Tuesday morning (May 22nd, 2012) at 3:44 AM (EDT), SpaceX will (again) attempt to take one large step forward on the path to the commercialization of space. The mission is an ambitious flight of the Falcon 9 rocket and Dragon capsule to the International Space Station (ISS), and is packed from countdown to splashdown with high-pressure performances.
5/22 Update: Congratulations SpaceX on another successful Falcon 9 launch! The Dragon is in orbit and all systems are nominal, with successful solar panel deployment and absolute GPS lock obtained.
Watching the Falcon 9 light up the sky on its way to its third completely successful launch, I had a strong feeling that I was watching America’s next astronaut launch vehicle… Great job, and good luck with the rest of the Dragon test mission!
5/19 Update: Approximately two seconds after ignition of the Falcon 9 first stage at 4:55 AM (EDT) on 5/19/2012, the rocket automatically aborted due to a high combustion chamber reading in Merlin engine #5. Because of the nearly instantaneous launch window, there was not enough time to recycle the countdown, and the flight was scrubbed until 5/22 at 3:44 AM (EDT). The hold-before-launch design is one of the reliability features of the Falcon 9, ensuring that the rocket doesn’t leave the ground unless all nine engines are operating nominally three seconds after ignition, but the drawback is more aborts. Good luck SpaceX with your next attempt on Tuesday!
To watch the mission, visit one of the following sites, or check out the #DragonLaunch Twitter hashtag.
Below is a rundown of the most challenging aspects of each phase of the flight.
The Falcon 9 booster has launched twice before but has yet to hit T-0 without delays, Gwynne Shotwell, SpaceX President, revealed at the pre-launch briefing on 5/18. The launch window to reach ISS is mere seconds long, so any glitch in the countdown after the last scheduled hold means that the rocket must wait until the next launch window, on May 22nd.
The countdown sequence is highly automated and SpaceX has performed remarkably quick turnarounds from technical glitches in prior countdowns, but the rocket is still young and the window is unforgivingly short. As a result, Ms. Shotwell estimated that there was a 50% chance of making it to T-0 on time 5/19.
The nine “Merlin” engines on the Falcon 9 first stage must ignite and evenly power the rocket through Max Q (the point of maximum aerodynamic stress on the rocket) and then to main engine cutoff (MECO) three minutes into the flight. Five seconds later the second stage is pushed away from the first stage. It coasts for seven seconds before igniting its engine, a vacuum-optimized Merlin. After a six and a half minute burn, the second stage releases the Dragon spacecraft into a precisely planned orbit, 310 km x 340 km.
The most common problems in this phase of flight are engine failures, staging problems, and inserting the payload into the wrong orbit. SpaceX’s smaller Falcon 1 rocket experienced an engine failure on it first test flight, and on its third test flight the first stage “rear-ended” the second stage.
But SpaceX has learned from its failures. To prevent another loss because of an engine failure, it now uses stainless steel nuts instead of the aluminum nuts that corroded in the salty ocean air and led to the fuel leak that ended the Falcon 1′s first test flight. It also designed the Falcon 9 to tolerate one or more engine failures during flight. To address its staging problem, SpaceX adjusted the timing of the staging separation. As a result of these (and other improvements), the next two Falcon 1 launches and both launches of the Falcon 9 have gone flawlessly, with accurate orbital insertions each time.
On orbit checkout
Once in orbit, the Dragon will embark on a series of tasks, most of which SpaceX has never attempted outside of a terrestrial test chamber. During the first ten hours in orbit, the spacecraft must deploy and test its solar arrays and proximity operations sensors. Then the Dragon must demonstrate its ability to abort from a simulated rendezvous with the space station. If the craft cannot complete any one of these tasks, the mission is over, the Dragon returns to Earth (if it can), and the remaining objectives are postponed to the next flight.
