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2020/07/04 Continuing review of RobertDyck's Large scale colonization ship topic:
Post 3 of planned 3
Planned for #76-#125
Notes 2020/07/04 RobertDyck's topic on Large scale colonization ship
#076 http://newmars.com/forums/viewtopic.php … 50#p159950 RobertDyck Lander concept Original Starship (images)
#077 http://newmars.com/forums/viewtopic.php … 52#p159952 kbd512 EML to orbit plus make + fusion from fission energy
#078 http://newmars.com/forums/viewtopic.php … 54#p159954 tahanson43206 Request for more on EML concept
#079 http://newmars.com/forums/viewtopic.php … 61#p159961 GW Johnson Analysis support for Starship plus loose sand
#080 http://newmars.com/forums/viewtopic.php … 62#p159962 kbd512 EMALS plus fusion propulsion by implosion + NERVA hours
#081 http://newmars.com/forums/viewtopic.php … 63#p159963 RobertDyck More on rotation for artificial gravity
#082 http://newmars.com/forums/viewtopic.php … 65#p159965 SpaceNut
#083 http://newmars.com/forums/viewtopic.php … 67#p159967 RobertDyck Elon's presentation video September 2018
#084 http://newmars.com/forums/viewtopic.php … 76#p159976 GW Johnson on Elon's presentation focus on aerobraking
#085 http://newmars.com/forums/viewtopic.php … 77#p159977 RobertDyck Permafrost on Mars implied by Mole failure
#086 http://newmars.com/forums/viewtopic.php … 80#p159980 GW Johnson Mole failure - poor drill design + SpaceX tipover
#087 http://newmars.com/forums/viewtopic.php … 86#p159986 RobertDyck Movie image GIF
#088 http://newmars.com/forums/viewtopic.php … 90#p159990 GW Johnson Reminder Colony Ships + on "exrocketman" blog
#089 http://newmars.com/forums/viewtopic.php … 91#p159991 SpaceNut re increased fuel load 1100t to 1200t
#090 http://newmars.com/forums/viewtopic.php … 93#p159993 Oldfart1939 re Mole drill failure
#091 http://newmars.com/forums/viewtopic.php … 97#p159997 RobertDyck re Mars Direct vs SpaceX need for ISPP at Mars
#092 http://newmars.com/forums/viewtopic.php … 98#p159998 RobertDyck Suggestion for subsurface probe before Starship
#093 http://newmars.com/forums/viewtopic.php … 99#p159999 Oldfart1939 re subsurface probes - beefy design for results
#094 http://newmars.com/forums/viewtopic.php … 00#p160000 RobertDyck re "real" drill designed by "real" experts
#095 http://newmars.com/forums/viewtopic.php … 12#p160012 RobertDyck Mars Homestead Project with images
#096 http://newmars.com/forums/viewtopic.php … 23#p160023 SpaceNut Reminder of earlier post about a drill on Mars
#097 http://newmars.com/forums/viewtopic.php … 30#p160030 RobertDyck Rube Goldberg 1930's plus Dr. Zubrin conversation
#098 http://newmars.com/forums/viewtopic.php … 35#p160035 Oldfart1939 on complexity of proposal for sample return
#099 http://newmars.com/forums/viewtopic.php … 39#p160039 GW Johnson on probability of existing life on Mars
#100 http://newmars.com/forums/viewtopic.php … 40#p160040 Oldfart1939 - agreement about life on Mars is likely
#101 http://newmars.com/forums/viewtopic.php … 41#p160041 elderflower - settle question with human expedition
#102 http://newmars.com/forums/viewtopic.php … 50#p160050 SpaceNut re chances of contamination of Mars by existing landers
#103 http://newmars.com/forums/viewtopic.php … 70#p160470 RobertDyck more on ship design: electronic tint window
#104 http://newmars.com/forums/viewtopic.php … 49#p169449 SpaceNut pebble reactors and slow glass
#105 http://newmars.com/forums/viewtopic.php … 53#p169453 Calliban on pebble bed in interplanetary ship
