Pet peeve: long term propellant storage is often implied as difficult, like violation of thermodynamics difficult. I think this is an absurd meme spawned because propellant depots are politically inconvenient for SLS, even though any long term BEO plans assume significant propellant storage.Even passive systems are meant to bring boiloff down to a few percent per year in a high orbit. Then you just add some active cooling. If you can't reliquify a very slow trickle of cold gas in an environment where oxygen lines freeze by accident then the notion of ISRU to aquire - then liquify and store - tons of hot gasses is absurd and the fact we have been doing this on earth for a century or so is absurd.
So Im thinking this MTH should also be this DSH. All these pieces won't emerge at once so it is just as interesting to think about what we do in the meantime. I think we can gain excellent confidence for a mars orbit mission just sitting in high lunar orbit, but without attention to our politicians we could end up with a lunar DSH that somehow proves irrelevant to Mars ambitions which would be a great pity.
At least SpaceX is shooting for completely reusable systems. SLS is not. It could have been.
I would prefer argon for SEP tugs vs xenon. Argon is in earths atmosphere and is far more abundant. It is also about 4-5% of Mars atmosphere. It could be extracted from Mars and launched up to fuel a SEP tug for it's trip back to earth, at least eventually. Xenon is very rare and with all the moving around between earth and Mars, to me it makes sense in the long run to use argon.
I don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.
My pet peeve is people counting their MCT's before they hatch. I believe mega rockets will return to being relevant when we're sending thousands of people to space every year...but we're not doing that for a long time and even multiples of current flight rates can be supported with systems that lift no more than 50 tons to LEO. I was personally amazed that those who slung mud at Ares/SLS for years completely changed tune with SpaceX saying about doing a rocket in that class, even though most of the arguments against the former system equally apply to any system SpaceX would field. I could be wrong about this and there are details to the MCT that make it a scalable system that has other commercial uses, but I've heard nothing of that nature yet. For expected near terms missions to Mars and the Moon, I overall think it makes more sense to do a single core reusable methane rocket that lifts about the same payload as Falcon Heavy, can support wider payloads; that can be later scaled up as demand increases. But hey, it's not my company!
Quote from: Darkseraph on 05/18/2015 02:43 amI don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.The problem is that argument is circular in that because they are not "off-the-shelf" (and if you refer to the ACES/Depot studies it nearly is) we should not put them on the "critical path" yet at the same time nothing that is NOT on the "critical path" is being funded so they will by default, never be "off-the-shelf" so they should never be on the critical path...This is exactly why we're here now. We choose a "goal" for which we develop a "critical path" but then specifically do not engage in any infrastructure or equipment development outside of that path but a lot of development within that path to achieve the goal. And pretty much ONLY the goal. This process has proved a failure at sustainment ever single time it has been followed, yet we continue to do the same thing over and over again and expect a different result. (This is the definition of crazy I will note)
What we further need is:-CH4/O2 rockets (Blue Origins' B-4 engine may remedy this in near future)-ISRU of CH4/H2/O2 on Mars (MOXIE on 2020 may establish O2, but still need CH4 & perhaps H2)-Aerocapture & General Improvement of EDL (bigger heatshields, some-kinda-flaps to extend said-shields, powered descent, and pintpoint landing)
Quote from: redliox on 05/16/2015 12:06 pmWhat we further need is:-CH4/O2 rockets (Blue Origins' B-4 engine may remedy this in near future)-ISRU of CH4/H2/O2 on Mars (MOXIE on 2020 may establish O2, but still need CH4 & perhaps H2)-Aerocapture & General Improvement of EDL (bigger heatshields, some-kinda-flaps to extend said-shields, powered descent, and pintpoint landing)I actually kind of disagree with that.CH4/O2 storage is nice to have, but hypergolics can do the job if combined with SEP. For example, the kick stage in the Raftery concept merely provides around 450m/s, that's no problem with an ISP of ~320. For Mars ascent hypergolics are ok too, you just have to land it on the surface. In fact a ~25t ascent vehicle with hypergolics can probably do the job if you only ascent to low Mars orbit.Agree with EDL though.
Btw., contrary to what I said in another thread, a 30t Habitat should be enough for a crew of 4 for 500 days.
The biggest problem with relying on hypergolics too heavily is, if you plan to reduce mass and to encourage long-term reusability, those fuels are a little too complex to produce on Mars. Not to mention they're A LOT more explosive than methane.
Quote from: redliox on 05/20/2015 08:52 amOtherwise I'd push for a SSTO Mars shuttle, but I know this would be a tough push.Well much less tough than SSTO on Earth
Otherwise I'd push for a SSTO Mars shuttle, but I know this would be a tough push.
