ULA claim gap reducing solution via EELV exploration master plan

The United Launch Alliance (ULA) have created an expansive plan to utilize the Atlas and Delta Launch Vehicle families to provide the United States with an architecture that both reduces the gap and provides greater flexibility – when compared to NASA’s current Ares-based plans. ULA’s plans range from Low Earth Orbit (LEO) access, to the ability to cater for NASA’s most ambitious lunar base plan.

Background/Human Rating:

Several papers (see bottom of article for download link) - due to be presented at an upcoming American Institute of Aeronautics and Astronautics (AIAA)/Space 2009 conference – outline ULA’s ambitious plans to not only provide US manned access to Low Earth Orbit (LEO), but also create an exploration plan, one which includes fuel depots and lunar landing craft.

Addressing several key items that resulted in the EELV family missing out as the preferred architecture during the creation of the ESAS (Exploration Systems Architecture Study), the papers claim the EELV systems hold compliance to Human Rating requirements defined by NASA Standard, boosted by a flight rate that quickly builds sufficient history to rely on flight demonstrated reliability.

“NASA embraced these designs by selecting the Atlas V and Delta IV to launch the crewed Orbital Space Plane (OSP) due to their robust, flexible designs, the reliability (calculated and demonstrated) and the confidence in these launch vehicles resulting from their evolutionary development approach, which minimized the historical first flight risk,” opens one of the papers.

“These systems offer the key to significantly reducing the Gap in US Human Spaceflight by providing flight proven launch systems that offer the benefits of early Initial Launch Capability (ILC), lowest nonrecurring and recurring costs, and demonstrated reliability that meets or exceeds NASA Loss of Mission requirements.

“With the addition of a robust launch abort system, we believe both Atlas and Delta can exceed stringent NASA Loss of Crew requirements. Both launch vehicles offer unique advantages for a commercial crew development program, or for the launch of the Orion Crew Exploration Vehicle.”

Playing to the key strength of flight history, the paper emphasizes the key difference between the current forward plan of Ares, and its Shuttle Derived Heavy Lift Launch Vehicle alternatives.

“Existing launch vehicles offer a number of benefits, most notably the demonstrated reliability offered by continuing uncrewed launches during on-going operations,” the paper continues. “This is evident in the significant reduction in the historical infant mortality rate of new launch vehicles. Design flaws manifest themselves in early flights, which is minimized by the evolutionary design approach demonstrated by Atlas and Delta.

“This means that with a common fleet of launch vehicles, the uncrewed missions bear the first flight risk, thus significantly reducing the risk for crewed missions.

“This illustrates the demonstrated reliability benefits of a common fleet of launch vehicles. Additionally, by 2015, the current Ares/Orion ILC, Delta IV will have flown over 50 Common Booster Cores, including 8 Delta IV-Heavy vehicles. Atlas V will have flown nearly 65 times.”

Citing the basis of their confidence on safety, the paper expands on the three primary factors of Human Rating a vehicle – specifically launch vehicle reliability, the addition of an Emergency Detection System, and intact abort capability.

“The combination of these three elements provides a common-sense, system-level approach to accomplish the goal of safe, reliable transportation to LEO.”

For EELV HR references:
http://www.nasaspaceflight.com/2009/04/study-eelv-capable-orion-role-griffin-claims-alternatives-fiction/
http://www.nasaspaceflight.com/2007/01/human-rated-atlas-v-for-bigelow-space-station-details-emerge/
http://www.nasaspaceflight.com/2007/04/spacedev-announce-dream-chaser-agreement-with-ula-atlas-v/

Gap Reduction:

Currently, Orion won’t be launched on its debut flight (IOC – Initial Operating Capability) via Ares I until March, 2015 – at the very earliest, due to a low confidence level. Another year will pass before Orion 4′s (FOC – Full Operating Capability) flight to the International Space Station (ISS).

ULA13This “gap” between the previously scheduled 2010 retirement of the shuttle and Orion’s working schedule is one of the key concerns facing NASA, and indeed at the Augustine Committee’s review into the future of the US’ Human Space Flight plans.

