LEO to TMI - discuss

Bill White · 2004-03-25 13:39:35

L1 isn't a station, its a transit point. Getting there is hard, correct? Getting elsewhere from there is easy.

Hence, bad location for a station. No need for it. Sending a pre-built Phobos facility through L1 might be a different story.

A nuclear tug could push payloads to L1 and then cut then loose on the right trajectory to anywhere then return to LEO for another payload.

Don't forget the capital costs (interest and crew salaries) tied up in a nuclear tug. Going all the ways to Mars and back will be far more expensive and justified only if the cargo is time sensitive. For less time sensitive items, use the nuke tug to push cargos over the edge at L1 and let them coast.

A trip to L1 and back to LEO with the cargo pod cut loose at L1 for a zero energy slow trip to Mars would be very financially efficient. A NERVA class tug could today throw massive inert payloads to Mars, correct?

Do MarsDirect or a NERVA Mars misison only after a few thousand tons of supplies have been pre-positioned on the surface of Mars.

= = =

I never liked the idea of L5 cities. An L5 class city in a free return orbit between the Earth and Mars always seemed more useful.

= = =

In another thread, folks were worried about shuttle derived flight rates. Deploy a NERVA tug (1960s technology, correct?) and start dumping SDV launched infrastructure components to Mars via L1 zero energy trajectory transit points.

Kevlar sheets, bulldozers, aluminium trusses, freeze dried plant food, freeze dried tofu emergency rations, clean jumpsuits, toilet paper and tooth paste, solar panels (how long do solar panels last if properly packaged for long term storgae?).

One NERVA tug is all you need to absorb as many SDV launches as can be funded.

Then send a crew to a wealth of pre-positioned supplies.

Edit: Including a 100 ton ERV pre-positioned in low Mars orbit! Launch a 100 ton ERV on Ares, send to Mars orbit via a slow low energy trajectory, and park in a stable orbit before sending crew.

Too bad I am a liberal arts major. I need someone to assure me these zero energy trajectory orbits are REAL!

So what if it takes SIX years (or TEN years) to pre-position a 100 ton ERV via one Ares launch and a long slow transit to Mars. Do it, then send the crew.

clark · 2004-03-25 14:06:48

Do you really want to depend on a return vehicle that has been in space for ten years?

Bill White · 2004-03-25 14:15:26

Do you really want to depend on a return vehicle that has been in space for ten years?

Either that or some flismy lightweight thingee thats been in space for 4 or 5 years. Okay, okay an 80 ton ERV with 20 tons of repair kits in storage. TransHabs deflated and inside the outer shell.

Don't forget this is a NEW ERV, with everything nice and shrinkwrapped. Besides, if the Mars crew checks out the ERV and has doubts, send a NERVA rescue craft.

With a few hundred tons of food and water they can safely wait. With 6 SDV a year a huge chain of incoming 100 ton payload modules can stretch from Earth to Mars, essentially forever, years before any human ever leaves LEO.

This supply chain would cost little more per year than the current STS budget.

clark · 2004-03-25 14:22:15

Bravo!

To bad it sacrifices Mars Direct, increases the cost and time neccessary to get people to Mars, and relies on undeveloped, or new technology.

But it's a better plan than Zubrin's.

SBird · 2004-03-25 14:27:11

OK, tons of stuff to reply to...

Rxke: Interesting idea but it would require going dangerously low into the upper atmosphere. Perhaps you could lower the refrigerator down on a tether but you'd still have a lot of problems with drag even then. I'll keep the idea in mind, though.

