Moonguy

This may surprise you: We can put a three-person crew in Mercury orbit for a payload mass of less than 10 metric tonnes.

In 1967, the Bellcomm Corporation developed a concept for a manned flyby of the planet Venus. That mission was to take 109 days to reach Venus, flyby, then return to Earth in a flight lasting about 400 days. This in many respects was very similar to a ballistic mission to Mercury. The ‘Mission Module’ for the Venus flyby was based completely on Apollo hardware. Its estimated mass was 12,480 kg. The entire mission was conducted with a single launch of a Saturn/Apollo stack. This mission is a starting point for designing the crew module for a manned flight to Mercury.

By reviewing the masses for individual systems of the Apollo/Venus mission, we can develop ma reasonable idea of a mass for the Mercury mission crew module.

A very important difference with the Mercury module is the complete absence of metallic structure. Using rigid composites will reduce the mass of the basic structure by 50%, from nearly 4200 kg to just under 2100 kg.

Food for the three crewmembers at 2 kilograms per-person/per-day, works out to 2430 kg for the entire 400-day Venus mission. The Mercury mission is 40 days longer. However, 178 days are spent on Mercury’s surface where supplies are cached prior to the crew’s arrival. Therefore, only 262 days of meals have to be provided for on the flight module. Mercury mission food mass is therefore 1591 kg for Earth-Mercury and Mercury-Earth transfers. Reviewing other elements of the Apollo/Venus Life Support System revealed possible weight savings for the Mercury module’s system of about 15% overall. This despite the fact the Mercury mission is longer and the spacecraft’s atmosphere is normal sea level pressure and mixture.

The power system for the Apollo/Venus module was based on approximately 56 m² of photovoltaic arrays providing 5.3 kw. This is an efficiency of about 7%. Photovoltaics today are easily four times as efficient and are mounted on much lighter support structuring. In the Mercury case, carbon composite panels similar to those now flying on Messenger are less than half the mass per unit area of the Apollo-era design. Total mass for the Mercury mission module power system would be a hard-to-believe 236 kilograms.

There is more, but I’m sure you get the general idea.

All of the above are still being reviewed and it is looking like the final figure for the Mercury module’s mass will be about 40% lighter than the Venus module. It is already under 10 metric tonnes. If LO²/LH² is used to propel this payload into Mercury orbit (ΔV~6.3 km/sec.) it would need a stage the size of the SLS Block II cargo carrier EDS. A second EDS would be needed to boost the payload + stage into the transfer orbit. It would have to depart from an orbit around the Earth-Moon L2 point and be fueled from lunar resources.

It sounds very grandiose, but by this time (ca 2035) we will be routinely launching cargo missions to the Moon using EDS stages. Retrieving one or two for a manned flight to Mercury would avoid having to launch complete SLS stacks for the Mercury Project. This frees up pad space for Mars mission hardware.

If we had a lunar base (which would be producing propellants for its own needs anyway) we could fly this mission today. Of course, there are alternative approaches. . .

Thanks to everyone who responded to my question. It helped a lot.

It depends on the lake.

 

You can measure the temperature of the water at the bottom of a lake using some hose and a small pump. Put cloth over one end of a hose, attach a weight to the same end, and let that end fall to the bottom of the lake, use a 12 volt DC pump (used for fountains) and a 12 volt battery to pump water through the hose from the bottom of the lake for a couple of minutes, measuring the temperature of that water continuously until the temperature is lowest. If the water temperature is about 40 degrees, you have a good refrigerator.

Useful suggestion. Thanks!

I am wondering how to calculate the temperature of water at the bottom of a lake, say, ten meters deep. Would it be possible to reliably refrigerate foods at such depth (in a sealed container, of course) ?

Thank you Janus,

Velocity increments to Mercury do not seem so daunting when you break them down by mission legs. Only manned missions would go by all-propulsive systems and they would be restricted to missions where the Mercury Orbit Insertion (MOI) was less than 9.2 km/sec. All calendar years have at least one such mission and sometimes two. Over a decade, there are between ten and fifteen such opportunities.

Cargo would go exclusively by solar sail and there are always three opportunities every calendar year - or 31 opportunities in a decade. If the base requires a thousand Metric tonnes, all of which is inert mass, we could conceivably divide 1000 tones by 31 opportunities, averaging only ~32 tonnes for each flight. To do the same for Mars, where you only have four launch opportunities per decade, you would have to send 250 tonnes at each opportunity. We could probably do that with solar sails, but it would mean a very ambitious launch schedule as it requires four Ares-V class launchers. The Mercury cargos can launch on a much smaller launcher or double up on Ares V requiring half as many launchers for the same cargo delivered.

