Interplanetary supply infrastructure - Cyclers vs. one way capsules

RobS · 2005-05-08 08:30:36

Whatever transport system you use, the big trick will be making sure the cargo is available when it is needed. People will arrive on Mars over a several month window--at most--every twenty-six months. When 100 or 1000 new people arrive, their life support equipment, housing, vehicles, and work equipment have to be ready. With solar sailers, you have to send the stuff from Earth close to a year before the people leave. With chemical rockets on hohman transfer trajectories, you have to send the cargo just a month or so before the people, which is logistically more complicated.

-- RobS

Fledi · 2005-05-10 15:15:47

Hmm haven't thought about the return problem of solar sails yet, but it looks like you're right, Martian Republic. Too bad it's not like with normakl ship sails where you can sail against the wind to some degree.
In this case sails would be only a one way design and I don't know if it would be worth all the work to deploy one. Maybe only if it proves to be really easy to do.
In the case of cyclers it might be more affordable to give a bigger ship some advanced nuclear engines and accelerate/deccelerate the whole thing. Would certainly be easier to maintain our star cruiser in low earth orbit.
For cargo transports I'm still for using a tether to accelerate them to an Earth -> Mars Hohmann trajectory (or somewhat faster to give them a wider launch window).

RobS · 2005-05-10 22:59:28

No no no, solar sails have nothing to do with the solar wind, and yes yes yes, they can return to Earth. Remember that planets move around the sun at right angles to the sun and to the photons flying outward from the sun. When flying around the sun at Earth distance, you are moving 66,000 miles per hour (about 107,000 km/hr) around the sun at right angles to it. If you want to move outward, you angle your sail to reflect the photons back toward the sun and "behind" you, thereby pushing you forward and making you move around the sun FASTER. This causes the ship to spiral outward into a larger orbit. Or, if you want to go to Venus, you angle your sail to bounce the sunlight back toward the sun and "in front" of you, thereby slowing down your speed around the sun and causing your spacecraft to drop into a lower, smaller orbit.

You can use sails to go anywhere in the solar system, but it will take time, especially as you head outward. Heading inward isn't so bad. It takes a lot of delta-v to go to Mercury and go into orbit around it, but the sun is much brighter in precisely the same amount as the gravity is stronger, because both light and gravity decrease by the inverse square law.

-- RobS

Fledi · 2005-05-11 06:11:42

That's what I thought first, too, when I read the posting.
But unfortunately, if you divert a stream of photons by let's say 90 degrees, so that the diverted stream points in the direction of your spacecraft's velocity vector, you get an impulse that decreases the speed along the actual orbital path, but also increases your speed outward from the sun.
So in the end I guess the best thing you can achieve is to change the orbit's shape, but not decrease orbital energy.

Austin Stanley · 2005-05-12 19:35:59

I wonder if it will ever be practical to utilise high-thrust high-impulse engines such as fusion, VASMIR, GCRN ect... to radicaly reduce transit times or to increase the launch window. While it is certianly desirable to decrease the amount of time people spend in zero G, the payload penalty you have to pay for this is high. In some cases it may outweigh the reduced amount of consumables/life support system equipment you would have to bring for a regular hohmann transfer. As long as cost of transporting equipment/propelant to orbit remains a signifigant part of transport cost these methods may not make any sense even for human transport.

--------

Now I am not an expert on orbital mechanics, but men much smarter than I have said that a solar sail can be used for trips both into and out of the solar system. Here is a paper by Eric Drexler, while I think he is an idiot when it comes to most of his talks about nanotechnology but he is dead on in this paper on solar sails. http://www.aeiveos.com/~bradbury/Author … .html]Link is Here.

------

As to the logistics time table, I think solar sails will actualy have an advantage here. While it may take there cargo longer to arrive, I think that the logistic bottle neck will likely be getting the cargo into earth orbit in the first place. Here solar sails have are advantageous as they can be launched all year long and can be scaled to meet any cargo size.

Fledi · 2005-05-13 03:10:41

Just looked up the chapter about solar sails of another space book. Looks like I was wrong with that guess before. As I reflect on it the fact that the resulting impulse vektor depends on the angle by which the stream is diverted is an indication of it being possible to deccelerate.
They give a system of differential equations to calculate the orbital motion of the sail. Since I'm not quite up to solve them at the moment, I'll just believe that the articles are right and I'm wrong

Hop · 2005-05-13 18:09:24

Just looked up the chapter about solar sails of another space book. Looks like I was wrong with that guess before. As I reflect on it the fact that the resulting impulse vektor depends on the angle by which the stream is diverted is an indication of it being possible to deccelerate.
They give a system of differential equations to calculate the orbital motion of the sail. Since I'm not quite up to solve them at the moment, I'll just believe that the articles are right and I'm wrong

Sounds like an interesting book. Could you give name and author or maybe an Amazon link?

Austin Stanley · 2005-05-14 00:24:10

Yeah, I was wondering the exact same thing. Sounds like something I would be intrested in.

Fledi · 2005-05-14 07:53:16

Ok, actually it's the script for Space Systems Engineering.
The long version I have here with lot's of explanation text and some extra stuff like solar sails is only aviable directly from the university, as far as I know.
But they're putting a shorter script+exercizes back up on the net as the year progresses. You can download that http://www.irs.uni-stuttgart.de/lehre/v … .html]here
but unfortunately it's all in German.
I can still post the equations for the solar sail here, if you wish, though.

Fledi · 2005-05-14 08:15:57

Found an interesting site on the net that seems to have most of the subjects from the script in English.
http://www.braeunig.us/space/]link

New Mars Forums

Announcement

#26 2005-05-08 08:30:36

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#27 2005-05-10 15:15:47

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#28 2005-05-10 22:59:28

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#29 2005-05-11 06:11:42

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#30 2005-05-12 19:35:59

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#31 2005-05-13 03:10:41

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#32 2005-05-13 18:09:24

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#33 2005-05-14 00:24:10

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#34 2005-05-14 07:53:16

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

#35 2005-05-14 08:15:57

Re: Interplanetary supply infrastructure - Cyclers vs. one way capsules

Board footer