Re: solar sail launch tonight, as part of Space X launch

From: Patrick Wiggins (paw@wirelessbeehive.com)
Date: Thu Aug 07 2008 - 04:43:42 UTC

  • Next message: Greg Roberts: "Optical 06 August 2008"

    On 02 Aug 2008, at 23:29, Jim Scotti wrote:
    
    > According to that webpage:
    >
    >> Posted August 2, 2008 - 20:38 PDT
    >>
    >> We have heard from launch control that there has been an anomaly.  
    >> More details will be posted to the website as available.
    >
    > That last message is almost 2 hours old now.  I wonder what the  
    > anomaly was but it's anyones guess, I suppose.  No further updates  
    > about the vehicle being in orbit or anything can't bode well for the  
    > Falcon 1....
    >
    > Jim.
    
    For those here who may not receive Space-X news releases, here's what  
    they sent out earlier this evening.
    
    patrick
    
    
    
    Message from Elon Musk: Falcon 1, Flight 3 Mission Summary
    August 6, 2008
    
    Timing is Everything
    
    On August 2 nd, Falcon 1 executed a picture perfect first stage  
    flight, ultimately reaching an altitude of 217 km, but encountered a  
    problem just after stage separation that prevented the second stage  
    from reaching orbit.  At this point, we are certain as to the origin  
    of the problem.  Four methods of analysis  vehicle inertial  
    measurement, chamber pressure, onboard video and a simple physics free  
    body calculation  all give the same answer.
    
    The problem arose due to the longer thrust decay transient of our new  
    Merlin 1C regeneratively cooled engine, as compared to the prior  
    flight that used our old Merlin 1A ablatively cooled engine.  Unlike  
    the ablative engine, the regen engine had unburned fuel in the cooling  
    channels and manifold that combined with a small amount of residual  
    oxygen to produce a small thrust that was just enough to overcome the  
    stage separation pusher impulse.
    
    We were aware of and had allowed for a thrust transient, but did not  
    expect it to last that long.  As it turned out, a very small increase  
    in the time between commanding main engine shutdown and stage  
    separation would have been enough to save the mission.
    
    The question then is why didn't we catch this issue?  Unfortunately,  
    the engine chamber pressure is so low for this transient thrust --  
    only about 10 psi -- that it barely registered on our ground test  
    stand in Texas where ambient pressure is 14.5 psi.  However, in vacuum  
    that 10 psi chamber pressure produced enough thrust to cause the first  
    stage to recontact the second stage.
    
    It looks like we may have flight four on the launch pad as soon as  
    next month.  The long gap between flight two and three was mainly due  
    to the Merlin 1C regen engine development, but there are no technology  
    upgrades between flight three and four.
    
    Good Things About This Flight
    
    	 Merlin 1C and overall first stage performance was excellent
    	 The stage separation system worked properly, in that all bolts  
    fired and the pneumatic pushers delivered the correct impulse
    	 Second stage ignited and achieved nominal chamber pressure
    	 Fairing separated correctly
    	 We discovered this transient problem on Falcon 1 rather than Falcon 9
    	 Rocket stages were integrated, rolled out and launched in seven days
    	 Neither the near miss potential failures of flight two nor any new  
    ones were present
    The only untested portion of flight is whether or not we have solved  
    the main problem of flight two, where the control system coupled with  
    the slosh modes of the liquid oxygen tank.  Given the addition of  
    slosh baffles and significant improvements to the control logic, I  
    feel confident that this will not be an issue for the upcoming flight  
    four.
    
    Elon
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