Aerobraking presents an interesting problem. You can get a payload to Mars' surface faster using a solar sail on a fast transfer, but the need to carry an aerobrake means a net payload decrease. This effectively increases the cost, per unit mass, for cargo delivered. Not a showstopper, but a frustrating reality - we never get something for nothing in space flight!

Hi. This is a an attempt to generate discussion on the prospects for the settlement of the planet Mercury. As of this writing I have been on SFN for only a few days, but I am very pleased that the response to the idea is high quality. I have yet to experience the hostility found on 'other' forum sites. Rules for SFN are that postings should stick to the subject of the original post. I have been posting on a thread about the (extremely important) discovery of water ice on Mercury, but my comments were along the lines of transportation to Mercury. Arguably related to the original post, but not really fair to the poster. So, for further discussion, I submit the following:

PREMISE: Establishing an industrial facility on Mercury will enable us ('mankind') to reduce the cost of operations throughout the Solar System. Science, spaceflight and commercial operations will all benefit either by Mercury enabling their expansion at low cost, or reducing the cost of current operations. The Mercury facility will be self-sustaining and economically viable.

RATIONALE: Mercury presents a number of qualities that allow it to facilitate our plans for other venues of operation in the Solar System. These plans include: broad expansion of astronomical observations on all wavelengths; manned bases on the planet Mars; mining of asteroids and comets; unmanned exploration of all outer planets on an expanded basis; near-term development of interstellar exploration capabilities.

The qualities Mercury presents are: much more frequent synodic launch opportunities to all planetary venues, including asteroids and comets; super-abundance of solar energy; industrially useful raw materials in abundant supply; substantial, but weaker, gravity; environmental conditions that support large-scale mining and mineral processing as well as fabrication operations; Extreme heat and extreme cold to enable both research and utilization of advanced technologies; very slow rotation rate; relative nearness to the Earth for 'rapid' (~100-day) access. . . I hope to develop all these and more as time goes on.

I insist on only one thing: civility. By all means challenge my assumptions, rationales. . . whatever. Just do it in an instructive, civil way. I have been researching this issue for several years, so I might come off as a know-it-all at times. Feel free to pour whatever cold water on me you deem appropriate, but just do so with civility.

Now, some points about where I am coming from. . .

I am 56 years old. I have a professional background in broadcast journalism, but I do not currently work in the field. I have a degree in business management and certifications as a medical billing specialist and a travel agent. My interest in science and space exploration has been a lifelong deal. My interest in Mercury settlement stems from the space colonization studies of the 1970's and earlier. They did not consider Mercury to any great depth. That was excusable for them because it was/is hard to get probes to Mercury to convert guesses to facts. We no longer have that excuse. The Messenger mission has given us ample information to at least begin the discussion.

Today I regard myself as a 'recovering space advocate'. I am not even remotely interested in spreading human DNA throughout the universe 'just because we can'. I do believe, however, that we can utilize certain venues to provide benefits to humanity in general.

In postings to come I will expand on all these points. Thanks. . .

PS: For reasons to be explained later, I need to keep my name secret for awhile. Fear not! I will very soon be able to divulge all in short order. . .!

That is his point.

 

Nonsense. There is no point other than scientific curiosity in going to Mercury. There is no point at all in sending humans there, at least not in our lifetime.

 

Getting to Mars is cheap. The delta V requirements for a one-way mission to Mars is less than a third, and maybe less than a quarter, of that for a one-way mission to Mercury. A round-trip mission to the surface Mars and back to Earth, while costly, is cheaper yet compared to a round-trip mission to the surface of Mercury and back to Earth.

 

To make matters worse, that factor of 3 or 4 or more in delta V translates into a huge factor in terms of fuel. The amount of fuel needed is not a linear function of delta V. Fuel costs grow exponentially as delta V increases.

 

Any resources on Mercury are much more easily obtained in the asteroids. Or for that matter, right here on Earth. The idea of mining asteroids (or the Moon, or Mercury) and sending the mined items back to Earth is, for now, science fantasy. The first materials that will be mined in space are things that are very easily obtained: water and other volatiles. There is no value in sending these materials back to Earth. Common metals mined in space such as iron and nickel will have zero value back on Earth. They're too common. Only the very rarest of materials might have value on Earth, but mining those falls into the category of "we haven't the foggiest idea how to do that."

