Thursday, July 6, 2017

(Part III) A Practical Timeline for Establishing a Permanent Human Presence on the Moon and Mars using SLS and Commercial Launch Capability

A rotating artificial gravity space station in Mars orbit beyond the orbital arc of Deimos. One ETLV-4 crew lander is docked at the station's central docking port while a crewed ETLV-4 approaches the station after visiting the surface of Phobos.


by Marcel F. Williams

Part III: Artificial Gravity and the Moons of Mars 


While traveling from Earth to the Moon or the Earth-Moon Lagrange points only takes a few days, human voyages between Mars and cis-lunar space will require a several months of travel time. So astronauts will have to be adequately  protected from the  deleterious effects of cosmic radiation (especially its heavy nuclei components), solar storms, and the microgravity environment. 

The notional crewed spacecraft proposed under this scenario all have habitat areas that provide at least 20 grams per centimeter squared of radiation shielding, enough to protect astronauts from the penetration of heavy ions and from harmful levels of radiation resulting from major solar events. Such levels of shielding in interplanetary vehicles should limit astronaut radiation exposure to less than 30 Rem per year during the worse cosmic ray conditions (the solar minimum).  Permanently occupied space stations beyond the Earth's magnetosphere and  that rotate to produce a simulated gravity will have their internal shielding (iron plates)  gradually increased until levels of internal radiation exposure for its human inhabitants  is below 5 Rem per year (the legal limit of radiation exposure allowed for radiation workers on Earth). 

In order to mitigate or eliminate the deleterious effects of microgravity, under this architecture, artificial gravity environments (0.5g) will be provided for astronauts for multimonth interplanetary journeys. Simple rotating spacecraft (AGH-I) composed of three pressurized SLS propellant tank derived habitats joined together by cables and twin expandable and retractable booms will be used for interplanetary voyages between EML1 and high Mars orbit. Similar artificial gravity producing habitats will also be used for permanent space stations (AGH-SS) deployed in orbits within cis-lunar space and in orbit around Mars. 


Flight paths between LEO and  EML1 and EML1 and high Mars orbit
NASA is currently contemplating a solar/xenon based interplanetary architecture. The scenario presented here, however,  advocates a propellant depot based interplanetary architecture similar to that advocated by the ULA (United Launch Alliance). The advantages are:

1. LOX/LH2 propellant allows astronauts to reach Mars faster than interplanetary vessels propelled by xenon gas, reducing radiation exposure and the psychological stress of longer travel times.

2. The continuous drive of xenon engines would make it difficult to accommodate artificial gravity habitats, forcing astronauts to endure the deleterious of effects and the physical and psychological stresses associated with a microgravity environment. So multi-month journeys within a microgravity environment could significantly increase that chances of fatal mishaps during an interplanetary mission.
3. Chemical rockets would have the advantage of being able to dump their water shielding just before their final trajectory burns,  substantially reducing vehicle mass as the spacecraft enters high Mars orbit or cis-lunar space. 

4. A xenon based interplanetary spacecraft would be dependent on an expensive fuel that has to be launched out of the Earth's enormous gravity well. A LOX/LH2 producing water depot, on the other hand, could eventually use extraterrestrial sources of water and oxygen from the Moon, Mars, the moons of Mars, etc.  

5. In order to reduce the mass required to be launched from the Earth's gravity well, a xenon based interplanetary architecture would still require substantial amounts of extraterrestrial water for drinking, food preparation, washing, radiation protection, the production of air,  and for the production of LOX/LH2 or LOX/methane propellant for vehicles landing and taking off from the surfaces of Mars or the moons of Mars. So it would be much simpler and cheaper for extraterrestrial resources to be used for the entire architecture instead of just part of it.


Bigelow BA-330 habitat which is inherently provided with enough shielding to protect astronauts from heavy nuclei penetration.


SLS and Commercial Launch Sequences to Establish a Permanent Human Presence in High Mars Orbit

2027

SLS Launches: 

SLS Launch 14: Two CLV-7B (Cargo Landing Vehicle) deployed to lunar outpost after refueling at EML1:

First CLV-7B   will be carrying  a second mobile hydrogen tanker (MHT) derived from the 2.4 meter cryotank technology plus  four  more Water Bug microwave water extraction robots.

