Decadal opportunities for space architects $ Brent Sherwood Jet Propulsion Laboratory, California Institute of Technology, USA article info Article history: Received 14 January 2012 Accepted 15 July 2012 Available online 13 October 2012 Keywords: Human space flight Space exploration Space passenger travel Space resource utilization Space industrialization Space solar power Space settlement Space colonization Space architecture Habitation Habitat Crew Passenger Space development abstract A significant challenge for the new field of space architecture is the dearth of project opportunities. Yet every year more young professionals express interest to enter the field. This paper derives projections that bound the number, type, and range of global development opportunities that may be reasonably expected over the next few decades for human space flight (HSF) systems so those interested in the field can benchmark their goals. Four categories of HSF activity are described: human Exploration of solar system bodies; human Servicing of space-based assets; large-scale development of space Resources; and Breakout of self-sustaining human societies into the solar system. A progressive sequence of capabilities for each category starts with its earliest feasible missions and leads toward its full expression. The four sequences are compared in scale, distance from Earth, and readiness. Scenarios hybridize the most synergistic features from the four sequences for comparison to status quo, government-funded HSF program plans. Finally qualitative, decadal, order-of-magnitude estimates are derived for system development needs, and hence opportunities for space architects. Govern- ment investment towards human planetary exploration is the weakest generator of space architecture work. Conversely, the strongest generator is a combination of three market drivers: (1) commercial passenger travel in low Earth orbit; (2) in parallel, government extension of HSF capability to GEO; both followed by (3) scale-up demonstration of end-to-end solar power satellites in GEO. The rich end of this scale affords space architecture opportunities which are more diverse, complex, large-scale, and sociologically challenging than traditional exploration vehicle cabins and habitats. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction 1 Work opportunities for space architects over the past three decades have been concentrated in four domains: Phase A of the International Space Station (ISS), technol- ogy programs like TransHab, NASA future-mission con- cepts, and commercial passenger launch startups. NASA’s direction has historically dominated, but the trends bear reexamination. This paper describes the array of project opportunities most likely available to space architects through 2040. The analysis includes all the spacefaring activities that cannot be done without HSF; derives rational sequences that are built from near-term to visionary scale and scope; synthesizes future scenarios by hybridizing the sequences; then compares them for their impact on space architecture opportunities. The analysis is anchored by four drivers already evi- dent: continuing operation of the ISS, severe NASA outyear budget limitations, increasing difficulty justifying NASA HSF, and nascent commercial space adventure travel. In prior work [1] the author clarified four options for the purpose of HSF, differentiated as salient by what technology investments they require and by what futures Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/actaastro Acta Astronautica 0094-5765/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actaastro.2012.07.021 $ This paper was presented during the 62nd IAC in Cape Town. E-mail address: [email protected]1 This work was done as a private venture and not in the author’s capacity as an employee of the Jet Propulsion Laboratory, California Institute of Technology. Acta Astronautica 81 (2012) 600–609
Transcript
Contents lists available at SciVerse ScienceDirect
A significant challenge for the new field of space architecture is the dearth of project
opportunities. Yet every year more young professionals express interest to enter the
field. This paper derives projections that bound the number, type, and range of global
development opportunities that may be reasonably expected over the next few decades
for human space flight (HSF) systems so those interested in the field can benchmark
their goals. Four categories of HSF activity are described: human Exploration of solar
system bodies; human Servicing of space-based assets; large-scale development of
space Resources; and Breakout of self-sustaining human societies into the solar system.
A progressive sequence of capabilities for each category starts with its earliest feasible
missions and leads toward its full expression. The four sequences are compared in scale,
distance from Earth, and readiness. Scenarios hybridize the most synergistic features
from the four sequences for comparison to status quo, government-funded HSF
program plans. Finally qualitative, decadal, order-of-magnitude estimates are derived
for system development needs, and hence opportunities for space architects. Govern-
ment investment towards human planetary exploration is the weakest generator of
space architecture work. Conversely, the strongest generator is a combination of three
market drivers: (1) commercial passenger travel in low Earth orbit; (2) in parallel,
government extension of HSF capability to GEO; both followed by (3) scale-up
demonstration of end-to-end solar power satellites in GEO. The rich end of this scale
affords space architecture opportunities which are more diverse, complex, large-scale,
and sociologically challenging than traditional exploration vehicle cabins and habitats.
& 2012 Elsevier Ltd. All rights reserved.
1. Introduction1
Work opportunities for space architects over the pastthree decades have been concentrated in four domains:Phase A of the International Space Station (ISS), technol-ogy programs like TransHab, NASA future-mission con-cepts, and commercial passenger launch startups. NASA’sdirection has historically dominated, but the trends bearreexamination. This paper describes the array of project
ll rights reserved.
n Cape Town.
not in the author’s
, California Institute
opportunities most likely available to space architectsthrough 2040.
The analysis includes all the spacefaring activities thatcannot be done without HSF; derives rational sequencesthat are built from near-term to visionary scale andscope; synthesizes future scenarios by hybridizing thesequences; then compares them for their impact on spacearchitecture opportunities.
