermal source right where we need it. Mercury does have a molten outer core and lots of volcanic vents. We have to investigate that further to have confidence in it for the initial operation. The first power system is a 'powersail' in a non-Keplerian orbit over Mercury's night side. It is equipped with a microwave power system. Ground equipment for that is a modular 'Surface Power Receiver' (SPR) that can be built up over time. CPV for daytime is preferred, but there are concerns about the longevity of cells under surface conditions. Not just the heat, but particle radiation too. It is the baseline at this point. Thanks for a good, if brief post!!
    A geothermal loop moves heat from one source (hundreds of degrees surface temp) to a cooler source (underground). On Earth it's generally used as a way to save on heating and cooling costs, because the temperature difference isn't that big. On mercury, it could be used to make lots of power.
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    Quote Originally Posted by John Galt View Post
    Hell of a delta V.
    Earth departure delta-V can be as low as 6.2 km/sec. This can be performed by a stage that is either jettisoned or returned to Earth but in any case does not ne4ed to be brought to Mercury. Mercury Orbit Insertion can be as low ads 6.3 km/sec. LO2/LH2 with the J2-X engine (assuming, of course, that it works as advertised) gives a mass ratio of about 4.1. The same stage can refuel for a nearly identical Delta-V six months later if we station a mass of propellant in orbit at the OTS mentioned earlier. The interplanetary stage stays in orbit anyway, while the landers are brought to Mercury attached to the OTS which ids delivered to Mercury orbit by solar sail.
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    Quote Originally Posted by TheUnknowable View Post
    Quote Originally Posted by moonguy View Post
    Quote Originally Posted by TheUnknowable View Post
    Sounds like you'd want to build a geothermal loop to utilize the intense surface temps. CPV cells would be necessary (some can handle up to 500 or more suns of light on earth at 40% or greater efficiency). So you'd build an underground shelter and load everyone and everything into it before day gets there, then build things remotely with robots?
    It would be awesome to find a geothermal source right where we need it. Mercury does have a molten outer core and lots of volcanic vents. We have to investigate that further to have confidence in it for the initial operation. The first power system is a 'powersail' in a non-Keplerian orbit over Mercury's night side. It is equipped with a microwave power system. Ground equipment for that is a modular 'Surface Power Receiver' (SPR) that can be built up over time. CPV for daytime is preferred, but there are concerns about the longevity of cells under surface conditions. Not just the heat, but particle radiation too. It is the baseline at this point. Thanks for a good, if brief post!!
    A geothermal loop moves heat from one source (hundreds of degrees surface temp) to a cooler source (underground). On Earth it's generally used as a way to save on heating and cooling costs, because the temperature difference isn't that big. On mercury, it could be used to make lots of power.
    I appreciate the clarification. It would require assembly on arrival of the crew, right? So does the powersail SPR unit. The difference is the SPR elements are simple modular (hexagonal in the most recent iteration) panels that ere attached together using fairly simple nut and bolt assembly. I could see the geothermal loop for a later application, when there is more time and tools to work with.
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    Quote Originally Posted by moonguy View Post
    The first power system is a 'powersail' in a non-Keplerian orbit over Mercury's night side. It is equipped with a microwave power system. Ground equipment for that is a modular 'Surface Power Receiver' (SPR) that can be built up over time.
    That's going to be built for Earth long before it gets considered for Mercury. (Mercury isn't the place to field test a new power system.)

    CPV for daytime is preferred, but there are concerns about the longevity of cells under surface conditions. Not just the heat, but particle radiation too. It is the baseline at this point. Thanks for a good, if brief post!!
    Keep in mind that orbital cells will see far worse conditions, since they do not even have Mercury's magnetic field to shield them.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    The first power system is a 'powersail' in a non-Keplerian orbit over Mercury's night side. It is equipped with a microwave power system. Ground equipment for that is a modular 'Surface Power Receiver' (SPR) that can be built up over time.
    That's going to be built for Earth long before it gets considered for Mercury. (Mercury isn't the place to field test a new power system.)

    CPV for daytime is preferred, but there are concerns about the longevity of cells under surface conditions. Not just the heat, but particle radiation too. It is the baseline at this point. Thanks for a good, if brief post!!
    Keep in mind that orbital cells will see far worse conditions, since they do not even have Mercury's magnetic field to shield them.
    Powersails have been considered for supporting a Lunar Base. that would be a logical to field test the technology before committing to Mercury. The powersail - as opposed to powersat - can fly to Mercury without propulsive assistance from either high-impulse thrusters or low-thrust ion drives. At Mercury, they can go into and maintain a given orbit indefinitely without expending a drop of any kind of propellant! The cost savings for this approach are enormous. MESSENGER is proving we can make cells for long-term use at Mercury. the trick now is to make them with a lightness that allows a powersail to deliver the powers levels we need. Given what the Japanese were able to do with IKAROS, we are confident about that.
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    Quote Originally Posted by moonguy View Post
    The powersail - as opposed to powersat - can fly to Mercury without propulsive assistance from either high-impulse thrusters or low-thrust ion drives. At Mercury, they can go into and maintain a given orbit indefinitely without expending a drop of any kind of propellant! The cost savings for this approach are enormous.
    Well, again, that's like saying the cost savings we get by switching to solar power satellites for all our (terrestrial) power would be enormous. Perhaps, but we just can't afford that kind of savings right now (or in the near future.)

