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Ceres/Mars as manufacturing outposts (analytic exercise)

  1. May 11, 2015 #1

    marcus

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    Note from mfb: This thread is a fork of our Dawn and Ceres thread, as we got multiple posts about potential missions to Mars and Ceres and further exploration. End note.


    Part of astrophysics is being able to calculate---things like the altitude of a geosynchronous satellite, for example. Even if you deplore futuristic visions---which can easily become self-indulgent and speculative---I think there is a real place for the solid analysis that can be motivated by related questions.
    It's a learning experience, and can mobilize mental resources.
    I was impressed by a new person who showed up in the Ceres thread and calculated the altitude of a geosynch. satellite on Ceres(!)
    And compared that with the height of a geosynch. satellite on Mars.

    Whatever you think about the MOTIVATION (consider the feasibility of a space elevator able to bring things down from orbit and get things up into orbit slowly and deliberately without chemical rocket...)
    I think the underlying analysis is valuable and would like it to have a place in Astrophysics forum.

    But it does not exactly fit in the Dawn mission Ceres thread. So at Mfb's suggestion I want to start a thread where we can continue discussion that got started in the Dawn thread.

    Actually it was not just one person, it was several, and they weren't all newcomers.

    I'll get links to a few of the posts in that other thread. It's pretty interesting, actually.
     
    Last edited: May 17, 2015
  2. jcsd
  3. May 12, 2015 #2
    Hi all, while I agree with your comment generally about Ceres, it's a mistake top think of Mars as a mostly dry planet. It has tons of frozen water, and considering the size difference probably more water than Ceres does. Recent surveys to detect water ice showed there are extensive regions in the mid-latitudes that are very likely water ice covered by a few meters of rubble.

    The ADVANTAGE Ceres has over Mars in regard to its water is its LOW gravity.

    Sure Mars only has about 30% of the Gravity of Earth, but when you consider the overall expense of a mission to mars, having to overcome Mar's gravity well on a return mission makes a round trip mission to Mars many times more expensive in terms of fuel costs than a trip to Ceres, even if Ceres is 2x further away.

    That low gravity makes Ceres water more valuable than Mars water, and ultimately makes it a a much better place to build the first human base in space, because Ceres water would be much cheaper to use on an ongoing basis to fuel further exploration than Mars Water.

    For those who don't know. Here is a bit a data to make it possible to compare the challenges the gravity wells of Mars and Ceres would pose.

    If you weigh 200lbs/91Kg on Earth, you'll weigh 72lbs/35kg on Mars. You'll weigh about 5lbs/2Kg on Ceres.

    Of course the notion that the best place to put the first human settlement in the System has been Mars for so long, it will be a long time before the facts that make Ceres a better option than Mars for the first base to sink in and change the minds of those who decide such things.

    The same facts make Ceres an infinitely better place to start building a base vs a vs any of the moons of Jupiter.

    Jupiter's gravity well is massive, and we won't be able to afford or build a mission that could make a round trip for that reason alone for decades to come.

    Also all the places receive deadly amounts of radiation at their surfaces. .

    Europa is the most lethal as it it receives enough radiation Jupiter's radiation belts to kill in less than a day. Also if it receives just a fraction of the electrical current coursing through Io, then the notion that Europe is doable in the same way Mars and Ceres are is absurd.

    Mars extremely thin atmosphere provides negligible protection from deadly solar radiation, and any extended surface activity would require expensive, durable protection from that.

    On this point, Ceres definitely is the better choice.

    I think some principle says it should get about 1/4 the amount of radiation Mars does, because it's 2x further out.

    That means the cost and difficulty of building on Ceres or just below the surface is automatically going to cost less and be easier to achieve since the amount of hardening the structures will require will be the least on Ceres.
     
  4. May 12, 2015 #3

    jkn

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    - Escape velocity from Ceres is 0.51 km/s and from Mars 5.027 km/s.
    Only 1.5 km/s needs to be added escape v to get from Earth to Mars.
    So Ceres is lot easier to go to.

    - Solar energy collectors produce 4* more energy on Mars.

