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#401 Re: Human missions » Hubble mistake - Action needed » 2004-12-09 15:01:37

I always like the orginal plan which was (I thought) to send the shuttle up to retrive the thing and put it up in the Smithsonian museum.  Sure it doesn't make economic sence, but it would be nice to have such a historic peice of space history preserved for all to see.

#402 Re: Human missions » International Cooperation-Not Worth The Effort? - Don't Think it is » 2004-12-09 14:58:15

International cooperation that furthers a nation's mission can be desireable. Tailoring the mission to attract international partners is folly.

I agree with this statement.  Take for example the shuttle, which was a US only program, but one that accepted international cooperation (such as the Candian arm) to further it's objective.  International cargos and expirments launched on the shuttle have also been succesfull, they expand and compliment the shuttle's mission (even if that mission was only to justify another shuttle flight).

On the hand take the ISS which is was tailored to the needs and requirments of other nations, to the extent of changing it's orbit so that the Russians could reach it.  It has been full of delay's and cost-overuns.  Making a mission dependant upon international partners for it's success is foolish.  If one of the partners fails, the plan fails.  On the other hand with only one nation pushing the scheme, failures can easily be taken in stride and the plan re-designed to work around them.

I would build a Mar's mission on the same basis that the Shuttle opperated on.  Open to international coperation to extend and augment it's mission, but not dependant upon them for success.  A mars program is going to be very big, there is pleanty of place for international partners to add to and augment it.  Just so long as a single nation with the will to actualy do it all controls it.

#403 Re: Human missions » Food drops to Mars Scientists - or: I am too lazy to plow the back forty » 2004-12-09 14:43:04

Radiation in space is no where near the levels necessary to damage food enrout.  It's dead after all, so any changes that ionizing radiation might cause to it's make-up are so minor as to be completely ignorable (and probably not even detectable).  It's not like it is going become radioactive or something.  In fact space can be an excelent enviroment for preserving food.  It's very cold in the shade, and exposure to vacume to leathal to most micro-organisims, and the radiation (which is harmless to the inert food) also helps to santize the rations.

But food is actualy a fairly minor part of the consumable requiments for a manned base, although one of the most complex.  I am most worried about nitrogen.  While it is not consumed in great amounts by any specific process on mars (plants and some bacteria consume a minor amount) it is a very necessary part of the hab-atmosphere, and some will be doubless be lost due to leakage and whatnot and there is no easy way to replace this lost gas.

#404 Re: Human missions » Effects of impacts on Mars as Landing Site - or: Mad Science 101 » 2004-12-07 16:29:16

I disagree.  If the asteriod in question is a so called "rubble pile" then a nuclear weapon because an even better solution.  Shatering the asteriod into many small peices is an ideal outcome.  Many of the peices will be thrown much farther than the entire asteriod would have been, perhaps causing them to miss the earth entirely.  Many of the other peices will be fragments to small to cause signifigant damage after re-entery.  Any remaining large fragments may be a problem, but these can be targeted by follow up bombs.  But even for these fragments the situation has been improved greatly, as they are much smaller and there path has already been diverted somewhat.

The whole nuclear weapon scheem has another thing going for it.  It could actualy work!  I find it very hard to belive that we are going to be capable of landing very large engines capable of extracting fuel from an asteriod and then burining it for hundreads to thousands of hours.  Simply to much can go wrong with such a plan.  And delivering such huge amounts of cargo to a destination in the outer solarsystem is very difficult as well.

#405 Re: Human missions » Turning Mars regolith into soil - or How can I grow potatoes on Mars » 2004-12-07 16:12:58

I wouldn't dismiss the problem of nitrogen so casualy.  Sure you can liquidate some of it from the air, but at only 2% concentration in Mar's thin atmosphere this is going to take alot of energy and some realitivly bulky/heavy equipment to get a decent output. On earth it idealy takes about 760kJ/kg to cool, compress, and liquify nitrogen, but given the inefficency of cooling and compression equipment the actualy energy requirments are likely twice as great.  On mars the atmosphere is colder, which helps but the atmosphere is so much thinner that the energy requirments are likely signifigantly greater. 