After the Dragon demonstrates that it’s operating properly, it performs a series of firings of its “Draco” orbital maneuvering rockets to carry it to precisely 2.5 kilometers from the station, arriving on the second day of the mission. At this point, NASA and SpaceX go through a series of communication and control tests using the COTS UHF Communications Unit – CUCU (yes it’s pronounced “cuckoo”). If the tests proceed according to plan, the capsule will fly under the station on day three, then loop over the station and drift behind it – a delicate demonstration of orbital dynamics in close proximity to the roughly $100 billion facility.
This is perhaps the most likely part of the mission to experience issues. Realizing this, SpaceX set up the mission to maximize the amount of propellant available, enabling them to make multiple attempts, should something go wrong.
On day four, the spacecraft incrementally steps towards the space station, approaching to 1.2 km, then 250 meters. At 220 meters, the ISS crew will command the Dragon to retreat to 250 meters and then re-approach in a test of its LIDAR and thermal imaging systems.
Assuming that these precise maneuvers can be performed to the satisfaction of SpaceX and NASA, SpaceX will command the Dragon to approach to 30 meters for one last hold. Flying in formation at over 17,000 mph, SpaceX will then command the Dragon to inch its way to its capture point, a mere 10 meters from the station. At this point, astronaut Don Pettit will use the station’s 58′ long robotic arm to grapple the capsule and gingerly berth it to the space station.
As with the rendezvous, the berthing operation is an extremely complex and difficult task. A Russian cargo ship rammed the Mir space station in 1997 during a similar operation (causing part of the station to depressurize), and SpaceX will likely be thrilled if they can succeed with a fraction of the steps while avoiding a similar fate, even if they must postpone the berthing until the next flight.
After the capsule is berthed and the hatch is opened the following day, the ISS crew will spend about 25 hours over a two week period unloading the one thousand pounds of cargo the Dragon is carrying – mostly food and clothing, but also student experiments on microbial growth and water purification in microgravity, among other things. They will also load almost 1500 pounds of experiments and hardware for return to Earth, the first time a significant amount of payload has been returned from the space station since the retirement of the Space Shuttle.
Following the cargo transfer, the ISS crew will grapple the Dragon again, removing it from the station and releasing it where they found it 5.7 million miles ago – 10 meters away from the station. The Dragon will then fire its Draco rockets again to carry it on a safe path away from the station.
Four hours later, the Dragon will perform a seven-minute deorbit burn and then reenter the atmosphere at over 17,000 mph.
Reentry is another risky part of the flight, and this will be the first time it’s had to perform the critical tasks of jettisoning its unpressurized “trunk” and closing its sensor bay hatch. The failure of either task could lead to a so-called “ballistic” (uncontrolled) reentry like the Soyuz TMA-11 mission, with the capsule likely landing hundreds of miles off target, or a breach of the heat shield like the Space Shuttle Columbia’s last mission, with the capsule possibly breaking up on reentry. However, SpaceX has tested its trunk separation and hatch mechanisms on the ground, and its SpaceX manufactured Phenolic Impregnated Carbon Ablator (PICA-X) heatshield and SpaceX Proprietary Ablative Material (SPAM) backshell performed better than expected on the first Dragon mission, so this dangerous phase of flight could also be considered one of the easier parts of the mission.
During reentry, the Dragon will repeatedly fire its Draco thrusters to steer the craft into a precise landing zone 250 miles off the coast of southern California. The Dragon deploys two drogue chutes at 45,000 feet followed by its three main parachutes at 10,000 feet. Although parachute deployments are another common problem (there were reportedly eleven partial failures of the Space Shuttle solid rocket boosters’ parachutes), the Dragon is designed to safely land a human crew with only two functioning parachutes, and all three parachutes performed perfectly on its first mission, with the Dragon landing within a mile of the center of its landing target.
Conclusion – failure is an option
This is an uncrewed test flight and failure is an option. SpaceX plans to fly the Falcon 9 probably twenty more times and the Dragon around ten more times before flying humans. There will be time to apply the lessons learned from this mission regardless of whether it’s a complete success, a partial success, or as rocket scientists say, a rapid unscheduled disassembly. Regardless of the outcome, it should be fun to watch.