a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.
I see no reason either of those couldn't be developed. You're going to Mars, an HLV is only a drop in a full bucket of expenses.
Fundamental Problems3) a) Radiation exposure is possibly too harsh, depending on the solar cycle.Remedies3) a) A long column of water can be used as a solar radiation shield.
Nice summary!
Are you intentionally disregarding concerns about GCR?
Instead of staging from LEO, stage at L-1.
Testing tethers for artificial gravity would more like environment of Earth to Mars transit.
How about two spacecraft with 2 crew instead one with 4 crew. And with tether one could pilot from both ends.
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.
I didn't suggest staging from LEO, did I?
Quote from: QuantumG on 11/14/2013 10:21 pmI didn't suggest staging from LEO, did I? The Oberth effect says that using your EDS down in LEO will be more efficient than at L1.
Quote from: M129K on 11/14/2013 08:06 pmProblem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.Can this be mitigated by proper crew selection? (Sounds crazy but a serious question, if you have millions of people to pick from. Tolerance to long time in small spaces sounds like something that could be tested for on Earth.)
Quote from: gbaikie on 11/14/2013 10:15 pmInstead of staging from LEO, stage at L-1.I didn't suggest staging from LEO, did I? QuoteTesting tethers for artificial gravity would more like environment of Earth to Mars transit.Sorry, what?QuoteHow about two spacecraft with 2 crew instead one with 4 crew. And with tether one could pilot from both ends. Double the mission risk, double the mass, double the isolation.. why?
...3) a) Radiation exposure is possibly too harsh, depending on the solar cycle....3) a) A long column of water can be used as a solar radiation shield....
Someone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.
Quote from: KelvinZero on 11/15/2013 05:35 amSomeone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.For the purposes of shielding solar radiation I can't imagine why you'd need more than a column. While the flux might not come from the direction of the Sun, it will come from just the one direction at a time. So you "just" need to be able to point it.
That's a misconception. It comes from very widely varying angles. The average velocity of a particle over one gyration is in the same direction, but because the radius of gyration is large, they end up coming at you from all sorts of different angles (possibly even from behind you, though not as common).
Elon himself doesn't realize this.
Quote from: Robotbeat on 11/15/2013 08:06 amThat's a misconception. It comes from very widely varying angles. The average velocity of a particle over one gyration is in the same direction, but because the radius of gyration is large, they end up coming at you from all sorts of different angles (possibly even from behind you, though not as common).Not at the same time....
Quote from: QuantumG on 11/15/2013 10:12 amNot at the same time....Yes, at the same time. The solar particles are gyrating all over the place at large angles.
Not at the same time....
Quote from: Robotbeat on 11/15/2013 11:12 amQuote from: QuantumG on 11/15/2013 10:12 amNot at the same time....Yes, at the same time. The solar particles are gyrating all over the place at large angles.From all directions with similar intensity or would there be a direction where the bulk of the particles come from?
If you are going fast enough to reach Mars in 3 months; either you use a Hell of a lot of propellant to propulsively capture into Martian orbit - or you are going way too fast for aerocapture!!
Quote from: guckyfan on 11/15/2013 11:23 amQuote from: Robotbeat on 11/15/2013 11:12 amQuote from: QuantumG on 11/15/2013 10:12 amNot at the same time....Yes, at the same time. The solar particles are gyrating all over the place at large angles.From all directions with similar intensity or would there be a direction where the bulk of the particles come from?Not /exactly/ similar intensity, but generally pretty isotropic, other than I believe downwind which is reduced (but not eliminated).
....but their velocity of gyration will be small (I think) in comparison to their forward velocity, so should seem to come from one direction. ...
What do you mean? You'd just use it as shielding material. Doesn't need to do dual purpose as a carbon dioxide scrubber.
It wouldn't be a Hohmann transfer.http://en.wikipedia.org/wiki/Hohmann_transfer_orbit
NASA can't afford to develop and operate their own launch vehicles anymore.
Quote from: QuantumG on 11/14/2013 08:18 pmNASA can't afford to develop and operate their own launch vehicles anymore.So they can't afford the 5-10 billion for an HLV, but they can afford the over 100 billion dollars to go to Mars? Right.
If it costs that much, they're not going. Perhaps you missed the thread title. Mars Direct is all about avoiding the Battlestar Galactica sticker shock. I think it does a pretty good job of that, but falls down with the comparisons to the 1960s - particularly the assumption that recreating a Saturn V class vehicle is a viable option for future exploration.
No In-situ Propellant Production: No ISRU (In-Situ Resource Utilization) or local production of liquid propellands (typically Methane) or buffer gasses (N2, O2) is assumed for this study. By eliminating ISRU, we eliminate a development and operational risk assiciated with this technique, as well as the costs to demonstrate the technology as a precursor mission. We recognize that the availability of in-situ propellants would have a significant and positive impact on the required transportation system, but the current funding climate at NASA does not place a high priority on developing a mature propellant production capability on Mars by 2030.
Are you kidding me?QuoteNo In-situ Propellant Production: No ISRU (In-Situ Resource Utilization) or local production of liquid propellands (typically Methane) or buffer gasses (N2, O2) is assumed for this study. By eliminating ISRU, we eliminate a development and operational risk assiciated with this technique, as well as the costs to demonstrate the technology as a precursor mission. We recognize that the availability of in-situ propellants would have a significant and positive impact on the required transportation system, but the current funding climate at NASA does not place a high priority on developing a mature propellant production capability on Mars by 2030.That's the entire lynchpin of the architecture, and the reason why the costs are supposedly so much lower for Mars Direct.Oh, and none of the development costs for the HLV are included in the costing in that paper. So it's not just 14% of the total cost, plus the facilities costs, etc, it's some unspecified amount. As we saw, that amount kept growing and growing for Ares I and Ares V..
Hey, gbaikie - something about my Hell of a lot of propellant bothering you?
I was merely pointing out that if you are traveling to Mars from Earth orbit at a velocity that would get you there in 3 months (what shape "Hohmann trajectory" would that be?! And how fast - 11kms?) then you are going to need a lot of delta vee to scrub that velocity for a propulsive Mars orbit insertion; even a very 'lopsided' orbit. And as for doing the 'seven minutes of terror' direct descent to Mars at that kind of velocity...
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.Quote a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.I see no reason either of those couldn't be developed. You're going to Mars, an HLV is only a drop in a full bucket of expenses.
