Tuesday, October 6, 2020

Commercial Advantages of a Large SLS Deployed Reusable Extraterrestrial Crew Landing Vehicle

Notional SLS deployed RLV-4 Crew lunar landing vehicle with a crew davit deployment system. 

by Marcel F. Williams
Before the end of the decade, the deployment of orbital propellant depots to LEO and NRHO (Near Rectilinear Halo Orbit) will probably make the SLS/Orion vehicle-- obsolete-- as part of an affordable and efficient crew transport  architecture to the lunar surface. So the-- crewed-- SLS/Orion configuration could be haulted just a few years after it started.  
However, the four major partners in SLS manufacturing and operations (Boeing, Northrup Grumman, Aerojet Rocketdyne, and Lockheed Martin) could take full economic advantage of the coming  propellant depot architecture by using the Space Launch System to deploy large-- reusable-- lunar landing vehicles into orbit to transport crews or heavy cargo to the lunar surface. 
I'll  call such a notional extraterrestrial landing vehicle, in this article, the RLV-4 (Reusable Landing Vehicle Four). And I seriously believe that if Boeing and their SLS partners finance and build a  RLV-4 type of vehicle for both crew and heavy cargo transport to the lunar surface, their partnership could easily end up economically dominating cis-lunar space and probably the rest of the solar system for the next 25 to 30 years-- with such a  simple single stage extraterrestrial vehicle and its inherently useful variants.
LOX/LH2 tank configuration in Boeing's Altair lunar lander concept (Credit: Boeing)

The notional  RLV-4 would be octagon shaped like Boeing's Altair lunar descent vehicle concept. But it will use a simplified propellant tank architecture requiring just two LH2 tanks and two LOX tanks, similar to Blue Origin's octagon shaped Blue Moon lunar lander which is basically a smaller-- simplified-- version of of the Altair lunar lander. 

Top view of LOX/LH2 tank configuration for Boeing's Altair lunar lander concept (Credit: Boeing)


The propellant tanks for the RLV-4 will be derived from Boeing's super light weight composite cryotank technology with the two large 3.8 meter in diameter hydrogen tanks and and the two smaller liquid oxygen tanks approximately 2.4 meters in diameter. Both cryotanks will stand nearly 6 meters high within the interior of the RLV-4 octagon. Gaseous compressed hydrogen will be used to pressurize the liquid hydrogen tanks and compressed gaseous oxygen for pressurizing the liquid oxygen tanks during liftoff and trajectory burns-- replacing gaseous helium. Gaseous hydrogen and oxygen will also be utilized for the vehicle attitude thrusters in this notional vehicle design. So hydrogen and oxygen will provide the propellant, attitude control, and tank pressurization for the RLV-4. 

Notional Boeing 3.8 meter in diameter composite LH2 tank and 2.4 meter in diameter LOX tank.

The RLV-4 would be somewhat similar in height with Boeing's Altair concept. But it would be able to store more than twice as much propellant (56 tonnes) thanks to the substantially larger  cryotank diameter of the liquid hydrogen tank and the larger diameter and height of the liquid oxygen tanks relative to those conceived for the Altair. So the RLV-4 would be capable of accommodating up to 56 tonnes of propellant which would be more than enough fuel to land a 16 tonne crew vehicle from LEO to the surface of the Moon.

The restartable engines for the RLV-4 could be provided by SLS partner, Aerojet Rocketdyne, who is currently developing the expendable RS-25 engines for the  SLS core vehicle and the RL-10 engines for the upper stage vehicle. The RL-10 derived CECE engines would be capable of throttling between 104% down to just 5.9% and would be capable of at least 50 in space starts. So the CECE engines should be capable of performing at least 12 round trip missions between NRHO and the lunar surface before having to be replaced. Using them in pairs would give the RLV-4 engine-out capability, enhancing crew safety.

However, the RLV-4 propellant tanks should be capable of at least 50 refills (50 round trips if  missions between NRHO and the lunar surface are conducted on a single fueling of propellant). So if two more engines were added to the RLV-4, 24 round trips could be possible if only two engines were used during a journey-- while propellant flow was shut off to the other pair of engines. Replacing the engines after 24 round trips with four more CECE engines could maximize the RLV-4's reusability allowing the vehicle to conduct up to 48 round trips to the lunar surface before-- if it is refueled less than 50 times. 

Basic RLV-4 cargo lunar lander with solar panels on four sides of the octagon shaped vehicle and radiators on four sides of the vehicle

At its corners, the maximum diameter of the RLV-4 octagon  would be 8.44 meters with a distance between each opposite 3.23 meter side of the octagon being approximately 7.8 meters. With the legs folded during launch aboard an SLS vehicle within a 10 meter fairing, the RLV-4 could easily fit within the internal  9.1 meter dynamic envelope of the payload fairing. 


Notional RLV-4 LOX/LH2 cyotank configuration within the octagon shaped vehicle

While NASA currently envisions only an 8.4 meter fairing for it's use of  the SLS, it would be in the economic interest for the  SLS partnership to quickly develop its originally intended 10 meter fairing in order to have a clear competitive advantage over vehicles like the Space X's future Starship which will have a 9 meter payload bay with probably an 8.1 meter dynamic envelope. However, Blue Origin's 7 meter in diameter New Glenn launch vehicle could be competitive since it should  also be capable of accommodating payload fairings up to 10 meters in diameter. With an 8.4 meter diameter for the SLS core vehicle, the SLS should be capable of accommodating  payload fairing sizes up to 12 meters in diameter with internal dynamic envelopes up to 11.1 meters in diameter.

