Practical propulsion methods for manned interplanetary travel

[crazyewok]

What about the main belt asteroid mission?

Pointless IMO without the nuclear option.

Beyond mars its a case of go nuclear or go home.

NERVA would get us to the astroids but again that's nuclear.

Chems wont cut it.

What about building ships on mars? Or the moon? The pesky political and enviromental issues wont be so much of a problem?

Mars chems yeah it will work. But I don't see us getting further than mars. Not with manned missions.

[mdatspace]

snip

I weighed down nuclear so other options could shine. Nuclear propulsion is a very good idea. But we need to innovate rather than saying "Nuclear or nothing." What challenge is there when the easiest choice is right in front of you? You could launch NTR into space and use it. I got rid of some crazier proposals by adding environmental and political restrictions.

I think chemical rockets can be used for further out than Mars, however.

[crazyewok]

I think chemical rockets can be used for further out than Mars, however.

We would be talking mission time of 5+ years though. That could be erm uncomfortable and not very healthy. Plus chemical propellents give quite a low energy yield its pretty inefficient. Just to take enough fuel could prove a issue.

Thing is it all comes down to energy. Im not sure innovate a none nuclear option as even things like VASMIR ect would need a huge energy source to be effective and I cant see anything other than a nuclear reactor doing the job. Unless you build giangantic solar panels and that would come with it own problems, like huge cost and fragile nature.

[mdatspace]

Snip

Chemical can go further than mars. New Horizons used mono-propellant and gravity assists to get to where it is now. Pioneer 11 used mono-propellant and gravity assists, too.

[Top8]

I think it isn't just a matter of what propulsion to use. It is a systems approch that matters. For example, a robotically constructed lunar mass driver could supply raw materials to missions further out - a major mass savings. In such a mission we'd need to examine what kinds of materials could be sent. A range of chemicals could be refined from regolith. Maybe we could even make aluminium oxygen boosters and launch them out. All robotic, all small continuous payloads that accrue supplies.

Mars sourced chems could be very useful for getting to and from the martian surface. Maybe they aren't the sole answer but again you'd use automated missions to produce all of this. Building everything into one giant ship is pretty inefficient anyway. Not suggesting any modern plan would do that but "mothership" concepts do pop up from time to time.

The disadvatnage of missions like this is complexity but if there are a few failures all thats lost is robots. Overall the mission has high redudnacy and is flexible. A major upside all this capacity could be engineered to keep working - and put an actual infrastructure up.

Edited January 28, 2014 by Top8

[crazyewok]

Chemical can go further than mars. New Horizons used mono-propellant and gravity assists to get to where it is now. Pioneer 11 used mono-propellant and gravity assists, too.

That's fair enough but you gotta get those launch windows right. Possible but practical for human spaceflight?

[Soda Popinski]

We would be talking mission time of 5+ years though. That could be erm uncomfortable and not very healthy. Plus chemical propellents give quite a low energy yield its pretty inefficient. Just to take enough fuel could prove a issue.

Not true. The Mars Reference Architecture 5, I mentioned, has the same mission duration time (for the crew) for either nuclear or chemical. The difference being, the nuclear option only requires 7 launches, while the chemical option requires 12. Also the chemical option will require aerocapture.

The plan is to assemble a robotic ship in orbit, send that to Mars. It'll have the Lander (SHAB) that will stay in orbit, and a descent/ascent vehicle (DAV) which will land, and start producing oxygen (for breathing and oxidizer) and water from the atmosphere (liquid methane fuel will be brought from earth). Later the crew will be sent on a 200 day trip to Mars, rendezvous with the SHAB in orbit, and land on the surface. After 18 months or so on the surface, they launch in the DAV to their orbiting Mars Transit Vehicle, and head back.

Edited January 28, 2014 by Soda Popinski

[mdatspace]

snip

A mission to the asteroid belt could use depots at mars. ISRU is a way for chemical rockets to be viable for interplanetary missions going past mars. Land on the asteroids and use resources. Ceres has ice. That can be used for water, oxygen and rocket fuel.

That's fair enough but you gotta get those launch windows right. Possible but practical for human spaceflight?

Yes. Set up a temporary fuel depot in Mars orbit. The ship will dock with the depot,fill up and get to the target asteroid.

You would use launch windows, but with depots it would be less of a concern.

Edited January 28, 2014 by mdatspace

[crazyewok]

Yes. Set up a temporary fuel depot in Mars orbit. The ship will dock with the depot,fill up and get to the target asteroid.

You would use launch windows, but with depots it would be less of a concern.

