Comments
jurek911 t1_izmm8y9 wrote
Mars trilogy was great! A little dense and slow at times, but absolutely worth reading if you’re a fan of sci-fi.
LakesideTrey t1_izn1lh0 wrote
My favorite series ever. Gonna reread again this summer once I wrap up the dune series.
jurek911 t1_iznoy54 wrote
I read it for the first time earlier this year, and it’s definitely a series that will be reread at some point in the near future.
SixIsNotANumber t1_izk061b wrote
Can someone ELI5/tl;dr for me why/how it could work going one way but not the other?
Icee777 OP t1_izk38tj wrote
The idea is for the space elevator from Phobos ending about 28 km from the surface of Mars just above the atmosphere to prevent friction.
borgendurp t1_izkivzf wrote
What's the point then? Isn't the first part the hard part? The first 28 km from Mars I mean
TerpenesByMS t1_izlcu59 wrote
Yes and no.
Mars atmosphere is much thinner than earth's. Gravity is already the hardest part of getting to orbit from the ground on both planets, on Mars the atmosphere component is smaller.
The bulk of acceleration to reach orbit isn't the up part, it's the sideways part. By having a low-hanging and sub-orbital "docking point" at the base of the elevator, you are still conserving a lot of fuel and delta-V even though it doesn't go "the whole way".
Also, having an asteroid anchor point gives space elevator architects more freedom. Unwinding the inner and outer tether doesn't need to be perfectly synchronized, and tether lengths and counterweights could further be used to adjust Phobos' orbit around Mars.
None of what I just said is fast or easy, but when we're talking about space elevators nothing really is. As described, this might be the "beta version" space elevator that's deployed before any are used on earth - lesser risk, more room to experiment and learn, still has some use if we're jacking around on Mars, etc.
SixIsNotANumber t1_izkjg6n wrote
Yeah, that's kind of a head-scratcher for me, too. I'm having a hard time wrapping my brain around it.
borgendurp t1_izkjle7 wrote
I think we get the principality behind it.. just not the point 😆
SixIsNotANumber t1_izklk1t wrote
Exactly!
I've loved the concept of space elevators ever since I read The Songs of Distant Earth, by Arthur C. Clarke, and I hope I live to see the day one actually gets built...but I don't get this at all. I'm hoping for a good follow-up answer though. Like I said, I want it to be real!
Icee777 OP t1_izkjvqg wrote
You can halve those 28km by launching from Pavonis Mons - a volcano on Equator. In that way you are out of the dense part of the atmosphere
borgendurp t1_izkkbvq wrote
Yeah okay.. but why? The atmosphere only goes up to 10.8 km. After that, why do you need 6000km of elevator for?
manicdee33 t1_izlwy08 wrote
Escape velocity from Mars is about 5km/s. The article explains that the bottom end of the elevator would be travelling at ~770m/s while the outer end of the elevator would be travelling at ~3.25km/s. This means a two-stage escape from Mars (one stage to get to the elevator, second stage to get from the elevator to escape velocity) would only need to provide ~0.8km/s to rendezvous with the elevator, and another ~1.75km/s to escape Mars, saving ~2.4km/s in delta-v overall. This results in significantly lower propellant requirements for cargo moving between Mars and Earth (and thus smaller spacecraft to carry the same payload).
borgendurp t1_izn1x0a wrote
I'm not too familiar with what you're talking about but from wiki;
In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non-propelled object to escape from the gravitational influence of a primary body
So I'm not entirely sure how that applies?
manicdee33 t1_iznadnx wrote
In celestial mechanics, escape velocity is the speed an object needs to reach in order for the force of gravity to never reduce the outward velocity to 0. As you travel further away from the primary body the force of gravity gets smaller and smaller, so the deceleration gets smaller and smaller, and the limit at the distance approaches infinity is for the deceleration from the force of gravity to reach 0. If the starting speed of the object was such that by the time it reaches that infinite distance it still has some radial velocity, it has escaped.