Luckily the seperation of CO2, Water, Argon, and O2 is not a very energy intensive process.  The water, CO2 and Argon will all liquify before the nitrogen, and are easily removed, while the Oxygen will still be a gas (although since you got it this far it makes sence to finish condenssing it as well).  Aditionaly argon is about 2.5 times as water soluble then Nitrogen so a good amount of it will be removed with the water.  Additionaly you could probably use all the waste heat you got from the cooling to power your Haber process.  You would need to find additional water to make the ammonia with however, as you won't liquidate enough out of the atmosphere.

It's all pretty difficult though.  I wonder if you couldn't just mine some nitrogen rich soil, although I'm not sure where you would find such.  Some of the salt in the soil likely contains cyanide (-CN) which could be a potential source.

#406 Re: Human missions » Effects of impacts on Mars as Landing Site - or: Mad Science 101 » 2004-12-06 19:12:14

As cool as Nadia's crashing phobos (or was it deminos?) into Mars was in the KSR trio, it's a cataclysmic waste of wonderfuly positioned resources.  Plus, I wouldn't be so certian that it would be a harmless experiment.  The KE of such an impact is huge, not only is there the danager of the heat and shock from the explosion (generaly a closerange phenomonon), but it will also throw tons of rock and dirt all about the planet, which could potentialy damage any one on the planet.  It would be cool though, and a neat chance to study such an impact.  But if that is what you realy want to do, it would probably be better to use something in orbit around the sun, who's orbit crosses that of mars, be it a comet, asteroid or whatever.  Changing the orbit of many of these to intersect that of Mars often takes supprisingly small amounts of energy.

As for the means of actualy changing the orbit of an asteriod, Zubrin and many-others have disregarded the use of nuclear weapons in favor gigantic engines or various types (NTR and Mass drivers mainly), which would get there fuel from the asteroid.  I think this approach is incorrect.  These huge engines will require burns of extream length, hundreads if not thousands  of hours, causing reliablity problems.  There is also the issue of gathering the massive amounts of fuel that would be necessary to power these engines.  Even if you get it "for free" on the asteroid/comet mining and processing hundreads of tons of material is no simple task.  You also have to worry about the direction your engines are facing, especialy since you will be changing the center of gravity of the rock as you throw huge chunks of away as propulsion.  This requires extra engines to ensure stability.  These and a many other little problems make such a method incredibly complicated, and unreliable.  Human presence will almost certianly be required and many, many tons of equipment will have to delivered in addition to the multi-ton engines themselves.

In contrast using nuclear weapons is simple and effective, nearly fool proof.  You send out a prob with a large nuclear weapon out to the asteroid, manuver it into close proximity/land it and then detonate the device.  The specific impulse isn't the greatest, but the program is simple and reliable.  After the detonation, you calaculate the new orbit (easily done from Earth), and if necessary detonate additional devices.  Most likely multiple weapons will be launched in a series arriving every 2-3 months untill the asteroid is signifigantly diverted.  Best of all little to know new technology need be developed.  We are certianly capable of building a probe designed to close in with an asteriod, and a nuclear weapon to arm it with.  Such a device should be well within our launch capacity as well.  Indeed, ifi we were to detect a asteroid threat tommorow, such a program would probably be our only hope.

#407 Re: Human missions » Has Dr. Zubrin Addressed Mars Direct Objections? - A few questions? » 2004-12-04 23:18:50

I agree wholeheartedly with Euler's statment.  While 55 billion may seem like a lot, you have to rember that this amount is spread out over time, and that NASA's budget is already some 16 billion dollars a year.  So over the 10 years or so it would take to put the program into action it realy wouldn't be that big a problem.

