Looking (far) ahead
by Jeff Foust
|SpaceX received telemetry from the rocket for a total of nine minutes, far longer than the couple minutes of video from the webcast. “We got further along than we thought, based on the webcast,” Shotwell said.|
More details about the failure came out during a previously-scheduled presentation at the conference on August 13 by Gwynne Shotwell, vice president of business development at SpaceX. The paper was originally intended to be about the integration of the payload for the launch, but Shotwell said it made more sense to talk about the flight results. “If I didn’t, I’m sure you’d all accuse me of being chicken,” she joked.
That included showing an extended version of the launch video on the SpaceX web site that included a few extra seconds after the web version cuts off, when the second stage engine ignites. (The extra footage isn’t online, she explained, out of concerns people would be able to examine it frame by frame, seeing details that might be sensitive or even restricted by export control regulations.) What the footage does show is the second-stage engine igniting and filling the screen with debris—“nasty bits”, as Shotwell described it—as the plume struck the first stage.
“We lit the second-stage engine in the can of the interstage and caused quite a bit of havoc, as one can imagine,” she explained. The stages did separate, but in the process the engine nozzle was ripped off, as was the parachute recovery system for the first stage. Despite that, the second stage engine did continue to burn, although without the nozzle it tumbled, she said. The payload fairing also cleanly separated, as a clip at the end of the web video shows, and SpaceX received telemetry from the rocket for a total of nine minutes, far longer than the couple minutes of video from the webcast. “We got further along than we thought, based on the webcast,” she said.
As SpaceX revealed just a few days after the launch, the cause of the failure was an unexpectedly long “thrust transient” from the Merlin 1C first-stage engine after it shut down. This was the first time this version of the Merlin engine had flown: previous flights used a version, 1A, that was ablatively cooled, while the 1C is regeneratively cooled, using fuel to cool the combustion chamber and nozzle before it is ignited.
Shotwell said the Merlin 1C engine is more reliable than the older Merlin 1A engine, and has better performance as well. “We didn’t have control over the manufacture of that particular ablative,” she said, and was unhappy with its performance. While the 1C is a better engine—and performed well during the flight—it generates a bit of additional thrust after shutdown from the fuel in the cooling system.
“It’s hard to measure that on the ground, because it’s less than 14.7 psi; as a matter of fact, it’s about 10,” she said. “More important was the timing, when that residual thrust actually kicks in. We should have timed the stage separation a little bit longer from the commanded shutoff of the first-stage engine.”
|“Better to learn it on our small rocket, the Falcon 1, than on our big rocket, the Falcon 9,” said Musk.|
Because the solution is relatively simple—extend the time between engine shutdown and stage separation—Shotwell said the company is confident that it can make another launch attempt, carrying only a dummy payload, very quickly. There is a “very narrow” launch window in September, and another in late October. “So look for us to get back to flight as quickly as we can.”
With the cause of the failure largely understood and being rectified quickly, SpaceX can even afford a little bit of humor. Shotwell described explaining the failure to an assistant of company CEO Elon Musk who is not technically minded. Her reaction, as recounted by Shotwell: “You mean to tell me we rear-ended ourselves?”
A few days after Shotwell’s presentation, Elon Musk gave a similar assessment of the recent Falcon 1 flight during a presentation at the 11th Annual International Mars Society Convention in Boulder, Colorado. “It’s a simple correction,” he said of the adjustment in the stage separation timing. “Better to learn it on our small rocket, the Falcon 1, than on our big rocket, the Falcon 9.”
“The plan going forward is to launch a bunch of Falcon 1’s,” Musk said. “I hope we make any remaining mistakes on the Falcon 1, so we make no mistakes on the Falcon 9.”
That plan ties into another announcement made immediately after the recent launch failure: the $20-million investment in SpaceX by Founders Fund, a venture capital firm in San Francisco. Many of the fund’s managing partners are, like Musk, alumni of PayPal. Musk explained that the investment wasn’t needed because of any short-term funding issues, but instead as insurance for any future problems.
“It’s just basically to top off the war chest,” he said. “At any given point, I want to make sure we have enough cash in the bank or from ongoing contracts to do another three launches. So if Flight 4 fails we’ll raise additional money.”
Musk wouldn’t discuss, though, details on the terms in the investment, including the stake in the company Founders Fund got and the resulting valuation of SpaceX. “It’s not that I care, but investors don’t like people to know what they paid.”
Even while SpaceX is working out the kinks with the Falcon 1, it’s looking ahead to even more powerful vehicles than the Falcon 9. Already on the drawing boards is the Falcon 9 Heavy, which would use three Falcon 9 first stages, analogous to the Delta 4 Heavy. Musk revealed that SpaceX is considering further augmenting its performance with a cryogenic upper stage engine powered by liquid hydrogen and liquid oxygen.
Musk said that the addition of the cryogenic upper stage—creating what he called the “Falcon 9 Heavy H”—could have important implications for Mars exploration and even settlement. “If you can do a couple launches of the Falcon 9 Heavy with a cryogenic upper stage, that would give you a sort of Saturn 5 capability,” he said.
|“It’s just basically to top off the war chest,” Musk said of the recent investment. “At any given point, I want to make sure we have enough cash in the bank or from ongoing contracts to do another three launches.”|
Musk said that development of the hydrogen engine would start “probably early next year”, with the aim of having the upper stage ready in about five years. “There are a lot of risks associated with that because it’s a very difficult stage to do and we want to ensure that, at least foundationally, it’s capable of very reliable restarts,” he cautioned. The development cost of the Falcon 9 Heavy H “is hard to say” at this stage, he said, but thought it was on the order of $1–2 billion, a large portion of which would be funded by ongoing revenues, with some additional outside investment.
“Things are certainly progressing,” Musk said. “Unfortunately not as fast as I would have liked, but we are still making good progress. And we’ll keep going until we ultimately have some ability to get to Mars.”