    Any near term base on any other planet will use proven technology that we know works. And the goals cannot be "well go to Mercury so we can go to Mars later more easily" - the goal has to be pretty concrete to justify spending the trillions it would cost.

    If we are considering farther into the future, then just assume He3-He3 fusion and all your power problems are solved.

    MESSENGER is proving we can make cells for long-term use at Mercury. the trick now is to make them with a lightness that allows a powersail to deliver the powers levels we need. Given what the Japanese were able to do with IKAROS, we are confident about that.
    If that does happen, then we'll use them on the surface of Mercury for power; we have some experience with that.
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    Quote Originally Posted by moonguy View Post
    Quote Originally Posted by John Galt View Post
    Hell of a delta V.
    Earth departure delta-V can be as low as 6.2 km/sec. This can be performed by a stage that is either jettisoned or returned to Earth but in any case does not ne4ed to be brought to Mercury. Mercury Orbit Insertion can be as low ads 6.3 km/sec.
    So, as I said, a hell of a delta-V. And a hell of a planet. A back-of-the postage-stamp cost-benefit analysis suggests it will be one of of last potential sites we visit in the solar system.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    The powersail - as opposed to powersat - can fly to Mercury without propulsive assistance from either high-impulse thrusters or low-thrust ion drives. At Mercury, they can go into and maintain a given orbit indefinitely without expending a drop of any kind of propellant! The cost savings for this approach are enormous.
    Well, again, that's like saying the cost savings we get by switching to solar power satellites for all our (terrestrial) power would be enormous. Perhaps, but we just can't afford that kind of savings right now (or in the near future.)

    Any near term base on any other planet will use proven technology that we know works. And the goals cannot be "well go to Mercury so we can go to Mars later more easily" - the goal has to be pretty concrete to justify spending the trillions it would cost.

    If we are considering farther into the future, then just assume He3-He3 fusion and all your power problems are solved.

    MESSENGER is proving we can make cells for long-term use at Mercury. the trick now is to make them with a lightness that allows a powersail to deliver the powers levels we need. Given what the Japanese were able to do with IKAROS, we are confident about that.
    If that does happen, then we'll use them on the surface of Mercury for power; we have some experience with that.
    You are equating the powersail a few thousand kilometers above Mercury delivering Megawatts to the surface with the powersats designed to deliver Terawatts of power to Earth from 36,000 kilometers? I agree that a powersail has not yet been built, but the basic technologies that would make up a powersail are proven and the scale of the technology (1 operational unit less than 100 tons vs. 100 powersats each 100,000 tons) suggests it is a realistic approach. With respect to 'going to Mars later. . .' There is no 'later'. The two programs run concurrently. There is a lot of heritage from the Lunar Base and Mars Base projects that go into the Mercury project, so it is not a simple multiplication of effort. As for He3, if they develop that to a point of useful output, I would be the happiest to hear about it. . .Mercury is bound to be loaded with the stuff.
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by moonguy View Post
    Quote Originally Posted by John Galt View Post
    Hell of a delta V.
    Earth departure delta-V can be as low as 6.2 km/sec. This can be performed by a stage that is either jettisoned or returned to Earth but in any case does not ne4ed to be brought to Mercury. Mercury Orbit Insertion can be as low ads 6.3 km/sec.
    So, as I said, a hell of a delta-V. And a hell of a planet. A back-of-the postage-stamp cost-benefit analysis suggests it will be one of of last potential sites we visit in the solar system.
    Since I have not yet discussed actual masses for the transportation elements, I'm wondering what there is about a mass ratio of 4 that frightens you? NASA routinely contemplates missions to Mars where individual DV's are above 5.5 to 6.0 km/sec. Your 'back-of-the-postage-stamp' cost-benefit analysis (I'll have to remember that one!) should be an interesting read. Care to share the details?
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    Quote Originally Posted by moonguy View Post
    You are equating the powersail a few thousand kilometers above Mercury delivering Megawatts to the surface with the powersats designed to deliver Terawatts of power to Earth from 36,000 kilometers?
    Equating? No. Suggesting that you have to develop similar technologies for both of them? Yes.
    I agree that a powersail has not yet been built, but the basic technologies that would make up a powersail are proven and the scale of the technology (1 operational unit less than 100 tons vs. 100 powersats each 100,000 tons) suggests it is a realistic approach.
    Sure. But consider that Von Braun himself had a vision of how to go to the Moon. It involved a reusable space transportation system with a large orbiting space station where the mission would be based. If we had taken that approach we at best would have landed 30 years after we did (if at all.)

