Quote from: Crispy on 10/09/2017 10:08 amQuote from: john smith 19 on 10/09/2017 07:10 amSo far the biological route regens the O2 but creates biomass which does not seem to have much use.On Mars? It will be very useful indeed.A one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.htmlThis could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.So it is possible to get the consumables down to 2kg/day per person. Mostly food and some water with a little bit of O2 to replace losses in the recycling system. A water tank will be needed to store the excess water generated over time because this is where some of the losses in the regen system for O2 will end up. Also a tank to store the waste sludge to be useful in farming at a latter date.At this rate stored consumables for 1 year for 1 person comes to 730kg. For 100 persons 73mt/yr. The weight of the person plus 400kg for personal baggage would make up the full weight capability of a BFR long duration flight and have enough consumables for their support for 1 year to handle any contingencies a 4X over supply of consumables for the expected duration of the trip. For the initial manned landings that 73mt of supplies must last 2X times the expected duration before an assured resupply event occurs. This duration is posited at being ~6.5 years or 3 synods. A 2X supply would be enough supplies for each person for 13 years. so that 73mt results in a crew size of 7.If the assumption is only 2 synods for max time for resupply then a crew size of 11.If the assumption is only 1 synod for max time for resupply then a crew size of 23.Remember in all cases the available supply is 2X needed to handle unforeseen contingencies and losses.
Quote from: john smith 19 on 10/09/2017 07:10 amSo far the biological route regens the O2 but creates biomass which does not seem to have much use.On Mars? It will be very useful indeed.
So far the biological route regens the O2 but creates biomass which does not seem to have much use.
Quote from: edkyle99 on 10/06/2017 06:31 pmQuote from: AncientU on 10/06/2017 05:13 pmBy the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t). Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC. (!)I've been trying to rocket-equation this, with little success. Here are the "knowns".GLOW 4400 tThrust Liftoff 5400 t, ISP = 330/356 secShip dry mass 85 tShip Mp 1100 tShip Thrust 775 t (4 engines) ISP 375 secShip Thrust 347 t (2 SL engines) ISP 330/356 secThese imply a first stage mass = 4400 t - 1185 t = 3215 tUnknown is first stage propellant mass fraction. When I plug the known numbers into the rocket equation, I get a first stage PMF required to be 0.97938 to get 250 tonnes to 9,200 m/s ideal delta-v (LEO). That's unrealistic because the first stage ends up with 20 tonnes lighter dry mass than the second stage "Ship". With PMF1 a more "reasonable" 0.96, I get total ideal delta-v = 9061 m/s, not usually good enough for LEO, but it depends on the details of the ascent. To get 9200 m/s with PMF1 = 0.96, payload maximum is 235 tonnes.S1: 3215 t > 128.6 t, ISP 347.4 sec, delta-v = 3734 m/sS2: 1185 t > 85 t, ISP 375 sec, delta-v = 5479 m/sPL: 235 t, delta-v total = 9217 m/sWhen I try to model the reusable alternative, assuming 10% propellant saved for first stage flyback landing and 6% for second stage retro and landing, I get only 105 tonnes of LEO payload, as follows.S1: 3215 t > 437 t, ISP 347.4 sec, delta-v (ascent) = 3265 m/sS2: 1185 t > 151 t, ISP 375 sec, delta-v (ascent) = 5446 m/sPL: 105 t, delta-v total = 9211 m/s Rough guesses, obviously, but I've yet to match the SpaceX charts. When I try to model the 20 tonne GTO mass, the numbers don't converge at all. I get no payload to GTO. - Ed KyleA big incorrect assumption here: that 9.2km/s is required. Technically the absolute minimum energy for a 200km orbit (i.e. Including the potential energy from 200km altitude) above the equator (so using Earth's spin to maximum effect) is just 7.5-7.6km/s.BFR doesn't use hydrogen, so it should get lower aero losses and higher averaged thrust to weight ratio (since your tanks empty sooner). Therefore the benchmark 9.2km/s need not apply, and I am nearly certain I've seen a legitimate estimate for BFR that shows a trajectory of 8.9something km/s to orbit.If you use the exact same mass fraction as last year's ITS booster (slightly better than 96%) and your numbers for Isp and stage mass, then you get 250 tons expendable to LEO at about 8.99km/s. That fits perfectly with all the rest of the info we have.No mystery. If you try to mess with SpaceX's numbers to fit more conservative assumptions, then of course you'll not be able to recreate their figures. That's not a mystery, either.