Payload masses are what determines how much propellant you need. Delta-V only determines how much propellant you need per unit mass of payload.

Getting to Mars is cheaper. My own figures say that. What I was saying is that a mission to Mercury is possible for propellant loads that are within the same mass range we are already planning for Mars.

Mercury is a multi-functional place where science ( mostly astronomy, solar physics and planetary science) and industry are uniquely facilitated - due mainly to solar sail's impact on transportation costs, the super-abundance of energy on site and the seven-fold grater frequency of launch opportunities for a given transport system..

Carefully note that I am not suggesting Mercury as an alternative to Mars, but as a synergistic relationship WITH Mars.

In a closed environment dependent on plants for Oxygen regeneration, it is necessary to balance CO2 supply for a needed level of O2. How does one calculate the O2 output in terms of the CO2 needed by the plants? Is there a range of efficiencies involved?

Look, in order to get to Mercury you have to shed a fair portion of the Earth's orbital speed. Just firing your engines in a direction opposing the Earth's orbital direction isn't going to do it unless you make a large enough change in ytour speed. Anything less just puts you in an eliptical orbit which has a perihelion further from the Sun than Mercury is. In order to get your trajectory to intersect with Mercury's orbit you have to get your orbital speed at Earth orbit distance down to, at most, 22 km/s, which means you have to change your velocity by ~8 km/sec.

 

As you fall in towards the Sun you will pick up speed and by the time you reach Mercury's orbit, you will be moving at 57 km/sec.

 

Mercury's orbital speed is 48 km/s. So in order to safely rendevous with it ( and not just slam into it at high speed) you are going to have to shed 9 km/sec. This puts the total velocity change needed 17 km/sec. And this doesn't even take into account what it would take to lower yourself to the surface.

 

In order to leave the solar system completely from Earth orbit requries a velocity change of only 12.4 km/sec.

 

As to what a 17 km/sec velocity change means in terms of fuel:

 

If we assume a exhaust velocity of 4500 m/s (about as good as you'll get with a chemical rocket), it works out that you'll need ~43 kg of fuel for every kg of payload you want to get to Mercury.

 

If you want to land, this jumps up to 116. If you want to include a return trip, you are now talking 13750 kg of fuel for every kg that you land on Mercury and return to Earth orbit.

 

Basically, the ratio of fuel to payload varies by the power of the total speed change divided by the exhaust speed of your rocket. If the velocity change doubles, the mass ratio increases by a power of 2.

All very accurate. But what exactly is your point? Are you trying to say it is too expensive in delta-v terms? If this were being done for a manned mission, the propellant requirements would be two to three times that required for a similar mission to Mars. Sounds bad, but the manned payload for Mercury would have a much lower mass because the total mission time is about 440 days, as compared to the ~900 days for the Mars mission. Less consumables have to be carried. Less spacecraft volume is needed to accommodate the remaining consumables while still holding to NASA's criteria for crew volume. Less volume equals smaller, lighter payload mass. All together, propellant mass for the Mercury mission would actually be about 1.2 to 1.5 times that needed for a Mars mission. Not the 2 or 3 times indicated by delta-V figures alone.

You were right about the exhaust velocity of 4500 m/sec. the J2X was intended to operate with Specific Impulse of 465 sec. (optimistic, IMHO) yielding exhaust velocity of 4561 m/sec. That is why we went with the Solar Thermal Rocket for manned missions only. Different sources gave a variety of figures for Isp starting at 980 and going up to 1300.sec. 1150 sec. seems conservative. This is very sustainable from Mercury's resources.

Supplying propellant in Mercury orbit enables the mission to be broken down into two distinct legs. This is nothing different than what is being contemplated for Mars missions. The ability to actually produce rocket propellant on Mercury itself makes the horrendous 'all-up' mass figure you noted (13750 kg/kg spacecraft) unnecessary.

This is why the matter needs in-depth study. Mercury is not Mars and flights to Mercury are not the same as flights to Mars. The spacecraft won't be the same either, if we are wise.

Very interesting. When I had read about the possbility awhile back, I thought it was a bit strange. With very little atmosphere, I would have thought that the ice would sublimate in short order. But I guess at those low temps, it may not happen.