Second CLV-7B  will deploy at least 160 KWe of  nuclear power to the lunar surface with at least a 10 year lifetime for the fueled reactors. 

SLS Launch 15: SLS deploys first artificial gravity habitat to LEO (AGH-I). An OTV-125 (an IVF modified EUS) transports the AGH-I to EML1

SLS Launch 16: SLS deploys WPD-OTV-400  EML1. The propellant producing water depot will be capable of storing up to 400 tonnes of LOX/LH2 propellant and up to 1000 tonnes of water.  

SLS Launch 17: SLS deploys OTV-400 to EML1. The SLS propellant tank derived vehicle will be used to transport crews between high Mars orbit and cis-lunar space.  


Commercial Launches:

1. First commercial deployment of reusable ACES-68 (ULA) and Shepard (Blue Origin) derived lunar landing tankers for transporting  lunar water from the lunar surface to EML1 (at least 1000 tonnes to EML1 per year)

2. Commercial launches of twin satellite communications and navigation system to Sun-Mars L4 and L5  plus a trio of satellites into Aresynchronous orbit in order to establish uninterrupted communications between Earth and Mars and between Mars orbit and the martian surface.

Notes:

 1. 2027 will be the beginning of four SLS launches per year by NASA

2. The AGH-I will be provided with water 30 centimeters of internal water shielding from water depots located at EML1. In 2027, the crewed structure will test its ability to provide 0.5 g of simulated gravity and its ability to routinely expand and contract its cables and booms and to increase and decrease its rate of rotation. 

3. The OTV-400 orbital transfer vehicle will be tested by sending it unmanned to Sun-Earth L2 and then back to cis-lunar space. 


SLS propellant tank derived Deep Space Hab (DSH). Requires additional water shielding to protect astronauts from heavy nuclei penetration (Credit NASA)

2028

SLS Launches: 

SLS Launch 18: Two DSH (Deep Space Habitats) deployed to LEO; one remains permanently at LEO while the other will  be transported by an  OTV-125 to EML1 and then to high Mars orbit

SLS Launch 19: Second WPD-OTV-400 to EML1

SLS Launch 20: SLS deploys third WPD-OTV-400 to EML1

SLS Launch 21: SLS deploys fourth WPD-OTV-400 to EML1

Notes:

1. Odyssey 1 (OTV-400 +AGH-1+ETLV-4) will travel to to  SEL2 (Sun Earth Largrange Point 2) in order to test the Odyssey vehicles interplanetary capability. It will take about 30 days to reach ESL2 and 30 days to return to cis-lunar space. 30 days will be spent at SEL2. 

2. LEO DSH (LEO Space Hab) will join the BA-330 as an additional way station for beyond LEO missions for NASA  


SLS propellant tank derived artificial gravity habitat (AGH). Requires 30 cm of water shielding for crewed interplanetary journeys and 50 cm of iron shielding as a permanent space station deployed beyond the Earth's magnetosphere. 

2029

 SLS Launches:

SLS Launch 22: Second AGH-I deployed to EML1

SLS Launch 23: Second OTV-400 deployed to EML1

SLS Launch 24:  Two ETLV-4 + OTV-125 are launched to LEO for redeployment to EML1

SLS Launch 25: Two CLV-7B vehicles deployed to LEO for redeployment at EML1:

Cargo Langer One: mobile magnetic iron extraction robots + 3D iron  panel manufacturing machines for internally radiation shielding AGH-SS space stations.

Cargo Lander Two: regolith bag manufacturing plant to enhance the protection of landing pod areas and for shielding the domed sections of future biosphere habitats

Commercial Launches:

1. Commercial launch of  BA-330 to LEO and transported to EML1 by ACES-68 OTV. The BA-330 will  be transported to high   Mars orbit by an OTV-125; departs in February of 2029 to arrive in high Mars orbit in July of 2029.
Notes:

1. Odyssey 2: Second crewed  mission of the Odyssey spacecraft will be a 235 day  round trip to SEL1 (Sun-Earth Lagrange point 1)

2. With four  WPD-OTV-400 depots at EML1, one will depart for  Mars  in January of 2029 to arrive at high Mars orbit in July of 2029. A second WPD-OTV-400 depot will depart EML1 in February of 2029 to also arrive in high Mars orbit in July of 2029. Both propellant depots will carry at least 550 tonnes of water to high Mars orbit. 