Quote from: AncientU on 10/06/2017 05:13 pmBy the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t). Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC. (!)I've been trying to rocket-equation this, with little success. Here are the "knowns".GLOW 4400 tThrust Liftoff 5400 t, ISP = 330/356 secShip dry mass 85 tShip Mp 1100 tShip Thrust 775 t (4 engines) ISP 375 secShip Thrust 347 t (2 SL engines) ISP 330/356 secThese imply a first stage mass = 4400 t - 1185 t = 3215 tUnknown is first stage propellant mass fraction. When I plug the known numbers into the rocket equation, I get a first stage PMF required to be 0.97938 to get 250 tonnes to 9,200 m/s ideal delta-v (LEO). That's unrealistic because the first stage ends up with 20 tonnes lighter dry mass than the second stage "Ship". With PMF1 a more "reasonable" 0.96, I get total ideal delta-v = 9061 m/s, not usually good enough for LEO, but it depends on the details of the ascent. To get 9200 m/s with PMF1 = 0.96, payload maximum is 235 tonnes.S1: 3215 t > 128.6 t, ISP 347.4 sec, delta-v = 3734 m/sS2: 1185 t > 85 t, ISP 375 sec, delta-v = 5479 m/sPL: 235 t, delta-v total = 9217 m/sWhen I try to model the reusable alternative, assuming 10% propellant saved for first stage flyback landing and 6% for second stage retro and landing, I get only 105 tonnes of LEO payload, as follows.S1: 3215 t > 437 t, ISP 347.4 sec, delta-v (ascent) = 3265 m/sS2: 1185 t > 151 t, ISP 375 sec, delta-v (ascent) = 5446 m/sPL: 105 t, delta-v total = 9211 m/s Rough guesses, obviously, but I've yet to match the SpaceX charts. When I try to model the 20 tonne GTO mass, the numbers don't converge at all. I get no payload to GTO. - Ed Kyle
By the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t). Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC. (!)
A one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.htmlThis could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.
Quote from: oldAtlas_Eguy on 10/09/2017 03:08 pmA one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.htmlThis could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.How intriguing. It recalls the "SolChem" project of the US Navy in the early 80's. Essentially the NRL's effort to work out what it would take to keep the USN on the high seas if the US was cut off from external oil supplies, using solar thermal conversion and molten salt conversion heat storage built entirely from resources found in the US. Those guys thought on a very large scale.
A packaging recycling machine that spits out 3D printer filament is being flown to Station soon.
...Also if 3 tankers accompany the deep space mission into a 4.2km transfer orbit that returns the tankers back to Earth, the total DV for the Deep Space Mission could be as high as 12km/s. This can be done as well from LEO but since you loose nearly 4km/s by not leaving from L2 would be like the first case L2 deep space mission...
My biggest concern with BFS is the heat shield. It covers a massive area. Nothing will fall on it and it shouldn't be in bird range while going fast enough to lose a battle, but MMOD damage seems like a real risk. It may be that because of its size and corresponding lighter heat load that it could take the inch or two damage that is likely from an MMOD strike and survive reentry. It certainly seems like a potential problem at really high flight rates.It is also inevitable that the heat shield will have to be replaced fairly regularly. (It is PICA-X so it is ablative right? why was it rendered silver...) Whether it is 10 flights or 100 flights it will likely be a pacing factor in refurbishing the ship. Tiles seem like the most likely method considering they are being used for dragon. It would be hard to make a shield as difficult to maintain as shuttle's, but it will still require a huge number unique tiles to be removed and reapplied and in this case they have to be replaced with new tiles or remanufactured.Are there any other technologies that may be helping them avoid these issues do they just consider them manageable?
(It is PICA-X so it is ablative right? why was it rendered silver...)
Quote from: intrepidpursuit on 10/09/2017 11:42 pmMy biggest concern with BFS is the heat shield. It covers a massive area. Nothing will fall on it and it shouldn't be in bird range while going fast enough to lose a battle, but MMOD damage seems like a real risk. It may be that because of its size and corresponding lighter heat load that it could take the inch or two damage that is likely from an MMOD strike and survive reentry. It certainly seems like a potential problem at really high flight rates.It is also inevitable that the heat shield will have to be replaced fairly regularly. (It is PICA-X so it is ablative right? why was it rendered silver...) Whether it is 10 flights or 100 flights it will likely be a pacing factor in refurbishing the ship. Tiles seem like the most likely method considering they are being used for dragon. It would be hard to make a shield as difficult to maintain as shuttle's, but it will still require a huge number unique tiles to be removed and reapplied and in this case they have to be replaced with new tiles or remanufactured.Are there any other technologies that may be helping them avoid these issues do they just consider them manageable?IIRC in his most recent presentation Elon made a fairly strong claim that the heat shield would only experience noticible ablation during a Mars Entry, and would not do so when entering Earths atmosphere.
Quote from: intrepidpursuit on 10/09/2017 11:42 pm (It is PICA-X so it is ablative right? why was it rendered silver...) IIRC the silver lining is a layer put on to prevent moisture intrusion prelaunch. It wasn't used on the first few launches, again IIRC.
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Quote from: oldAtlas_Eguy on 10/08/2017 04:07 pmHow much and how big would all the ECLSS equipment be for the support of 100 people for a couple of years?Turn the question on its head. The NASA baseline for crew consumables is 5Kg/person/day, of which maybe 3.5Kg is water.
How much and how big would all the ECLSS equipment be for the support of 100 people for a couple of years?
Organic waste from 100 people on board the BFR should produce a fair amount of methane on its own. Any thoughts on how much could be produced during a 4 to 6 month voyage and if it would be worth collecting?