Quote from: Chris Bergin on 02/17/2017 11:46 amI'll ask around.Got any answers?
I'll ask around.
Quote from: Burninate on 02/25/2017 08:17 pmQuote from: envy887 on 02/19/2017 12:47 pmQuote from: ZachF on 02/19/2017 12:33 pmSo if all-composite tanks don't pan out (at least for O2 tanks), what kind of weight increase are we talking about?Depends how thick the Invar liner needs to be and whether they can use its strength to reduce the weight of the composite.If it's 1 mm thick over the area of the ship's LOX tank, that only adds about 3 tonnes.I spent most of a year iterating my way through a projected MCT built of aluminum and moderate-pressure engines. The case for Mars missions does close, but a few things, like 1-synod reuse, get very difficult. I also ended up penciling in a system of additional propellant shipments sent to Mars orbit via a long SEP trip.http://forum.nasaspaceflight.com/index.php?topic=37808.msg1589654#msg1589654In that analysis, the LOX tank sidewall comes in at 34mm, the CH4 tank & hab sidewall 7.5mm. Tank skin mass for the interplanetary stage alone is ~46 tons, hab skin mass is ~8 tons. This is not counting ribs, trusses, heatshields, vacuum insulation, vacuum flask, plumbing, engines, anything. There's some mild sandbagging in there (in a pessimistic assumed tensile strength for aluminum) to add a margin of error.That looks remarkably prescient. But why did the LOX tanks end up nearly 5 times thicker? They are pressed to the same flight pressure and see lower dynamic loads.
Quote from: envy887 on 02/19/2017 12:47 pmQuote from: ZachF on 02/19/2017 12:33 pmSo if all-composite tanks don't pan out (at least for O2 tanks), what kind of weight increase are we talking about?Depends how thick the Invar liner needs to be and whether they can use its strength to reduce the weight of the composite.If it's 1 mm thick over the area of the ship's LOX tank, that only adds about 3 tonnes.I spent most of a year iterating my way through a projected MCT built of aluminum and moderate-pressure engines. The case for Mars missions does close, but a few things, like 1-synod reuse, get very difficult. I also ended up penciling in a system of additional propellant shipments sent to Mars orbit via a long SEP trip.http://forum.nasaspaceflight.com/index.php?topic=37808.msg1589654#msg1589654In that analysis, the LOX tank sidewall comes in at 34mm, the CH4 tank & hab sidewall 7.5mm. Tank skin mass for the interplanetary stage alone is ~46 tons, hab skin mass is ~8 tons. This is not counting ribs, trusses, heatshields, vacuum insulation, vacuum flask, plumbing, engines, anything. There's some mild sandbagging in there (in a pessimistic assumed tensile strength for aluminum) to add a margin of error.
Quote from: ZachF on 02/19/2017 12:33 pmSo if all-composite tanks don't pan out (at least for O2 tanks), what kind of weight increase are we talking about?Depends how thick the Invar liner needs to be and whether they can use its strength to reduce the weight of the composite.If it's 1 mm thick over the area of the ship's LOX tank, that only adds about 3 tonnes.
So if all-composite tanks don't pan out (at least for O2 tanks), what kind of weight increase are we talking about?
Without calculating it. It doesn't seem more pressure vs insulation is a good trade off for weight. Insulation can be extremely light.
Quote from: rsdavis9 on 02/28/2017 07:19 pmWithout calculating it. It doesn't seem more pressure vs insulation is a good trade off for weight. Insulation can be extremely light.I suspect it isn't so much insulation as the fact that if you want any insulation you need a "between" to put it in, hence you can't have common bulkhead between the tanks. Once you have separate bulkheads then yes multilayer insulation in vacuum won't add much weight at all.
The vehicle needs active and passive thermal management, both are required for flying people and cryogenic fuels on the same vehicle. If the vehicle flies with engines pointed at the sun for thermal management, then the CH4 tank will likely be warmer than the LOX tank because it's closer to the engines.I think that the sidewall area is large enough for radiative cooling to keep both the LOX and CH4 below boiling - or at least limit the thermal energy transfer to a very small amount of boiloff which can be recycled by a small refrigeration system.
Just for clarification, in the SpaceX ITS presentation they showed the same ITS booster landing in the cradle and repeatedly taking off in quick succession to fuel the ITS spaceship in orbit. Was that just done to illustrate the refuelling concept, or is the intention truly to have the exact same booster land and take off again with as little as a day turnaround time 5 times in a row?I fully understand the concept of getting maximum reuse out of the same booster in order to bring the average cost per use down as much as possible, but surely the risk of some malfunction caused by one of the repeated launches and atmospheric re-entries could scupper the entire mission?Are we realistically perhaps rather looking at 5 separate boosters, each taking off one after another to refuel the spacecraft, and then those 5 boosters getting reused for each new ITS launch? But getting refurbished in-between launches?Then you are still looking at full reuse, but you have a group of 5 boosters per upper stage, used to launch and fuel it for each Mars trip. And these 5 get reused the next month again, for the next ITS launch, etc.Surely relying on just ONE booster to repeatedly launch and land at a daily cadence is a somewhat unrealistic goal to aim at or what?