Gennaro - The Mars to LEO SSTO isn't a BAD idea, just not a terribly optimal one. Another disadvantage of a combined SSTO/interplanetary freighter is that you tie up your SSTO for long periods of time. One of the advantages of an SSTO is that it's got a short turnaround time. If your SSTO then spends 5 months puttering off to Earth, you lose that advantage. Also, SSTOs inherently tend to be small in terms of cargo load. Because of Mars' smaller gravity well, it might be realistic to expect 20 MT to orbit for an SSTO. If you want to move decent amounts of cargo from here to Mars, you have to have seperate vehicles.
For example, let's say that we want to move a couple of heavy earth movers(bulldozers, etc), a bunch of H2 stock, a few km^2 of clear plastic sheeting and a polymer production plant to Mars totalling 100 MT. In return, the Martian colony has a deuterium isolation facility and is going to send 10 MT of the stuff back to Earth(worth about $1 million at present prices), 5 MT of Mars rocks and other samples. The SSTO can realistically carry, maybe 5 MT back to the surface of MArs with each trip (SSTOs are already riding a fine line to get themselves back down as it is) so the whole process would either take 50 trips or a huge fleet of vehicles.
In contrast, as long as you can accept slow travel, high Isp engines and 0-energy pathways can be used for a freighter to carry all 100 MT of cargo to Mars, pick up the return material and head home. A couple SSTOs operating on a 1 week turnaround could bring down most of the cargo (except the 2-25 MT earth movers) in about 5 weeks. The earth movers can be equipped with their own reentry systems.
This analysis doesn't even include the fact that a hybrid SSTO/freighter with two completely seperate engine systems would have much lower performance. The freighter wom't be availabe for maintainance but it's never under very much stress and therefore can operte for long periods without being worked on. The Mars SSTOs can be serviced once a week if necessary, not once every 6 months like a hybrid vehicle.

Gennaro/GCNRevenger - the GCNR is a cool idea and I like it as well. However, it stands that we've never built an operational one and still don't really know how. Our continuing problems with controlled fusion show that our grasp of high density plasma physics leaves much to be desired. Many of the problems in GCNR are the same as with fusion. Until we've got the latter licked, I'm not going to bet the farm on GCNR.

GCNRevenger - I don't think tha NWSR is even worth thinking about in getting to Mars - it's just too dangerous. It depends on a very carefully controlled rate of flow of the fissible salts through the reaction chamber. If the rate of flow drops, the critical reaction area moves up into the engine and basically detonates a tactical nuclear warhead there. If anything caused the fuel flow rate to drop, the engine will blow up. It's not even clear how one of these things could be safely started or stopped. Furthermore, if the engine explodes, those fragile boron nitride neutron absorber baffles are going to get shattered - the entire fuel supply could go up in a multi-megaton fireball.
That doesn't even begin to deal with the political implications of throwing around huge quantities of radionucleotides out the back of the engine as it runs. Sure, they might be aimed away from Earth and at greater than solar escape velocity but do you really think that the public and by proxy, the government will let this fly? I seriously doubt it.
NSWR is a great idea for the exploration of the outer solar system or the nearby stars. I think its a great idea as long as we don't put people on it or fire it up anywhere within lunar orbit.

I do agree with you on the shortcomings of ETP. I also just noticed that there might be limitations on the total thrust, regardless of the power available due to limitations in the free electron availability in LEO. However, a thrust of 10-20 N is entirely possible and realistic. The power supply only need supply an average power flux of about 1 kW/N thrust. Since you would have to operate in a perigree thrust/apogee raising mode, the actual constant power supply can be much lower. Existing solar power systems for high altitude balloons already exist that would make the system work quite well with low mass. We'll be able to say how well the system works soon. The ProSEDS mission got delayed because of Columbia but is scheduled to go up soon. Check out [http://www.tethers.com]www.tethers.com - they're the contractor for that mission. They're enamored with rotovators ??? but also have a cool product called a terminator tether for deorbiting LEO satellites that they are already offering commercially.
Of course, ETP is for slow cargo - the thrust is on the same order as an ion engine. However, for things like heavy equipment, the ability to get a 1.0 mass ratio from LEO to LMO is worth pursuing.

dicktice - kinetic momentum tethers are cool but have limitations. For one, you've got to catch your payload - this a is a non-trivial problem. Also, you're limited to stuff of maybe 5 MT, tops. Beyond that, the counterweight just gets too heavy and the stresses on the tether too high. To boost a 140 MT Mars mission to Mars with one of these tethers, your counterweight has to weigh 700 metric tons! Ther e is no way to get this kind of mass to orbit other than 5 heavy lift booster launches and in-orbit assembly. It would be a much better use of money to just send 5 missions to Mars with that money. Rotovators do have quite a bit of promise for small sattelites but that's about it.

Bill White · 2004-03-25 14:28:14

Bravo!
To bad it sacrifices Mars Direct, increases the cost and time neccessary to get people to Mars, and relies on undeveloped, or new technology.
But it's a better plan than Zubrin's.