The analysis is anchored by four drivers already evi-dent: continuing operation of the ISS, severe NASA outyearbudget limitations, increasing difficulty justifying NASAHSF, and nascent commercial space adventure travel.
In prior work [1] the author clarified four options forthe purpose of HSF, differentiated as salient by whattechnology investments they require and by what futures
B. Sherwood / Acta Astronautica 81 (2012) 600–609 601
they lead to. Listed in order of increasing numbers ofspacefarers enabled after a few decades of $1010/yeargovernment investment, the four are: Explore Mars, enableSpace Solar Power for Earth, Settle the Moon, and acceleratedevelopment of commercial Space Passenger Travel. Of thefour only the first has motivated HSF government invest-ment throughout the six decades of the field, with theironic exception of 1961–1972 when HSF was driven by acompetitive geopolitical agenda.
The present analysis focuses on in-space HSF activities.Again there are four, mapped to the HSF goals as follows:(1) deep-space servicing and construction (cross-cuttingapplication); (2) exploration (Explore Mars); (3) industrialdevelopment of resources (Space Solar Power for Earth)and (4) human ‘breakout’ into space (Space PassengerTravel, and Settle the Moon). From these we can derivepotential time-phased project opportunities for spacearchitects.
2. Why HSF
About 10,000 years ago humans began the large-scaleengineering of their world by creating the first works werecognize today as architecture. In the last 100 years, just1% of humanity’s engineering history, a few pioneersenvisioned realistic ways to get off the Earth, beyondthe atmosphere, and away from the pervasive and funda-mental experience of weight. The feat was finallyachieved only half a century ago, when the world’spopulation was half what it is now.
The space age is part of what makes us modern. In thatsame half-century we have visited the deepest seafloortrenches, occupied permanent research stations in Ant-arctica, built vast airports where there was only seabefore, made climbing Earth’s highest peaks an adventuresport, networked our collective thinking, and begunreshaping our DNA. Step by step we are expanding thedomain of human presence and the very nature of what itmeans to be human.
Space awaits as an incomparable frontier of humanexperience: with vistas, sensations, opportunities andrisks, and resources and places without limit. Considerwhat human space flight has accomplished in just its firsthalf-century: proved we can survive off Earth; visited theMoon; brought nations together continuously for a dec-ade in the ISS; and renovated the Hubble Space Telescopeseveral times.
Our robots and telescopes reach much farther than wedare imagine we ever could ourselves. As we learn aboutour planet, solar system, and universe almost out to thebeginning of time, we come to understand the shape ofthe potential human domain. It ranges from the soils ofhome to the sands of Mars, and includes thousands ofsmall, weird places as well.
Extending human experience to these limits is thesustaining purpose of human space flight. This purposeis neither easy nor quick to achieve, yet it beckons.President Obama has said:
‘‘Our goal is the capacity for people to work and learnand operate and live safely beyond the Earth for
extended periods of time, ultimately in ways that aremore sustainable and even indefinite’’ [2].
These 34 words define a powerful vision that capturesfour key yardsticks to measure our ambition and pro-gress: making space our home; far from Earth; using whatwe find there; irreversibly. This open-ended challenge isnot fixated on a particular destination, nor is it intendedto be the province only of government action; rather it isabout humanity stepping outward, to all attainable desti-nations, forever.
Recognizing that stepping out into the solar system isthe underlying goal of our HSF investment can help clarifypriorities. Moon and Mars are both meaningful andworthy because they are both eventually attainable. GEOsatellite servicing is meaningful and worthy because itoffers us the earliest possible human toehold outside thegeomagnetic shield. Proposing to step—rather thanleap—tempers vision with pragmatism, because itmatches the reality of our limited resources.
The most serious sociological challenge to an open-ended vision—one felt by both space advocates and theindustrial-political machine—is that there is no urgencydiscernible in it. Most often this dissatisfaction is formu-lated as the criticism that NASA has no ‘clear destination.’But naming one would not by itself spark urgency, andthe ‘long view’ requires a kind of patience not evident inAmerican culture. The dilemma for space supporters isthat those who seek faster progress cannot command thebroad popular mandate needed to make it so. In today’sworld they can neither arrange a significant increase ofpublic investment for an aggressive HSF vision nor sustainit for several decades. And the evidence suggests thatneither strident Senate speeches nor op-ed essays canredress this structural mismatch.
For most Americans, non-urgent advancement of HSFcapability is a non-issue, but for space supporters it isunpalatable. Noble though it may be, HSF is a ‘boutique’technology. Electricity, refrigeration, motive power, com-puters, and networking are technologies that have playeda very different role in humanity’s progress. They weredeveloped and became ubiquitous because they directlyimproved the human condition so dramatically that theirvalue was never seriously questioned. However, HSF isseriously challenged to compete with today’s other tech-nology frontiers: biotechnology, nanotechnology, cleanwater, robotics, artificial intelligence, genetic engineering,manufactured food, alternative energy, and climatechange. Indeed HSF is self-limiting when cast as equiva-lent to ‘space exploration;’ the farther out it looks, the lessrelevant it is to urgent considerations. This is a secondstructural mismatch that cannot be wished away.