Not entirely on topi but also not entirely off as well. I want to share a story with you.First the off-topic part:Some of my colleges were on a workshop about cryogenic vacuum systems the last days. The workshop was for detector systems operated at cryogenic temperature but most of the stuff they told me applies to all kinds of vacuum systems, cryogenics or not. For example, if a device contains a ball bearing, the vacuum would evaporate the lubricant, which would lead to a failure of the ball bearing, not to mention a contamination of the vacuum. What you have to do is to (and I kid you not) coat the ball bearing halves with gold and replace the balls with rubies. Gold because it is soft and self-lubricating and rubies because they conduct heat pretty well so that a large temperature differential between the ball bearing halves is prevented. As someone without experience in vacuum systems, stuff like that is utterly unexpected and unpredictable.Now the on-topic part:SpaceX will operate its ITS and many Mars-surface machinery in near vacuum. Many of them also in cryogenic environments due to the fuel cooling. After hearing the story above, I realize that there is a whole zoo of knowledge regarding vacuum systems that SpaceX needs to develop and get experience with before they can send their ITS ship to Mars. They dont want to have it fall apart half way to Mars because they overlooked some stuff unique to vacuum systems. Of course, they are professionals and probably have many people with lots of experience in vacuum systems. But still, its some task and knowledge base that I completely underestimated so far. Do they have large vacuum testing and development facilities? I find this quite fascinating to be honest. The ISS Canadarm team must have tons of experience with stuff like that..PS: please dont see this as concern trolling. Its not, I am generally fascinated by the difficulties concerning vacuum system. Really unexpected!
Maybe ITS is too big and needs to be scaled down, like some people have said, to say 50 passengers or 50 tons to Mars instead of 100 passengers or 100 tons of cargo. ...
Again, a smaller BFR to launch fuel to a depot, then a 3 core heavy version to launch ITS. I know this isn't what they are doing, but a single stick BFR can do double duty to the Moon and refueling a depot.
The Mars environment, happily, is not even considered low grade vacuum. There's enough atmosphere to prevent cold welding, to keep many lubricants working, to convect... And, you don't worry about molecular contamination.This is one of the many reasons Mars colonization is easier than moon and asteroids. Designing for full vacuum, while understood, is very difficult, and requires a lot of trade offs.
Quote from: meekGee on 03/10/2017 01:55 pmThe Mars environment, happily, is not even considered low grade vacuum. There's enough atmosphere to prevent cold welding, to keep many lubricants working, to convect... And, you don't worry about molecular contamination.This is one of the many reasons Mars colonization is easier than moon and asteroids. Designing for full vacuum, while understood, is very difficult, and requires a lot of trade offs.What lubricants which can't tolerate a hard vacuum do well at ~600 Pa? Curiosity, for example, uses Castrol Braycote 601 EF, which is also used on ISS (hard vacuum tolerant).Also, I'm not following the logic, because whatever you send to Mars has to spend a long time in hard vacuum in-transit. Unless you send it as pressurized cargo, which comes at a significant mass penalty.
Robinson Manuel , with the New York Observer, Could you give us an update on the development of the Interplanetary Transport System, and what's next in terms of - what's the nex component to be tested following the carbon fuel tank and the Raptor engine?E: I think we'll provide an update on the design of the Interplanetary Transport System - Interplanetary Transport System also includes the propellant depot on Mars - that's why it's sort of - I actually usually don't like the word 'system', but we can't call it a rocket if it includes a propellant depot. So the Mars planetery transporter or Mars Transporter, ir Interplanetary Transporter - We've come up with a number of desibn refinements, and I hope I'll be ready ot put that on the Website withing a month or so.RM: Just want a follow-up The timeframe has shifted since Gh, I was wondering if if yuo guys had any updated timeframe of when you think that firstmission will be launched - If I'm correct, the first one is uncrewed amd I rightE: Yes the first one will be uncrewed, I don't want to steal thunder from that announcement. I'm pretty excited about the upgrades strategy since Gh, it makes a lot more sense, it's - we have to not just get it done technically, but figure out how to get this done without going bankrupt. So it's like, our goal is to get people on Mars before we're dead, and the company is dead. So like, either one of that. Ideally, the first. We don't want to take so long that dead by when that happens, and we don't want to kill the company in the process. So we have to figure out not just solve the technical issues, but the economic issues. I think the new approach is going to be able to do that. Hopefully.
From robbak's transcript of SES-10 post launch press conference, "E" is Elon:QuoteRobinson Manuel , with the New York Observer, Could you give us an update on the development of the Interplanetary Transport System, and what's next in terms of - what's the nex component to be tested following the carbon fuel tank and the Raptor engine?E: I think we'll provide an update on the design of the Interplanetary Transport System - Interplanetary Transport System also includes the propellant depot on Mars - that's why it's sort of - I actually usually don't like the word 'system', but we can't call it a rocket if it includes a propellant depot. So the Mars planetery transporter or Mars Transporter, ir Interplanetary Transporter - We've come up with a number of desibn refinements, and I hope I'll be ready ot put that on the Website withing a month or so.RM: Just want a follow-up The timeframe has shifted since Gh, I was wondering if if yuo guys had any updated timeframe of when you think that firstmission will be launched - If I'm correct, the first one is uncrewed amd I rightE: Yes the first one will be uncrewed, I don't want to steal thunder from that announcement. I'm pretty excited about the upgrades strategy since Gh, it makes a lot more sense, it's - we have to not just get it done technically, but figure out how to get this done without going bankrupt. So it's like, our goal is to get people on Mars before we're dead, and the company is dead. So like, either one of that. Ideally, the first. We don't want to take so long that dead by when that happens, and we don't want to kill the company in the process. So we have to figure out not just solve the technical issues, but the economic issues. I think the new approach is going to be able to do that. Hopefully.Can't wait to see how they address the economic issues, let the speculation begin...