    - Part of cosmic radiation has very high energy. Thick radiation
    shield is needed to stop it. That shield will easily stop
    everything coming from the Sun. Travel time to Ceres is longer, so
    better radiation protection is needed. This makes trip to Mars
    easier.

    - Does Mars have life? Did it have life? This should be studied before
    manned mission to Mars.

    So we need heavily shielded ship to take astronauts to martian moon
    and to Ceres. Both should have permanently manned underground bases.
    This ship would then ferry people and supplies between Earth, Mars and
    Ceres. It does not need to match speed with Earth, Mars or Ceres.
    Less shielded shuttle can do that. Martian moon base will study Mars
    with telepresence tools, after checking if moon is hollow.

    Same base design, same transport -> costs will not double. Ceres is
    colder than Mars, so I guess it has at least some water. So it can
    support water for Mars moon base and fuel for whole transport system.

    Interesting simulation exercise would be to look for minimum delta-v
    orbit for this transport. Perhaps it cannot pass every base in
    every orbit, even with gravity assists.

    Bases must be disk or short cylinder shaped. So that inside can rotate
    to simulate gravity.

    Third base to some heavy metal (gold, platinum,...) rich asteroid.

    Radio telescopes to all bases for really long baseline interferometry.
    Now somebody will protest: Space is better for telescopes than planet
    or moon surface. Yes it is, until your telescope needs service.
     
  5. May 12, 2015 #4
    Definitely true, but considering the massive cost with going and coming to Mars I imagine that would be an incidental cost. Also solar panels are on the cost of a dramatic increase in efficiency coupled with a drop in the cost of production which could make that difference inconsequential.

    My main thing is cost, because cost is the #1 driver behind the decisions space agencies make today.

    Fuel is a big cost, space and safety issue.

    You cannot probably cannot reduce costs by opting for Mars over Ceres, but you can dramatically cut back on fuel requirements for Ceres and thus significantly lower the cost of a mission to Ceres.

    Lifting off is the biggest single use of fuel for such missions.

    Lifting off from Mars to return to Earth requires almost as much fuel as it does to do the same from Earth.


    Every extra bit of weight added to a mission dramatically increases the cost of the fuel AS WELL AS the space dedicated to carrying what you need to go back and forth.

    So while superficially it might make sense to think building Mars worthy shielding would be cheaper than building Ceres worthy radiation shielding when you calculate the fuel cost and space requirements Etc for dragging that stuff back and forth to Mars vs. Ceres that superficial sense disappears.

    That extra shielding is going to be many times heavier on Mars and add tremendously to the fuel budget.

    So no It's not an easy safe assumption that for that point Mars is a better option.

    Yes Ceres is a longer journey, but fuel traveling in frictionless, gravity free space goes a long way. So it being longer doesn't come close to making the fuel requirements nearly as expensive as going to and from Mars.

    That's why Ceres minuscule gravity becomes such an overwhelming factor in its favor.

    Everything I said regarding the options all pale next to the extra EVERYTHING you need to compensate for Mars higher gravity.

    If going to and coming from there affordable enough to make it repeatable, then should Ceres prove to have plentiful, easy to access water, then it would win the cost argument.

    As far as the life question, it's ironic that you think it's an additional motivation to go to Mars, when in reality all the Missions to Mars have done their very best to avoid going to the places where life if it still exists on Mars is most likely to be found.

    That's why we haven't bothered to spend a rover to the likely mud volcanoes on the northern plains, or bothered to figure out how to get to the bottom of the Hellas Basin where the only place where water can exist at its triple point thanks to having the highest atmospheric pressure on Mars.

    Our missions have avoided that and will continue to avoid it out of fear of contaminating Mars with Earth Microbes.

    And this cannot be dismissed out of hand as a consideration, because it's the reason why Galileo was crashed into the Jupiter clouds and Cassini probe will do the same into Saturn's clouds to avoid the infinitesimally small risk that earth organisms that have somehow survived being in space for over a decade would still be able to infect Europa or Titan.

    If the paranoia level hadn't been so irrational and extreme they could have crashed Galileo into Europa and do the same for Cassini into Encelidus when its time came and get incredibly close up pictures of both Moons up to the moment of impact.

