Boeing discusses use of SLS for robust lunar program

by Chris Gebhardt

As the Space Launch System (SLS) rocket continues development for its debut mission in December 2017, the Boeing company has identified several exploration architectures that would be enabled by the superior capability of the Heavy Lift Launch Vehicle (HLV) – ranging from missions to the Moon, through to expeditions to Mars.

SLS architecture paves the way for human return to lunar operations:

Capitalizing on the express capability of the SLS launch system to provide space-based access to areas beyond Low Earth Orbit (LEO), Boeing has identified several exploration architectures that will provide a base for a set of space exploration missions between the 2020 and 2040 timeframe.

Specifically, Boeing points toward large mission parameters and vehicle characteristics that will enable humanity to achieve and realize a step-by-step approach toward the creation of reliable and cost-effective access to the lunar surface.

As stated by the presentation “Space Launch System capabilities for enabling crewed lunar and Mars exploration,” available to download on L2. “The Boeing company has identified several exploration architectures that are enabled by the new Space Launch System launch vehicle.

The SLS is a national asset with performance capabilities for enabling a promising set of space exploration missions.”

To begin full exploration, Boeing identified the most logical first place to visit as humanity begins to once again push outside of LEO and out into the other regions of the inner solar system.

That first destination is the Moon.

Building a base at the Earth-Moon Lagrangian points:

Instead of launching a mission directly to the Moon, as was the case with the Apollo missions, the Boeing presentation suggests using the Earth-Moon Lagrangian points (EML points) as regions to build in-space platforms – known as the previously reported Gateway – that can then be utilized as bases for lunar and non-lunar missions.

EML2 LocationPlacing any space-based work platform into any of the Earth-Moon Lagrangian points would provide a staging ground for not only lunar operations but would also allow for the departure of any spacecraft assembled at an EML point to any point in space via the use of “libration manifold technologies.”

This approach would significantly reduce the amount of propellant needed to push a spacecraft out of an EML point and onto course for a specific destination.

Moreover, EML point locations would provide an advantage to in-space spacecraft assembly as spacecraft assembled at EML points would not have to contend with the LEO debris field that currently requires spacecraft to have extensive shielding.

A Simple Gateway PlatformSpecifically though, in the case of lunar exploration, a platform of this kind would enable multi-functional operations and reusability of lunar architecture to provide a reliable and cost-effective exploration platform to our closest celestial neighbor.

As stated in the Boeing presentation, “The EMLP (Earth-Moon Lagrangian point Platform) provides the services necessary to allow reuse of the [lunar] lander. Consumables such as fuel, air, lithium hydroxide canisters, and water are provided as well as the ability to make small repairs necessary to keep the lander operational.”

Comparison between Lunar LandersFurthermore, the EMLP would allow a lunar lander to be serviced both internally and externally based on mission requirements at the EMLP, thus negate the need for the reusable lander to ever be returned to Earth for servicing.

For this lunar-based stepping stone program, Boeing – as have NASA – identified the EML-2 point as the most logical placement for the EMLP as such a location would allow any lunar lander mission access to “any site on the lunar surface with approximately equal propulsive energy, thus providing flexibility in the lunar science program.”

Using the EMLP as a base of operations:

Once in location at an EML point, the EMLP would see the following set of three mission types, as proposed by Boeing, for lunar operations – as presented to the 63rd International Astronomical Conference in Naples, Italy.

SLS Multi-Capability, carrying landers to EML2 hardwareThe first mission type would involve the launch of an SLS rocket and an accompanying MPCV (Multi-Purpose Crew Vehicle) Orion capsule to the EMLP.

Once there, the crew would use the EMLP for tele-operation of lunar surface assets. This kind of mission would allow astronauts to manipulate lunar surface robotic assets in near real-time communication – allowing instantaneous reaction between the surface instrument and the astronauts on the EMLP.

This type of mission would give EMLP crews in-space training in tele-operation procedures and reduce the requirement for Earth-based tele-operations that encounter long signal lag time as the at-the-speed-of-light commands travel the vast distances between planet and moons.

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Moreover, it would provide astronauts the physical training experience of having to interact with surface robotic assets that will be crucial in eventual Human missions to Mars where astronauts will, by the sheer distance separating them from Earth, have to have more authority to make decisions in real-time without the immediate support of a mission control center.

