Monday, July 31, 2017
LightSail 2 Needs to Compensate for the Decrease in Perigee Periodically
One can compare the energy change in LightSail 2's orbit that with that required to go into a transfer orbit. After a number of revolutions however the perigee of the light sail starts to drop. This loss of energy has to be compensated for if one desires to go into a circular orbit at the light sail's apogee.
In the plot above the blue curve indicates the velocity change Δv required to go from a point of the light sail's orbit into a circular orbit. The solid red line is the total Δv required to go from the original circular orbit into a circular orbit at the apogee of the transfer orbit. The dashed red line indicates just the Δv required to go from the apogee of the transfer orbit into a circular orbit. Initially the orbit injection Δv's of the light sail match up with the Δv's for the transfer orbit. After about six revolutions more Δv is required to compensate for the drop in perigee. The implication appears to be that the orbit of the light sail needs to be periodically corrected to a circular orbit to keep the light sail from becoming parasitic. The major deficiency of the light sail is that the direction of its thrust is limited. It's lack of angular acceleration requires an auxiliary propulsion system for some orbit changes.
Supplemental (Aug 1): The deviations in the Δv's for the light sail when going to the higher circular orbit are affected by the step size. Here the step size was Δt=60 seconds. Compare next blog.