Hindawi Publishing Corporation International Journal of Aerospace Engineering Volume 2015, Article ID 341384, 9 pages http://dx.doi.org/10.1155/2015/341384 Research Article LARES: A New Satellite Specifically Designed for Testing General Relativity Antonio Paolozzi,1,2,3 Ignazio Ciufolini,3,4 Claudio Paris,2,3 and Giampiero Sindoni2 1 Scuola di Ingegneria Aerospaziale, Sapienza Universita` di Roma, Via Salaria 851, 00138 Roma, Italy 2Dipartimento di Ingegneria Astronautica Elettrica ed Energetica, Sapienza UniversitadiRoma,ViaEudossiana18,00184Roma,Italy` 3Centro Fermi, Via Panisperna 89, 00184 Roma, Italy 4Dipartimento di Ingegneria dell’Innovazione, UniversitadelSalento,ViaperMonteroni,73100Lecce,Italy` Correspondence should be addressed to Antonio Paolozzi; [email protected] Received 30 August 2014; Accepted 24 November 2014 Academic Editor: Linda L. Vahala Copyright © 2015 Antonio Paolozzi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. It is estimated that today several hundred operational satellites are orbiting Earth while many more either have already reentered the atmosphere or are no longer operational. On the 13th of February 2012 one more satellite of the Italian Space Agency has been successfully launched. The main difference with respect to all other satellites is its extremely high density that makes LARESnot only the densest satellite but also the densest known orbiting object in the solar system. That implies that the nongravitational perturbations on its surface will have the smallest effects on its orbit. Those design characteristics are required to perform an accurate test of frame dragging and specifically a test of Lense-Thirring effect, predicted by General Relativity. LARES satellite, although passive, with 92 laser retroreflectors on its surface, was a real engineering challenge in terms of both manufacturing and testing. Data acquisition and processing are in progress. The paper will describe the scientific objectives, the status of the experiment, the special feature of the satellite and separation system including some manufacturing issues, and the special tests performed on its retroreflectors. 1. Introduction not still well identified but seem related to the specific lunar environment such as particle deposition on CCR front face Typical satellite lifetime is about 10 years, but for passive due, for instance, to micrometeorites induced dust. Based on satellites such as LARES (LAser RElativity Satellite) there is that information it can be hypothesized that a lower limit no such estimate because duration is basically only limited for LARES lifetime could be about 50 years. Besides that, by the stability of the optical properties of the retroreflectors LARES, as the densest orbiting body in the solar system, and therefore is extremely long; for example, the LAGEOS will reenter very slowly. Orbital lifetime for LARES can be satellite is efficiently operating since 1976, that is, since 38 estimated of several thousand years [3] which is a remarkable years.PassivesatellitesoftencarryCubeCornerReflectors duration considering the relatively low orbit. According to (CCRs) that have the property of reflecting back to the other estimates the reentry will happen in about 100 thousand laser ground stations a laser pulse regardless of the CCR years. The possibility to rely on a long mission duration is orientation. By measuring the exact flight time of the laser an interesting point, because LARES experiment requires pulse it is possible to measure the distance with errors that both the accurate orbit determination and the most accurate canbeaslowasfewmillimeters.EventhelunarCCRs gravitational and nongravitational perturbation estimation. areoperationalsinceyear1969[1] when the Apollo 11 Measurement techniques and knowledge of gravitational mission left an array of CCRs on the Moon. However a perturbations have been dramatically improving over time severe degradation on the reflecting performances of all in the last decades. It is expected that in the future further lunar CCRs arrays has been observed [2]. The causes are improvements will be achieved so that a longer lifetime for 2 International Journal of Aerospace Engineering LARES could allow a more accurate experiment. This trend Mathematically the gravity field of a planet can be expanded has been already experienced with two other passive satellites: in spherical harmonics [21]. The ones critical for LARES the LAGEOS satellites. In [4]afirstobservationoftheLense- experiment are the so-called even zonal harmonics: Thirring effect (a General Relativity prediction) has been 2 4 ⋅⋅⋅2.Theeffectof2 (which physically corresponds obtained using EGM-96 