    Likewise there are ways to set up a base on Mercury. If it involves a powersail to power the base, your great grandkids might be alive to see it happen.

    With respect to 'going to Mars later. . .' There is no 'later'. The two programs run concurrently.
    OK. Maybe your great great grandkids, then.
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    Equating? No. Suggesting that you have to develop similar technologies for both of them? Yes. Hmmmm. What do you see as the level of challenge to this? Solar sail has flown successfully, but needs to be scaled up for this application. Photovoltaics are a common technology, and have been scaled down in mass to enable this application (the powersail). Microwave transmission of electrical power from 1000+ km distances is untied AFAIK. So I agree there is development work to done. Powersail is not a done deal. What I'm less clear is are you saying the entire concept falls apart because of that? Powersail is the best concept at this point, but if that were unavailable, there are alternatives. The base could just as easily be powered by nuclear reactors, multiple arrays of solar panels or solar-thermal generators. . . Even so, I'd bet on the powersail to be available. Believe me, I am appreciating your input!
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    Quote Originally Posted by moonguy View Post
    What do you see as the level of challenge to this?
    Let's see -

    Efficient lightweight microwave power transmitters that can operate at very high temperatures
    Efficient lightweight microwave power receivers that can operate at very high temperatures
    Stationkeeping and attitude control in an environment with strong and varying solar winds
    Long term survivability in the above environment

    What I'm less clear is are you saying the entire concept falls apart because of that?
    No, it just gates it. And the more untested technologies you have to develop the longer the project timeline becomes, and the lower the odds of it surviving to its final form. In the US especially, no project survives more than about ten years. Thus if it's a 20 year development effort you're going to have to start it, shut it down, start it again over and over until enough gets done piecemeal to actually launch the mission.

    That's not saying powersails are a bad idea, it's just a lot to try to cram into an already hideously expensive and complex undertaking. To paraphrase Zubrin, if you want to develop a powersail develop a powersail. If you want to go to Mercury go to Mercury. Don't try to do both at once.
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    Quote Originally Posted by moonguy View Post
    Since I have not yet discussed actual masses for the transportation elements, I'm wondering what there is about a mass ratio of 4 that frightens you?
    Nothing about the proposal frightens me. I have yet to be frightened by projects that while imaginative are also impractical and offer little of value in return and are very high risk and are politically unattractive and come with delta-V calculations I am wary of.

    Quote Originally Posted by moonguy View Post
    NASA routinely contemplates missions to Mars where individual DV's are above 5.5 to 6.0 km/sec.
    You will notice that they have been contemplating manned missions to Mars almost since their creation. So after more than fifty years the nearest manned mission by NASA to Mars remains a tantalising fifteen to twenty years in the future - where it has always been. And where it is likely to remain. NASA as a proponent of manned space flight is a spent force. If it were otherwise I doubt you would be making your proposal.

    Quote Originally Posted by moonguy View Post
    Your 'back-of-the-postage-stamp' cost-benefit analysis (I'll have to remember that one!) should be an interesting read. Care to share the details?
    There are no details. That's why it's on a postage stamp and not an envelope. I have a track record for a high percentage of hits on 'gut feel' judgements. I don't expect these to convince anyone else, but I am comfortable with my conclusion. It is your proposal. If you wish to convince sceptics, such as myself, you will have to address many issues, in detail. Zubrin presented an outstanding and only marginally optimistic case for going to Mars and you notice how that idea caught on. Good luck - you'll need it.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    What do you see as the level of challenge to this?
    Let's see -

    Efficient lightweight microwave power transmitters that can operate at very high temperatures
    Efficient lightweight microwave power receivers that can operate at very high temperatures
    Stationkeeping and attitude control in an environment with strong and varying solar winds
    Long term survivability in the above environment With the exception of 'long term survivability', the MESSENGER people faced and overcame the same issues as would be faced by other equipment. They won on each issue. If the same caliber of people are put on design of a powersail, they will win. I do not hhave yto resort to 'gut feel' to believe that. I have evidence. What evidence do you have to say otherwise?

