![]() This mass efficient 2nd stage is what's allowing SpaceX to put 5 to 6 metric tons to Geostationary transfer orbit (GTO) using a two stage all kerolox launch vehicle, no other launch vehicle in human history can do this. Semi pressure stabilized propellant tank (can support its own weight when unpressurized but need pressure to handle flight load)Ĭooled Helium storage using COPV inside LOX tank Merlin's superior Thrust-to-weight ratio (TWR) The exact method SpaceX used to achieve this remarkable PMF is not spelled out, it's their secret sauce after all, but my guess is it's a combination of: A simple division would show for each metric ton of vehicle structure, F9 S2 can take 22 metric tons of propellant, while Centaur can only take 10.4 metric tons of propellant. This means given the same metric ton of vehicle structure, F9 S2 can take a lot more propellant, and thus provide more delta-v. In rocket equation, PMF has the same importance as Isp, but rookies usually focused on Isp and ignores PMF, which is a big mistake.į9 S2's PMF is 95.7% while Centaur's PMF is 91.2%, this is a huge difference when it comes to rocket equation. So how did SpaceX do this? The general answer is that F9 S2 is simply more mass efficient, as measured by Propellant mass fraction (PMF), which is the ratio between the propellant mass and the initial mass of the vehicle. This is very remarkable since Centaur is using RL10, a hydrolox engine which has much higher Isp than F9 S2's Merlin Vacuum engine, and Centaur uses a pressure stabilized propellant tank which is very mass efficient (but couldn't support itself without pressurization). Source is : Falcon 9, Atlas V)Īs you can see, while empty the F9 S2 has basically the same delta-v as the Centaur upper stage on Atlas V, once you start to add payload, the delta-v provided by F9 S2 quickly surpassed Centaur. (Disclaimer: SpaceX doesn't disclose the exact 2nd stage empty or propellant mass, so the numbers here is an estimate, but I think it's a conservative estimate. It looks to me that there's a misconception that Falcon 2nd stage is "bad", but is it? A straight forward comparison would tell you otherwise: This was also briefly discussed on SpaceXMasterrace here SpaceX Time Machine - searchable mission archiveĬheck out our multireddits for spaceflight companies and solar system bodies! Industry RelationsĪre you in the rocketry/spacecraft industry? Attending a conference? Want subreddit flair? If so, please contact the subreddit moderators at where did this rant comes from? The trigger is this tweet from someone who has no idea how rocket equation works:.SpaceXLaunches - launch campaign tracking.SpaceX Stats - countdown and statistics.Rocket Emporium general spaceflight (SpaceX channel).There may be an unknown number of launches before the next public assignment. The next assignment does not necessarily mean the next launch of a booster. No transportation delays currently scheduled Well-formed - Is the post/comment in the right thread? Does the post have a descriptive and accurate title, a clean link, and the appropriate format?įor more, please read our community rules, and check out the Wiki & FAQ! Select Upcoming Events Substantive - Does the comment consist of something other than a joke or meme? In threads with a flair, does it contribute to a serious, thoughtful and technically-oriented discussion? Q5. ![]() ![]() Substantive - Does the post contribute to a serious, thoughtful and technically-oriented discussion? Q4C. Novel - Does the post contribute meaningful new information or questions to the community? Q4P. Relevant - Is the post directly and causatively related to SpaceX? Is the comment on-topic? Q3. Respectful - Is the post/comment conducive to a healthy community and a civil discussion on the merits? Q2. Community Rulesīefore posting or commenting, please ask yourself the following five questions: Q1. This board is not an official outlet for SpaceX information. Welcome to r/SpaceX, the premier SpaceX discussion community and the largest fan-run board on the American aerospace company SpaceX. Upcoming launches include: Starlink G 5-7 from SLC-4E, Vandenberg SFB on Jun 22 (05:36 UTC) and Starlink G 5-12 from SLC-40, Cape Canaveral on Jun 23 (13:10 UTC) This subreddit is fan-run, and is not an official SpaceX website. ![]()
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