LISA Project Update

W. M. Folkner, Jet Propulsion Laboratory, Caltech
william.folkner@jpl.nasa.gov

The last 18 months have been very important for the Laser Interferometer Space Antenna project. Several advisory panels have made very positive recommendations regarding the prospects for a gravitational-wave observatory in space. NASA has begun serious planning for funding the LISA project and associated technology development starting in 2002 while continuing mission studies. The European Space Agency has continued technology development in key areas and funded a Phase A study under a contract led by Dornier Satellite Systems (now part of Astrium). Informal discussions on a partnership arrangement between NASA and ESA have continued and are about to transition to a more formal working arrangement. The prospects for achieving a launch of LISA towards the end of the decade are very good. In 1999 NASA Office of Space Science conducted a series of meetings for the purpose of updating its Strategic Plan. (These updates are held approximately every three years.) A key meeting of the Structure and Evolution of the Universe Subcommittee was held in February 1999 to consider future missions within the SEU theme. Following that meeting the SEUS recommend that LISA be included in the 2000 OSS Strategic Plan as a candidate for a New Start in the 2005-2008 time frame. The SEUS recommendations are published in the SEU Roadmap (http://universe.gsfc.nasa.gov/roadmap.html ). The recommendation of the SEUS was forwarded for consideration by the NASA's Space Science Advisory Committee. At a meeting held in November 1999 (in Galveston) the SSAC endorsed the SEUS recommendation of LISA for inclusion in the 2000 OSS Strategic Plan, which will be reflected in the Plan when published in the upcoming months. Outside NASA two panels commissioned by the National Research Council have given LISA high priority for future missions. The Committee on Gravitational Physics, chaired by Jim Hartle, gave a low-frequency gravitational-wave observatory its highest priority for space missions in gravitational physics (http://www.nap.edu/books/0309066352/html/). The Astronomy and Astrophysics Survey Committee, chaired by Joe Taylor and Chris McKee, ranked LISA as second highest priority among moderate-scale projects for the coming decade (http://books.nap.edu/catalog/9839.html ). NASA funding for the implementation of moderate missions has historically been provided by specific congressional line items in the NASA budget for each project. More recently congress has approved several continuing line items for multiple missions (e.g. Origins, Mars Exploration). NASA has decided to request a new continuing line item, called Cosmic Journeys, for the SEU theme to cover multiple future missions including LISA. If approved, significant advanced technology development for LISA would begin in 2002 with a nominal launch date in 2010. Prior to approval for construction of the mission, the technology needed to achieve the science goals must be demonstrated to a suitable level. For Technology Plan for LISA has been developed and reviewed by an advisory group. One of the key technology issues for LISA is for the test masses to be free of unwanted forces that would cause motions larger than those cause by gravitational waves. For the frequency and sensitivity desired for LISA the disturbances are required to be less than 10^-16 G for times scales of 100 to 10,000 seconds. This level of performance seems achievable, and detailed calculations of expected forces for some designs indicate that the requirements can be met. But the required performance is far beyond any experiment done so far. Furthermore it seems unlikely that the required performance can be demonstrated on Earth. Therefore it is desirable to consider a space experiment to demonstrate the required level of performance. Several concepts have been proposed for a mission to demonstrate technologies needed for LISA. In 1999 NASA's New Millennium Program supported a Phase A study of such a mission concept. The Disturbance Reduction System would have included two test masses and a laser interferometer to measure the distance between them. If the forces on each test were small enough then the distance between them would change very little, showing that the level of force noise was near the LISA requirement. The DRS concept was studied along with two other mission concepts for demonstrating technologies for future space science missions. DRS was not selected for implementation, primarily because the estimated cost the achieve the DRS goals exceeded the cost cap. (The selected mission was the Nanosat Constellation Trailblazer: http://nmp.jpl.nasa.gov/st5/). Because of the high priority status of LISA with NASA and NRC reviews, there are continuing efforts to find the best way to implement the desired technology demonstration. One possibility being very actively studied is the possibility of adding a LISA Test Package to the ST3 Separated Spacecraft Interferometer mission (http://origins.jpl.nasa.gov/missions/st3.html). The ST3 mission is planned for launch into an Earth-trailing orbit in 2005. An Earth-trailing orbit is very desirable for a LISA technology demonstration because the thermal, magnetic, and gravitational environment is much more stable than for an Earth-orbiting mission. The environmental stability is key for achieving the low level of forces needed for the LISA demonstration. At this time, the possibilities for allocating the required funding from NASA, and for forming a partnership arrangement with ESA, for this option are being actively pursued.