    What I'm less clear is are you saying the entire concept falls apart because of that?
    No, it just gates it. And the more untested technologies you have to develop the longer the project timeline becomes, and the lower the odds of it surviving to its final form. In the US especially, no project survives more than about ten years. Thus if it's a 20 year development effort you're going to have to start it, shut it down, start it again over and over until enough gets done piecemeal to actually launch the mission.
    That's not saying powersails are a bad idea, it's just a lot to try to cram into an already hideously expensive and complex undertaking. To paraphrase Zubrin, if you want to develop a powersail develop a powersail. If you want to go to Mercury go to Mercury. Don't try to do both at once.
    Shuttle was started as a development project in 1968, did not fly until 1981 and went on to a 30-year flight program, even though each flight was a billion dollar effort. ISS was initiated in 1984, was not completed until early 2000's and is still flying. The powersail, as a project, is nowhere near as complex as either of these were.
    Both of these projects could be described as excessively expensive. They tell me that, right or wrong, big-dollar projects can be sustained even when their returns are marginal. NASA is banking on doing Mars on the same basis: make it too big to fail so the money keeps rolling. I don't believe they can get money for Mars if they don't find a way to reduce the costs or expand the returns dramatically.
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    Quote Originally Posted by moonguy View Post
    Long term survivability in the above environment With the exception of 'long term survivability', the MESSENGER people faced and overcame the same issues as would be faced by other equipment. They won on each issue. If the same caliber of people are put on design of a powersail, they will win.
    I am not saying it's impossible; far from it. With ten years and a few tens of billions you could do it.

    If all you have is ten years and a hundred billion, would you want to build a powersail or would you want to go to Mercury?

    Shuttle was started as a development project in 1968, did not fly until 1981 and went on to a 30-year flight program, even though each flight was a billion dollar effort. ISS was initiated in 1984, was not completed until early 2000's and is still flying. The powersail, as a project, is nowhere near as complex as either of these were.
    I think it rivals it in complexity. A mission critical system that uses as-yet unproven technology? That's a very complex project. You are not just betting that you can do it - you are betting the lives of every explorer on the base you can do it. In such cases 99% certainty isn't good enough.

    Both of these projects could be described as excessively expensive. They tell me that, right or wrong, big-dollar projects can be sustained even when their returns are marginal. NASA is banking on doing Mars on the same basis: make it too big to fail so the money keeps rolling. I don't believe they can get money for Mars if they don't find a way to reduce the costs or expand the returns dramatically.
    Agreed, which is my point. Building powersails and Mercury bases is not the way to reduce costs. It increases costs. Now, if you want powersails and Mercury bases it might be worth it. Otherwise save the money and go to Mars.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    Long term survivability in the above environment With the exception of 'long term survivability', the MESSENGER people faced and overcame the same issues as would be faced by other equipment. They won on each issue. If the same caliber of people are put on design of a powersail, they will win.
    I am not saying it's impossible; far from it. With ten years and a few tens of billions you could do it.

    If all you have is ten years and a hundred billion, would you want to build a powersail or would you want to go to Mercury?

    Shuttle was started as a development project in 1968, did not fly until 1981 and went on to a 30-year flight program, even though each flight was a billion dollar effort. ISS was initiated in 1984, was not completed until early 2000's and is still flying. The powersail, as a project, is nowhere near as complex as either of these were.
    I think it rivals it in complexity. A mission critical system that uses as-yet unproven technology? That's a very complex project. You are not just betting that you can do it - you are betting the lives of every explorer on the base you can do it. In such cases 99% certainty isn't good enough.

    Both of these projects could be described as excessively expensive. They tell me that, right or wrong, big-dollar projects can be sustained even when their returns are marginal. NASA is banking on doing Mars on the same basis: make it too big to fail so the money keeps rolling. I don't believe they can get money for Mars if they don't find a way to reduce the costs or expand the returns dramatically.
    Agreed, which is my point. Building powersails and Mercury bases is not the way to reduce costs. It increases costs. Now, if you want powersails and Mercury bases it might be worth it. Otherwise save the money and go to Mars.
    All of the issues you mention are valid enough. I take very seriously your point about the lives of crew depending on technologies being proven. Someone comes along making big, bold statements about how we can do this or that. . . I can see where that looks reckless. I would never put my personal rep on something that I could not say there was very strong evidence for being able to do. Mercury settlement is a relatively new idea and it takes a good, hard look to see if it has merit. You raised a good point about the powersail and that is why I brought the issue to this forum. I'm actually grateful for the doubt you have as it gives me a sense of where the proposal might be weak. Now I'm wondering if you would be willing to challenge yourself and work out how you would resolve the points you raised. . . Maybe even join the project team. . .
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    Quote Originally Posted by moonguy View Post
    Now I'm wondering if you would be willing to challenge yourself and work out how you would resolve the points you raised. . . Maybe even join the project team. . .
    Honestly I'd do the powersail first as a demonstration project and put it in Earth orbit. That way it is actually useful and we get the benefit of the power. And if that kicks off a wave of orbital solar power projects we all come out ahead.

    However if the goal were "go to Mercury" then I'd just plan to land at one of the poles and put a three sided PV array on the top of a mountain. With Mercury's tiny axial tilt it would always be in the sun. (Alternatively use a tracking array, but a three sided array isn't that much more expensive or heavy.)
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    Now I'm wondering if you would be willing to challenge yourself and work out how you would resolve the points you raised. . . Maybe even join the project team. . .
    Honestly I'd do the powersail first as a demonstration project and put it in Earth orbit. That way it is actually useful and we get the benefit of the power. And if that kicks off a wave of orbital solar power projects we all come out ahead.

