this engine can double the orbital
lifetime of a CubeSat in some cases
(the extension depends on the height
of the CubeSat’s orbit).
In high altitude orbits where the
air density is low, a PPT only requires
0.04 watts of power to counteract
the effects of air drag. In a lower
earth orbit, the increased air drag
means a CubeSat carrying a PPT
needs to expend over two watts of
power to overcome the effects of
Another CubeSat propulsion
system is the resistojet. Surrey
Satellite Technology Ltd (SSTL) sells a
resistojet consisting of a hot wire in
which a liquid propellant is forced
into contact with it. As the liquid gets
hot, it vaporizes and creates thrust.
What kinds of propellant are
used? The propellant used in the
Surry Training, Research, and
(STRaND-1) CubeSat uses butane as
its propellant. The system is called
BPS for Butane Propulsion System
and has an Isp of 90 seconds. With
the amount of propellant available
and the design of the resistojet,
STRaND-1 can change its velocity by
a total of two meters per second.
I found another interesting
product for CubeSats: braking sails. A
One way to mitigate this risk is to
place CubeSats into low earth orbits
(LEO) that decay after a year or two.
A second way is to install braking
systems on CubeSats.
The orbital lifetime of a
spacecraft depends on its size, shape,
Once a CubeSat has
completed its mission,
there’s usually no reason
for it to remain in orbit.
Therefore, an end of life
system to return
CubeSats back to the
atmosphere in a
destructive manner fills
an important need.
Clyde Space is
creating AEOLDOS, or Aerodynamic
End Of Life Deorbit System for
CubeSats as a way to remove
CubeSats from orbit. AEOLDOS is a
system to de-orbit CubeSats, as Clyde
Space puts it. It acts like the reverse
of a solar sail.
Instead of using solar radiation
pressure to propel a CubeSat, the
braking sail increases the surface area
of a CubeSat in order to slow it
down. The increased surface area
increases the drag that the
atmosphere imparts to the CubeSat.
The lower the CubeSat’s altitude, the
greater the density of earth’s
atmosphere and the greater the drag
created by the sail. The braking sail
will remove a CubeSat from orbit
much more quickly than it would
This was a brief discussion about
attitude control and change of
velocity systems available for
CubeSats. Next time, I’d like to
acquaint readers with some of the
CubeSat programs out there. You’d
be surprised to learn where some
people want to send CubeSats.
Onwards and Upwards,
Your near space guide NV
April 2015 73
This artwork by the University of Michigan depicts a test of the ion
engine they are designing. This engine uses permanent magnets in
order to reduce the power requirements of the engine.
An artist impression of the Aerodynamic End
Of Life Deorbit System for CubeSats doing its
thing. The sails are folded up inside a thin
module attached to a CubeSat. At the
appropriate time, the sails deploy out from