  Nanosatellites, and especially CubeSats, at low earth orbits (LEOs) are a low
cost option for monitoring atmospheric and environmental conditions around
Earth. For instance, data for weather forecast reports can be obtained
periodically with these kind of small satellites. Therefore, to academic
institutions, universities, etc., this fact makes nanosatellites a very
attractive way for researching with a moderate budget.
  In this project we compute orbital lifetimes (or simply lifetimes) for
hypothetical missions involving nanosatellites at LEO, focusing our attention
on exploring regions along the equatorial line. Thus, in the framework of
orbital mechanics, we show the viability for these kind of missions in a long
and a short term. Applications are projected for countries in northern South
America, central Africa and islands/countries in southern Asia.
  To compute lifetimes, we take into account three effects: i) gravitational,
ii) Earth deformations and iii) atmospheric density. These effects are included
in the motion equation for a nanosatellite around Earth. After solving this
equation for initial altitudes in 200-800 km above mean sea level (AMSL), we
compute and report flight times to arrive at 150 km AMSL. These results are
defined here as lifetimes and they are calculated for different
atmospheric-density profiles according to experimental data and estimations.
  In conclusion, we find lowest and highest lifetimes for hypothetical missions
involving small satellites at LEO orbiting along the equatorial line, and
propose upper limits for density relative uncertainties in order to estimate
reliable lifetimes.