#106 http://newmars.com/forums/viewtopic.php … 64#p169464 RobertDyck hand sketches of vehicle concept: wheel around hub
#107 http://newmars.com/forums/viewtopic.php … 66#p169466 tahanson43206 Nice sketch plus note Planetary Society meetings
#108 http://newmars.com/forums/viewtopic.php … 67#p169467 RobertDyck re Planetary Society meetings on hold
#109 http://newmars.com/forums/viewtopic.php … 68#p169468 tahanson43206 re Zoom and Twitch online meeting services
#110 http://newmars.com/forums/viewtopic.php … 72#p169472 RobertDyck answer re water layer for radiation protection
#111 http://newmars.com/forums/viewtopic.php … 73#p169473 RobertDyck off-topic report on virus re-opening progress
#112 http://newmars.com/forums/viewtopic.php … 75#p169475 tahanson43206 reminder of work by GW Johnson re Mars 2 year plan
#113 http://newmars.com/forums/viewtopic.php … 84#p169484 RobertDyck confirming vehicle orientation during flight
#114 http://newmars.com/forums/viewtopic.php … 85#p169485 tahanson43206 Confirmation of confirmation re "aft" >> Sun
#115 http://newmars.com/forums/viewtopic.php … 31#p169531 RobertDyck Bump. Read the beginning of the thread.
#116 http://newmars.com/forums/viewtopic.php … 15#p169615 GW Johnson reminder of recent work showing aerocapture risk
#117 http://newmars.com/forums/viewtopic.php … 22#p169622 tahanson43206 Plan to re-read topic from the beginning
#118 http://newmars.com/forums/viewtopic.php … 29#p169629 SpaceNut re water for radiation shielding plus re fuel plans
#119 http://newmars.com/forums/viewtopic.php … 32#p169632 tahanson43206 Clarification >> water to make fuel/oxidizer
#120 http://newmars.com/forums/viewtopic.php … 35#p169635 GW Johnson in appreciation of RobertDyck ship concept
#121 http://newmars.com/forums/viewtopic.php … 38#p169638 RobertDyck re use of purified water for nuclear thermal push
#122 http://newmars.com/forums/viewtopic.php … 39#p169639 RobertDyck to GW Johnson reprise of bomb back-and-forth
#123 http://newmars.com/forums/viewtopic.php … 42#p169642 Void re Orion pusher augmented by bags of water throw mass
#124 http://newmars.com/forums/viewtopic.php … 44#p169644 tahanson43206 Post 1 of 3 showing entire topic summary 1-50
#125 http://newmars.com/forums/viewtopic.php … 48#p169648 tahanson43206 Post 2 of 3 showing summary 51-75
(th)
Last edited by tahanson43206 (2020-07-04 14:42:06)
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Tahanson 43206:
The easiest and best thing to do about the spreadsheet is a column of all the kinematic dV's that must be achieved. That gets followed by a column of the appropriate factors reflecting gravity and drag losses, or hover and divert requirements. Their product is the mass ratio-effective delta-vees that you need to use the rocket equation. MR req'd = exp(factor*dV/Vex).
Be aware that Vex depends upon your engine selection for the burn, and its Isp performance at expected backpressure conditions. Vex = gc * Isp, where gc is 9.80667 metric, and 32.174 for US customary. It does NOT depend upon where you are, being only a units conversion factor. These are all additional columns in the spreadsheet.
Now you need a weight statement, and a strategy for how to allocate it across your mission. There is the inert structural mass of your vehicle, the dead-head payload it carries, and the propellant mass that fits within its tanks. These sum to its ignition mass. Ignition minus propellant is the dry tanks mass. PERIOD. END OF ISSUE.