An argument often made relates to changing course after several years of Ares development and several billion dollars of expenditure. More so, it has been argued that moving to a different launch vehicle architecture now would actually increase the gap between the shutte’s retirement – now likely in 2011 – and the operational capability of its successor.

ULA counter this, claiming they have a proven history of being able to refine their family of vehicles for manned flight in a timescale that would result in Atlas V being ready to launch Orion in less than four years.

“Atlas and Delta have a long history of successful launch vehicle development and launch pad activation. ULA has built on that experience by developing a detailed plan and schedule to provide crew launch services for NASA and commercial providers. Based on our understanding of the requirements, we believe that that an Atlas V can be ready for commercial Human Spaceflight in less than 4 years and that the Delta IV-Heavy can be ready to launch Orion in 4-1/2 years.

“These schedules are consistent with the US experience during the Mercury-Atlas and Gemini-Titan Program experience, both of which flew the first manned mission within 4 years of the selection of the launch vehicle.”

Outlining the elements of their current ground and launch systems for the purpose of conforming to the Human Rating requirements, the paper cites the need for modifications to be carried out at the launch site, plus redundancy/safety upgrades, and the inclusion of an Emergency Detection System (EDS).

“We anticipate that this system will be similar for either Atlas or Delta, and will use the recent Atlas V Fault Tolerant Inertial Navigation Unit (FTINU) as the point of departure for design and development,” the paper added on the specific note on the EDS.

“The FTINU was developed in less than 3 years and was launched on an Atlas 551 for the NASA Pluto New Horizon mission in 2006. With EELV vehicle subsystem highly characterized, and with added flights-of-opportunity to check out the EDS (without its LAS) EELV has lowered schedule, technical, and cost risk for EDS development.”

All of which factors in to the EELV’s Loss of Mission (LOM)/Loss of Crew (LOC) ratings, which range from the Atlas V 401′s rating of 1/250 for a LOM and 1/2500 for LOC, to the Delta IV-Heavy’s 1/80 LOM and 1/800 for LOC, although the table notes that all the values represent 50 percent confidence level – in part due to Delta IV’s lack of flights.

“System reliability was one of the most important design considerations for the EELV systems, Atlas V and Delta IV. It was one of only four critical performance parameters specified by the Operational Requirements Document (ORD),” added the paper on the LOM and LOC values. “As such, a tremendous amount of effort was expended to develop credible reliability estimates to prove that the requirements were met.

“Probabilistic Risk Assessment (PRA) type analysis was used to determine so-called design reliability. But mission reliability, what the program called the true reliability, was calculated by applying a Bayesian update to incorporate actual flight experience of similar systems or subsystems.

“This approach was arrived at through lengthy technical interchanges between the EELV contractors and the Aerospace Corporation, representing the Air Force customer. The results of the analysis (are based) with the associated LOC numbers assuming the probability of a failed abort is 1/10.”

For CxP Gap References:
http://www.nasaspaceflight.com/news/constellation/

Atlas V vs Delta IV Human Rating:

With the paper continuing by citing the attributes of both the Atlas V and Delta IVs on preference for which vehicle would be best to Human Rate.

Atlas AV-018 PAN launch, September 8, 2009, 5:35PM Eastern timeAtlas V has numerous benefits, not least due to the minimal modifications the vehicle would require to launch humans into space, with only ground support and the addition of a EDS required.

“The Atlas V 401 and 402 vehicles are well suited for commercial human spaceflight. They are simple, low cost, reliable systems with a long successful heritage. They use two flight proven propulsion systems (RD-180 & RL-10), with only two engine starts, and two separation events.

“They have benign, well characterized environments, robust margins, and high demonstrated reliability (100% for the 401) and design reliability (.9960 for the 401 and .9942 for a 402). Atlas 401 and 402 can provide up to approximately 27,500lbs of performance to LEO, depending on the specific configuration of the crew vehicle.

“Trajectories can easily be shaped to eliminate ‘Black Zones’ with no appreciable impact to performance. (‘Black Zones’ are defined as any period of flight when an abort would result in unsafe landing conditions if: 1) the aborting capsule falls into hostile terrain; or 2) High-g loads occur during a reentry.