3. OTV-125 transports DSH  to high Mars orbit; departing EML1 in January of 2029 to arrive at high Mars orbit in July of 2029.

LOX/LH2 fueled OTV-400 and EUS derived OTV-125. Both reusable vehicles will use the ULA's Integrated Vehicle Fluid technology for eliminate the need for helium and hydrazine while utilizing ullage gases for attitude control. 

2030

 SLS Launches:

SLS Launch 26: Third OTV-400 deployed to EML1

SLS Launch 27AGH-SS deployed to EML4 for DOD

SLS Launch 28: NASA deploys a second AGH-SS  to EML1. The partially iron shielded artificial gravity space station will  be transported to high Mars orbit by an OTV-400.

SLS Launch 29: Two Ares R-ETLV-4  deployed to EML1+ OTV-125


Commercial Launches:

1. First commercial crew  shuttles to the lunar surface: reusable  Xeus (ULA), reusable Lunar Shepard (Blue Origin)?
 
Notes:

1. Odyssey 3:  Crewed Odyssey mission ( OTV-400/AGH-I/ETLV-4)  to high Mars orbit with a flyby past Venus.  Departs from EML1 in February of 2030, flying past Venus in  July of 2030 and arriving at Mars in January 2031. The AGH-I will replenish its water shield by rendezvousing with one of  the WPD-OTV-400 water depots.   The Odyssey 3 will use one of the WPD-400 depots to refuel with LOX/LH2 propellant in order to depart  Mars orbit in April 2031,  returning to cis-lunar space in December of 2031

During the crew's three months stay in Mars orbit, the crew will use the two ETLV-4 vehicles in Mars orbit to visit the surfaces of Deimos and Phobos. The crew will also visit the  BA-330 storm shelter and the DHS previously deployed to  high Mars orbit 

2. Second ETLV-4 is not transported with the Odyssey vehicle but self deploys itself to high Mars orbit for utilization in the crewed mission, following the same flight pattern as the Odyssey 3. 

Reusable ETLV-4 will allow astronauts to visit the moons of Mars. The ETLV-4 will also be used to transport the the ADEPT attached Ares-ETLV-4 to low Mars orbit for missions to the surface of Mars.


2031

 SLS Launches: 

 SLS Launch 30: Two ETLV-4 + OTV-125 are launched to LEO for redeployment to EML1


SLS Launch 31: OTV-125+ LRH (Lunar Regolith Habitat) to Moon for DOD
 
SLS Launch 32: SLS deploys OTV-125+LRH (agronomy hab) to lunar outpost

SLS Launch 33: Two CLV-7B cargo landers deployed to LEO to be transported to EML1.

CLV-7B One will transport four mobile crew vehicles to the lunar outpost; two for NASA and two for the DOD.

CLV-7B Two will transport two mobile optical telescopes to the lunar surface: one for NASA and one for the DOD



Commercial Launches:

1. Start of commercial launch of ADEPT deceleration shields to LEO by Vulcan launch vehicles. The ADEPT shields will be transported to high Mars orbit by reusable  OTV-125 vehicles and possibly by ACES-68 vehicles.  

 Notes:


1. An OTV-400 will transport the partially shielded AGH-SS to high Mars orbit, departing in February of 2031 and arriving in high Mars orbit in September of 2031.  

2. Second crewed Odyssey mission (Odyssey 4) will be transported to high Mars orbit by another OTV-400. The Odyssey 4 will depart EML1 in March of 2031, arriving in high Mars orbit in August of 2031. Beginning of permanent human occupation of Mars AGH-SS space station

3. Lunar manufactured iron radiation shielding plates for the AGH-SS will be transported to high Mars orbit over the years by several OTV-125 vehicles, decreasing cosmic radiation exposure to less than 30 Rem per year to less than 5 Rem per year during solar minimum conditions. 

