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AbstractThere are several emerging technologies with potential to completely change theapproach and key participants in future Space Exploration endeavors. Such technologiesinclude a Cost-Optimized, Heavy-Lift, Launch System (COHLLS), several types of InSitu Resource Utilization (ISRU), Solar Electric Propulsion (SEP) Reusable Tugs, andhigh strength carbon nanotube (CNT) cables. In this paper each disruptive technologywill be characterized, an example exploration scenario utilizing each developed, and thecost and operating advantages relative to use of previously exposed explorationapproaches delineated. These results will show that disruptive technologies are apowerful catalyst to commercial development of space and can reduce the cost ofNASA’s Baseline Exploration Program by about a factor of two.
IntroductionThe United States is embarking on a program to establish a base on the moon as aprecursor to a similar base on Mars. We, at Andrews Space, have espoused anexploration architecture we call “Mars Through The Moon”, where you determine themost effective approach to explore Mars and then demonstrate the key technologies andtransportation elements to be used at Mars during the Lunar Exploration Program (LEP).This reduces the cost and risk of the Mars Exploration Program (MEP), and successfuluse of these elements on the moon demonstrates that you are ready to move on the Mars(i.e. provides the lunar exit strategy). In this context, disruptive technologies aretechnologies that cause the Mars exploration paradigm to shift, and introduce newfeatures and benefits not available with the old MEP. Our goal in this paper is tointroduce the current NASA MEP, and then show there are better, cheaper, and saferapproaches if we embrace some disruptive technologies such as those described below.Using the Mars Through The Moon approach, the first step in defining the LEP is todetermine how to we should optimally explore Mars.
Reference Mars Exploration Program - The NASA Mars Exploration DesignReference Mission (DRM) is very similar to that shown in figures 1 and 2 below1. ThisDRM is a variant of Mars Direct first proposed by Zubrin and Baker2. We have updatedthis DRM to meet the Level 1 requirements from the Constellation Exploration Office,which requires human exploration in the vicinity of Mars (Spiral 4), followed by humanexploration of Mars (Spiral 5). As it turns out, the Mars Exploration Program is beingreorganized as this paper is being written and the new Exploration plan will not beavailable until after this paper is published, so we chose to abbreviate the human lunarexploration program using robotic lunar explorers to reduce program cost and schedulerisk, and start Human Mars Exploration early on the 2020 launch opportunity, because it
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is nearly optimal (Mars is near periapsis at arrival). Since Mars surface exploration willbe robotic during the first five years, we can demonstrate Mars elements on the moonbetween 2015 and 2020 while we demonstrate the Phobos habitat in LEO.
Figure 1. NASA Mars Exploration Design Reference Mission (DRM) circa 1998
Figure 2. Mass Breakdown for 1998 Mars Exploration DRM
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Therefore, the first human mission to Mars orbit occurs in 2020 and for the NASA DRMit would consist of two aeroshell payload packages; one containing a transit habitat (withcrew) plus a CEV and TEI stage, and the other a Mars Lander carrying three MarsExploration Rovers, a nuclear powerplant to regenerate the rover’s fuel cell reactants , anascent stage with sample carrier, and a teleoperated utility crawler with constructionattachments and navigation aids to prepare a site for the permanent Mars base which willarrive 26 months later.
