I think that like everyone else, I have always assumed that any manned station in orbit around Mars will be at/around Phobos or Deimos, but I just remembered that Mars' equator (and Phobos and Deimos orbits) is at ~25 degrees to the ecliptic.So any craft going to Phobos or Deimos is coming in on a hyperbolic trajectory at 1.85 degrees to the ecliptic (Mars' inclination), and has to aerobrake into an orbit 25 degrees to the ecliptic.I presume that this is possible if your approach to the limb of Mars occurs during the time point when the Mars equator is co-planar with your trajectory. BUT (someone please correct me if I'm wrong), doesn't this mean this can only occur twice per Martian year? Even if you assume you can do some plane-change adjustment burns of (5?) degrees, that puts some serious time constraints on launching to Phobos and Deimos, doesn't it?It would probably be far easier to have manned stations in orbit around Mars at 1.85 degrees to the ecliptic? Or is this the main reason that people prefer direct-to-Mars-surface missions?
Phobos has it's points of interest. However it has a surface area of only 1500 km2. For comparison the 100 km radius exploration zone for the first crewed missions has a surface area of over 30,000 km2, more than 20 times that of Phobos. Plus Phobos by it's nature will be a much simpler and less diverse body than the surface of Mars. It's won't take long for it to be fairly exhaustively explored. A month at most.
Quote from: Dalhousie on 03/05/2017 05:01 amPhobos has it's points of interest. However it has a surface area of only 1500 km2. For comparison the 100 km radius exploration zone for the first crewed missions has a surface area of over 30,000 km2, more than 20 times that of Phobos. Plus Phobos by it's nature will be a much simpler and less diverse body than the surface of Mars. It's won't take long for it to be fairly exhaustively explored. A month at most.Astronauts would spend half a year going to, and another half a year coming home from, Mars' moons. So there remains one year to 14 months or so of a conjuncture period to spend there. 1,500 km^2 for 4 astronauts to explore in milligravity EVA's at a world of a kind thus far completely unknown, is plenty of work, plenty, trust me! And two moons at that.
Quote from: TakeOff on 03/13/2017 07:56 pmAstronauts would spend half a year going to, and another half a year coming home from, Mars' moons. So there remains one year to 14 months or so of a conjuncture period to spend there. 1,500 km^2 for 4 astronauts to explore in milligravity EVA's at a world of a kind thus far completely unknown, is plenty of work, plenty, trust me! And two moons at that.Phobos is worth a visit, but is hardly worth spending an entire long stay mission there. There is far more of interest on the surface.
Astronauts would spend half a year going to, and another half a year coming home from, Mars' moons. So there remains one year to 14 months or so of a conjuncture period to spend there. 1,500 km^2 for 4 astronauts to explore in milligravity EVA's at a world of a kind thus far completely unknown, is plenty of work, plenty, trust me! And two moons at that.
I love the Martian moons, and certainly would support visiting them. Personally, I favor Deimos over Phobos because it is closer to synchronous orbit as well as the gravity well edge; both of which would be a boon to orbiting craft; Phobos of course is more scientifically interesting and easier to reach Mars. The odds of visiting them after seeing Mars are good, but setting up a permanent habitat is more difficult to figure.The Flexible Plan NASA's currently following favors orbital vehicles. Because of weak gravity, the same vehicles can double as asteroid/Martian moon landers with minimal tinkering. Currently the NASA idea to orbit Mars include a Phobos habitat to stay at. However, that could easily change with politics, and if Red Dragon proves equipment (not crews, but definitely habs) can be directly landed on Mars, NASA might switch funds for a Mars camp instead of a Phobos station.If a Phobos station is cobbled together, I'd assume it'd be built first in orbit and then fixed to the moon; dust in micro-gravity would be a titanic pain. Taking the Bigelow ideas for a Lunar station, which likewise would be assembled in orbit before landing it in once piece, could easily be implemented for Phobos (and Deimos). There could be surface science for the moon, remote observations on Mars with perhaps telerobotics, and even the return vehicles could dock to the station.Pros: Easily compatible with orbital missions;unique 'asteroid' science with some Mars science (including telerobotics); potentially useful staging point (at either moon)Cons: Less desirable than Mars camp; micro-gravity and radiation effects; redundant rather than essential v.s. MarsI believe in any case all that's genuinely needed is an orbital vehicle to visit Phobos. A habitat is basically the same thing pinned to the moon; you only really need it if the visit lasts more than 30 days (and, especially if the crew are otw home, shorter visits are more likely). IMO a dedicated habitat is unnecessary, but ultimately it will depend on how NASA's plans get revised in the near future, especially in light of a Red Dragon landing bypassing the orbital route.