Thus a core problem for ‘why HSF’ is: How mightstepping out into the solar system be made central enough
to society’s needs throughout the 21st century to stimulateand sustain increased public investment in it?
Antarctica and the continental shelves offer instructivemodels. Both are destinations analogous to space: remote,alien, risky, and needful of advanced technology. Human-ity has stepped out onto Antarctica for routine scientific
B. Sherwood / Acta Astronautica 81 (2012) 600–609602
research without large-scale industrialization (resourceextraction is prohibited by treaty) or large-scale living. Ishuman presence in Antarctica central to civilization? Thescience done there—paleobiology, geology, extremo-philes, climate history, ice-sheet dynamics, atmosphericozone, astronomy, and meteoritics are just some of thefields—is no less or more important than the science—
structure and evolution of the universe, comparativeplanetology, solar dynamics, history of the solar system,origin and distribution of life—done by exploring space.Albeit fundamental to modern civilization, science existsonly vaguely in the public consciousness. So the level ofpublic investment in science, including space exploration,has found a fairly stable equilibrium within our economythat is unlikely to change significantly. Exploration for thesake of science cannot be the lever HSF advocates seek.
The continental shelves offer a contrasting example.Humanity has stepped out onto the continental shelves,again for exploration and research and—albeit still with-out permanent settlement—with large-scale industrialoperations. The continental shelves are a well explored,well funded, hotly contested, and critical part of both ourpetroleum energy base and food base. New industrieswith specialized technologies have been created, politicallobbies and controlling interests have emerged, and theassociated activities are regulated, taxed, and embeddedin modern society. Is human presence on the continentalshelves central to civilization? The answer is un-equivocally yes.
Could there be an analogous basis for large-scalehuman activity in space, which is even more remote,risky, and expensive than either Antarctica or the con-tinental shelves? If expanding human presence off theEarth, sustainably and indefinitely, is to be a valid‘why’—meaningful enough to motivate sustained or evenincreased investment—then what could HSF accomplish,and where?
3. What, Where
The minimum set of useful things that only humanscould do, and that could only be done in space, containsfour types.
3.1. Service and build assets
Space already contains thousands of high-value assets:satellites for communication, navigation, reconnaissance,and science. Hubble servicing missions have demonstratedthe unique value of human space flight for upgrading andrepairing systems beyond their designed capacity. Manyvaluable spacecraft are defunct because of straightforward
Service assetsin polar, HEO,
GEO orbitsastro
• Radiation shielding ••
Construct largeGEO telescopes
• Advanced operations
Fig. 1. Progressive Servicing sequence uses HSF to
subsystem failures; and many others are purposely retiredbefore their propellant is exhausted to assure that they donot expire in operational orbits.
Today we cannot yet salvage wasted orbiting assetsbecause we cannot get humans into polar orbits, highEarth orbits (HEO), or the geosynchronous belt (GEO). Norcan we service advanced telescopes in Earth-trailingorbits (e.g., Spitzer), at Sun–Earth L2 (e.g., the JamesWebb Space Telescope currently in development), or atSun–Earth L1 (e.g., potential synoptic observatories ofEarth’s day-lit disk).
Beyond maintaining, repairing, and upgrading exist-ing and planned spacecraft, small human crews couldassemble spacecraft too large to deploy autonomously.A notable example is assembly of 20–30 m class telescopes.Platforms located at GEO would enable ‘persistent,’ high-resolution reconnaissance of any spot on Earth for scienceor security missions. A large, focusing X-ray telescopewould enable revolutionary astrophysics like investigationof the earliest black holes in the universe. Located fartheraway—whether assembled or deployed there—large opti-cal and infrared telescopes would enable spectroscopy ofexoplanet atmospheres, the keystone way to search forsigns of life throughout the galaxy.
How essential is HSF for such scenarios? Some advo-cates of in-space servicing assert advanced robotics couldavoid government-dependent, high-orbit HSF, an under-standable viewpoint when justifying a business plan toinvestors. But everyone recognizes that human crewswould be quickest and most effective for handling bothunforeseen complications and the wide range of config-urations and needs posed by servicing and assemblingdiverse target types.
Servicing and building space-based assets could pro-vide a progressive sequence that extends human presencebeyond LEO (Fig. 1). In order of increasing challenge anddecreasing frequency:
1.
Connom
Mu Re
max
Service assets in the three remaining classes of Earthorbit not yet accessible to HSF (polar, HEO, and GEO).In different ways these orbits require radiation protec-tion for routine operations. GEO offers the highest-value targets.
2.
Construct large GEO optical and/or IR telescopes. Thiswould require weeks-long durations and advancedoperations.
3.
Construct large optical, IR, UV, or X-ray astronomicaltelescopes at Earth–Moon L1, a few days’ travel away.Such large telescopes could then be positioned moreremotely by electric propulsion for operation.
4.
Visit Sun–Earth L1 and L2, with trip times akin to earlyasteroid exploration, to service telescopes built in step
struct largeical telescopes
at EM-L1
Service telescopesat Sun-Earth L1
and L2
lti-week durationmote fail-safe
• Multi-month duration• Remote fail-op
imize utility of high-value space assets.