SLS partner, Lockheed Martin, could supply basically the same Orion derived crew habitat module for the RLV-4 as it will for the Artemis National Team (Blue Origin, Lockheed Martin, Northrup Grumman, Draper) that will deploy a lunar crew lander to the Moon for NASA-- but without the added complexity and the expense of the ascent propellant architecture. 

A tall 10 meter in diameter SLS fairing should  be able to easily deploy two RLV-4 crew vehicles and other variants into orbit per launch-- cutting  RLV-4 deployment cost in half per launch. And the SLS should be able to deploy each vehicle to orbit with enough propellant for each vehicle to self deploy practically anywhere within cis-lunar space.

Utilizing propellant depots deployed at LEO, the RLV-4 should be able to transport crews from LEO to NRHO with less than 24 tonnes of propellant

But round trips between NRHO and the lunar surface could require nearly 48 tonnes of LOX/LH2.

Supplying a propellant depot at LEO with enough propellant for a RLV-4 crew mission to NRHO would only require a single Vulcan-Centaur launch (Vulcan-Centaur 562). 

However, supplying water or propellant to depots located at NRHO for a single lunar mission would require eight Vulcan-Centaur launches for the round trip between NRHO and the lunar surface plus an additional  four Vulcan-Centaur launches to NRHO to fuel the return trip of the RLV-4 back to LEO from NRHO. 

So a single lunar mission would require at least 13 Vulcan-Centaur propellant launches costing more than a billion dollars in propellant cost alone for a single mission. But such cost  would still be competitive with architectures that require at least one SLS/Orion launch plus additional commercial launches for a lunar crew missions. 

However, propellant cost for the RLV-4 architecture would fall dramatically once hydrogen and oxygen were being produced on the lunar surface. And that would mean that only a single Vulcan-Centaur propellant launch to LEO would be required for a lunar mission. 

Propellant destined for depots located at NRHO could come from the lunar surface. And a RLV-4 tanker variant could supply nearly 50 tonnes of water or propellant to an NRHO depot per launch from the surface of the Moon, up to 1200 tonnes of water or propellant until its four engines would have to be replaced, and up to 2400 tonnes of water or propellant to NRHO before the entire vehicle would have to be replaced. So two RLV-4 tanker vehicles deployed-- by a single SLS launch-- might be able to deploy 2400 to 4800 tonnes of lunar propellant to NRHO.

Simple solar  powered RLV-4 variants could serve as orbital propellant depots at LEO and NRHO and on the lunar surface.  Each depot could store up to 56 tonnes of propellant plus up to 100 tonnes of water for possibly making propellant.  The appropriate solar arrays for lunar and orbital RLV-4 derived propellant depots could be developed by SLS partner Northrup Grumman which already specializes in developing and deploying extraterrestrial solar arrays. 

By sharing the cost for the development and deployment of the RLV-4, starting in 2021, Space Launch System partners: Boeing, Aerojet Rocketdyne, Lockheed Martin, and Northrup Grumman could have the RLV-4 lunar lander and its variants ready to be deployed within a 10 meter in diameter SLS payload fairing by the year 2027.

By 2030, future RLV-4 passengers (astronauts and tourist) would simply have to take a Vulcan-Centaur-Dream Chaser or another commercial crew configuration to a commercial orbital habitat at LEO-- such as a commercial SLS derived Dry/Wet Shop mega habitat.  At the orbiting habitat,  passengers would transfer to an RLV-4 that has already docked at the habitat and already refueled at a nearby RLV-4 derived propellant depot or another commercial depot. 

It would take the RLV-4 about four days to transport up to 8 people to another private microgravity  habitat located at NRHO which would serve as a gateway to the lunar surface. There, passengers would transfer to another RLV-4 vehicle that was fueled on the lunar surface at a lunar outpost with enough propellant to transport them to the surface of the Moon in just 12 hours time. Or the RLV-4 that they arrived in could be refueled to transport them to the lunar surface. 

The RLV-4 Crew vehicles located at NRHO  could also utilize the cheap lunar propellant exported to NRHO depots for bi-weekly crewed missions to other areas on the lunar surface-- lasting 6 days-- before returning the the NRHO Gateway.  But if two RLV-4 vehicles are available at an NRHO Gateway, then weekly missions practically anywhere on the lunar surface could be conducted by a group of astronauts on a weekly basis.

Once passengers have completed their stay on the lunar surface, lunar propellant could be used to transport them on a four day trip from the Moon all the way back to LEO where they could take a Dream Chaser back to Earth, landing at any accommodating airport or spaceport in America.  

But as advantageous the RLV-4 would be as a commercial extraterrestrial crew lander, it would be even more economically viable as a lunar cargo vehicle for transporting exceptionally large and heavy SLS LEO launched payloads to the lunar surface. The RLV-4 as a heavy cargo vehicle will be discussed in my next article on the Reusable Landing Vehicle IV
Links and References

 Lunar Lander Vehicle Design Overview

Concept for a Crewed Lunar Lander Operating from the Lunar Orbiting Platform-Gateway

System Architecture Design and Development for a Reusable Lunar Lander

Boeing's Composite Tank Could Greatly Improve Launch Vehicles

 Blue Origin's National Team Lunar Lander


Deploying a Ginormous SLS Derived Dry/Wet Workshop Habitat with a Single SLS Launch

Delta V Calculator


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