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from the next-capsule-arriving-at-platform-one dept.
Jeff Williams, Alexey Ovchinin, Oleg Skripochka have returned to Earth from the International Space Station:
Less than a week after winding up a successful spacewalk, outgoing space station commander Jeff Williams, America's most experienced astronaut, joined two Russian cosmonauts for a fiery return to Earth Tuesday, closing out a 172-day mission with an on-target landing in Kazakhstan.
[...] The four-minute 41-second burn slowed the ship by 286 mph, just enough to drop the far side of the orbit deep into Earth's atmosphere. After a 25-minute free fall to just above the top of the discernible atmosphere, the three modules making up the Soyuz TMA-20M spacecraft separated. A few moments after that, the central crew cabin, the only module protected by a heat shield, slammed into the atmosphere at an altitude of 62 miles and a velocity of some 17,000 mph. Using atmospheric friction to slow down, the descent module's main parachute deployed at an altitude of a little less than seven miles and the spacecraft settled to the steppe of Kazakhstan.
[...] For Williams, the end of the mission marked a personal milestone. On Aug. 20, he surpassed the U.S. record for most cumulative time in space -- 520 days -- that was set earlier this year by astronaut Scott Kelly at the end of his nearly yearlong mission. With landing Tuesday, Williams' mark will stand at 534 days aloft over four missions, moving him up to 14th on the list of most experienced spacemen. The overall record is held by Gennady Padalka, who has logged 878 days in space over five missions.
(Score: 0) by Anonymous Coward on Thursday September 08 2016, @04:02PM
Very informative answer, especially on the seals, many thanks.
I wish they had some schematic out and some details on the hydraulics of the ISS, as it is always mandatory to service those systems against vacuum since the ISS never lowers its altitude. I can only assume that when an outer component fails, they will have to create a live bypass and weld/replace on spot while 'live', otherwise all fluid will be sucked outside of the system, and even the best serviceman would never manage 0% leaks (especially in a clumsy astronaut suite)
I am still very much in doubt as to what is the material used in seals, valves and (even worse) pumps, as the wear-and-tear has to be enormous tolerating that temperature range, vacuum which evaporates and petrifies lubricants, all while maintaining its geometry and acting as an effective seal. They did show two o-rings on that 'Smarter Every Day' video so I can only guess that this might be the 'viton' you mentioned. I still don't get the 'cupola' shutter contraption, though, as demonstrated live by the astronaut: it has no actuators at all!
(Score: 2) by LoRdTAW on Friday September 09 2016, @05:03PM
They use a lot of connectors and valves between modules and components to avoid needing to weld. Connectors I see are similar to VCR/VCO and JIC flared fittings for tubing. They probably design everything to be removable and easily replaced without cutting or joining. So its just a few basic tools like wrenches, sockets and screwdrivers. Same with electronics, they use circular pin and sleeve connectors as well as D-sub, coaxial and so forth.
No such thing as zero leaks. We deal with them all the time. You just have to perform basic PM and have a procedure for leak checking. If you think about it, the pressure differential between the inside and outside is atmosphere or 14.7PSI/1013kpa. So it's not very hard to seal.
The trick is dealing with the radiation, temperature, and vacuum. Most metals are fine in a vacuum as with radiation. But common plastics will out gas in a vacuum becoming brittle and also don't like ionizing radiation for the same reason. Nylon wire ties in our vacuum chambers used to support cables running to our CNC fixtures will become brittle and crumble because of vacuum and x-ray bombardment. So we use kapton tape and metal supports or replace nylon ties when necessary. They may last a few months or more depending on quality.
As for the temperature, more exotic alloys and metals are used such as inconel, chromoly, molybdeum Invar, Kovar, titanium and more. Invar and Kovar are the two commonly used alloys for high temp differential stuff. We weld a lot of that stuff going into satellites.