Your looking at a extremely expensive way of doing it though!

[mdatspace]

Your looking at a extremely expensive way of doing it though!

It is expensive. Remember, you can utilize the resources of the objects you are landing on.

But there is a lot less development cost involved. You do not need to develop new engines. You do not need to dispose of said engines. And, it has no political problems.

[crazyewok]

It is expensive. Remember, you can utilize the resources of the objects you are landing on.

But there is a lot less development cost involved. You do not need to develop new engines. You do not need to dispose of said engines. And, it has no political problems.

It would likely be cheaper and more sustainable though to set up shipyards on the moon or mars. That way you can build what you like free of enivriomental or political issues and a with a much easier launch base due to less gravity. That my opinion though. I guess there likely wouldn't be much in it expense wise short term but with the moon and mars shipyards they have a cheap way to get craft home from coloneys and the craft home can be conventional to avoid environmental and political issues.

[mdatspace]

It would likely be cheaper and more sustainable though to set up shipyards on the moon or mars. That way you can build what you like free of enivriomental or political issues and a with a much easier launch base due to less gravity. That my opinion though. I guess there likely wouldn't be much in it expense wise short term but with the moon and mars shipyards they have a cheap way to get craft home from coloneys and the craft home can be conventional to avoid environmental and political issues.

Why not assemble the ship in LEO? Set up resource extraction on the Moon or Mars.

[Kryten]

It would likely be cheaper and more sustainable though to set up shipyards on the moon or mars.

Setting up an industrial base on mars sufficient to produce spacecraft is going to be cheaper than just sending fuel to the same distance? Seriously?

[crazyewok]

Why not assemble the ship in LEO? Set up resource extraction on the Moon or Mars.

Could do but LEO you still have political and Enviromental problems, on mars or moon? Can do what you like. Plus on the mars and moon you have a lower gravity which means launching easier so if you can mine stuff on the moon or mars it could be a lot easier to build and send ships up rather than send stuff up from earth as if you build stuff in LEO from stuff made on earth you still have the earth to LEO expense.

[crazyewok]

Setting up an industrial base on mars sufficient to produce spacecraft is going to be cheaper than just sending fuel to the same distance? Seriously?

Well they are looking into 3D printing applications for that very use.

http://www.washingtonpost.com/blogs/innovations/wp/2013/06/27/get-ready-3d-printing-may-be-coming-to-a-planet-near-you/

In 2038? which the op has set who know how far 3D printing will have developed?

Its a technology that could have some revolutionary applications. And it seems a lot of the space agency think so too.

Plus it would have a two fold goal. If you have say a colony (unlikely I know) a way for a colony to produce and launch there own ships would be cheaper then sending ships there and back from earth.

[mdatspace]

snip

Like Kryten said, just refueling the ship would be easier than building the whole craft there. It is harder to send payloads to the moon and mars compared to LEO, and you are sending the materials needed to construct the ship. You need to supply that shipyard and its workers. It is essentially a colony.

You need to launch a ship up there for assembly, which is expensive. Why not build the ship on earth and launch it? Resource extraction is a better reason to have a colony than construction. A fuel depot makes the reasoning behind a shipyard moot. You can just refuel the ship rather than launch it from there.

Edited January 28, 2014 by mdatspace

[Top8]

Setting up an industrial base on mars sufficient to produce spacecraft is going to be cheaper than just sending fuel to the same distance? Seriously?

Depends on definitions of cost and the mission profile. Fixed costs are certainly raised while setting up the industrial base (capital investment). Then again, if the industrial base is useful in and of itself you have to factor in return on investment. Variable costs with an industrial based are almost certainly low - perhaps extremely low - realtive to lifting everything out of Earth orbit.

[sgt_flyer]

Well, industrial grade 3d printing of rocket equipment is already avaible here on earth - that's what they plan to use to recreate the F-1 engine for the sls block II pyrios booster, by using the Selective laser melting in order to reduce the number of parts from 5000 to under 100 parts. (Basically, parts made with this technique are 'weaker' as a whole, but they don't have weak spots in the weldings (no weldings needed with this technique, as they can produce complex parts)

[crazyewok]

It is harder to send payloads to the moon and mars compared to LEO, and you are sending the materials needed to construct the ship.

Depends on the state of 3D printing in 2038 and if it easier to use the resources on site rather than ship them from earth. A lot could change in 24 years, look at computers! Or nothing could change..... Though with the leaps and bounds the technology in 3D printing has made in a few short years I can see progression carrying on.

Why not build the ship on earth and launch it?

