Author Topic: How to fly to and from Mars to support permanent bases?  (Read 1490 times)

Offline anonymous

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As I said in a previous thread, I'm writing a science fiction story with a Martian setting. It takes place about a hundred years from now - a Mars of scientific bases, rather like the Antarctic bases of today.

The plot calls for the protagonist to fly from Mars to Earth. So what's the spaceship she flies in like? My original idea was to base it largely on Elon Musk's Interplanetary Spaceship proposal for his Mars colony, but then I thought that might seem too derivative and not advanced enough for a hundred years' time. I began to think about and read more about alternatives.

When I was young, people talked about flying to Mars on Hohmann transfers. Then Robert Zubrin came along and it became about doing it in six months. Then the infamous Ad Astra 39-day study came along and everyone started competing to do it as fast as possible. The 80 to 150 days Musk is proposing seems almost conservative by comparison.

Aside from the obvious advantages in terms of less exposure to radiation and weightless conditions, I've read that Musk's plan also allows the spaceship to fly to Mars just before opposition and back to Earth just after opposition, allowing the ship to do a round trip in a single launch opportunity, increasing the return on the capital invested in the spaceship, even if it requires more fuel than on a slower transfer.

The thing which seems very unconventional about the IPS compared to science-fiction spaceships is that it flies planetary surface to planetary surface. That enables it to take fast trajectories that would normally require a lot of propulsive delta-v to slow down on arrival at a planet by simply entering the atmosphere and losing the delta-v that way. It's an approach, though, that is very much contrary to all that I read when young about how interplanetary spaceships had to always stay in space and never land on a planet because of all that wasted mass from heat shields, etc. I've seen comments that his approach is more about SpaceX's limits in terms of capital, experience operating in space and areas of technological expertise, rather than because it's really the best way for an interplanetary spaceship to operate. Would Musk's approach still be better than the traditional one in a hundred years?

Is chemical propulsion still the way people would be flying to and from Mars a century from now? There are certainly more fuel-efficient technologies.

Nuclear thermal was once the most popular approach for flying people to Mars, but from an economic perspective there are real problems with the reusability of your spaceships. What's more, it now seems you can get the same performance more cheaply from a chemical/solar-electric hybrid, which leaves nuclear thermal out of the running for me.

Solar-electric itself is criticised as requiring solar arrays that are just too large and flimsy, but I'm not sure that's a fundamental objection to it in the long term as our materials technology advances. It suffers from a plot point of view because of its very slow acceleration, but maybe in real life it will be the winner?

A chemical/solar-electric hybrid is a possibility for my story, but I wonder if it's very much of our time, before solar-electric is ready to do the job by itself. Will solar-electric displace it in the future?

Nuclear-electric is touted as the most advanced realistic technology, but it has problems with getting the mass per kW down enough because of the weight of the reactors and the huge radiators it needs to disperse the heat from the nuclear reactor. I also have a feeling that anything nuclear is expensive, which is one of the main reasons why nuclear is on its way out on Earth. Solar-electric seems likely to be much cheaper.

If we're talking a hundred years from now, of course we have to consider fusion. Magnetic fusion approaches seem to have the same massive radiators problem as nuclear electric, but magneto-inertial fusion as proposed by MSNW could offer performance that would blow the socks off any other spaceship propulsion technology if it can be made to work. Can fusion be made to work? After sixty years of failure, of nuclear fusion having been fifty years away all my lifetime, it seems like one of those science-fiction cliches that will never happen in real life. What's more, fusion research on Earth is threatened by the way that the price of solar power on Earth is getting cheaper than fossil fuels and is already cheaper than nuclear energy. Since fusion is projected to cost about the same as nuclear power, that seems ominous for fusion. Solar power with battery storage looks set to become cheaper than electricity from natural gas long before anyone can make fusion a workable energy source, let alone an economic one.

So what should I do? What kind of propulsion technology should I go for in my story? Chemical? Solar-electric? Chemical/solar-electric hybrid? Nuclear thermal? Nuclear-electric? Fusion? I'm sort of leaning towards a chemical/solar-electric hybrid, but I'm not at all sure.

Something I'm really interested in is how wide the launch windows would be for these different approaches. I've looked a lot for information about that, but I've been able to find very little solid information, only that the launch windows for chemical are very narrow. It seems to me that you'd really want wide launch windows, preferably propulsion that allows you to fly between the two planets any time in a reasonable time, but I'm not sure any of the technologies could do that.

I'm looking at it from two perspectives: what seems most plausible to actually happen and what would work best in my story. Is there anything that you can tell me to help with this decision?

Offline gospacex

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Re: How to fly to and from Mars to support permanent bases?
« Reply #1 on: 08/15/2017 09:08 PM »
Use cyclers - large, well-shielded spacecraft on permanent Hohmann orbits. People board and leave them on smaller, light craft.