Also in celestial mechanics, a "propelled object" is one that can thrust forever (basically a torch ship). A non-propelled object includes an object which has accelerated by burning a rocket engine and has stopped consuming propellant (it's no longer propelled). If that rocket can reach escape velocity, it can coast out of the influence of that primary body. This is how rockets can push space craft from one planet to another: they reach escape velocity to escape the gravity well of one planet, and carefully aim to be caught in the gravity well of the destination.
Hope this helps.
charlesfire t1_izln658 wrote
Gravity is still a thing.
ItsAConspiracy t1_izwxc4b wrote
Delta-v to launch from the surface and dock with the space elevator, according to the article: 0.52 km/sec.
Delta-v to launch from the surface into Martian low orbit: 3.8 km/sec.
So less than a seventh as much velocity change. Now let's use the rocket equation. A methane rocket has specific impulse of about 370 seconds (that's a measure of how fuel-efficient the rocket is). We'll use a starting mass including fuel of 10,000 kg.
For a delta-v of 520 m/sec, we get a final mass of 8380 kg. We only had to burn 1620 kg of fuel to get 8380 kg of rocket and payload up to the elevator.
For a delta-v of 3800 m/sec, our final mass is only 2748 kg. We had to burn 7250 kg fuel, to put only 2748 kg of rocket and payload into orbit.
Assume in both cases that the rocket is 1000 kg, then with the space elevator we're getting 7380/1620 = 4.55 kg payload per kg fuel, and without the space elevator we're getting 1748/7250= 0.24 kg payload per kg fuel.
SixIsNotANumber t1_izkk81h wrote
OK, that part of it does make some sense, but I'll echo the other reply to your reply: what's the point?
Isn't the harder part of the process getting off of Mars? (And please don't take my questions the wrong way, I promise I'm not trolling or trying to JAQ-off, I really just want to wrap my brain around why this is meant to be a good/useful thing.)
Icee777 OP t1_izkyhai wrote
It makes sense once you have an industry large enough to move substantial amounts of mass to and from Mars. Space elevator saves energy. In the proposed form you need only 0.52 km/s of Delta-v to get from Mars' surface to the elevator. And on the other end of the elevator you can release (or catch when importing) that mass at 3.52 km/s of Delta-v. Of course, there will be some energy loss moving up and down the elevator, but you don't need the acceleration that a rocket launch demands.
Mr_Lobster t1_izknnn4 wrote
Better idea: Just blow up Phobos.
strvgglecity t1_izksgug wrote
If president Camacho has any say you'll be the next secretary of space
thiosk t1_izzp5lv wrote
Secretary General avasarala Ive found you
Mr_Lobster t1_j0v0ju5 wrote
That actually is where I got the idea. They blew up Deimos in the show and I was like "Could they really do that?" So I calculated the gravitational binding energy of it and found that, yes, they totally could.
gilareefer t1_izl0iv7 wrote
It would be cool if we found out that obelisk on Phobos is the remains of an ancient space elevator
Icee777 OP t1_izk3iit wrote
Building a Martian space elevator would be complicated by the Martian moon Phobos, which is in a low orbit at ~6,028 km above the Martian surface and intersects the Equator regularly, thus getting in the way of a traditional geostationary space elevator. But there is an idea instead to build a space elevator from Phobos itself. More in the article linked.
TelluricThread0 t1_izkfkgx wrote
How much of a benefit is a space elevator on Mars where gravity is much less compared to Earth?
Icee777 OP t1_izkz838 wrote
It makes sense once you have an industry large enough to move substantial amounts of mass to and from Mars. Space elevator saves energy. In the proposed form you need only 0.52 km/s of Delta-v to get from Mars' surface to the elevator. And on the other end of the elevator you can release (or catch when importing) that mass at 3.52 km/s of Delta-v. Of course, there will be some energy loss moving up and down the elevator, but you don't need the acceleration that a rocket launch demands.
FuturologyBot t1_izk5fzy wrote
The following submission statement was provided by /u/Icee777:
Building a Martian space elevator would be complicated by the Martian moon Phobos, which is in a low orbit at ~6,028 km above the Martian surface and intersects the Equator regularly, thus getting in the way of a traditional geostationary space elevator. But there is an idea instead to build a space elevator from Phobos itself. More in the article linked.
