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I'm curious as to what rocket engine in a launched rocket burned the longest in a continuous fashion. I'm not interested in testing burns or inter-planetary engines which are designed for low-thrust long-duration use (such as ion engines), but rather launched chemical-powered engines which require an oxidizer of some sort to allow burning of the fuel (whether hydrogen, RP1, solid fuel, etc.)

In doing some casual searching, I've pulled together the following numbers for well-known launches:

  • Saturn V first stage: ~ 168 seconds
  • Falcon 9 first stage: ~ 170 seconds
  • Space Shuttle deorbit burn: ~ 240 seconds
  • Friendship 7: ~ 300 seconds
  • Saturn V third stage: ~ 347 seconds
  • Falcon 9 second stage: ~ 376 seconds
  • Saturn V second stage: ~ 384 seconds
  • Energia: ~ 500 seconds
  • Space Shuttle Main Engines: ~ 513 seconds

Based on these numbers it looks like the Space Shuttle main engines (then Energia) are the ones on my list which have the longest burn time. I would attribute this to their continuous burn from ground launch to orbit, where most other rockets are multi-stage. Am I missing other rockets which had a longer continuous burn time, whether from a ground launch, or in-orbit?

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    $\begingroup$ My personal guess is in the centaur upper stage as it has very low thrust to weight. Looking for sources though. $\endgroup$ Oct 12 '17 at 20:42
  • $\begingroup$ I think you are correct with SSME, but there may be some outlier I'm not aware of. $\endgroup$ Oct 12 '17 at 20:48
  • $\begingroup$ Wouldn't high ISp, low thrust chemical engines used in transfer stages of interplanetary missions top the engines used for launch into LEO, which normally take a very high thrust, mass flow, and as result don't burn all that long? $\endgroup$
    – SF.
    Oct 12 '17 at 21:09
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    $\begingroup$ @JakeBlocker I think that would be indeed some upper stage, but not necessarily the Centaur. Even single-engine Centaur can burn all its fuel in ~900 seconds whereas Briz-M would take ~3000 seconds to use it all. The real issue is that they usually work in several burns. $\endgroup$
    – OON
    Oct 12 '17 at 21:11
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    $\begingroup$ By the way most of the interplanetary missions didn't actually used ion engines. Most of them used chemical engines and being low-thrust they could have quite a burn time. E.g. ExoMars performed a deep space maneuver burn that took ~ 50 minutes using some bipropellant engine (I assume fueled by UDMH/N2O4) $\endgroup$
    – OON
    Oct 12 '17 at 21:57
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As @OON mentions, some small spacecraft maneuvering engines do really long burns. Juno's orbital insertion burn at Jupiter is 35 minutes.

Here are some notable launcher/bus stage burns:

Ariane 5 upper stages routinely burn for 16 minutes for GTO insertion missions.

I can't find a precise timeline for the New Horizons launch; that would be a likely candidate for a really long Centaur burn.

ExoMars 2016, Briz-M second burn was ~18 minutes, in addition to ~5, ~12, and ~11 minute burns.

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    $\begingroup$ New Horizons' longest Centaur burn was ~9 and a half minutes. It's way down in this long article. spaceflight101.com/newhorizons/project-history-mission-profile $\endgroup$ Oct 13 '17 at 3:53
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    $\begingroup$ If you are looking for longest burns, they are normally orbit insertion, which is largest delta-V budget at normally relatively low thrust. Messenger was about 15 minutes, ExoMars TGO lasted 139 minutes ! Juno 35 minutes $\endgroup$
    – kert
    Oct 14 '17 at 1:40
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I'm going to go with the SSME, specifically SSME serial numbers 2020 and 2021. These were the engines installed in the left and right positions on Challenger for mission STS-51F.

When the center engine failed at 5:43 after liftoff, the other two engines had to burn longer to make it to the MECO (Main Engine Cutoff) target. So they burned for ~ 587 seconds (MECO was 9:41 and the engines started ~ 6 seconds before liftoff).

Source: Space Shuttle Missions Summary, page 2-20.

h/t to ikrase who asked in a comment about ground testing: In August 1988 an SSME was fired on the ground for 2017 seconds; over 33 minutes.

Source: 1988 Aeronautics and Space Report of the President p. 25

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    $\begingroup$ Have these or other large launch vehicle engines been tested for longer? $\endgroup$
    – ikrase
    Dec 10 '20 at 4:42
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    $\begingroup$ @ikrase edited answer; thanks for the comment $\endgroup$ Dec 10 '20 at 13:41
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Mir deorbit burn, done by Progress M1-5 main engine and control engines firing together, lasted for about 22 minutes (burning to depletion). Progress M1-5 carried 2,678 kilograms of fuel, its the only payload, while some likely has been spent on also long (21.5 and 24 min preparatory) burns, done by control engines only.

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