If zero energy trajectories are real, I am certain Zubrin will gleefuly change his plans.

clark · 2004-03-25 14:36:34

I think so too. The man likes to sell books.

SBird · 2004-03-25 14:45:10

ARGH! Even more stuff to reply to now!

I figure that a LEO to LMO tug could operate largely autonomously. The SSTOs from Earth and Mars would have pilots that would come up, dock and load/unload cargo.

The 0 energy trajectories exists, the NASA Genesis mission is using them right now. Martin Lo, the guy that found the low-energy routes was the mission trajectory designer. It should be returning this fall with a sample of solar wind for analysis.

I think that the low energy routes are actually fairly close in transit times to the existing Mars Direct routes. I think that I should just contact Martin Lo and ask him what a Mars transit time would be. It will almost certainly be < 1 year. This is why NASA is so excited about these trajectories.

Building on what we've discussed so far, here's a cargo-hauling system:
1: SSTO the cargo to LEO or use HLV for stuff that can't be shipped in pieces or pumped into a tank.
2: a LEO to LMO tug gathers up the stuff into cargo bays. I imagine that there would be some sort of standard cargo size unit, not unlike the cargo container ships and trucks used today on Earth. In many ways, the tug would resemble a cargo container ship. The tug also gets refueled at this point.
3: the tug somehow gets from LEO to Lunar L1. This can be done with chemical, NTR, ion, CGNR, ETP, whatever. It doesn't have to be fast since getting to lunar L1 isn't that challendging and we're not in a huge rush. Basically whatever works out to be the cheapest and mot reliable transportation system.
4: low energy trajectory to the Mars L1. The Phobos/Deimos L1 points might even be feasible but I suspect that they're too small of targets to be practical.
5: The tug powers from Mars L1 to LMO.
6: Martian SSTOs come up and gather the cargo for return to the surface. Alternately, the cargo can have its own reentry systems. (these might even be provided by the Mars SSTOs) The tug gets refueled again and heads back to MArs L1 to start over again.

GCNRevenger · 2004-03-25 15:45:37

Before we get all "zero energy! mars on the cheap!" i'd like to hear exactly how fast you can get there using this trajectory, and how stringent is orbital alignment.

Bill White · 2004-03-25 16:01:50

Before we get all "zero energy! mars on the cheap!" i'd like to hear exactly how fast you can get there using this trajectory, and how stringent is orbital alignment.

Exactly! That was the origin of my suggestion that the Mars Society consider distributed computation =IF= the problem is amenable to such a solution. It has been suggested that just using a few slightly older PCs might do the trick as well.

This is what I propose someone attempt to do:

The Wikipedia article (and the AIAA article) say that low energy trajectories can be used to travel from Earth's libration points to pretty much anywhere, including Mars.
One of the knocks on MarsDirect is the tight mass budget.
So, why send the first uncrewed Sabatier/ERV mission on a Hohmann? If there is a 19 month slow boat to Mars which allows double the net payload for the same sized launch, we need to know when and where those exist.
It might change the timing of available launch windows, right?
Therefore, create a Farmer's Almanac of ALL low energy trajectories we can possibly find for Earth-Mars over the next 20 to 30 years.
A four year trip to Mars? Useless for Mars #1 but if an Ares worth of freeze dried plant food; long lived MREs; spare kevlar building mats; hand tools and a big dozer were launched on a 52 month slow boat to Mars, with 180% of a normal Hohmann payload actually getting there, and it would arrive in time for the Mars #2 or Mars #3 mission, well, isnt it worth it to at least know the option exists?
Does this make sense? Could a handful of PCs crank out ALL of these potential low energy trajectories as hypotheticals for future unplanned missions?
or this:
Suppose you decide to come to Chicago for the Mars Society Convention. Anyway, you can query Expedia two ways. By date, by asking to fly from your home to Chicago on 18 August 2004 or you can query by price; regardless of when you fly or what cities you lay over in you just want to fly at the lowest price.
Okay, what I want to create for Mars is a database of EVERY low energy trajectory that costs LESS than a Hohmann in terms of Delta V. So instead of saying we choose to fly in 2016, what will it cost? we ask instead
We need to deliver at least 150% of the payload that would arrive via a nomal Hohmann transfer. So, how long will it take and when can we go.
I propose to create a database we can query to answer such questions.
Does this help explain where I am coming from?

