: 1958-Beta 2
was the fourth artificial Earth satellite
launched and the first satellite to be
. Although communication
with it was lost in 1964, it remains the oldest manmade satellite
still in orbit and as such is the oldest piece of a cloud of
orbiting Earth. It was
designed to test the launch capabilities of a three-stage launch vehicle
as a part of Project Vanguard
, and the effects of the
environment on a satellite and its systems in Earth orbit. It also
was used to obtain geodetic
through orbit analysis.
The spacecraft is a 1.47 kg (3.2 lb) aluminum sphere
6.4 inches (165 mm) in diameter. It contains a
10 mW, 108 MHz transmitter powered by a mercury battery
and a 5 mW,
108.03 MHz transmitter that was powered by six solar cells
mounted on the body of the satellite.
Six short antenna
protrude from the
sphere. The transmitters were used primarily for engineering and
tracking data, but were also used to determine the total electron content
satellite and ground stations. Vanguard also carries two thermistors
which measured the interior
temperature over sixteen days in order to track the effectiveness
of the thermal protection
version of Vanguard 1 is on display at the Kansas
Cosmosphere and Space Center.
The three stage launch vehicle placed Vanguard into a
654×3,969 km (406×2,466 mi.), 134.2 minute elliptical
at 34.25 degrees on March
17, 1958. Original estimates had the orbit lasting for 2,000 years,
but it was discovered that solar radiation pressure
and atmospheric drag
during high levels of
solar activity produced significant perturbations in the perigee
height of the satellite, which caused a significant decrease in its
expected lifetime to only about 240 years.
A 10 mW mercury battery powered transmitter on the
108 MHz band used for International Geophysical
(IGY) scientific satellites, and a 5 mW,
108.03 MHz transmitter powered by six solar cells were used as
part of a radio phase-comparison angle-tracking system. The
tracking data was used to show that the shape of the Earth
has a north-south
asymmetry, occasionally described as pear-shaped with the stem at
the North Pole. These radio signals were also used to determine the
total electron content between the satellite and selected
ground-receiving stations. The battery-powered transmitter provided
internal package temperature for about sixteen days and sent
tracking signals for twenty days. The solar cell powered
transmitter operated for more than six years. Signals gradually
weakened and were last received at Quito, Ecuador in May 1964 after
which the spacecraft was optically tracked from Earth.
Satellite drag atmospheric density
Because of its symmetrical shape, Vanguard 1 was used by
experimenters for use in determining upper atmospheric densities as
a function of altitude, latitude, season, and solar activity. As
the spacecraft continuously orbited, it would lag its predicted
positions slightly, accumulating greater and greater delay due to
drag of the residual atmosphere. By measuring the rate and timing
of orbital shifts, together with the body's drag properties, the
relevant atmosphere's parameters could be back-calculated. It was
determined that atmospheric pressures, and thus drag and orbital
decay, were higher than anticipated, as Earth's upper atmosphere
tapered into space gradually.
This experiment was extensively planned prior to launch. Initial
(NRL) proposals for the project included conical
satellite bodies; this eliminated the need for a separate fairing
and ejection mechanisms, and their associated weight and failure
modes. Radio tracking would gather data and establish a position.
Early in the program, optical tracking (with a Baker-Nunn camera
network and human spotters
) was added. A panel of
scientists proposed changing the design to spheres, at least twenty
inches in diameter and hopefully thirty. A sphere would have a
constant optical reflection, and constant coefficient of drag
, based on size
alone, while a cone would vary with orientation. James Van Allen
proposed a cylinder, which
became the first US satellite
finally accepted a 6.4-inch sphere as a "test vehicle," with twenty
inches for follow-on satellites. The weight savings, from reduced
size as well as decreased instrumentation in the early satellites,
was considered acceptable.
As the three Vanguards are still orbiting, with their drag
properties essentially unchanged, they form a baseline atmospheric
dataset fifty years old and counting.
Fiftieth (50th) anniversary
The Vanguard 1 satellite holds the record for being in space longer
than any other human-made object. On March 17, 2008 it logged its
50th year in Earth orbit.
group of former NRL and NASA workers has
been in communication, and a number of government agencies were
asked to commemorate the event.
The Naval Research
Laboratory commemorated the event with a day-long meeting at NRL on
March 17, 2008. The meeting concluded with a simulation of the
satellite's track as it passed into the orbital area visible from
Washington, D.C. (where it is visible from the Earth's surface).
National Academy of Sciences scheduled some seminars to mark the 50th
anniversary of the International Geophysical Year, which were the
only official observances known.