Offline anonymous

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Re: How to fly to and from Mars to support permanent bases?
« Reply #2 on: 08/15/2017 09:15 PM »
I did include cyclers in my story originally, but after reading about them more I went off the idea. They seem too inflexible and too easy to miss.

Offline lamontagne

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Re: How to fly to and from Mars to support permanent bases?
« Reply #3 on: 08/15/2017 09:27 PM »
Does your story need speed?  Is space an important element of the economy or just a small prestige occupation?

Offline anonymous

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Re: How to fly to and from Mars to support permanent bases?
« Reply #4 on: 08/15/2017 09:44 PM »
The story doesn't need speed, but because recent thinking about journeys to/from Mars has been about doing it in three or four months, I've been working my plot around that. The timings of when there are launch windows is important for the plot, which would be easier if you could ignore launch windows. Even if you're not constrained by launch windows, it's much quicker to fly between the two planets when they're near, rather than far away. That means that people will tend to fly then.

Space isn't an important element of the economy in the story. Indeed, the difficulty of making money out of Mars is one of the elements of the plot. The real reason why countries have Mars bases is as a bolt hole for the political leaders and the super-rich in the event that a planetary disaster befalls Earth.

Offline anonymous

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Re: How to fly to and from Mars to support permanent bases?
« Reply #5 on: 08/15/2017 09:59 PM »
The reason why I worried about the slow acceleration of solar-electric (or nuclear-electric) is because it would make the spaceship the protagonist is travelling in too easy to intercept on its approach to Earth.

Online Coastal Ron

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Re: How to fly to and from Mars to support permanent bases?
« Reply #6 on: 08/15/2017 10:17 PM »
The story doesn't need speed, but because recent thinking about journeys to/from Mars has been about doing it in three or four months, I've been working my plot around that.

Consider that we've had Mach 3 aircraft for over 50 years, but airliners of today fly below the speed of Mach 1. So I would not focus on what is the fastest potential modes of transportation, but what are the least expensive modes of transportation.

Also, our commodity transportation systems of today are built around long-distance segments that then terminate at transition points for short-distance transportation segments, which I would think would be the modes used in the future of space transportation too.

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The timings of when there are launch windows is important for the plot, which would be easier if you could ignore launch windows. Even if you're not constrained by launch windows, it's much quicker to fly between the two planets when they're near, rather than far away. That means that people will tend to fly then.

It's a fact of planetary body movement that the length of the trips to/from Mars & Earth are going to be longer at certain times, and unfortunately only increased energy usage can overcome that. So just like some people plan travel seasonally here on Earth, I think the same think might end up being true with the "seasons" of travel between Mars & Earth.

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Space isn't an important element of the economy in the story. Indeed, the difficulty of making money out of Mars is one of the elements of the plot. The real reason why countries have Mars bases is as a bolt hole for the political leaders and the super-rich in the event that a planetary disaster befalls Earth.

If the rich are OK with being away from Earth, then it probably doesn't matter how long it takes to get to Earth.

However, they will want to travel in comfort, and zero-G is not comfortable for rich people, so I would assume that there would be rotating spacecraft that would be flying some sort of Mars cycler route, which then identifies what the transit times would be.

Best wishes on the book!
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline KelvinZero

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Re: How to fly to and from Mars to support permanent bases?
« Reply #7 on: 08/15/2017 10:40 PM »
btw, ITS can exploit SEP or nuclear fairly trivially by using pre-accelerated depots. Also ISRU could greatly reduce the mass launched from earth to LEO. Orbital SEP atmosphere gatherers are one interesting example.

So you could just have something similar to ITS with multiple refueling events. Sounds like you do not need to go into much detail. Also, maybe you launch from earth with 300 people packed like sardines, but then transfer 100 people each to 3 other ITS decked out for the longer trip. These don't land on earth but could be serviced on Mars.

There was also an idea to join ITS during the coasting phase and spin them for gravity. At the very least, the different vehicles would stay close enough to help their neighbour in an emergency.

Since you want budget problems, the fact you are still using this really old hardware could be part of the plot. The ships could be well beyond their intended life and dropping in number rather than growing. It could represent stagnation. The version you took to orbit could be shiny new, shuttling tourists to and from casinos in LEO, and then you transfer to these battered mars vehicles.
« Last Edit: 08/16/2017 12:00 PM by KelvinZero »

Offline anonymous

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Re: How to fly to and from Mars to support permanent bases?
« Reply #8 on: 08/15/2017 11:18 PM »
Spinning two cruising IPS-like ships on a tether was something I had planned originally, but you can't do that if you're using electric propulsion. When I'd convinced myself that solar-electric would probably be the cheapest technology, I changed the plan to a rotating torus for the passengers, but solar-electric created plot difficulties in terms of avoiding interception. I think the difficulty I'm having is that what I think would be most economic and the demands of the plot are pointing in different directions. Am I right or wrong to think that solar-electric will be the propulsion option with the lowest life-cycle costs?

