Video of SpaceX Falcon 1 Flight 3 Launch Shows Stage Separation Anomaly
Written by Ian O'Neill
Falcon 1 lifts off from Kwajalein Atoll, South Pacific August 2nd (SpaceX)
On August 2nd, SpaceX made the surprise announcement that the third flight of the Falcon 1 rocket system would launch at 8pm (PST) that day. The world rushed to watch the first commercial flight of this impressive private-sector rocket via the web from a live feed on board. The first launch attempt was aborted due to a minor parameter fluctuation of 1% out of "normal" operating conditions, but the launch crew very quickly re-fuelled and prepared Falcon 1 for a second launch attempt within the hour. The second launch attempt appeared to be flawless, Merlin 1c engine roaring to life, lifting the rocket into the atmosphere. All seemed good, SpaceX seemed on track and very confident. However, minutes into the flight, the live video feed was cut and it was being reported an anomaly had occurred. It wasn't until later in the week that SpaceX CEO Elon Musk gave details about the "anomaly." SpaceX recently released video footage of the entire launch, up to the point where the stage separation problem occurred, spinning the ill-fated vehicle out of control…
So what did happen on that frustrating Sunday evening? On August 6th, Elon Musk announced the findings of the investigation into the launch anomaly. According to the launch engineers, the SpaceX Merlin 1c engine in the first stage performed perfectly. Even after the false-start on the launchpad, the engine was ready to go within the hour. This fast turnaround from launch abort to re-launch is a huge advantage for the company, a great testament to the flexibility of the technology SpaceX has developed in-house. The problems started during stage separation at an altitude of 35 km.
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. – Elon Musk, Aug. 6th statement.
From this statement and from viewing the video, it would seem that during first stage separation a small amount of fuel left over creating a small thrust just after the stages were forced away from one another (a.k.a. "stage separation pusher impulse"). At separation, it would appear that just as the first stage was beginning to fall away from Falcon 1, it regained some forward thrust, making it crash into the second stage engine. This small thrust anomaly prevented the spent first stage from falling clear of the igniting second stage. This sequence of events is captured in the series of screenshots below:
The Falcon 1 separation anomaly at an altitude of 35 km. From left to right: First stage separation appears to be going well until frame 3. Frame 4 shows the first stage thrust back into the second stage. Frame 5 shows the second stage firing when the first stage is not clear, Falcon 1 tumbles out of control (SpaceX)
As the first stage was not clear, the second stage engine fired into the spent first stage. This would have caused a loss in control in rocket trajectory. However, the SpaceX editors appear to cut the video from the instant the second stage fires to when the rocket is in full tumble, blacking the frames out in between with the text "Faring Separation." It's not obvious what this means and there is no mention of it in the accompanying text. Most probably it means the camera was blown away from the rocket after second stage ignition.
See the full Falcon 1 launch »
The anomaly was down to what has been called a "thrust transient" and Musk points the blame at the tiny thrust that couldn't be measured on the ground during test firing as the force generated was simply too small to be detected. However, in the vacuum of zero-gravity space, any thrust, large or small, matters:
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 – Elon Musk, Aug. 6th statement.
Although this event is an obvious set back, and deeply saddening for SpaceX and the owners of the payloads Falcon 1 was supposed to put into orbit, lessons have been learnt and Musk is positive the next launch will be a total success. After all, no one said rocket science was easy…
Source: SpaceX
Filed under: Space Flight
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August 16th, 2008 at 10:13 pm
"However, in the vacuum of zero-gravity space"…
Hehe…space = zero gravity? Since when? Gravity is everywhere.
This seems to be all about an unaccounted-for pressure differential. Sucks that their tolerances were so close and this caused a problem. They'll get it next time.
August 17th, 2008 at 12:32 am
Jason
The thing was in free-fall in a vacuum, but didn't you know that Space Reporters aren't allowed by their Union to write "free-fall" in place of "zero-gee"?
It's the first thing any space-nut learns – that gravity doesn't have limited range and "zero-gee" is really free-fall – but it's a handy shibboleth to distinguish between all us space-nuts and Joe-Public.
August 17th, 2008 at 3:28 am
Did they have Separation problems 40yrs ago? Can't understand why they should have such problems now… With modern technology and all…
August 17th, 2008 at 7:37 am
With all their functionality, it would seem that payload disaster recovery would be high on the list – especially this early in the game. Is there a reason they couldn't jettison the payloads and have them parachute down? Seems like even if they had to detonate the rocket the debris field would be a safe parachute zone as well.
Perhaps their track record will greatly improve but i for one would wait for investing in an expensive payloads until they flip their success ratio around by a LARGE margin
August 17th, 2008 at 3:37 pm
35 km or 217km which is the correct height for first stage sep?
More like 21.7 Miles??
The Falcon 1 separation anomaly at an altitude of 217 km
SpaceX Surprise Launch of Falcon 1, Suffers "Anomaly" at an Altitude of 35 km,
unless this machine can coast for over 150km after seperation, in which case this would make it a wonderful machine.
August 17th, 2008 at 5:42 pm
Hi David – there are some really strange variations in reported altitudes and stage separation times. I've checked up on the sources for both articles (the one at 35km and this one at 217km) and they are accurate. I'm trying to check the ties now to see if they tally… mmmm interesting!
Thanks, Ian
August 17th, 2008 at 6:13 pm
Ah, now I get it. Stage separation happened at 35 km, but the rocket had enough momentum to continue higher, even after the anomaly (I think), to reach 217km. So stage separation happened at 35km (after 150 secs) , but the max altitude the rocket reached was 217km. I'll correct for this mistake…
Cheers!
Ian
August 19th, 2008 at 7:06 am
Richie,
It wasn't so much a separation problem as it was an engine which continued to run when it should have been shut down.
Byron,
Different methods of recovery would be dependent on altitude of the problem. However of the failures which occur most of the time this isn't feasible because 1- its destroyed because the rocket goes BOOM!
2- it gets into space, just not into the originally planned orbit. Therefore, it isn't functional, but nothing could really be parachuted directly back to Earth. Eventually it will return and burn up in the atmosphere, since it isn't protected for re-entry.
In the small percentage where it may be feasible to recover, it would cost extra money for the recovery system, and add weight which cannot be afforded.
August 20th, 2008 at 7:43 am
Hi Ian
How much do aerodynamic forces come into play at 35000m. Sure there's probably not much air at this altitude but that rocket is really moving. Could there not also be a relative vacuum generated between the two stages just as seperation takes place similar to the effect of blowing across the top of a straw lifts the liquid. Think also NASCAR, F1 tailgating to sit in the relative vacuum created by the leading car. F1 cars actually overheat if they do this for too long, thats how big the difference in air density is.
I was surprised that a hydraulic impulse is enough to complete stage seperation. I would have thought something a little more pyrotechnical would be in order. Think of that famous footage of the Apollo stage tumbling flaming away, brilliant !!! Good PR. SpaceX should have given us footage of the thing hitting the ocean. Every 10yr old in world would know who SpaceX is tomorrow.