Particularly the first and second stages into earth orbit - were the stages run dry before separation? On first thoughts, It would seem to be safer to do so, but I realised the engines required liquid fuel to act as a coolant prior to ignition in the combustion chamber. Also, the final orbit might not be so precise if there's variation to the launch profile.

So, the question becomes: how much fuel was left in each stage?

I'd expect any excess fuel to be kept to a minimum since it is expensive (fuelwise) to lift unburnt fuel.

If answers can include the third stages and supply modules, that'd be great.

  • 2
    $\begingroup$ No. There are questions on the site about this already. 10s of thousands of lbs were left in the first stage. It's more expensive to blow up your rocket by running the engines dry. $\endgroup$ Commented Jul 15, 2019 at 12:03
  • 2
    $\begingroup$ Related but not quite duplicate IMO: space.stackexchange.com/q/21704/195 $\endgroup$ Commented Jul 15, 2019 at 13:15
  • 3
    $\begingroup$ A good source is Apollo by the numbers, see 1, 2, 3. You may write an answer yourself by using these tables. $\endgroup$
    – Uwe
    Commented Jul 15, 2019 at 14:00
  • 1
    $\begingroup$ @HenningMakholm no, of course not - the point is keeping them "operational" (read - "they, and the rest of your rocket, in one piece") until you have ditched them. $\endgroup$
    – Baldrickk
    Commented Jul 16, 2019 at 12:46
  • 2
    $\begingroup$ @HenningMakholm The big picture stage separation sequence for the Saturn was like this 1) Shut down first stage engines 2) Physically separate stages 3) ignite second stage engines. If the booster exploded in step 1) it would have affected the mission negatively. $\endgroup$ Commented Jul 16, 2019 at 13:26

2 Answers 2


For the Saturn V, the first and second stages both cut off when a low-propellant-level sensor tripped in the tanks. Most launchers' booster stages do something similar -- burning to total depletion would be dangerous for a number of reasons noted here.

For the S-IC first stage, it wasn't unusual to leave 30 tons of propellant unconsumed, as Apollo By The Numbers notes. This is a little more than 1% of the total stage tankage, and represents about 2 seconds of burn time.

For the S-II second stage, the residual propellant was usually 3-4 tons -- less than 1% of the initial amount, and again representing 2-3 seconds of burn time.

The orbital insertion burn on the S-IVB third stage, as with most orbital launchers, was cut off when the desired target velocity was reached. This allowed the stage to correct for off-nominal performance of the first and second stages -- it would do whatever it needed to do to get to the right altitude and speed.

Most of the fuel in the third stage was saved for the translunar burn, which was likewise stopped when the desired change in velocity was accomplished, again typically with 3-4 tons of fuel remaining, though that represents 10-15 seconds of burn time for the smaller, single-engine stage.

I believe all the other major burns on Apollo missions (course correction, lunar orbit insertion, etc) used velocity-based cutoffs as well.

  • 8
    $\begingroup$ 15 tons of propellant pr second! impressive! $\endgroup$ Commented Jul 15, 2019 at 23:12
  • $\begingroup$ From Apollo By The Numbers, overall program averages for the remaining fuel for the first three stages was, respectively, 1.50%, 0.82% & 8.42% $\endgroup$ Commented Jul 16, 2019 at 22:01
  • $\begingroup$ Fun fact: The Saturn V third stage engine could light three times. No third ignition was ever used in flight. $\endgroup$
    – Joshua
    Commented Aug 18, 2019 at 0:30
  • 4
    $\begingroup$ @Joshua - Actually the engine was ignited three times in Apollo 9 -- Once to put the CSM/LM stack into low earth orbit, and two for testing purposes. The second burn put the SIVB into an elliptical Earth orbit, and the third burn ejected the stage from the Earth-Moon system into Solar orbit. These burns were unusual in that they weren't pushing the CSM/LM, so they probably had quite a bit more acceleration than normal for an SIVB. klabs.org/history/history_docs/jsc_t/apollo_09_saturn_v.pdf $\endgroup$
    – kwan3217
    Commented Aug 18, 2019 at 6:22
  • $\begingroup$ I thought I checked everything. :( $\endgroup$
    – Joshua
    Commented Aug 18, 2019 at 14:33

I took the numbers from 'Apollo by the Numbers' and entered them into a spread sheet.

enter image description here

Still a lot of work to do with Apollo 9 to 17.

Any suggestions?

The left fuel is less than 3 % for stage 1 and 2 but less than 10 % for stage 3 final burn.

  • $\begingroup$ These can be programmatically found, although the data is a little dirty. I might fill in the table if I find the time. There is an interesting tidbit they provide with the Program Totals: For example, the total fuel consumption across all launches for fuel & oxidizer was: S1C: 1.50% SII: 0.82% SIVB 1st burn: 71.10% 2nd burn: 12.05%. In total just shy of 1 million lbs of propellant was left unused across all launches. $\endgroup$ Commented Jul 16, 2019 at 21:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.