Revisions to What thickness/depth of water would be required to provide radiation shielding in Earth orbit?

'exponentially' implies a mathematical exponential relationship between the mass of the fuel needed to escape LEO and #of launches. This isnt the case as described, however, one only needs about 2x the fuel required to get some mass to LEO. That's a linear relationship not exponential

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edit approved May 5, 2016 at 18:55

Community Bot

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Given that we could achieve getting this much mass into LEO, getting it to break orbit and out into interplanetary space is that much harder; going to Mars using a Hohmann transfer orbit takes about as much delta-V as getting to LEO in the first place, so all the fuel expended to get the craft and its water shield into space has to be brought up into orbit, requiring exponentiallymany more launches. Using a gravity assist, say from Venus, would be a logistical nightmare requiring all three planets to be in alignment as of departure from LEO, and while it would save fuel it would require us to cover much more distance and take much more time, possibly placing the mission further beyond our current capabilities.

MathJax + removing pointless vestige of previous rhetoric

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edited Apr 20, 2016 at 17:35

Nathan Tuggy

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The volume of shielding water needed is the difference between those two cylinders, or 22π(2.75²) - 20π(1.75²) ~= 522.68 - 192.42 = 330.26 m³$22\cdot\pi\cdot2.75^2 - 20\cdot\pi\cdot1.75^2 \approx 522.68 - 192.42 = 330.26 m^3$. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 330,260kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 33 Saturn V rockets, which is less than were launched during the Apollo program. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 2. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 14 missions. The SLS Block II (130 tonnes payload to LEO) would take just about 3 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 50 and 100 launches.

The volume of shielding water needed is the difference between those two cylinders, or 22π(2.75²) - 20π(1.75²) ~= 522.68 - 192.42 = 330.26 m³. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 330,260kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 3 Saturn V rockets, which is less than were launched during the Apollo program. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 2. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 14 missions. The SLS Block II (130 tonnes payload to LEO) would take just about 3 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 50 and 100 launches.

The volume of shielding water needed is the difference between those two cylinders, or $22\cdot\pi\cdot2.75^2 - 20\cdot\pi\cdot1.75^2 \approx 522.68 - 192.42 = 330.26 m^3$. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 330,260kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 3 Saturn V rockets. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 2. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 14 missions. The SLS Block II (130 tonnes payload to LEO) would take just about 3 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 50 and 100 launches.

There was a calculation error, where the cylinder volume calculation had become 4 times bigger, in that the original calculation stated DIAMETER squared times pi times cylinder height, while, it is in actual sense the RADIUS which is squared, then times pi, and cylinder height / [email protected]

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edit approved Apr 20, 2016 at 17:35

David T. Svarrer

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However, let's do some more math. Let's say that the Mars vehicle that will get them there and back is a cylinder roughly 3.5m by 20m (same as was used for the MARS-500 experiments; that is a very small tin can in which to spend 3 1/2 years with 4 or 5 other people). With 1m of shielding water around all surfaces of that cylinder, the outer hull would be about 5.5m by 22m.

The volume of shielding water needed is the difference between those two cylinders, or 22π(52.575²) - 20π(31.575²) ~= 1,321m522.68 - 192.42 = 330.26 m³. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 1,321330,000kg260kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 123 Saturn V rockets, morewhich is less than were actually launched during the Apollo program. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 72. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 5214 missions. The SLS Block II (130 tonnes payload to LEO) would take just over 10about 3 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 20050 and 400100 launches.

However, let's do some more math. Let's say that the Mars vehicle that will get them there and back is a cylinder roughly 3.5m by 20m (same as was used for the MARS-500 experiments; that is a very small tin can in which to spend 3 1/2 years with 4 or 5 other people). With 1m of shielding water around all surfaces of that cylinder, the outer hull would be about 5.5m by 22m. The volume of shielding water needed is the difference between those two cylinders, or 22π(5.5²) - 20π(3.5²) ~= 1,321m³. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 1,321,000kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 12 Saturn V rockets, more than were actually launched during the Apollo program. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 7. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 52 missions. The SLS Block II (130 tonnes payload to LEO) would take just over 10 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 200 and 400 launches.

However, let's do some more math. Let's say that the Mars vehicle that will get them there and back is a cylinder roughly 3.5m by 20m (same as was used for the MARS-500 experiments; that is a very small tin can in which to spend 3 1/2 years with 4 or 5 other people). With 1m of shielding water around all surfaces of that cylinder, the outer hull would be about 5.5m by 22m.

The volume of shielding water needed is the difference between those two cylinders, or 22π(2.75²) - 20π(1.75²) ~= 522.68 - 192.42 = 330.26 m³. As one cubic meter of water weighs 1 metric ton (1,000kg), that's 330,260kg to get into space.

Putting that in perspective, the current record holder for payload-to-LEO is the Saturn V rocket, which had a maximum LEO payload of 120,000kg (said payload being the S-IVb, including CSM, LEM and Earth departure stage, for most of its missions). To put the volume of water we'd need into orbit would require 3 Saturn V rockets, which is less than were launched during the Apollo program. The planned-but-never-built Ares V was spec'ed to have 188 tonnes P2LEO capacity, which would have cut down the number of launches to only 2. Doing it with Space Shuttles (25 tonnes cargo to LEO) would take 14 missions. The SLS Block II (130 tonnes payload to LEO) would take just about 3 launches. Doing it with any orbital rocket currently in service, manned or unmanned (Soyuz II, Soyuz FG, Delta IV, Atlas V, Falcon 9) would require between 50 and 100 launches.