SpaceX aims to bring both stages safely back to the ground after each use
Last week, the U.S. space company, Space Exploration Technologies (SpaceX), successfully launched its Falcon 9 rocket with an unmanned capsule carrying cargo for the International Space Station. The mission also took a step towards making the rocket reusable, with its spent first stage making a controlled descent into the Atlantic Ocean.
Much of the human conquest of space has been achieved with ‘expendable launch vehicles,’ rockets that are used just once. Such one-time use has made space travel exorbitantly expensive. Although it was hoped that reuse of the Space Shuttle would lower launch costs, this complex flying machine ended up being more expensive than expendable rockets.
SpaceX, a company established by Internet entrepreneur Elon Musk, is trying a different path for making its rockets capable of undertaking multiple launches.
“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred,” Mr. Musk, the company's CEO and Chief Designer, is quoted as saying in a document about reusability published earlier this year on the SpaceX web site (www.spacex.com).
The Falcon 9 currently carries a price tag of about $54 million (nearly Rs.330 crore), of which the cost of propellants account for just 0.4 per cent. “The majority of the launch cost comes from building the rocket, which flies only once. Compare that to a commercial airliner. Each new plane costs about the same as Falcon 9, but can fly multiple times per day, and conduct tens of thousands of flights over its lifetime,” the document noted.
The Falcon 9 is a two-stage rocket. SpaceX would like to bring both stages safely back to the ground after each use. But even returning the first stage is no easy task. The rocket is at a height of about 80 kilometres and travelling at 10 times the speed of sound when the first stage engines shut down and the stage itself separates from the upper stage. The first stage must then be slowed and brought down in a carefully controlled descent.
SpaceX carried out some preliminary testing for such descent using the ‘Grasshopper,’ a Falcon 9 first stage with just one liquid-propellant engine (instead of the usual nine) and equipped with four landing legs. In a series of test flights that began in September 2012, the Grasshopper lifted off from a launch pad, rose to a certain height and then landed back on the pad. In October last year, the rocket went to a height of 744 metres before returning to the ground.
Earlier this month, the company tested the Falcon 9 Reusable (F9R), a first stage with the full complement of nine engines and landing legs, which rose to a height of about 250 metres before returning to the pad.
Last September, when the Falcon 9 took a satellite into orbit, an attempt was made to manoeuvre the first stage after its separation so that it slowed and descended vertically. However, the stage started spinning and its engines shut down prematurely.
A second attempt was made when the Falcon 9 was launched last week, carrying a Dragon cargo capsule. This time, the manoeuvre appears to have been successful.
“Data upload from tracking plane shows landing in Atlantic was good!,” exulted Mr. Musk in a series of tweets. “Flight computers continued transmitting for eight seconds after reaching the water. Stopped when booster went horizontal.”
High seas and bad weather had hampered efforts to retrieve the stage, said Emily Shanklin, the company spokesperson, in an email.
The Falcon 9 first stage had been equipped with four legs intended for a future touchdown on land. The legs, folded against the sides of the stage at liftoff, would have deployed before it splashed down in the ocean. More ocean landings are likely before the SpaceX attempts to bring the booster down on land.
But, if a stage is brought back in this fashion, some of the propellant it carries must be set apart for manoeuvres leading to touchdown. That will reduce amount of payload the rocket can take.
The payload that a reusable version carried would be 40 per cent lower than an expendable one, Mr. Musk indicated in a 2012 interview with Popular Mechanics. But even with that penalty, reuse would greatly reduce drop launch costs, he argued.