The aeroshell containing the crew would probably be launched into a free returntrajectory, where the crew has the option of doing a Mars flyby without stopping andreturning to earth about 900 days later (This allows a safe abort if a problem developswith the aeroshell or the TEI stage during the outbound leg). If the aerocapture goes asplanned the crew elements will be inserted into a 250 km by 33793 km orbit that issynchronous with the permanent base site to give daily rendezvous opportunities. Duringtheir stay in Mars orbit the crew would teleoperate the utility crawler to prepare a basesite and the three Rovers to explore Mars for indigenous life and collect potentialbiological samples. Halfway through the mission the Rovers would transfer samples tothe ascent stage, which would deliver them to the orbiting habitat for human analysis.This avoids human DNA contaminating the samples before they were collected.Following the NASA DRM, this first crew departs Mars orbit on 31 July 2022 and arrivesback on earth after a 922-day total mission.The second Mars crew departs Earth on 7 September 2022 and arrives at Mars on 7 April2023, where the aeroshell containing the crew, CEV, TEI stage, and habitat aerocapturesinto the same synchronous orbit. Two cargo aeroshells to support their mission wouldleave Earth on 14 September 2022 and arrive on Mars 22 October 2023, some 6 ½months after the crew arrives. Hence, the crew must continue the teleoperated roverexploration until their equipment arrives. The first cargo payload is an aeroshell with alander carrying an ascent stage with liquid hydrogen and an ISRU Unit. After landing itwill deploy a small nuclear powerplant and convert CO2 out of the atmosphere into LOXand LCH4 using a Sabatier reactor and an electrolysis unit. This process uses hydrogen asfeedstock with additional LOX coming from direct reduction of CO2 to CO. The secondpayload is an aeroshell with a lander carrying the Mars habitat module and constructionsupplies.The third crew departs Earth 18 October 2024 and arrives at Mars on 19 May 2025,where the aeroshell containing the crew, CEV, TEI stage, and habitat aerocaptures intothe familiar synchronous orbit. Two cargo aeroshells to support their mission would leaveEarth on 5 October 2024 and arrive on Mars 15 September 2025, only 4 months after thecrew arrives. The first cargo consists of an aeroshell with a lander which first aerocaptureinto a rendezvous orbit with the transit habitat and then descend to Mars carrying thecrew and a fully fueled ascent stage (to make safe abort possible). The second cargo is anaeroshell with a lander carrying two long-range pressurized rovers, an inflatablepressurized garage for the rovers, and equipment to build a closed ECLSS attached to thebase. The mass breakdown for each payload package in the DRM is shown in Table1.After the first human landing we assume the Mars exploration goes into a sustainingmode where six crew and 30 tonnes of cargo are delivered to Mars at each launchopportunity.
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There are several improvements which could be made to this DRM. First of all, spendingthe entire 900+ days with marginal protection against solar flares and almost noprotection against Galactic Cosmic Radiation (GCR) is asking the crew to acceptsubstantial risk against their future health. Secondly, if a serious penetration or fireshould occur in the transit habitat while in the vicinity of Mars, there are few if anyoptions available for safe haven and future rescue. Finally, in Mars Direct, the crew landswith an empty ascent stage and hence no way to abort a failed entry and landing. Thisadds significant risk and there are safer, lower cost DRM options available.