Usually, there is a factored launch or departure burn (for each stage), a mid course correction burn, and some sort of landing or arrival burn. Your spreadsheet should reflect that. Same is true for any return to Earth. If you refuel somehow at destination, there are separate weight statements for the outbound and return trips. Otherwise, the propellant available for departure is the propellant remaining at landing, less any evaporative loss correlations. Don't forget to adjust payloads outbound and return, as appropriate.
Each burn has a factored dV that results in a mass ratio for that burn. The end of burn vehicle mass is its ignition mass divided by the mass ratio required of that burn. The propellant used is that burn's ignition mass minus its end-of-burn mass for that burn. Propellant remaining after that burn is what you had to start with, minus what you used on that burn. If your propellant remaining goes negative, your analysis is infeasible. PERIOD. END OF ISSUE.
That's pretty simple actually, and can be tailored in a variety of ways for this-or-that mission. Just put the right stuff in the appropriate cells for the spreadsheet.
Any particular spreadsheet I have, is rendered obsolete if one just does that. And I have NO IDEA how to use "drop box" or any of that sort of thing. I can hardly make email, "exrocketman", and the NewMars forums work at all. There is NOTHING about any of this stuff that is in the least intuitive to me. I simply don't, and cannot, think that way.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Spreadsheet sent to tahanson43206
Nice index run down of the topics posts and is the sort of thing required to draw from all of them for mars, moon and other places with regards to ships, science and more.
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The one I have been using to evaluate Starship/Superheavy for Mars and the moon might be one of the best versions of this spreadsheet yet. You can see images from it in the "exrocketman" articles. The moon article should be "up there" soon.
I put the outbound and return weight statements "up top", as reference data for the burn calculations in the main calculation block. As described just above, I start with kinematic delta-vees for all the burns, and the appropriate loss or budget factors. Their products become the mass ratio-effective delta-vees that are the basis for the burn calculations.
The same format can serve to analyze refueled return or unrefueled return. The cell that defines ignition mass for the return launch burn can refer to the cell containing the final outbound end-of-burn mass, or to a fully-fueled return weight statement in the block above.
This turns out to be a very convenient way to lay these calculations out in an Excel spreadsheet.
GW
update 7-5-20: both the Starship evaluation for direct moon landings, and a guide to the spreadsheet I used for Starship at Mars and the moon are now "up" at "exrocketman". The spreadsheet guide gives the formulas in every cell.
Last edited by GW Johnson (2020-07-05 12:17:11)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For RobertDyck re topic ...
This topic has covered a lot of ground since you started it.
You've attempted to bring discussion back to a heading you have in mind, after interesting digressions.
However, there is a serious flaw in the opening post that GW Johnson has courteously tried to help you address.
To this point, you have (as nearly as I can tell) held steady to your opening concept of using atmospheric deceleration for your deep space vehicle.
Are you willing to make changes to your vision, or will you hold steady despite offers to help make it better?
If you ** are ** willing to make changes, I'd like to suggest you edit your opening post to remove the aerocapture specification, and replace it with whatever GW Johnson and you can agree on.
(th)
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The lunar gateway is the big brother to the iss as to mars the ship we need is even larger so as to not go with such a small crew as to get a good foot hold on mars.
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I'm not saying that one cannot do aerocapture at Mars. I'm saying that if you go that route, you'd better be prepared with some propulsion to make up the difference between what you get and what you needed from aerobraking. The Martian upper air density is erratically factor 2 variable about its average values.
That makes your pathwise drag integral factor-2 variable. Which makes the energy you can subtract from your approach kinetic energy also factor 2 variable. And uncorrected factor 2 variability in that subtraction is enough to either bounce off into deep space, or dive too deep too fast, and get crushed. You may have to speed up or slow down to make the drag integral correct on that critical first pass.
And you will NOT know what you have to do to correct for this, until you are already well into that critical first pass! You will get that assessment real-time from your on-board accelerometer readings.
See also the update to my post 129 above. I put some stuff people have wanted to see "up" over at "exrocketman".
