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Pseudolites (Pseudo- Satellites) (1) Washington, October 11- 12, 2005 Positioning and Navigation On the Moon Walking On the Moon Items to be addressed Premises • Positioning and Navigation services on the Moon: key issues for MOON BASE Program • Integration of localisation with other services (e.g.: TLC, MO): a “must” for Program sustainability Understanding of the problem • “Indoor” and “outdoor” positioning: local / wide range, global. Viable solutions and respective domain and advantages Next steps • Exploiting the partnership with Europe / Italy • Activity Plan to satisfy MOON BASE Program 2 Positioning and Navigation needs on the Moon 3 Positioning and Navigation needs • Moon Base program perspective of permanent settlements on the Moon, both for scientific as well as industrial resources exploitation, implies: – Large infrastructures set up, which requires precise positioning for surveying, – Navigation capability for automatic movement of robots inside infrastructures, which requires local, precise navigation, – Navigation capability to move among different settlements, which requires medium precision, wide range or global navigation, – Geographic information availability for Lunar resources exploitation which require medium or low precision, and global navigation. – Search and rescue services, which requires precise positioning. – Precise positioning of scientific instrumentation, which in some cases is required both in a global, selenocentric as well as a geocentric system 4 Drivers for Local and Global Positioning • Surveying and Positioning for complex infrastructure set up • Indoor/outdoor navigation of people and automatic drive of unmanned rovers and crews • Lunar far side and polar regions operations • Need to improve personal safety in an adverse and risky environment, with limited or no support means and infrastructures • Lunar resources localisation and exploitation • Safe spacecraft flight and exploration • Definition/adoption of a Global Lunar Reference System, linked to the terrestrial one with known transforms • Science ⇒Summary of Needs 5 Integrating techniques to exploit “services” 6 Integration to exploit “combined services” • A Lunar GNSS system is the final step of a process, which implies the use of different methods and instruments for positioning and navigation, locally and globally • As far as the Lunar GNSS constellation and facilities is concerned, the possibility of multi-service / multi-function constellations has to be explored, addressing the integration and cooperative work, on the same platform, of different payloads, covering functions that span from navigation, to communication and Lunar observation • Necessity to implement personal safety concepts (e.g.: global search and rescue), with a return channel available, is also felt as a crucial aspect and “service” • Instrument remote control and data return, up to Earth laboratories, is also to be addressed 7 Viable solutions for “Local” and “Global” Positioning 8 Where am I? Localisation Indoor Outdoor Define user position in 3D, local tangent coordinates, with Local a restricted coverage Define user position in 3D, selenocentric coordinates, Global over the whole satellite 9 Local Positioning: the initial step Local Indoor Outdoor ons Pseudolites i ut ol s e t Optical Signal Generators da ndi Ca ⇒Pseudolites 10 Global Positioning (1) • Global Positioning requires to define and adopt a 3D Global Reference Frame. • Various approach and Space Geodesy techniques can be used to realise the Global Reference System: – Lunar Laser Ranging (LLR) technology, based upon use of retroreflectors placed on Moon surface establishing reference points – Very Long Baseline Interferometry to measure 3D baseline vectors among points on the moon and on the Earth; – Lunar positioning systems based on a GNSS constellation 11 Global Positioning (2) • Using LLR and VLBI techniques, it will be possible to measure reference points on the cislunar face of the Moon; a Lunar Global Reference Frame can be defined, with respect to the Earth Reference System • To extend such a network of lunar reference points to the translunar face of the Moon implies to measure reference points on the Lunar surface directly, from the Moon itself • The Moon centre of mass is the focus of any Lunar satellite orbit. It is the origin of force model to be used for computing orbits. GNSS constellation can “locate” the Moon barycentre, allowing to place properly the origin of the Global reference Frame • Such a capability of “measuring the Moon from the Moon itself” is crucial: merging LLR and/or VLBI information together with raw navigation ranging data, obtained from the Lunar GNSS constellation already orbited, will be the key to achieve a precise definition of Lunar Global Frame and obtain a precise user positioning accuracy 12 System Concepts and Figures of Merit ⇒Principles of Positioning ⇒Dilution of Precision ⇒Constellation Value 13 Sample Lunar Constellation (1) Constellation with 8 satellites on 2 orbital planes (4 satellites per plane), at a distance of about 3 Lunar radii 3 or 4 satellites are simultaneously visible only at Lunar polar regions. At lower latitudes, only 1 or 2 satellite signals can be accessed at the same time Possible augmentations • More polar satellites ? • 2 Additional satellites at L4, L5 Lagrange points ? • Displacement of complementary ⇒Lagrange Points Lunar Pseudolites ? 