Remember - a nuclear tug can get from LEO to a libration point in a week, correct? Even at maximum burn, Mars is a very much longer trip, correct?

Using these "tunnels" one tug can create a pipline of monthly payloads of 100+ tons. 1200 tons per year of cargo if Energia & SDV can maintain the schedule. Crew doesn't go until the pipeline fills up and payloads start falling on Mars.

SBird · 2004-03-25 16:48:36

We've got a discussion devoted to these low energy trajectories in a new thread. For the purposes of this thread, let's just assume that these trajectories are potentially possible and work on more mundane stuff like engine technologies. If it turns out that low energy trajectories are possible, we can just use the estimates in this thread that rely upon them, otherwise we use the more consevative estimates.

OK, let's take stock of what we've got so far:
chemical, NTR, ion, GCNR and possibly ETP. I'm open to the other technologies like NSWR but I think that they just really don't fit into this particular discussion.

We've largely dismissed ion engines but how well do they perform on the way to Mars? Let's assume that in 15 years, we have ion thrusters capable of 6000 Isp and a thrust of 20 N (when the engines are used in clusters). While it's true that high thrust engines allow shorter thrust times, if we're in the context of a 6 month Mars transit, do ion engines catch up? Assuming a nuclear power source (let's ignore the difficulties in a 100kW+ nuclear reactor for now) and a 100 MT spaceship that is doing a 4.5 km/s delta V to Mars. You get the necessary deltaV in 260 days of solid thrusting. That requires a fuel fraction of 8%. Of course, orbits will have to be modified to accomodate the gradual velocity gain but I think that it's fairly clear that next gen ion engine clusters have great potential.

I checked my calculations and can't find a problem - could someone check them for me? I want to make sure I did them correctly.

GCNRevenger · 2004-03-25 18:47:46

Ion drives are fine for nonperishable cargo, i'm fine with using them for stuff that isn't time sensitive. The big deals with using ion engines is where do you get that much Xenon from (or what efficency hit do you take with other fuels?), where do you get the electricity from (solar is problematic, especially at Martian distances), and how often/how long does a flight last.

Two pieces of hardware that should be developed before ion drives start running cargo:

Must build a powerful nuclear reactor that produces >100kW and doesn't have those rediculus giant low temperature radiators. Nasa is apparently resorting to the use of low-temperature light liquid or inert gas coolant radiators to reject the 66% of heat produced by the core that is not converted to electricity. This is a pretty silly idea, which quickly cuts into the mass of the vehicle and makes it terribly vulnerable to damage. Nasa should instead make small radiators that run at high temperatures by running liquid metal coolant directly from the reactor coolant loop through armored pipes to the radiators through thermal conduction. Nasa seems to be moving to ISS-style light liquid radiators being run from the inert gas secondary coolant loop.

~Must likly also carry a small gas liquifier, to counter fuel boiloff when used in the tanker role. On such a long flight, the fuel an ion tanker would carry would partially boil off. This being undesireable, the evaporated gas should be compressed and reliquified using power from the nuclear reactor.

SBird · 2004-03-25 19:49:16

IIRC, the Soviets had quite a bit of experience in building liquid sodium cooled reactors for their attack submarines. Perhaps NASA could get some of their expertise on the cheap.

One thing I've always wondered about is why you don't use thermocouples to get some power out of the radiators? My understanding isthat RTGs use the thermal gradient between the core and the radiator to generate electrical power. It seems like a good way to maximize the power coupling efficiency.

Gennaro · 2004-03-25 20:04:03

SBird, I think you're doing a good job in summing up the posts and setting the discussion, at least until someone wrecks it again with wayward digressions... (hehum!)

I'd also like to thank you for the extensive reply about the hybrid SSTO/freighter. I more or less suspected as much and it was never that a serious suggestion, so it's good we that one cleared out and dropped.

For now, I'm going to continue like the L1 scenario doesn't really exist (never heard about it before).

Concerning cyclers, perhaps what we are seeing here is a division getting made up between slow, unpiloted freight ships, where ion features in the discussion, and prevalently piloted passenger/fast freight types, typically nuclear powered.

