Notional ETLV-4 rendezvous with propellant producing water depot @ EML1 with orbiting solar power plant (where propellant depots dock when converting water into LOX/LH2) in the background.

by Marcel F. Williams

In 2018, NASA will launch the first unmanned test flight of its wide body super heavy lift vehicle, the Space Launch System (SLS). That first launch will also test the first uncrewed version of the Orion spacecraft. Coincidentally, 2018 will also be the same year that private companies, thanks to the financial help of NASA, will return American astronauts into orbit aboard private spacecraft. Crewed Orion/SLS missions are not scheduled to occur until at least the year 2021.

Congress has directed NASA to reveal the design of a microgravity Deep Space Habitat (DSH) by 2018. Unfortunately, the American space agency continues to ignore the use of a DSH as a gateway for crewed missions to the lunar surface while simply ignoring the significant physiological problems associated with potential multiyear interplanetary missions within a microgravity environment.

Orion MPCV docked @ SLS propellant tank derived Deep Space Habitat (Credit NASA)

The primary purposes for a Deep Space Habitat (DSH) should be to:

1. Serve as a gateway to the lunar surface. Astronauts traveling from the Earth or from the lunar surface could dock their spacecraft at an EML1 habitat, taking temporary advantage of the more spacious accommodations before transferring to vehicle fueled destined for the lunar surface.

2. Serve as a storm shelter during the occurrence of major solar events. This will probably require at least 30 cm of water shielding for the areas within the habitat that the astronauts will be occupying. Major solar events can last for several minutes to several hours.

3. Serve as a maintenance and repair station for reusable lunar shuttles (ETLV) and orbital transfer vehicles. Flex Craft docked at the DSH could also be utilized for extravehicular repairs to nearby water/propellant depots and associated solar arrays at EML1.

4. Test the effectiveness of various levels of water shielding required to mitigate cosmic radiation and potentially brain damaging heavy nuclei. In theory, 20 cm of water would be enough shielding to to stop the penetration of the heavy nuclei component of cosmic rays while 30 cm of water would reduce overall annual cosmic radiation exposure to less than 25 Rem per year during solar minimum conditions. Solar storm events would also be significantly mitigating with 30 cm of water protection. Minimizing the mass of radiation shielding required for safe interplanetary travel would be essential for reducing the amount of propellant required for such missions.

5. Test the integrity and reliability of the pressurized habitat structures that might also be used for habitats on the surface of the Moon and Mars and for rotating artificial gravity habitats for space stations placed in cis-lunar orbits, Mars orbit, and for crewed interplanetary journeys.

Of course, a DSH would be a-- destination to nowhere-- without developing vehicles capable of transporting humans and heavy cargo to the surfaces of the Moon and Mars. And, in my opinion, most Americans and members of Congress will continue to believe that America's glory years in space are in the past until American astronauts are once again walking on the surfaces of other worlds-- this time to stay.

NASA's beyond LEO ambitions are severely hampered by the fact that it continues to operate a relatively expensive (~$3 billion/yr) LEO program (ISS) without a significant increase in the NASA budget for its beyond LEO program. While it has been presumed that much more funding will be provided for NASA's beyond LEO missions once the ISS program comes to an end, there are still efforts to extend the ISS program beyond 2024, again, without increasing the NASA budget in order to pay for its continuation.

Bigelow Aerospace plans to deploy its first private commercial space habitats to LEO in 2020 aboard the ULA's Atlas V rocket. If this private space company is successful then there's really no reason for NASA to continue the ISS program beyond 2020 since private companies will be able to do research and development at LEO. This, of course, would allow NASA to use ISS related funds to develop the cargo and crew landing vehicles, habitats, and related infrastructure for crewed missions to the Moon and Mars.

Allowing foreign astronauts to participate in NASA's beyond LEO program could provide additional funding for NASA. By 2018, Russia plans to charge NASA, $81 million per astronaut for transport to an from the ISS. NASA could charge foreign space agencies $150 million for each astronaut participating in one of its beyond LEO missions. The Orion MPCV is capable of accommodating as many as six astronauts. If two of those astronauts were from foreign space agencies paying NASA to join the mission then NASA could save $300 million per crewed SLS launch.

The Center for Strategic and International Studies (CSIS) has estimated that the cost of developing a crewed two stage lunar lander at approximately $12 billion. Former NASA director, Charlie Bolden, estimated the cost of developing a lunar landing vehicle at approximately $8 to $10 billion.