    So the bottom line is when that same paranoia eventually gets calculated into the decision making process about which solar system body to build on first, Ceres should be the winner, because the likelihood that there is or was life there is considered zero. In making that choice the worry warts can leave Mars free of the taint of invasive Earth organisms. ;)
     
    Last edited: May 12, 2015
  6. May 12, 2015 #5

    marcus

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    This is very interesting! thanks to both for raising these points and bringing lots of extra information into the thread! No time to reply at the moment. I was thinking people might hollow out sealed bubble habitats down in the Ceres ice layer. Sub-surface chambers would be protected from radiation, vacuum, etc. a good manufacturing site, if raw materials turn out to be available.
     
  7. May 12, 2015 #6

    jkn

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    On Ceres we need 4 times larger solar panels than on Mars.
    Manufacturing cost of panels is insignificant, transport cost is not.

    Travel to Ceres takes more than twice as long. Total radiation damage
    should not exceed what human body can tolerate. So when traveling to
    Ceres ship must have more than twice heavier radiation protection.
    Same for air, water and food.

    I don't want astronauts to surface of Mars. Only to martian moon.
    Even surgical operations have already been made with telepresence.
    Everything can be made from moon base. I don't know delta v needed
    for visiting martian moon, but I'm sure it is much smaller than delta
    v for surface of Mars. I guess it is about same as delta v needed for
    Ceres visit.

    When we have developed, with great cost, technology to go to Mars or
    Ceres, we should use it more than once!

    First we should build permanently manned base on moon. When it is
    well tested, copy it to martian moon. Ceres comes third because of
    longer travel time.
     
  8. May 12, 2015 #7

    mfb

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    @johnnymorales: There are some points you missed, mainly the fuel to get further away from the sun (see point 3).

    • the lower gravity on Ceres is a health disadvantage, similar to life on the ISS.
    • shielding requirements are the same for both objects, as jkn explained. More problematic for Ceres if you take travel time into account.
    • Ceres is two times further away if you are at the sun. We are not. Compare the Hohmann orbits (neglecting the eccentricity of Mars' orbit):
      -- Start at earth, get 2800 m/s delta-v, wait 10 months, get 2600 m/s (can be done via aerocapture), and you are at Mars.
      -- Start at earth, get 6400 m/s delta-v, wait 26 months, get 4900 m/s (no aerocapture available), and you are at Ceres.

    The escape velocity of Mars is 5 km/s. Getting from Earth to Mars via aerocapture, landing on the surface, getting back to orbit, getting back to Earth with another aerocapture: a two-way trip to mars costs the same delta-v as the one-way trip to Ceres!

    You can use a gravity assist at Mars to reach Ceres but that will make the trip longer, and it also makes launch windows rare (probably once per 10 years).

    Getting delta-v at Earth is a bit easier as you can use the Oberth effect, but the delta-v requirements for Ceres are still massive compared to a trip to Mars.

    Do you have a source for that claim?
     
    Last edited: May 12, 2015
  9. May 12, 2015 #8

    Janus

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    Earth escape velocity: 11.19 km/sec. Mars escape velocity; 5.03 km/sec.
    Rocket equation:

    [tex] \DeltaV = V_e \ln (MR)[/tex]
    where MR the mass of fully fueled rocket divided by the mass of the rocket after the fuel is burned.
    If you rearrange the above equation, you can get the fuel to rocket mass ratio.
    Assuming a typical chemical rocket exhaust velocity of 4.5 km/sec:

    For Earth, this works out to ~11 kg of fuel for every kg of rocket to attain escape velocity.
    For Mars, it works our to ~2 kg of fuel to every kg of rocket.
    or at less than 1/5 the amount of fuel to lift off from Mars as it does from Earth.


    It's a 1 to 1 ratio. doubling the weight doubles the fuel. What increases the fuel requirements dramatically is Delta V.
    It's not "gravity free" you are climbing out of the Sun's gravity field. This isn't just a matter of straight line free flight, you have to take orbital mechanics into account.

    Using a minimum energy Hohmann transfer orbit, it takes a delta v of ~2.952 km/sec to get to Mars. It then takes an additional 2.66 km/sec to match orbital speed with Mars when you get there. Add on ~5 km/sec to affect a soft landing. This works out to roughly 10.6 km/sec total delta V. Double that for a round trip.