Well as I already stated your free from political and environmental problems on mars or the moon so you have a lot of leeway on propulsion methods and energy production.

[mdatspace]

snip

You still have to develop the engines you send there. The colony could be controlled by a certain nation, so the politicians still control what goes. That applies even if the colony is an international effort.

There is simply no reason to build a whole shipyard and colony there. The base could be used for the production of fuel and oxidizer from resource extraction. That could fuel ships on their way.

But that is not a way around restrictions on propulsion.

Edited January 28, 2014 by mdatspace

[crazyewok]

You still have to use chemical.

Well if the only awnser is chemical then there is no debate If that the only way you allow well that's it then

[mdatspace]

Well if the only awnser is chemical then there is no debate If that the only way you allow well that's it then

When did I say you were not allowed to use anything other then chemical engines? Quite a misrepresentation.

Building a shipyard on the Moon or Mars just because you can supposedly bypass restrictions on propulsion systems does not justify the costs compared to just sticking with chemical engines and using fuel depots. This is what I think.

This thread has gone off topic.

Edited January 28, 2014 by mdatspace

[crazyewok]

When did I say you were not allowed to use anything other then chemical engines? Quite a misrepresentation.

Building a shipyard on the Moon or Mars just because you can supposedly bypass restrictions on propulsion systems does not justify the costs compared to just sticking with chemical engines and using fuel depots. This is what I think.

This thread has gone off topic.

Well im not sure if you can use anything other than chemical under your restrictions.

Though you could use a aldrin cycler for the mars part, that just useses gravity assist. But useless beyond mars.

[Nuke]

MPD Thrusters.

They have a crazy high specific impulse and a potential thrust of up to 200N

Here's the result from a Russian prototype test:

Organization Power (kW) Current (kA) Speciï¬Âc Imp. (s) Efï¬Âciency (%)

NIITP 300–1000 6–15 3500–5000 40–60

As for the power source, LFTRs (Liquid-Flouride Thorium Reactors), They're more compact (and much more flexible in size), more efficient and safer than conventional nuclear reactors, they also produce (MUCH) less waste.

Well, getting to mars in say, 2 weeks, assuming going in a straight line and closest approach, you'd need to go about 48 km/s on average, that's (very) roughly 80 km/s of deltaV needed ( given that we're not startin from nor ending at 0 m/s velocities).

And i'm neglecting a lot of details increasing this number, like the fact that you'd have to go above the 48 km/s to compensate for time needed to accelerate and decelerate, gravity (although that works both ways) and more.

Given, i'm also neglecting factors reducing that number, like gravity(again), aero breaking, slingshot maneauvers etc.

Point being: I think a trip to mars lasting only days, is very far off

mpd is pretty effective. but they are power hungry, you need a 1MW reactor minimum. molten salt reactors (the ones we tested in the 50s for aircraft reactor experiments) are pretty compact and have been operated before. lftr on the other hand hasn't even been made to work on the ground yet. we also dont have a very long track record for running space capable reactors. there have been a few, but never has one operated at 1MW (the russian reactor did 3kw). these reactors were liquid metal cooled, so i can imagine it shouldn't be to hard to get a molten salt reactor (not lftr) to work in space right now. the real problem isnt the reactor itself those are well understood. the problem has always been its hard to convert heat to electricity in space. obvious way is to use the reactor as the hot side of a brayton cycle, and a radiator as the cold side. you need really large radiators, but it can work (the down side is your space ship gets heavy). there are also thermionic converters, which were actually used in the russian space reactors, but these converters have horrible efficiency (5-20%). you can make it work but it wont be pretty.

polywells would be nice if they work. you could get a theoretical 100gw out of a polywell, and thats doing direct conversion on the p-b11 reaction. so you could run large mpd thrusters off of that (well beyond the theoretical designs we have now, so potentially enough thrust for a moon launch). its also small enough to stick the polywell (sans the heavy vacuum system you dont really need in space) on a rocket and launch to space. problem then comes how do you start the thing when you are not on the power grid anymore. there are other small reactors, like dpf, and the thing being worked on at the skunkworks that would fit on a rocket. you will never see a tokamak on a space ship, they are just too freaking heavy. this is years down the pipe if we have to wait for fusion. we could do it now on nuclear but we would have to overthrow all the governments first.

[mdatspace]

Well im not sure if you can use anything other than chemical under your restrictions.

Though you could use a aldrin cycler for the mars part, that just useses gravity assist. But useless beyond mars.

The restrictions are real. The populace thinks of Chernobyl and Fukushima when they hear the word nuclear. You know who politicians represent.