8.1 FUTURE MISSIONS

The recommendations of the GRAPWG are divided into the following categories: future intermediate-class missions ($75M to $300M), future MIDEX and SMEX missions ($70M and $35M respectively), current missions, supporting programs, and new technologies.

8.1.1 INTERMEDIATE MISSIONS

Although several important science objectives can be met with small missions in hard X-ray and gamma-ray astronomy (see below), major progress on a broad front depends on intermediate-class missions. The HIGHEST PRIORITY recommendation of the GRAPWG is:

• A next-generation high-energy gamma-ray mission. Such a 10 MeV to 100 GeV mission would follow on the successes of EGRET and address the questions of the nature of jets and AGN, the origin of the diffuse high-energy gamma-ray background, the origin of cosmic rays, the high-energy emission from gamma-ray bursts, the nature of the unidentified high-energy sources. For a mission like the GLAST concept, point-source sensitivity improvements could be one to two orders of magnitude compared to EGRET. New pair tracking technology would be used to give arcminute angular resolution over a field-of-view of 1 steradian or larger. Timely approval of such a mission is imperative to provide the unique and important observations that can be made in this energy range.

The GRAPWG identified two other missions as very high-priority for initiation within the next decade. These programs would serve pressing scientific needs and represent areas where prompt support for technology development and mission study promises great gains in the capabilities and efficiency of these substantial future missions.

• Focusing hard X-ray mission. Such a mission would address the questions of the nature of jets and AGN, the sites of recent galactic supernovae (through ⁴⁴Ti line observations), the origin of cosmic rays, the nature of neutron stars, black hole systems and the accretion process. MicroCrab (3x10^-9 photons cm^-2 s^-1 keV^-1 at 50 keV) sensitivities in the 10 - 100 keV range could be obtained. This is more than two orders of magnitude more sensitive than RXTE. Arcminute imaging would be possible over small (~10 arcmin) fields-of-view.

• Next-generation nuclear line and MeV continuum mission. Such a mission would address the questions of the sites of nucleosynthesis, the supernova rate in the galaxy, the nature of supernova explosions, the origin of cosmic rays, the origin of the diffuse background, the nature of jets and AGN, and how the accretion process works. A large array of position sensitive detectors, possibly configured as a Compton telescope, could give an order of magnitude better detection sensitivity for gamma-ray lines than that expected from INTEGRAL and two orders of magnitude better continuum sensitivity at 10 MeV than COMPTEL. The GRAPWG views this mission as a follow-on to INTEGRAL.