GW
Last edited by GW Johnson (2020-07-05 12:18:17)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW Johnson, I said before that before you send a large colonization ship that uses aerocapture, you first need a comprehensive system of Mars satellites to monitor the upper atmosphere. Earth has that, but could use an upgrade. Mars doesn't have it now. Will need it. With fine detail about Mars atmospheric conditions before the ship arrives, with detailed real time updates, the ship can use aerocapture.
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For SpaceNut re #131: read Dr Robert Zubrin's comments about the Lunar Gateway. Aka Lunar tollbooth. He's mentioned it a number of times, do I have to cite a specific book?
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Lunar gateway is a distraction for Mars and he favored moon direct to get it done. For that buying 4 falcon heavy was the plan I think all expendable with a Lunar lander still required that has not been designed yet.
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Robert Zubrin is vehemently opposed to the Lunar Gateway concept. It's another make-work project for the "Old Space" contractors that will eat up Billions and serve no real useful purpose other than frying some astronauts from Coronal Discharge events. If there weer a Solar Flare storm shelter included it would be an OK idea, but having a manned lunar space station is absurd.
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Shelter designs are something wwe know going in needs to be done. But the 4 rocket Moon Direct is not happening since Space x has invested its funds into the Starship prototyping....and its not a full scale unit....
The slumber is over as The Sun Just Woke Up. ‘M-Class’ Solar Flare Ends 925-Day Solar Snooze
Lunar shelters for future moon landings to be bare-bones affairs
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Large ships in general have this one issue that is where we need cheap lift to solve as its earths gravity well that makes it cost so much for going any where let alone get there fast...
The question is can we do better once we are on the moon to satisfy this cheap need and faster translon to mars by building and launch from the moons surface.
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Not only do we need a system of satellites to provide real-time data on the upper atmosphere of Mars. To adjust aerocapture for current atmosphere conditions. We can also test this with a robotic (unmanned) spacecraft tanker to carry propellant from one of Mars' moons to Low Earth Orbit. To fill a propellant depot, used to refuel the large colonization ship before departing Earth. That propellant can be sold to refuel satellites in Earth orbit, or other spacecraft. This will demonstrate aerocapture repeatedly before doing so with humans.
One astronomer told me the only C-type asteroids that will still have ice will be at or beyond the orbit of Mars. Any closer, heat from sunlight would have boiled off the ice long ago. Both moons of Mars show spectra indicating surface material are the same as asteroids, so these look like captured asteroids. There is high probability that the moons of Mars have ice. And by using aerocapture with Mars atmosphere, we can rendezvous with the moons with less propellant than any asteroid.
Yes, that also means aerocapture into Earth orbit, followed by aerobraking down to the orbit of the propellant depot. Last little manoeuvres will require propellant, but aerocapture and aerobraking will take the vast majority of the delta-V.
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Regarding ice in asteroids: there is not only a distance-from-the-sun heat effect, there is also a distinct size-of-the-body effect, which is also grounded in some very well known physics.
The distance effect is thermal radiation from the sun absorbed into the body, raising its temperature. Once any ice present is warm enough, it sublimates. Precisely because the equilibrium vapor pressure of the icy material exceeds the local ambient pressure (zero).
The size effect applies because most of these objects are partly or completely rubble piles, or at least coated in loose regolith, so that they are up to 50% empty void space between the particles. There are torturous paths around these particles from the interior to the surface, where the ambient pressure really is zero.
As volatiles sublimate, there is vapor-phase fluid flow with drag, through these torturous paths to the surface. That drag shows up as a pressure drop streamwise along the path, with the exit pressure set to zero by the vacuum of space. The interior pressure can be higher than zero (but still a very small number). This effect renders the ice stable against sublimation, to slightly solar-heated higher temperatures, than if it were exposed on the surface. Small effect, but real. And it is a larger effect with increasing body size.
Because this interior pressure effect is larger on larger bodies, it delays their final drying out of volatile ices under the action of sunlight. It is not much of an effect on the smaller bodies, since the dimension is small. So they dry out quicker.
