Sunday, June 28, 2015

Loss of Falcon-9 Launch to ISS

Observation and Condolences

The Sunday morning launch of a Falcon-9 / Dragon spacecraft supply mission to the ISS ended abruptly in an explosion a couple of minutes after launch.  My condolences to Spacex over this,  and may God speed their efforts to find out what caused this,  and to fix it. 

We will need them flying again,  sooner rather than later,  to send supplies to the ISS,  and later,  to send astronauts there.  With both them and Orbital ATK “down” with vehicle explosions,  the only other way to send supplies is via the Russian Soyuz / Progress cargo vehicle,  which itself has had a fatal problem just a few months back.

The ISS crew has sufficient supplies through to October.  After that,  they would be forced to abandon and come home in the emergency Soyuz craft docked to the station.  Somebody has to be flying and make a successful trip by then.   We really do need all three outfits up-and-flying. 

Suggestions and Recommendations

If I were them,  I'd be looking real hard at propellant leaks in the second stage.  Early at lower altitude I saw signs of propellant flash-burning erratically alongside the rear end of the first stage.  Then I saw flashes of white "cloud" moving down the side of the vehicle coming from the interstage. 

The higher the altitude and thinner the air,  the more of this leaking "something" I saw.  When the explosion occurred,  I saw "for sure" in the video that the first stage was still intact with all engines firing,  for a finite amount of time.  It was the second stage that exploded first. 

That suggests to me that something reactive was leaking from the second stage into the interstage volume around that engine.  You need that protected space to have a fume buildup that can be ignited.  They were approaching the staging point,  and systems were firing up electrically to make that happen.  Electricity and loose propellants are an explosive combination. 

It couldn't have been just kerosene,  there's almost no air up there with which it could burn. You can see that by the first stage rocket plumes ballooning out in the nearly-zero backpressure. 

It had to be both kerosene and liquid oxygen that were leaking!  Holes in both tanks cannot be ruled out,  but that seems most unlikely.  Especially as there is no internal path to get leakage from the forward tank into that interstage. 

I'd be looking very,  very seriously at the propellant line stop valves to the turbopumps (or even the engine chamber itself) that might have opened prematurely somehow. 

UPDATE 7-23-15

Elon Musk recently said the best of their thinking is that a strut internal to the second stage LOX tank failed,  releasing a container of helium pressurant,  which leaked,  causing the tank to overpressurize and burst within seconds.  His message said they use lots of these internal struts.  This one seems to have failed at 5 times lower force that it is rated to carry,  according to Musk.   

They'll have to figure that one out,  for sure.   If the failure of one small part can be catastrophic,  then some sort of redundancy seems to be called for.  At least somebody should be looking at that issue.  

The other issue is what they (Spacex) seem to be focused upon:  how to prevent installation of  low-strength parts.  This is very important:  the environment is extreme.  LOX is very cold,  a temperature at which all materials behave in a brittle fashion.  Plus,  rocket vehicles inherently suffer vibration.  Vibration + brittleness is a recipe for bad outcomes in flight vehicles.


UPDATE 8-31-15

News item posted today indicates "two months away from launch",  and "taking longer than envisioned".  They have decided to err on the side of caution.  The news release still mentions the failed strut,  but gives no further details.  

From that I conclude that they know "for sure" it was a bad strut as described above,  but they are not yet sure they can prevent it from happening again.  


UPDATE 10-14-15:

News stories indicate that Falcon-9 returns to flight in early December (this year).  Apparently they have resolved whatever went wrong with the internal strut.  I find no news releases about this on their website.  I hope they have this fully and completely resolved,  and wish them well with the upcoming launch and first stage recovery attempt.  

UPDATE 12-25-15:

Spacex has just returned Falcon-9 to flight status with a successful orbital launch of some 11 small satellites.  In this same mission,  they also for the first time successfully landed and recovered its booster rocket first stage.  That is an amazing recovery.  Kudos to Spacex.


  1. Some clues. It happened soon after second stage engine "chill down", which sends small amounts of LOX through the engine to cool the engine in preparation for the large amounts of LOX flow when the engine is firing. Perhaps this leaked out of the interstage and ignited on the outside. On the other hand perhaps this chill down LOX is supposed to be vented to the outside.
    Another clue. AmericaSpace has reported from "insiders" that the upper stage insulation has problem with cracking. And, Elon tweeted that they got indications of overpressure in the upper stage LOX tank. Could the cracked insulation have allowed greater heating than expected and this caused the LOX to expand and leak?
    Or perhaps this insulation could have ignited with the leaking LOX?

    Bob Clark

    1. I dunno, Bob. The flashing I saw on the aft side of one folded landing leg would have been kerosene, not LOX. That says more was going on than just a LOX leak. Unless it was separation-zone back-feed of fuel-rich exhaust from the first stage engines. If that was the case, then there's a potential heating problem that hasn't yet cropped-up as an anomaly. -- GW