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I'm afraid this is a highly speculative question, but I wanted to put it out and see if anyone can provide more insight.

Let's say that at some time in the future, during a Falcon 9 launch, but before stage separation, an anomaly is detected with the second stage that is going to cause a loss of mission. Theoretically, could the Falcon abort the assent and proceed to land with the second stage and payload still attached?

The extra weight might even help the landing. It would provide a more manageable T/W ratio and allow the F9 to avoid the tricky hover-slam landing. Of course the higher centre of mass isn't going to help things, and the landing software would need completely rewriting and new flight profile would need to be created.

TL;DR: Are the any engineering problems that would completely rule out a Falcon 9 aborting an assent and landing with its payload?

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Dry mass of the first stage from SpaceFlight101 suggests 25,600 kilos.

Dry mass of the second stage is 3,900 kilos, and 92,670 kilos fueled.

Ignoring payload, that is one heck of a top heavy vehicle, an empty first stage, and a fully fueled second stage, almost 4 times the mass in the second stage.

The current control facilities (Cold gas thrusters, Grid fins, Engine gimbal control) seem highly unlikely to be able to control such an unbalanced vehicle on landing.

The core issue would be the mass of the fuel/oxidizer in the second stage, not the empty mass of the second stage.

The Centaur (LOX/LH2 RL-10 powered upper stage, a variant still used by Atlas V and Delta IV and possible SLS Block I) was being considered for use in the Shuttle, but venting the fuel and oxidizer in case of an abort was too much work to figure out (And for the Shuttle, sometimes it seemed like money was not a problem most of the time). It is a bit easier in the case of the Falcon 9, where there is no Orbiter walls to get the fuel dumped out through.

A venting system for the upper stage might make it possible.

Secondarily, a landing with a fully fueled upper stage that tipped over, for whatever reason, like the landing of the CRS-6 flight on the ASDS JRTI barge, has the potential for a VERY bad explosion. Consider how much burning we saw with a mostly empty first stage on the CRS-6 almost landing, with how bad a fully fueled second stage might cause.

For that reason, the FAA might have a hard time accepting it as well.

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  • $\begingroup$ Top-heavy vehicle? Not a problem - just borrow some of Bill Kerman's superpowered reaction wheels. :-P $\endgroup$ – Sean Feb 20 at 4:20
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The aerodynamic model of the first stage return is defined by heavy engine machinery at the base, lightweight empty tanks above, and the grid fins at the top. That's a very stable configuration for downward flight, much like a throwing dart.

Loaded or dry, an attached second stage completely ruins all of that.

I can't imagine this would be possible.

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    $\begingroup$ I think you might have fallen for the Pendulum Rocket Fallacy. The height of the center of mass is completely irrelevant while in flight. It only becomes relevant on ground contact. A throwing dart flies the way it does because of the fins in the back. $\endgroup$ – Philipp May 5 '15 at 20:14
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    $\begingroup$ Nothing to do with the pendulum fallacy. A throwing dart is stable because the aerodynamic center (defined mostly by the airflow on the fins) is behind the center of mass (defined by the weight of the metal head of the dart versus the light plastic body). Ditto for the returning Falcon core. en.wikipedia.org/wiki/… $\endgroup$ – Russell Borogove May 5 '15 at 22:51
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    $\begingroup$ (Specifically, the difference is that the thrust force vector in the pendulum fallacy is aligned with the rocket body, while the drag force is aligned with the velocity vector.) $\endgroup$ – Russell Borogove May 5 '15 at 23:57

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