No volatile would have a vapor pressure of exactly zero except at absolute zero temperature. So, no volatile is permanently stable exposed to the vacuum of space. It just takes a longer or shorter time to vaporize away, varying with distance from the sun-as-heat-source (the so-called "frost line" near Mars), and with the size of the object (the internal torturous path effect).
After 4.6 billion years since solar system formation, the only small bodies (asteroids, comets, meteroids, whatever you call them) that still have any ice in them will be the ones farther out, and only the larger ones at that!
In effect, the location of the so-called "frost line" is actually a function of object size, being located farther out from the sun, for the smaller the body size. Anything smaller that ventures closer in, can only temporarily have any ices, which volatize quicker the nearer they get to the sun. Which is what we call a "comet".
The consensus of opinion among the astronomers who study these things is shifting away from the conventional wisdom of the last century: the distinctions beween asteroids, comets, and meteroids actually blur into a smooth spectrum of mineral/metal bodies of varying volatile content.
The initial load of volatiles in these bodies depends upon their formation location near or far from the sun, but all have undergone considerable depletion over time at rates dependent upon size. Expect considerable variability in volatile content, but do not expect a large volatile content except in the very largest of any inner solar system bodies (by which I mean inside the orbit of Neptune).
The volatile contents we have seen with the probes to "comets" and "asteroids" show them to be pretty dry, excepting rather larger objects like Ceres, which has differentiated, and more properly classifies as a dwarf planet. Smaller things nearer the size of Phobos have been notably rather dry of volatiles, including the supposed "comet" cores we have visited.
It is that picture, supported by the sparse ground truth that we do have, that induces me to think the possiblity of mining volatiles from Phobos to make propellant is pretty near zero probability. Even the smaller main belt objects look rather dry of volatiles.
Keep in mind that mining ices as volatiles is quite distinct from recovering oxygen and hydrogen atoms from minerals, particularly hydrated minerals. That recovery-from-minerals process requires enormous amounts of applied energy per unit mass of product; mining in-situ ice does not.
Whatever other uses there might be for Phobos, I don't put much faith in the concept of using it as the supply mine for a propellant depot of any kind anywhere. And I just told you why. I could easily be wrong, but the odds, as we currently imperfectly understand them, are with me.
My advice is then to look at any other possible uses for Phobos to justify a tranportation system based on going there. My best guess is that we won't really understand what those uses might really be, until after we have gone there (drawn by curiosity) and explored properly (find out what all is there, and where exactly it is).
Right now, the only uses I can think of are that Phobos is (1) a place with just enough gravity to safely stash loose stuff, and (2) a place that is easier to reach from Earth, in terms of delta-vee requirements, than is low Mars orbit. Maybe the rest of you can think of other uses.
It is NOT a place from which the surface of Mars is more easily accessed (that place really is low Mars orbit). That much we know, because I already looked at the delta-vee requirements for multiple paths, and found out what worked best.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW Johnson re #140
SearchTerm:IceOnAsteroids
SearchTerm:AsteroidsIceOn
SearchTerm:PhobosUseOf
Your contribution to this topic has the potential to inspire RobertDyck to keep going a bit further, rather than letting the flow of creative energy fade out.
We (humans alive in 2020) have the distinct advantage over our predecessors of 500 years ago, when Magellan's expedition was stumbling its way around the world. We can see the full vista of development on Earth, thanks to the documentation provided by so many over so long.
The fact that we are watching the equivalent of ocean going canoes reaching orbit should not cause us to shrink from understanding what will come to pass as technical problems are solved, and incentives to build newer and larger solutions for transportation, infrastructure and whatever else is needed.
RobertDyck started out with the rough equivalent of a two masted barque, when three and four masted versions were already sketches on drawing boards.
This forum is in a position to foster both realistic proposals and fantastic visions.
The ticket to success (it seems to me) is to create an environment which is attractive to the kind of talent that will be required to inspire legions of workers to build the industries we can expect in the decades ahead, if we can (somehow) keep ourselves from making too many simultaneous messes.