A quick review of the Mars Direct mission mode:
A quick review of the Mars Direct mission mode:Fundamental Problems1) a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available. b) As there is no current commercial use for a 100 ton to LEO class vehicle, the total cost of development and operations would have to be borne by NASA. c) The average flight rate of one launch per year (two every two years) is too low to anticipate reliable operations, increasing both loss of mission and loss of crew risk. d) The low flight rate also increases operations cost.2) a) The artificial gravity system is immature, with no tethers of the required length ever flown successfully in space. b) Without artificial gravity, the tuna-can hab is possibly too small to maintain crew health in zero-g.3) a) Radiation exposure is possibly too harsh, depending on the solar cycle.4) a) No nuclear reactors are available and this is seen by some as a political roadblock.
Remedies1) a) Use commercially available rockets to maximize cost sharing and higher launch rate benefits. b) As these are at least half the payload-to-LEO class (53t for Falcon Heavy), and of smaller core size (~5m diameter payload), at least the habitat (~9m diameter) will have to be redesigned. c) The various parts of the ERV and hab will need to be staged and assembled on-orbit during the two year build-up between each Mars transit window. d) Docking of fuel tanks can be done last to minimize boil-off of cryogenic propellants.2) a) Although artificial gravity experiments could be done, the now modular habitat design allows larger, while lighter, structure, suggesting a zero-g transit may be preferred. b) Astronauts will utilize exercise equipment and zero-g mitigation drugs to maintain bone and muscle mass.3) a) A long column of water can be used as a solar radiation shield.4) a) Use flexible photovoltaic power. The rover will need to be able to unpack and lay out the power system under remote control.
I am not really in favor of 6 month travel times {or 8 months}- prefer 3 month. And with 3 month I would skip any attempt of using artificial gravity. And only use one ship.But if going to do 6 month and if going to have artificial gravity- then maybe two ships??
If you are going fast enough to reach Mars in 3 months; either you use a HELL of a lot of propellant to propulsively capture into Martian orbit - or you are going way too fast for aerocapture!!
Mars Semi-Direct has always been my preference for the concept - with a dedicated MAV, so you don't have to manufacture heaps of ISRU propellant to fly all the way to Earth, just to Martian orbit. Similar to NASA's DRM-3 but with less 'bloat'.
Would still like a HLV capable of throwing 40 tons to TMI, but perhaps a commercially-derived launcher by Space X or similar. If the Commercial HLV was partially or fully re-usable, all the better.
Quote from: QuantumG on 11/17/2013 10:55 amIf it costs that much, they're not going. Perhaps you missed the thread title. Mars Direct is all about avoiding the Battlestar Galactica sticker shock. I think it does a pretty good job of that, but falls down with the comparisons to the 1960s - particularly the assumption that recreating a Saturn V class vehicle is a viable option for future exploration.I recall Mars Semi Direct being estimated at 55 billion dollars back in 1993. In modern day dollars, that's almost $90 billion. Mars Direct, even when avoiding an HLV, would still be well over 50 billion dollars and probably closer to $80 billion.
Quote from: gbaikie on 11/15/2013 03:14 amI am not really in favor of 6 month travel times {or 8 months}- prefer 3 month. And with 3 month I would skip any attempt of using artificial gravity. And only use one ship.But if going to do 6 month and if going to have artificial gravity- then maybe two ships??I'm no expert, but based on my limited understanding, there are problems with 3 month travel times.The 6 month travel time to Mars is like the Apollo 3 day travel time to the Moon. We could get there faster, but then we'd be going so fast that it would take an unreasonable amount of propellant for LOI.
As I understand Mars is the same way. To get there faster, you need to go faster. To go faster you need more dV requirements to brake into Mars orbit.
I think much faster than the 6- month time, your velocities are so fast that aerobraking/aerocapture become difficult or impossible. (if I'm incorrect, someone with more knowledge please correct me. :-) ) and then you need a lot of fuel to brake.
So that's part of the reason why that 6 month transit time is so often uses as the minimum time. I think one of the only concepts I've seen that speeds that up is VASIMR. And that's because it is so ISP efficient, it accelerate to VERY fast speeds for the first half of the trip, and then decelerates itself for the 2nd half, so when it arrives at Mars it can perform it's own MOI. Otherwise it'd get to Mars going so fast it'd fly right on by out for deep space.
Direct-entry, my friend! 10 gees, bah! Give me 20! They can take it!
Quote from: Robotbeat on 11/19/2013 05:39 pmDirect-entry, my friend! 10 gees, bah! Give me 20! They can take it!Give em a nice suit made out of 2 meters of gel and I'm sure they won't mind
Nothing has ever gotten to Mars in 6 months, unless one includes fly-by or crossing Mars orbit-
The link below points to a paper from 2006, called Mars for Less, where a variant of the Case for Mars solution was made using 25-tonne rockets to LEO. This was pre-SpaceX-FH9. I'm sure a "middle of the road" variant can be accomplished with less amount of launches using FH9.http://www.marsdrive.com/Libraries/Downloads/Reaching_Mars_for_Les_-_The_Reference_Mission_Design_of_the_MarsDrive_Consortium.sflb.ashx
Quote from: gbaikie on 11/19/2013 01:45 pmNothing has ever gotten to Mars in 6 months, unless one includes fly-by or crossing Mars orbit-Wow, that took three minutes of googling:Mars Odyssey launched 7 April 2001, Mars orbital insertion on 24 October 2001.Unless you intend to make some argument about rounding, that's 6 months isn't it?
Quote from: catiare on 11/18/2013 06:42 pmThe link below points to a paper from 2006, called Mars for Less, where a variant of the Case for Mars solution was made using 25-tonne rockets to LEO. This was pre-SpaceX-FH9. I'm sure a "middle of the road" variant can be accomplished with less amount of launches using FH9.http://www.marsdrive.com/Libraries/Downloads/Reaching_Mars_for_Les_-_The_Reference_Mission_Design_of_the_MarsDrive_Consortium.sflb.ashxVery interesting. Looks kinda like Mars Direct, but with something like an Atlas V-heavy. Looks like it utilizes the economics of scale. Keep things standardized and simple, and make a lot of them. namely the cyro stages. Launch the ERV, and then launch a bunch of Centaurs or DCSS's to LEO and stack them up behind it and do a multiple stage boost. (Actually it'd be a CPS with a fairly long duration loiter capability)Wonder if there'd be problems with so many stages linking in orbit and operating properly?On the subject of their ERV and Hab lander, I'd been pondering this myself. What is does look like? Kinda like a big dragon capsule to me. It's been shown that a Dragon capsule could land on Mars with it's LAS system and heat shield. So...could that just be scaled up? A much larger Dragon Capsule, with methalox engines on it's sides rather than hypergolic superdracos? It would trade a smaller heat shield with less dV for more propulsion to make up for it. I think such a craft to get on the surface pretty readily, but getting it back off the surface could be an issue with it's engines angled off in the sidewall. That makes for a big performance hit I think for ascent and TEI. So, is there any mechanical way to reposition those sidewall engines so that they do point directly down? Could they pivot, or actuate, out and down so the downward plume would not impinge on the craft too much?They wouldn't need to do that during EDL, just while on the surface prior to lift off. No need for that on the Hab lander. It's not getting back off the surface.Side mounted engines also means the lander itslef can be closer to the surface, with out landing on it's engines.This would assume a larger LV like FX/FXX/MCT rather than the smaller EELV class in this paper.
