Quote from: Comga on 07/27/2020 05:35 pmQuote from: Tulse on 07/27/2020 02:32 pmWhat is the reason for not separating the trunk after de-orbit? I would have thought disposing of the trunk would be good practice, rather than leaving it as debris.This has been EXTENSIVELY discussed, up-thread and elsewhere, in many posts. If you read thru you will understand the issues without repeating the question. As to the trunk being orbital debris, the ISS is flown low, around 400 km altitude, partly so that the exosphere scrubs debris out of orbit. The ISS requires frequent boosting to keep it from being dragged down. (Check out the ISS altitude vs time graph on Heavens Above.) The trunk is low density, quite hollow , so will have a relatively short lifetime at an altitude with few satellites.Well not that I would call "more than a year and a half" a "short lifetime" in orbit. The trunk from Demo-1 is still up there and hasn't really gone down too much. It may still take another year until it decays and reenters
Quote from: Tulse on 07/27/2020 02:32 pmWhat is the reason for not separating the trunk after de-orbit? I would have thought disposing of the trunk would be good practice, rather than leaving it as debris.This has been EXTENSIVELY discussed, up-thread and elsewhere, in many posts. If you read thru you will understand the issues without repeating the question. As to the trunk being orbital debris, the ISS is flown low, around 400 km altitude, partly so that the exosphere scrubs debris out of orbit. The ISS requires frequent boosting to keep it from being dragged down. (Check out the ISS altitude vs time graph on Heavens Above.) The trunk is low density, quite hollow , so will have a relatively short lifetime at an altitude with few satellites.
What is the reason for not separating the trunk after de-orbit? I would have thought disposing of the trunk would be good practice, rather than leaving it as debris.
The director of SpaceX's Commercial Crew & Cargo is leaving the company after Demo-2's success:
Some professional news all: After over 10 years, this will mark my last week @SpaceX. It was an extremely difficult decision, and I will be leaving with a deep sense of gratitude for the excellent, elite team I have worked with. [A thread...]
I arrived @SpaceX just before the maiden launch of the F9 rocket. I participated in that launch from ~500ft off the deck of the Atlantic, watching for an intact rocket to fall into the ocean so I could direct recovery forces to it. The rocket had other ideas.
I leave @SpaceX at apogee, having played my small part in bringing back @astro_doug and @astrobehnken safely and completing my goal of helping return humans to space from America
Development of the Crew Dragon ECLSS
SpaceX designed the Crew Dragon spacecraft to be the safest ever flown and to restorethe ability of the United States to launch astronauts. One of the key systems required forhuman flight is the Environmental Control and Life Support System (ECLSS), which wasdesigned to work in concert with the spacesuit and spacecraft. The tight coupling of manysubsystems combined with an emphasis on simplicity and fault tolerance created uniquechallenges and opportunities for the design team. During the development of the crewECLSS, the Dragon 1 cargo spacecraft flew with a simple ECLSS for animals, providing anopportunity for technology development and the early characterization of system-levelbehavior. As the ECLSS design matured a series of tests were conducted, including withhumans in a prototype capsule in November 2016, the Demo-1 test flight to the ISS in March2019, and human-in-the-loop ground testing in the Demo-2 capsule in January 2020 beforethe same vehicle performs a crewed test flight. This paper describes the design andoperations of the ECLSS, the development process, and the lessons learned.
The suit fluid module which feeds the umbilical is a small valve tray mounted inside the seat structure shellcontaining the main components of the suit fluid management system: a solenoid isolation valve with manualoverride, a regulator, flow control orifice, suit air check valve, and buddy breathe quick disconnect. The buddybreathe functionality permits a crewmember in a seat with a malfunctioning solenoid valve or regulator to receivegas from an adjacent seat.