Neil Armstrong and Buzz Aldrin landed on the surface of the Moon just seven years after NASA invited eleven private firms to submit proposals for the Lunar Excursion Module (LEM) in July of 1962. So if we assume that it will take seven years to develop an extraterrestrial landing vehicle or vehicles ( using a COTS type of funding for more than one vehicle), then annual development cost over the course of seven years might range from approximately $1.1 billion to $1.7 billion. We can also assume that an additional $1.1 billion a year to $1.7 billion a year over the course of an additional seven years would then be needed to fund the development of a future Mars landing vehicle. Such annual funding for extraterrestrial landing vehicles would still leave ample funds for financing the development of lunar and martian habitats and the associated infrastructure.

Boeing Aerospace 2.4 meter Super Light Weight cryotank (Credit Boeing Aerospace)

However, the development time, cost, and recurring cost for an extraterrestrial landing vehicle (ETLV) could be substantially reduced if:

1. A single stage vehicle, or vehicles, were developed instead of a-- two stage vehicle

2. An ETLV was developed that was largely derived from technology that either already exist or is currently in development

3. An ETLV was developed that utilized LOX/LH2 common bulkhead propellant tanks instead of two different tanks for liquid oxygen and liquid hydrogen

4. An ETLV was developed that were capable of transporting cargo and crews to the surfaces of both the Moon and Mars and back to the orbits of the Moon and Mars

5. An ETLV was developed that had pressurized habitat and airlock areas derived from re-purposed ETLV propellant tanks.

6. An ETLV was developed that was capable of being reused for at least for ten round trips to and from their destinations (the surfaces of the Moon or Mars)

7. An ETLV was developed that was capable of also being utilized for unmanned robotic and cargo missions

8. An ETLV was developed that was capable of also being utilized as a crewed orbital transfer vehicles between LEO, Low Lunar Orbit, and the Earth-Moon Lagrange points

Front view of notional singe stage reusable ETLV-4 derived from 2.4 meter in diameter cryotanks

Side view of notional singe stage reusable ETLV-4 derived from 2.4 meter in diameter cryotanks

ETLV-4

Up to 40 tonnes of LOX/LH2 propellant in four 2.4 meter in diameter propellant tanks

Four RL-10 derived CECE engines

2.4 meter in diameter propellant tank derived central crew habitat area with lower heavy ion shielded storm shelter

Twin 2.4 meter in diameter propellant tank derived airlocks

Inert mass without heavy ion water shielded area: ~12 tonnes

Inert mass with heavy ion water shielded area (22 cm of water): ~17 tonnes

Gross mass: 57 tonnes

specific impulse: 445 seconds

Due to reduced vehicle mass, reductions in vehicle components, and reduced vehicle complexity, Lockheed-Martin concluded that the development cost and recurring cost for a lunar lander could be substantially reduced if a reusable single stage vehicle were developed instead of a two staged spacecraft. NASA reached a similar conclusion back in the late 1980s when JPL proposed its own single stage LOX/LH2 lunar landing vehicle.

Boeing developed and tested a 2.4 meter cyrotank as a prelude to its development of a 5.5 meter in diameter, Super Light Weight Tank, that might possibly be used for the 5.5 meter LOX tank for the SLS upper stage (EUS). The 2.4 meter tank was successfully filled with liquid hydrogen chilled at –423 °F and cycled through-- twenty-- pressurization and vent cycles. If Boeing's 2.4 meter tank were utilized in a common bulkhead configuration for storing LOX/LH2 propellant in an Altair-like vehicle then such tanks could be utilized for a reusable single staged spacecraft.

Four RL-10 derived CECE (Common Extensible Cryogenic Engine) engines, currently in development by Aerojet Rocketdyne, could enhance vehicle safety with engine out capability and would be capable of up to 50 restarts. This should enable the vehicle to be used for at least 10 round trips from the surfaces of the Moon or Mars and to various orbital regions near each celestial body. The CECE engines are also supposed to be designed to have a throttle capability ranging from 104% of thrust down to just 5.6%, which should allow an extraterrestrial landing vehicle to land on worlds as large as the Moon and Mars or as small as the moons of Mars. However, thrusters near the bottom of an ETLV could also be used to land on the surfaces of the small low gravity martian moons.

Utilizing Integrated Vehicle Fluid (IVF) technology currently being developed by the ULA, helium and hydrazine would no longer be required for an extraterrestrial spacecraft with some ullage gases even being utilized for attitude control. With the addition of NASA emerging cryocooler technology, solar powered cryocoolers could reliquify some ullage gases, eliminating the boil-off of hydrogen and oxygen.