#408 Re: Human missions » Manned Missions To Callisto and Titan - Looking Beyond Manned Missions To Mars » 2004-12-04 03:49:10

I think a concurrent program targeting all potential system resources makes the most sence.  There is no reason to say well, Mars is done, what's next?  In this way I disagree with Mars Direct.  After you have done the hard work of developing a HLLV to get stuff off of earth, it makes no sence to exclude the moon as a target for you missions.  Not that a mars mission should be dependant upon the moon, but both could certianly proceded at the same time.

Likewise, the next generation of mission, brought on by NTR and NEP should target the resources of the outersytem as well.  However, I would be warry of missions to Jupiter.  The planets gravity well is immense, and a mission inside it could have a very hard time getting back out.

Titan however is a dream come true.  I would start sending missions as soon as it becomes possible.

#409 Re: Human missions » Landing On Mars » 2004-12-04 03:34:00

First off, they are pretty small, and they aren't designed to be moved. On early missions, they will probobly be the heaviest object we bring, and trying to get them to move when your rovers have so much less traction (less gravity) will be no easy feat. The HAB still has the same inertia as it does here.

The habs are pretty small, which is why you would want to re-use them if possible, to increase your living space.  As for moving them, it would certianly be tough, but the utility of it certianly makes giving it a try worth-while.  At 25 tons the hab certianly isn't light, but this isn't an impossible sum to try and move.  Towing it certianly would be tricky, but that's now how I would go about it.  I would design one of the light rovers to fit-underneath and then carry the hab module.  A pretty beefy engine would still be needed, but not nearly so bad as if you were trying to tow the thing, and you wouldn't have to add mass to your tractor to give it more traction.

In any case, powerful earth-moving equipment is going to be a necessity at any Mars base.  Buldozers, dumptrucks, cranes, ect.  These sorts of vehicles could all be modified for doing the task.

Second, the nuclear reactor won't last forever. Since mass is at a premium, the reactor will probobly not have enough Uranium to operate more then 5-6 years or so before its output begins to drop off, which isn't very long when you have to wait a ~2 years between landings.

True, but with landings coming in every 2 years or so that gives you a 1-2 reactor margin, which you can elimnate on a mission to save mass.  Furthermore, the reactors could be designed to be refuled, greatly lengthing there lifespan.  Also since there should be little reason to run more than one reactor at a time, the un-used one can be shut off, pro-longing their life.  A more heavy-duty reactor should be a high priority though.

Plus, you can't move the reactor around near the base for about a year after it has been shut down because of the intense decay radiation. Most likly, the reactor will just be driven into a crater or a ring of dirt piled up around it for shielding.

Care of spent fuel/reactors is certianly a tricky issue.  But since the reactors don't weigh an huge amount it is not unreasonable to assume that an un-manned rover might be able to handle disposal tasks.

LSS systems will also be getting pretty old after 2.5yrs of continuous use.

I disagree with this.  If the LSS system is designed to last 3-5 years (it has to provide for tansit in as well, and possible an extended stay if something goes wrong), it mean time to failure is going to be alot longer than 3-5 years to ensure it's safety.  The things is going to have to be pretty bullet proof, it's going to be designed to last.  And any repair/maintness equipment is bound to weigh alot less than a complete system in any case.

#410 Re: Human missions » Landing On Mars » 2004-12-04 02:34:42

Parachute design in complicated because there are so many variables and design requirments.  Air density, drag coeficent, and velocity all change throught the deployment.  And you have to design around not only these variables but also the mass (duh) and amount G-Force you can safely inflict upon your cargo.

Anyway here is the relevent equation:
F=1/2*d*C*A*V^2
F = force of drag (Newtons)
d = air density (variable with altitude, .015kg/m^3 at the datum)
C = Drag Coefficent (variable with parchute design and conditions .5~2)
A = Area of parachute (m^2)
V = Velocity (m/s)

This is compared with the force of gravity (3.7N/kg) to determine it's effect.

