From the Sputnik rocket's Wikipedia page, the specific impulse of the boosters and the engine are both ~307 s. Low Earth Orbit requires a Delta V of ~9400 m/s. The mass of Sputnik is ~85 kg. Plugging these into the rocket equation gives an initial mass of just about 2000 kg. But the actual Sputnik rocket had a mass of 267,000 kg. Obviously, the engine, tanks, and all the engineering takes up mass, and it's likely that the Soviet Union wasn't operating with full efficiency, but nonetheless it's a massive discrepancy. Where does it come from?

  • $\begingroup$ Remember, Sputnik was put together in a hurry using off-the-shelf parts wherever possible. The booster which sent Sputnik into orbit was designed to be an ICBM, and at the time, ICBM warheads were considerably larger than 85 kg. The point of the exercise was to get a satellite into space as quickly as possible, not as efficiently as possible. $\endgroup$ – user16622 Jun 20 '16 at 18:28
  • $\begingroup$ Sputnik was a demonstration of the R-7 rocket, en.wikipedia.org/wiki/R-7_Semyorka, which was supposed to carry 3-5 ton nuclear warheads. In general the rocket equation is completely useless to estimate the actual mass of a launcher, we need to do much more precise simulations with correct estimates for the mass of the tanks and engines. Even the Falcon 9 has a ratio between rocket and payload mass of 30:1 for LEO missions, far more than the rocket equation suggests. $\endgroup$ – CuriousOne Jun 20 '16 at 18:29
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    $\begingroup$ This would also be good for Space Exploration, where they probably know all the relevant numbers off the top of their heads. I'll just note that it's pretty hard to accelerate 85 kg to orbit without also accelerating several tons of deadweight almost to orbit too. $\endgroup$ – user10851 Jun 20 '16 at 18:36

The payload isn't the dry mass of the rocket that appears in the rocket equation.

The dry mass is the payload plus the tankage, engines, skin, guidance system, payload deployment system and so on—basically everything that isn't thrown out the back of the rocket.


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