B. Sherwood / Acta Astronautica 81 (2012) 600–609 603
#3 without the multi-year downtime required to cyclethem through E–M L1 again using electric propulsion.
3.2. Open space resources
A special case of assembly and servicing of large spacestructures is the construction and operation of solarpower satellites (SPS) in GEO. Well-studied technically,but not economically viable until it outprices dwindlingpetroleum supplies, SPS would harvest inexhaustible,continuous, unattenuated solar energy in GEO, convert itto microwaves, transmit it to the Earth’s surface, andreconvert it into electricity for the terrestrial grid. Thebeam power density would be safe enough for animalsand airplanes to fly through it, and the terrestrial rectennafarms, albeit large in area, would be sparse wire gridssuperimposed over other land uses like agriculture.
The vision has many skeptics; yet no other apparentcombination of in-hand, post-petroleum technologies andland use can maintain the first-world standard of living,raise the rest of humanity on par with it, support hydro-gen mobile power, desalinate huge quantities of water,and do these things anywhere on the planet, day andnight, sustainably. Conversion to an SPS-based energyeconomy would signal our graduation from a KardashevType-I civilization (utilizing the resources of our planet)into the very first stages of Type-II (utilizing the energyoutput of our star).
But the SPS alternative is not academic. Demonstratingits end-to-end practicality could be done within themeans of existing government space programs. Doing sowould prove that civilization’s dependence on oil could bebroken without disrupting western living standards.Nations that go on to scale it up for full-scale implemen-tation would quickly become major energy exporters,leading to a ‘state change’ in geopolitical balance. Of thespacefaring nations so far, Japan and India have indicatedthe most serious interest in developing SPS.
Rudimentary calculations reveal the magnitude of spaceoperations required for SPS to make a difference. Todayhumanity’s total power consumption is about 15 TW. To geta sense of scale, assume that in the extreme all of this issupplied from SPS. Further assuming global energy con-sumption leveled to a first-world standard of living, con-tinued population growth, scaled-up implementation ofwater desalination, and scaled-up hydrolysis to producehydrogen for motive power, we should carry a consumptionrequirement of about 102 TW. At 1 AU in free space thepower density of solar energy is about 1400 W/m2. Con-temporary but conservative values for photovoltaic conver-sion efficiency and solid-state transmission efficiency are
Fig. 2. Progressive Resources sequence industrializes space and
about 0.3 and 0.8 respectively [3]. So using SPS to provide areasonable mid-century projection of humanity’s energyneeds would require roughly 90,000 km2 of satellites inGEO. For perspective, this is more than 25 times the totalpaved area of the US Federal Interstate Highway System,and about the same area as the state of Maine. Mega-engineering to be sure, this is feasible nonetheless, andmore practicable than other post-petroleum schemes—
except that it requires space operations.Proponents point to advances in robotics to assert that
in-space construction and maintenance at this scale wouldnot require HSF, perhaps to sidestep yet another advocacycomplication. A less extreme view would conceptualizemodest onsite human crews supervising—andrepairing—fleets of construction and maintenance robots.Again, continental-shelf industrialization is a helpful ana-logy. The most reasonable scenario would require 102–103
professional workers in GEO depending on constructionrate, who would in turn require dormitory, eating, enter-tainment, health care, maintenance, and other supportservices. Opening space energy resources would thereforenot just ‘change the game’ for terrestrial energy; it wouldcreate several new industries in space.
Energy is by far the most straightforward use of spaceresources for Earth, because photons have no mass,energy conversion and transmission technologies are wellunderstood, the resource is obtainable close to Earth, andenergy on Earth is in great need yet increasingly con-strained supply. However, in the distant future materialresources from space could conceivably become transfor-mative. High-leverage concepts discussed in the literaturefor direct terrestrial benefit include platinum-groupmetals mined from the lunar surface or near-Earth aster-oids; and 3He mined from lunar regolith for use in as-yet-unvalidated terrestrial fusion reactors to generate elec-tricity. Concepts posited for in-space benefit includewater and other volatiles extracted from lunar depositsor regolith, asteroids, Phobos, or Mars for use as propel-lant, and construction materials refined and fabricatedfrom Earth Trojan asteroids at Sun–Earth L4 and L5 [4].
Like asset servicing, opening space resources couldprovide a progressive sequence that expands humanpresence beyond LEO (Fig. 2)
1.
urcoonEA
ontnt/ha
incr
Conduct SPS scale-up demonstrations in GEO, leadingto large-scale industrialization to provide powerto Earth.
2.
Demonstrate resource extraction and scale-up at theMoon, Earth Trojans, and other energetically favorablenear-Earth asteroids (NEAs), leading to expandeddeep-space operations.
e,s
Leverage Phobos,Mars resources for
repeated travel
hsb
• Multi-year duration• Mars descent/ascent/hab• Mission-critical ISRU
eases energetic efficiency of reaching Mars routinely.
B. Sherwood / Acta Astronautica 81 (2012) 600–609604
3.
