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Old January 18th 20, 11:53 PM posted to sci.space.policy
Niklas Holsti
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Default SpaceX Dragon 2 In Flight Abort Test

On 2020-01-19 0:11, JF Mezei wrote:
On 2020-01-18 10:17, Jeff Findley wrote:

NASA knows the details of this for sure. But I believe that the Super
Draco engines are sized to pull Dragon 2 away from Falcon 9 at the same
time the engines are shutting down.


Media articles tend to "Readers Digest" what is given to them by
authorities which are already a Reders Digest version of reality.

Say an abort happens for causes other then engines. If engines are
already giving astronauts a 3G acceleration, and you fire the Super
Dracos that give 4G, the crew would go from 3G to 7G


No. If the Dragon is still attached to the launcher when the Dracos
fire, the acceleration would only increase a little, as the Draco thrust
is added to the Merlin thrust to accelerate the launcher+Dragon assembly.

If the Dragon is not attached to the launcher when the Dracos fire, the
Dragon will simply pull ahead of the launcher, at 4G, losing contact
with the launcher which will fall behind, the distance increasing at 1G.
In theory, the launcher's acceleration might increase a little when the
Dragon pulls away, because the launcher no longer has to accelerate the
Dragon's mass, but I believe that the control SW keeps the launcher's
acceleration at its programmed value, and the Dragon's mass is anyway
only a fraction of the mass of the launcher and its fuel.

Also, I believe that typically Falcon-9 will accelerate at much less
than 3G around Max-Q. In an earlier discussion, numbers in the range
0.5G - 1G (on top of gravity) were used, taken from some time-velocity
diagrams of actual launches.

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Niklas Holsti
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