Phobos is worth a visit, but is hardly worth spending an entire long stay mission there. There is far more of interest on the surface.
I agree that the surface is far more interesting. But if the choice was between a simple LMO mission, or a mission that involved a stay on Phobos or Deimos, which would you choose?
And I don't think the local propellant options should be played down. Both Phobos and Deimos have absorption spectra indicative of unmodified volatile-rich carbonaceous bodies, similar to carbonaceous chondrites (regardless of how they actually formed / ended up as moons of Mars). I've seen estimates suggesting that they're up to 20% water. And IMHO, if they do actually have carbon similar to carbonaceous chondrites, that's really fascinating and potentially more useful for industry than Mars's plain, low pressure CO2. Carbonaceous chondrites contain a wide range of organics, including aliphatic and aromatic hydrocarbons, polycyclics like naphthalene and PAHs, carboxylic acids, alcohols, aldehydes, and tons of other things, including nitrogen-bearing compounds like ammonia, amino acids, urea, etc. I guess the closest earth analogy to the mixture would be something like bitumen, but with more nitrogen. Sounds like a great feedstock for varying combinations of hydrocracking and distillation, you could get a full petrochemical industry going based on just that without having to take the sabatier + partial oxidation, or alternatively, SOFC -> syngas -> liquids -> combinations of cyclization and pyrolysis route.
If you are going to go to Mars orbit then you should visit at least one of the moons. But neither probably justify the cost, except as a stepping stone to surface missions. You could also visit one of the moons as a part of a surface mission as well.
But there's the rub. Early studies suggested they were carbonaceous chondrite-like in composition, either C or D-type. More recent work has questioned it, suggesting that are represent material related directly to Mars, formedas left over co-accretion debris (which means they are possibly more silicate rich than carbonaceous) or re-accretion of Mars impact debris (in which case they are probably largely anhydrous, like our moon). The problem is the spectra of Phobos and Deimos are quite nondescript.
Studies using visible to near infrared spectroscopy show that the moons’ surfaces resemble D- or T-type asteroids or carbonaceous chondrite meteorites (e.g. Murchie and Erard, 1996, Rivkin et al., 2002 and Fraeman et al., 2012), although their specific mineralogy is difficult to determine because they lack strong diagnostic absorption features....Comparison to asteroid spectraFeatures similar to both the 0.65 μm and 2.8 μm absorptions are observed on dark asteroids interpreted to have primitive compositions (C-, G-, P-, and D-class asteroids). A search through the Vilas asteroid spectral catalog (Vilas et al., 1998) revealed several asteroids with 0.65 μm absorptions that are similar in shape and wavelength to the corresponding features observed on Phobos and Deimos (Fig. 6). Asteroids that exhibit these features sometimes have an additional absorption near 0.43 μm or 0.9 μm, but all of them are dark and red sloped. Absorptions near 0.7 μm on low albedo asteroids have been ascribed to Fe-bearing phyllosilicates, and almost always are accompanied by additional absorptions associated with hydration or hydroxylation near 3 μm (Vilas and Gaffey, 1989, Vilas et al., 1993, Vilas, 1994 and Rivkin et al., 2002)....5.2. Spectral feature at 2.8 μmThe position and asymmetric shape of the 2.8 μm feature is uniquely diagnostic of a fundamental vibration caused by a M–O–H (hydroxyl) stretch (Clark et al., 1990). The specific position of this absorption can vary depending on the cation attached to the hydroxyl, although the lack of reliable CRISM data around 2.7 μm makes it difficult to assign a band center with enough precision to provide a constraint for phase identification. Because this feature is generally stronger in pixels with stronger 0.65 μm bands and the 0.65 μm band is consistent with desiccated clays, the 2.8 μm band could result from an M–OH in a desiccated clay. Alternatively, this feature be caused by solar-wind induced hydroxylation because of the exposure of Phobos’ and Deimos’ surfaces to the space environment.
QuoteOf course, any offworld "mining" process at all has serious TRL issues to overcome. Even just water production.Indeed it does. It's going to be a lot easier to manufacture propellant on the martian surface.
Of course, any offworld "mining" process at all has serious TRL issues to overcome. Even just water production.