Please reply to OP's comment here: https://old.reddit.com/r/Futurology/comments/zh3mao/phobos_orbit_prevents_a_traditional_geostationary/izk3iit/
ML4Bratwurst t1_izkmfw7 wrote
So the end of the elevator would move how fast over the surface of Mars?
Icee777 OP t1_izkzflf wrote
The bottom end at 0.77 km/s if the elevator would end 28 km above surface.
strvgglecity t1_izkruaa wrote
Questions for futurology fans and followers: do you believe Mars will actually become inhabited and meaningful?
Boxofcookies1001 t1_izkxzn2 wrote
Definitely. Probably take around 3 centuries or more to get there but for sure. It's only a matter of time till we begin to take nuclear power space side.
It'll probably take around 5 for mars to be a standalone and we begin to colonize the solar system.
strvgglecity t1_izkykvg wrote
So you trust that earth's societies will somehow weather the growing storms and still have both the means and the will to pursue extra-earth exploration. Understood.
Predictions that far out aren't really worth serious discussion, however. I wonder why anyone is even spending time thinking about a Mars elevator. That was my first reaction. "Who is being paid to even consider this?"
Icee777 OP t1_izl0w3j wrote
How much resources you needed to kikstart the American colonies which eventually grew into the most powerful nation now on Earth - the United States? ... a few expeditions in 16th and 17th centuries. I think we can spare that much to become a multiplanetary species.
Ulyks t1_izx5zno wrote
Didn't the first colonist almost starve, if not for the food they got from the natives, as celebrated during thanksgiving?
There are no natives on Mars, neither is there breathable air, soil, livable temperatures or potable water.
So you need to take all of that with you, which is impossible. Or instead take entire industrial supply chains to mars to create those essentials. Which is almost impossible but perhaps not entirely.
Anyway, it will cost endless resources to kickstart Martian colonies.
Trillions of dollars at least.
Can we spare that? Perhaps but we will need to tighten the belt somewhere.
strvgglecity t1_izl4ayy wrote
Going across an ocean is 0% like going to another planet. There was air here. And water. And trees. And food. And animals. The travel itself was the only obstacle. On Mars every breath, calorie, H20 molecule and poop has to be accounted and provided for, literally. Neil deGrasse Tyson himself has come out against focusing on a permanent mars settlement.
I am not shitting on Mars exploration - only explaining the immense challenge it poses and resources it would require to settle there permanently. It's likely that in the first several decades, human trips will be one way due to water and food constraints unless some sort of hibernation is achieved, which means anyone who goes is stuck there til they die, which could be as little as a few years.
It's just a much, much more difficult proposition than any media outlet or SpaceX employee is willing to discuss. I also am unsure of the value of a permanent settlement. I have not seen the results part of the missions.
Icee777 OP t1_izl6gwo wrote
Going in deep ocean in 15th century is comparable to going in deep space in 21st century. Most of the expeditions were lost and the first colonies barely survived. And they needed to wait for the next year (or even a few) for a supply mission. But they tried again and again till a meaningful foothold was established.
strvgglecity t1_izl7fsn wrote
It's not even close. These people will go knowing they can't come back. You're only talking about getting lost. Space involves far more pernicious dangers. It's a 9 month trip just to get there, and then years before you eventually die or a method of return travel arrives. We don't know how Mars gravity or radiation will affect the human body long-term. You can't go outside ever again. Can't see a blue sky or watch a bird fly. In modern terms, you'll never again access the internet. It's possible that minor injuries are likely to be death sentences. And the money involved is astronomical compared to building wooden ships. Essentially, the psychological stress will be unlike anything humans have encountered to date.
I strongly suggest looking at astrophysicists' discussions about life on Mars and travel to Mars for a more complete understanding of the possibilities and challenges.
strvgglecity t1_izlacjx wrote
There's also a separate option that for profit corporations will undoubtedly exploit: the singularity is predicted for 2029, when machine general intelligence will surpass human intelligence. Subsequent advances in robotics will likely result in fully humanoid robots capable of self maintenance and repair by the 2040s or 2050s, which eliminates the need for food and water and places unrestricted timelines on operations. Human settlements are likely to be built by said robots because not a ton of people will be up for one way trips and the cost of sending robots is significantly lower.
