Realistic Timescales for Travel within the Solar System

[eltoddi]

First things first: Happy New Year to everybody!

I have got a few questions regarding travel throughout the solar system within realistic timescales. Unfortunately I am not versed in orbital mechanics, and before I embark on months of possibly futile study I am hopeful that some of the bright people on this forum may be able to offer some advice on the following:

1) Using ‘realistic’ near term propulsion technologies (thermal nuclear rockets maybe? Suggestions would be welcome here as well), what would be the approximate travelling timescales for manned missions to the asteroid belt and the Jovian system beyond (specifically Europa)? The relative positions of Earth and the destination obviously introduce variations here, but can anyone give an approximate figure?

2) Jupiter’s gravity appears to make a return from the system back to Earth difficult. Could this problem be overcome using said propulsion technologies, or is this a show stopper for sample return or manned missions? (Assuming the radiation problem could be dealt with).

3) For long duration manned missions, extended exposure to microgravity will be detrimental to the crew’s health. As an alternative to the ‘spinning' of modules to create artificial gravity, would it be feasible to have the vessel accelerate at 1g (or thereabouts) for half the journey, the decelerate at 1g for the remainder? I guess a problem would be fuel and energy for continuous engine firing, but if these problems could be solved (nuclear or fusion power plants?), does anything speak against the concept?

I would be really grateful for some input on this, even if it is only point to some blatantly obvious thinking errors I have made. I am not afraid of equations either, if someone would like to suggest a few analytical means of getting to what am after.

Thanks in advance, I hope some lively discussion will ensue…

Thor

[ozark1]

First things first: Happy New Year to everybody!

I have got a few questions regarding travel throughout the solar system within realistic timescales. Unfortunately I am not versed in orbital mechanics, and before I embark on months of possibly futile study I am hopeful that some of the bright people on this forum may be able to offer some advice on the following:

1) Using ‘realistic’ near term propulsion technologies (thermal nuclear rockets maybe? Suggestions would be welcome here as well), what would be the approximate travelling timescales for manned missions to the asteroid belt and the Jovian system beyond (specifically Europa)? The relative positions of Earth and the destination obviously introduce variations here, but can anyone give an approximate figure?

There was a programme on BBC last year. A practical mission with a fully developed Prometheus type engine would take around 2 years to get to Jupiter, 4 years to Pluto.


2) Jupiter’s gravity appears to make a return from the system back to Earth difficult. Could this problem be overcome using said propulsion technologies, or is this a show stopper for sample return or manned missions? (Assuming the radiation problem could be dealt with).

Just need enough fuel/specific impulse


3) For long duration manned missions, extended exposure to microgravity will be detrimental to the crew’s health. As an alternative to the ‘spinning' of modules to create artificial gravity, would it be feasible to have the vessel accelerate at 1g (or thereabouts) for half the journey, the decelerate at 1g for the remainder? I guess a problem would be fuel and energy for continuous engine firing, but if these problems could be solved (nuclear or fusion power plants?), does anything speak against the concept?

Actually radiation would be the bigger problem. Long stays have been tried on Skylab/Salyut/Mir/ISS with no lasting issues.

1g acceleration would be a great trick - runs out of fuel real quick. However if you could do it - 4 years to the nearest star, 20 years to the galactic core, 25 years to M31 (relativity of course).

I would be really grateful for some input on this, even if it is only point to some blatantly obvious thinking errors I have made. I am not afraid of equations either, if someone would like to suggest a few analytical means of getting to what am after.

Thanks in advance, I hope some lively discussion will ensue…

Thor[/QUOTE]

[Dr Nigel]

The problems as I see them are:

Reaction mass. The quicker you want to travel, the more you have to carry with you out of low Earth orbit.

Radiation. While near Jupiter in particular, but also during solar flares or coronal mass ejections, you would need to shield your intrepid travellers against a high flux of energetic particles (mostly protons and electrons, I believe). This would require several cms of aluminium (or aluminum) but is not all that difficult. It just adds to the weight you have to drag around with you.