“Atlas V can accommodate commercial human spaceflight with no changes to the existing vehicles. The only enhancements will be the addition of the Emergency Detection System and changes to the Mobile Launch Platform to allow crew ingress and egress. Once a particular crew vehicle is selected, Atlas V will conduct a series of analyses and system testing to integrate vehicle on a 401 or 402. These include Hazard Analyses, Design Margin Analyses and Mission Unique Analyses specific for the Crew vehicle configuration.

“In addition, we may conduct wind tunnel tests and subsequent aerodynamics and loads analyses to ensure that we maintain our existing vehicle margins. The Atlas V 4XX offers the lowest risk, lowest cost solution for commercial crew.

“The demonstrated reliability record and robust vehicle design allows Atlas the flexibility to meet the needs of a variety of commercial crew vehicles currently being contemplated and designed.”

ULA12Delta IV-H wins on performance, with over 4 metric ton of margin for both ISS and Lunar Orion delivery, even after taking into account the elimination of black zones – often cited by Constellation as one of EELV’s main flaws in being able to Human Rate.

“The Delta IV has ample performance margin. For the ISS crew mission, based on current Orion weight allocations, the Delta IV Heavy has 4.8t of margin for lifting the Orion capsule to the ISS delivery orbit. This drops to 4.3t of margin for the Lunar Crew delivery mission. These 20 percent margins are very healthy, especially given that Orion would be flying on a demonstrated launch vehicle.

“These margins are after depressing the trajectories to close all Black Zones. (Performance margins would have been ~1t higher if this had not been done.) These performance margins are so big that they can cover almost any conceivable human rating penalty, or combination of penalties, including a 1.40 safety factor, and significant RL-10 derating.

“NASA has now acknowledged that they believe that the Delta IV Heavy has adequate performance margin and no Black Zones. This should refocus any questions about EELV compatibility onto human rating, reliability, and schedule.

“The human rated Delta IV Heavy fundamentally is the same Delta IV vehicle that has flown successfully three times, and is expected to fly 10 times by the projected mid 2014 IOC date. (32 total Delta IV CBC booster elements are projected to have flown by this same date.). This is a huge benefit from a crew safety standpoint.

“Though there are many measures of reliability, demonstrated reliability is the least subjective measure. Even with an analytic reliability which is higher, the EELVs cumulative launch total before the 2014 IOC, and additional accumulation of launches including DoD, means that the Ares 1 or another new vehicle might effectively never catch up with Delta’s demonstrated reliability.”

However, more work is required on this vehicle when it comes to modifications in order to provide the necessary Human Rating safety additions – which would also need to satisfy the Delta IV’s main customer at present, the Department Of Defense (DOD).

“Delta IV vehicle changes include removal of the fairing, and replacement with the Orion System, including service module and launch abort system and adapters. The Emergency Detection System will be incorporated into the launcher. An array of relatively small redundancy and safety modifications have been identified based on NASA requirements, but these remain modest in scope compared to the legacy design.

“We anticipate these upgrades to be acceptable to the DoD customers, and expect these to be incorporated fleetwide with no need for a unique NASA vehicle design apart from the EDS kit. Currently 1.40 safety factor has been removed from NASA requirements, though a return to this requirement driving some regauging and requalification could be accommodated within the same proposed schedule.”

Numerous upgrades and modifications are listed, but also with cited uncertainty as to how many of the modifications would be required.

“The details of redundancy upgrades on Delta remain an area of interest. Of note is that quite a few of the requirements are not driven by explicit redundancy requirements, but on other anticipated safety criteria as the desire to reduce the release of burning H2 at RS-68 start,” added the paper.

“Also, in some cases different redundancy upgrades (RS-68 backup valves, feedline prevalves, and hydraulics redundancy) need to be traded off to find the smartest implementation path. This makes the final suite of upgrades somewhat uncertain. However, the anticipated total scope and cost of these safety upgrades is programmatically small, with engine mods the most expensive due to high intrinsic recertification cost.

