EDL is more difficult for larger spacecrafts. ...This is why I do not understand, why people assume full resuability being easier for larger rockets.
NASA astronauts Doug Hurley and Bob Behnken stand in front of their Tesla Model X ride to the launchpad during a SpaceX launch dress rehearsal on Friday in Florida.Photo credit: NASA/Kim Shiflett
Quote from: livingjw on 01/18/2020 06:34 pmQuote from: joncz on 01/17/2020 07:02 pmQuote from: geza on 01/17/2020 06:57 pmQuote from: Tulse on 01/17/2020 05:33 pmAs I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one. Why is this, exactly?Surface area and volume increase faster than mass. A larger stage is "fluffier"This is wrong:- Volume is close to linearly proportional to vehicle mass. This is due, primarily to tanks and engines being proportional to mass.- Surface area increases slower than volume. Area is proportional to volume to the 2/3rds power for the same shape. If you want to maintain a constant Ballistic Coefficient, BC, then Area will be nearer to being proportional mass as well. - Bottom line, for a reusable rocket constrained by reentry BC, not much changes with gross weight.JohnJohn, I understand only the first half of what you wrote. Volume and mass scale together but surface increases slower. It implies that BC (mass/area) increases with increasing gross weigth. That is EDL is more difficult for larger spacecrafts. If I understand correctly, this is why it is non-trivial to scale-up the existing Martian EDL systems. This is why huge deployable heat shildes are often proposed for large Mars landers. And this is why Starship entry is sideways.This is why I do not understand, why people assume full resuability being easier for larger rockets.
Quote from: joncz on 01/17/2020 07:02 pmQuote from: geza on 01/17/2020 06:57 pmQuote from: Tulse on 01/17/2020 05:33 pmAs I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one. Why is this, exactly?Surface area and volume increase faster than mass. A larger stage is "fluffier"This is wrong:- Volume is close to linearly proportional to vehicle mass. This is due, primarily to tanks and engines being proportional to mass.- Surface area increases slower than volume. Area is proportional to volume to the 2/3rds power for the same shape. If you want to maintain a constant Ballistic Coefficient, BC, then Area will be nearer to being proportional mass as well. - Bottom line, for a reusable rocket constrained by reentry BC, not much changes with gross weight.John
Quote from: geza on 01/17/2020 06:57 pmQuote from: Tulse on 01/17/2020 05:33 pmAs I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one. Why is this, exactly?Surface area and volume increase faster than mass. A larger stage is "fluffier"
Quote from: Tulse on 01/17/2020 05:33 pmAs I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one. Why is this, exactly?
As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.
So many people like to get all googly-eyed at the latest, biggest, baddest heavy lift LV and spacecraft. In the discussion of Dragon vs. Starship, there is room for both. I like to look at the aircraft industry for a real-world comparison....As SpaceX advances Starship into an operational vehicle, I truly hope they do not abandon the small craft industry to others. That would be a huge mistake imo.
The #Starlink may have scrubbed today, but #SpaceX has it's crew on the #GoSearcher working with what appears to be a #CrewDragon capsule. #News13Brevard @GPallone13
In the commercial human spaceflight panel at the FAA conference, Nick Cummings of SpaceX says the upcoming Demo-2 crewed test flight will be the “most important event in the history of SpaceX.”
Cummings: we’ve had numerous discussions about private Dragon missions, but nothing to announce now.
NASA officials say SpaceX will complete construction of the Crew Dragon capsule for its first operational mission "3 months earlier than originally planned," according to the GAO, citing manufacturing efficiencies and SpaceX modifying facilities and bringing in more resources.
https://twitter.com/thesheetztweetz/status/1224422018566754304QuoteNASA officials say SpaceX will complete construction of the Crew Dragon capsule for its first operational mission "3 months earlier than originally planned," according to the GAO, citing manufacturing efficiencies and SpaceX modifying facilities and bringing in more resources.
What GAO RecommendsWe recommended in 2018 that NASA develop a plan to maintain access to the ISS; this recommendation has yet to be implemented. In this report, we add two recommendations to improve communications on waivers between NASA and FAA. Both agencies agreed.
