MightySat-2.1,[2] also known as P99-1 or Sindri was a small spacecraft developed by the Air Force Research Laboratory[3] to test advanced technologies in imaging, communications, and spacecraft bus components in space.

Power was provided by 2-axis articulated Si solar arrays with a designed end-of-life power output of 330 W. The attitude determination and control subsystem featured a 3-axis zero-momentum-bias reaction wheel assembly with a Sun sensor, a star tracker and inertial measurement units, delivering an attitude jitter of 15.7 arcsec/sec, and pointing accuracy and knowledge of 648 and 540 arcsec, respectively.

The communication was compatible with the US Air Force space-ground link system with data rates of 1 Mbit/s for payload/experiments data downlink, 2.0 kbit/s for command uplink, and 20 kbit/s for telemetry downlink.

Computing and data handling was done by a RAD6000 CPU @ 20 MIPS with an IEEE VME backplane 128 MByte CPU RAM, and a 21.6 MBytes/sec transfer rate, and a 2 Gbit solid state recorder for science data.

It deorbited in November 2002 due to natural decay of its orbit, exceeding more than twice its nominal lifetime.