When anyone says "six months" they mean you count the months. The number of days is just nitpicking.May, June, July, August, September, October = 6 months.I really thought you weren't going to make a rounding argument, but you did. Do you know what this does to my faith in this forum? Please, try not to do that.
I just found the original paper in an old hard drive. Its from circa 2003 and the author presented an alternative to centaur by using a CH4/O2 Propulsion System and used a 20-Tonne budget instead. Attached is the PDF.
But fastest travel time to Mars has been about 180 days. And in terms of flybys it could be as little as about 80 days. If using hohmann transfer and launching from Earth surface with the available chemical rockets.
Anyways, my point is one can get to Mars in 2 to 3 month starting from Earth high orbit using chemical rockets. You simply make a spacecraft have same velocity as *if* it were coming from Venus and doing a gravity assist off Earth. Or it's not a hohmann transfer from Earth distance, it's a hohmann transfer from Venus distance [or range orbital distances near Venus or near Mercury distances].
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars. This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc. Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.
One thing I happened to notice last night.. there's quite a number of people who have said the crew would return to Earth in zero-g in the Mars Direct scenario. I don't know where this came from, but it isn't Zubrin. He suggests the ERV should have a propulsion half and a cabin half, and the two could separate on a tether to produce artificial gravity, just like the tuna-can hab and the earth departure stage.
Quote from: gbaikie on 11/20/2013 01:17 amBut fastest travel time to Mars has been about 180 days. And in terms of flybys it could be as little as about 80 days. If using hohmann transfer and launching from Earth surface with the available chemical rockets. 180 days ~ 6 months is what I've seen before, I believe in NASA DRM's and such. (I think Zubrin too, but it's been awhile since I've read "The Case for Mars" so I can't remember for sure what he recommneded after evaluating several possibilities).Maybe that's just a good confluence of speed to get there without exposing the crew to too much radiation and time in zero-g like some of the lower energy 270 day trajectories, not needing an unreasonable amount of propellant, and still not going so fast that aerobraking/aerocapture cannot be used?Maybe that's why that transit time gets referenced as a baseline?We have a lot of experience with crews in zero-g for 6 month stays on the ISS, but I don't know we've let anyone stay much longer than that. That seems to be where our knowledge base is. Although obviously the Russians have done longer. We still need our crews to get to Mars and be able to function without a lengthy rehabilitation time. So maybe that's a component of it, as well as leaving aerobraking/aerocapture options when we get there and not needing -too- much fuel to do it in that time like some of the shorter trajectories.
My knowledge of orbital mechanics is limited enough that I cannot comment on the merits of your concept. I'd only ask why I can't recall seeing any concepts (other than VASIMR) that gets to Mars and can make Mars Oribt still that are faster than 6 months?
And VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part. And thus doesn't need any aerobraking/aerocapture when it gets to Mars.
Can your 2-3 month trajectory still do free returns back to Earth?
I think the 6 month ones can, but perhaps I'm mistaken on that.
That may be a consideration in case there's a problem en route. They can always swing by and can still get home. (which is a potential issue with Mars Direct or Semi-Direct. On a free return trajectory back to Earth, I don't think a Hab Lander could get safely through EDL on Earth?)
QuoteAnd VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part. And thus doesn't need any aerobraking/aerocapture when it gets to Mars.Well, since this thread is about Mars Direct and it's Zubrin's baby. Let's look at what Bob says aboutVASIMR:The VASIMR HoaxBy Robert Zubrin | Jul. 13, 2011"VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have."And:"But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system."http://www.spacenews.com/article/vasimr-hoaxI would have different arguments about it. But I will leave it there.
Quote from: gbaikie on 11/21/2013 01:24 amQuoteAnd VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part. And thus doesn't need any aerobraking/aerocapture when it gets to Mars.Well, since this thread is about Mars Direct and it's Zubrin's baby. Let's look at what Bob says aboutVASIMR:The VASIMR HoaxBy Robert Zubrin | Jul. 13, 2011"VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have."And:"But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system."http://www.spacenews.com/article/vasimr-hoaxI would have different arguments about it. But I will leave it there.I think you misunderstand what I meant. I wasn't clear. I think VASIMR -is- game changing technology....if it could be ever be feasibly built some day.
What I mean by game changing, is a self contained vehicle that has enough on board propellant to get itself all the way to Mars, and all the way back with the fuel it leaves Earth with. It uses both powered acceleration and powered deceleration. And, hypothetically, it would generate at least some artificial gravity.
In the mean time, I think if our crew transits were kept to 6-7 months each way, the effects of zero-g on the crew could be mitigated enough via conventional means that they'd arrive at Mars able to function fine, and then on the return trip, it's not necessary because it wouldn't be any different than a crew returning from a 6 month stay on the ISS. Let's focus on what's -necessary- to develop, rather than adding the complexity of spinning tethers and artificial gravity.Again, start with the lowest common denominator. The most simple thing that would work, and then work out from there adding cost and complexity in exchange for capability until we find a happy medium.
Quote from: JasonAW3 on 11/20/2013 09:16 pmThis is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars. This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc. Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.
Quote from: LegendCJS on 11/20/2013 09:25 pmQuote from: JasonAW3 on 11/20/2013 09:16 pmThis is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars. This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc. Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.Good point. And you don't want to leave things there for -too- long, subjected to the surface conditions for years before humans are there if you can help it.I think you make sure you have an adequate system of satillites for constant communications with Earth 24/7 for the duration of the mission. (or in the case of Mars, 24.6/7. Heh.)Once you have that, I think you launch two HLV's in quick succession, to launch the MAV and ERV (if Mars Semi-Direct), or MAV and Hab lander (if using a Cycler), or just one launch for the ERV if goind Mars Direct.Then two years later launch the crew. So you don't have a "ghost town", just a couple of major elements ahead of the crew.
