Planetary Science Vision 2050 Workshop 2017 (LPI Contrib. No. 1989) 8172.pdf

EXTRA-TERRESTRIAL SPACE ELEVATORS AND THE NASA 2050 STRATEGIC VISION T. Marshall Eubanks1, C.F. Radley1, 1Asteroid Initiatives LLC, Clifton, VA 20124 USA; [email protected];

Introduction: Extra-terrestrial space elevators can provide a transportation network to help fulfill NASA’s Counterweight strategic exploration goals for the next three decades. 15000 Probe While a terrestrial space elevator is not currently pos- 10000 5000 sible without developments in material science, space Moon elevators for the Moon and Mars are possible with ex- 0 isting and commercially produced tether material. El- -5000 evators for Ceres and other asteroids are also techn- -10000 cially feasible and may become relevant within the next -15000 Earth Perpindicular to Lunar orbital plane (km) -30000 -20000 -10000 0 10000 20000 30000 three decades. We have proposed a Deep Space Tether Earth-Moon Radial Direction (km) Pathfinder (DSTP) to provide a solid scientific return while testing tether engineering in deep space, a Lu- nar Space Elevator (LSE) Infrastructure (LSEI) for de- ployment as a functional lunar transport system, and a Figure 1: Trajectories of the two tips of the DSTP during Phobos-Anchored Mars Space Elevator (PAMSE) for a sample collection from the Lunar South Pole, as seen delivery of material to and from the Martian surface. from a selenocentric reference frame [2]. The counter- This paper discusses how these elevators can be inte- weight is considerably more massive than the probe and grated into the NASA Strategic Vision for 2050. is thus closer to the tether center-of-mass, which exe- cutes a smooth ballistic motion. This Figure represents The Deep Space Tether Pathfinder: The DSTP ∼6 hours of total motion. would be a 5000 kilometer long “rotovator” tether [1]. The DSTP would fly by the Moon with a sampling probe on the far tip to collect lunar samples in a touch-and- be a very long tether extending from the lunar Surface, go manner [2], rotating every 2.44 hours to match the through the Earth-Moon Lagrange L1 point (EML-1) velocity of its sampling tip with the lunar surface (see 56,000 km above the Moon, and deep into cis-lunar Figure 1). The sampling capability of the DSTP would space [5]. Table 1 indicates the enormous scale of even a enable sample return from difficult to reach and scientif- prototype LSE; once deployed it could be used to trans- ically interesting regions of the Moon, such as the per- port materials to and from the lunar surface through the manently shadowed regions at the lunar poles [2]. Ap- use of solar-powered climbers traveling up and down proximately 2 hours after sample collection the DSTP the tether, and to provide measurement stations at non- would use its rotational velocity to sling-shot the sam- inertial locations in deep space. The LSEI prototype, ple back to Earth for a ballistic reentry with a minimal scaled to be deployable with one launch of a heavy lift expenditure of fuel. vehicle, would be able to lift roughly 5 tons of lunar The primary scientific justification of the DSTP mis- samples per year, deploy a similar quantity of equip- sion would be lunar sample return; its lunar science ob- ment onto the lunar surface, and provide lunar surface jectives address every one of goals in the “Lunar Polar samples to astronauts orbiting in cis-lunar habitats. Volatiles and Associated Processes” white paper sub- The LP attached to the tether descends to the lunar mitted to the 2011 Decadal Survey [3]. Current DSTP surface in the initial prototype deployment, referred to mission planning has focused on sampling volatiles on after landing as the Landing Station (LS); the planned ◦ the shadowed floor of Shackleton Crater at the lunar nearside LS location is Sinus Medii, near 0 Latitude South Pole, which is a cold-trap and should collect sub- and Longitude. The primary initial science goal of the stantial amounts of surface volatiles from collisions and LSEI prototype mission would be the return of the lu- out-gassing on other areas of the Moon [4]. nar samples to Earth, returning up to 100 kg of samples The DSTP would have a tether taper comparable to at a time using a reusable solar-powered lifter. Return future space elevators (see Figure 2), providing an in- to Earth from a nearside LSE can be done in principle space test of the crucial technology of tether tapering, without fuel, as a sample return capsule could be sim- providing a substantial advance in the technological ply released at the right moment for a direct reentry tra- readiness of tether-based space tethers. jectory to a desired landing location; anything separated Prototype Lunar Space Elevators for the Near from the LSE an altitude & 220,670 km above lunar sur- ∼ and Farside: A LSE is an efficient means of cargo face will re-enter the Earth’s atmosphere in 1.4 days ∼ −1 transport if there is enough demand for delivery of ma- at a velocity of 10.9 km s without any expenditure terials to and from the lunar surface. The LSEI would of fuel. This same technique can be used to return high Planetary Science Vision 2050 Workshop 2017 (LPI Contrib. No. 1989) 8172.pdf