Because mars's atmosphere is a lot thinner than earth's, a parachute still has to be alot bigger than a terrestial one to get the same effect.  Let's consider what would be necessary for a parachute assited soft landing using optimal conditions.

M*G=1/2*d*C*A*V^2
we want the drag equal (if not greater) than gravity for a soft landing
G = 3.7m/s^2 on mars
d = .015kg/m^3 (really alot less at high altitudes)
C = 1.5 (typical for a circuler chute)
V = 3m/s (speed you want to land at)

This works out to an 986m^2/kg.  For the 25 ton hab module, that is going to be one big chute!  Nearly 25 square kilometer of chute would be necessary.  Clearly impracticle.  And this is for a simple circle chute, in optimal conditions.  For a steerable chute (which has a smaller drag co-efficent) in more realistic conditions the situation is even worse.

A parachute might be usefull at high altitudes to shed some speed (I didn't know spirt used one like that) especialy since martian terminal velocity is going to be alot given the thin-air, probably >250m/s but for the final decent it is impossible.

BTW, could someone check my math on this?  I was expecting the parachute to be big, but not THAT big.

#411 Re: Human missions » solar power towers on mars - km-high vertical wind tunnel turbo-elec » 2004-12-04 00:41:03

Well according to the figues you list RobS, the BWC XL-50 is about 37% efficent (not bad).  So for the optimal mars condition Viking 1 collected data for the unit would collect about 7kW during optimal conditions, a little better than your estimate, but those are during optimal conditions.  Actualy come to think of it, those conditions (25m/s or about 55mi/hr) would probably be sub-optimal in practice.  The windmill is not designed to deal with those kinds of windspeeds and so would probably produce alot less energy.

Which brings up my secound point.  Windmills are designed to produce energy within an optimal set of wind conditions.  Outside of those (either above or below) they lose efficency.  Which creates problems when designing a windmill to capture windenergy during a dust-storm.  It maybe able to generate alot of energy then, but it will generate little to none the rest of them time.  The net effect would be alot less energy produced total.  You can see the effect I'm talking about in the http://www.bergey.com/Products/XL.50.Sp … itterature   for the unit you are talking about.  Notice the curve in the power production graph, above a certian windspeed, power production drops off.  This is due to a number of reasons, chief among them is the need to slow the mill to prevent it from damageing itself.

#412 Re: Human missions » Landing On Mars » 2004-12-02 23:48:38

I tend to think that an acurate landing is certianly very possible. Spirit landed within 200m of it's target, and that was a direct aerocapture.  A manned mission, which would presumably aerobreak and be able to correct it's trajetory further before re-entery should be able to perform similarly if not better.

That said, an inacurate landing is still a major risk that should be planned for.  Which is why either having the rover land with the hab, or have some method of getting it there is pretty critical.

As for landing correction methods, I am not so optimistic.  I think you are pretty much going to have to pick a trajectory from orbit and stick with it until you hit the earth.  Manuvering with the heat shield is tricky and dangerous.  Overcorrect in this manner and you could potentialy tumble the craft, exposing it's unprotected side, which would spell disaster.  Parachutes steerable and otherwise are out all together.  Mar's atmosphere is too thin for them to be effective (which is why no mars probe has ever used them). 

The only method that can work is using thrusters to correct after re-entery.  This is how you are going to have to cushion your landing in any case.  But as GCN points out, it is expensive in terms of fuel.  Some correction is possible but not much.  You will be more worried about doging boulders than you will be about landing down near the ERV.

#413 Re: Human missions » solar power towers on mars - km-high vertical wind tunnel turbo-elec » 2004-12-02 23:28:22

Well you've got most of the math there for you.  According to the data the Viking probe collected, a windmill would generate ~130W/M^2 of rotar area during the optimal conditions at that location.  All you need to do is come up with a model for how much your windmill would mass and cost per unit of rotar area.

I'm not going to say that it would be impossible to build a windmill on Mars, just that other alternatives are more practicle.