Pressurized crew areas and airlocks derived from re-purposed ETLV propellant tanks, could further reduce development and recurring cost. The twin cryotank derived airlocks allows more room within the cabin while allowing astronauts to leave the vehicle without having to decompress and then re-pressurize the crew cabin. With the airlocks positioned just a few meters above the landing pods, pressure suited astronauts could depart the vehicle just few meters above a planetary surface, reducing the difficulty and risks associated with exiting and entering the spacecraft. The low position of the airlocks should also make it convenient for mobile robotic vehicles to be deployed to the surface of a the Moon or Mars or the moons of Mars for robotic exploration and potential sample returns to orbit.

NASA's ADEPT deceleration shield concept (Credit NASA)

Developing a landing vehicle that could be used for crewed missions to both the lunar and martian surfaces would, of course, substantially reduce development cost. A spacecraft capable of transporting astronauts from surface of Mars to Low Mars Orbit (~4.4 m/s delta-v) would also be easily capable of transporting astronauts from the surface of the Moon to Low Lunar Orbit or to any of the Earth-Moon Lagrange points (less than 2.6 m/s delta-v).

Landing such an extraterrestrial landing vehicle on the surface of Mars, however, would require the development of a deceleration shield. NASA is currently doing research on two types of deceleration shields: HIAD and ADEPT. The rigid ADEPT deceleration shield could allow spacecraft to deploy up to 40 tonnes of payload practically anywhere on the surface of Mars. After the ADEPT deceleration shield was discarded, a delta-v of less than 0.6 meters per second would only be required to land the vehicle on the martian surface

Notional ADEPT deployment of 40 tonnes of cargo to the martian surface (Credit NASA)

An extraterrestrial landing vehicle capable of transporting astronauts from the surface of Mars to low Mars orbit would also be capable of transporting astronauts from LEO to Low Lunar Orbit or to any of the Earth-Moon Lagrange points. Utilizing the ETLV in such a manner, however, could make the Orion MPCV obsolete, allowing astronauts to be transported into orbit by Commercial Crew vehicles and then transferred to a propellant depot fueled ETLV for easy access to the Earth-Moon Lagrange points and Low Lunar Orbit and to the lunar surface.

Notional CLV-7B cargo lander derived from 2.4 meter diameter cryotanks

A cargo lander (CLV) derived from the crew version of the ETLV could easily be derived using all seven 2.4 meter in diameter pressurized tanks to carry propellant. With a diameter of at least 7.2 meters, such a cargo transport could deploy large and heavy structures as large as 8.6 meters in diameter to the surfaces of the Moon and Mars. Pressurized habitats derived from an SLS propellant tank technology with diameters up to 8.4 meters could easily be deployed to the surfaces of the Moon and Mars by such an ETLV derived CLV.

ATLETE robots could be used for offloading heavy cargo to the surfaces of the Moon and Mars aboard a notional CLV-7B (Credit: NASA)

CLV-7B

Up to 35 tonnes of LOX/LH2 propellant in seven 2.4 meter in diameter propellant tanks

Four RL-10 derived CECE engines

Specific impulse: 445 second

Inert mass without payload: ~8 tonnes

Gross mass without payload: ~43 tonnes

Capable of accommodating cargo with diameters as large as 8.6 meters

Notional SLS propellant tank derived regolith shielded habitat for the Moon and Mars with an 8.4 meter in diameter pressurized habitat area that could be deployed to the lunar or martian surface using the CLV-7B and ATHLETE technologies.

Once the cargo lander is on the surface of the Moon and after its payload is deployed, water bags could be securely attached to the top of the CLV-7B. This could allow the CLV to be reused as a water transport tanker capable of transporting at least 35 tonnes of water from the surface of the Moon to EML1. Using its CECE engines for ten round trips could enable the CLV to deliver more than 300 tonnes of water to propellant producing water depots located at EML1.

With the capability of landing crews and payloads on the Moon and Mars, the ETLV-4 crew lander and the CLV-7B cargo lander should also be capable of someday landing crews and cargo on the surfaces of the planet Mercury and on Jupiter's moon, Callisto, two other viable worlds for potential commercialization and human settlement. Within Jupiter space, automated unmanned ETLV-4 spacecraft operated from an outpost on Callisto could transport mobile robotic vehicles to the Jovian moons within Jupiter's deadly radiation belt (Ganymede, Europa, and Io) for continuous robotic exploration and sample returns from these interesting but heavily radiation inundated worlds.

Links and References

Composite Cryotank Technologies; Demonstration

CECE (Common Extensible Cryogenic Engine)

An Integrated Vehicle Propulsion and Power System for Long Duration Cryogenic Spaceflight (ULA)

The SLS and the Case for a Reusable Lunar Lander