Except that NASA (and other agencies) have repeatedly done studies Mars orbital missions with no surface landing to save cost. So it's worth considering, since that's a type of mission that's gotten significant consideration - whether you like that kind of mission or not.
http://www.sciencedirect.com/science/article/pii/S0019103513004934Quote Studies using visible to near infrared spectroscopy show that the moons’ surfaces resemble D- or T-type asteroids or carbonaceous chondrite meteorites (e.g. Murchie and Erard, 1996, Rivkin et al., 2002 and Fraeman et al., 2012), although their specific mineralogy is difficult to determine because they lack strong diagnostic absorption features.Comparison to asteroid spectraFeatures similar to both the 0.65 μm and 2.8 μm absorptions are observed on dark asteroids interpreted to have primitive compositions (C-, G-, P-, and D-class asteroids). A search through the Vilas asteroid spectral catalog (Vilas et al., 1998) revealed several asteroids with 0.65 μm absorptions that are similar in shape and wavelength to the corresponding features observed on Phobos and Deimos (Fig. 6). Asteroids that exhibit these features sometimes have an additional absorption near 0.43 μm or 0.9 μm, but all of them are dark and red sloped. Absorptions near 0.7 μm on low albedo asteroids have been ascribed to Fe-bearing phyllosilicates, and almost always are accompanied by additional absorptions associated with hydration or hydroxylation near 3 μm (Vilas and Gaffey, 1989, Vilas et al., 1993, Vilas, 1994 and Rivkin et al., 2002).5.2. Spectral feature at 2.8 μmThe position and asymmetric shape of the 2.8 μm feature is uniquely diagnostic of a fundamental vibration caused by a M–O–H (hydroxyl) stretch (Clark et al., 1990). The specific position of this absorption can vary depending on the cation attached to the hydroxyl, although the lack of reliable CRISM data around 2.7 μm makes it difficult to assign a band center with enough precision to provide a constraint for phase identification. Because this feature is generally stronger in pixels with stronger 0.65 μm bands and the 0.65 μm band is consistent with desiccated clays, the 2.8 μm band could result from an M–OH in a desiccated clay. Alternatively, this feature be caused by solar-wind induced hydroxylation because of the exposure of Phobos’ and Deimos’ surfaces to the space environment.There is no water visible on their surfaces, which is expected because the surface will quickly lose water to space at those distances. However, even if their is no water beneath the surface - something that is suggested - there are at a bare minimum significant levels of surface minerals with hydroxyl groups, aka, hydrogen-bearing. As for carbon, regardless of how Phobos and Deimos formed, their spectra are similar to that of carbonaceous chondrites.No, we certainly can't say at this point that Phobos and Deimos are good places for ISRU. But the data is suggestive that they might be.
Studies using visible to near infrared spectroscopy show that the moons’ surfaces resemble D- or T-type asteroids or carbonaceous chondrite meteorites (e.g. Murchie and Erard, 1996, Rivkin et al., 2002 and Fraeman et al., 2012), although their specific mineralogy is difficult to determine because they lack strong diagnostic absorption features.Comparison to asteroid spectraFeatures similar to both the 0.65 μm and 2.8 μm absorptions are observed on dark asteroids interpreted to have primitive compositions (C-, G-, P-, and D-class asteroids). A search through the Vilas asteroid spectral catalog (Vilas et al., 1998) revealed several asteroids with 0.65 μm absorptions that are similar in shape and wavelength to the corresponding features observed on Phobos and Deimos (Fig. 6). Asteroids that exhibit these features sometimes have an additional absorption near 0.43 μm or 0.9 μm, but all of them are dark and red sloped. Absorptions near 0.7 μm on low albedo asteroids have been ascribed to Fe-bearing phyllosilicates, and almost always are accompanied by additional absorptions associated with hydration or hydroxylation near 3 μm (Vilas and Gaffey, 1989, Vilas et al., 1993, Vilas, 1994 and Rivkin et al., 2002).5.2. Spectral feature at 2.8 μmThe position and asymmetric shape of the 2.8 μm feature is uniquely diagnostic of a fundamental vibration caused by a M–O–H (hydroxyl) stretch (Clark et al., 1990). The specific position of this absorption can vary depending on the cation attached to the hydroxyl, although the lack of reliable CRISM data around 2.7 μm makes it difficult to assign a band center with enough precision to provide a constraint for phase identification. Because this feature is generally stronger in pixels with stronger 0.65 μm bands and the 0.65 μm band is consistent with desiccated clays, the 2.8 μm band could result from an M–OH in a desiccated clay. Alternatively, this feature be caused by solar-wind induced hydroxylation because of the exposure of Phobos’ and Deimos’ surfaces to the space environment.
Of course, microgravity mining suffers from significant challenges concerning anchoring. On the other hand, removing overburden is much simpler (surfaces are generally only loosely bound, and you can throw large amounts of material significant distances with little energy). Given that we have no experience with either microgravity mining or offworld surface mining, it's quite a bit of speculation as to which would be "easier" overall.
