CRAWFORD, SMITH: MOONLITE MoonLITE: A UK-led mission to the Moon Downloaded from https://academic.oup.com/astrogeo/article/49/3/3.11/218588 by guest on 24 September 2021 Ian 1: Farside view of the Moon Crawford as seen by the and Alan Clementine spacecraft. Smith Penetrators discuss the launched by the MoonLITE orbiter scientific would allow surface objectives of investigations in areas not visited by Luna, the proposed Surveyor or Apollo missions. MoonLITE mission. (NASA/JPL/USGS) hile the surface missions to during the Apollo programme (see Wiec- the Moon of the 1960s and 1970s zorek et al. 2006, for a review). Moreover, the Wachieved a great deal, scientifically recent remote-sensing missions have themselves much was also left unresolved. The recent ABSTRACT raised questions that will require new surface plethora of lunar missions (flown or proposed) measurements for their resolution, of which reflects a resurgence in interest in the Moon, not MoonLITE is a proposal for a UK-led one of the most important is the circumstantial only in its own right, but also as a recorder of mission to the Moon that will place four evidence for water ice, and by implication other the early history of the Earth–Moon system and penetrators in the lunar surface in order volatiles, within permanently shaded craters at of the interplanetary environment 1 AU from the to make geochemical and geophysical the lunar poles (Feldman et al. 1998). Sun (e.g. Spudis 1996, Crawford 2004, Jolliff measurements that are impossible from In order to make significant further progress et al. 2006, NRC 2007). Although the Clemen- orbit. It has the potential to make major in lunar science, and to make better use of the tine and Lunar Prospector missions have greatly contributions to lunar science, while at lunar geological record to understand solar sys- added to our knowledge of the geochemical and the same time providing knowledge that tem evolution more generally, it will be neces- mineralogical makeup of the lunar surface, and will be of central importance in planning sary to return to the surface. It will be especially these observations will soon be supplemented by future human missions to the Moon. Plus, important to make geophysical and geochemi- results from Kaguya, Chang’e-1, Chandrayaan-1 MoonLITE will demonstrate technologies cal measurements from areas not visited by and Lunar Reconnaissance Orbiter, our knowl- that will have wide applications for the previous missions, including the poles and the edge of the lunar interior is limited and relies exploration of other solar system bodies. farside. MoonLITE (Moon Lightweight Inte- largely on geophysical measurements made rior and Telecommunications Experiment) is a A&G • June 2008 • Vol. 49 3.11 CRAWFORD, SMITH: MOONLITE THROWING LIGHT ON MOONLITE (a) (b) Downloaded from https://academic.oup.com/astrogeo/article/49/3/3.11/218588 by guest on 24 September 2021 (c) (d) 2:Stages in the development of MoonLITE. (a) Cross-section of the type of penetrator to be used, with payload bays at the rear. (MSSL/ QinetiQ) (b) Full-scale penetrator outer body (with tip removed) for impact trials. (QinetiQ) (c) Impact trials showing penetrator-like object passing through 2 m of concrete. (QinetiQ) (d) An artist’s impression of the MoonLITE orbiter just after the release of one of its penetrators. (SSTL) proposed UK-led lunar science mission that To obtain “ground truth” geochemical data seismometer network, which would address the ● will contribute to these objectives by emplac- to complement orbital remote-sensing observa- following scientific questions. ing four scientific penetrators at widely spaced tions; and Size and physical state of the lunar core. Such ● localities on the lunar surface (Gao et al. 2008). To collect in situ surface data that will help in knowledge of the lunar core as we have has been ● In addition, a telecommunications experiment the planning of future lunar exploration. obtained from studies of the Moon’s moment of (the “TE” in “MoonLITE”) will be used to These top-level science objectives require that inertia and physical librations, and electromag- develop expertise in Moon–Earth communica- the penetrators emplace instruments capable of netic induction studies (Wieczorek et al. 2006). tions that will benefit UK involvement in future contributing to at least four different areas of These studies favour a small (R < 400 km), lunar missions. scientific investigation: seismology, heat-flow, partially liquid core, with suggested composi- In 2007 MoonLITE was considered by the geochemical analysis, and volatile detection/ tions ranging from iron–nickel, Fe–FeS alloy, BNSC–NASA Joint Working Group (JWG characterization. These are discussed in more to molten silicates. Confirmation of the size, 2008), which was established to explore avenues detail below. composition and physical state of a lunar core for UK–US collaboration in space exploration would have profound impacts on our under- following the signing of