After getting acclimated to the microgravity environment in low Earth orbit, the crew has a busy docket of research investigations, science experiments and educational outreach to occupy their time over the eight-day mission. The Ax-2 crew will join the seven members of the current Expedition 69 aboard the space station. Whitson has already spent more time in space than any other American astronaut (665 days), and with Ax-2 becomes the first woman to command a private spaceflight. AlQarni and Barnawi are the first Saudis to visit the space station, and Barnawi is the first woman from the kingdom ever to reach space. Businessman and paying customer John Shoffner serves as pilot, and Ali AlQarni and Rayyanah Barnawi, two members of Saudi Arabia’s inaugural astronaut class, are Ax-2 mission specialists. (Image credit: NASA TV)Īx-2 is commanded by Whitson, a former NASA astronaut who now works as the director of human spaceflight for Axiom Space, the Houston-based company operating the mission. The Station safety rules dictate a rather cautious approach to rendezvous.Astronauts welcome four new crewmembers from the private Ax-2 mission inside space station after SpaceX's Crew Dragon Freedom docked on May 22, 2023. Ensuring that a vehicle that has sustained two failures will not collide mandates a gradual phasing (which takes time) and a very, very slow final approach (which takes a lot of time). A manned vehicle that goes reeling off into space because it suffered two failures is not a manageable loss.ĭealing with those failures takes time. The difference between the two: An unmanned SpaceX that goes reeling off into space because it suffered two failures is a loss, but a manageable loss, so long as it doesn't crash into the Station. In fact, it has to be two failure safe for unmanned vehicles coming to the Station, and two failure tolerant for manned vehicles. The thruster remains off, just as expected, up until that "thruster on" command. That failed valve doesn't manifest itself as an error until the next time the control system commands the thruster on. When the thruster is commanded off and a valve breaks so it stays off, permanently: That's a fault. A thruster might provide 97% of nominal thrust one time, 102% the next. Errors are what confound the vehicle when things don't behave according to spec. Uncertainties are what confound the vehicle when everything is behaving according to spec. There's a big difference between uncertainties and errors. An easy solution to dealing with these uncertainties: Take your time. That launch uncertainty was one of the key reasons TMA-12M had to use the standard slow approach rather than the planned fast track approach. Having a 20 km uncertainty in altitude an even bigger uncertainty in along-track is typical. The vehicle might well be placed in orbit, but not the planned one. There are lots of uncertainties in launching a vehicle into space. An easy solution for dealing with reaching the target: Take your time. A vehicle could make the Hohmann transfer from the insertion orbit to the Station orbit immediately after launch, but that means zero tolerance for uncertainties, errors, and safety. The target vehicle has to reach a specific point on the Space Station's orbit at a specific time to dock or berth with it. That's not nearly good enough when it comes to rendezvous. National Aeronautics and Space Administration, International Space Station, SpaceX 6K views, 208 likes, 35 loves, 0 comments, 74 shares, Facebook Watch Videos from Reuters: LIVE: SpaceX Crew 6. Just do a Hohmann transfer and be done with it. I'll deal with these in reverse order.Īchieving the Space Station's orbit is easy. Why is docking such a slow process? The answer is safety, errors (faults), uncertainties, and reaching the target (phasing). Approach and rendezvous is typically measured in days, not hours. The Soyuz expedited docking is rather bold. The last 400 feet were incredibly slow, taking about 40 minutes. Relative velocities became slower as the Shuttle closed in on the Station. With 3 hours to go, the Shuttle was about 50,000 feet (15 km) behind. With 4½ hours to go, the Shuttle was 250,000 feet (76 km) behind the Space Station. The Space Shuttle rendezvous timeline took 6 hours from start to finish.
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