I don't follow. 1) Mars, too, is offworld.2) I had just argued in my previous post that there are factors that argue for Phobos/Deimos propellant production vs. on the surface.So I'm not getting how your comment follows from what I had written.
There is no water visible on their surfaces, which is expected because the surface will quickly lose water to space at those distances. However, even if their is no water beneath the surface - something that is suggested - there are at a bare minimum significant levels of surface minerals with hydroxyl groups, aka, hydrogen-bearing. As for carbon, regardless of how Phobos and Deimos formed, their spectra are similar to that of carbonaceous chondrites.No, we certainly can't say at this point that Phobos and Deimos are good places for ISRU. But the data is suggestive that they might be.
Quote from: Rei on 03/16/2017 10:12 amThere is no water visible on their surfaces, which is expected because the surface will quickly lose water to space at those distances. However, even if their is no water beneath the surface - something that is suggested - there are at a bare minimum significant levels of surface minerals with hydroxyl groups, aka, hydrogen-bearing. As for carbon, regardless of how Phobos and Deimos formed, their spectra are similar to that of carbonaceous chondrites.No, we certainly can't say at this point that Phobos and Deimos are good places for ISRU. But the data is suggestive that they might be.The logical course of action is to send a probe, complete with drilling mechanism to evaluate some 10s of metres below the surface. If there is indeed 20% water or Kerogen bearing materials, then from an exploration point of view, Phobos (or Deimos) becomes the most interesting place in the solar system. If there isn't, then it's not particularly interesting - unless we want to build space habitats with mega-tonnage of radiation shielding.
So any craft going to Phobos or Deimos is coming in on a hyperbolic trajectory at 1.85 degrees to the ecliptic (Mars' inclination), and has to aerobrake into an orbit 25 degrees to the ecliptic.
Quote from: mikelepage on 03/05/2017 04:26 amSo any craft going to Phobos or Deimos is coming in on a hyperbolic trajectory at 1.85 degrees to the ecliptic (Mars' inclination), and has to aerobrake into an orbit 25 degrees to the ecliptic.for an incoming craft, the velocity vector when it enters Mars' sphere of influence is pretty much co-linear with the hyperbola's asymptote. And the hyperbola's focus is the center of mars. This asymptote and focal point set the plane of the hyperbolic orbit.Any craft incoming from an earth to Mars Hohmann will have a velocity vector pointing the same direction as Mars wrt sun. So no matter what latitude the ship enters the sphere of influence, the velocity vectors would still be parallel to Mars velocity vector.The inclination is set by what latitude of the Sphere of Influence the ship enters. No big periapsis burn is needed to match inclination with Phobos or Deimos. It is more a question of timing and how precisely we can set the approach path.I've attached a rough pic indicating different hyperbolic orbits entering the SOI at different latitudes.
Quote from: Hop_David on 03/24/2017 08:24 pmQuote from: mikelepage on 03/05/2017 04:26 amSo any craft going to Phobos or Deimos is coming in on a hyperbolic trajectory at 1.85 degrees to the ecliptic (Mars' inclination), and has to aerobrake into an orbit 25 degrees to the ecliptic.for an incoming craft, the velocity vector when it enters Mars' sphere of influence is pretty much co-linear with the hyperbola's asymptote. And the hyperbola's focus is the center of mars. This asymptote and focal point set the plane of the hyperbolic orbit.Any craft incoming from an earth to Mars Hohmann will have a velocity vector pointing the same direction as Mars wrt sun. So no matter what latitude the ship enters the sphere of influence, the velocity vectors would still be parallel to Mars velocity vector.The inclination is set by what latitude of the Sphere of Influence the ship enters. No big periapsis burn is needed to match inclination with Phobos or Deimos. It is more a question of timing and how precisely we can set the approach path.I've attached a rough pic indicating different hyperbolic orbits entering the SOI at different latitudes.Thanks for responding David, but my question was not just about matching inclination (which I now see can be done easily), but also matching argument of Phobos' ascending node. As you say, the vector of any approaching ship is parallel with Mars', so does that not mean that a direct approach to Phobos would only be possible twice per year?Presumably there are other transfer orbits that can be used to precess your starting orbit around quickly, but I'm not sure what the best way to do that is.
Thanks for responding David, but my question was not just about matching inclination (which I now see can be done easily), but also matching argument of Phobos' ascending node. As you say, the vector of any approaching ship is parallel with Mars', so does that not mean that a direct approach to Phobos would only be possible twice per year?