    However if the goal were "go to Mercury" then I'd just plan to land at one of the poles and put a three sided PV array on the top of a mountain. With Mercury's tiny axial tilt it would always be in the sun. (Alternatively use a tracking array, but a three sided array isn't that much more expensive or heavy.)
    The goal is to 'Go to Mercury. . . and make it useful!' I like the idea of getting the cells off the ground. They are going to be hot, but some (not all) of the heat can re-radiate into vacuum. I'm thinking that integrating the cell panels with thermal radiator panels to keep them cooler would be more efficient if the panels were up off the ground.
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    Quote Originally Posted by moonguy View Post
    The goal is to 'Go to Mercury. . . and make it useful!'
    OK. And how do we make it useful? (And sending another mission somewhere else is insufficient reason.) If it's long term mining for profit, great; make the case for the profits we will see. If it's exploration, also great. Quantify the science done for the money spent.

    I like the idea of getting the cells off the ground. They are going to be hot, but some (not all) of the heat can re-radiate into vacuum. I'm thinking that integrating the cell panels with thermal radiator panels to keep them cooler would be more efficient if the panels were up off the ground.
    Wouldn't it be better to just use the planet as a heat sink? It's around -90C permanently at the poles. You don't need much of a heatsink at -90c.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    The goal is to 'Go to Mercury. . . and make it useful!'
    OK. And how do we make it useful? (And sending another mission somewhere else is insufficient reason.) If it's long term mining for profit, great; make the case for the profits we will see. If it's exploration, also great. Quantify the science done for the money spent.

    I like the idea of getting the cells off the ground. They are going to be hot, but some (not all) of the heat can re-radiate into vacuum. I'm thinking that integrating the cell panels with thermal radiator panels to keep them cooler would be more efficient if the panels were up off the ground.
    Wouldn't it be better to just use the planet as a heat sink? It's around -90C permanently at the poles. You don't need much of a heatsink at -90c.
    Yes, the ground sink makes sense for this. As I mentioned, not all of the heat from panels would be re-radiated into space; the remaining heat would have to be 'dumped' somewhere else.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by moonguy View Post
    The goal is to 'Go to Mercury. . . and make it useful!'
    OK. And how do we make it useful? (And sending another mission somewhere else is insufficient reason.) If it's long term mining for profit, great; make the case for the profits we will see. If it's exploration, also great. Quantify the science done for the money spent. 'Sending another mission' is understating Mercury's potential as a launch platform for interplanetary missions. Over the course of a decade - NASA's usual planning period for exploration missions - Mercury will have 31 potential launches to Mars, 20 to Venus, 40 to each of the outer planets. . . Solar sails are low budget 'upper stages' for such missions and the spacecraft themselves require only instrument payloads. That means any number of probes can be launched at each opportunity. A well equipped machine shop could fabricate hundreds of instrument packages in that time using only a few tons of instrument hardware imported from Earth. None of this requires any new or risky technology. Just a new approach to mission planning. As for quantifying the science, you only need to look at NASA's current mission plan to see where they want to go in astronomy. There is the exploration of Mercury itself. Solar observations requiring high-res detail is best done form Mercury or by spacecraft that can be managed from Mercury. Maybe these things do not excite you or fit into your value system. You are the one who has control over that. As for 'profit' from mining. . . I never suggested this would be a private commercial venture, if that is your expectation. I do have thoughts along those lines, but they are not the major driver for the plan.

    I like the idea of getting the cells off the ground. They are going to be hot, but some (not all) of the heat can re-radiate into vacuum. I'm thinking that integrating the cell panels with thermal radiator panels to keep them cooler would be more efficient if the panels were up off the ground.
    Wouldn't it be better to just use the planet as a heat sink? It's around -90C permanently at the poles. You don't need much of a heatsink at -90c.
    'Sending another mission' is understating Mercury's potential as a launch platform for interplanetary missions. Over the course of a decade - NASA's usual planning period for exploration missions - Mercury will have 31 potential launches to Mars, 20 to Venus, 40 to each of the outer planets. . . Solar sails are low budget 'upper stages' for such missions and the spacecraft themselves require only instrument payloads. That means any number of probes can be launched at each opportunity. A well equipped machine shop could fabricate hundreds of instrument packages in that time using only a few tons of instrument hardware imported from Earth. None of this requires any new or risky technology. Just a new approach to mission planning. As for quantifying the science, you only need to look at NASA's current mission plan to see where they want to go in astronomy. There is the exploration of Mercury itself. Solar observations requiring high-res detail is best done form Mercury or by spacecraft that can be managed from Mercury. Maybe these things do not excite you or fit into your value system. You are the one who has control over that. As for 'profit' from mining. . . I never suggested this would be a private commercial venture, if that is your expectation. I do have thoughts along those lines, but they are not the major driver for the plan.
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    Umm... the deltaV situation is much more worse than you think it is. It takes more deltaV to leave Earth and land on Mercury than it does to reach any other planet in the Solar System, or to leave the Solar System completely.


