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Showing content with the highest reputation on 01/15/2018 in all areas

  1. 6 points
    I have compiled some data on the payload fraction (payload to LEO / Gross mass) of various rocket systems; From this, several thing can be seen; Solid rocket boosters utterly ruin your payload fraction. Despite having a significantly higher specific impulse than other engines (365 seconds for the RS-68 vs. 285 seconds for the RD-275), hydrogen-fueled launch systems only have a slightly better payload fraction than hypergolic systems, or are even significantly worse. Larger rockets generally have a larger payload fraction (Saturn I vs. Saturn V, Falcon 9 vs. Falcon Heavy). Titan II and Titan IV are not entirely comparable. STS is a stupid pile of trash. Kerolox first stage provide significantly better payload fractions in almost all cases, while avoiding the difficulties associated with liquid hydrogen. Hypergolics generally have inferior performance to both, but are significantly easier to handle, and the difference is not extreme. Data via wiki, except where noted (the gross weights for Delta IV Heavy and Atlas V 551 were horribly off, especially for the latter). Encylopedia Astronautica data mostly agreed, but that site is severely lacking in info on the Falcon family. @Sturgeon@Collimatrix@T___A
  2. 1 point
    For whatever reason Encylopedia Astronautica and wiki give the Ariane 1 a lower value for payload to LEO vs. GTO (1400 vs. 1850), which is highly odd. I can't think of any reason why that would be the case (GTO requires much more delta v than LEO). Going by the payload fraction to GTO, I get 1850/207200 = .0089, vs. 6300/705000 = .0089 for Proton-M, and 14220/738960 = .0192 for Delta IV Heavy. I think this is explainable by Ariane 1 being an older rocket with somewhat less efficient engines (the Viking-2s on Ariane 1 have 248 sec. sea level isp vs. 285 on the RD-253 and 365 on the RS-68). EA gives the LEO performance for Ariane 5 as 16000 kg, but to a 51.5 degree inclination orbit, which is going to cut into the performance a lot. Arianespace's site gives a payload to LEO of 20 tons, which gives a payload/mass fraction of .0257, which is better but still not great. Payload to GTO is 10000/777000, which gives a mass fraction of.0129. Also, Ariane 5 does a bit of the same thing STS does and uses a hydrolox first stage with solid boosters. All the Ariane variants look like they are optimized for launches to GTO/GEO, so their payload fraction to LEO is going to suffer a bit. This explains why Ariane 4 and 5 have lower payload fractions to LEO (as far as I can tell your Ariane 4 numbers are correct). *** To build on my previous calcs; STS gets hurt a bit in the payload/mass calcs since it reuses so much of what it lifts to orbit. A better comparison would be Shuttle C, which likewises uses hydrolox/solids, and has a payload/mass fraction of 77000/1966675 = .0391, which is comparable to Delta IV Heavy. Atlas V 552 (actually any Atlas variant without "0" in the middle digit) has solids in the first stage, which, if my thesis is correct, will lower the payload fraction. Theoretically the best Atlas V config for payload/mass fraction would be the Atlas V 402. Performance data for it can be found in the archived Atlas V Handbook. Adding components from page 25 of that doc, we get a gross mass of 331702 kg for Atlas V 402. Wiki says that 402 has a payload to LEO of 12500 kg, which gives a payload/mass fraction of .0377, which is better, but not by much compared to 552. Interesting.
  3. 1 point
    roguetechie

    General news thread

    At this point politics and professional wrestling are so close to the same thing that if you're not tuning in at least partially for the smack talk you'll just get your heart broken by the lack of real action.
  4. 1 point
    Mighty_Zuk

    Israeli AFVs

    Graduation video: Part of a recent propaganda series to educate people on the role of the armored corps due to its decline in recent years. This time they show a live operational firing on 3 targets in a Hamas outpost. You can see them exiting the tank after firing and celebrating with the bunch, but that's just editing for the sake of smooth transitioning. https://he-il.facebook.com/2055812101320752/videos/2085466998355262/
  5. 1 point
  6. 0 points
    roguetechie

    General news thread

    What I wouldn't give for Trump to tweet "if CNN says shithole one more time I'm gonna punch someone in the cocksucker" Just send these assholes straight into fucking orbit... Fuck Elon musk and Space X! Trump's Twitter account boosts shit to geosynchronous for pennies on the pound!
  7. 0 points
    LostCosmonaut

    Scale Models Megathread

    Picked up a model during my Colorado trip. @EnsignExpendable
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