I feel the same way towards nuclear fusion electrical power plant for use on Earth. So it's unlimited cheap electrical energy, and it would be wonderful.But they aren't developed.
And there are other ways to get unlimited cheap electrical power.I think more money spend on NASA would be better path to unlimited cheap electrical power, than money spent on fusion research. But then again, rather than cut fusion research, I would have many other higher priority of government programs I would want cut, as compared to the apparent uselessness of fusion research.
Likewise VASIMR or something like VASIMR may be developed in the future. I would bet on cheap fusion power plant as more likely than VASIMR.And likewise there ways to get to Mars which can as fast, but due to costs, I would limit it to 60 to 90 day Mars transit time for crew. 39 days to Mars would be quite challenging [expensive] with chemical rockets. But if make rocket fuel in space, which means we develop electrical market in space, which means one could buy a lot electrical power- like a 100 million dollars worth at $10 per kW hour and get this much power within hour of time. So one can get 10,000 MW hour of electricity and beam this energy at spacecraft which use the energy, one could manage to get some high velocities. Of course this quantity of energy would cheap compared to the laser that used it. Or energy storage you might need. But there was enough need for it- you had human settlement on Mars, it might worth the high costs. But point is if you have already the energy producing infrastructure being used for something else, then you don't have to start with building power plants, so can then make some laser.Rather you can simply buy the electrical power you need for the project. So VASIMR might look quite different if it didn't have make a power plant and accelerate it's power plant.
Well it could be useful to find things- they will tend to be at back of ship.But a 1/10th of gee for one hour is .98 * 3600 or 3.5 km/sec. So 2 hr: 7 km/sec. 4 hr 14 km/sec and8 hr 28 km/sec.1/100th of gee is 8 hr: 2.8 km/sec, 16 hours: 5.6 km/sec, 32 hours is 11.2 km [and look out widow and Earth is still there:) ], 64 hours is 22.4 km/sec [Earth will be at fair distance away but Mars does not look closer].1/1000th of gee: 64 hours is 2.24 km/sec [Earth hasn't moved much], 128 hours is 4.48 km [You certain Earth has moved away], 256 hours [10.6 days] is 8.96 km/sec [You feel like you making progress but Marsdoes not look any closer.].Now perhaps you start with 1/10th and do 1000th for rest of trip. But at 1/1000th of gee, 200 lbs is .2 lbs and many things will essentially float or bowling ball takes few minutes to hit the floor and bounce-surprising well.
The thing is, if you aero brake into orbit, you don't have to send everything down at once. Keep the habs and supply modules in orbit until you decide on a final landing zone.
Use a flying probe to low level map possible landing sites. (Radar could also be used to determine ground stability and if there are any potentile voids under the intended landing site). Use a lander to confirm the flyers observations (And to act as a beacon for the other equipment and hab landings.)
In reading this thread it occurs to me that it is not a big leap to say that chemical rocket propulsion is inadequate for cheap sustainable manned Mars travel. Its use requires too much propellant and longer than desirable transit times because of the limited energy from chemical reactions. VASIMR, breeder type fission, and fusion have been posited as answers but each are at present undeveloped to the necessary TRL and likely require considerable time and money to change that. if this is accepted as true then shouldn't one look at the elephant in the room - the other obvious possibility?
Quote from: Solman on 11/23/2013 09:03 pm@ Lobo I think you missed my point. Solar concentrator tech offers more than an order of magnitude improvement over existing solar PV. If you wanted hot water this might be right. If compared to using PV to make hot water in a home- sunlight to electric power and electrical power to make hot water- in terms of costs....So on Earth concentrated solar power is not 10 times better unless you confining what you are comparing....
@ Lobo I think you missed my point. Solar concentrator tech offers more than an order of magnitude improvement over existing solar PV.
Concentrator PV using the L'garde concentrator would likely exceed 5000W(elec.)/kg. for perhaps 3+ KW/kg (at 70% efficiency and allowing for the mass of power supply equip. and the elec. engine itself)
Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...] 5) Mars to Mars Orbit 6) Mars Orbit to Earth Orbit
Quote from: kkattula on 11/25/2013 03:50 amTaking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...] 5) Mars to Mars Orbit 6) Mars Orbit to Earth OrbitAre you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory will have a lower delta-v than the sum of the two maneuvers you list?Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?
I would assume the early missions to Mars would be one-way due to the low-cost, simplicity and desire to create a colony. Those who want to return to Earth probably dont have the right stuff.We might still possess the infra-structure of reusable cyclers for crew comfort on the trip to Mars .I think after a few years on Mars we should be able to have enough ground equipment to allow for the safe launch to orbit and rendezvous with the cycler.
Are you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory have a lower delta-v than the sum of the two maneuvers you list?
Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?
That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.For a single mission the rendezvous and docking may be better. For a (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent....
Quote from: guckyfan on 11/25/2013 06:43 amThat's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.For a single mission the rendezvous and docking may be better. For a (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent....I think you've got that around the wrong way. For a one-off mission, there's no need to re-use any component, so you can throw away your outbound habitat, propulsion systems, ERV, etc, and subject the crew to extreme conditions.In an extended settlement scenario, you can't afford to send a new disposable ERV every time. Let alone all the rest. I will grant you ISRU is more affordable across multiple missions, but it should lead to the path of re-usable descender/ascender.
Quote from: Solman on 11/23/2013 09:03 pmConcentrator PV using the L'garde concentrator would likely exceed 5000W(elec.)/kg. for perhaps 3+ KW/kg (at 70% efficiency and allowing for the mass of power supply equip. and the elec. engine itself) References? Hardware built?
My opinion on the Mars Direct plan is that landing an ERV is a poor idea. Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture.
Quote from: sdsds on 11/25/2013 05:22 amQuote from: kkattula on 11/25/2013 03:50 amTaking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...] 5) Mars to Mars Orbit 6) Mars Orbit to Earth OrbitAre you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory will have a lower delta-v than the sum of the two maneuvers you list?Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.For a single mission the rendezvous and docking may be better. For a (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent.ISRU on Phobos would change the equation again.