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    Quote Originally Posted by moonguy View Post
    Sending another mission' is understating Mercury's potential as a launch platform for interplanetary missions.
    No it's not. It might be totally awesome at sending other missions. It's still sending other missions.

    It's like saying "we should take over Central America and invade Colombia, and move our space industries there - because it's much easier to launch from the equator. We would save so much money!" I mean, that's very true, and such an invasion would be a lot cheaper than building a manned Mercury shipyard. But it's still a bad idea (unless you have to invade for other reasons, like they're launching missiles at us.)

    Over the course of a decade - NASA's usual planning period for exploration missions - Mercury will have 31 potential launches to Mars, 20 to Venus, 40 to each of the outer planets. . .
    Thus far planetary missions have not been limited by not having enough launch windows.

    Solar sails are low budget 'upper stages' for such missions and the spacecraft themselves require only instrument payloads.
    True from Earth orbit as well. And they'd be easier to launch from Colombia . . . .

    There is the exploration of Mercury itself. Solar observations requiring high-res detail is best done form Mercury or by spacecraft that can be managed from Mercury.
    That's a much better way to make the case for such a base.

    Maybe these things do not excite you or fit into your value system.
    I wish we could have bases on most of the planets and moons of the solar system. But in a world of limited resources we have to make good decisions on what to spend money and time on. If you could just have one of the following, which one would it be?

    Commercial fusion power
    A cancer cure
    Anti-senescence technology
    A Mercury base

    One can imagine we could just get all that - but in the real world money that goes to one comes from somewhere else.

    I never suggested this would be a private commercial venture, if that is your expectation. I do have thoughts along those lines, but they are not the major driver for the plan.
    Any mission has to make economic sense, even if it's value of the scientific research returned.
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    It sounds to me like the real purpose of putting infrastructure on Mercury would be for industrial purposes. Maybe iron working situations where it's convenient to be able to keep the metal really hot for a long time (and not have to use electricity or fuel to do it). Or situations where extreme cold is handy.

    For human habitation, it looks pretty dismal.

    The thing to remember in space is that, if we ever colonize the moon, shipping materials back and forth between other areas of the solar system is pretty easy. Just give it a good strong push in the right direction/velocity, and it will drift to its destination on its own.

    Outer space is like a big huge, frictionless ocean.
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    Quote Originally Posted by kojax View Post
    The thing to remember in space is that, if we ever colonize the moon, shipping materials back and forth between other areas of the solar system is pretty easy. Just give it a good strong push in the right direction/velocity, and it will drift to its destination on its own.
    Well, that "good strong push" is the expensive part. It took a Saturn V to give us enough of a push to get to the Moon, for example.

    Outer space is like a big huge, frictionless ocean.
    Except there are mountains and valleys in this ocean . . . .
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    Quote Originally Posted by kojax View Post
    It sounds to me like the real purpose of putting infrastructure on Mercury would be for industrial purposes. Maybe iron working situations where it's convenient to be able to keep the metal really hot for a long time (and not have to use electricity or fuel to do it). Or situations where extreme cold is handy.

    For human habitation, it looks pretty dismal.

    The thing to remember in space is that, if we ever colonize the moon, shipping materials back and forth between other areas of the solar system is pretty easy. Just give it a good strong push in the right direction/velocity, and it will drift to its destination on its own.

    Outer space is like a big huge, frictionless ocean.
    A good strong push is one way. A steady, gentle push also works. Solar sails are the real game changers for sending payloads to/from Mercury economically. Using solar thermal power to break down material is right on the mark. Thanks for the post!
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by kojax View Post
    The thing to remember in space is that, if we ever colonize the moon, shipping materials back and forth between other areas of the solar system is pretty easy. Just give it a good strong push in the right direction/velocity, and it will drift to its destination on its own.
    Well, that "good strong push" is the expensive part. It took a Saturn V to give us enough of a push to get to the Moon, for example.
    Yeah. That's why the Moon is really the priority. If we had basic infrastructure on the Moon, and we were able to manufacture some kind of propellant fuel in situ on the Moon, then Saturn V rockets would be obsolete.

    Instead, a space shuttle could get materials into low orbit, and then a second rocket could launch from the Moon, go down into low Earth orbit, rendezvous with the Shuttle, and refuel it for the rest of the trip. The object launching from Earth's surface would no longer have to be carrying enough fuel to get out to the Moon.

