It doesn’t take a rocket scientist to figure out that reusing hardware saves money, though rocket scientists are on the recycling mission too. SpaceX is getting on the reusability bandwagon first with its Dragon capsule (it’s designed to be reused, but no capsules have flown more than once) and now with its Falcon rocket stage. The goal is to create a rocket first-stage that can autonomously return to the launch site and land vertically on dry ground. From there, it can be refurbished and relaunched. And SpaceX is making its first steps, or hops, towards this goal with the Grasshopper.
The Grasshopper is a vertical takeoff and landing test vehicle (VTVL), a prototype vehicle for the autonomous landing rocket. Its body is a Falcon 9 first stage with four insect-like spindly little legs on the bottom – hence the name. It’s powered by one of SpaceX’s powerful Merlin 1D engine that burns kerosene and liquid oxygen to generate up to 147,000 pounds of thrust.
The glider designed to return Saturn 1’s first stage
The name Grasshopper is also fitting since the test vehicle isn’t exactly flying. It’s hopping. The first demonstration test two weeks ago (on Sept. 21) at SpaceX’s test facility in McGregor, Texas had the vehicle rise just six feet off the ground before landing gently on its legs. Still, it’s a step (hop) in the right direction. Having a reusable first rocket stage will complement the reusable Dragon capsule making the SpaceX system cheaper on the whole. It’s also a level of reusability reminiscent of NASA’s space shuttle, which means there might be some lessons to learn from the recently terminated program.
The space shuttle’s solid rocket boosters are the only rocket stages that have been successfully recovered after one launch and reused on another. These twin booster stages mounted on either side of the main fuel tank and provided more than 80 percent of the thrust that shot the space shuttle into orbit. Both separated and fell away once their fuel was exhausted (about two minutes after launch) and splashed down by parachutes in the Atlantic Ocean.
The empty casings were recovered and towed to a seaside disassembly facility area. They were taken apart by a team at the recovery site for a preliminary structural analysis to determine whether any anomalies had popped up during the flight and whether any specific repairs that need to be done. Then the pieces were loaded on rail cars and returned to contractor Thiokol’s facility in Utah where individual segments were refurbished. Each piece was tested before being shipped back to NASA’s launch site in Florida. It was a lengthy process that took a lot of workers at every stage, but it worked. The solid rocket booster casings were successfully reused on subsequent missions to cut overall program costs.
Nearly two decades before NASA turned the process of refurbishing the shuttle’s rocket boosters into a well-oiled machine, the agency tried to recover the Saturn rockets’ first stages for refurbishment and reuse. There were a few proposals bandied about in the 1960s. One called for the use of a paraglider wing. This triangular wing would lie flat against the rocket during launch. As the first stage separated and it fell away, a parachute would pull the wing out, and the booster would glide back to land. Another proposal came from Boeing and used basically the same system the shuttle boosters used: parachutes would bring the Saturn first stage to an ocean splashdown where it would be recovered and reused. For this latter method, cost savings were projected around 49 percent over the cost of building a new stage every time. Of course, cost estimates rarely predict the true cost, or in this case cost savings, in spaceflight.
Boeing pointed out in a mid-1960s study that the real value of refurbishing the Saturn first stage increased dramatically with the number of launches. This might be one of the reasons Saturn boosters were never recovered. There were technical problems with the paraglider recovery system, but there also weren’t too many planned launches. When NASA decided to reuse the solid rocket boosters on the shuttle, the agency was expecting to launch 50 missions each year. But after three decades, the shuttle only flew 143 missions instead of the 1,500 that were projected over the same time frame. What this did the to projected cost saving of refurbishing the boosters isn’t entirely clear.
But I’m sure the clever people at SpaceX have thought this through. It’s not exactly a secret that they plan to be around and launching rockets for a while. Not to mention they use the technology across the board – the falcon heavy is a Falcon 9 with two extra first stages strapped on the sides. Theoretically, the system that autonomously lands the Falcon 9 first stage can also land these Falcon 9 external stages. It might be the beginning of a really cost effective approach to spaceflight, or at least as cost effective as spaceflight can get for now.