• To detect neutrinos from energetic astrophysical objects and events; and

• To measure the full energy spectrum and flavor content of neutrinos from the Sun.

Because of the fundamental and novel new phenomena that can only be studied by a long-baseline gravitational-wave detector in space, and because of its strong and well-developed science and technology plans, the Laser Interferometer Space Antenna (LISA) is the highest priority project of the panel. The mission has generated considerable interest within NASA and has become a cornerstone mission of the ESA program. It is hoped that LISA will be put forward as a joint mission for launch before the end of the first decade of this new century. LISA should observe, for the first time, the coalescence of supermassive black holes as distant galaxies merge. Although merger rates are quite uncertain, event rates are estimated to range from 1 to 100 per year. Location of events in the sky depends on frequency, ranging from several degrees at 10⁻⁴ Hz to 30 arcmin at 10⁻² Hz, with an angular resolution of 1 arcmin in the last few days before coalescence. This should be sufficient for gamma-ray detectors to point and observe the final explosion. LISA will also survey the gravitational radiation from galactic white-dwarf binaries and possibly study gravitational fluctuations from the early universe. The LISA team will carry out a major theory challenge by computing the expected gravitational waveforms from black-hole mergers. This will require developing three-dimensional general relativistic codes with adaptive mesh refinements.

LISA consists of three spacecraft maintained in an equilateral triangular configuration with sides 5×10⁶ km long (Figure 3.1). The system is placed in solar orbit at 1 AU with the plane of the triangle at 60 deg to the ecliptic. The orbit requires little station keeping. The three spacecraft are launched by a single Delta rocket and then deployed into the triangular configuration. The triangle enables the operation of three almost independent interferometers along adjacent pairs of sides. The interferometry is done by heterodyne detection with a single optical pass. Both the frequency range and the science of LISA are complementary to those of the ground-based interferometers (Figure 3.2).

The LISA team has identified three technical areas that would benefit from a dedicated technology mission in space: the inertial reference