It all depends on how much money you have available. The cheapest and simplest mission is going to be one-way and it also saves the danger of taking off from Mars, possibly having to rendevous with the return craft or alternatively ensuring the whole craft for the return trip arrives safely on the surface (with fuel on board or the extra complexity of manufacturing fuel from the Martian resources).A well financed return mission, with the return equipment pre-delivered to Mars and tested, could be the safest for the astronauts but I expect the probability of construction staff (Earth, LEO) being accidentally killed would be much higher on such a massive project. The project would also be so expensive, it will probably never happen.
Quote from: colbourne on 12/04/2013 03:53 amIt all depends on how much money you have available. The cheapest and simplest mission is going to be one-way and it also saves the danger of taking off from Mars, possibly having to rendevous with the return craft or alternatively ensuring the whole craft for the return trip arrives safely on the surface (with fuel on board or the extra complexity of manufacturing fuel from the Martian resources).A well financed return mission, with the return equipment pre-delivered to Mars and tested, could be the safest for the astronauts but I expect the probability of construction staff (Earth, LEO) being accidentally killed would be much higher on such a massive project. The project would also be so expensive, it will probably never happen.How can a one way mission be cheaper than a return mission? I thought I had read somewhere on this forum that it takes about 7 times the fuel/kg of payload to return from Mars to Earth, than it takes to get from here to there. How can the supplies needed by the colonists for the rest of their lives, be less than 7 times the weight of the ERV? Especially if that ERV (and the separate launch vehicle) is designed to be as light as possible. I'm ignoring ISRU at the moment, because any technology suggested so far is actually going to be subjected to incredible heavy usage and wear, and is going to INCREASE the mass of the needed supplies.
How can a one way mission be cheaper than a return mission? I thought I had read somewhere on this forum that it takes about 7 times the fuel/kg of payload to return from Mars to Earth, than it takes to get from here to there. How can the supplies needed by the colonists for the rest of their lives, be less than 7 times the weight of the ERV? Especially if that ERV (and the separate launch vehicle) is designed to be as light as possible. I'm ignoring ISRU at the moment
Personally, I think one way trips really only make sense if you're convinced that you can grow crops on Mars.. but it appears sending a 10 ton resupply mission from Earth every launch window would be sufficient to keep a small crew alive on Mars indefinitely, if that's what you wanted to do.
I would pretty surely think that in any Mars architecture, SpaceX or NASA, that all of the first several crews would come back. It wouldn't be until a much later time after a lot of technology on the surface of Mars has been demonstrated and proven, and a lot of study of the effects of stays on the Mars surface..they might want to be showing they can grow food and produce water in-situ reliably
Ethylene can be produced pretty directly from methane (which we'll be making anyway). Ethylene is useful for all sorts of substances, but most relevant is that it can be made into Dyneema/Spectra pretty easily and can also be made into typical greenhouse plastic pretty easily. These two together can allow you to expand your living space or the space you grow stuff in relatively easily.
Imagine well-insulated (enough to prevent over-night freezing) giant bubbles of polyethylene with water, seed algae, and CO2 inside... distributed across the landscape (perhaps with simple aluminum reflectors to maximize output)... after the CO2 in the bubbles is consumed and converted into algae biomass, you collect the bubbles, suck out the O2 for use on the colony, suck out the water for recycling, then reprocess the rest into new plastic and food or something. You could design a machine would could produce these bubbles in an automated process, allowing a dramatic increase in growing area without a lot of infrastructure or work.
Quote from: Robotbeat on 12/18/2013 06:08 amEthylene can be produced pretty directly from methane (which we'll be making anyway). Ethylene is useful for all sorts of substances, but most relevant is that it can be made into Dyneema/Spectra pretty easily and can also be made into typical greenhouse plastic pretty easily. These two together can allow you to expand your living space or the space you grow stuff in relatively easily.Actually, not it can't just yet. It would be a very useful process to have here on earth with increasing methane production but so far it is only a lab capability but cannot be done on a technical scale. Intense research is ongoing though to achieve it. Yes it will be very useful on Mars.
Quote from: Robotbeat on 12/18/2013 06:08 amImagine well-insulated (enough to prevent over-night freezing) giant bubbles of polyethylene with water, seed algae, and CO2 inside... distributed across the landscape (perhaps with simple aluminum reflectors to maximize output)... after the CO2 in the bubbles is consumed and converted into algae biomass, you collect the bubbles, suck out the O2 for use on the colony, suck out the water for recycling, then reprocess the rest into new plastic and food or something. You could design a machine would could produce these bubbles in an automated process, allowing a dramatic increase in growing area without a lot of infrastructure or work.I think they would use pipes or hoses to circulate water for algae growth instead. Also very easy to manufacture once you have ethylene and does not need significant strength for the needed pressure. Also sunlight can get to the algae very easily. Efficiency would drop during duststorms but production would not stop if you can keep the temperature in the needed range.
I agree. Tubes are a better plan.
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.
Quote from: Robotbeat on 12/18/2013 05:37 amSure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal. (Yes, cyanobacteria are not technically algae, but...)
Quote from: Vultur on 12/19/2013 03:19 amQuote from: Robotbeat on 12/18/2013 05:37 amSure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal. (Yes, cyanobacteria are not technically algae, but...)Ammonia is useful for other things, and it's one of the easier things to synthesize, given a stream of hydrogen and nitrogen.
Quote from: Robotbeat on 12/19/2013 05:48 amQuote from: Vultur on 12/19/2013 03:19 amQuote from: Robotbeat on 12/18/2013 05:37 amSure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal. (Yes, cyanobacteria are not technically algae, but...)Ammonia is useful for other things, and it's one of the easier things to synthesize, given a stream of hydrogen and nitrogen.How low mass can you get the synthesis equipment though? IIRC it involves pretty high pressures...I don't think farms in a Mars colony would need very much fertilizer at all - on Earth massive fertilizer is needed because crops are removed from the system. But if human wastes are recycled into the agriculture, relatively little nitrogen will be lost.
Quote from: kkattula on 11/25/2013 03:50 amMy opinion on the Mars Direct plan is that landing an ERV is a poor idea. Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. Actually I think the opposite. I think it's probably the lowest common denominator of a Mars mission. The most basic and simple (not complex) way to do a mission.It's also the most mass inefficient way to do it. I agree with the rest of your post though. Although it does leave a crew hab and equipment on the surface that future crews could access. Zubrin's planned called for each subsequent mission to land within rover range of the previous mission hab lander, so if there was a problem with their hab lander, they could travel to the other one and use it as a life boat until the orbital mechanics were such they could enter their ERV and head home. And each mission after would do the same, leap frogging accross Mars to establish a pattern of exploration. That was the idea anyway.
