What has the Indian Space Research Organisation (ISRO) got in common with legendary aerospace designer Burt Rutan, Microsoft co-founder Paul Allen, and billionaire entrepreneurs Jeff Bezos and Elon Musk? They are all in the hunt for the Holy Grail of rocketry: a space launch system that can loft satellites into low earth orbit (LEO), re-enter Earth’s atmosphere and glide back like an aircraft to either land on a runway or splash down in the sea to be retrieved. Its short turnaround ensures that after refuelling, it can be used quickly for another launch. These reusable launch vehicles (RLVs) could be used many times, cutting mission costs dramatically and making access to space much more affordable. Advanced RLVs that ride straight into orbit (single-stage-to-orbit, or SSTOs) could carry their own fuel, unlike conventional launchers that typically piggyback on expendable rockets.
More than 50 years after the first space shots of the 1960s, reaching LEO remains a costly affair, with launch prices topping the $12,000 per kilogram mark. Although agencies like ISRO take pride in being able to offer low-cost satellite launches, the fact remains that even the most advanced rockets of today can hardly lift two percent of their launch weight into orbit. This ratio hasn’t really changed in more than half a century of spaceflight! Even if cheaper air-breathing engines were used to penetrate Earth’s atmosphere, it’d still cost a lot of money to loft a kilo into orbit. The chief reason for this has a lot to do with contemporary launch systems, which are all of the ‘use-and-throw’ kind. Once launched, a booster rocket cannot be re-used for another launch. NASA’s iconic Space Shuttles (the erstwhile Soviet Union’s winged spaceplane, Buran, made just one experimental flight before being mothballed) are the only RLVs to have flown successfully. In fact, the Shuttle represented a semi-reusable launch system where the orbiter could re-enter and land and only its solid rocket boosters were recovered using parachutes. The Shuttle fleet, however, was grounded after flying 30-odd years of ferrying crews and supplies to and from the International Space Station and undertaking repair missions to the Hubble Space Telescope
With advanced avatars of crewed spacecraft like the Orion on the horizon, space agencies have turned to private enterprise for help in developing reliable RLV systems that could achieve economies of scale. Which is easier said, considering no space agency would dare to economise by using less expensive launchers with their attendant risks. In rocketry, after all, one just cannot be too careful—a nut tightened carelessly here, or a rubber bush sitting loosely there is enough to send hundreds of tons of metal and fuel up in a terrible fireball. NASA, whose Shuttles are lodestones for developing RLVs, learned this the hard way in January 1986 when the Challenger blew up two minutes into its launch. The shuttle designers of the time had in mind an RLV system that would form—along with an orbiting space station and a moon base—a staging post for astronauts bound for Mars and elsewhere. But in their eagerness to show that space flight could be as routine as air travel, NASA managers cut corners by forcing engineers to stick to tight launch schedules. And on that grey January morning in 1986, the Challenger exploded, killing the seven astronauts on board. Investigators later found that private contractors had supplied an erosion-prone, if less expensive, ‘O’ ring (a rubber seal used in fuel tanks of the shuttles’ booster rockets). NASA managers made it a double jeopardy by failing to install a metal latch on the booster rocket to lock the leaky ‘O’ ring seal tightly.