My pitch is to locate the landing site near a large source of water. Recent articles have shown that water is abundant in the form of dust-covered glaciers. This is not so critical for the initial explorations, but a build-up of equipment will make the site attractive for further exploration and then colonization. Rather than squeeze a few ml out of the regolith, let's go ahead with electrolysis to produce substantial quantities of H2 and O2 -- long term benefits.
This seems to show a spot with more water around the equator. Does anyone know what it is called and why it is higher in water? (The caption says something about hydrogen measured in the top meter of soil)water in lower latitudes?I also thought it would be interesting to start a thread purely on landing sites for HSF.
Here's the latest article in the New Yorker on Mars colonization:http://www.newyorker.com/magazine/2015/06/01/project-exodus-critic-at-large-kolbert
Argon is a much cheaper SEP propellant than Xenon and is a waste product from the production of LOX. Currently most is just thrown away.Boiling point of Argon 87.302 K (−185.848 °C, −302.526 °F)Boiling point of Oxygen 90.188 K (−182.962 °C, −297.332 °F)
A minimal lander/ascent vehicle. When I originally started this was specified as being around 1.5 tonnes in mass (dry). That was pretty minimal and it really had very limited life support capability and no pressurised environment. I since refined that concept and came up with a lander/ascent vehicle that can provide up to 2 weeks of life support in a pressurised environment but is still fairly light weight for what it does - about 3 tonnes. Some will argue that this is to light but I hasten to add that materials and manufacturing have improved a lot since the days of the lunar lander and this is not designed for aerodynamic braking stresses. Its designed to land fully propulsively on Mars and as such is also quite capable of ascent from mars. It has a notional delta-V capability of 5Km/s. That means fully fueled it carries 2 tonnes of methane and 7 tonnes of oxygen.
A transit vehicle. This vehicle is designed entirely to live in space. It doesn't land. It doesn't ascend. It just goes from Earth orbit to Mars orbit and back again. It can carry notionally about 30 tonnes of fuel but that can be added to with strap on tanks. It has all the necessary life support, storage crew space etc for half a crew and if necessary can support a full crew in cramped conditions. Two of these vehicles are used for the months long journey to Mars and likewise two of these vehicles are used for the months long journey back to Earth. They can be coupled to form one vehicle with shared space and specialisation of galley, sleeping etc. And in a coupled form they can be spun to provide a low level of gravity.
Prior to all of this, a fully fueled transit vehicle is pre-positioned in high Mars orbit. Also the lander/ascent vehicle would be pre-positioned either in low Mars orbit or left attached to the waiting transit vehicle. Now if it were the latter it could travel with the crewed transit vehicle on its descent to lower orbits.
I have to wonder. What if the lander/ascent vehicle were instead to spend its time waiting for the crewed mission stationed on one of the moons? This would be a somewhat more protected environment. It also occurred to me that the 50 tonne class transit vehicle could actually attempt a landing on at least the smaller of the two moons. Its mass would amount to something like 50Kg of Earth weight there. Its just a thought anyway.
Quote from: Russel on 05/31/2015 06:06 pmA minimal lander/ascent vehicle. When I originally started this was specified as being around 1.5 tonnes in mass (dry). That was pretty minimal and it really had very limited life support capability and no pressurised environment. I since refined that concept and came up with a lander/ascent vehicle that can provide up to 2 weeks of life support in a pressurised environment but is still fairly light weight for what it does - about 3 tonnes. Some will argue that this is to light but I hasten to add that materials and manufacturing have improved a lot since the days of the lunar lander and this is not designed for aerodynamic braking stresses. Its designed to land fully propulsively on Mars and as such is also quite capable of ascent from mars. It has a notional delta-V capability of 5Km/s. That means fully fueled it carries 2 tonnes of methane and 7 tonnes of oxygen. What you suggest sounds a bit light, but I do take to heart the possibility that a Mars lander (at least the crew variety) could be made into a smaller vehicle than usually assumed. I think there could be a chance something derived from a commercial capsule into a SSTO Martian vehicle may come into play. More than likely someone will come up with a simple design for a Mars lander/shuttle.Quote from: Russel on 05/31/2015 06:06 pmA transit vehicle. This vehicle is designed