(th)
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The main use I can see for Phobos is as a source of reaction mass for an interplanetary transfer vehicle. It is already conveniently located outside of Earth and Mars gravity wells. This is dependant on having a space drive that can use it of course. A mass driver or something similar. If we can avoid having to ship propellant from Earth to refuel the transfer vehicle, then Phobos provides a huge advantage in eliminating the launch cost of that propellant. It is almost irrelevant what it is made of. If it just happened to contain huge quantities of pure water that could be electrolysed to produce hydrogen propellant in a NTR, that would be perfect. But loose dust would work in an electrically powered reaction engine.
Last edited by Calliban (2020-07-11 19:48:06)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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I had originally envisioned a propellant depot in Earth orbit, with source coming from an asteroid mine. C-type asteroids are carbonaceous chondrite. An automated mine could land on the asteroid, with spikes that have solid rocket motors embedded in spikes to secure the drill rig to the asteroid. Drill down into the body of the asteriod. An electric heating element on the drill head would melt the ice. Initially the ice would sublimate, but very quickly build up enough steam pressure for liquid water. Triple point of water is 6.12 mbar; any pressure above that allows liquid water. Earth at sea level is 1,013.25 mbar. So 10 mbar is only 1% atmospheric pressure, but enough for liquid water. You don't want so much pressure that it'll split the asteroid, cause a pressure leak. You want the pressure to force liquid water up the drill pipe. At only 10 mbar, water has a very small temperature range in which it's liquid, 20 mbar might be easier, depending how much pressure the loose rubble of the asteroid can withstand. C-type asteroids are pebbles of rock embedded in a soft matrix of ice, dry ice, clay, gypsum, other soft hydrated minerals, and tar. So you'll get dirty water up the pipe. Filter that water, then put the clean water in an electrolysis tank to split into hydrogen and oxygen. Spin the tank for artificial gravity, to separate water from gasses. Tar can be processed just like any petroleum on Earth. CO2 can be separated, purified, and re-frozen as dry ice. Or CO2 can be combined with hydrogen in a Sabatier reactor to form methane and water. Energy for the mine is photovoltaic panels, so powered by sunlight.
Liquid hydrogen is great rocket propellant, but storage temperature is colder than the ambient temperature of space. So use in deep space requires active refrigeration. Liquid methane may be a better fuel for deep space because liquefication temperature is warmer than the ambient temperature of space. Both LOX and LCH4 can be kept liquid in tanks by keeping them in shade, cooling simply by exposing them to the dark of space.
Water ice and dry ice can be transported by robotic tankers. The propellant depot in Earth orbit could melt ice, split into O2 & H2, refrigerate for LOX and LH2. That depot would have to actively refrigerate LH2. If there are customers that require it.
Metal asteroids require copious quantities of carbon monoxide (CO) as working fluid to process ferrous metals with the Mond process. That can be transported as water ice and dry ice. Hydrogen and CO2 can be processed via the Reverse Water Gas Shift (RWGS) to form CO and water.
So now, where are C-type asteroids with water? A Near Earth Asteroid (NEA) would be convenient. Problem is all the volatiles may have long since boiled off. Asteroid 3552 Don Quixote has a coma, it's dripping with water. Problem is it's in the main asteroid belt. Is there a closer source? A couple other individuals on this forum convinced me to look at Mars moons. Surface spectra of both Deimos and Phobos are consistent with asteroids, either C-type or D-type. Phobos looks more like D-type. D-type is as dark as coal. One radio astronomer told me that the only asteroids to retain their ice will be at the orbit of Mars or farther. Ok, so Mars moons may be ideal sources of propellant.