a statement of intent Seismology standing of the Moon’s origin, mantle evolu- in April. This report strongly endorsed the Seismology is the most powerful geophysical tion and magnetic history. For these reasons, MoonLITE concept, describing it as an “inspi- tool available for determining the interior struc- constraining the nature of the Moon’s core is a rational” project and “the primary mission for ture of a planetary body. However, the only top scientific priority of the penetrator-deployed potential [UK–US] cooperation”. Cooperation object other than the Earth where it has been seismic network. with other partners is also a possibility. In successfully applied is the Moon, where the Deep structure of the lunar mantle. One of ● the coming months, MoonLITE will undergo Apollo seismometers yielded important infor- the main contributions lunar studies can make an assessment of the science case by an inter- mation on the Moon’s natural seismic activity, to planetary science is an enhanced understand- national peer review panel and a formal Phase-A and the structure of the lunar crust and upper ing of the internal differentiation processes that technical study. If approved for implementation mantle (Goins et al. 1981, Lognonné 2005). take place immediately after the accretion of a it will fill an important gap within the proposed However, the deep interior of the Moon was terrestrial planet. Magma oceans are likely to international lunar mission portfolio and help only very loosely constrained by Apollo seis- have been a common phase in the early evo- facilitate the future scientific and ultimately mology because the network was geographi- lution of rocky planets and, in contrast to the human exploration of the Moon. cally limited (essentially an equilateral triangle more evolved mantles of the larger terrestrial on the centre of the nearside between the Apollo planets, the structure of the lunar mantle may Scientific objectives 12/14, 15 and 16 sites; figure 3), so the informa- preserve a record of these early times. Seismol- The principal scientific objectives of the Moon- tion obtained on crustal thickness and mantle ogy may help elucidate these processes by con- LITE penetrator mission are: structure may not be globally representative. straining the initial depth of the magma ocean To further understanding of the origin, differ- There is now a pressing need for a more widely and its mineralogy (Lognonné 2003). Again, ● entiation, internal structure and early geological spaced network of lunar seismic stations, new, and more widely spaced, seismic data are evolution of the Moon; including stations at high latitudes and on the required if this record is to be deciphered. To obtain a better understanding of the origin farside. Penetrators delivered from orbit are Thickness of the farside lunar crust. Reinter- ● ● and flux of volatiles in the Earth–Moon system; ideally suited as a means of emplacing a global pretations of the Apollo seismic data have 3.12 A&G • June 2008 • Vol. 49 CRAWFORD, SMITH: MOONLITE now constrained the thickness of the nearside least of the abundances of the major rock-form- both of which will be ejected before impact. anorthositic crust to between about 30 and ing elements (e.g. Mg, Al, Si, Ca, Fe and Ti). Each penetrator will impact the lunar regolith 40 km (e.g. Wieczorek et al. 2006, Lognonné This could be achieved by penetrator-deployed at a speed of ~300 m s–1 (equivalent to a free 2003). However, the thickness of the farside X-ray fluorescence spectrometers. As well as fall from 30 km onto the lunar surface). It is crust has not been seismically constrained. teaching us much about the geology of the sites entirely feasible for an instrumented package Estimates based on gravity data are typically in that have yet to be sampled, such measurements to survive an impact at such speeds and a vast the range 70–90 km (Wieczorek et al. 2006) but would provide additional “ground truth” for amount of resource has been devoted to such these are non-unique, and farside seismic meas- the calibration of remote-sensing instruments conditions within a defence context. “Penetra- urements are required to determine the average on forthcoming lunar orbital missions. tors” are common-place within that sector lunar crustal thickness, which has significant and a (limited) range of components are avail- implications for understanding the bulk com- Polar volatiles able off-the-shelf that will survive impacts of position, and thus origin, of the Moon. As is well known, the Lunar Prospector neu- >50 000g (MoonLITE expects up to 10 000g). Studies of natural moonquakes. Understand- tron spectrometer found evidence for enhanced This expertise is by no means purely empirical ● ing natural lunar seismicity, and especially the concentrations of hydrogen at the lunar poles, in nature; a very sophisticated predictive mod- relatively strong (up to magnitude 5) shallow which has been widely interpreted as indicating elling capability also exists.