“Generally speaking, schedule impacts on IOC (effecting the US human spaceflight “gap”) is a more significant consideration.”

One interesting line near the end of the “Atlas and Delta Capabilities to Launch Crew to Low Earth Orbit” paper is a reference to both vehicles being used to launch humans into space.

“Though we assume Orion on Delta IV, and commercial crew capsules on Atlas, the difference in human rating is intrinsic to the launch vehicles, and not to assumed differences in human rating requirements.”

In summary, the “winner” of becoming a Human Rated launcher between the Atlas V and the Delta IV comes down to a question of schedule, risk numbers and performance.

“The EELVs are ready to support crew lift with flight proven vehicles that will have an even longer legacy of flights by the crewed IOC date with superior demonstrated reliability compared to any new system. Our schedules are grounded by ULA’s unmatched legacy of vehicle development and modifications programs and launch pad developments,” the paper summarizes.

“The Atlas V, with the relatively minor addition of an Emergency Detection System and a dedicated NASA Vertical Integration Facility (VIF) and Mobile Launch Platform (MLP), is ready for commercial human spaceflight and complies with NASA human rating standards. The 3 1/2 year integration span is likely shorter than the development for any new commercial capsule that might fly on it.

“The Delta IV has ample performance to support the existing Orion vehicle, without Black Zones. The Delta IV can support a mid-2014 Crewed IOC, which is superior to Orion launch alternatives. The proposed 37A pad is a look-alike counterpart to the existing 37B pad with low development risk.

“Human rating the Delta is a relatively modest activity, with the addition of an Emergency Detection System, an array of relatively small redundancy and safety upgrades, both in the vehicle and the engines that are minor compared to the original development of the Delta IV.”

An architecture complimented by fuel depots:

ULA are proposing a change of direction that is unmatched by the other alternative architectures, combining the use of vehicles that are already flying, with an on orbit ability to refuel in space via fuel depots.

ULA6As a result, one of the greatest challenges vehicles face – the need to launch with all the propellant they intend to use on orbit – can be staged in space.

“The present ESAS architecture for lunar exploration is dependent on a large launcher. It has been assumed that either the ARES V or something similar, such as the proposed Jupiter ‘Direct’ lifters are mandatory for serious lunar exploration,” another associated paper opened.

“These launch vehicles require extensive development with costs ranging into the tens of billions of dollars and with first flight likely most of a decade away. In the end they will mimic the Saturn V programmatically: a single-purpose lifter with a single user who must bear all costs. This programmatic structure has not been shown to be effective in the long term. It is characterized by low demonstrated reliability, ballooning costs and a glacial pace of improvements.

“The use of smaller, commercial launchers coupled with orbital depots eliminates the need for a large launch vehicle. Much is made of the need for more launches – this is perceived as a detriment. However since 75 percent of all the mass lifted to low earth orbit is merely propellant with no intrinsic value it represents the optimal cargo for low-cost, strictly commercial launch operations.

“These commercial launch vehicles, lifting a simple payload to a repeatable location, can be operated on regular, predictable schedules. Relieved of the burden of hauling propellants, the mass of the Altair and Orion vehicles for a lunar mission is very small and can also be easily carried on existing launch vehicles. This strategy leads to high infrastructure utilization, economic production rates, high demonstrated reliability and the lowest possible costs.

“This architecture encourages the exploration of the moon to be conducted not in single, disconnected missions, but in a continuous process which builds orbital and surface resources year by year. The architecture and vehicles themselves are directly applicable to Near Earth Object and Mars exploration and the establishment of a functioning depot at earth-moon L2 provides a gateway for future high-mass spacecraft venturing to the rest of the solar system.”

ULA provide a “Proposed Architecture Concept of Operations” in the paper, which shows a logistics stream and a crew stream feeding off depots, including one at L2 (Lagrange point). However, the paper notes that “the architecture is illustrated using ULA vehicle concepts for convenience. In reality, no single industrial entity can entirely support this architecture.