    Using the same type of transfer orbit, it takes a DV of 6.332 km/sec to get to Ceres and an additional 4.87 km/sec to match orbital velocity. Add on the .5 km/sec for soft landing and you get a total of 11.7 km/sec. Double that for a round trip.

    For the same chemical rocket as above, We get ~110 ratio of fuel to rocket for a Mars round trip and an 180 ratio for a Ceres round trip or ~64% more fuel to reach Ceres than for Mars via chemical rocket. ( Higher efficiency rockets would drive both the fuel ratios and the fuel ratio difference between the two trip down. For example, just doubling the exhaust velocity decreases the extra fuel needed to for a round trip to Ceres down to 30% more than that needed for Mars. But, no matter how you cut it, it still will take more fuel per kg to get to Ceres vs. Mars)

    As the time factor goes, it takes ~258 days to make the Mars trip and ~471 days for the Ceres trip, one way.

    EDIT:

    Another factor in getting to either Mars or Ceres is that they don't orbit in the same plane as the Earth. Mars is inclined at 1.85 degrees and Ceres at 10.5 degrees.

    So unless you launch at the moment Earth is aligned with either the descending or ascending nodes of these bodies, (which really limits available launch windows). You are going to have to do a "broken plane" maneuver somewhere along the way to match orbital inclination. For Ceres, this will require a delta v somewhere between 2.42 and 5.54 km/sec (the exact value depends on how your trajectory aligns with the same ascending and descending nodes.) For Mars, with less of an inclination, it comes out somewhere between 0.696 and 0.968 km/sec, so on average, this maneuver adds an additional 3 km/sec to the delta V difference between getting to Ceres vs Mars.
     
    Last edited: May 12, 2015
  10. May 12, 2015 #9

    marcus

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    Hi Janus,
    thanks for joining thread and sharing thoughtful comments! I think this is all good stuff because it gets us to visualize and think concretely about stuff like for example orbit inclination, and delta-V, and escape velocity, and possible composition of Ceres and element abundances etc.

    I think of Ceres in terms of eventual "manufacturing in orbit, on steroids". I can't guess whether manufacturing (of chemicals and perhaps gear and parts) will eventually be done by robots, or humans, or some combination. But however that is done, I think that the resources of Ceres have premium value because easier to lift off the surface than for instance Earth or Mars resources.

    So to me that seems to make Ceres exceptionally interesting from a technical/economic standpoint. I'm very interested to know what elements are present in salts and minerals dissolved in the icy layer, and what elements are present in the presumably thin crust (of rubble, regolith...). We may not know really for many years, but I hope there will be hints soon, about the outer crust makeup.

    As a minor point, I would like to distinguish between the spaced out gradual ΔV of getting from 1 AU to 2.8AU at a different inclination, with mid-course corrections as needed, and on the other hand the very intense ΔV of landing and taking off from surface of Mars. Which involves RISK as well as fuel cost. And fuel cost to get the fuel to the point where it is needed. So there is possibly a different cost schedule. Not all ΔV is the same : ^)

    this is one reason that, intuitively (and based on conjectured assumptions) I tend to find Ceres especially interesting long term

    but the main thing at this point is to increase our knowledge and become more conversant with all these factors. thanks to everybody participating in thread!
     
  11. May 12, 2015 #10

    mfb

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    If you want to go for a large-scale engineering project, you can attach a space elevator to Ceres (can be done with materials today, very easy) and/or make some ground-based launch track. The latter is also possible for Mars, the atmosphere is thin enough. A space elevator on Mars would require moving Phobos away (or into Mars) first.
     
  12. May 12, 2015 #11

    marcus

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    Mfb this exemplifies how this kind of apparently "futury" ideation is a catalyst for presentday learning and understanding. Good point about Phobos.
    for beginners, the point is that a "space elevator" concept uses the existing rotation speed at the equator to approach circular orbit speed
    by extending the radius of rotation.

