The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

microsat
A satellite with an on-orbit mass of 10 to 100 kg. See
satellite mass categories.
MicroSat
A constellation of seven 22-kg microsatellites, sponsored
by DARPA (Defence Advanced Research Projects
Agency), and launched on July 16, 1991, by a Pegasus
rocket into a 359 × 457 km × 82° orbit, rather than the
higher intended orbit of 833 × 833 km. The satellites
supported “bent-pipe” relay for voice, data, fax, and slowspeed
video communications, as well as high-fidelity
secure voice and encrypted data and limited store-andforward
communications, and were intended to provide
data for ArcticSat, a system for communicating with
nuclear submarines under the polar cap. However, this
ability was compromised by the lower-than-planned
orbit, which caused the satellites’ footprints to be separated.
All the spacecraft decayed in January 1992 after little
operational use. The mission was also known as the
Small Communications Satellite (SCS).
Microscale Coronal Features probe
A spacecraft designed to provide images and spectroscopic
details of the Sun’s corona at an unprecedented
level of resolution. By showing activity in the corona
that happens very quickly and at small spatial scales, this
data will help distinguish among the various heating
mechanisms that have been proposed. The Microscale
Coronal Features probe has been identified in NASA’s
Office of Space Science Strategic Plan as a potential mission
after 2007.
microwave plasma thruster
An experimental form of electrothermal propulsion
that works by generating microwaves in a resonant, propellant-filled
cavity, thereby inducing a plasma discharge
through electromagnetic coupling. The microwaves sustain
and heat the plasma as the working fluid, which is
then thermodynamically expanded through a nozzle to
create thrust.
microwave radiation
Electromagnetic radiation with wavelengths between 30
cm and 1 mm, corresponding to frequencies of 1 to 300
GHz. Microwaves appear in the electromagnetic spectrum
between longer radio waves and infrared radiation.
MIDAS (Missile Defense Alarm System)
An obsolete and largely unsuccessful system of U.S. military
early-warning satellites launched between 1960 and
1966; it preceded the IMEWS (Integrated Missile Early
Warning Satellite) program. MIDAS spacecraft were
Mightysat 279
designed to detect ballistic missile launches from low
Earth orbit using infrared sensors. They represented one
arm of the first American spaceborne reconnaissance (spy)
system that also included Corona and Samos. The first
MIDAS satellite, launched in February 1960, failed to
reach orbit. MIDAS 2, launched in May 1960, did achieve
orbit to become the first infrared reconnaissance satellite,
but its telemetry system failed after two days. MIDAS 3,
successfully launched in July 1961, also made it into orbit
and was the heaviest American satellite up to that time.
Altogether, there were 12 MIDAS launches, deploying
four different types of increasingly sophisticated sensors,
which paved the way for the development, launch, and use
of IMEWS. Details of MIDAS became publicly available
only on November 30, 1998, when the Air Force Space
and Missile Systems Center declassified the information.
(See table, “Midas Spacecraft,” on page 280.)
midcourse
For lunar and planetary missions, the period between
escape from the originating point and commitment to
entry or orbit at the destination. A midcourse maneuver is
a change to a spacecraft’s flight path during midcourse to
maintain the desired trajectory.
MIDEX (Medium-class Explorer)
Low-cost (typically not more than $140 million for development)
NASA science missions. The first two to be
launched were IMAGE (Imager for Magnetopause-to-
Aurora Global Exploration) and MAP (Microwave
Anisotropy Probe). The next spacecraft in the series, the
Swift Gamma Ray Burst Explorer, is scheduled for
launch in September 2003. NASA will select two from
four MIDEX proposals—ASCE (Advanced Spectroscopic
and Coronagraphic Explorer), Astrobiology
Explorer, NGSS (Next Generation Sky Survey), and
THEMIS (Time History of Events and Macroscale Interaction
during Substorms)—for launch in 2007 and 2008.
Midori
See ADEOS (Advanced Earth Observation Satellite).
Mightysat
Small, relatively inexpensive U.S. Air Force satellites
intended to demonstrate new technologies in space.
Mightysats are developed by the Air Force Research Laboratory
and carry multiple experiments. The first was
launched from the Space Shuttle via the Hitchhiker Ejection
System, the second by a Minotaur. Mightysat 1’s
payload included experiments on composite materials,
advanced solar cells, advanced electronics, and a shock
device. Mightysat 2, also known as Sindri, carried a
hyperspectral imager for Earth imaging and spectroscopy,