Lazy evaluationIn programming language theory, lazy evaluation, or call-by-need, is an evaluation strategy which delays the evaluation of an expression until its value is needed (non-strict evaluation) and which also avoids repeated evaluations (by the use of sharing). The benefits of lazy evaluation include: The ability to define control flow (structures) as abstractions instead of primitives. The ability to define potentially infinite data structures. This allows for more straightforward implementation of some algorithms.
Test automationIn software testing, test automation is the use of software separate from the software being tested to control the execution of tests and the comparison of actual outcomes with predicted outcomes. Test automation can automate some repetitive but necessary tasks in a formalized testing process already in place, or perform additional testing that would be difficult to do manually. Test automation is critical for continuous delivery and continuous testing.
Four-accelerationIn the theory of relativity, four-acceleration is a four-vector (vector in four-dimensional spacetime) that is analogous to classical acceleration (a three-dimensional vector, see three-acceleration in special relativity). Four-acceleration has applications in areas such as the annihilation of antiprotons, resonance of strange particles and radiation of an accelerated charge. In inertial coordinates in special relativity, four-acceleration is defined as the rate of change in four-velocity with respect to the particle's proper time along its worldline.
Falcon 9 first-stage landing testsThe Falcon 9 first-stage landing tests were a series of controlled-descent flight tests conducted by SpaceX between 2013 and 2016. Since 2017, the first stage of Falcon 9 missions has been routinely landed if the rocket performance allowed it, and if SpaceX chose to recover the stage. The program's objective was to reliably execute controlled re-entry, descent and landing (EDL) of the Falcon 9 first stage into Earth's atmosphere after the stage completes the boost phase of an orbital spaceflight.
Falcon 9 Full ThrustFalcon 9 Full Thrust (also known as Falcon 9 v1.2, with variants Block 1 to Block 5) is a partially reusable medium-lift launch vehicle, designed and manufactured by SpaceX. Designed in 2014–2015, Falcon 9 Full Thrust began launch operations in December 2015. As of , Falcon 9 Full Thrust had performed launches without any failures. Based on the Lewis point estimate of reliability, this rocket is the most reliable orbital launch vehicle currently in operation.
Falcon 9Falcon 9 is a partially reusable medium-lift launch vehicle that can carry cargo and crew into Earth orbit, designed, manufactured and launched by American aerospace company SpaceX. It can also be used as an expendable heavy-lift launch vehicle. The first Falcon 9 launch was in June 2010. The first Falcon 9 ISS commercial resupply mission to the ISS launched on 8 October 2012. In 2020 it became the first commercial rocket to ever launch humans to orbit and is currently the only such vehicle capable of doing so.