Osteoporosis (and other symptoms of prolonged exposure to microgravity). Setting part of the spacecraft spinning is a good principle, but there seem to be several problems with the execution. First, if you spin only part of the spacecraft in one direction (or all of it), you will need to compensate for the gyroscopic effect. You could avoid this by having two parts spinning in opposite directions. Second, if your spacecraft is a modest size, you will get quite steep gradients in the strength of the centrifugal force. You could overcome this by making the rotating parts of your vessel quite large - this would allow you to reduce the rotation speed and also reduce the steepness of the gradient in centrifugal force. Third, anyone who looks out of the window will become disoriented and probably nauseous (although you would need to have a section that remains in freefall, and this could be kept stable relative to the sun and stars). Fourth, while this would require the travellers to work in freefall at times (unless they stay in one of the rotating sections the whole time), they would not become accustomed to freefall and would probably become repeatedly space-sick. Fifth, the bearings upon which all this rotation took place would need to be (a) strong; (b) smooth; (c) reliable; and (d) airtight. This is quite a serious engineering challenge.

Otherwise, it should be eminently feasible.

[eltoddi]

Thanks for the replies so far, that's already a great help.

Regarding the effects of long term exposure to microgravity, I attended a presentation by the Head of the German Institute for (Space)Flight Medicine a couple of months ago, where he mentioned a new branch of research being investigated to combat osteroporosis in astronauts. My recollection of the details is somewhat patchy, but the approach seems to be based on enzymes that may be able to slow or even completely hold the loss of bone mass. That would of course have not only major implications for spaceflight, but for millions of sufferers on Earth as well.

Who knows, eventually there may be drugs that, coupled with exercise, will allow long term expose to weightlessness at least in this respect.

As to the radiation protection, how good is water in stopping hard radiation? John S. Lewis gives a little story in his book 'Mining the Sky' where a mining vessle docks at an asteroid and 'refuels' by tanking up water there, which is then subsequently used as fuel for a nuclear rocket engine. Assuming that would work, could you build the tank around the crew compartments to act as radiation protection? One would have to ensure a minimum water level to provide minimum protection levels, but if you go the water route that might be a way to kill two bird with one stone, so to speak.

Again, just throwing ideas around here, go ahead and shoot me down if this is just nonsense...

[eburacum45]

For what it's worth, I made a model of an antimatter driven ship with an array of Penning traps and large radiators; it is a little different to the I-CAN ship, but I find that design very inspiring.
Here it is in Youtube (http://www.youtube.com/watch?v=4o2Ag-TTvpI)

[Ilya]

1) Using ‘realistic’ near term propulsion technologies (thermal nuclear rockets maybe? Suggestions would be welcome here as well), what would be the approximate travelling timescales for manned missions to the asteroid belt and the Jovian system beyond (specifically Europa)? The relative positions of Earth and the destination obviously introduce variations here, but can anyone give an approximate figure?
There was a programme on BBC last year. A practical mission with a fully developed Prometheus type engine would take around 2 years to get to Jupiter, 4 years to Pluto.
What's your definition of "realistic" and "near term"? I'd be amazed if Prometheus-type engine were fully developed and operational before 2045 or so. Also, I'd like to see that BBC programme, because 4 years to Pluto seems to me awfully fast even with Prometheus. 2 years to Jupiter is realistic, though.

[schlaugh]

Also, I'd like to see that BBC programme, because 4 years to Pluto seems to me awfully fast even with Prometheus. 2 years to Jupiter is realistic, though.

Yes, New Horizons was Launched January 19, 2006 and is on track for a Jupiter gravity assist next month on February 28 - slightly more than 13 months after launch.