Mars Aerocapture Heat Shield, t 9.00 Mars Aerocapture Heat Shield, t 9.00 Mars Aerocapture Heat Shield, t 9.00Transit Habitat, t 23.5 Transit Habitat, t 23.5 Transit Habitat, t 23.5CEV for Earth return, t 8 CEV for Earth return, t 8 CEV for Earth return, t 8Cruise Bus/Utilities, t 3.00 Cruise Bus/Utilities, t 3.00 Cruise Bus/Utilities Module, t 3.00Two COMSAT for Mars Orbit, t 4.40TEI Stage (LOX/LH2), t 5.32 TEI Stage (LOX/LH2), t 5.32 TEI Stage (LOX/LH2), t 5.32TEI LOX/LH2 Propellants, t 18.95 LOX/LH2 Propellants, t 16.76 LOX/LH2 Propellants, t 15.93TEI Delta Propellants, t 0.00 Delta Propellants, t 0.00 Delta Propellants, t 0.00IMLEO - Crew Payload, t 72.16 IMLEO - Crew Payload 65.58 IMLEO - Crew Payload 64.75
Mars Entry Heat Shield, t 9.00 Mars Aerocapture Heat Shield, t 9.00 Mars Aerocapture Heat Shield, t 9.00Cruise Bus/Utilities, t 3.00 Cruise Bus/Utilities, t 3.00 Cruise Bus/Utilities, t 3.00Mars Samples Module 0.45 Mars Crew Module 5.00 Mars Crew Module 5.00Mars Ascent Stage, t 3.86 Mars Ascent Stage, t 6.36 Mars Ascent Stage, t 6.36LOX/LH2 Propellants, t 10.54 Ascent LOX/LH2 Propellants, t 0.00 LOX/LH2 Propellants, t 27.11Nuclear Powerplant, t 6.00 Delta Propellants, t 0.00 Delta Propellants, t 0.00Utility Crawler w/ Construc Equip,t 17.50 Backup Nuclear Powerplant, t 5.00Exploration Rovers (3), t 9.00 ISRU Plant w/ Storage, t 26.00 Construction Supplies 3.90Mars Lander 6.72 Mars Lander, t 6.72 Mars Lander, t 6.72LOX/LH2 Propellants, t 3.97 LOX/LH2 Propellants, t 3.97 LOX/LH2 Propellants, t 3.97Delta Propellants, t 0.32 Delta Propellants, t -0.47 Delta Propellants, t -2.22IMLEO - Mars Robot Rovers 70.04 IMLEO - Crew RT to Mars Surface 65.05 IMLEO - Crew RT to Mars Surface 65.06
Mars Entry Heat Shield, t 9.00 Mars Entry Heat Shield, t 9.00Cruise Bus/Utilities, t 3.00 Cruise Bus/Utilities, t 3.00Mars Habitat, t 30.00 Mars ECLSS Package 10.00Heavy Construction Equip, t 12.40 Pressurized Rovers (2), t 20.00
Garage for Rovers, t 12.40Mars Lander, t 6.72 Mars Lander 6.72LOX/LH2 Propellants, t 3.97 LOX/LH2 Propellants, t 3.97Delta Propellants, t -0.07 Delta Propellants, t 0.12IMLEO - Mars Surface elements 65.09 IMLEO - Mars Surface Elements 65.09
Cargo 2 (Mars Exploration Elements)
2022 Mission - 200 days outbound & 200 daysinbound
2024 Mission - 219 days outbound and 200days inbound
Cargo 1 (Mars ISRU and Human Backup Elements)
Crew w/ RT Habitat captured into 250 km by 33793 km Orbit
Mars Crew Lander/Ascent Stage
2020 Mission - Free Return Trajectory (Cargoarrive just prior to Aerocapture Maneuver)
Table 1 Mass Breakdown for Reference Mars DRM
Phobos First Exploration Program – Our alternative program would incorporate twodisruptive technologies, (the SEP Tug and ISRU propellant generation on Phobos insteadof Mars), to reduce program LCC and improve crew safety. We call this the Phobos Firstapproach. In Phobos First, two SEP Tugs depart LEO on 10 July 2019, rendezvous with aCEV delivering six crew in High Earth Orbit (HEO) on 1 June 2020, flyby the moon on 6June 2020 and rendezvous with Phobos on 21 February 2021 to establish a human baseand set up the ISRU propellant plant. The tug carrying the crew habitat would power theISRU propellant plant on Phobos, while the tug carrying the Mars lander would drop offthe 50 tonne aeroshell in a parabolic entry orbit, circularize three COMSATs in Marsstationary orbits, and then depart for Earth using a Venus flyby. The aeroshell would landthe same payloads as the reference DRM except for a slightly larger sample carryingascent stage (because it must rendezvous with Phobos). The first Phobos crew departsPhobos on 26 June 2022 using the remaining SEP Tug, and returns to the earth-moon L1point on 12 January 2023.The 2022 and 2024 launch opportunities follow the same pattern except that the landerand ascent stage propellants are loaded after they arrive at Phobos. A small expendableLOX/LH2 stage then de-orbits each aeroshell (using Phobos-generated propellants).
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Except for the ISRU package, the differences between Phobos First and the ReferenceDRM total payloads to the surface of Mars are minor (see table 2). The Phobos FirstISRU package stayed on Phobos, which accounts for the 26 ton difference.