“The production and launch rates are simply not sustainable by a single team. It must be a concerted effort of several launch providers, perhaps a consortium linking industry and NASA.”

ULA7The backbone of the architecture is the ACES (Advanced Common Evolved Stage), which is currently being developed by ULA, and expected to replace the three existing cryogenic upper stages presently being used.

“Containing 41 mT of liquid hydrogen and liquid oxygen it is powered by four RL10 class engines. ACES builds on over 200 flights of Centaur and Delta, fusing technologies from both programs: sharing the Delta IV 200” tank diameter but with a common/nested intermediate bulkhead. ACES uses tank geometry, low conductivity tank structures, passive thermal protection and vapor cooling to suppress cryogenic propellant loss to boiloff,” noted the paper.

“Since it is wholly protected from aeroloads during launch a thick MLI blanket surrounds every exposed surface – drastically reducing external heating. ACES has no helium or hydrazine systems- all pressurization, attitude control and power is generated by consuming its two main propellants. Most importantly ACES is designed to be refilled with propellants once in space.”

The 41 mT ACES propellant capacity is sized for usage with DoD, NASA science and commercial payloads. Because ACES sub-systems are concentrated on an aft mounted equipment deck the propellant capacity can be readily modified through changes in tank side wall length.

However, thanks to the use of propellant depots lunar exploration can efficiently be accommodated with as few as two tank volumes, the basic 41 mT. ULA provide an outline of Orion riding with ACES, Altair with ACES and the ACES tanker.

“In the Orion Service Module configuration, an ACES 41 is mated to an ECLSS module and the Orion Command Module. ACES provides its own power and that for Orion by consuming its ullage gases. Solar arrays and dedicated radiators are unneeded – ACES provides these services,” the paper adds.

“Attitude control is provided by ACES working in concert with the Orion RCS (Reaction Control System). The Orion-peculiar services such as N2 replenish , CO2 scrubbing and voice communications are provided by the ECLSS module.

“In the Altair configuration, ACES 41 is mated to a Lunar Cargo Module or the Crew Ascender as well as multiple 1,000 pound thrust lateral-facing engines and landing gear for the final hover and landing phases.

ULA8“In its simplest and most common configuration the ACES tanks are stretched so that they contain 71 tons of propellants. This ACES 71 vehicle has no payload attached and uses the very simplest of payload fairings. Its principle purpose is to deposit or remove propellants from a depot. The ACES tanker is capable of supporting propellants that are subcooled.

“Subcooling of the LH2 and LO2 allows propellants to absorb heat while stored in LEO without saturation pressures rising excessively. This permits extended storage times in high heating conditions without suffering excessive mass losses.”

The result of this multi-use of the ACES system is the ability to create the fuel depots in space, which is an idea that was heavily supported by the Augustine Review panel.

“The ACES depot is an ACES 41 mated to a modified ACES 71 Tanker. The tanker has a shifted intermediate bulkhead to maximize LH2 storage. The main engines have been removed and a high performance deployable sunshield installed. The LH2 storage element is launched empty as a payload on an Atlas 554 or Delta IV HLV,” the paper continues.

“Because it is not filled with cryogenic propellants on the ground it can dispense with external conductive insulation such as foam. Its thermal protection is strictly optimized for vacuum operations. The depot provides the multiple interfaces for transferring propellants to and from the docked vehicles and can supply power and support services to those vehicles for extended periods.

“Multiple Orion, Altair and tanker vehicles can be simultaneously docked. The proposed architecture relies on two depots – one in LEO and the other at L2.

“Being an empty shell the depot is extremely light, weighing approximately 12 mT. Launched on a Delta HLV results in nearly 20t of residual propellant remaining in the ACES 41 upper stage. Once in LEO, the ACES-41 residual LH2 is transferred into the LH2 depot tank. The ACES-41 LO2 residuals are then transferred to the now empty ACES-41 LH2 tank, after the tank has been evacuated of any residual H2.”

Other solutions are noted, such as a passive Thermal Protection System (TPS) for the depot in Low Earth Orbit (LEO), to protect against propellant boiloff, whereas the far lower heating rate for the depot at L2 can establish near-zero boiloff losses – amounting to a few pounds per day which also nearly matches the minimal station keeping requirements at the quasi stable L2.