Online Coastal Ron

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Re: How to fly to and from Mars to support permanent bases?
« Reply #9 on: 08/15/2017 11:57 PM »
Spinning two cruising IPS-like ships on a tether was something I had planned originally, but you can't do that if you're using electric propulsion.

You can't do that for many reasons, so please ignore such options.

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When I'd convinced myself that solar-electric would probably be the cheapest technology, I changed the plan to a rotating torus for the passengers, but solar-electric created plot difficulties in terms of avoiding interception.

Just like using solar panels on your car to power your trips would result in slow trips, so I would imagine would be the same with a solar-powered rotating space ship. The masses involved don't favor SEP.

Kim Stanley Robinson was very good with just touching lightly on describing the technology for his Mars trilogy, so maybe don't sweat the details. From the research I've been doing into rotating artificial gravity structures, saying something like a "habitable torus" should be fine, and then leave out the details for how the engines are attached and how everyone gets on or off of the vehicle.

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I think the difficulty I'm having is that what I think would be most economic and the demands of the plot are pointing in different directions. Am I right or wrong to think that solar-electric will be the propulsion option with the lowest life-cycle costs?

There are always trade-offs, and I think you are focusing on the wrong features. SEP may provide the lowest overall cost to use, but the speed and flexibility that it will provide would probably not be the best choice. Since you're talking about 100 years down the road, just say "nuclear power" and leave off the details - people will fill in the details in the minds.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Online savuporo

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Re: How to fly to and from Mars to support permanent bases?
« Reply #10 on: 08/15/2017 11:59 PM »
https://en.wikipedia.org/wiki/Spacecraft_propulsion#Table_of_methods

A few interesting ones like propulsive mass drivers, plenty of other things from there can be worked out in a 100y timeframe
Orion - the first and only manned not-too-deep-space craft

Offline lamontagne

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Re: How to fly to and from Mars to support permanent bases?
« Reply #11 on: 08/16/2017 11:20 AM »
How about slow SEP or NEP for cargo and rapid chemical for people?
Think sea ships and airplanes.  Not either or but complementary.
A vehicle on a fast aero braking orbit from Mars will be coming in at a few km per second until it hits the atmosphere. Essentially impossible to intercept, due to the trajectories.
There might be a transition going on to high power fast NEP with high energy density thrusters, or to fusion with a lot of propellant mass, if useful to the story.  But you would need high traffic to pay for the development of these, or a very dedicated mid sized country that decided to invest for some internal reason.

Offline gospacex

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Re: How to fly to and from Mars to support permanent bases?
« Reply #12 on: 08/16/2017 11:30 AM »
I did include cyclers in my story originally, but after reading about them more I went off the idea. They seem too inflexible and too easy to miss.

You can have as many cyclers as you want, in different orbits, even every week.

Offline philw1776

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Re: How to fly to and from Mars to support permanent bases?
« Reply #13 on: 08/23/2017 06:32 PM »
One hundred years from now?
First, start by thinking how people 100 years ago would envision transportation and technology today.
That should put you in the imaginative frame of mind.  Forget next 3-4 decades tech, like ITS family vehicles.  Forget messy NTRs with their inherent problems of long time re-use.

https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Fusion_Enabled_Pluto_Orbiter_and_Lander

At 100 years you should be firmly in the fusion camp*.  Who is going to prove you wrong?


* Guaranteed that assuming we really do continue with human space flight (not a given) this will look ludicrously unimaginative in 3 generations time.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline KelvinZero

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Re: How to fly to and from Mars to support permanent bases?
« Reply #14 on: 08/24/2017 09:48 AM »
One hundred years from now?
First, start by thinking how people 100 years ago would envision transportation and technology today.
That should put you in the imaginative frame of mind.  Forget next 3-4 decades tech, like ITS family vehicles.  Forget messy NTRs with their inherent problems of long time re-use.

https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Fusion_Enabled_Pluto_Orbiter_and_Lander

At 100 years you should be firmly in the fusion camp*.  Who is going to prove you wrong?
I don't think anyone would object to fusion in a hundred years. It is certainly very plausible.

On the other hand I would argue chemical is still pretty reasonable over that period.

* the 747 is about 50 years old and it takes about a decade to design a new aircraft, even without paradigm-changes.
* Spaceflight may not get as fast development as airplanes, and that is implied by this scenario.
* It does seem likely we will get fusion in that period, but there is also a good chance other options will have better power density, such as fission, or huge disks of thin-film solar power cells, spinning very slowly to hold them rigid.

