[extropy-chat] SpaceX launch attempt later today

[Brian Atkins]

Here's an update... sounds pretty good and easily fixable:

http://www.nasaspaceflight.com/content/?cid=5056

Falcon I flight - preliminary assessment positive for SpaceX
By Chris Bergin, 3/24/2007 11:14:51 PM

SpaceX CEO Elon Musk has noted that the preliminary assessment of the Falcon I 
flight shows that the second stage shut down only a minute before schedule - and 
still managed to deploy its satellite mass simulator ring.

The shutdown appears to have been caused by the sloshing of propellant in the 
LOX tank, increasing observed oscillation, which would normally have been 
successfully dampened out by the second stage Thrust Vector Control (TVC) 
system. However, the impact on the second stage nozzle during separation caused 
a 'hard slew' correction, over-compensating previously simulated



The Falcon I launch vehicle lifted off from its Kwajalein Atoll launch pad in 
the Pacific Ocean last week, putting behind the failure - which occurred just 
seconds into first stage flight ascent ? of its debut launch a year ago.

Although the video of the launch webcast cut off just after 5 minutes of flight, 
SpaceX have now gained visuals from the entire flight, past the point of the 
premature second stage shutdown.

'Except for a few blips here and there, we have now recovered video and 
telemetry for the entire mission, including well past 2nd stage shutdown, which 
only occurred about a minute before schedule (roughly T + 7.5 mins),' noted Musk 
to NASASpaceflight.com. 'Including all the video, we have somewhere close to a 
terabyte of information to review.

'This was far too much to send over the T1 satellite link from Kwaj and had to 
be brought over in person after the flight. A number of our engineers have only 
just returned from Kwaj and we have not had a chance to caucus, so please 
consider this still a preliminary assessment.'

As observed on the webcast, an increasing level of oscillation could be seen on 
the second stage. While this is initially being blamed on the sloshing of 
propellant in the LOX tank, SpaceX had simulated - and planned for - such a 
scenario. However, the impact on the second stage nozzle, which was subsequently 
corrected by the TVC system, added an extra - unexpected - parameter for the TVC 
to counter.

'In a nutshell, the data appears to show that the increasing oscillation of the 
second stage was due to the slosh frequency in the LOX tank coupling with the 
thrust vector control system,' added Musk.

'Our simulations prior to flight had led us to believe that the control system 
would be able to damp out slosh, however we had not accounted for the 
perturbations of an impact on the stage during separation, followed by a hard 
slew to get back on track.'

While the impact observed during separation failed to damage the second stage 
engine's nozzle, the cause is currently being blamed on the vehicle's rotation 
being fives times higher than the expected maximum.

'The nozzle impact during stage separation occurred due to a much higher than 
expected vehicle rotation rate of about 2.5 deg/sec vs. the maximum expected of 
0.5 deg/sec. As the 2nd stage nozzle exited the interstage, the first stage was 
rotating so fast that it smacked the niobium nozzle,' Musk noted. 'There was no 
apparent damage to the nozzle, which is not a big surprise given that niobium is 
tough stuff.

'The unexpectedly high rotation rate was due to not knowing the shutdown 
transient of the 1st stage engine (Merlin) under flight conditions. The actual 
shutdown transient had a very high pitch over force, causing five times the max 
expected rotation rate.'

Initial commentary in the media was based mainly on five minutes of webcasted 
video. However, now that the full video and data has now been acquired by 
SpaceX, a number of bonuses have been noted.

'On the plus side, the data shows that this is the only thing that stopped the 
Falcon 1 test flight 2 from reaching full orbital velocity,' said Musk. 'The 
second stage was otherwise functioning well and even deployed the satellite mass 
simulator ring at end of flight!'

More evaluations will follow, as SpaceX engineers pore over the vast amount of 
data they now have available to them. The initial findings raise the hopes of 
medium level modifications being able to correct the issues noted.

'We definitely want both the diagnosis and cure vetted by third party experts, 
however we believe that the slosh issue can be dealt with easily by adding more 
baffles, particularly in the LOX tank. The Merlin shutdown transient can be 
addressed by initiating shutdown at a much lower G level, albeit at some risk to 
engine reusability.

'Provided we have a good set of slosh baffles, even another nozzle impact at 
stage separation would not pose a significant flight risk (although obviously we 
will work hard to avoid that).'
-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/