ItilityMSP t1_izluymf wrote
Settling the ocean with floating cities and Antarctica are far easier than Mars.
strvgglecity t1_izm3n62 wrote
And the moon! Ha.
Icee777 OP t1_izkzsv5 wrote
>Yes, I believe. You can read a detailed speculative timeline of Mars colonization here: https://www.humanmars.net/p/mars-colonization-timeline.html
strvgglecity t1_izl1sic wrote
Wow whoever wrote that envisions a permanent settlement in 2032? Wonder what Ray Kurzweil has to say on the subject.
I'm not yet sure I understand the goal here. Mars is not a habitable planet and I would expect the resources expended to establish a settlement will be the largest project in human history, probably by an order of magnitude.
Leading futurists are talking about the singularity occurring in 2029 and being able to upload an entire human brain by the 2040s. The unpredictability of technological development and societal acceptance/adaptation means such a long timeline likely has a very high chance of error.
To be certain I'm only here for education and discussion.
Ulyks t1_izx6jrf wrote
Yeah singularity is one thing. Freeing up resources for the massive investments needed to terraform Mars is another.
I'm sure a superintelligent AI could come up with a detailed and feasible plan by 2040 to start terraforming Mars.
But it will probably involve everyone on earth paying 10% more taxes to fund the endeavor.
It's a no go until we solve many pressing problems on earth first.
SpiritualTwo5256 t1_izln68f wrote
By then we could send a ton of asteroids past Phobos to shift its orbit a few degrees.
tanrgith t1_izm6sbi wrote
Honestly, if we had the capability to build a space elevator on Mars, then we'd also have the capability to move a relatively tiny moon such as Phobos into a different orbit
sunnyinphx t1_iznets0 wrote
Probably gonna wanna get to mars and then start thinking about moon elevators but hey no expert here. I forgot about how earth totally already has a moon elevator.
KillerNinja86678 t1_izk83hg wrote
No damnit fix the hungry and needy first. We cant wait on space but we cant wait on our own people? All these billions wasted all for nothing. When we fix our problems on earth, we could have quintillions for space.
Nettius2 t1_izkecgt wrote
If all the money were taken from the overall space budget, we’d build a handful more smart missiles. Space exploration isn’t preventing us from taking care of the hungry and needy. People who profit from a hungry and needy “class” are doing it.
For example: some individual states prevented 100% free lunch for school children. It wasn’t for budgetary reasons.
strvgglecity t1_izks6ss wrote
No but it does keep trained scientists and engineers from demonstrably more meaningful pursuits. Human capital is all we really have, and it's not much different paying scientists to target Mars than asking them to make a 4 dimensional candy bar. It is wildly outside the scope of our current needs. Once again the issue comes down to who profits: society, or individuals.
Nettius2 t1_izl47zx wrote
The highly specialized scientist is doing pretty much the only thing that they were trained to do. It’s not like they’re suddenly go cure cancer now that they aren’t busy with Mars. I don’t know enough about engineer shortages to comment on that.
It gets worse. Why do you think it took so long to get back to the moon? Because the institutional knowledge was gone.
FYI: save the 4th dimensional candy bars for physicists and mathematicians
strvgglecity t1_izl5rej wrote
Why not? They are smart people. It's troublesome that smart scientists and engineers are largely guided by paycheck size and "exciting"ness, I stead of actual benefit to society or individuals. Scientists make lots of money developing chemicals, for instance, with little to no concern over whether the chemicals are positive or negative. They are just doing a job. Everyone at SpaceX is likely a true believer, but as I've pointed out, they don't like discussing the realities of the mission beyond whether they CAN do it or not.
SixIsNotANumber t1_izklxpr wrote
Go bug the DoD & the Pentagon.
NASA isn't the problem here.
esprit-de-lescalier t1_izk7szw wrote
I remember the scene in Kim Stanley Robinsons Red Mars where the space elevator was destroyed and wrapped around the planet a few times causing death and destruction. Was a fun read, recommended!