In a contingency involving a depressurizing cabin, the two primary cabin repress valves are commanded open tofeed the leak and attempt to maintain cabin pressure above 8 psia (55 kPa). For equivalent hole diameters of up to0.6” (15 mm), the flow rate from two repress valves is more than that through the hole, and thus cabin pressure canbe maintained above 8 psia for as long as nitrox consumables permit. There are sufficient consumables to feed a leakfrom a 0.25” (6 mm) hole for the worst-case emergency deorbit duration. For larger hole sizes, Dragon will stopfeeding the leak when a nitrox reserve mass is reached and allow the cabin to depressurize, feeding oxygen to thesuits. When reentering with a depressurized cabin, the repress valves flow nitrox into the cabin as the externalpressure increases.
Another contingency in which the AVVs are used is a contaminated atmosphere resulting from a fire. If toxiccombustion product levels are below a defined threshold, the cabin is purged with nitrox using the primary repressvalves while the AVVs maintain a cabin pressure of 8.0-8.5 psia (55-59 kPa). If the atmosphere is even morecontaminated, it can be vented to near-vacuum and replaced with clean nitrox using both cabin repress valve sets.
The single nitrox manifold has triplicated pressure transducers to monitor system status. If high manifoldpressure is detected, the manifold is “burped” to relieve pressure by opening downstream primary repress valvesbriefly. If manifold pressure continues to rise, the system is safed and the tank isolation valves are closed. Should pressurization above 1.22 MPa occur, burst discs and relief valves passively open to keep pressure below themaximum design pressure of 1.72 MPa. Gas is vented out of the pressure section through two pass-throughs in theforward bulkhead to prevent damage to downstream components.
The derived requirement is approximately five days of free flight for the worst case. Given a crew size of four, this means that the ECLSS consumables must last for 20 person-days using conservatively high metabolic loads and conservatively low efficiency of utilizing each consumable. No additional safety factor is applied since each input to the consumables analysis is worst-case. Some consumables are sized for a worst-case scenario other than total mission duration; for example, nitrox quantity is driven by the vent and repress scenario (see page 4).
SpaceX’s internal posture on controlling catastrophic hazards is to incorporate two-fault tolerance wherever the impact of doing so (such as in complexity or mass) is not extreme, going beyond the customer requirement. To this end, most groups of sensors used in the ECLSS are triplicated, and most airflow requirements are met by a single fan out of a group of three.Reusability is central to SpaceX’s goal of lowering the cost of space transportation, so the Crew Dragon ECLSS is designed for rapid refurbishment to support multiple missions with the same vehicle. The focus on reusability motivated placing the entirety of the ECLSS, as well as all TCS components other than the radiator, within the reentry vehicle rather than the disposable trunk.
Lithium hydroxide (LiOH) cartridges are used for scrubbing crew-generated carbon dioxide (Figure 6). Each cartridge contains four LiOH cubes originally developed for submarines. The actively scrubbing cartridge can be replaced in flight as needed, with one swap required for a mission of nominal duration. The air sanitation box provides a storage location for three replacement cartridges.
The trace contaminant, HEPA, and ammonia filters are replaced on the ground between missions.
Humidity in Dragon is controlled by a dehumidifier system while on-orbit (Figure 7). The dehumidifier uses thevacuum of space to draw humidity across water-permeable (but air-impermeable) Nafion membranes. Controlvalves allow for selective enabling of four Nafion banks to autonomously control the rate of water vapor removal.Two vacuum lines allow for removed water to be vented to space. Each line has an isolation valve to turn off thesystem when the capsule is in the atmosphere or on-station.Compared to a condensing heat exchanger, the Nafion dehumidifier is passive and does not require water phaseseparation and storage to successfully operate; instead, the water remains in the vapor phase on both the cabin sideand vacuum side of the membrane and is rejected to space. This saves power or cooling that otherwise would beneeded to condense the water during flight. Additionally, the mass of the water leaves the vehicle and does not needto be stored or dumped using another system
Overall, although this system design is well suited for the mission scope of Crew Dragon, its architecture is notdirectly applicable to long-duration ECLSS since it would be impractical to recover the rejected water. However, lessons learned from the design and production processes will nevertheless be useful to the development of future systems that use physically and chemically sensitive membranes.