To support an operational mission in March 2020, program officials told us that SpaceX plans to complete construction of flight spacecraft 4—now the first operational mission spacecraft—3 months earlier than originally planned. SpaceX and program officials identified two reasons why this acceleration may be possible. First, they told us there will likely be manufacturing efficiencies that could allow SpaceX to meet the accelerated schedule for its first operational mission. Program officials said the spacecraft design for the first operational mission is the same as the other spacecraft, and that this would be SpaceX’s fourth time building the spacecraft. Second, SpaceX officials said they modified their facilities and brought in additional resources.
In addition to incorporating hardware changes instituted after the anomalyand accelerating its hardware builds, SpaceX continues to addresstechnical risks identified by program officials. These include (1) SpaceX’splan to conduct launch vehicle propellant loading procedures after theastronauts are on board and (2) the design of its launch vehicle engine.The propellant loading procedure risk remains open because, as ofNovember 2019, SpaceX still needed to demonstrate the loading processat several upcoming events, including the in-flight abort test. The launchvehicle engine risk remains open because SpaceX needed to completethe required follow-on test campaign of its engines as of November 2019.
From the GAO report (emphasis mine):QuoteIn addition to incorporating hardware changes instituted after the anomalyand accelerating its hardware builds, SpaceX continues to addresstechnical risks identified by program officials. These include (1) SpaceX’splan to conduct launch vehicle propellant loading procedures after theastronauts are on board and (2) the design of its launch vehicle engine.The propellant loading procedure risk remains open because, as ofNovember 2019, SpaceX still needed to demonstrate the loading processat several upcoming events, including the in-flight abort test. The launchvehicle engine risk remains open because SpaceX needed to completethe required follow-on test campaign of its engines as of November 2019.Do we have any info on what that risk was? Is that still referring to the issue with turbopump blades cracking?
Quote from: FutureSpaceTourist on 02/03/2020 07:22 pmhttps://twitter.com/thesheetztweetz/status/1224422018566754304QuoteNASA officials say SpaceX will complete construction of the Crew Dragon capsule for its first operational mission "3 months earlier than originally planned," according to the GAO, citing manufacturing efficiencies and SpaceX modifying facilities and bringing in more resources.Did we forget to post this report earlier? It came out five days ago.edit: also, much of the information is outdated. That capsule supposedly being readied for an operational flight in March doesn't need to be ready yet since the first operational flight probably isn't until the third quarter now.
It’s interesting to see that SpaceX is throwing more ressources into the program than is necessary [...] because Elon/Gwynne want to free up those ressources needed for Dragon 2 earlier to transition them to crewed starship. Possibly both. Dragon 2 engineering/manufacturing teams might be the primary subjects for the new San Pedro facility.
Quote from: Bananas_on_Mars on 02/04/2020 09:15 amIt’s interesting to see that SpaceX is throwing more ressources into the program than is necessary [...] because Elon/Gwynne want to free up those ressources needed for Dragon 2 earlier to transition them to crewed starship. Possibly both. Dragon 2 engineering/manufacturing teams might be the primary subjects for the new San Pedro facility.AFAIK Dragon 2 has no particular need to be made at a port. After adding the Triumph building SpaceX isn't lacking for room at Hawthorne, either. Looking solely at Dragon for Dragon's sake, any move seems unlikely.The only good reason Dragon 2 engineering/manufacturing might move to San Pedro, would be if there was commonality of people or tooling between Dragon and some non-Dragon thing that actually needed to be done at the port. Further reading of totally-hypothetical tea leaves about things that aren't Dragon is maybe for another thread, though.
Dragon rocket fishing in Florida! 🐉🚀🎣✨
https://twitter.com/bluemoondance74/status/1224784188773142529QuoteDragon rocket fishing in Florida! 🐉🚀🎣✨
NASA Aerospace Safety Advisory Panel chair Patricia Sanders, at start of its quarterly meeting: not a question of whether SpaceX will be ready to fly crew in the near term, but when.