Utilize the volatiles resources of Phobos, and then thesurface of Mars, relying on experience gained closer toEarth, for Mars exploration.
3.3. Enable the human breakout into space
After 50 years of HSF, about 500 people have traveledin space. That cohort could be increased by orders ofmagnitude, thereby accelerating the ‘human breakoutinto space.’ Space passenger travel accomplishes thebreakout objective of having ordinary people be ableto ‘go.’
Space passenger travel for construction and serviceworkers—business passenger travel—is intrinsic to thebusiness case for large-scale SPS as discussed above.However, space passengers travel for the leisuremarket—space tourism—is different in four fundamentalways: location, duration, amenities, and elasticity.Regarding location, although two salient experientialfeatures of HSF (high acceleration and weightlessness)are common to all HSF, a third is specific to LEO: theincomparable, ever-changing view of Earth. So even if HSFsteps out to GEO for industrialization, leisure travel wouldremain concentrated in LEO. Second, the duration of mostleisure travel would be of the same order as terrestrialvacations, between a few days and a few weeks, ratherthan the months-long tours of duty for GEO constructioncrews. Third, expectations for amenities would rise withtraveler cohort size, which will be inversely proportionalto market price. Industrial crews would tolerate moreSpartan accommodations as in harsh locations on Earth.Fourth, leisure travel is likely a highly elastic market inwhich demand is a function of safety first, and flight rate(the principal driver of per-seat price) second.
Early space passenger travel markets are in develop-ment now and it is reasonable to project slow marketgrowth. Investment barriers are high for enabling andemplacing the levels of capability needed to access theelastic growth regime. However, government investmentsin key areas like flight safety, launch system reusability,and orbital system volume and longevity could havesignificant leverage on growth rate. Advocates for thispath envision the space population becoming self-sus-taining over time.
Enabling the human breakout into space could alsoprovide a progressive sequence that expands humanpresence beyond LEO (Fig. 3)
1.
Commercial enterprise creates leisure destinations andservice industries in LEO, increasing HSF capacity anddiversifying its capabilities.
2.
Governments utilize the commercial LEO capabilitiesat marginal cost to extend the reach of HSF throughoutcis-lunar space and develop lunar surface technologiesincluding resource utilization.
3.
Commercial providers leverage the government-funded technologies to extend the reach of passengertravel to lunar orbital cruises and lunar surfaceexcursions.
4.
Routine round-trip travel between the Moon and Earthopens the Moon to settlement.
5.
A similar public–private cycle establishes trans-lunarfree-space settlements at Sun–Earth L4 and L5 if localasteroidal resources are conducive.
6.
A similar public–private cycle settles Mars, if one-waytravel becomes sociologically acceptable.
3.4. Explore new environments and faraway places
The fourth HSF activity would seek to explore all theplaces that can be reached with human crews. Beyond LEOthis has traditionally meant simply the Moon and Mars,although NEAs have recently become admissible as inter-mediate destinations. To complete the set we could includelate-21st-century, decadal-duration human missions into themain asteroid belt where thousands of unique worlds await,using the solutions to space radiation, life-support, andpropulsion that would have been developed for Mars-classmissions. All other natural destinations in our solar system—
Venus, Mercury, the outer planets and their moons, andprobably the trans-belt small-body populations—are eithertoo inimical or too remote, or both, for human exploration tobe reasonably foreseeable with technologies we know andrisks we could manage.
Directly bringing human capacities for observation,cognition, interpretation, experience, dexterity, and adap-tive behavior to faraway places has always yieldedincomparably rich exploration. Project Apollo proved thathuman space exploration has the potential to be globallyhistoric and scientifically valid. While we can arguewhether more extensive exploration of the Moon, orexploration of deep-space asteroids, could match thatsociological and scientific benchmark, humans exploringMars would. Human exploration of Mars may be essentialfor definitively concluding the epochal investigation ofwhether Mars ever supported life, whether it still does inprotected places, and if so whether that life shares thesame chemical basis as life on Earth.
Direct human exploration of natural bodies in spaceoutlines the ‘traditional’ progressive sequence to expandhuman presence beyond LEO (Fig. 4)
1.
Mount expeditions to the nearest visible destination,the Moon. Of the four sequences described in this
analysis, this is the only step that has been taken so far,
by Apollo.
2.
Return to the Moon, with methodical lunar explorationthat increases staytime to months and takes crews toregions invisible from Earth.
3.
Mount expeditions to deep-space destinations thatcannot be seen easily but are within �1-year travel(NEAs).
4.
Use a sequence of confidence-building missions toNEAs that incrementally increase duration and dis-tance, culminating with Phobos at Mars.
5.
Mount surface expeditions at Mars, with staytimesranging from opposition-class (�1 month) to conjunc-tion-class (2 years).
6.
Sustain continuous presence on Mars with rotatingcrews, if thorough exploration of the planet requiresHSF over the long term.