A dedicated paper further outlines the depot plan, and available options for alternative paths.

Lunar Exploration:

With the combination of the EELV heavy lift options and the fuel depots en route, the proposed path to returning to the moon involves the ACES/Altair duo being launched on a Delta IV HLV booster with ACES/Altair replacing the Delta IV upper stage providing a total LEO lift mass of 36t.

ULA10“Refueled from the LEO depot the ACES/Altair can deliver in excess of 30 tons of combined cargo and vehicle mass to L2,” notes the paper. “Generally however it arrives at L2 with substantial propellant residual. If the Altair is intended to be cached at L2 for future crew use it deposits its propellants into the depot for efficient long term storage.”

The result of using depots at LEO and L2 would allow for 20mt and a crew of four astronauts to be landed on the lunar surface.

“The ACES/Altair is loaded or topped from the L2 depot just prior to lunar descent. This includes the loading of the Ascender propellant tanks which are used during the terminal hover/landing phase. Fully loaded, it can deliver a combined mass of vehicles (such as the ascender), cargo and unused propellants greater than 40t to the lunar surface.

“The ACES tanks on the landed descenders are used for cryogenic propellant storage on the lunar surface and just as at L2 they gradually build their stores. The cycle of power generation would be established with fuel cells active during the lunar night and solar systems during the day. The conversion of water to the reactants and back in rhythm with the lunar day would be established.

“The support of a substantial crew on the lunar surface requires the storage, handling and transport of industrial quantities of reactants, water, sewage, nitrogen, scrubbed CO2, etc. The landed descenders each have substantial capacity to support the storage and processing of these materials and with each landing the ACES tanks are added to this lunar base tank farm.

“The ability to close the local ecosystem would gradually increase with a subsequent reduction in lost mass. Transfer of fluids between tanks is enabled by the ability to move the ACES/Altair after landing. It can be driven or towed to be adjacent to other landed vehicles so their systems can be joined.”

The paper outlines each of the paths required to launch the crew, pass them through the depots – including transportation to L2 – to the lunar surface and subsequent return to Earth. It also provides a roadmap for the move to the ACES system.

“ACES first flight would occur with either a commercial or DoD payload nearly five years before the first crewed flight to the moon. The final six crew flights to ISS would be conducted using ACES and the Orion capsule. To demonstrate the lunar lander as quickly as possible a robotic lander mission is included in 2016 with a direct lunar descent.

ULA9“Initial crewed landing would occur in 2018. Either a single crewed mission per year coupled with 20mT of cargo or two crewed missions per year can be supported within the anticipated budgets. The assumed cost of transport to LEO ranged from 9.2 to 10.2 $M/mT depending on launch vehicle. This scenario also assumes the cost of flights to the ISS are included at a rate of 2/year commencing in 2013.”

Expanding on costs, one graph lays out the funding requirements for as far downstream as 2024.

Four to five billion a year would cover the costs of development and operation through to 2017 – which includes lunar systems (which the current Constellation Program has been struggling to find monies for) – before rising to seven billion per year from 2020 to 2024.

Lunar Lander – DTAL:

At the center of the lunar landing plan is the DTAL – or Dual Thrust Axis Lander. The vehicle – which lands horizontally, uses an RL10 engine to accomplish the descent deceleration to just above the lunar surface. Final landing is accomplished using thrusters mounted along the DTAL body. ULA claim this configuration places the crew and payloads safely and conveniently close to the lunar surface.

“ULA’s Centaur and Delta IV upper stages provide an excellent cryogenic propulsion framework for developing a reliable, mass efficient lunar lander.

“Initial DTAL-enabled large robotic missions allow NASA to return to the moon quickly and demonstrate hardware to be used by crews that follow. This same mission design supports placement of large lunar base elements (habitats, power plants, rovers, excavation equipment, etc),” the paper on the DTAL notes.