#414 Re: Meta New Mars » FAQ - Does New Mars have any? » 2004-12-02 05:38:22

Hmm...  a list of acronyms could be helpful.  I'll start one.

NTR - Nuclear Thermal Rocket
TSTO - Two State to Orbit
SSTO - Single Stage to Orbit
NEP - Nuclear Electric Propulsion
MAV - Martian Assent Vehicle
TMI - Transmartian Injection (stage)
RTG - Radioscopic Thermal Generator
DRM - Design Refrence Mission
RLV - Reusable Launch Vehicle
GEO - Geosynchronous Earth Orbit
LEO - Low Earth Orbit
ISS - Internation Space Station
SSME - Space Shuttle Main Engine
ICE - Internal Combustion Engine

well thats a start at least

#415 Re: Human missions » solar power towers on mars - km-high vertical wind tunnel turbo-elec » 2004-12-02 05:21:07

Here's the facts that show that wind-power is not practicle on Mars.  The http://www-k12.atmos.washington.edu/k12 … tml]Viking Weather Data pretty much tells the whole story.  The atmospheric pressure is to low, and the wind speeds are to weak.  Mars's atmosphere is 100 times less dense then ours but it's winds speeds are only marginaly greater.  The wind is also fairly variable in it's output from one day to the next.  All this makes windpower fairly impracticle.

But you still probably don't belive me, so here is some more data for you.  Wind power (the amount of energy in the wind) can be calculated by the following equation:

w = 1/2dAV^3
w = wind power (in watts)
d = air density (about .015kg/m^3 for mars)
A = Rotar area (square meters)
V = Wind Velocity (meters per secound)

Now plugging in the best data from the chart (25m/s), we find that even on the windiest day on recoard, the martian wind could only produce about 130 watts per square meter of rotar area.  This isn't that great.  Terrestrial windmills do about 4 times this amount, and we were using the best data for a whole 2 year period! 

You also have to take all alternatives in comparison.  While you might be able to build some ultra-giantic/super low-weight windmill on mars and generate some electricity, you have to compare the effort necessary to acomplish that with what would be necessary to build an alternative system.  It is not praticle when compared with the alternatives.

For my money the best bet for a home-grown non-nuclear power source on mars is either photo-voltaic or reflectors powering a turbine or stirling engine.  Or geo-thermal but I bet finding a good source for it may be tricky.

#416 Re: Human missions » What Kind of Manned  Program Should We Push For? - A Time to choose » 2004-12-02 00:26:33

I think it is still to earlier to make a defentive rulling on Scramjets, there is still alot of work to be done in this area.  We've barely even proved that supersonic combustion is possible.  A multi-mode scramjet engine (one that can convert over to a pure rocket for orbital operations), may help with some of the issues you are talking about.  If nothing else, they may be practicle as reusable high altitude boosters for some sort of reusable vehicle.

FTLwright, love the name btw,

#417 Re: Human missions » What Kind of Manned  Program Should We Push For? - A Time to choose » 2004-12-02 00:18:35

Maybe you need to "take me to the bathroom" as it were, because your hand waving of important issues such as exactly how a private coporation is going to develope a space based revenue scheem is illustrates exactly why it wont work.

How exactly is it going to work?  What scheem are they going to use to turn a profit on there investment?  And who exactly is going to foot the bill?

If you wish to exclude public coporations, thats fine.  But the largest private coporations are at best half the size of those giants, and there are alot fewer of them in billion dollar revenue range.

There is no workable buisness plan for making money off of large scale human space development.  Certianly not for building such things as space-stations, moon bases, or trips to mars.

And frankly, even if making a profit was not an issue, it still couldn't be done outside of goverment.  Because no single individual, or small group of individuals have the billions of dollars necessary to captilise such a venture, the ability to liquidate and spend those billions of dollars, and the willlingness to do so.

-----------

Just as a correction, I mispoke in one of my earlier posts.  I said revenue when I ment profit.  Coporations may have reveneus in the 100 billion dollar range, but there profits are generaly only in the 100 million dollar range.