Commercialdestinations andservices in LEO
•• Five-9s reliable launch• Diverse in-space amenities
Governments leveragecommercial LEO services to
reach cis-lunar space
• Lunar descent/ascent/hab• Surface operations
Commercial passenger travelreaches Moon using government-
funded technologies
Routine travel opens theMoon to settlement
Bootstrap trans-lunar free-spacesettlements at Sun-Earth L4, L5
Bootstrap Mars settlementwith one-way transportation
•••• Diverse ISRU, manufacturing, food growth
• •
Fig. 3. Progressive Breakout sequence establishes full-fledged human societies in space.
Expeditions tothe Moon
• Sortie habitation• Methodical lunar exploration• Duration months• Ops out of Earth view
Expeditions toNEAs
• ~1-yr duration• Fail-op habitation
NEA mission sequenceculminates at Phobos
• Duration up to 3 yr• Artificial gravity?• Significant self-sufficiency
Mars surfaceexpeditions
• ~500d surface duration• Mars descent/ascent• Surface ops and mobility
Fig. 4. Progressive Exploration sequence extends direct human presence
as far as possible. The first two steps can arguably be taken in either order.
Fig. 5. Spacefaring population potential vs. destination class varies
significantly among alternative post-ISS HSF activity sequences. Color
code is common with Figs. 1–4.
B. Sherwood / Acta Astronautica 81 (2012) 600–609 605
7.
Mount multi-year expeditions into the main asteroidbelt.
4. Rational capability sequences
All four activity sequences would expand humanpresence into the solar system if implemented, but noneof them alone is likely to justify or cause the expansion(Fig. 5). Each has strengths and weaknesses.
The Exploration sequence offers a way for governments towork together peacefully developing advanced technology;but supports only a thin, possibly sporadic series of missionsbecause it cannot occur near Earth yet getting away fromEarth requires enormous—even global—investment for everymission. The Breakout sequence offers direct public rele-vance, an elastic LEO ‘onramp’ already moving forward, and away for governments to avoid developing their own HSFlogistics tail; but farther out it faces technical barriers to
feasibility that can be surmounted only with governmentinvestment. The Resources sequence offers an elastic path tolarge-scale space industrialization because it would create apyramidal economic structure of public–private partnershipto feed modern energy appetites indefinitely; but beyondGEO it becomes brittle, speculatively dependent on eitherlarge-scale lunar mining operations or non-terrestrial mar-kets that would value materials in situ. The Servicingsequence has the lowest barrier to entry from the currentstate but becomes extremely thin beyond GEO because evenin the best case there would be only a few large, long-liveddeep-space astronomical facilities to service.
However, the four activity types are not mutuallyexclusive, and promising scenarios can be constructedfrom the best features of each. Fig. 6 shows how stepsfrom multiple sequences might be combined. Best under-stood as a precedence diagram (i.e., read from right toleft) it shows that Settlement goals at various destinations
Materials resource extraction at Moon, Earth Trojans, NEAs
Leverage Phobos, Marsresources for repeated
travel
Commercial passenger travelreaches Moon using government-
funded technologies
Routine travel opens theMoon to settlement
Bootstrap trans-lunar free-spacesettlements at Sun-Earth L4, L5
Bootstrap Marssettlement with one-way
transportation
Expeditions tothe Moon
NEA mission sequenceculminates at Phobos
Mars surfaceexpeditions
Continuous presenceat Mars
Expeditions intomain asteroid belt
Governments leveragecommercial LEO servicesto reach cis-lunar space
Expeditions toNEAs
Fig. 6. Hybrid sequences create rational scenarios. Vision-reining costs force a choice for government investment between Exploration and
Settlement goals.
B. Sherwood / Acta Astronautica 81 (2012) 600–609606
would be enabled (necessarily but not sufficiently) bothby government-developed technologies and by spaceresource development. Choices about which resources todevelop are constrained by a fundamental governmentchoice between two tracks: one leading through NEAmissions to Mars and beyond; or one leading towardsettlement of the lunar surface.
It is financially unrealistic to expect government HSFinvestment to enable both paths even though they inter-connect on the diagram. The Mars (upper) path imple-ments multiple, progressively-distant missions andbegins with the currently-stated USG goal of a humanNEA mission. The lunar (lower) path uses commercialinfrastructure to minimize development and operationscosts, and begins with the objective stated by today’scommercial orbital transportation players: selling LEOservices to the government. Alternative diagrams are ofcourse possible, for example a NEA-Mars sequence couldbe designed to leverage commercial LEO services. Butbecause of the high cost barrier, government investmentfaces a stark choice between divergent goals: the lunarpath leads towards bringing the Moon within the eco-nomic and sociological sphere of the Earth, while theNEA-Mars path leads towards more distant places with alesser number of humans.
Strangely, given the persistently vehement debateabout it, this critical choice can be deferred becausetoday’s issue is how to get going on any roadmap at all.Overcoming the high barrier to entry for HSF beyond LEOis the core government-HSF challenge of the next twodecades. Constellation showed that realistic levels ofUSG investment alone could not attain lunar sorties, letalone open-ended surface operations. Neither can USG
investment alone achieve even a first NEA mission withina politically acceptable time, as shown by recent HEFT(Human Exploration Framework Team) and HAT (HumanExploration Architecture Team) analyses [5].