SSTO's should naturally be piloted and might it be added, if it's not done already, that LEO SSTO must be H2/O2 while LMO SSTO's could be CH4/O2 powered for an Isp of 380 s, which is good enough from Mars. CH4 needs smaller tanks, don't evaporate and its manufacture is already institutionalized on Mars through the Sabatier reaction.
The only reason I suggested H2/O2 previously was because of the hybrid concept.

A second consideration regarding high-thrust/high Isp cyclers come to mind however. The reason for GCNR with an Isp of 4000 s, strikes me partly as being borne out of the eventual need to overcome restricted launch windows. Such a need might possibly arise out of commercial factors (getting the most out of a reusable craft for example) or fast transfers of men and material.

If indeed this is a valid point, I'm afraid the service problem again rears its hugly head. Replacing fuel elements, servicing and refurbishing a nuclear engine is likely not a trivial matter. Can such be safely carried out on orbit with nothing more than a visiting SSTO?
Naturally the same applies to solid core designs.

I might add that from the layman's perspective (mine), I'd prefer nuclear (NERVA, Advanced DUMBO, Particle Bed, GCNR or VASIMR or whatever) to handle passenger freights. Not only for speed but also because of conveniences, such as a built in gravity tether for example, extending and retracting during coast periods.

Note: I'm not desperately trying to reinvoke the space station (believe me, I'd rather not), just posing a question.

Moreover, it would be nice to know how you figure to get the SSTO's to Mars. Could they be sent in "model kits" for instance, containing a do it yourself 1:1 scale methane SSTO to be assemblied on Mars, riding on a heavy launcher(s)?

GCNRevenger · 2004-03-25 22:30:27

Russia's navy has some experience with liquid bismuth cooled reactors if memory serves, but these aren't very reliable. What they did do was make the Topaz mini-reactors to power the Russian naval space radars. These were real nuclear reactors, and not RTGs by the way. The little reactors didn't produce quite as much energy as the one Nasa wants, but they were cooled by the passively pumped liquid cesium coolant to very small radiators, which is what Nasa ought to have in mind.

The trouble with thermocouples is they have terrible output per mass, and they need to have a very cold "cold end" to operate efficently, requiring signifigant cooling systems. The best thermoelectric systems might be 10-15% efficent, with most being around 5-6%, but a Brayton turbine system can do 33% thermal efficency...

I actually don't see why you want every SSTO to be piloted. If you are making alot of flights hauling materials and basic cargo, why outfit the thing with all the stuff needed for people, and for that matter why risk people at all? If it blows up unmanned... big deal. We have the technology today for fully automated spacecraft, and remote control is always available for backup.

Eventually we'll need some way to get 100-ton class payloads to Mars without it taking too awful long (perishable cargo, radioisotopes, radiation sensitive computers), and it would be awfully nice if a lighter manned ship could make the trip in, say, 100 days. GCNR would be able to pull this off though it is a day-after-tomorrow technology. The GCNR engine should be pretty reliable, since there isn't alot to it - A vortex chaimber that has few moving parts, the hydrogen turbopump that we can do already, and the fuel vapor injectors. You would want to check the interior of the engine for ablation and make sure the vortex control mechanism can move freely, but other then that it should be pretty trouble free.

RobS · 2004-03-26 09:57:47

Where is this article about the low energy trajectories through the lagrange points? As I understand it, the lagrange points are low points in the "lip" of the earth's gravity well, not the portals to interplanetary worm holes. By the time a spacecraft reaches a lagrange point, it's already felt 99% of the effect of the Earth's gravity. Possibly the advantage is more for an ion engine, but even then I doubt one gains more than a hundred miles an hour or so.

-- RobS

Gennaro · 2004-03-26 17:09:10

I actually don't see why you want every SSTO to be piloted. If you are making alot of flights hauling materials and basic cargo, why outfit the thing with all the stuff needed for people, and for that matter why risk people at all? If it blows up unmanned... big deal. We have the technology today for fully automated spacecraft, and remote control is always available for backup.