Even after ITS becomes old, reliable technology, there are big improvements without radical technology that wont reset the clock on all that hard earnt reliability, such as the notoriously difficult mars landing.
* propellant depots in earth orbit, exploiting lunar ISRU, NEO ISRU or atmosphere scoops could get rid of refueling flights. (I think there were 2-4 of those?)
* Preaccelerating a depot and refueling the ITS one more time as it leaves earth orbit could at least halve your trip time.

Im just saying it is perfectly justifiable to stay pretty close to something like ITS too, if you want to, especially given this scenario where the mars presence is still just Antarctica research bases only. It is an option that allows being very hardsf, while also being lazy because you can just use something like that 12m ITS presentation for your stats.

Offline Oli

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Re: How to fly to and from Mars to support permanent bases?
« Reply #15 on: 08/28/2017 01:20 PM »
So what should I do? What kind of propulsion technology should I go for in my story? Chemical? Solar-electric? Chemical/solar-electric hybrid? Nuclear thermal? Nuclear-electric? Fusion? I'm sort of leaning towards a chemical/solar-electric hybrid, but I'm not at all sure.

I would go with MW-class NEP/SEP for all transfers, Argon refueling in Mars orbit.

Offline Ludus

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Re: How to fly to and from Mars to support permanent bases?
« Reply #16 on: 08/30/2017 01:25 AM »
The scenario stipulates that Mars only has scientific bases, something like Antarctica, not a million settlers so that sets requirements for what kind of transport system you have.

Is the rest of the solar system more settled and different or is humanity still only barely spacefaring? If Mars is set aside for some reason it's a different scenario than if a few Mars bases is the limit of what humanity has achieved.

If it's set aside, why? What's the backstory. If it's all we can do, why? What crippled efforts in the prior 100 years?

Offline anonymous

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Re: How to fly to and from Mars to support permanent bases?
« Reply #17 on: 09/01/2017 11:36 PM »
Thank you for your comments.

My thinking about space technology is rather influenced by the way that as a child in the late 1970s, I read a lot of science fiction involving Moon bases, Mars bases, etc. I read about how the Space Shuttle was going to transform spaceflight, about colonies in space and about about manned Mars mission studies. How much of that actually happened in the last forty years? It's not quite like The Who's "Won't Get Fooled Again", because I also remember that at the time more sensible people seemed to be thinking space station c. 1990, Moon base c. 2010 and Mars landing c. 2030. I knew even then that it was realistically all going to take a long time, but it's taking even longer than that.

The work on NTP for Mars was done 1955-1972 and then abandoned. The spaceship Discovery in 2001: A Space Odyssey was NEP. We're talking about nearly fifty years ago and those technologies are still far from reality.

I know the reason why it hasn't happened faster is really economic: it's all so expensive. Lowering launch costs with full reusability will (if it happens) get over the first economic hurdle, but there are a number of other hurdles. There's the difficulty of finding anything profitable to export from Mars or anywhere else in the solar system except possibly a platinum-rich NEO. There's the medical difficulties dealing with low gravity and radiation. I find it hard to believe in Elon Musk's Mars plans because of the economics and the human factors.

It's my science fiction story and I can do what I want in it, but that's the rationale.

In what I originally wrote, I was a bit facetious about fast transfers, but the reason for them is really about radiation exposure. Physical or magnetic shielding require so much mass that it's more cost-effective to try to travel as quickly as reasonably possible.

The story is set around a hundred years in the future because it takes place mostly on a space habitat based on the Kalpana One design, but smaller (3 rpm) orbiting Mars. I don't think that would happen so soon, but even with 3D printers it was as early as I thought it could be projected with any credibility.

Writing something set so far in the future is interesting because you have to allow for so many changes. After a period from 1970 until a few years ago, where technological innovation very much concentrated on computers, electronics and communications and everything else developed quite slowly, there's currently a push to make all sorts of science-fiction cliches actually come true. So of course they have full-dive virtual reality, state surveillance of thoughts, synthetic meat, synthetic recreational drugs, artificial wombs and ideas about gender and sexuality that are hopefully as much more liberal than today's as today's are than those of a hundred years ago.

The plot of the story really forces me to use chemical, NTP or fusion to travel between planets. Chemical is possible and it may well still be used a hundred years from now, but it does seem retro. I have an aversion to NTP, although that does seem to be NASA's latest thinking because it can be faster than chemical and involves less new technology development than similarly fast SEP or NEP. It seems even more retro than chemical, though. Fusion is the most futuristic option, but I forgot to mention another objection earlier: tritium and helium-3 are extremely expensive. Even if you had commercial fusion on Earth, they would be very expensive because of their use as an energy source. D-D fusion is much harder and p-B fusion is even harder than that. So I remain unsure. I'm thinking about following Coastal Ron's advice and just not saying anything about which propulsion technology is being used...
« Last Edit: 09/02/2017 10:35 AM by anonymous »

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