Yeah, that's what it seems like it will be. Though I think it can fly with or without the hab module portion. Perhaps even be detachable (that way they can use MCT for launching commsats, too). Speculation, of course. But that's essentially what the Twitter exchange that Musk had with someone implied.
A quick review of the Mars Direct mission mode:1) a) A heavy lift launch vehicle in the 100 ton to LEO class launches an Earth Return Vehicle (ERV). b) After remote checkout in LEO, the LH2/LOX Earth departure stage throws the ERV to an 8 month transit to Mars. c) The ERV aerobrakes into Mars orbit, and remote checkout is made again. d) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed. e) The parachutes are detached and the ERV lands under rocket power.2) a) A hatch opens on the ERV, an a rover carrying nuclear reactor and trailing an electrical cable is deployed. b) It drives the nuclear reactor some distance away and preferably over a hill or two. c) The nuclear reactor is offloaded and started. d) The ERV begins processing the Mars atmosphere to produce methane and LOX, using a supply of LH2 brought from Earth. e) The rover searches for an appropriate landing site and marks it with a radar beacon.3) a) A heavy lift launch vehicle in the 100 ton to LEO class launches another Earth Return Vehicle (ERV). b) See steps 1 and 2, a different landing site is chosen within travel range of the first landing site.4) a) A heavy lift launch vehicle in the 100 ton to LEO class launches a "tuna can" habitat with 4 astronauts. b) After checkout in LEO the LH2/LOX Earth departure stage throws the hab on a 6 month transit to Mars. c) The now spent upper stage is used as counterweight to spin up the hab on a ~150m tether, at 2 rpm, to produce artificial Mars gravity for the crew. d) After aerobraking into Mars orbit, the crew inspects the landing site for weather, marker signal strength, etc. e) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed. f) The parachutes are detached and the crew lands under rocket power at the transponder.5) a) 500 day ground operations begins b) The crew drive a pressurized rover to the ERV to obtain methane and LOX for powering the rover and breathing, etc.6) a) When it's time to leave, the crew get into the ERV and liftoff. b) The ERV returns directly to Earth. c) Reentry is direct (the ERV doesn't go into orbit first). d) Landing is preferably on land for quick recovery.Fundamental Problems1) a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available. b) As there is no current commercial use for a 100 ton to LEO class vehicle, the total cost of development and operations would have to be borne by NASA. c) The average flight rate of one launch per year (two every two years) is too low to anticipate reliable operations, increasing both loss of mission and loss of crew risk. d) The low flight rate also increases operations cost.2) a) The artificial gravity system is immature, with no tethers of the required length ever flown successfully in space. b) Without artificial gravity, the tuna-can hab is possibly too small to maintain crew health in zero-g.3) a) Radiation exposure is possibly too harsh, depending on the solar cycle.4) a) No nuclear reactors are available and this is seen by some as a political roadblock.Remedies1) a) Use commercially available rockets to maximize cost sharing and higher launch rate benefits. b) As these are at least half the payload-to-LEO class (53t for Falcon Heavy), and of smaller core size (~5m diameter payload), at least the habitat (~9m diameter) will have to be redesigned. c) The various parts of the ERV and hab will need to be staged and assembled on-orbit during the two year build-up between each Mars transit window. d) Docking of fuel tanks can be done last to minimize boil-off of cryogenic propellants.2) a) Although artificial gravity experiments could be done, the now modular habitat design allows larger, while lighter, structure, suggesting a zero-g transit may be preferred. b) Astronauts will utilize exercise equipment and zero-g mitigation drugs to maintain bone and muscle mass.3) a) A long column of water can be used as a solar radiation shield.4) a) Use flexible photovoltaic power. The rover will need to be able to unpack and lay out the power system under remote control.
I'm in favour of landing the whole ERV.Today we are watching nervously unmanned rockets' stage separations and opening a hatch in the ISS and so on, so imagine what it would be with Mars orbit rendezvous with people on board with the spacecrafts that have been launched from Earth years ago. So having absolutely minimum amount of critical steps after launching the ERV is important.About the ERV, did Zubrin plan it to be only a single module which would land on Earth? Or could it have separate hab module and landing capsule? With single module you would not have to turn the capsule and move the crew to the hab module after launch (which worked fine in Apollo though). And with hab + lander configuration you could probably have some abort possibility back to Mars if the launch fails (with vehicle like propulsive Dragon) and the heat shield mass would be smaller when landing only a small capsule to Earth.
Zubrin briefly outlines Mars Direct
talks a little about what can be done with the Falcon Heavy.
During the question period, he mentions that the one thing he would change about Mars Direct, is that he wouldn't send any cryogenic hydrogen. Just make it there from Mars water. His company, Pioneer something, did a study -baking water out of soil that is 5% water (Mars obviously has a lot higher concentrations in some areas).
But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.
QuoteBut the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.Could use something like bunker buster which impacts areas of deeper permafrost. ...
Quote from: MikeAtkinson on 02/09/2014 09:33 amBut the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.I don't get the soil thing. Why not land near the ice cap and use ice that you can just cut out of the ice cap right on the surface? It will be incredibly cold anyway...
Regarding Mars Semi-Direct (where the ERV remains in LMO rather than stages from Mars's surface) one thought that always occurred to me is that it makes the Mars Ascent Vehicle potentially overpowered. I suppose it means that you could carry 200% of the required propellent from the Martian surface to LMO and pump the remainder into the ERV, increasing its delta-V budget.To me, Mars Direct always had one enormous problem and that was it was a hyper-optimistic plan assuming best cases in space environment, crew psychology, ISRU efficiency, politics and budget. Any real mission plan would probably have to be a lot more conservative.
Zubrin briefly outlines Mars Direct, and talks a little about what can be done with the Falcon Heavy.
Because you can make so much propellant you make extra propellant that allows you to propel ground vehicles using chemical engines which is really what you want because ground vehicles using chemical engines, combustion engines, have much higher power to mass ratio than you can get with fuel cells or batteries or radio isotopes. And that's why they're so much more popular here on Earth. In a frontier environment like Mars where you really do need the long range, the speed, the torgue, the hauling capability of having real car instead of a golf cart you really want to have one. It's essential you are going to Mars to explore the key requirement is mobility.
