Mercury Settlement: A New Direction For Man In Space

[Moonguy]

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. . .!

 

 

[Janus Sunaj]

Items for consideration when comparing transport to Mercury with that to Mars:

• Hohmann (minimum-energy) transfer time Earth-to-Mercury (105 days) is much less than Earth-to-Mars (259 days)

• Escape velocity from Mercury (4.3km/s) is a bit less than that from Mars (5.0km/s)

• Significant atmospheric aerobraking for Mars landing, none for Mercury

[Moonguy]

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!

[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. . .

[Moonguy]

How would crews get to Mercury? Is there any way we can beat the high delta-V penalties for classic style ballistic flights? Yes, there is: Cyclers.

Mercury’s orbital period is 87.97 days. Earth’s is 365.25 days, or 4.15 Mercury ‘years’. A cycler deployed to a 351.5 day orbit, with Earth’s orbit as the aphelion and Mercury’s orbit as the perihelion, will encounter Mercury every time it (the cycler) reaches perihelion.

Crews departing Earth would still have to generate a high delta-V. In fact, cycler missions would require a delta-V around 9.5 km/sec. while some standard (‘Hohmann’) transfers can be done for 6-7 km/sec. The difference is that a cycler mission puts most of th payload mass required for the ~176 day transfer time on the cycler. This drastically lowers the payload mass injected into the transfer. In a classic Hohmann transfer scheme, a manned payload would be injected with an upper stage able to effect the Mercury rendezvous and orbit insertion. For a 10 ton payload and a stage using a J2-X engine, a mass ratio of at least 4.1 would be needed for even the most favorable MOI delta-V, which is about 6.3 km/sec. The resulting stage would be about 60 tons. Pushing this into a transfer orbit from Earth would require a stage which also has a 4.0 mass ratio – and hence masses over 100 tons by itself.

The cycler reduces the requirement to launching the crew in their Earth-return capsule. This could be an Orion, A DragonRider derivative or something similar. If it had the same 10-ton mass as the first example, it would not need to be boosted with a second stage. Instead, propellant for the maneuvers at Mercury would be derived from water stored on the cycler. Food and living accommodations would also be on the cycler as well. A 15 ton cycler could easily store enough food and consumables for several mission cycles. These supplies would be replenished to the cycler periodically by the same solar sail that deploys the cycler to the 351 orbit. The water used for propellant would also be supplied using solar sails. Initially this would be from Earth, but it would eventually come from Mercury.

With an orbit of 351 days, the cycler would encounter Earth every third orbit of the cycler. This is due to the synodic period of Earth and Mercury is 115.9 days. Multiplied by three yields 347.7 days. There is just over a 4 days discrepancy between an exact encounter., However, launch windows to Mercury are open for about 20 days, so it could be assumed a delta-V penalty would be incurred to make up for the 4-day difference.

The cycler mission requires much less propellant be available in Earth orbit. Only one stage is used. This is refueled at the cycler for the MOI burns and again for the return to the cycler for the return trip. If the Earth-entry interface velocity is too great for the return module’s heat shield, the crewed stage could refuel a third time to execute a burn into Earth orbit. This architecture enables a crew to launch to Mercury every 347 days. Twice as frequently as flights to Mars.