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

nuclear reactor, to reach speeds of about 95 km/s (20
astronomical units per year), enabling it to travel 1,000
AU (0.016 light-years) within a 50-year mission time. Its
primary science objective would be to measure directly
the distance to stars throughout our galaxy using stellar
parallax. Secondary science goals would include particles
and fields measurements, a search for the heliopause, a
search for the Oort Cloud (a postulated ring of ice-rock
bodies, which, when perturbed by the passage of nearby
stars, may fall into the inner solar system to become
comets), tests of gravitational effects based on changes to
the spacecraft’s trajectory (which could be caused by a
tenth planet or other dark companions in the solar system),
and tests of relativity. TAU would be equipped with
a 10-W laser communications system capable of transmitting
20 kilobits/s from interstellar space.
three-axis stabilization
A type of stabilization in which a spacecraft maintains a
fixed attitude relative to its orbital track. This is achieved
by nudging the spacecraft back and forth within a deadband
of allowed attitude error, using small thrusters or
reaction wheels. With a three-axis stabilized spacecraft,
solar panels can be kept facing the Sun and a directional
antenna can be kept pointed at Earth without having to
be de-spun. On the other hand, rotation maneuvers may
be needed to best utilize fields and particle instruments.
Three-Corner Constellation
A constellation of three nanosatellites due to be
launched from the Space Shuttle in 2003. The mission is
Data for Various Thor-Based Launch Vehicles
Thor ICBM Thor-Able Thor-Able Star Thor-Agena D
Length (m) 22.0 26.9 29.0 31.0
Diameter (m) 2.4 2.4 2.4 2.4
Mass (kg)
Thrust (N)
49,300 51,600 53,000 56,500
Stage 1 670,000 670,000 761,000 759,000
Stage 2 — 33,700 35,100 71,200
Stage 3
Propellants
— 12,300 — —
Stage 1 RP-1/LOX RP-1/LOX RP-1/LOX RP-1/LOX
Stage 2 — IRFNA/UDMH IRFNA/UDMH IRFNA/UDMH
Stage 3
Payload (kg)
— solid — —
LEO — 140 450 1,200
thrust 435
sponsored by the Air Force Research Laboratory, DARPA
(Defense Advanced Research Projects Agency), and
NASA, and supported by design teams at Arizona State
University, the University of Colorado, and New Mexico
State University. Among its goals are to experiment with
stereo-imaging of the atmosphere and to test formationflying
techniques. The satellites will each have a mass of
about 15 kg and be placed into a 380-km-high orbit
inclined at 51°.
throat
In rocket and jet engines, the most constricted section of
an exhaust nozzle.
throatable
A nozzle whose size and profile can be varied. A throatable
nozzle can be especially useful in a solid-fuel rocket
motor to maintain uniform thrust throughout the burn
time of the fuel.
thrust
The forward force generated by a rocket. Thrust is produced
by the expulsion of a reaction mass, such as the
hot gas products of a chemical reaction.
In an optimum situation (see below), thrust equals the
product of the mass expelled from the rocket in unit time
(the propellant mass flow rate) and the exhaust velocity
(the average actual velocity of the exhaust gases). If F is the
thrust, mp the propellant flow rate, and ve the effective
velocity, then
F = m pv e
(1)