14 Sample Lunar Constellation (2) Initial constellation (*) with 12 satellites on 2 orbital planes (6 satellites per plane) It guarantees four-signal coverage over most areas of interest However, there are two “blind” spots, where visibility reduces down to 1 satellite. • Augmentations with pseudolites are obviously possible (*) College of Engineering, Utah State University, “AEGIS” System 15 Sample Lunar Constellation (3) Final constellation (*) with 18 satellites on 3 orbital planes (6 satellites per plane). Two orbits are polar, one equatorial It guarantees five-signal coverage over all surface, with zones were up to 11 satellites contemporary visible • RAIM (Receiver Autonomous Integrity) techniques start to be applicable (*) College of Engineering, Utah State University, “AEGIS” System 16 Bringing GNSS satellites to the Moon • To reach polar Lunar orbit from sun-synchronous earth-orbit requires a plane change of 6.5°. • Equatorial Lunar orbit requires a plane change of 7.5° from GTO. • It is necessary to determine where the plane change for the Lunar mission should take place. • The plane change should take place while in Moon orbit rather than Earth orbit, due to a smaller spacecraft velocity • The transfer spacecraft use a Hohmann transfer to reach lunar orbit. Shortly before reaching the point of Lunar orbit insertion, the plane change will take place 17 Exploiting the partnership with Europe / Italy 18 Exploiting partnership (1) • Cooperation between the two sides of the Atlantic Ocean in the field of Space Geodesy is lasting more than twenty years. • As a result of this Heritage, many geodetic fundamental stations accredited in the international community are based in Europe and Italy. In particular very few of these stations can support VLBI, SLR and GNSS Techniques; Matera Space Geodesy Centre of the Italian Space Agency can furthermore support Lunar Laser Ranging. • We believe that such a model of cooperation should be extended to the establishment of a GNSS system on the moon 19 Heritage and Background (3) • Italy is active as well in implementation of satellite navigation systems since 1997, with the successful test of a minimal infrastructure –the Mediterranean test Bed– , built up and operated at Telespazio, Fucino Space Centre, to generate and uplink a SBAS (MOPS DO-229A compliant) complementary signal • Today, Telespazio cooperates with ESA, providing RIMS data to ESTB CPF and having settled two EGNOS signal uplink stations at Fucino and Scanzano Space Centres 20 Road Map to satisfy the Moon Base Program 21 Development Perspectives • The deployment of Lunar GNSS system is a cost effective approach to satisfy Moon Base Program Global Positioning needs. From a logical stand point it could be the last step of a road map where other local positioning techniques are applied. In facts the Global Positioning requirements would follow the progress of colonization and deployment of infrastructures • However, the possible synergies with communication and Lunar Surface Observation needs, could justify an earlier deployment of navigation payloads on board of a multi mission constellation. • The large experience gained by the international community needs to be adapted and transferred from the Earth to the Moon surface. All the steps to support such a transfer must be timely undertaken. • System studies first must be pursued to identify the potential configurations and then the needed technologies selected for pre- development 22 A Road Map for Future Studies • Feasibility studies has to be undertaken quite soon to address at least the following issues: – Analysis of the advantages and drawbacks of different technical solutions of positioning needs depending upon definition and refinement of Lunar Mission profile – Analysis of the feasibility of the deployment of multi-service/multi- function satellites constellation including Moon Observation, TLC and Navigation/Positioning capability. – Go more in depth with benefits, needs, requirements related to positioning and navigation and arising from identified sub-mission chimneys, e.g.: Search & Rescue, model of territory, autonomous guidance on Moon, radioastronomy from
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