A second-generation test vehicle called F9R Dev1 was built with extensible landing gear. The prototype was flown four times—with all landing attempts successful—in 2014 for low-altitude tests before being self-destructed for safety reasons on a fifth test flight due to a blocked engine sensor port. The orbital-flight version of the test vehicles–Falcon 9 and Falcon Heavy—includes a lightweight, deployable landing gear for the booster stage: a nested, telescoping piston on an A-frame. The total span of the four carbon fiber/aluminum extensible landing legs is approximately , and weigh less than ; the deployment system uses high-pressure Helium as the working fluid. The first test of the extensible landing gear was successfully accomplished in April 2014 on a Falcon 9 returning from an orbital launch and was the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital booster. After a single successful booster recovery in 2015, and several in 2016, the recovery of SpaceX booster stages became routine by 2017. Landing legs had become an ordinary operational part of orbital spaceflight launch vehicles. The newest launch vehicle under development at SpaceX—the Starship—is expected to have landing legs on its first stage called Super Heavy like Falcon 9 but also has three landing legs on its reusable second stage, a first for launch vehicle second stages. The first prototype of Starship—"Starhopper", built in early 2019—had three fixed landing legs with replaceable shock absorbers. In order to reduce mass of the flight vehicle and the payload penalty for a reusable design, the long-term plan is for vertical landing of the Super Heavy to land directly back at the launch site on a special ground equipment that is part of the launch mount, but initial testing of the large booster in 2020 is expected to occur with landing legs. Spacecraft designed to land safely on extraterrestrial bodies such as the Moon or Mars are known as either legged landers (for example the Apollo Lunar Module) or pod landers (for example Mars Pathfinder) depending on their landing gear. Pod landers are designed to land in any orientation after which they may bounce and roll before coming to rest at which time they have to be given the correct orientation to function. The whole vehicle is enclosed in crushable material or airbags for the impacts and may have opening petals to right it. Features for landing and movement on the surface were combined in the landing gear for the Mars Science Laboratory. For landing on low-gravity bodies landing gear may include hold-down thrusters, harpoon anchors and foot-pad screws, all of which were incorporated in the design of comet-lander Philae for redundancy.