Always, in general - a matter of speaking. It may be that technology is making advances, in fact pilotless planes and all the smart battlefield gadgets on the drawing boards of the leading military nations might possibly give your argument full credit.
On the other hand, I've heard accident loss rates of unpiloted craft are significantly higher than piloted. The Rocket Company (yes it's only a novel) over at Hobby Space sets it as high as ten times. How many craft have been lost at Mars? The percentage is awfully high. Europe lost a lander only a few months ago. Granted, those were not SSTO.
Whether losing a SSTO is a big deal or not is dependant on the size of your fleet. Mars in the early stages of colonization, just as it emerges from the base building phase, is likely to furnish quite a limited number of vehicles. Losing spaceships, in other words, might risk having substantial implications for the entire operation, not mentioning that trans-gravity craft will remain a non-trivial piece of hardware investment at said stage.
To replace it, you'll have to send a new SSTO all the way from Earth. No, I don't believe Mars with its freezing cold, low-pressure and CO-2 atmosphere environment and rudimentary industrial assets will realistically be able to manufacture its own at this time. It's like building rockets on Spitzbergen, just without any air supply.
Putting a crew on a SSTO will reduce payload capacity, but considering the Martian Delta-V, even a methane/oxygen SSTO of 380 s will probably remain quite formidable in my opinion.
The human aspect of saving lives is another matter, but all depending on the stakes, taking risks might result in saving more lives or benefiting the colony to a higher extent than the possible loss of a handfull of individuals.
Besides, why not make a man proud? "So what do you do?" "I'm a pilot on a Martian Ascender". "Wow!"
:;):

SBird · 2004-03-26 19:50:51

Waht I think that most people forget is that commercial airplanes these days basically fly themselves. The pilot is responsible for taxiing and taking off. Everything else is handled by the autopilot unless something goes wrong. I think that the only reason to have a pilot is to load and unload cargo. Even that can be largely circumvented by using standardized cargo loading/unloading proceedures that are compatible with automated pilots. If you launch several SSTOs, perhaps one could be piloted and that pilot could be up there to manually take control of any other craft if the need arose.

GCNRevenger · 2004-03-26 22:17:47

And if you think airplanes are automated, think about the Shuttle... All the pilot really has to do is dock and land, the rest is handled by computer. You basicly push "execute" on the flight computer and hold on tight. Very tight.

The mass ratio of an SSTO will be lousy enough as it is, and adding the extra room and mass and reliability/escape option for pilot(s) doesn't make much sense to me for a tanker. The archaic 1960's Progress cargo hauler doesn't need a pilot, why should the SSTO?

If somthing does go wrong with the automated controls, thats why you have a second set driven by remote control from the ground. Extra computers don't weigh as much as a crew cabin...

Getting people to and living on Mars will be hazardous enough as it is without putting them in make-work pilot roles on freighter rockets. An unessesarry risk.

Gennaro · 2004-03-27 08:28:51

I think that the only reason to have a pilot is to load and unload cargo. Even that can be largely circumvented by using standardized cargo loading/unloading proceedures that are compatible with automated pilots.

In fact I was thinking about cargo loading/unloading as well, but as you say, maybe human presence isn't so important to get the job done anyway.

The mass ratio of an SSTO will be lousy enough as it is, and adding the extra room and mass and reliability/escape option for pilot(s) doesn't make much sense to me for a tanker. The archaic 1960's Progress cargo hauler doesn't need a pilot, why should the SSTO?

Can't really argue with that, but on another note how do you picture passenger operations between MLO to Mars surface? If done by SSTO, should that include pilots in your opinion?

There should be a great deal of difference as regarding the negative implications of a crew for Mars SSTO's in comparison with Terra SSTO's. Delta-V to MLO is only 4.0 km/s with a mass ratio of 2.9 for CH4/O2. Basically, this tells me that if for any reason you wanted to include a pilot you'll have mass to spare.

SBird · 2004-03-27 12:04:49

Yeah, Mars is a lot more forgiving for SSTOs. As it is, they're barely possible on this planet. Of course, advances in artificial diamond manufacturing could change this. There's some academic research (and some commerical as well) that can grow perfect single crystal diamonds at about 0.1mm/hour. Given enough money, we could actually grow industrial sized diamonds. Diaomnd is brittle but very strong and has the highest heat conduction capacity of any know material. There has got to be an application for something like that for SSTOs.
On the other side, though, Martian SSTOs won't be able to be retrofitted and maintained as well. Here on Earth, we've got entire aerospace companies that can give an SSTO a once over when it lands. On Mars, at least fora few decades, your repair and maintainance will be very rudimentary. As a result, your SSTO design will have to be MUCH more robust and therefore lower performance.