4. The two Ares R-ETLV-4 vehicles will rear dock with two ADEPT deceleration shields. An ETLV-4 will dock and transport an Ares R-ETLV-4  from high Mars orbit to low Mars orbit. The unmanned Ares-ETLV-4 will land on Mars, testing the ADEPT shield. Teleoperated robots will be deployed to collect regolith samples and samples of the martian atmosphere. The Ares R-ETLV-4 will return to low Mars orbit where it will be transported by an ETLV-4 back to high Mars orbit. Both Ares-R-ETLV-4 vehicles will be used multiple times,  mating with other expendable ADEPT shields for unmanned sample retrieval missions to the martian surface.  This will also test the reliability of the ADEPT shields for future crewed missions to the martian surface.

5. First DOD outpost on the lunar surface (just a few kilometers away from NASA’s lunar outpost). Mobile crew transport vehicles will be used to transport astronauts between   NASA and DOD facilities.  



Odyssey interplanetary space craft. After trajectory burns to insert the Odyssey into a Mars Transfer Orbit, the AGH-I will separate from the OTV-400 and the ETLV-4 in order to rotate and expand its cables and booms to provide 0.5g of simulated gravity in the twin counter-balancing habitat modules. The AGH will dump its water shield and reattach itself to the OTV-400 and the ETLV-4 for the final trajectory burns into orbit around Mars. 


A Permanent Human Presence in High Mars Orbit

So under this propellant depot architecture, the first crewed mission (Odyssey 3) to high Mars orbit will depart from EML1 in February of 2030 and arriving at Mars in January 2031, flying past the planet Venus during the nearly year long journey. Once the crew arrives, a DSH (Deep Space Habitat) and storm shelter (BA-330) will already be deployed in high Mars orbit in order to enhance their safety. After their orbital transfer vehicles (OTV-400) has been refueled by one of the twin propellant depots (WPD-OTV-400), the Odyssey 3 will depart from Mars in April 2031 and returning to cis-lunar space in December of 2031.

WPD-OTV-400 propellant producing water depot in high Mars orbit refueling an OTV-400 that will transport the Odyssey back to cis-lunar space.


The second crewed mission to high Mars orbit (Odyssey 4) will depart from EML1  in March of 2031, arriving in high Mars orbit in August of 2031. This mission will include the first use of ADEPT deceleration shields to land   R-ETLV-4 vehicles on the martian surface for the robotic retrieval of lunar regolith samples. 
Ares-ETLV-4 simply adds additional thrusters to the top of the ETLV-4 to provide sufficient attitude control while entering the martian atmosphere behind and ADEPT deceleration shield. 


Unmanned Ares-ETLV-4 attached to an ADEPT deceleration shield. Teleoperated robots will be deployed to retrieve regolith and atmospheric samples to be returned to low Mars orbit and back to the AGH-I.



Landing Humans on Mars will be the last part (Part IV) of this article.  
 

2 comments:

Doug Space said...

Why iron plates? Wouldn't the same amount if mass in the form of polyethylene be better?

Marcel F. Williams said...

Polyethylene has a density of about 0.97gm/cm3. Iron has a density of about 7.87 gm/cm3.

Internally shielding a-- permanently-- orbiting habitat that's only 8.4 meters in diameter (SLS propellant tank derived) so that annual radiation exposure is less than 5 Rem per year (maximum annual radiation exposure allowed for radiation workers on Earth) would require iron shielding about 50 cm thick. This would allow a habitable floor diameter of 7.4 meters.

A polyethylene shield with equal radiation protection would require internal radiation shielding more than 4 meters thick, allowing only 40 cm wide of floor space.


Only 30 centimeters of polyethylene shielding would be practical for interplanetary missions since that would be thick enough to protect astronauts from the heavy ion components of cosmic radiation and would also protect astronauts from major solar events.

But that would still expose astronauts to more than 25 Rem per year during solar minimum conditions. While that would be well below NASA's 50 Rem per year policy, that would be substantially above the 5 Rem per year rule on Earth. Such high levels of radiation exposure might severely limit the number of future space missions an astronaut can participate in. NASA's career limit of radiation exposure for a 25 year old female is only 100 Rem.

So being able to reduce high levels of cosmic radiation exposure within an appropriately regolith shielded habitat on the surface of the Moon or Mars or in an appropriately iron shielded space stations beyond the Earth's magnetosphere or in Mars orbit could allow astronauts and scientist to work and explore beyond the Earth for years and possibly decades without excessive radiation exposure.

Marcel





Blog Archive