SLS Launching Lander and OrionThe second EMLP mission currently envisioned by Boeing would see the SLS rocket launch and Orion capsule and the reusable lunar lander to the EMLP. Under this mission, no lunar sortie missions would occur, only the delivery of materials to the EMLP for follow-on lunar surface operations.

These follow-on surface ops missions would occur during mission option three – which actually involves two different options.

The first option for mission three would be the launch of an SLS rocket with an Orion crew capsule and an In-Space Stage. This In-Space Stage would be complete with a refill of propellant for the lunar lander and would be used to transfer the Orion capsule and crew to the EMLP, a journey expected to take approximately four (4) days.

Once at the EMLP, the crew would undock the In-Space Stage from the Orion and re-dock it to the already-present lunar lander.

Refuel The LanderThis would then be followed by the transfer of fuel (CH4 -methane- and LO2-liquid oxygen) from the In-Space Stage to the lunar lander and the transfer of any pre-stocked supplies to the lunar lander for a maximum seven (7) -day lunar surface operation mission.

Once all supplies have been transferred (an operation expected to take about one day), the crew of three (maximum) would board the lunar lander and undock the vehicle from the EMLP.

The In-Space Stage would then be used to propel the lunar lander toward the Moon – a 2.5 day journey.

Inside one of the Lander ConceptsAfter arriving in lunar orbit via a 631 m/s Orbit Insertion burn by the In-Space Stage, a Descent Orbit Insertion burn of 27 m/s half an orbit before landing would be performed.

After this, the lander and crew would perform a Powered Descent Initiation maneuver to bring the lander/In-Space Stage to within 5km of the lunar surface.

Once this altitude was achieved, the lander’s engines would fire and the In-Space Stage jettisoned (impacting the lunar surface some time later).

At this point, the lander would perform a 500 m/s terminal descent to the lunar surface.

NASA SurveyorThis type of staged approach to landing was used back in the 1960s during the Surveyor series of missions by the United States and during the Luna landers missions by the Soviet Union.

According to the Boeing presentation, “This approach has proven successful in past robotic lunar landings and allows a significant reduction in the required size and mass of the landing system. This staged descent approach, that jettisons a large propulsion stage before touchdown, significantly reduces the dV (delta Velocity) of the landing system, allowing a smaller and lighter lander.”

Moreover, it would allow the lunar lander to have lower thrust engines and be lighter in weight than the Apollo lunar lander.

Lander with SLSTo this end, the EMLP-based reusable lunar lander would use three LO2/CH4 engines “positioned under a single O2 tank and seven CH4 tanks.”

Each engine would have an Isp of 370s vacuum thrust at a chamber pressure of 750psia.

The lander would be designed to operate with only two functional engines, thus allowing mission completion and preservation of crew safety in the event of a single-engine-out scenario.

Engines and other elements of the lunar lander could be replaced at the EMLP.

However, this is just lunar surface mission option one. The second option involves the use of a High Lunar Orbit (HLO)-based lander.

This mission would involve constructing and outfitting the EMLP at an EML point and then moving the entire EMLP from the EML point into a HLO position.

SLS In Space StageThis operation would involve using an In-Space Stage from an SLS rocket to provide 120 m/s dV to accomplish a move of the EMLP over a 60 day period.

Once in a HLO, the EMLP would receive its HLO lunar lander – which would differ quite significantly from its EML point-based counterpart described above.

This lander would only be able to support a crew of two, not three, and would require the use of the storable propellants Monomethylhydrazine and Nitrogen Tetroxide.

These propellants are more dense than the LO2/CH4 propellants used by the EMLP-based lander.

As such, the HLO-based lander would be physically smaller (but not lighter in weight) than its EMLP variant.

SLS with Lander and OrionFor these missions, the HLO-lander would use a smaller, storable propellant In-Space Stage, here called a Lunar Transfer Vehicle (LTV).

The LTV would be launched with the Orion capsule and crew by the SLS rocket and docked to the HLO EMLP. It would then be used to take the HLO lander from the EMLP down to a Low Lunar Orbit (LLO).

The lander would then separate from the LTV and navigate to the lunar surface on its own. Meanwhile, the LTV would wait in orbit for lunar lander.

After completion of surface operations, the lander would return to the LTV and the LTV used to return the lander to HLO and the EMLP.

The lander would then be preserved for future lunar surface missions, while the LTV could either be discarded after each mission or reused.

Boeing’s proposals for Martian missions will follow next week.

(Images: Via Boeing and L2 content from L2’s SLS specific L2 section, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. Other image via NASA).

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