 

So it might be a more ideal first colony when compared to Mars in some ways. But, I think there is still the issue of radiation. The interior of the planet would be protective, but a ship would need to get there, and would be exposed.

The asteroid 24 Themis has similar thermal conditions to Mercury's poles. Water ice has been discovered on it's surface which was surprising as the sublimation rate that far from the Sun (~3.5 AU) would suggest the surface should be devoid of ices. It was suggested the water came from Themis' interior, but Themis is about 200 km diameter and would not likely have a warm enough core to support volcanic heating of subsurface water. Mercury is actively volcanic in its core, however. We may be seeing the surface manifestation of subsurface water being driven to the surface in aeons past.

I have predicated my proposal on the idea that energy is key to doing anything in space. The more you have of it, the better off you are. Carefully note that I started by talking about astronomy. Not always the first choice for most space advocates. We are already doing astronomy. Mercury is just a better (more cost-efficient) location for it. I didn't talk about Helium-3. Now that is a technology that is way off practically and economically.

At this point I have seriously strayed from the original subject of this post and that is a no-no. I apologize to the poster. . . Perhaps I/we should post in a different forum?

 

Actually, we don't see any 'serious proposals' to go to Mercury for the sort of operations you are proposing. The space settlement advocacy is the quintessential source of non-serious proposals of all sort. Space settlement on an extremely small scale, on close-by objects *might* happen in the next few decades. Space settlement on the scale advocated by those advocacy groups: It ain't gonna happen, not in my lifetime, probably not in yours.

 

You have predicated your Mercury proposal on a large number of technologies that we don't know how to do from an economic or engineering perspective. Space mining? We don't know how to do that. Space manufacturing? We don't know how to do that, either. The same applies to large solar sails, solar thermal propulsion, getting people to and from Mercury. We don't know how to do any of them. All of these are at a very low technology readiness level. TRL 4 is where we can start saying we know how to do that. None of these is even close.

I agree with your assessment of space advocacy groups being the source of non-serious proposals. The Mercury study is all about determining how - not if - we could mine Mercury on an economical basis. The Japanese flew their IKAROS solar sail to Venus successfully. It operated for months under their control and performed as expected.

We have been operating large cryogenic propulsion stages in space for decades. That is all a Solar Thermal Rocket is and it is based on known technologies from Nerva and Apollo operations. It is not just theoretical conjuring.

You are missing the point. It takes a great amount of fuel to escape a gravity well such as near a black hole, whereby it takes none to get "pulled in" by gravity, less fuel to go to Mercury than to leave it going back. This is not Sci Fi.

 

 

 

We don't have to get stationary relative to the sun. By going opposite the rotation of the Earth the sun's gravity helps pull you toward your destination. 30km/sec is 108,000 Km per hour. We have no problem achieving half that speed. The point is that the pull of the sun's gravity can assist a craft inward toward the sun.

 

 

 

I agree with your point that presently there is little point to sending nuclear waste inward toward the sun. But with nuclear rockets, or better, less expensive propulsion systems, I expect it will happen someday.

 

 

 

OK

 

 

 

We may be on the same page here but I think the technology of nuclear powered spacecraft is already here. It just needs the political will to do it, and the time to perfect and debug such a system. I also expect positron rocket propulsion is maybe only 50 years away, even though we haven't even started on it in earnest as yet.

 

I think we will see serious proposals for man to go to Mercury within the next century. I also think there will be one or more mining colonies there within the next few centuries.

//

Actually, we see 'serious proposals' to go to Mercury now. The only problem is they come from the space settlement advocacy and not NASA itself or its industrial support. That is why I'm here. There is polite tolerance in some industry circles for going to Mercury, but it is premature to commit to the idea before we resolve important issues - such as the radiation effects on people who go there. This site offers a real shot at getting these issues addressed by people who actually know how to work them. Sadly, I'm only a journalist.

As Enthalpy says, it's the density that matters. You can actually calculate surface gravity based on density using the following:

 

[math]g = \frac{4\pi}{3} Gpr[/math]

 

Where [math]p[/math] is the density of the object at radius [math]r[/math].

 

Since [math] p = \frac{mass}{volume} [/math] you can compute the change in the surface gravity based on the changes in volume and mass of the planet as compared to earth.

'Density of the object. . .' What is the effect of moving from the object's surface into an orbit? I assume we just apply the inverse square rule, right?.