    Getting an object out of the Moon's gravity well is pretty easy. Getting it out of Earth's gravity well is a lot harder.
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    Quote Originally Posted by SpeedFreek View Post
    Umm... the deltaV situation is much more worse than you think it is. It takes more deltaV to leave Earth and land on Mercury than it does to reach any other planet in the Solar System, or to leave the Solar System completely.
    That was my perception. Moonguy seems to dismiss the delta-V issue. I suppose that's one way of dealing with it.
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    Quote Originally Posted by kojax View Post
    Quote Originally Posted by billvon View Post
    Quote Originally Posted by kojax View Post
    The thing to remember in space is that, if we ever colonize the moon, shipping materials back and forth between other areas of the solar system is pretty easy. Just give it a good strong push in the right direction/velocity, and it will drift to its destination on its own.
    Well, that "good strong push" is the expensive part. It took a Saturn V to give us enough of a push to get to the Moon, for example.
    Yeah. That's why the Moon is really the priority. If we had basic infrastructure on the Moon, and we were able to manufacture some kind of propellant fuel in situ on the Moon, then Saturn V rockets would be obsolete.

    Instead, a space shuttle could get materials into low orbit, and then a second rocket could launch from the Moon, go down into low Earth orbit, rendezvous with the Shuttle, and refuel it for the rest of the trip. The object launching from Earth's surface would no longer have to be carrying enough fuel to get out to the Moon.

    Getting an object out of the Moon's gravity well is pretty easy. Getting it out of Earth's gravity well is a lot harder.
    (Emphasis mine) I could not agree more! It is unfortunate that many people do not seek synergy and prefer to see things as 'ours vs. theirs'.
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    I'm glad somebody does. Most of the tech is already there.

    The docking issue is already not a big issue, since space shuttles dock with the International Space Station all the time, or when conducting repairs on Hubble. It's not easy, but it's clearly inside NASA and RKA's capabilities.

    The next logical step would be to analyze the chemicals found in Regolith, or maybe find a specific location on the moon that has useful chemicals, and send up a robot that is capable of making a propellant out of it. Even a very weak propellant might suffice, because the physical size of a rocket already in space doesn't much matter. Only its mass matters. If it needs to have a really ginormous fuel tank, but the tank is made out of light materials, then that's just fine.

    Then we need bring up a Moon-fuel-powered-rocket, get it on the Moon, and we're in business.

    When we want to send a person to the Moon, we'd first send them to the International Space station on a normal space shuttle. Then the Moon-fuel-powered-rocket would launch from the Moon, come down to low Earth Orbit, and dock with the International Space station and pick up its passenger and go back to the Moon with the passenger onboard. Moon flights would become just as standard as Space Station flights.
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    Quote Originally Posted by kojax View Post
    Yeah. That's why the Moon is really the priority. If we had basic infrastructure on the Moon, and we were able to manufacture some kind of propellant fuel in situ on the Moon, then Saturn V rockets would be obsolete.
    Not for a long, long time. If any propellants are available on the moon they'll have to be dug out of the ground, which requires enough infrastructure to mine the regolith. That's a lot of infrastructure and a lot of Saturn V (or equivalent) launches.

    Getting an object out of the Moon's gravity well is pretty easy. Getting it out of Earth's gravity well is a lot harder.
    Right - but that's also true of your moon rocket that just rendezvoused with the shuttle.
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    Quote Originally Posted by billvon View Post
    I wish we could have bases on most of the planets and moons of the solar system. But in a world of limited resources we have to make good decisions on what to spend money and time on. If you could just have one of the following, which one would it be?

    Commercial fusion power
    A cancer cure
    Anti-senescence technology
    A Mercury base

    One can imagine we could just get all that - but in the real world money that goes to one comes from somewhere else.
    Fusion power, then use the profits for the medical research. Afterwards, you can cure the cancer your scientists get from damaged radiation shields and they can live there without having senile scientists on a planet they can't return from.
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by kojax View Post
    Yeah. That's why the Moon is really the priority. If we had basic infrastructure on the Moon, and we were able to manufacture some kind of propellant fuel in situ on the Moon, then Saturn V rockets would be obsolete.
    Not for a long, long time. If any propellants are available on the moon they'll have to be dug out of the ground, which requires enough infrastructure to mine the regolith. That's a lot of infrastructure and a lot of Saturn V (or equivalent) launches.
    I don't know enough about the elements available to be sure if it's feasible, but it's not so much what you find as what you do to it. If the fuel making robot were sent up with some mirrors, it could set up a pretty powerful solar oven for cooking in.

    Maybe find some compounds that aren't really meant to be rocket fuel, but then super heat it, break it down, and recombine it to make some kind of basic explosive mixture.

    Worst case, it could focus on getting iron droplets, and magnetically hurling them for propulsion. Use solar panels to get electricity to power the electromagnets. (There's no shortage of solar power in space.)

    I think this article is a good starting point to determine what would be readily available:

    http://en.wikipedia.org/wiki/Moon_rock


    Getting an object out of the Moon's gravity well is pretty easy. Getting it out of Earth's gravity well is a lot harder.
    Right - but that's also true of your moon rocket that just rendezvoused with the shuttle.
    Not exactly.

