ditto to the above posts by landis and whitster.
Next you need to realize that the FED isn't trying to save the stock market. They are preventing a credit market collapse. We function on a fractional reserve system. Banks lend out much more than they have. A liquidity crunch puts this in jeopardy and there can be runs on the banks' reserves.
If banks go bankrupt then many people are hurt and the economy stalls. The FED may be independent in a political sense, but they are not unbiased. Their job is to keep the expansion phase going without letting inflation get out of control. They accomplish this through monetary policy, because fiscal policy doesn't work as well in a large country with free-floating exchange rates.
Anyway, is the market rigged. No! That is an excuse of losing traders. The FED is simply doing its job. One can argue whether their method is the most effective, but they are doing what is generally accepted as the most effective way of protecting against a currency crisis. They really don't care about the stock market. The stock market reacts violently because of trader speculation. The FED doesn't care about this.