Ha, Martian combustion engines vindicated!
Quote from: ZubrinBecause you can make so much propellant you make extra propellant that allows you to propel ground vehicles using chemical engines which is really what you want because ground vehicles using chemical engines, combustion engines, have much higher power to mass ratio than you can get with fuel cells or batteries or radio isotopes. And that's why they're so much more popular here on Earth. In a frontier environment like Mars where you really do need the long range, the speed, the torgue, the hauling capability of having real car instead of a golf cart you really want to have one. It's essential you are going to Mars to explore the key requirement is mobility.Ha, Martian combustion engines vindicated!
Quote from: R7 on 02/09/2014 07:58 pmHa, Martian combustion engines vindicated! Zubrin suggests ISRU demo on the sample cache rover mission, but I'd rather see a Red Dragon ISRU that's quick, cheap, and independent of a rover mission.
I also would want to see an independent mission, MSL 2 (or whatever it is called) will have very limited mass, power, volume and time budgets for ISRU. Much better a dedicated mission with two or three orders of magnitude more in each of these dimensions. The difficulty in ISRU is making it reliable at full scale, but in proving that 19th century chemistry works, and ISRU demo on MSL2 does not seem to be able to retire much of the risk of full scale ISRU.
Desirable landing spots will be much nearer the equator.
Quote from: guckyfan on 02/09/2014 04:33 pmDesirable landing spots will be much nearer the equator.Why? Less delta-v?
I still think Hellas Basin is a good choice. I know it's dusty, but it's got the highest pressure and I believe contains buried glaciers. Pressure is high enough to be above the triple point of water. If you're using fission, it's a great spot.
Quote from: Robotbeat on 02/12/2014 08:28 amI still think Hellas Basin is a good choice. I know it's dusty, but it's got the highest pressure and I believe contains buried glaciers. Pressure is high enough to be above the triple point of water. If you're using fission, it's a great spot.At 30° on its northernmost part I think it fits also my wish to be near the equator well enough. Yes it looks like a good location with water and high pressure, good for landing.
There are some advantages of being near the polar ice caps ie.1) There should be easily available water, which is an essential resource.2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere. In the summer this means solar power all the time. Nuclear power probably would be used in the winter.3) I could see ice caves being used for living space.4) This is an interesting area to explore due to the slight possibility of life and the effects of the ice.
2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.
In the summer this means solar power all the time. Nuclear power probably would be used in the winter.
Quote from: colbourne on 02/13/2014 10:43 am2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.Solar power is a lot less at the poles than at the equator - it's why the ice caps are at the poles!
Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.
Solar power is a lot less at the poles than at the equator - it's why the ice caps are at the poles!
But if normal levels of dust and sun is low on horizon if pointing solar panels at the sun [rather than having them lying on level surface] one can get almost as much watts per square as get with sun directly over head [and solar panel pointed at sun].
Zubrin briefly outlines Mars Direct, and talks a little about what can be done with the Falcon Heavy. During the question period, he mentions that the one thing he would change about Mars Direct, is that he wouldn't send any cryogenic hydrogen. Just make it there from Mars water. His company, Pioneer something, did a study -baking water out of soil that is 5% water (Mars obviously has a lot higher concentrations in some areas).
...
On an airless body, the angle of the sun doesn't matter, as long as you have your arrays pointed at the right angle and don't self-shadow. For flat planels not tilted, then yeah, poles will have basically no sun at any time. But if you tilt the panels toward the sun, then as long as the sun is up, you'll get the same amount of sun as at the equator.For an airless body.
If the extra hydrogen to account for boil-off wasn't included, its a stunning omission...
Since the hydrogen component of the bipropellant mixture represents only about 5% of the total propellant weight it can be imported from Earth. Heavy insulation of tanks with multi-layer insulation (MLI) can reduce in-space boiloff of liquid hydrogen to less than 1% per month during the 6 to 8 month interplanetary transit without any requirement for active refrigeration. Since the hydrogen raw material is not going to be directly fed into an engine, it can be gelled with a small amount of methane to prevent leaks. Gelling of the hydrogen cargo will also reduce boiloff further (as much as 40%) due to suppression of convection within the tank.Referencing:8. Aerojet Techsystems, "Gelled Cryogenic Fuels: Past Experience and Future Needs," presentation to McDonnell Douglas Corp. , St. Louis, MO, March 10, 1987.
Quote from: Darkseraph on 09/07/2014 12:09 amIf the extra hydrogen to account for boil-off wasn't included, its a stunning omission...LH2 boiloff was accounted for in the 1991 paper.Quote from: Bob ZubrinSince the hydrogen component of the bipropellant mixture represents only about 5% of the total propellant weight it can be imported from Earth. Heavy insulation of tanks with multi-layer insulation (MLI) can reduce in-space boiloff of liquid hydrogen to less than 1% per month during the 6 to 8 month interplanetary transit without any requirement for active refrigeration. Since the hydrogen raw material is not going to be directly fed into an engine, it can be gelled with a small amount of methane to prevent leaks. Gelling of the hydrogen cargo will also reduce boiloff further (as much as 40%) due to suppression of convection within the tank.Referencing:8. Aerojet Techsystems, "Gelled Cryogenic Fuels: Past Experience and Future Needs," presentation to McDonnell Douglas Corp. , St. Louis, MO, March 10, 1987.It's actually more than I've seen any other architecture say about boiloff.
Oh fair enough, that avoids that problem. I've never seen it mention in any of the talks, slides, op-eds and other avenues of ranting that Zubrin takes to. Has this approach actually been tried or intended for use on say, propellant depots?
Quote from: Darkseraph on 09/07/2014 12:29 amOh fair enough, that avoids that problem. I've never seen it mention in any of the talks, slides, op-eds and other avenues of ranting that Zubrin takes to. Has this approach actually been tried or intended for use on say, propellant depots?The gelling? Well, no, because LH2 in propellant depots is "going to be directly fed into an engine".
Solar powered cryocoolers are the low-tech solution - the general term is refrigeration.Insulation and sun shades with careful thermal management are still the rage, I think.
It just occurred to me I have never seen the option of using hydrogen fuel discussed for mars...
