A scale model of the SLS in a NASA wind tunnel. Image: NASA/ARC/Dominic Hart
There’s one basic truth behind every single mission that any nation has ever launched into space: Where you can go, and the weight of the spacecraft you'll use to get there, are dictated by how powerful your launch vehicle is.
NASA had a heavy lift launch vehicle in the 1960s in the Saturn V rocket, which powered the Apollo lunar missions. But the agency lost that capability when it discontinued the mammoth rocket in favour of the Space Shuttle. Now, a heavy lift rocket is back on the books with the Space Launch System, or SLS. While there’s plenty of skepticism surrounding the rocket’s development and proposed launch schedule, scientists say that we absolutely need this enormous rocket if we’re going to continue exploring the solar system.
The SLS is, by design, a fantastic rocket. Various configurations and will allow it to lift both manned and cargo missions to low Earth orbit and destinations well beyond our home planet.
The provisional launch schedule for the SLS is impressive, though subject to change since the rocket remains in its early test phase. The first two flights, which are still set for 2017 and 2019, will see an unmanned mission to the Moon and an unmanned mission to a near Earth asteroid, respectively.
The initial 70-metric-ton SLS configuration. Image: NASA
The third mission, currently slated for 2021, will be the first manned launch and will take a crew to the Moon, a shakedown cruise in support of a manned mission to an asteroid. The next few launches are split between manned and unmanned missions, some sending probes to distant planets and moons and other carrying out the asteroid capture mission. In the 2030s, NASA expects to have the capability and know-how to start launching the first SLS missions in support of a manned Mars landing.
But SLS isn’t out of the woods and onto the launch pad yet. It’s still threatened by a lack of vision. David Hitt, sitting on a panel alongside South West Research institute scientist Dan Durda, systems engineer Hoppy Price from NASA’s Jet Propulsion Laboratory, and retired NASA mechanical engineer Stan Barauska at last week’s Spacefest in Pasadena, unanimously agreed that solid plan for the rocket is what we need and what we don't have.
The lack of strong leadership and defined goals behind this project remain the two biggest issues. They, and other in attendance, also agreed that if we want to move forward in space, both on manned and unmanned missions, we need to commit to SLS.
When it comes to future manned missions, Hitt, senior writer and editor for the SLS program, pointed to the International Space Station. The ISS is a fantastic test bed, research station, and source of inspiration that we have built in orbit by assembling multiple modules.
Imagine, he said, how much more we could do if we could launch more modules both into orbit and further away, building other stations like the ISS. The SLS has the ability to launch modules from from Earth, theoretically providing us with deep space research stations and waypoints beyond Earth orbit.
The modular ISS could have been built more quickly with higher payload capabilities. Image: Wikipedia
(I spoke with Hitt before the news broke yesterday that Russia wants to stop the ISS mission after 2020, which adds a bit of a wrinkle to the SLS program. On one hand, a larger launch system could help the US supply and maintain the ISS without Russia's help—especially considering Russia is currently contracted to sell the US seats aboard its Soyuz spacecraft until 2017. On the other hand, Russia's play may give private companies, and especially SpaceX and its own heavy lifter, room for growth.)
There’s also the potential to launch a manned multi-planet flyby mission, Hitt said, which is reason enough to excitedly pursue the SLS program.
Flyby missions are how the pair of Voyager spacecraft toured the outer Solar System in the 1970s and 1980s, and how spacecraft get to distant planets and moons today. NASA also studied manned multi-planet flyby missions in the late 1960s as a possible followup to Apollo missions.
By replacing the Apollo lunar module with an environmental and habitat modules, NASA theoretically could have launched dual- and triple-planet flyby missions with only minor modifications to Apollo software. With missions lasting anywhere from 500 to 850 days, long transit times filled with scientific exploration of interplanetary space would have been punctuated by exciting close up studies of our neighboring planets.
1989 concept art of a manned mission to Mars by Les Bossinas of NASA Lewis Research Center. NASA now hopes to get to Mars by 2030, and if it does, it will require something like the SLS. Image: Wikipedia
But it’s not just the renewed possibility of manned multiplanet missions that has scientists excited about SLS, it’s the potential to launch missions without multiplanet flybys. Part of the value of multiplanet flyby missions is the ability to use gravity to slingshot a spacecraft farther, saving fuel. But such flight plans are indirect; using different configurations of the rocket—a smaller Block I or the larger Block II version—the transit time to distant planets and moons can be drastically lowered.
The Block I SLS could get a mission like Europa Clipper to its Jovian destination on a direct path in a little under three years; the same mission using a gravity assist path, by comparison, would take almost six and a half years. The larger Block II SLS could get a two ton payload to Saturn in three years, whereas the same payload launched on an Atlas V would need eight years to get the same spacecraft to the ringed planet. The Block II could send a one-and-a-half ton payload all the way to Uranus in just seven years, compared to the 13 year transit it would take with a Jupiter or Saturn gravity assist after launching on a smaller rocket.
And of course, as it relates to NASA’s ultimate goal (for the time being) of sending men to and eventually landing them on Mars, the SLS is vital. The spacecraft and all the fuel, provisions, and hardware Mars astronauts will need to land, explore, and come home is a heavy payload, and that payload will need a launch vehicle the size of SLS. (Whether we need an asteroid mission as a stepping stone on the way is still a matter scientists disagree on, but that’s another matter.)