    So if there is something already in a nearly circular orbit at the equator it might bump the rotation arm extension
    as long as its orbit altitude is less than that of a stationary satellite
    or that is to say as long as its orbit period is shorter than the planet rotation

    so a beginner might want to check the orbit period of Phobos and compare it with the rotation period of Mars.

    So Mfb is sketching a didactic idea and I really hope if anyone not conversant already is reading the thread they will follow through. I didn't yet, so I will go to Wippikidia and check the orbit period of Phobos to make sure I understand the idea.
    :woot:
     
    Last edited: May 12, 2015
  13. May 12, 2015 #12

    marcus

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    Woah! Phobos has an orbit period of 7.7 hours and Mars has a rotation period of 1 day!
    That means Phobos is an elevator killer!
    Any newcomers please understand the reasoning, or ask Mfb for explanation. The altitude of Phobos is way less than the altitude of a stationary satellite in equatorial circular orbit
     
  14. May 12, 2015 #13

    Janus

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    In addition, due to it's short orbital period, it undergoes tidal deceleration and is getting closer and closer to Mars as time goes by.
     
  15. May 12, 2015 #14

    Janus

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    Since you need to move it anyway, you might as well move it into position to be used as the counterweight for the elevator.
     
  16. May 12, 2015 #15

    marcus

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    Good point!
    These are simple ideas but very good to understand, if any newcomers see post #435 figure out how that works, or ask or both. Give Janus and Mfb something to do. Otherwise we have to rely on imagined hypothetical or future newcomers which we think may exist, and tailor our posts to.

    If you are a spacecraft in circular orbit then braking speeds you up so if you thrust in reverse, like Dawn is now doing with its solar electric ion drive, you will spiral in slightly and speed up. And we can SEE THIS in the simulated view of Dawn
    http://neo.jpl.nasa.gov/orbits/fullview2.jpg [Broken]
    this is a concrete example.
    while in its first circular orbit, for about 15 days, Dawn was at altitude 13,500 km and going at speed right around 150 mph.
    On the 10 May it began a braking thrust with its ion beam pointed in the direction it was going.
    Now simulated view says it is going 153 mph. Return tomorrow to see if that speed has increased!
    And it says the altitude is now (7PM pacific on 12 May) about 11.7 kkm that is almost 2000 km nearer the surface than it was to start with.
    Because of a delay in refreshing, this image as it currently appears is out of date. Click on REPLY to see the current sim-view version. You don't have to reply you can just cancel or back out of replying, if you want, but when you click "reply" at the bottom of this post it will show you the current version of the sim-view graphic. It is now as of 10PM pacific 12 May and the speed is 154 mph (more than what the outdated version the system provides currently shows).
    UPDATE: As of now 7AM 13 May pacific, when you press "reply" the updated version says
    158 mph. So quite a lot of speeding up has happened.
    http://neo.jpl.nasa.gov/orbits/fullview2.jpg [Broken]
    This image shows an earlier version but it will change to an updated one if you click "reply", so i am describing the situation for 7PM pacific on 12 May when I say she is flying up the night side of Ceres heading for the N pole, and thrusting to slow down. The Sun and Mars are visible so we can see the plane of the solar system currently in this sim-view.
    UPDATE: Currently it says altitude 11.7 kkm and speed 154 mph, for 8PM pacific on 12 May. So we see speed continuing to climb in accordance with the reverse thrust braking by the craft.
    Click on the link to get the latest sim-view figures.
    UPDATE: as of 7AM 13 May, altitude 11.2 kkm and speed 158 mph.
     
    Last edited by a moderator: May 7, 2017
  17. May 16, 2015 #16

    jkn

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    Marcus,

    Phobos does not completely kill space elevator.
    It could be vibrating and tuned to miss Phobos every time:)

    More practical: Elevator 5500 km down from Phobos. Lower end of it
    would have lower orbital speed than satellite at that altitude. It
    would be easier to reach from surface.

