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Previous manned spaceflight vehicles, that had a Launch Escape System (Excluding you space shuttle!) usually seemed to favor the notion of a tractor (Puller) style LES.

That is, the manned module is at the top of the stack, there is a motor (often in a tower) that contains solid or liquid engines for an abort, to drag the manned module away from the stack in times of woe.

With the newcomers to the manned space business (SpaceX, SNC, Blue Origin) and the old school approaches (Boeing and Lockheed Martin) we start to see different approaches, where SpaceX (DragonRider), Boeing (CST-100), SNC (Dream Chaser), and Blue Origin (SV? Darned if anyone knows what they plan to call it. New Sheppard is the sub orbital vehicle name, and Space Vehicle, SV is the current name I last saw for their orbital version) are working towards the idea of pusher escape systems.

NASA with Mercury, Apollo, and now Orion seem to favor tractor LES.

New guys are seeming to favor pusher systems.

Soviets have used tractor systems for Soyuz, and while some of the fun proposals in Anatoly Zak's book suggested pusher systems, none of those have really seen the light of day (Looking at you Klipper, NPK-TP, etc). What is neat is that even though the manned module is the middle of three in Soyuz, they still went with the tractor system.

Chinese with Shenzou seem to have gone with tractor systems as well.

Are there examples of actually flown hardware, using pusher escape systems, or will the new guys be the first, assuming any of them actually get to launching a manned system? (I hope they all succeed, but who knows! If you are reading this in 2020 and in hindsight laughing at my naivete, please enjoy).

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    $\begingroup$ According to Blue Origin, they call the crew module for New Shepard "Crew Capsule" and the orbital space vehicle "Biconic Space Vehicle" :) $\endgroup$
    – TildalWave
    Nov 25, 2013 at 17:19
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    $\begingroup$ @TildalWave Well that is whimsical. :) $\endgroup$
    – geoffc
    Nov 25, 2013 at 17:29
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    $\begingroup$ I suspect its due to stability of flight issues. Pusher designs are inherently more unstable (inverted pendulum). When trying to attain extreme thrust needed for an LES, a pusher would have significant design issues to ensure uniform timing and thrust. A poorly balanced system would more likely tumble than push the crew module away from the vehicle. Whilst a tractor design, even quite badly balanced systems would more or less describe a long arc (perfect for an LES). $\endgroup$
    – Aron
    Oct 7, 2014 at 14:12
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    $\begingroup$ In 1973 Soyuz 7K-T No.39 (en.wikipedia.org/wiki/Soyuz_7K-T_No.39) aborted using its main engines, having already jetisoned the tractor LES. So a pusher system has been used for an abort, even if that wasn't its primary function. However by this logic the shuttle had a pusher abort system as well: en.wikipedia.org/wiki/… So the point is still debatable. $\endgroup$
    – ForgeMonkey
    Oct 18, 2014 at 15:39
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    $\begingroup$ @Aron umm... Isn't that the Pendulum rocket fallacy? Tractor designs may be more stable due to aerodynamic effects, but I don't think the inverted pendulum is a good analogy. $\endgroup$
    – Jack B
    Jul 7, 2017 at 12:41

3 Answers 3

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No. Dragon V2 will likely be the first capsule with a built in "pusher" LES, an array of SuperDraco engines. The reason it has never been done is because the LES is usually considered dead weight once the craft has reached orbit. Jettisoning the LES as early as possible saves payload mass. The reason SpaceX and Dragon keep it is twofold. Falcon 9 v1.1 is overpowered for sending cargo Dragon to the ISS. Payload capacity is volume limited on CRS missions. There is no reason to save weight by jettisoning the LES during flight.

Second, the SuperDracos can be useful on EDL by providing a controlled, accurate landing on solid ground. SpaceX has always planned Dragon to be reusable; however, salt water ocean landings are terrible to the spacecraft. Being able to gently land on solid ground saves the spacecraft systems from wear and tear and greatly eases recovery.

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  • $\begingroup$ The LES is generally considered dead weight well before orbit. The Saturn V, for example, discarded the LES shortly after second-stage ignition, when the CSM engine was sufficient to get away from an exploding rocket. $\endgroup$
    – Mark
    Feb 28, 2019 at 3:21
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Looks like these are the first (according to http://www.newscientist.com/article/dn19239-whats-the-best-way-to-eject-astronauts-during-liftoff.html). I believe Elon indicated it had never been done before in his D2 reveal.

Saying something has never been done before is a bit difficult to prove.

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The proposed, but never completed and flown, Gemini B spacecraft might have used its solid-fuel retrorocket package, normally used for de-orbiting the spacecraft, for early launch aborts.

The NASA Gemini flights launched on a Titan II, using only hypergolic liquid fuels, which can't explode quite as dramatically as non-hypergolics or solids, so ejection seats were an acceptable escape route.

The USAF Gemini B, on the other hand, would have launched along with the Manned Orbiting Laboratory on a Titan IIIM with solid rocket boosters. Ejection seats might not get the crew to a safe distance from a SRB accident, so two additional retrorockets were added to the capsule (totaling 6), and the retros would be fired simultaneously in the event of an abort.

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  • $\begingroup$ The launch escape system is used also for reentry in this case. But if a launch escape system should be removed to save weight after a sucessful launch, a pusher system requires separation and docking again to the service unit or last stage of the rocket. This maneuver is avoided whenever possible. Separation is much easier than redocking and sucessful docking requires more hardware than separation only. $\endgroup$
    – Uwe
    Jul 7, 2017 at 15:33
  • $\begingroup$ There's a huge number of design options, really -- if the pusher unit do double duty (as service module propulsion, or deorbit engine as in Gemini B, or landing engine as in Dragon 2) you don't need to jettison it. You could also mount jettisonable pusher escape engines on the sides of the crew capsule. $\endgroup$
    – Russell Borogove
    Jul 7, 2017 at 18:26
  • $\begingroup$ Note that it's generally thought, in retrospect, that the Gemini ejection seats were not "an acceptable escape route", and would likely have killed the crew had they ever been used. $\endgroup$
    – Vikki
    Jun 26, 2019 at 3:23

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