GW Johnson just raised an issue that most people on this forum agree with. He's trying to push my buttons. No, the moons of Mars are *NOT* a "stepping stone" on the way to Mars. No, you cannot remotely operate rovers from Mars orbit or worse, one of the Moons. The safest place for humans in our solar system next to the surface of Earth itself is the surface of Mars. Mars has sufficient gravity that humans will not experience zero-G effects. Yes, as GW Johnson has pointed out many times that is supposed to have been verified by the Centrifuge Accommodation Module on ISS. But President Obama cancelled it. Yes, we should have data to verify that. Until someone can provide data, I'm going to continue to assert that the gravity of Moon or Mars is sufficient to prevent zero-G effects. Gravity causes convection of fluids within cells and within the human body. I could give more justification, again this has to be verified with data, until there is data I will continue to say Mars gravity is enough. Radiation on Mars is half that of ISS. This has been measured by the MARIE instrument on Mars Odyssey, and verified by radiation instruments on the Curiosity rover. There are no micrometeoroids on Mars surface; they burn up in Mars atmosphere 30km above the surface. Leaving astronauts stranded in Mars orbit is not just stupid, it's deliberately malicious! Leaving astronauts on a Mars moon has all the harmful effects of Mars orbit, plus the danger of landing. The moons of Mars are useful resources. They're for the settlement phase, not initial exploration.
As for anyone who wants to send astronauts to Mars orbit just to remotely operate rovers on Mars surface? Are you stupid!?! Again, GW Johnson and I are in agreement on this point. He's just trying to push my buttons.
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The most obvious use for Phobos is as a very large momentum bank for a tether system. Pick up and drop off payloads from Mars with far lower delta-V requirements, and fling them into interplanetary space.
The other use is material for Martian space stations. How else are we going to get a 5m thick shell for radiation protection? Perhaps we can make rock fibre out of it that will be strong enough for habitats, too.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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For RobertDyck re #143
SearchTerm:ButtonsPushed
For Terraformer re #144 ... thanks for picking up on the (to me obvious) use of Phobos as a momentum bank.
It is good for at least 2 km/s for any imaginable size vehicle seeking to match orbit with Mars.
Recently GW Johnson has provided additional figures to show the potential of that application, but I am still working on a tether system for Phobos and have not had time to look at them.
One complication for a spacecraft navigator is that the momentum benefit is maximized if the navigator can plot a course that brings the ship into the Korolev crater on Phobos ** just ** when Phobos is in maximum retreat in its orbit. Once safely "docked" inside the crater, the ship will be accelerated by Phobos as it swings around Mars. At the end of the several hour acceleration, the ship will be moving at the same velocity as Phobos, which will be 2 km/s faster than when it arrived.
(th)
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RobertDyck, I was not trying to push anybody's buttons. Sorry if I did. I think your large ship ideas are quite intriguing. I did not fully understand what you had in mind for the aerobraking, which was some sort of monitoring satellites to take out the upper-air density uncertainty problem.
With that issue solved, I see no reason aerocapture of your big ship won't work at Mars, as long as the approach velocity is not too high. There's a limit there. Somewhere. I just don't know where, myself. But that is awfully thin air, even deep down.
Some of the discussions here involve mining Phobos for volatiles to make propellant. I could be wrong, but I see rather good reasons to doubt significant volatile ice deposits exist within Phobos. That is where Robert and I differ.
I'm not knowledgeable enough about the fine nuances of orbital mechanics to evaluate gravity-assist effects. But, I would offer Murphy's Law as the reason gravity assist delta-vee potential would be lower than the orbital speed of the object providing the assist. I don't really know, but I'd bet the potential is lower.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Gravity assist: many years ago I proposed a small probe to go from Earth to Mars. Slow route using ion propulsion. Minimum launch mass for cost. Spiral out of LEO, head to the Moon, use gravity assist from the Moon and continue on to Mars. I mentioned this idea to someone from the European Space Agency; he liked it so much that they used the technique to send a small probe to Earth's Moon. But my idea was to continue to Mars. Found someone who could do the gravity assist calculation; he said only 0.5 km/s delta V from Earth's Moon. Not much; his claimed it's not worth it. Moons of Mars are significantly smaller.