#418 Re: Human missions » Has Dr. Zubrin Addressed Mars Direct Objections? - A few questions? » 2004-12-01 23:58:31

To be bluntly honest, 80% failure is not unacceptable because there is a 20% chance that the crew will die, it is unacceptable because there is a 20% chance that billions of dollars will go to waste.  I'm sure you could find volunteeres even for a one-way mission to mars, but it's not so much the cost in human lives as it is the billions of dollars down the tube.

#419 Re: Human missions » My Change To Mars Direct/Semi-Direct Mission Plans - An alteration that might help » 2004-12-01 23:39:39

I like the idea of a re-useable MAV, but I think it is probably a little to ambitious for the first mission.  Making the MAV reusable adds alot of mass, as there is the whole re-entery thing to worry about.   Also shipping enough hydrogen feed-stock for multiple assents is just impractical.

However, a reusable MAV should be way high up on the priority list for cargo to deploy at a developing martin base.  I like the idea of using a stripdown/bulked up NTR/CO2 hopper.  Such a vehicle could provide both continental mobility and re-usable access to orbit.

The main thing that worries me is, will it ever be practical to build a reliable reusable MAV?  Most rocket engines have to be heavily serviced every couple of launches to ensure their continued opperation, and most have to be retired after only a smaller number of missions.  The heat shield will also probably need heavy servicing and replacment.  A NTR would be even more difficult in this respect as servicing it's engine would be both difficult and dangerous.

#420 Re: Human missions » What Kind of Manned  Program Should We Push For? - A Time to choose » 2004-12-01 01:42:10

How, comstar how.  You promise explinations, but your responses are lacking in details. How are coporations going to do all this?

#1.  How will the pay for it?
They do not have the revenue streams to support a multi-billion dollar space development program.  Even if a large coporation was to devote ALL of their revenue into space development (something they could not do, mind you), 100 million dollars a year would just begin to scratch the surface of what is needed.

#2.  How will they make a profit?
There is currently little potential for profit in space.  It's to expensive to get up there, and developing technologies that would bring this cost down are to expensive as well.  This is especialy true for the major space development programs we talk about here such as space-stations, moon bases, and mars trips.  All of these enterprises have expensises that are FAR to great to be offset by any potential income.

#3.  Why would a major company do it?
Even if you assume that a profit could be made in space, a major company would not start pumping their money into it.  Ford knows cars, Exon-Mobile knows oil, Wal-mart knows retail.  These are all safe bets for them and they have tremendous amounts of assets devoted to performing these tasks.  If they have revenue to reinvest, they are not going to take their money away from their core-buisness which they understand and is a sure bet, and put it into space, a buisness which NOONE knows anything about and is a crap-shoot.

#4.  Why would I WANT the major companies to do it?
Don't get me wrong, I am all in favor of space development, but I do not benifit if it is done by big coporations.  You are right that in this case individuals, instead of goverments would hold the rights to space and these technologies.  However, these rights would be concentrated in the hands of very few.  In America alone 10% of the population has 80% of the wealth.  In the world at large the diffrence is even greater.  If coporations develope space the rights to it will not be held by "the people", the will be held by a small fraction of the super-rich.  The goverment certianly is not perfect, but they at least have the pretense of doing what they do for everyone they represent, coporations act only on behalf of those who own them.

#421 Re: Human missions » What Kind of Manned  Program Should We Push For? - A Time to choose » 2004-12-01 00:22:32

I agree with GCN completely.

Not only is there currently no profit to be made in deep space, it is far beyond the reach private indavidules and large coporations.

Even if a big coporation honestly wanted to put its money into space exploration, they would be unable.  While big coporations like Wal-Mart, Exon Mobile, Ford, IBM, GM, exct... might have billions (perhaps even trillions) of dollars in assets, they cannot simply liquidate all that and put it into space.  Indeed there revenues are only about 100 million or so a year.  And they can't even take all that money and put it into space, as they have debts to finance, dividens to pay, and they must re-invest the money in their own coporation to stay competative and profitable.