The ice is not exposed. v vIt seems to be either covered by or misxed with a regolkith component containing hydroca4rbon material. This suggests it is cometary in nature as such minerals are freq

uently found in comets. We do not yet know, exactly, the chemical make-up of the material, but the insulating properties are likely to be at least as good as the regolith found elsewhere on Mercury.

Sorry for the typos. . .

Getting back is the same problem as getting there: having a transportation system that can develop the velocity change needed. The confirmed presence of large quantities of water means we can definitely support either LO²/LH² or H² systems on an economical basis. This means we can reasonably contemplate using all-propulsive ballistic transfers. These have flight times averaging 105 days (some flights are only 85 days long) with important implications for a human crew's payload mass.

Mass ratios for Mercury orbit Insertion (MOI) range between 4 and 7.7 for the LO/LH systems.A hydrogen burning Solar Thermal stage would do very much better with mass ratios of 1.75 to 2.3. I base these on Specific Impulse of 465 sec. for LO/LH and 1150 sec, for LH systems.

More generally, neither the Moon or any of the planets are 'easy' to reach. They all require billions of dollars in infrastructure to access and utilize. What matters is what we get in return. With Mercury, at a minimum, you access resources, energy in great quantity and a launch window advantage (compared to Earth's situation) that is unmatched anywhere else. Ditto for Mercury as a science platform.

Energy + Resources + Location + Environment = Potential For Colonization

Mercury provides energy via the Sun, of course, but there is also a still-molten (outer?) core that almost certainly still changes things on parts of Mercury's surface occasionally.

Resources there are typical of asteroids - rather mediocre, to be frank - but the thermal energy surplus makes them economically viable as so far 'ores' are defined.

Mercury's orbit is a good place to launch operations to other planets from. With the exception of Venus, it is possible to launch to other planets at least three times every calendar year. For outer planets it is four times.

Relying on robotics assumes the number and endurance of the robots is sufficient to operate essentially trouble-free as there is no way to fix them (except maybe with other robots). what miught be the cost of a robot to do both mining and telescope building? I have to believe it gets prohibitive. . .

I would like to re-open this discussion. . .

Reading these posts, I noted two things:

1) There was no discussion of why we would want to send people to Mercury.

2) There was no mention of solar sails, which are a game changer for travel to Mercury.

Mercury has awesome potential as an astronomical observatory. All wavelengths are available to the surface for 88 straight days of observing. Mercury provides most of the materials one would expect to build optical and radio telescopes out of - seriously reducing mass required from Earth/Moon. We are spending 8 billion dollars to build & launch the James Webb Space Telescope alone. when you consider that Kepler, Chandra, and other orbiting telescopes all are approaching the end of their useful lives, the total replacement costs are well into the tens of billions - with no technicians in orbit to ensure the 'scopes keep working or are upgraded periodically. A base on Mercury could do that rather handsomely. Of course there are other reasons for settling Mercury. . .

Solar sails are able to move large masses to Mercury from Earth in reasonable time periods. The late Robert Forward, of JPL, outlined capabilities of 185 metric ton payloads delivered to Mercury orbit in flights of 2.3 years. Manned flights would not need anything near that massive for exploration missions, suggesting they would be faster. Mercury's photon flux is so great that the sail material to be used was a relatively 'heavy' (10 gm/m²) material that was already available in 1980. Contrast that with our maximum payload capability to Mars of about 50 tons every 2.13 years.

I hope to discuss this further. The possibilities for Mercury are simply awesome!

I am trying to establish whether humans could ever explore Mercury's surface during daylight periods. Essentially, the issue is how long the crews could be directly exposed to solar radiations before absorbing excessive (cancer-causing) doses of radiation.

Solar heat is always noted as a principle threat to humans should they ever go to the surface of Mercury. However, after sunrise, it takes several weeks for the surface temperature to rise to the boiling point of water, set here as an arbitrary limit for crew safety. This suggests crews could have sufficient time to perform surface exploration before temperatures exceed safety limits.

The issue here concerns particle radiations. Particle flux at Mercury would be expected to range between 6 and 10 times the flux at 1au. NASA requirements for astronaut exposure limit dosage to 50 Sieverts per year. Not having a background in physics, I am not clear on how to translate the flux rate to a dosage figure.

Does the flux rate noted automatically preclude human excursions?

An important secondary question is what would be suggested for sufficient radiation shielding (thickness) for habitats if regolith were used?