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