Delivering critical payloads to the International Space Station requires software that ensures tight tolerances
With the retrieval of the Dragon from the Pacific Ocean, Space Exploration Technologies Corp. (SpaceX) became the first commercial company to launch and recover a spacecraft from low-Earth orbit. Placed into space atop the company’s Falcon 9 launch vehicle, Dragon completed two orbits with speeds topping 17,000mph. After its three-hour, 50,000 mile flight, Dragon splashed down just one mile from the center of its targeted landing zone.
This is the first of three test flights under NASA’s Commercial Orbital Transportation Services (COTS) program. Following two additional test flights, Dragon started transporting cargo to the International Space Station, preparing for the company’s plans to undertake manned flight by the end of 2015. For these future missions, SpaceX will again turn to its portable CMM (PCMM) systems to maintain the precision it achieved when first launching and returning Dragon from orbit.
SpaceX is a different kind of company, in part due to its founder and CEO, Elon Musk, who was co-founder of PayPal and is the CEO of Tesla Motors. In a post-flight press conference, Musk says, “The reason I am doing SpaceX is that I just happen to have a very strong passion for space, and I want us to become true space faring civilization and even a multi-planetary civilization.That is my goal for SpaceX.”
|SpaceX's Grasshopper vertical takeoff and landing test vehicle at the company's rocket testing facility in McGregor, TX.
To make his goal a reality, SpaceX intends to change 40-year-old paradigms with a family of launch vehicles and spacecraft that increase reliability and performance, while ultimately reducing costs by a factor of 10. The underlying philosophy is a focus on simplicity to both increase reliability and lower cost for vehicle development and launch services.
According to Larry Mosse, SpaceX’s tooling operations manager, the company counts on its PCMMs to deliver this reliability and cost reduction, while counting on Verisurf metrology software to drive all these devices in a powerful yet simple way. “Verisurf metrology software is doing its part in maintaining precision in the shop and on the launch pad. We use it for everything from tooling fabrication to pre-launch preparation,” Mosse states.
Falcon 9 lifted off from Cape Canaveral AFS launch pad SLC-40 at 10:43am EST on December 8, 2010. At 10:46am, the first stage separated. At 10:52am, Dragon entered low-Earth orbit. At 2:00pm, Dragon splashed down. At every point in this mission, the launch vehicle and spacecraft hit their marks precisely. According to the company, Falcon 9 delivered Dragon to orbit with near bull’s-eye insertion, and Dragon then splashed down in the center of its targeted landing zone.
The accuracy of the flight path requires careful alignment of Falcon 9’s sections and precise launch vector positioning. The SpaceX crew used its PCMM metrology systems, which includes laser trackers and Verisurf software.
|TOP: SpaceX engineers test one of the Merlin engines that powers the Falcon 9 rocket in McGregor, TX.
BOTTOM: The Falcon 9 Flight 2 second-stage tank structure and interstage in a structural test stand.
Falcon 9 is 180ft tall and is 12ft in diameter. Nine of SpaceX’s Merlin engines power the first stage; the second stage uses one. Final assembly of this amazing piece of engineering is completed at the launch site. To position and align Falcon 9’s components, SpaceX used laser trackers and Verisurf’s BUILD application, which is a virtual gage. The trackers fed measurement data directly to Verisurf, which reported, in real time, the accuracy of each section relative to the CAD model used in design and manufacturing.
After assembly, the SpaceX crew raised Falcon 9 into its vertical launch position. To follow its intended flight path, launch specifications allowed the vector of the vehicle to deviate by only 0.02° from the 180ft length. Mosse says that they again turned to the PCMMs and Verisurf Software to confirm a ready-to-launch status. “The specs allowed the nose to be off of vertical by 6". Verisurf reported that we had only a 0.01" deviation East to West and 0.03" from North to South,” he says. “And from the ground up, all sections were at their nominal positions.”
Mosse notes that this alignment accuracy was possible because of the controls used in manufacturing and assembly operations at the company’s Hawthorne, CA, facility.
“We have a set of five fixtures that we use to position rocket components and drill a pattern of 144 holes. These holes dictate the alignment of Falcon 9’s sections,” Mosse says. As he did in pre-flight preparation, Mosse used Verisurf to place the fixtures before committing to the drilling operations.
“With Verisurf, we are looking directly at the CAD model and the measurement results,” Mosse stated. “We see the measurements reflected against the 3D model. This makes the process faster and reduces mistakes.”
He notes that before Verisurf, his team had to interpret page-after-page of 2D drawing dimensions. “We had to rely on people’s ability to visualize 3D measurements from 2D drawings which result in interpretation problems,” Mosse says.
Before assembly, Mosse used his Verisurf solution to measure parts and tooling during fabrication and manufacturing. For example, SpaceX will drive both laser trackers and articulating arms with Verisurf when measuring composite tooling or weld fixtures.
“We inspect these items to the CAD data. In many cases, we will inspect to profile tolerances only.” Mosse says, “We are not drawing free, yet, but like the rest of the aerospace industry we are striving to implement model based definition to achieve its many benefits.”
For SpaceX the most important benefit is time. Model based definitions (MBD) with profile tolerances eliminate the time to document an engineering drawing; reduce the time to create inspection plans and reports; and accelerate identification and resolution of manufacturing issues. With an aggressive schedule and a 25-launch manifest over the next four years, including 12 space station deliveries, every moment counts.
SpaceX’s philosophy for its launch into space is simplicity that yields reliability and savings. To achieve this, it counts on Verisurf. “With Verisurf, we have very quick assurance that we are in the proper 3D space,” concludes Mosse. This, in turn, puts Falcon 9’s launch and Dragon’s orbit in their proper position in space.
|1. One of the new Merlin 1D engines that will power the Falcon 9 rocket on future missions is test fired at SpaceX's Rocket Development Facility. 2. SpaceX's Falcon 9 rocket with a Dragon spacecraft rests horizontally in the company's hangar in Cape Canaveral, FL. 3. SpaceX CEO and Chief Designer Elon Musk watches Dragon's progress inside of SpaceX Mission Control in Hawthorne, CA. 4. Artist Rendering of Dragon, with Solar Panels Extending, in Orbit. 5. Engineers work on a Dragon spacecraft at SpaceX Headquarters, a 550,000ft² facility in Hawthorne, CA. 6. The COTS UHF Communications Unit system, shown here prior to delivery to NASA, arrived via the space shuttle to the ISS. The system was installed prior to the approach and berthing on the final COTS mission and will see regular use in support of SpaceX's continuing CRS cargo resupply missions.
Technologies Corp. (SpaceX)