New Mission Concepts for SLS With Use of Large Upper Stage

Boeing recently released a set of proposals for new missions beyond low-Earth orbit for NASA’s Space Launch System, or SLS, utilising a newly designed Upper Stage.

The SLS is NASA’s next generation heavy-lift launch vehicle (HLV), which is on schedule to make its inaugural unmanned test flight in 2017. It will be used for launching the Orion Multi-Purpose Crew Vehicle, or MPCV, the space agency’s next manned spacecraft currently under construction, to deep-space destinations such as the Moon and Mars—a capability that had been lost with the cancellation of the Apollo lunar missions more than 40 years ago.

Although the first two launches of the SLS in 2017 and 2021 respectively are designed to be test flights of the initial Block I configuration capable of delivering 70 metric tons to low-Earth orbit (LEO), NASA is designing the heavy launch system to be evolvable, with the final Block II configuration having a payload capacity of 130 metric tons to LEO—rivaling the capability of the Saturn V rocket that sent humans to the Moon during the 1960s and ’70s.

As reported at the NASA Spaceflight.com website, Boeing, which is the prime contractor for designing and building the SLS’s core and upper stages, recently presented its proposal for a new Large Upper Stage, or LUS, for use on the SLS, which would enable new missions to low-Earth orbit and beyond.

The currently designed upper stage for the Block I version of SLS is an Interim Cryogenic Propulsion Stage (ICPS), also known as the Delta Cryogenic Second Stage, or DCSS. This is the same upper stage used on the Delta IV rocket, and it employs a single RL-10B2 engine developed by Pratt & Whitney. Although the ICPS would boost a 70-metric-ton payload to LEO in the SLS Block I version, Boeing’s proposal for the LUS would significantly advance this capability to more than 90 metric tons, allowing for even more ambitious deep-space missions. “A new 8.4m Large Upper Stage (LUS), as a follow on to the interim Cryogenic Propulsion Stage (ICPS), can provide significant increases in SLS payload injection capability,” notes the company in its presentation.

“Someone reminded me that, up until the last two modules were put up on the ISS (via Shuttle), Skylab had more crew volume,” says Jim Crocker, Vice President and General Manager, Civil Space, Lockheed Martin Space Systems Co. “Skylab was done with one Saturn V. Sometimes it requires re-thinking of what you’re doing.”

These new mission concepts studied by Boeing fall into four main categories: LEO destinations, cislunar and lunar missions, Mars and Outer Solar System destinations.

One of the payloads that could take advantage of the SLS’s LEO payload capability, according to the Boeing study, is Bigelow Aerospace’s proposed BA 2100 inflatable habitat. Bigelow Aerospace is best known for its innovative and ambitious work on designing and launching inflatable modules in orbit, based on NASA’s TransHab technology. The private company has already launched two experimental modules in low-Earth orbit, Genesis I and II in 2006 and 2007 respectively. It is already planning to send a Bigelow Expandable Activity Module, or BEAM, on the International Space Station in 2015 and plans to develop the first privately built space station called Bigelow Commercial Space Station, constructed from several BA 330 modules that are currently under development.

Yet the company revealed even more ambitious plans in the 2010 International Symposium for Private and Commercial Spaceflight held in Las Cruces, N.M., with the unveiling of the BA 2100, or Olympus module concept. As the number on its name implies, BA 2100 would feature a living area of 2,100 cubic meters of volume, completely dwarfing the smaller BA 330. This enormous habitat would have a calculated mass of 70 to 100 metric tons, making the SLS the only heavy-lift vehicle capable of placing it into orbit. That fact was acknowledged by Bigelow Aerospace Vice President Jay Ingham as well. “If a super-heavy-lift launch vehicle ever did exist, probably in the range of around 100 metric tons, would require an 8-meter fairing to launch the BA-2100,” Ingham discussed during the Symposium.

“SLS allows delivery of the BA-2100 via direct insertion to a low earth orbit and is the only launch vehicle capable of delivering a payload this large to LEO,” notes Boeing in its LUS concept presentation. Besides being used as a space hotel complex or space science research laboratory in low-Earth orbit, the BA 2100 could also be used as a large self-sufficient crew habitat for long interplanetary missions to Mars or anywhere else in the Solar System.

The main purpose of the SLS is to enable beyond-Earth orbit human space exploration. In 2011 Boeing proposed a design for a cislunar Exploration Gateway Platform, located in the L1 or L2 Lagrangian points of the Earth-Moon system. This mission concept envisioned the use of existing left-over hardware from the ISS program for the construction of a cislunar manned outpost that would enable regular access to cislunar space and the lunar surface itself. Many within the space agency view this concept as the next logical step beyond low-Earth orbit for human exploration, serving as a testing ground for long-duration missions prior to a human trip to Mars. “Building a translunar outpost is an important first step in retrieving an asteroid, returning to the moon or venturing to Mars. Using the SLS/LUS would allow the Exploration Platform to be constructed and crewed in only two launches, as opposed to the four missions required using SLS/ICPS (interim Cryogenic Propulsion Stage), thus saving cost and significantly shortening the time required to start accruing the benefits of a crewed Exploration Platform in translunar space,” notes the new Boeing study.