No, for the forseable future if space development is going to happen it is going to be the goverment that does it.

#422 Re: Human missions » What Kind of Manned  Program Should We Push For? - A Time to choose » 2004-11-30 23:38:29

I favor a slight variation of the NASA DRM or Mars-Semi Direct.  I would put a greater emphisis on base-building and possible add a launch dedicated to bringing additional cargo and equipment down. 

If something has to be designed to last 2 years on mars without failure, then it might as well be designed to last forever.  Not that it will, but equipment designed to last 2 years safely is going to have a much longer mean time to failure, why not take advantage of it.  It's wastefull to launch all the expensive science equipment only to practicaly abandon it by the next mission.

To use antartica as an example, while Scott, Shackleton, and Amundsen were heroic exploerers that inspired many, they achieved little, if any science.  Not untill more modern times with the establishment of permanent bases on the continent have we begun to do some real science there.  Indeed, more was probably learned by the small antartic whaling camps then was by any of the great expeditions to the pole.

Another place war Mars Direct goes wrong is it's total avoidance of in-orbit redevous and construction.  While I do not think that it is practicle to build a Battlestar Galatica in oribt, there is no reason that a two parts could not be launched seperatly, then docked in orbit, and then sent to mars.  Both the US and Russia have done many such missions, staring with Gemini 6 & 7, Skylab, Apollo-Soyuz, and many more orbital redevues.  Pretty tride and true techonology to me, no reason not to use it if necessary.

#423 Re: Planetary transportation » Running on Compressed Air? » 2004-11-30 23:10:11

I'm not crazy about the remote driving solution, but it may be one of the best ones that exists.  If the trip is taken slowly enough, there should be little risk that the rover will fail due to some terrain problems.  Given the duration of the crews stay on mars, taking the time to be safe should not be an issue.  Additionaly, the crew on mars should be able to opperate the vehicle remotely, eliminating the issue of time lag.  Communication bettwen the two might be an issue however, I'm not sure if the long-distance radios would be able to handle the necessary bandwith, necessitating a satilite-uplink.

More serious issue to me are the fact that the rover might simply break down on it journy, or the two sites might be simply inacessible to one another.  Mars contains some extream geography, and it is not inconceivable that you just might not be able to get there from where you are (within you range limitations especialy).

The two factors are concurns no matter how the launch is configured.  Having the rover at the base camp does not prevent the ERV from being landed in an inacessible location or the rover from breaking down on its way bettwen the sites.  Indeed, if the Hab and ERV are widely seperated the crew are in some distress even if everything goes well.  The ERV represents a signifigant portion of there equipment and safety margin, and if the crew are not able to get there easily in the advent of an accident, it may well spell disaster.

My solution to these issues is two-fold.
#1.  There should be two pressurised rovers at the base, and only one should sortie at any one time.  This ensures the base as a fall-back shelter in case of some sort of disaster, and it provides a method for rescuing the crew of the other rover should the have  some sort of accident.

#2.  The first mission will always be the most dangerous.  But follow up missions can be relived of some of this danger by being targeted at the first base.

#424 Re: Human missions » Gravity - Gravity » 2004-11-30 15:30:31

Spending a couple of months in high gravity isn't going to turn anyone into superman.  Plus it may not be very safe.  The astronauts would be more likely to break bones or injure themselves in some way on there trip there.  Also heavier gravity would put much more stress on the heart.  There is about as little data on the human effects of long duration high-g's as there is on low-g's.

#425 Re: Interplanetary transportation » Nuclear Transfer Vehicle Design » 2004-11-30 15:12:02

With 1,000sec Isp why even bother with electric propulsion except for deep space probes and station keeping?

Because it can only produce that ISP for a short period of time.  The temperatures are to great to handled by conventional methods and the engine litteraly burns itself out.

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