Tuesday, April 25, 2017

About the launch abort system for the New Shepard capsule.

Copyright 2017 Robert Clark

 Blue Origin has revealed the format of its suborbital tourism capsule for the New Shepard suborbital launcher:

Take a Peek Inside Blue Origin’s New Shepard Crew Capsule.
Published: 29 Mar , 2017
by Nancy Atkinson

   The cylinder in the middle is the launch abort motor. It is only supposed to fire in case of an emergency to pull the capsule away from the rocket launcher.

 Normally, it would not even fire. Still its presence inside the passenger cabin is rather disconcerting. Moreover, it is a solid rocket motor. For solid motors, the combustion chamber is the entire rocket, so if a failure, i.e., a breech does occur it can happen anywhere along the motors length.

 A Blue Origins video animation from 2015 shows the solid rocket escape motor with handholds at about the 2:25 point:

 Be careful to mind your head while floating though!

   The reason Blue Origin decided to put the abort motor inside the cabin likely was for reasons of positioning of the center of gravity(CG) with respect to the center of pressure(CP). A well known rocket stability rule of thumb is the center of pressure should be below the center of gravity

The trunk and fins helped that for the SpaceX launch abort test by bringing the CP rearward:

 But compare this to the Blue Origin abort test:

  Notice that the capsule is gyrating while the rocket motor is firing. This would be very unpleasant for the passengers since they would be subjected to high g's while being thrown right and left, albeit while strapped in.

 Then for these reasons I suggest giving the New Shepard a trunk with fins as has the SpaceX Dragon capsule.

 This could be done by instead of having the ring structure at the top of the New Shepard stay attached to the New Shepard, let it act as the trunk for the capsule:

 Then you would move the solid rocket abort motor down into this structure, so it is no longer inside the passenger compartment.

 However, this ring structure does have a function as far as the landing of the New Shepard rocket; it holds the fins and the speed brakes used during the landing:

 So how could we maintain those functions if that ring structure is instead attached to the capsule? Two possible approaches you could duplicate it so the New Shepard has its own as does the capsule. 

 Or another possibility would be to have the ring structure only detach along with the capsule only during an abort scenario. For the normal launch, with no abort, the ring structure would stay attached to the New Shepard rocket, carrying also inside the abort motor, while the capsule detaches for the normal flight to suborbital space.

 But if there is a need for an abort, the solid rocket abort motor would fire carrying the ring structure and the capsule away from the New Shepard. In this scenario where there would need to be an abort presumably there would be a failure of the New Shepard anyway and you would not expect to recover it.

  Bob Clark


  1. A decent idea, but don't you think it is simpler to give the capsule its own set of airbrakes? It would add very little mass to the rocket: the emergency airbrakes only really need to function in the lower atmosphere.

  2. Actually, having the abort rocket motor inside the capsule is analogous to having the ejection seat rocket motor inside the aircraft cockpit. One is bigger than the other, but so what? -- GW

    1. From your knowledge on solids, how often do they experience a breech? Then consider that for space tourism there will be many more launches than there are now just launching satellites.

      This increases the chances for a failure. Of course the liquid booster would also have to fail first so this would need to be factored into the calculus.

      But also alarming were the gyrations apparent in the New Shepard abort test while the solid abort rocket was firing. This was near the end of the burn so likely the thrust was reduced, but still that would have been very unpleasant for the passengers.

      Bob Clark

    2. Solids can be made extremely reliable, or they can be quite dangerously unreliable. Depends upon your QC approach (TQM works great, typical gov't QC does not).

      Don't forget that rocket science ain't just science. It's only about 40% science, it's 50% art, and it's 10% blind dumb luck, and that's in production work. In development work, the art and luck factors are higher. The art is the part never written down.

      Escape ride quality is less of an issue than is successful escape. The motor represents a last-ditch attempt not to be killed.

      I have been told by test pilots that ejections seats are a means of committing suicide in order not to be killed in the crash, but that's an exaggeration.

      Most seats do peak at 40 gees, though. There are nearly always injuries to survivors who ejected. -- GW

  3. Dual separation planes not only adds mass but sound like a S&MA nightmare. -philip