“As the uncrewed missions are completed, and the system matures, astronauts will then use the same, now proven system to access the lunar surface.

ULA3“The reliable DTAL propulsion stage provides the flexibility to visit destinations other than the moon. DTAL’s mass and thermal efficient design provides the capability to visit NEO’s or possibly even Mars. By supplying the life support consumables with O2 and H2 from the large primary propellant tanks long duration missions are possible.”

The DTAL looks completely different to the current Altair design that NASA are working on – although the Constellation Program have noted Altair is likely to change in design as it matures. Interestingly, it’s that very design of Altair that reduces crew safety during their expeditions on to the lunar surface.

“Even with the multi-tank, imbedded engine design, Altair results in the crew and cargo being over 6 m above the lunar surface. This configuration results in increased risks to the crew who must regularly access the lunar surface from the equivalent of a three story building.

“There is the potential added risk of the crew being required to work under suspended loads during cargo off-loading. For the dedicated cargo missions, the Altair design requires dedicated cranes or a building sized ATHLETE, JPL’s lunar rover, to support habitat and other large cargo transfer to the lunar surface.”

The horizontal design of the DTAL places the crew near the surface, with the descent engines mounted on the side – as opposed to the bottom – of the vehicle. Design images even show wheels on the bottom of the DTAL.

“The Dual Thrust Axis Lander (DTAL) provides another solution that addresses the conflicting requirements of descent and landing while keeping the lander intact all the way to the surface. Like the DASH concept (from the Langley Flight Research Center), DTAL utilizes efficient LO2/LH2 propulsion for descent, but transitions to small engines mounted along the stage allowing horizontal landing.

ULA2“The use of high side-mounted thrusters for terminal descent and landing provides the pilot with a clear view of the surface, unobscured by entrained regolith, easing DTAL’s ability to adjust touchdown to ground terrain.

“DTAL uses the RL10 to perform most of the descent burn and then rotates until its long axis is parallel to the ground. At about 6,000 feet above the lunar surface DTAL transitions to the lateral thrusters, turning off the RL10. The lateral thrusters, which are aligned perpendicular from the RL10, support the final descent and terminal landing.

“The small, responsive lateral thrusters allow precision control of the descent and translation rates. DTAL will build on ULA’s existing propellant slosh – vehicle dynamic control logic experience to ensure that induced slosh does not adversely couple with flight control system.”

The variants of the DTALs are based around crewed and robotic missions. Initially, robotic missions (DTAL-R) would be launched, allowing for precursor flights and the ability to prove reliability.

“Commonality between DTAL-Crew, DTAL-R and ACES provide a large number of flights prior to the first crew mission will ensuring that the propulsion system design is sound,” the paper added.

“Exploration of the moon benefits from combining robotic and crewed missions. Exploratory robotic science missions provide the early, initial inspection of new locations, and enable investigation of a greater number of locations than would otherwise be possible.

“Subsequent larger robotic missions enable much deeper understanding and prepare for larger cargo missions deploying habitats, rovers, power systems and other elements required to support human life beyond Earth. Once people are habitually living and working on the moon, robotic cargo missions will provide the supply chain to support their daily needs.”

The proposed DTAL-R lander would be utilized for the “larger” missions, capable of landing over 15 mT of payload depending on exploration architecture. DTAL-R provides the lunar surface access for large, oversized payloads that would be required for setting up a lunar outpost – another casualty of the current Constellation funding issues that was identified by the Augustine Review.

See here for NASA’s Altair Lander:
http://www.nasaspaceflight.com/2008/02/altair-project-buying-into-orion-lessons-for-development-process/

This is where the widely spaced landing gear comes into play, providing DTAL with stability even on rough or uneven terrain. This horizontal configuration results in the cargo-hold resting just a meter above the lunar surface, providing surface obstacle clearance for all proposed landing sites.

“Multiple 3m long rovers could disembark from DTAL-Rs cavernous 5m diameter cargo hold. DTAL-R’s 5 m cargo hold and lunar performance are capable of supporting all of NASA’s planned lunar surface systems, including hard shell and inflatable habitats, crewed rovers, ATHLETE, in-situ resource plants, lunar telescopes, or large drilling rigs. Egress is a simple matter of descending a shallow ramp to the surface.”