Fig. 7 shows a scenario that breaks through thisproblem. First, the Servicing sequence offers an incre-mental way for the USG to get humans beyond LEO.Demonstrating the practicality of recycling high-valuespace assets is a legitimate purpose for HSF. It has alreadybeen done to great effect in LEO, and affordable invest-ments beyond various combinations of existing and con-templated space transportation systems could extend it toother Earth orbits. GEO in particular offers diverse servi-cing challenges, nearby experience outside the geomag-netic shield, and a way for HSF to validate or assistentrepreneurial robotic servicing startups. GEO opera-tions experience would then enable more complex activ-ities like building large telescopes (for Earth science, forsurveillance, and/or for astronomy) and demonstrationof SPS.
Early end-to-end SPS technology demonstrations at GEOdistance would not require HSF, but deployment demon-strations to validate scale-up assumptions would. The HSFexperience gained would prove useful even if space-basedpower fails to gain traction as a viable terrestrial energyoption. And if it does, the dashed line indicates thatsubsequent HSF roadmaps would become fundamentallyshaped by the capabilities its full-scale implementationwould emplace: very high-capacity, high-rate, heavy-liftlaunch; large numbers of GEO workers; advanced robotics;and essentially unlimited in-space power.
Again, other scenarios are feasible. For example USGmission architectures to reach and operate at GEO or even
Service assets inpolar, HEO, GEO
orbits
Construct largeastronomical
telescopes at EM L1
Service telescopes atSun-Earth L1 and L2
Demonstrate andindustrialize SPS in
GEO
Commercial LEOdestinations and
services
Governments leveragecommercial LEO servicesto reach cis-lunar space
Expeditions toNEAs
Lunar surface?
Mars distance?
Construct largeGEO telescopes
Fig. 7. Potential startup scenario outlines a pragmatic onramp to the futures in Fig. 6. Government ‘destination’ decision between investing in lunar
surface operations or deep-space NEA/Mars missions is deferred until beyond-LEO progress is demonstrated on clearly useful missions.
B. Sherwood / Acta Astronautica 81 (2012) 600–609 607
EM-L1 could leverage commercial LEO services, therebyavoiding unique system developments, accelerating sche-dule and boosting commercial business.
Strategically hybridized scenarios hold more promise forbootstrapping HSF beyond LEO than does the ‘pure’ sequenceof destination-driven USG missions (Fig. 4) persistentlyproposed by NASA planning teams. Four strategic leversappear to differentiate ‘rich’ from ‘impoverished’ HSF futures:
1.
Move away from the specious conceptual constraintthat USG HSF must always be about Exploration. OtherHSF objectives worthy of USG investment providemore feasible onramps.
2.
Focus first on GEO as a versatile, beyond-LEO locationto demonstrate capabilities useful to multiple possiblefutures.
3.
Implement architectures that leverage commercialLEO capabilities to the maximum possible degree:launch, orbit transfer, habitation, and eventually labor.Use USG investment for technologies that lower thebar for commercial providers (e.g., high-reliabilitylaunch, reusability, and in-space habitat assembly)rather than to develop unique all-in systems (e.g.,launch vehicles) as in NASA’s past.
4.
Defer programmatic commitment to either theExploration or Settlement paths until SPS has beendemonstrated—it might change everything.
5. Space architecture requirements flowdown
Potential opportunities for space architects over the nexthalf century can be derived from this analytical foundation.How optimistic could—or should—our profession be, andwhat informed advice can we provide to hopeful youngprofessionals seeking to enter our field?
Pacing constraints are:
1.
Strategic flexibility of government space programs(particularly the best-funded ones, NASA and CNSA)in choosing investment objectives other than plane-tary targets.
2.
Resource allocations to and by those space programs. 3. Private capital applied to entrepreneurial space endeavors. 4. Disruptive ‘wild cards’ that cannot be predicted,
including economic and geopolitical shifts; technolo-gical progress in relevant domains; HSF accidents; andevolving sociological norms.
As a bounding case Table 1 details a ‘fast-onramp’ futureadapted from Fig. 7 and leading to the ‘rich’ future of Fig. 6.Predictive resolution is limited to decadal time intervals andorder-of-magnitude spacefaring populations.
Repeated HSF GEO servicing missions could be underwayby 2020. With in-hand technologies large telescopes could beconstructed by the mid-2020s, and SPS scale-up demonstra-tions could be conducted by 2030. COTS (commercial orbitaltransportation service) providers would partner with entre-preneurial habitation providers to expand boutique tourismfrom suborbital rides to continuous multi-day orbital staysand occasional cis-lunar excursions for the very rich by 2030.By that time Mars habitability would have been characterizedby NASA and ESA robotic science missions, positioninggovernments to choose among the HSF pathways: towardsMars exploration, towards lunar settlement, or towardsindustrial exploitation of space power in GEO. The finalcolumn of Table 1 indicates, using terms familiar fromterrestrial applications, the types of space architectureneeded to meet these needs.
This scenario has profound implications for spacearchitects:
1.
Significant opportunities to begin developing planet-surface space architecture do not emerge until at leastthe 2020s.