Quote from: Alexphysics on 07/27/2020 06:10 pmQuote from: Comga on 07/27/2020 05:35 pmQuote from: Tulse on 07/27/2020 02:32 pmWhat is the reason for not separating the trunk after de-orbit? I would have thought disposing of the trunk would be good practice, rather than leaving it as debris.This has been EXTENSIVELY discussed, up-thread and elsewhere, in many posts. If you read thru you will understand the issues without repeating the question. As to the trunk being orbital debris, the ISS is flown low, around 400 km altitude, partly so that the exosphere scrubs debris out of orbit. The ISS requires frequent boosting to keep it from being dragged down. (Check out the ISS altitude vs time graph on Heavens Above.) The trunk is low density, quite hollow , so will have a relatively short lifetime at an altitude with few satellites.Well not that I would call "more than a year and a half" a "short lifetime" in orbit. The trunk from Demo-1 is still up there and hasn't really gone down too much. It may still take another year until it decays and reentersIt's also large and easily tracked, so it's not really a problem. US regulations require defunct satellites (which does include things like the Dragon's trunk) be either sent to a safe graveyard orbit, or to be deorbited within 25 years.
CREW DRAGON DEMO-2 DEBNORAD ID: 46024 Int'l Code: 2020-033B Perigee: 285.9 km Apogee: 413.0 km Inclination: 51.6 ° Period: 91.4 minutes Semi major axis: 6720 km RCS: Unknown Launch date: May 30, 2020 Source: United States (US) Launch site: AIR FORCE EASTERN TEST RANGE (AFETR)
The trunk from DM-2 has a much lower perigee than the trunk from DM-1, it should deorbit much faster.
Quote from: gongora on 08/07/2020 06:45 pmThe trunk from DM-2 has a much lower perigee than the trunk from DM-1, it should deorbit much faster.In general, the perigee effects the orbital lifespan much more than the apogee?I know the ultimate calculation is much more complicated than that, but I have that feeling for the orbital decay..(Like the perigee effects the apogee which increases the length of drag on the next orbit...)
Excellent story by @jackiewattles @CNN about the true history behind this amazing accomplishment- it wasn’t easy! How SpaceX and NASA overcame a bitter culture clash to bring back US astronaut launches - CNN
How SpaceX and NASA overcame a bitter culture clash to bring back US astronaut launchesBy Jackie Wattles, CNN BusinessUpdated 1226 GMT (2026 HKT) August 9, 2020New York (CNN)In May, millions of Americans watched as Robert Behnken and Douglas Hurley, two veteran NASA astronauts, strapped into a SpaceX Crew Dragon capsule and took a 17,000 mile per hour ride to the International Space Station. It was the first time NASA astronauts launched from US soil since 2011 — and the first time in history that a privately owned vehicle carried humans into Earth's orbit.The astronauts returned safely home last weekend, and once again, NASA and SpaceX employees cheered together, celebrating their coordinated accomplishment.That moment of solidarity, however, came after years of infighting, politicking and mutual distrust, according to current and former employees from NASA and SpaceX.
A NASA spokesperson tells me the agency is in the final stages of the SpaceX Demo-2 data reviews needed for Crew Dragon's certification.NASA and SpaceX will provide an update on the process during next week’s Crew-1 media briefings. (Photos: @ingallsimages / @NASA)
https://twitter.com/SpaceX/status/1315743656716853253
Quote from: gongora on 10/12/2020 08:04 pmhttps://twitter.com/SpaceX/status/1315743656716853253I don't see any more vestigial window features in either photo. That speaks to a thorough design upgrade from both the COTS Dragon 1 and the Crew Dragon.
Were they able to reclaim the space taken over by the SuperDraco internally (inside the pressured shell) ? Or they just cover it up on the surface without changes inside?
