  Low gravity environment can have a profound impact on the behaviors of
biological systems, the dynamics and heat transfer of fluids, and the growth
and self-organization of materials. Systematic research on the effects of
gravity is crucial for advancing our knowledge and for the success of space
missions. Due to the high cost and the limitations in the payload size and mass
in typical spaceflight missions, ground-based low-gravity simulators have
become indispensable for preparing spaceflight experiments and for serving as
stand-alone research platforms. Among various simulator systems, the magnetic
levitation based simulator (MLS) has received long-lasting interests due to its
easily adjustable gravity and practically unlimited operation time. However, a
recognized issue with MLSs is their highly non-uniform force field. For a
solenoid MLS, the functional volume $V_{1\%}$, where the net force results in
an acceleration less than 1\% of the Earth's gravity $g$, is typically a few
microliters ($\mu L$) or less. In this work, we report an innovative MLS design
that integrates a superconducting magnet with a gradient-field Maxwell coil.
Through an optimization analysis, we show that an unprecedented $V_{1\%}$ of
over 4,000 $\mu L$ can be achieved in a compact coil with a diameter of 8 cm.
We also discuss how such an MLS can be made using existing high-$T_c$
superconducting materials. When the current in this MLS is reduced to emulate
the gravity on Mars ($g_M=0.38g$), a functional volume where the gravity varies
within a few percent of $g_M$ can exceed 20,000 $\mu L$. Our design may break
new ground for various exciting future low-gravity research.