2.
In-space habitation needs through the 2020s can bemet by systems with capacity of tens of people.
3.
Transportation systems to and from orbit need notcarry more than tens of people until at least the 2030s.
4.
Commercial passenger travel in LEO dominates gov-ernment exploration as a driver for both the numberand diversity of space-architecture systems. Competi-tive granularity (multiple competitors and parsedcustomer demographics) proliferates the space
Table 1Hybrid on-ramp scenario bounds the types of space architecture that may be commissioned out to �2040. Industrialization of GEO for SPS is the most
significant wild card.
Decade Location Function Capacity�Frequency Duration System class
2010s Earth–LEO Access/
return
101 passengers�101
trips/yr
Days Small-plane-size cabin in reusable launch/entry
vehicle
LEO–GEO Orbit
transfer
100 crew�100 trips/yr Days Short-duration deep-space cabin on in-space tug, possibly
reusable
GEO EVA/EVR
operations
100 crew Hours total Telerobotics stations/tools, airlock/spacesuit
2020s LEO Orbit
transfer
101 touristsþ100
crew�101 trips/yr
Days Short-duration LEO bus for tour excursions around and among
102 workers Continuous Routine, quick-egress EVA (e.g., suitport, man-in-can)
B. Sherwood / Acta Astronautica 81 (2012) 600–609608
architecture opportunities within this market evenmore than the table implies directly.
5.
Orbital passenger travel even in the 2020s requiresarchitecture solutions for non-professionals on shortstays, for professional staff for long stays, and forrecreation, life support, and food appropriate for pay-ing non-professionals.
6.
A decision by one or more governments to invest inSPS rather than HSF exploration significantly augmentsthe market need for space architecture: quantitatively(capacity and duration), qualitatively (traffic directlyto and from GEO), and demographically (workers inaddition to tourists and staff).
7.
Habitation solutions for thousands of tourists per yearin LEO may be adaptable into solutions for hundreds of
SPS construction workers and support staff continu-ously in GEO.
Using the spacefaring human-factors model proposedby Sherwood [6] the space architecture ‘frontier’ can bemapped in time (Fig. 8). Today the primary space archi-tecture needs are immediately physical for small, profes-sional crews. The 2020s sees this same set of challengesexpand to passengers. Crew psychology does not evolvesignificantly because even multi-week trips into cis-lunarspace are filled with task-directed activity. By the 2030spassenger psychology begins to shift away from sheeradventure and towards richer accommodation, crewpsychology begins to reflect the reality of staff hiredfor partial-year tours of duty, and the number of
Mission Crews
Passengers Settlers
Ergonomic
Biological
Psychological
Sociological
Mission Crews
Passengers Settlers
Ergonomic
Biological
Psychological
Sociological
Mission Crews
Passengers Settlers
Ergonomic
Biological
Psychological
Sociological
Mission Crews
Passengers Settlers
Ergonomic
Biological
Psychological
Sociological
Fig. 8. Evolving market will call for space architecture to solve increasingly sophisticated challenges driven by spacefarer type, group size, flight duration,
and distance from Earth. No reasonable scenario requires development of ‘settler’ solutions by 2030. Darker cells indicate full need.
B. Sherwood / Acta Astronautica 81 (2012) 600–609 609
simultaneous tourists introduces sociological considera-tions. Again the wild card in the 2030s is SPS industria-lization, which would add the dimension of (construction)crew sociology due to large numbers of spacefarers.
6. Conclusion
Meaningful work for space architects will occur indirect proportion to the vibrancy of development ofhabitable space flight systems. The opportunity para-meters that matter most to practicing or hopeful spacearchitects are immediacy, number, and diversity. Theevolutionary HSF sequence that maximizes these para-meters leverages three enabling markets: (1) commercialorbital passenger travel leading to LEO hotels and (2)parallel government expansion of HSF capability from LEOinto GEO, both followed by (3) demonstration of end-to-end SPS to inform decisions by governments and energyinvestors regarding implementation scale-up. Govern-ment investment in HSF exploration capability yieldssignificantly fewer and less diverse opportunities forspace architects over the decadal timescales of theirworking careers.
Acknowledgments
The publication support was provided by the JetPropulsion Laboratory, California Institute of Technology,under a contract with the National Aeronautics and SpaceAdministration.
References
[1] B. Sherwood, Comparing future options for human space flight, ActaAstronaut. 69 (2011) 346–353.
[2] B. Obama, Space Policy Speech at Kennedy Space Center, April 15,
2010.[3] John C. Mankins, The vision & challenge of solar power satellites:
abundant & affordable solar power on earth & in space, InternationalSymposium on Solar Energy from Space, September 8, 2009. /http://
www.spacecanada.org/docs/Presentation-John-Mankins.pdfS.[4] M. Connors, P. Wiegert, C. Veillet, Earth’s Trojan asteroid, Nature 475
(2011) 481–483. Published online 27 July 2011.[5] B. Muirhead, B. Sherwood, J. Olson, Human Exploration Framework
Team: Strategy and Status, IEEEAC #1759, 2010. IEEE 978-1-4244-
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