    A large-scale engineering for mfb: 24773 km long space elevator from
    Ceres. Tip of it would have speed 2*3.1415*(24773 + 487)/9 = 17634
    km/h = 4900 m/s. Let go from end of it at exactly right moment and you
    get to Earth without any rockets. Unfortunately rotation axis of Ceres
    would not usually point to exactly correct direction.

    a = 4900^2/(24773000 + 487000) = 0.95 m/s² = 0.1 g
    Surprisingly small number, but I cannot find an error. No super
    strong materials needed! Even ships arriving from Earth could use it.
    7 coordinates must be exactly correct: position, speed and time. 10 s
    before docking tip of elevator would be 0.5*0.95*10² = 47.5 m away. 1
    s before docking tip of elevator would be 0.5*0.95*1² = 0.475 m away.
    If you miss, you need to quickly accelerate 4900 m/s or you are in big
    trouble.


    I thought reasons to go to Ceres. Not a very long list.

    1: If it has plenty of water and no other asteroid or any of 3 moons
    has it. Mars is more difficult source for raw materials, because we
    need large delta v from chemical rockets + small from ion engines.
    From Ceres we need small delta v from chemical rockets + large from
    ion engines. We could break CO2 to CO + O2 and use that as rocket
    fuel. Then Mars could compete. Smaller asteroids are easier to land
    and get away than Ceres.


    2: Gravity at surface of Ceres is 1/34 of Earths. When drilling hole
    into Ceres, pressure would increase 34 * slower than on Earth. Even
    slower, because density of Ceres is lower. Deepest borehole on Earth
    is 12 km. 34 * 12 = 408. So we could drill to center of Ceres. I
    guess it is not too warm. Perhaps gravity has collected some weird
    stuff there... That would be well protected place for a space
    station...


    mfb,

    Since johnnymorales has not answered: Best places for life on Mars are
    most dangerous to land (deepest valleys). It is not surprising that
    those have not been visited.
     
  18. May 16, 2015 #17

    marcus

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    JKN, if you are reading this (and I hope you will be) let's simplify the problem and just ask what height pylon you need to get goods and material into circular orbit.
    Ion engines are efficient and can take it from there---spiral out from circular orbit and head off to wherever the goods are wanted (not necessarily Earth!)

    Ceres mass is estimated at M = 943e18 kg.
    We have to find R such that circular orbit speed (GM/R)1/2 is equal to 2πR/9 hours.

    That will give the orbit radius and we can just subtract 487 km from that to get the orbit altitude. (I use your figure for the equatorial radius of the little planet)

    That should be simple algebra, to find R. We can use google calculator where you just paste things in the google window.

    GM/R = (2πR/9hours)2

    R3 = GM*(9 hours/2π)2

    Are you with me so far? Have I made any mistake?
     
  19. May 16, 2015 #18

    marcus

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    Google calculator knows Newton G and pi, so one just types in G and pi as needed. It likes to give the answers in metric units like meter and kilometers, so that is OK.

    See if this works, pasted into google window:

    (G*943e18 kg*(9 hours/(2 pi))^2)^(1/3)

    It works! Google understands this, pasted in just like that, and comes back with the orbit radius:

    1187 km

    So if JKN is right about the equatorial radius, the tower would have to be 1187 - 487 = 700 km high.
    And then its tip would be weightless in circular orbit, because of the 9 hour rotation period of Ceres.
     
    Last edited: May 16, 2015
  20. May 16, 2015 #19

    mfb

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    I'll try to separate the discussions as good as possible. The thread will look messy until it is done.

    Edit: Done.

    The materials are not needed for g, they are needed for the total velocity. Such a space elevator would have to be tapered significantly with materials available today. Not as bad as an elevator on Earth, but in the same way as an elevator for Mars.

    Oscillations are a serious problem for space elevators, trying to use them in a controlled way sounds... challenging.
     
    Last edited: May 16, 2015
  21. May 16, 2015 #20

    marcus

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    I think it is fine, Mfb. The new thread,split off from the Dawn Mission Ceres thread, makes good enough sense to me. I'm happy that both Janus and you had some physics-based comments. I hope other people see this one and think of stuff to contribute.

    JKN mentioned drilling down (through the frozen ocean?) to the core of Ceres. I'm not sure what the motivation for that would be (geothermal energy production?)

    He also mentioned solar panels. Well if humans and or robots are eventually going to establish a bulk chemical industry on Ceres they need electric power! It makes sense : ^)
     
    Last edited: May 17, 2015
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