Phobos First Mars Surface Elements Reference Mars Surface Elements2020 Cargo to Surface 2020 Cargo to Surface
Nuclear Powerplant, t 6.00 Nuclear Powerplant, t 6.00Utility Crawler w/ Construc Equip, t 9.18 Utility Crawler w/ Construc Equip,t 17.50Exploration Rovers (3), t 9.00 Exploration Rovers (3), t 9.00
2022 Cargo to Surface 2022 Cargo to SurfaceMars Building Materials, t 3.33 Backup Nuclear Powerplant, t 5.00
ISRU Plant w/ Storage, t 26.00Mars ECLSS Package, t 10.00 Heavy Construction Equip, t 12.40Mars Hab/Lab w/Airlocks, t 30.00 Mars Hab/Lab w, Airlocks, t 30.00
2024 Cargo to Surface 2024 Cargo to SurfacePressurized Rovers (2), t 20.00 Pressurized Rovers (2), t 20.00Construction Supplies 10.97 Construction Supplies 3.90Garage for Rovers, t 12.4 Garage for Rovers, t 12.40Heavy Construction equip 11.93 Mars ECLSS Package 10.00Misc Crew Equip 3.50Total cargo on Mars, t 126.31 Total cargo on Mars, t 152.20
Total IMLEO 2080Mars Direct Architecture (LOX/LH2)SDV launches (90 t) 6 9 9 6 6 6Transit Habitats Produced 1 1 1 1 1 1LOX/LH2 TEI stages Produced 1 1 1 1 1 1LOX/LH2 TMI stages Produced 4 6 6 4 4 4Mars Aeroshells produced 2 3 3 2 2 2Mars CEV Launches (30 t) 1 1 1 1 1 1
Total IMLEO 3750Mars Direct Architecture (NTR)SDV launches (90 t) 4 6 6 4 4 4Transit Habitats Produced 1 1 1 1 1 1LOX/LH2 TEI stages Produced 1 1 1 1 1 1NTR TMI stages Produced 2 3 3 2 2 2Mars Aeroshells produced 2 3 3 2 2 2Mars CEV Launches (30 t) 1 1 1 1 1 1
Total IMLEO 2560Table 3. Launches and Transportation Elements for each DRM
The principal differences between the two DRMs are safety and cost. In Phobos First, thecrew spends 500 days dug into the Mars-facing surface of Phobos, totally protected from
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both solar flares and GCR. In thereference DRM, the crew has a minimalstorm shelter in the habitat and someshadow shielding from the TEI stage forsolar flares, but almost nothing forprotection from GCR.The total number of launches and thetransportation elements required for eachof the candidate Mars ExplorationArchitectures is shown in table 3 above.The high specific impulse available tothe baseline Phobos First architecturemore than makes up for the ∆Vadvantages of the high thrust systemsused in Mars Direct DRMs. In addition,since the SEP Tugs are reusable, once afull complement is available no moreneed be built. Table 4. ROM Element Costs
Total Transportation Cost 25,640Table 5. ROM Mars Spiral 4 and 5 Total Transportation Costs ($M)
Phobos First requires 2080 tonnes IMLEO to support Spiral 4 and 5 (45% less than aDRM using LOX/LH2 TMI stages and 19% less than a DRM using NTR TMI stages).After the initial human landing on Mars in 2025, it is assumed that Mars ExplorationSpiral 6 goes into a sustaining mode with one six person crew and 30 tons of surfacesupplies and equipment arriving at every launch opportunity. This level of effort was
Launch Element CostsSRB unit cost, $m 6090 t ET Derivative Unit cost, $M 8570 t ET Derivative Unit cost, $M 75Expendable SSME Unit Cost, $M 25EUS Unit Cost, $M 60Integration Costs 5090 t SDV Unit Cost, $M 39070 t SDV Unit Cost, $M 355Yearly Base Ops Cost, $M 800
In-Space Transportation ElementsSEP Tug Unit Cost, $M 400LOX/LH2 TMI Stage Unit Cost, $M 150NTR TMI Stage Unit Cost, $M 250Mars Entry Aeroshell unit cost, $M 150TEI Stage Unit Cost, $M 100Transit Habitat Unit Cost, $M 850
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assumed to continue through Spiral 5. ROM costs were assumed for each transportationelement and for the operations cost of the launch base (see Table 4), and then used togenerate a total Mars Exploration Transportation Cost for Spiral 4 and 5 as shown inTable 5.In this analysis it was assumed the Mars exploration payload elements are similar foreach of the three architectures, therefore the differences in payload costs would not be notsignificant. Key assumptions in the ROM costing were use of a Shuttle-Derived LaunchSystem; automated production of the SEP Tug Stretched-Lens, Solar Panels; and batchpurchase of dual-mode NTR engines. This DRM requires an advanced NTR, better thanthe 1960s version, but probably costing $8B to $10B to redevelop given the currentpolitical environment with respect to nuclear testing in the atmosphere. Assuming amodular design, total DDT&E for the SEP Tug is estimated to $700 including an orbitaltest of a single module. Development of the chemical TMI stage is estimated to cost isestimated to cost about $1.5B, including two orbital tests. Comparing total transportationrelated costs, Mars Direct using chemical propulsion will cost roughly $12B more thanPhobos First, and Mars Direct using NTRs will cost roughly $16B to $18B more thanPhobos First (including two orbital tests of the NTR TMI stage).
