466 Requirements 

As the packaging layout of the reference mission progressed, these key requirements for the design of  this tiny actuator became evident:   Tiny envelope of less than 9.83 cm3 (0.6 in3) – the device needed to fit into an approximately 2.54  x 2.54 x 1.524 cm (1” x 1” x 0.6”) envelope.   Low power availability - Since power for the CubeSat  reference mission was at a premium, we  needed to minimize the amount of power drawn by the actuator. The conductive heat loss between the cup and the plug, as well as the cup and the spacecraft, was a priority.     Low upper temperature limit – The avionics on the reference mission didn’t have the capability to  sense the temperature of the actuator; therefore we needed to use a set time for resistor power cutoff. This limitation forced the design to release at a much lower operating temperature in order to reduce the risk of damaging the resistor heating source.   A relatively large holding capacity for the actuator’s size – the load requirement with test factor of  1.5 was 143 N (32.25 lb).   A tension-only boundary condition – due to the short distance from the hinge, a spherical ball  boundary condition was needed, with no room for a spherical bearing.   Low shock – The CubeSat specification prohibits pyrotechnic devices. APL also chose to  minimize shock generated by the chosen release mechanism to protect CubeSat avionics and mechanisms. The CTERA produces negligible shock.   Easily resettable – The device used in the APL CubeSat needed to be easy to reset. Removing  the device from the SV for re-set would cause unacceptable delays in the I&T process.   Use of non-magnetic materials throughout the mechanism. 

Trade Study Results 

We conducted a quick electrical characteristic comparison, shown in Table 1, between the CTE actuator and commercial  devices, with a particular focus on the energy required to actuate them. The table shows  five release actuators and their electrical characteristics. We did not attempt to differentiate mechanical characteristics, since only one other device in the table fits the size constraints to which the CTE actuator was designed.  Table 1 - Device Trade Study  Device Current  (A) Voltage  (V) Power  (W) Resistance  (Ω), Total Δtime  (s) Energy  (W-s) % Battery  Energy  Device #1 (SMA) 1.00 9.00 9.0 9 35 315 0.20%  Device #2 (SMA) 5.36 7.50 40.2 1.4 0.032 1 0.0008%  Device # 3 (Paraffin  Initiated Actuator) 0.36 28.08 10.1 78 150 1516 0.94%  Device #4 (SMA) 3.50 14.70 51.5 4.2 0.035 2 0.0011%  APL CTE Actuator 2.60 7.28 18.9 2.8 17.8 337 0.21% 

Device # 1 can be used in applications similar to those for which the CTE Actuator can be employed. This  device has lots of heritage, produces almost no shock, and is a highly reliable device in APLs experience. Its nominal power performance is slightly better than that of the actuator. This device must be removed from the space vehicle (SV) or instrument to be re-set and it consumes notched bolts with each actuation. This particular model would need to have a custom heater resistance to be used on a CubeSat, since the 9-ohm resistive heater wouldn’t dissipate enough power to actuate the device at minimum voltage (6V). This device, unless non-recurring engineering was expended to re-size it, simply would not fit in the volume allotted in the APL CubeSat.