Parameter Elevator DSTP Nearside LSE Farside LSE PAMSE Length (km) 5000 278544 297308 5828 System Mass (kg) 3043 48700 48700 5355 Surface Payload (kg) 150 128 110 150 Total Taper (max / min area) 3.50 2.49 2.49 7.67 Maximum Force (N) 988 517 446 4107 Landing Site Lunar Poles 0◦ E 180◦ E Equatorial

Table 1: Prototype Space Teathers and Elevators [5, 6].

String Linear Density for the Deep Space Tether Pathfinder Prototype Elevators be a Phobos-Anchored Mars Space Elevator (PAMSE) 1.4 Phobos Anchored Mars SE [9, 10], which would use the mass of the Martian moon DSTP 1.2 Lunar Space Elevator as a counterweight, considerably shortening the length, and reducing the total mass required, at the cost of not 1 being able to anchor to the Martian surface. A PAMSE 0.8 with the same carrying capacity of a LSE would have ∼ 0.6 only 12% of the mass of the prototype LSE. Although a PAMSE would not have a zero velocity 0.4 relative to the Martian surface, the average relative ve- String Linear Density (kg / km) 0.2 locity between the PAMSE lower tip and the surface of Mars is ∼530 m/sec, roughly Mach 2 in the cold Mar- 0 0 1000 2000 3000 4000 5000 6000 tian atmosphere, slow enough that it should not cause Distance from lower tip in km significant heating of the tip even near the Martian sur- face. With a height of 14 km the Pavonis Mons volcano Figure 2: The linear density (taper) of various optimum is by a good margin the highest feature underneath the tether models, the full length of the PAMSE (the solid elevator. This mountain could serve as a surface base for red curve) and the DSTP (the dashed blue curve) and elevator logistics, or the elevator tip could use its veloc- the near surface part of the much longer LSE (the dot- ity to act as a fast transport near the surface, potentially dashed green curve). See Table 1 for more details on even rendezvousing with aircraft in the Martian atmo- these models. (These tethers use Zylon with a design sphere. maximum stress of 4.64 Gigapascals.) References: [1] R. L. Forward (1991) in AIAA/ASMA/SAE/ASEE 27th Joint Propulsion Confererence value ore samples or mining products from a lunar min- AIAA–91–2322. [2] T. M. Eubanks (2012) in Lunar and Planetary Science Conference vol. 43 of Lunar and ing enterprise. Planetary Inst. Technical Report 2870. [3] National Research An elevator on the lunar farside could fulfill many of Council (2011) Vision and Voyages for Planetary Science in the scientific and logistical goals of a nearside LSEI, the Decade 2013-2022 National Academies Press, but would also provide unique advantages of its own Washington, D.C. [4] D. A. Paige, et al. (2010) Science [6, 7, 5], including facilitating farside sample return. 330:479 doi. [5] T. M. Eubanks, et al. (2016) Space Policy The farside landing point would also be an ideal location 37P2:97. [6] T. M. Eubanks (2013) in Annual Meeting of the for a farside radio telescope sensitive to the virtually un- Lunar Exploration Analysis Group LPI Contributions 7047. explored radio spectrum at frequencies . 10 MHz [8]; [7] T. M. Eubanks, et al. (2015) in Annual Meeting of the an EML-2 LSEI would considerably reduce the cost of Lunar Exploration Analysis Group vol. 1863 of LPI building and supplying a lunar farside radio telescope Contributions 2014. [8] S. Jester, et al. (2009) New doi arXiv:0902.0493 system, enabling both the installation of antennas on the Astronomy Reviews 53:1 . . [9] L. M. Weinstein (2003) in Conf.on Thermophysics in surface at the LS, as well as vertically using the lower Microgravity; Commercial/Civil Next Generation Space portion of the elevator as a antenna tower [7]. Decamet- Transportation; Human Space Exploration vol. 654 of AIP ric and kilometric radio astronomy could be conducted Conference Proceedings 1227–1235. [10] T. M. Eubanks during the lunar night, when radio interference from the (2012) Global Space Exploration Conference Sun is also blocked and when solar powered climbers GLEX–2012.02.P .2x12186 IAF/AIAA. would not be using the near surface part of the LSE. The Phobos Anchored Martian Space Elevator: A logical follow-on to the DSTP and the LSEI would