Cost-Optimized, Heavy-Lift Launch System (COHLLS) – Twenty years ago NASAand the USAF combined resources to design an Advanced Launch System (ALS)optimized to deliver 150,000 lbs (68 tonnes) to LEO for under $300/lb. They successfullyfound several designs that would work, but the program was canceled before anysignificant hardware got built (the prospective payload, an orbital laser battle station, wascanceled). This system was modular using combinations of reusable Flyback Boosters(FBB), partially reusable Propulsion/Avionics Modules (PAMs), and low-cost,expendable tankage manufacturing using automated machinery to satisfy a wide range ofpayloads and missions. At the time, the development of two new large rocket engines wasrequired which put the ALS Program DDT&E in the vicinity of $6B to $15B (1987 $).Today we have access to better materials and to rocket engines already developed whichare nearly perfect for ALS (e.g. RD-181, RS-68, and SSME). Updating the cost per lb to2005 dollars we estimate a launch cost of $510/lb (~ $77M/flight). The competition forthe COHLLS is the Shuttle Derived Heavy Lift Launch Vehicle (SDHLLV), which willuse the components and facilities from the Shuttle program after it is shut down. From thedata presented in Tables 3, 4, and 5, it is obvious that a COHLLS has the potential toreduce launch costs by two thirds, which reduces the cost of Phobos First transportationby more than $10B. This is certainly significant but development costs will be high, soboth options deserve a more in-depth comparison beyond what can be presented in thispaper.
In Situ Resource Utilization (ISRU) – There are numerous ways reduce launch mass byusing In Situ resources. We prefer approaches that extract a complete propellant sourcelike water from In Situ materials. For instance, our preferred approach to generatingpropellants on the surface of Mars is to extract water vapor from the atmosphere usingadsorption by 3A zeolites3. Provided the permanent Mars base is located at relatively lowaltitude near the equator and hopefully close to sub-surface water deposits to increasesaturated water vapor, this approach should produce abundant water for 10 to 20 kW-
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hr/kg. Hence, a 50 kW water generation plant could produce at least 22 tonnes of waterper year, which provides a healthy margin over the projected propellant usage. Theadvantage of producing propellant from 100 % In Situ material, instead of reacting aproduct brought from earth (hydrogen) with an In Situ material (carbon dioxide) to formmethane, is that you will never run out of propellant, which is a good thing when you areat the end of a very long supply line. Drilling a well to harvest subsurface water would bethe preferred approach, but current analysis indicates liquid water may only be found inthe lower latitudes at depths below 2 km.4
The preferred approach to generating propellants on the Earth’s moon or on Phobos is tolocate water, either in the form of ice or hydrated silicates (clay). At this time, we lack thedata needed to be sure water can be found on either moon, so our fallback position is toreduce oxygen out of abundant metal oxides found in regolith on both Earth’s moon andPhobos, and bring the needed hydrogen up from Earth. Although unsatisfactory as a longterm solution, this does reduce the IMLEO by about 33%.Solar-Electric Propulsion (SEP) Tug – Most of what gets hauled up out of Earth’sgravity well is propellant, followed by cargo, and finally the crew modules. Only thecrew need travel rapidly through Earth’s radiation belts, and it’s easy to show thatmoving propellants and cargo into lunar or Mars orbit using a high specific impulse SEPTug reduces the total IMLEO for the Moon Exploration Program by 25% and the totalIMLEO for the Mars Exploration Program by 45% (relative to advanced chemicalpropulsion plus aerocapture). The SEP Cargo Tug also reduces the total IMLEO for theMars Exploration Program by 19% relative to NASA’s baseline Nuclear