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For RobertDyck re #147
Thank you for noting my attempt to show that Phobos is of significant value to a space traveler. The fact that my (poor, admittedly) description of the benefit led you to think of gravity assist maneuvers is encouraging.
I'll try again ... If my understanding of the physics is correct, the Phobos Maneuver will become a standard practice for passenger carrying vehicles headed to Mars, because it will save millions of monetary units in fuel and oxidizer expense.
Think of the Panama Canal ... Passenger ships (and large cargo vessels) are happy to pay on the order of $1,000,000 US for the privilege of spending 8 hours crossing the canal through the six locks, in return for the much greater savings of time and money for fuel that would be needed to round the Horn.
Phobos (as Terraformer pointed out) is a reservoir of momentum.
Here's a word picture that may help. Imagine a sailor falls overboard from the prow of a carrier, similar to the ones that kbd512 sailed.
Actually (come to think of it) kbd512 related an anecdote about falling overboard, but I never did hear/read how that turned out!
In any case, our (hypothetical) sailor falls overboard at the prow of the ship, and a quickwitted shipmate located at the back of the ship pulls a life ring on a strong rope and tosses it to the (by now thoroughly wet) sailor below. For a brief moment, the life ring and the sailor are at rest with respect to each other.
The sailor grasps the ring for all he is worth, because in short order the rope pulls taut and the sailor experiences acceleration sufficient to bring him up to the velocity of the aircraft carrier. Naturally, if we follow the logic of kbd512's story, the on-deck assistant pulls in the rope and our (very lucky) "passenger" is once again traveling at the velocity of the aircraft carrier.
In the case of the docking in Korolev crater I am trying to persuade you to consider ...
The navigator of your passenger liner (with 1000 souls on board) slows by 1.88 km's to "dock" gently in Korolev crater, just at the precise moment when Phobos is traveling down the back stretch around Mars.
Almost immediately your ship and her passengers begin to experience acceleration (by ** Phobos **) as it swings on around Mars. A full circuit of Mars takes Phobos on the order of 7 hours, but your ship and her crew and passengers will be accelerated to the full velocity of Mars within precisely 1/4th of the full circuit, or (approximately 1.75 hours).
It is this gradual but powerful acceleration by Phobos that will save your navigator millions of dollars in fuel and oxidizer costs.
A few posts back I posted a sketch that shows a simplified version of the action.
The ship approaches Mars on a Hohmann orbit, which means Mars (and Phobos) are approaching rapidly. Exact numbers have been posted by GW Johnson in numerous posts here and in exrocketman blog.
The ** key ** number to keep in mind is 1.88 km/s, which (I am remembering from the posts of GW Johnson).
Your navigator needs to spend 1.88 km/s worth of fuel and oxidizer to "dock" in Korolev crater. Phobos will then deliver in excess of 2 km/s of velocity to the vehicle over (about) 1.75 hours, so that the vehicle ends up possessing the velocity of Mars, without having had to pay for that 2 km/s with fuel and oxidizer.
The navigator will expect to be rewarded for the success of the maneuver. I'd suggest a sirloin steak with trimmings at the Captain's table, if the purser was clever enough to pack one in the freezer in anticipation of this important moment in the flight.
In separate posts (here and in exrocketman blog) GW Johnson has worked out a system for landers able to make their way from Phobos to Mars and back. There is no need for your huge vessel (with the always rotating habitat section) to move from Phobos until it is time to return to Earth. At ** that ** point, your navigator will earn another dinner at the Captain's table by launching the vessel when Phobos is moving ** faster ** than Mars, so that (about) 2 km/s will be imparted to the vehicle at another savings of substantial monetary units.
(th)
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Think of the orbiting phobos moon and a whey station like the ISS once created for stops to be made for future use of ore and other means to make large mass to the planet possible.
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Here's another question: how reliable is mini-magnetosphere. Could this technology protect the big ship from space radiation? The idea is to reduce the mass of the water wall. It would require a lot of electrical power.
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