Quote from: KelvinZero on 09/06/2014 04:25 pmIt just occurred to me I have never seen the option of using hydrogen fuel discussed for mars... Hydrogen as fuel is unpopular with rocket designers unless the greater performance is a necessity because of the much greater difficulties in handling and storage etc. And that's on Earth with all its manpower and other resources.Also, the Carbon in methane shouldn't be discounted. It may have a lower Isp than the Hydrogen (what would the Isp of Carbon be?) but it's readily available.
Quote from: CuddlyRocket on 09/08/2014 08:49 amQuote from: KelvinZero on 09/06/2014 04:25 pmIt just occurred to me I have never seen the option of using hydrogen fuel discussed for mars... Hydrogen as fuel is unpopular with rocket designers unless the greater performance is a necessity because of the much greater difficulties in handling and storage etc. And that's on Earth with all its manpower and other resources.Also, the Carbon in methane shouldn't be discounted. It may have a lower Isp than the Hydrogen (what would the Isp of Carbon be?) but it's readily available.Fair enough, but the second part of my post was how it was strange that the moon ISRU always focuses on the water when the evidence suggests that there is even more carbon monoxide in the LCROSS result.
As for hydrogen fuel being unpopular with rocket designers, hasn't methane been much less popular? Who currently uses it?
I also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)
Quote from: KelvinZero on 09/08/2014 09:56 amI also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)That would apply to all propellants and hence not a valid reason not to use H2.
I admit this was totally a laymans guess but I thought I had good reasons. So you would argue H2 storage does not have increased risk of developing leaks?The reason I assumed it would were:(*) materials having to deal with greater cold.(*) A greater motivation to optimize tank mass, since the tank is larger.(*) The ability of the hydrogen molecule to slip through smaller cracks.Does the history of hydrogen fueled rockets suggest they do not have increased risk of leaks?
Quote from: QuantumG on 09/07/2014 12:51 amSolar powered cryocoolers are the low-tech solution - the general term is refrigeration.Insulation and sun shades with careful thermal management are still the rage, I think.I had always assumed that was just for demonstrators. Active cooling can be investigated separately, and sure, it might not even prove necessary, depending on the application. Probably not a good idea for propellant depot proponents to bulk up the price with nice-to-haves in the current environment. But the result is that people always quote values predicted for these passive demonstrators as if this is evidence that zero boil-off is impossible with our current knowledge. I have yet to see an argument that it is even hard. (.. I am guessing)
For example, the solar constant is 1370 W/m2 for Earth, 588 W/m2 at Mars. Perfect MLI reduces the heat load by 1/n+1. the projected area of the tank is Do * L. As an example, choose 5m by 6m Long and 99 layers of MLI. So the heat load is now 13.70 W/m2 * 30 m2 or 411 Watts(Earth) or 176 Watts (Mars)--this is the amount of constant thermal load into the LH2. Uh-Oh, what is the boiloff rate at this heat load?
Not enough to disqualify it from manned missions far away from home.
Quote from: muomega0 on 09/09/2014 01:37 pmFor example, the solar constant is 1370 W/m2 for Earth, 588 W/m2 at Mars. Perfect MLI reduces the heat load by 1/n+1. the projected area of the tank is Do * L. As an example, choose 5m by 6m Long and 99 layers of MLI. So the heat load is now 13.70 W/m2 * 30 m2 or 411 Watts(Earth) or 176 Watts (Mars)--this is the amount of constant thermal load into the LH2. Uh-Oh, what is the boiloff rate at this heat load?I'm not sure where you're getting the numbers you're using from (since Kelvin didn't provide any), or why you're so focused on passive methods when both QuantumG and KelvinZero are clearly talking about using cryocoolers and actively cooling LH2?
How hard would it be to crack methane so that you could combine the O2 and hydrogen for potable water?Could a Fuel Cell be configured to use Methane to generate power and potable water?
100s of watts of cooling at 20K is a great engineering challenge when faced with mass and cost budgets. Hence 'not hard' just does not seem to fit. Conservative paper studies backed with low TRL data indicated the active concept can be achieved however, but over 100W of cooling! Contrast this with other space cryocooler programs
I think I remember something about Robert Zubrin more recently going to the option of exploiting local water..
Quote from: KelvinZero on 09/06/2014 04:25 pmI think I remember something about Robert Zubrin more recently going to the option of exploiting local water..If you send the return vehicle + ISRU equipment before you send people, that seems like the better approach.
Estimates are 200-450 meters at the equator, 50-200 meters at 30-55 degrees latitude, and less than 100 meters poleward of 55 degrees.
Sounds fiddly though, with teleoperation.
Hartmann's book on Mars (very highly recommended) says that water ice is at depths as follows:QuoteEstimates are 200-450 meters at the equator, 50-200 meters at 30-55 degrees latitude, and less than 100 meters poleward of 55 degrees.The book describes how they arrive at these figures. The Phoenix mission landed at 68 degrees north and it found some ice just under the surface, but did not carry equipment to judge how substantial it was.If the Hydrogen/Sabatier approach is not used, I would say locations near the poles would be seriously considered for a first landing, just to guarantee access to the ice. Later missions migh want to bring deep drilling equipment.
http://en.wikipedia.org/wiki/Glaciers_on_Mars#Water_source_for_future_colonists(but doesn't seem to have much information about depth)I think you should definitely be sending some precursors to verify the ice and probably help with landing navigation. Possibly worth checking the ground is stable also. Couldn't a bit of the ice have since evaporated leaving just a crusty bit on top? that would be embarrassing
What would you consider a more realistic mass breakdown for the components of Mars Direct or Semi-Direct?I agree that it shouldn't be done with two direct launches of a SHLV (>100 mT). The mission should involve a smaller launcher (but large enough to launch the components) with little-to-no orbital assembly that takes place in LEO, with some trips to refuel a departure stage and take advantage of a slightly higher flight rate.
By smaller, I mean, the minimal launcher that can carry the Mars vehicle (however large it may be) and/or departure stage into LEO before departing for Mars. Something that can carry the same capacity as Falcon Heavy but with wider stages and fairings.The Mars vehicles may have to be larger due to "optimistic/underestimated mass budgets," so a direct-to-Mars SHLV may become harder to develop or manage. But I am curious as to what people think that masses should really be.Why multiple launches with refueling (not a depot - direct refueling)? As it was said before, if you fly a super-heavy launcher only 1 time every two years, the fixed costs get divided over less launches, resulting in more cost per flight.Maybe it will involve one launch to carry the ERV/Hab/(probably MAV?) with an unfueled departure stage into LEO. The alternative is to have several stages that link up to perform the TMI burn, but that involves more orbital assembly.