gravitational field released in 1996. to the Earth polar flattening) on the LARES orbit is similar Later [5] a more accurate measurement has been obtained to frame dragging but million times bigger. That means that with an accuracy of about 10% [6]thankstotheGRACEspace the knowledge of the Earth gravitational field has to be very mission and to the accurate release of the EIGENGRACE02S accurate to be able to distinguish the Lense-Thirring effect gravitational field7 [ ]. from the effect of 2 and of the other even zonal harmonics. Unfortunately the present accuracy of gravitational fields is 2. Scientific Objectives notsufficientbyitselftomeettheobjective.Infacteventhe most accurate gravitational fields determinations available Although LARES data can be exploited by geodesists today, such as EIGENGRACE02S, have uncertainties on the to improve the International Terrestrial Reference Frame effect of 2 that are still of the order of the Lense-Thirring (ITRF) by about 25% [8] and to perform other geodesy and effect.Awayoutofthisproblemhasbeenproposedby geodynamic studies, its main objective is to test the gravita- combining the results of the two LAGEOS satellites. This tional theory of General Relativity. It has been confirmed by wayitisinfactpossibletoeliminatetheeffectof2 and all the tests performed so far starting from the famous Mer- consequently of its uncertainty, reaching a final accuracy of cury perigee shift9 [ ] to the light deflection due to a mass [10], the Lense-Thirring effect of about 10%. The LAGEOS 1and to the equivalence principle [11, 12],tothetimedilationinthe 2 satellites were launched in 1976 by NASA and in 1992 by presence of a mass (Gravity Probe A experiment) [13, 14], and NASA and ASI, respectively. The 10% error is mainly due to to the time-delay in the propagation of electromagnetic waves the uncertainties of 4 that will be eliminated with the new near a mass. Also gravitational waves, although not directly LARES satellite as shown by the error analysis performed observed by the many detectors developed so far, have been in [22] and, using an indepented approach, in [23]. Since indirectly observed through their effects on binary pulsars the17thofFebruary2012,whenthefirstlaserreturnsignal [15]. Frame dragging is another intriguing effect guessed was received from the orbiting LARES satellite, millions of by Einstein before the publication of the General Relativity ranging data have been acquired by ILRS [24]. However theory [16]:acurrentofmass-energywilldragspacetime, there are some other periodical perturbations related to the time [17], and the local inertial reference frames. The axis Luni-Solar tides whose uncertainties can be eliminated by of an inertial reference frame orbiting Earth, a gyroscope, averaging and fitting for their orbital effects over a sufficiently will not always point towards “fixed” stars, as in Galilei- long period of time. That means it will take a few more years Newton mechanics, because it will be dragged by the Earth before one can further reduce the error in the Lense-Thirring rotation. The effect is very small but measurable: in polar effect measurement from the 10%, already obtained, to about orbitat650kmitwouldamounttoonly39.2milliarcsec/year. 1%. On the other hand from the first data analysis it has been The most direct and intuitive way to physically realize an verified that LARES is indeed the best test particle today inertial reference frame is through three mutually orthogonal available in the solar system [25]. gyroscopes in free fall. This type of reference frame has been actuallymanufacturedandlaunchedin2004inapolarorbit at 650 km altitude after 40 years of development and has been 3. Mission Description called the Gravity Probe B experiment. It has been among the most expensive experiments ever built because of its very The opportunity provided by the European Space Agency high technological achievements. Some unpredictable effects (ESA) for the qualification launch of VEGA was taken by the on the four spherical gyroscopes limited the accuracy in Italian Space Agency (ASI) that decided to support LARES themeasurementofthedriftofthegyroscopeaxesdueto mission in 2008. This launch opportunity was also taken by frame dragging to about 19% [18]. In principle, another way three more Italian spacecraft (ALMASat-1 from University of realizing a gyroscope is to consider the vector orthogonal of Bologna and two Cubesats from Politecnico of Turin (E- to the orbital plane of a satellite in the ideal case of an ST@R) and Sapienza University, Gauss (UniCubeSat-GG)). unperturbed orbit and of a perfectly spherical gravitational Besides those three satellites, the educational