GCNRevenger · 2004-03-27 12:25:00

Mars is somewhat more forgiving, though the air is much thinner nor all that uniform, which will make aerobraking following a deorbit burn a more delicate maneuver.

If there is going to be a ten-ton-payload class DC-X style SSTO rocket on Mars, then the ease of maintenance does depend on how well its built, but I wonder if when this stage of development is reached - where you can make gobs of fuel and have at least some surface infrastructure - could a TransHab style pressurized hanger be built? The only part that wouldn't be collapsable for transport would be the hatch and the handling gear.

SBird · 2004-03-27 13:04:20

Gennaro - to answer your older post:
I'd like to keep the L1 gatway in mind at least. Let's not rely upon it but make sure to do rough mass fraction calculations for our cargo transport technologies to see how applicable it is. From what I can tell, the 0-energy trajectories save about 1km/s at the expense of a longer travel time. For chemical NTR and ion engines, I think that there is a significant benefit. for GCNR, there's probably no point.

I agree that something like a GCNR for fast transit would be great for human flights. However, if we get teh technology perfected, there's no reason to not use it for all our missions. The high Isp means that your fuel expenses are minimal. You could send crew via high-speed flat trajectories and cargo standard high speed Hohmann trajectories.

I think that the Mars SSTo would have to be sent as a kit or lander or something. The facilites to build such a craft on Mars won't exists for a long time.

SBird · 2004-03-27 13:09:13

RobS - go to the zero energy trajectories thread. There's more info there. It's got nothing to do with wormholes. It uses the equivalent potential energy of the lagrange points to largely eliminate the energy of transfering between planets. Basically, the Trans Mars injection burn and MArtian orbital injection burn are eliminated. This probably saves a km/s of delta V. Since the relationship between total delta V and fuel mass fraction is an exponential one, the savings are quite large. I've been estimating a 30% increase in Martian payload using chemical thrusters. If you've got a way to get to lunar L1 via space tug or other low or 0 cost means, your Mars payload goes up by at least a factor of 2.

GCNRevenger · 2004-03-27 17:35:39

The GCNR engine is the best we've got (short of wacky Orion/NSWR) for fast transit that doesn't require any serious leaps in technology, but if all you are doing is pushing tons of digging equipment, ammonia for fertilizer, or plain old water then the Isp of ion engines might be nice. Depends on how heavy the reactor setup is versus a GCNR engine (which would be quite heavy).

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#26 2004-03-25 13:39:35

Re: LEO to TMI - discuss

#27 2004-03-25 14:06:48

Re: LEO to TMI - discuss

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Re: LEO to TMI - discuss

#29 2004-03-25 14:22:15

Re: LEO to TMI - discuss

#30 2004-03-25 14:27:11

Re: LEO to TMI - discuss

#31 2004-03-25 14:28:14

Re: LEO to TMI - discuss

#32 2004-03-25 14:36:34

Re: LEO to TMI - discuss

#33 2004-03-25 14:45:10

Re: LEO to TMI - discuss

#34 2004-03-25 15:45:37

Re: LEO to TMI - discuss

#35 2004-03-25 16:01:50

Re: LEO to TMI - discuss

#36 2004-03-25 16:48:36

Re: LEO to TMI - discuss

#37 2004-03-25 18:47:46

Re: LEO to TMI - discuss

#38 2004-03-25 19:49:16

Re: LEO to TMI - discuss

#39 2004-03-25 20:04:03

Re: LEO to TMI - discuss

#40 2004-03-25 22:30:27

Re: LEO to TMI - discuss

#41 2004-03-26 09:57:47

Re: LEO to TMI - discuss

#42 2004-03-26 17:09:10

Re: LEO to TMI - discuss

#43 2004-03-26 19:50:51

Re: LEO to TMI - discuss

#44 2004-03-26 22:17:47

Re: LEO to TMI - discuss

#45 2004-03-27 08:28:51

Re: LEO to TMI - discuss

#46 2004-03-27 12:04:49

Re: LEO to TMI - discuss

#47 2004-03-27 12:25:00

Re: LEO to TMI - discuss

#48 2004-03-27 13:04:20

Re: LEO to TMI - discuss

#49 2004-03-27 13:09:13

Re: LEO to TMI - discuss

#50 2004-03-27 17:35:39

Re: LEO to TMI - discuss

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