    1)- Most of the fuel spent by the Saturn V was for the purpose of lifting fuel. The amount needed to get from Low Earth Orbit to the moon was just a very tiny fraction of the total fuel it had started with. But lifting that (comparatively) tiny amount of fuel into space required a colossal amount of fuel to be burnt during the initial take off phase.

    2)- There is no requirement for rapid acceleration. Once in orbit, gravity is no longer decelerating you, so you can make the trip as slow as you want. It doesn't reduce your fuel needs too much directly, but it does allow for use of some of the more efficient propulsion systems, like an ion drive or something.

    3) - There's no need for the moon-fuel-rocket to be aerodynamic. Depending on what kind of propellant it is using, the fuel tank might even be a big bag or balloon instead of a rigid tank.
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  52. #51  
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    Mercury has a synodic period relationship with Earth that presents a launch opportunity every 115.9 days resulting in three potential flight opportunities every calendar year. These launch opportunities repeat in a cycle extending over 13 years. In that time, at least nine flight opportunities have arrival delta-V of 6.5 km/sec. or less. It happens these opportunities occur in ‘clusters ‘ of four consecutive years. It is interesting to note that the lower the arrival delta-V, the longer is the optimum stay time on Mercury. For the 6.1 - 6.5 km/sec. range, stay times range between 76 and 183 days. Manned missions to Mercury are designed to minimize radiation exposure by taking the shortest flight times possible. In Mercury’s case, minimum energy Hohmann transfers are not all that minimum energy, particularly for the shorter transfer times.
    As an example, the shortest trip times for ‘lowest energy’transfers is 85 days. There will be four of these available in any 13-year cycle. To use these opportunities, the arrival delta-V at Mercury would have to range between 6.9 and 9.0 km/sec. This is over a 6.5 km/sec. limit for the crew transport vehicle’s propellant capacity for this series of flights. The mission opportunities that do come underthe 6.5 km/sec. limit have flight times ranging between 95 and 130 days. It should be noted that a given delta-V doesnot always correlate with a given flight time. This is due to Mercury’s orbit being elliptical and depends on the configuration of the transfer orbit for a specific launch opportunity. The lowest arrival delta-V possible is 6.1km/sec., with a transfer time of 105 days.
    Balancing for the longest stay time and the lowest arrival delta-V, the mission opportunity chosen for the first manned mission (‘MercuryAlpha’) has an outbound flight time of 105 days; arrival delta-V of 6.1 km/sec.; a 179-day stay and a Mercury departure delta-V of 6.3 km/sec. The return flight takes 80 days for that particular opportunity. Total mission time is 364 days.
    Departure from Earth is of course a particular concern because most of the propellant mass is expended in this maneuver. This maneuver is not subject to the 6.5km/sec. limit as two or more stages, docked in Earth orbit, can be reasonably contemplated as an option if needed. In the Mercury Alpha mission scenario, the departure is from an orbit around the Earth-Moon L2 location. Departure velocities from this location are on the order of 140 m/sec. An upper stage from the lunar base logistic support program is utilized for this delta-V.
    Generally, delta-V for Mercury missions are two to three times higher than for Mars missions. Actual propellant masses, however, are a function of a stage’s dry mass; the payload’s mass and the performance of the engine(s) used. These are the subject of the next posting. . .
    Last edited by moonguy; September 13th, 2013 at 08:31 AM.
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  53. #52  
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    Quote Originally Posted by kojax View Post
    1)- Most of the fuel spent by the Saturn V was for the purpose of lifting fuel. The amount needed to get from Low Earth Orbit to the moon was just a very tiny fraction of the total fuel it had started with. But lifting that (comparatively) tiny amount of fuel into space required a colossal amount of fuel to be burnt during the initial take off phase.
    Agreed; you significantly reduce the amount of fuel needed. But you still needed most of the fuel in that third stage to put the CM/LEM onto a TLI - and you would still need that fuel no matter whether you launched from Earth or from the Moon.

    2)- There is no requirement for rapid acceleration. Once in orbit, gravity is no longer decelerating you, so you can make the trip as slow as you want. It doesn't reduce your fuel needs too much directly, but it does allow for use of some of the more efficient propulsion systems, like an ion drive or something.
    Slow acceleration actually increases fuel needs. Engine burns at higher speeds/lower in gravity wells are, in general, more efficient due to the Oberth effect. However as you mention the advantages of the efficiency of an ion engine may overcome the inefficiency of not taking advantage of the Oberth effect.

    3) - There's no need for the moon-fuel-rocket to be aerodynamic. Depending on what kind of propellant it is using, the fuel tank might even be a big bag or balloon instead of a rigid tank.
    The mass of fuel, however, would not be reduced. Modern fuel tanks have very high fuel/structure weight ratios, so you wouldn't gain much.
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