Thermal Rocket.Beyond the savings in launch costs, the SEP Tug is reusable and returns from Mars to L1where it can be used again and again.One of the issues with respect to the SEP Tug is the availability of Xenon. Xenon iscurrently $1000/kg and the total yearly production is about 25 tons/year. This productionlevel is an artifact of supply and demand. There is 450 million tons of Xenon in theearth’s atmosphere, so it isn’t scarce; it’s just energy intensive to separate. The currentsource is the residuals from air liquefaction plants and further production requiressomewhat expensive modifications to older plants. Since supply pretty well matchesdemand, introducing further supply will only serve to drive down the price, and this isn’tlikely. There are other sources of Xenon, especially separating it as a byproduct of naturalgas liquefaction and that needs to be pursued. Another option is the stand aloneseparation of Xenon and Krypton from air as a standalone product. That is probablycommercially viable if NASA is willing to sign a long term purchase agreement.
High-Strength Carbon Nanotube (CNT) Fiber - The ultimate goal of our spaceprogram is to improve life on Earth and high-strength CNT fiber can move thosepotential life improvements from far in the future to the very near future. CNT cable withstrength of 40 GPa (predicted to be available within five years) makes it possible tolaunch an entire lunar space elevator in four COHLLS launches. This elevator wouldstretch from the Lunar nearside surface through L1 and down to a counter-weight station157,000 km above the Earth’s surface (see figure 3). If CNT fiber is available prior to2010 it maybe more cost effective to explore the moon using robots and build the lunarelevator to deliver the lunar base components in the 2020 timeframe. The lunar base
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would be occupied from 2020 to 2025 to demonstrate the elements to be used on Marsfrom 2025 on.
L1 Station
DownBelowStation
Earth’sSurface
(~157,000 km)59,500 km
TransferStation #1
TransferStation #2 Moon
159,800 km
Figure 3. Lunar Space Elevator DimensionsAfter the elevator is built, materials processed on the moon can be moved from the lunarsurface to the Down Below Station using solar generated electrical power, coated with asimple heat shield manufactured from regolith, and then released to enter Earth’satmosphere and land at a predetermined collection spot. Down Below Station is located atthe point where any object released just skims the Earth’s outer atmosphere, and anyobject pushed out the bottom of the station will reenter. Likewise, a rocket propelled intoa transfer orbit from LEO to Down Below Station will approach the station withnegligible velocity and can easily be grappled and berthed. These features makecommerce between the moon and Earth possible. In fact, it appears possible to pay off acommercially developed elevator in about 10 years with a freight charge of around$50/kg. Assuming the main freight carried are high-tech products manufactured in a hardvacuum, or refined energy metals like uranium and thorium, or even valuable metals likegold, platinum, and paladium; and all have values around $1000/kg, the freight chargeappear to be quite reasonable.
ConclusionsFour design options using disruptive technologies to reduce the cost of the proposedMoon/Mars Exploration Program were presented. The SEP Tug option is low risk withhigh payoff and certainly deserves serious consideration in the current studies. The otherthree (COHLSS, ISRU, and Lunar Elevator) are high payoff if certain circumstances orconditions are met. Therefore, key research needs to be funded in the near term to enablethose future cost saving activities to happen.
AcknowledgementsMuch of the data used in this paper was generated originally in support of the NASAConstellation Program. We wish to acknowledge our NASA COTR Neil Woodward forallowing us to pursue innovative approaches.
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