Ozark1 wrote that "1g acceleration would be a great trick...4 years to the nearest star, 20 years to the galactic core, 25 years to M31 (relativity of course)." True, but it would take more than 4 Earth years to reach the A. Centauri system because even at a steady 1 G acceleration it will take some time to reach lightspeed, and when you reach the system you wouldn't be able to stop. Conversely if you accelerate at 1G for half the trip and then flip over and decelerate for the other half it will take you even longer to reach your destination. See this link for a discussion:


http://www.daviddarling.info/encyclopedia/O/one-g_spacecraft.html


A pretty interesting work of fiction on this method of stellar transport was Robert Heinlein's Time for the Stars in which telepathic twins are used as instantaneous communication "devices" between the ships and Earth. A good read for kids and adults, even if dated.

[eltoddi]

What's your definition of "realistic" and "near term"?

Basically I am trying to project a realistic timeframe to show just how far and fast humans could expand through the solar system, based on technologies that conform to today's understanding of physics (so excluding stuff like hyperspace, impulse and warp drives, etc...), even if they don't exist in any usable form today. Near term I would call within the next few centuries or so, no rush.

One of the main questions would be whether things like industrial exploitation of NEOs, Asteroid Belt objects and/or planetary bodies (planets and moons) is practical when the distances and travel times involved are considered. Or to put it another way: How good does propulsion and life support technology have to be to make it feasible and profitable?

I did see the BBC programme last year, it was pretty interesting but cannot remember many of the specifics. I think they went for chemical rockets, not some more futuristic propulsion technology.

As for the 1g ship, looks like the raction mass problem will be the biggest spanner in the works, so that a quick trip to the asteroid belt and back in the order of weeks or a couple of months probably won't be happening anytime soon.

[Romanus]

<<1) Using ‘realistic’ near term propulsion technologies (thermal nuclear rockets maybe? Suggestions would be welcome here as well), what would be the approximate travelling timescales for manned missions to the asteroid belt and the Jovian system beyond (specifically Europa)? The relative positions of Earth and the destination obviously introduce variations here, but can anyone give an approximate figure?>>

The best-case scenarios I've seen for NTP deliver impulses twice as high as possible with chemical rockets. I'm no rocket scientist, but if the impulse is directly proportional to the thrust, I'm guessing we could expect the best current travel times to be halved--that is, ignoring the cost of weight, or the fact that you're not going to want to get to where you're going too fast if doing so is costly. For instance, suppose NTP could halve the travel time to Jupiter to ~7 months (roughly half that of New Horizons). For a flyby, this would be great, but for an orbital mission, one would want to go much slower to ease orbital insertion.

In short, I think that a one-year travel time to Jupiter is probable for NTP.

[eburacum45]

One solution to the problem of rotating accomodation in spaceships requires few moving parts or bearings;
http://www.grc.nasa.gov/WWW/RT/2004/PB/PBM-mcguire.html
as can be seen in the graphic, the whole ship rotates longitudinally.

[Ronald Brak]

One of the main questions would be whether things like industrial exploitation of NEOs, Asteroid Belt objects and/or planetary bodies (planets and moons) is practical when the distances and travel times involved are considered. Or to put it another way: How good does propulsion and life support technology have to be to make it feasible and profitable?

If you mean mining and manufacturing things in space and then transporting them to earth, I don't think it will ever be economically feasible for as improved technology lowers the cost of space travel it will also lower the cost of extracting and recycling resources on earth. Of course extracting resources in space for use in space is very different and pretty much necessary for an extensive human or robotic presence in space.

[eltoddi]

If you mean mining and manufacturing things in space and then transporting them to earth, I don't think it will ever be economically feasible for as improved technology lowers the cost of space travel it will also lower the cost of extracting and recycling resources on earth. Of course extracting resources in space for use in space is very different and pretty much necessary for an extensive human or robotic presence in space.

I was thinking of a self-sustained space economy that does not heavily rely on resources being lifted out of Earth's gravity well, to extend human presence in space as you said. The option of returning resources back to Earth may never be economical, but maybe one day it may become preferrable to ruining the planet.

Eburacum45, thanks for the link, that looks pretty interesting!

Romanus, thanks as well, your post has given me the rough timescale I was after in the first place. I shall look into NTP more closely I think...