ULA4This increased ability to place large payloads on the lunar surface supports the most ambitious lunar base plans NASA has previously spoken of.

“DTAL-R can support NASA’s most massive current lunar surface system (LSS) elements including the 9.6 mT Fission Surface Power System (FSPS),” the paper claims. “NASA’s current plan calls for the surface elements to be launched horizontally on Altair’s large diameter deck inside a 10 m shroud.

“With DTAL-R, most of these elements would be launched axially and land horizontally on the lunar surface for easy egress. DTAL’s slim 5 m diameter design is compatible with existing EELV payload fairings as well as side-mounted and in-line shuttle derived launch vehicles.

“At this early stage in the surface element designs, potential design modifications for vertical launch are not anticipated to be challenging. The Lunar Electric Rover (formerly the Small Pressurized Rover) with its 5m length is an example of a system that would have to be packaged vertically on DTAL-R, similar to the rovers.

“JPL’s ATHLETE can be folded for flight and stowed in whatever orientation is most convenient for packaging with other LSS elements.

“The heaviest pressurized habitat module is currently estimated to be just under 8 mT. DTAL-R’s performance capability allows NASA to grow the habitats capability, or co-manifest habitats with other LSS elements. For human presence beyond Earth to be sustainable, we must eventually learn to ‘live off the land’.

“In-Situ-Resource-Utilization (ISRU) takes advantage of local material to derive useful products. Oxygen production from lunar regolith may well be one of the first ISRU steps toward a sustainable human presence.”

Again, safety and reliability are referenced in the paper, citing the four RL10 engine configuration that ensures that the vehicle will survive and continue the mission even with multiple engine failures. The paper also claims the DTAL (Crew) ascent module “is placed far forward with a clean, unencumbered separation plane allowing for full flight abort capability.

“The clean separation plane and gimbaled lateral thrusters ensure that the ascent module can separate from the descent vehicle even under severe spin conditions and through all phases of descent.”

Also, the pilots are placed at the front of the DTAL, allowing them a downward facing, panoramic window viewpoint for a clear view of the landing terrain. The high mounted distributed lateral thrusters also minimize surface dust entrainment, maximizing pilot visibility throughout the descent and landing.

ULA5Departing from the surface of the moon involves the DTAL’s “Ascender” – which separates from the front of the DTAL, rising back up into the lunar orbit.

“To return to lunar orbit after the surface mission the Ascender propellant tanks are brought to pressure. With the Descender stage systems stowed and umbilicals retracted the Ascender thrusters are brought to 30 percent power to achieve positive upload at the Descender/Ascender separation interface. Commanding separation, the Ascender then ramps up thrust, departing the lunar surface and descent vehicle at a steep angle.

“With this benign separation orientation the Ascender does not directly blast the spent descent stage with its engine plume allowing the descent stage to be preserved without damage for potential future use.”

Future use is also central to an option of creating habitable volume from the DTAL’s LH2 tank, in additional to the volume already allocated at the forward section of the craft.

“Converting DTAL’s tank for living space once on the lunar surface offers a mass ‘free’ habitat: This very large volume compares very favorably to habitable volumes provided by ISS, Altair, Orion, proposed lunar habitat volumes, LaRC’s proposed DASH lander or even Bigelow’s planned Sun Dancer module.

“The conversion of the LH2 tank support crew quarters provides an attractive option for the start or addition to a lunar base.

“The forward, ‘payload’ habitat node includes the entire infrastructure to support people, environmental control and life support system (ECLSS), bathrooms, showers, galley, etc. fully integrated on Earth. A tunnel leading aft to the DTAL LH2 tank would open up a lot of extra habitable volume once on the lunar surface.

“Prior to opening the node-tank connecting tunnel, the H2 tank would be vented to evacuate any residual H2 and allowed to warm up to room temperature and filled with air.”

The associated papers are being published on ULA’s site here:
 http://www.ulalaunch.com/index_published.html

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