On Dec. 11, 2017, President Donald Trump reignited the nation’s human space exploration program by signing Space Policy Directive 1. The executive order calls for NASA to work with commercial and international partners to create a sustainable space exploration program that will enable human travel to the moon and eventually to Mars. In effect, it creates a roadmap for humanity’s next giant leap.
Deliberate, Sustained Exploration
A core element of this new initiative, which NASA calls its Exploration Campaign, will be a Lunar Orbital Platform — Gateway, or lunar gateway for short. The Gateway will serve as a combination “base camp” for exploratory excursions down to the lunar surface, a laboratory to conduct experiments about the effects of prolonged space travel on humans, and a platform for assembling payloads and transport vehicles that will carry astronauts on to Mars.
The Exploration Campaign, however, is far more than a retread of NASA’s Apollo program.
“During Apollo, we learned how to fly to the Moon, but we were limited logistically to relatively brief stays and short periods of exploration,” explained Charlie Precourt, a former NASA astronaut who serves as vice president and general manager for the Propulsion Systems Division of Northrop Grumman Innovation Systems. “With Exploration, we’re going to stay on the Moon longer, explore more extensively, and conduct more thorough research, not unlike scientists who spend time at McMurdo Station in Antarctica. The Moon can become a powerful stepping stone to Mars.”
NASA’s campaign will help motivate advances in space technology, inspire a new generation of students to pursue careers in science, technology, engineering and mathematics fields, and position the nation to take advantage of financial opportunities that could emerge from exploration, Precourt added.
Multi-Purpose Launch Vehicle
Central to the Exploration Campaign will be NASA’s new Space Launch System (SLS), a heavy-lift launch vehicle capable of carrying humans and large cargo to the moon in a single mission. According to NASA documents, “SLS offers more payload mass, volume capability and energy to speed missions through space than any current launch vehicle.” NASA describes the vehicle as “flexible and evolvable,” and claims that it may be also be used to support robotic scientific missions to the moon, Mars, Saturn and Jupiter.
The SLS is a hybrid system based on space shuttle-derived components and heavy-lift rockets developed for Constellation, NASA’s previous campaign to return humans to the moon. The rocket comprises a core stage powered by four shuttle-legacy RS-25 liquid propellant engines, two five-segment, strap-on solid rocket boosters (SRBs), and initially, a cryogenic upper stage derived from the Delta IV rocket program. SLS will use a version of the Constellation-era Orion crew vehicle to carry humans to the lunar gateway.
Legacy Team, Innovative Approach
Northrop Grumman, which produced the SRBs for NASA’s shuttle program, is “remodeling” those original four-segment SRBs for use on SLS. “By going from four segments to five, we’re giving NASA 25 percent more propellant and a little more thrust delivered over a longer period of time,” said Mike Fuller, a senior business development manager. “The detachable SRBs provide a much more efficient way to lift the SLS off the Earth’s surface to its initial orbit.”
NASA opted to reduce costs by going with an expendable version of the SRBs instead of recovering and reusing them for every mission, he added.
Over time, NASA plans to evolve the SLS to meet increasingly complex human and cargo carrying requirements. First flight of the rocket, which will launch an uncrewed version of Orion around the moon, is expected in 2020. That initial flight will be used to test all aspects of the planned flight environment. The first crewed mission of the SLS is expected in 2022. Future versions of the SLS will feature a new, more powerful Exploration Upper Stage and be capable of carrying payloads of up to 45 metric tons (99,000 lbs.) to the moon.
Gateway to Mars
Ongoing travel to the moon and beyond will require development and deployment of the lunar gateway. According to NASA, this lunar-orbiting spaceship will serve as a temporary home and office for astronauts for up to three months at a time. It will include a power and propulsion element (PPE), a habitat module and logistics module capable of carrying pressurized and unpressurized cargo. The PPE will be used to maintain the Gateway’s position in orbit, move it between orbits and provide power and communications for the spaceship. NASA plans to use the SLS to ferry major sections of the lunar gateway to orbit and assemble it in space.
One of the more interesting aspects of the Gateway, explains Fuller, is its orbit. “Unlike the Apollo spacecraft, which orbited the moon at an altitude of about 60 miles, the lunar gateway will be placed in a highly elliptical orbit ranging from about 1,000 miles at its closest (perigee) to tens of thousands of miles at its farthest (apogee),” he said. “The high altitude of the orbit guarantees that the Gateway will remain visible to ground stations on Earth at all times, which will allow uninterrupted communication with crewed, cargo and robotic science missions.”
Reaching for the Stars
There is much work yet to be done on NASA’s Exploration Campaign, but an exciting future of human space exploration beckons.
“We’ve learned through our experience with the International Space Station that humans can live for extended periods of time in low-Earth orbit,” said Precourt. “With this campaign, we’re ready to take on two more fundamental questions about the universe: is the human species truly sustainable off our planet … and are we alone? The day we uncover hard evidence to answer these questions will be a game changer for our civilization.”