entirely to live in space. It doesn't land. It doesn't ascend. It just goes from Earth orbit to Mars orbit and back again. It can carry notionally about 30 tonnes of fuel but that can be added to with strap on tanks. It has all the necessary life support, storage crew space etc for half a crew and if necessary can support a full crew in cramped conditions. Two of these vehicles are used for the months long journey to Mars and likewise two of these vehicles are used for the months long journey back to Earth. They can be coupled to form one vehicle with shared space and specialisation of galley, sleeping etc. And in a coupled form they can be spun to provide a low level of gravity. You pretty much summarized what Buzz Aldrin was trying to sell in his latest idea, although I think his idea is basically a larger version of yours with SEP, inflatables, among other things. As far as artificial gravity, I fear NASA dislikes the idea of spinning a spacecraft entirely. Mars Direct had a nice idea of using an empty stage on a rope to do the trick, but I can sort-of-understand why NASA is phobic about spinning...unless it's aligned right a spacecraft spinning in the wrong way can be a recipe for disaster. For better or worse I'm guessing astronauts will be stuck with treadmills and calcium pills.Quote from: Russel on 05/31/2015 06:06 pmPrior to all of this, a fully fueled transit vehicle is pre-positioned in high Mars orbit. Also the lander/ascent vehicle would be pre-positioned either in low Mars orbit or left attached to the waiting transit vehicle. Now if it were the latter it could travel with the crewed transit vehicle on its descent to lower orbits. You do realize you just reiterated the Mars Semi-Direct scheme there...Quote from: Russel on 05/31/2015 06:06 pmI have to wonder. What if the lander/ascent vehicle were instead to spend its time waiting for the crewed mission stationed on one of the moons? This would be a somewhat more protected environment. It also occurred to me that the 50 tonne class transit vehicle could actually attempt a landing on at least the smaller of the two moons. Its mass would amount to something like 50Kg of Earth weight there. Its just a thought anyway.I don't think your idea of a super-simplified-bare-bones Mars lander would be the best fit for exploring the Mars moons; your kind of vehicle's priority is getting back to the mothership asap, otherwise you're consuming the safety margin of fuel. Since you're talking 50 tonne vehicles though, I do agree it would be child's play for the mothership to directly visit the moons itself. With the nonexistent gravity, the various small free flying 'toys' (CEVs I think is their acronym) might not even be necessary as opposed to just giving the crew an updated version of the MMU and have them fly over to objects like the Phobos monolith to investigate.I have been gravitating more towards your idea of a small lander Russel, but even at its smallest making it an intact capsule with at least a week's worth of life-support should be the baseline. You talk to any engineer, NASA or otherwise, and while they might agree your ultra-lite-style AV may work there should be some safety margin added. Some seeds for thought, but basically give your ship a sturdier frame.
You know one of the things that still bugs me about a lot of missions is the combination of zero-g conditions followed by high-g aerobraking.
Taking the mothership directly to the moons is something I'm seriously considering. Its not without its own risks mind you and even with tiny gravity, the mothership still exerts a force equivalent to the weight of a human (or thereabouts) and it still needs a controlled landing, some kind of landing "feet" and attention to the usual landing problems like debris. The lander/ascent vehicle is still quite capable though with a weeks life support at minimum. And you probably wouldn't want the mothership to go hopping. Indeed you'd probably invent some other local transport. Main reason I'm attracted to landing the mothership is giving it a relatively protected base and freeing it from station keeping.
I should also add that since I wrote all of this up as an exercise in showing how we can get to Mars with relative style and simplicity and still not have to loft a thousand tonnes or more of fuel into orbit, I've been struck by how close SpaceX really are to success with reusability. That really is a game changer in terms of bucks per Kg of fuel. With that in mind, future versions of my mission will have more redundancy (especially with the landers) and more margins all round. For instance there will an extra couple of landers from mission one, both for redundancy/safety and for flexibility of mission. I'm also leaning towards outfitting one of my transit vehicles as a fuel tanker with some of what would have been crew space taken up by extra tankage. Life support will still be a feature of the vehicle though.