Besides human space exploration, the LUS could greatly advance robotic exploration as well, with its ability to directly send large interplanetary spacecraft to their destinations to the outer Solar System, mitigating the need for multiple gravity-assist manuevers that greatly prolong the mission duration to many years or decades.

The Interim Cryogenic Propulsion Stage currently designed for the SLS Block I version uses a 5m payload fairing that is capable of sending approximately 3 metric tons of payload to Jupiter, 1.8 tons to Saturn, and just 0.13 tons to Uranus. The proposed LUS upper stage, featuring an 8.4m payload fairing, would be capable of sending three to four times more massive payloads to these destinations. Depending on the LUS variant being used (having a single, dual, or 4-engine configuration), the new upper stage could directly send a payload of approximately 8.5 metric tons to Jupiter, 6 tons to Saturn, and 2 tons to Uranus. This payload capability would enable new and exciting missions to Europa, Titan, Enceladus, and Uranus that just aren’t possible with existing launch vehicles today. “The SLS provides a critical heavy-lift launch capability enabling diverse deep space missions,” states the Boeing report. “The added payload to destination that can be provided by a new Large Upper Stage, would be an enhancement for future science, astronomy, and Human spaceflight missions.”

The new SLS/LUS lift capability would enable a Europa orbiter or lander to reach the Jovian moon in approximately three years after launch, and a similar mission could reach Titan in four. “Imagine the science return with SLS, where we can get there within a few years, and how that can accelerate scientific discovery,” says Crocker. “We don’t know what we’re going to find in science, but we do know that if you find it sooner, you get a much higher science return for your investment.”

A dedicated Uranus orbiter has also been the longing of the planetary science community. A Uranus orbiter is listed as the third highest priority Flagship mission after Mars and Europa in the 2013-2022 U.S. Planetary Science Decadal Survey. Dr. Mark Hofstadter, a planetary scientist at NASA’s Jet Propulsion Laboratory, stressed that point during a presentation at the January 2013 meeting of the Outer Planets Assessment Group, in Atlanta, Ga. “The Group is concerned that no action was taken on its findings last year regarding a Uranus mission study,” notes Hofstadter in the presentation, “and again urges that NASA initiate such a study responsive to Decadal Survey science goals for the ice giants.”

Planetary exploration wouldn’t be the only field in space science that could benefit from the use of the SLS/LUS concept. The new upper stage would also be able to lift the proposed Advanced Technology Large Aperture Space Telescope, or ATLAST, that is under consideration by NASA. ATLAST is a next generation space telescope, featuring a monolithic 8m primary mirror, four times bigger than the one on the Hubble Space Telescope. An alternative design also calls for a 16m segmented primary mirror, which could also fit inside the bigger LUS payload fairing. According to the Space Telescope Science Institute’s project website, “ATLAST will have an angular resolution that is 5 – 10 times better than the James Webb Space Telescope and a sensitivity limit that is up to 2000 times better than the Hubble Space Telescope … It is envisioned as a flagship mission of the 2025 – 2035 period, designed to address one of the most compelling questions of our time. Is there life else where in our Galaxy? It will accomplish this by detecting ‘biosignatures’ (such as molecular oxygen, ozone, water, and methane) in the spectra of terrestrial exoplanets.”

Maybe the most important aspect of the LUS design is its cost-saving approach to the SLS’s development. If chosen by NASA, the LUS would be constructed at the agency’s Vertical Weld Center at Michoud Assembly Facility in New Orleans, where Boeing already will be constructing the SLS’s Core Stage, without the need for extra welding or other machining equipment, thus helping to further bring the SLS’s development costs down.

Video Credit: NASA/Marshall Space Flight Center

Since its inception in 2011, the SLS has been heavily criticised by many within the space community for its perceived lack of missions. During her recent appearance on a radio talk show, former NASA Deputy Administrator Lori Garver heavily criticised SLS as being a rocket to nowhere.“Where is it going to go?” she asked during the show. Although Boeing’s LUS upper stage concept hasn’t been yet approved by NASA, it nevertheless largely invalidates Garver’s criticism by showcasing that the space agency’s newest heavy-lift vehicle could be used for all shorts of exciting and ambitious human and robotic missions throughout the Solar System.

The article is based in part on the opinions of the author that do not necessarily represent those of AmericaSpace.

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