Quote from: Russel on 06/22/2015 11:17 amYou know one of the things that still bugs me about a lot of missions is the combination of zero-g conditions followed by high-g aerobraking. I've come to agree, which is why I evolved Mars Aligned to take aerocapture away from the crewed element but focus it for the cargo half (or mainly anything that won't arrive with live crew at first). Aerocapture is the most straightforward way to brake around Mars without fuel, so it should be applied wholesale to cargo. The crew would brake into high orbit, but the crew lander could aerobrake and still lessen the need for fuel.Quote from: Russel on 06/22/2015 11:17 amTaking the mothership directly to the moons is something I'm seriously considering. Its not without its own risks mind you and even with tiny gravity, the mothership still exerts a force equivalent to the weight of a human (or thereabouts) and it still needs a controlled landing, some kind of landing "feet" and attention to the usual landing problems like debris. The lander/ascent vehicle is still quite capable though with a weeks life support at minimum. And you probably wouldn't want the mothership to go hopping. Indeed you'd probably invent some other local transport. Main reason I'm attracted to landing the mothership is giving it a relatively protected base and freeing it from station keeping. Considering how feeble the gravity is...I'm honestly thinking parking the mothership (in my case the MTH-ITIT) 50 meters above the satellite would suffice. RCS thrusters could easily halt the extreme-slow-motion fall toward the moon and keep it near-perpetually suspended. If a landing is required, it could just sit on a single modest pad the crew could stick to a docking port. However I'm thinking just keeping it "hovering" might be wiser to minimize dust on the ship. Just give the crews a newer version of a Manned Maneuvering Unit and let them roam the immediate surroundings.Quote from: Russel on 06/22/2015 11:17 amI should also add that since I wrote all of this up as an exercise in showing how we can get to Mars with relative style and simplicity and still not have to loft a thousand tonnes or more of fuel into orbit, I've been struck by how close SpaceX really are to success with reusability. That really is a game changer in terms of bucks per Kg of fuel. With that in mind, future versions of my mission will have more redundancy (especially with the landers) and more margins all round. For instance there will an extra couple of landers from mission one, both for redundancy/safety and for flexibility of mission. I'm also leaning towards outfitting one of my transit vehicles as a fuel tanker with some of what would have been crew space taken up by extra tankage. Life support will still be a feature of the vehicle though. I keep an eye on SpaceX; they seem the most genuinely ambitious regarding Martian goals and game-changing spacecraft. I readily see the Falcon Heavy or "lite" heavy-lifters akin to it as an immediate "plan B" to SLS; whatever the giant NASA rocket doesn't have room to launch should immediately be shuttled to an alternative. Also, this is a direct reason I'm sizing many of my elements around 30-50 tonnes so the FH (with its 52 mt capacity) can loft them at least to LEO.
What is Tea Monster?
Quote from: Russel on 06/29/2015 12:08 amWhat is Tea Monster?Not so much what as who -- one of our fellow posters.
As I think I said before, I don't think you can get away with hovering that close. Even with the micro gravity that would require quite a number of Kg (equivalent) of thrust continually. What would be nice is being close to an L point and dropping an anchor. Of course if you had the crew fly down with an MMU they could take a few Km of tether and attach it to something.
......I have issues with SEP because of the economics of having massive and expensive vehicles which engage in long mission cycles and the longer the mission cycles the fewer times the investment can be recovered by reuse. This is why I have serious issues with using SEP to get all the way to Mars, and I still do. A suitable SEP tug in the order of 500KW to 1MW isn't going to cost $100M. Its going to cost many times more. And the development isn't going to be cheap either. But I think the technology can be gotten to the point where assembly is largely automated. So its in the right ballpark. And we're talking in the order of 6 months or so to raise a 50 tonne payload from Low Earth Orbit to High Earth Orbit. So reuse 20 times is a possibility. This is not the case for SEP to Mars involving years-long cycles will never see the investment returned. ... ...
Quote from: Russel on 06/29/2015 04:01 pm......I have issues with SEP because of the economics of having massive and expensive vehicles which engage in long mission cycles and the longer the mission cycles the fewer times the investment can be recovered by reuse. This is why I have serious issues with using SEP to get all the way to Mars, and I still do. A suitable SEP tug in the order of 500KW to 1MW isn't going to cost $100M. Its going to cost many times more. And the development isn't going to be cheap either. But I think the technology can be gotten to the point where assembly is largely automated. So its in the right ballpark. And we're talking in the order of 6 months or so to raise a 50 tonne payload from Low Earth Orbit to High Earth Orbit. So reuse 20 times is a possibility. This is not the case for SEP to Mars involving years-long cycles will never see the investment returned. ... ...I recently posted on the MCT speculation thread the idea that SpaceX, who are considering SEP in their for their architecture, are also considering an all-propellant option. IMHO the reason for a non-SEP option would be to avoid the high development cost for SEP that you have pointed out. Have you ever considered an all-propellant option?One way that SpaceX could avoid SEP is by having the MCT cargo/tanker do double duty. In this scenario BFR is a stage one booster and MCT (both passenger or cargo versions) would be a second stage to reach LEO using their own propulsion units. A propellant depot in LEO would receive MCT tankers to accumulate fuel and oxidizer in the depot storage tanks.My idea was that one of the tankers could serve double-duty as a booster for a Mars-bound MCT. A fully-fuelred MCT would attach to a fully-fueled MCT-tanker at the LEO depot. The MCT-tanker would boost both units from LEO to HEO. After separation the Mars-bound MCT would then initiate the TMI burn for a fast transit to Mars and the tanker would return to depot or to Earth for propellant refill.Are there instances where vehicles in your architecture could serve double-duty in a non-SEP option?