DINO Trade study – Independent tip-mass power system vs tip-mass power from main S/C system

1.  Tip-mass powered by main DINO power system

  1. Pros
  2. No need to design another power system
  3. No need to have it pass additional safety reviews
  4. Tip-mass can last as long as needed
  5. Less batteries needed
  6. Requires less inhibits and simplifies monitoring from GSE
  7. Widens the allowable thermal ranges in the tip-mass
  8. Cons
  9. Must run power leads across 20 meters of tether – heavy line losses
  10. Charged lines can interact with Earth’s magnetic field, which messes with ADCS
  11. Voltage is very low, but there is possibility of plasma buildup around the tether – this will prevent wireless communications in addition to accelerating tether material decay
  12. Addition of wires will dramatically alter the mechanics of unfurling the tether, possibly the most delicate and risky segment of the mission
  13. Power leads vulnerable to breakage due to Z-fold storage configuration – extremely tight bends

2.  Tip-mass powered independently

  1. Pros
  2. Eliminates problems with running power leads along the tether
  3. Allows the main DINO system to be developed separately, while keeping the TM-EPS as simple as possible
  4. Allows CSGC students to build a space-craft power system with minimal outside help, other than with flight-certifying the batteries
  5. TM-EPS need not be commanded by C&DH, except perhaps to turn on and off
  6. Cons
  7. TM instruments only last until battery dies
  8. Must certify two power systems instead of one
  9. More reviews from NASA
  10. A separate power system will require a second set of inhibits and monitors
  11. Must provide a separate plug on the TM for the GSE to verify the power system
  12. TM battery must be kept between 0 and 40º Celsius

3.  Trade Study Conclusions

Upon completion of this trade study, the use of an independent EPS for the

Tip-Mass system is clearly the best route. While having essentially two power systems aboard DINO is going to make getting through the NASA reviews a much taller order, the risks associated with running power leads along the tether are simply unacceptable. Tether deployments are a relatively new technology in satellite design, and notoriously finicky. Tethers tend to get out of control and wrap around the parent spacecraft, or bounce back causing a tumble.

Since DINO is relying on the tether system to establish gravity-gradient stabilization to achieve a nadir-pointing spacecraft, the tether deployment is very mission-critical. Therefore, anything that decreases the odds of successful tether deployment must be avoided. In this case, if the TM-EPS fails to activate, no pictures of the FITS or EMC hinges will be available. Contrast this to what happens if the tether fails due to having added material to it, which is complete mission failure.

Clearly, an independent power system will be more complex to design, simply because it requires its own set of inhibits and battery protection, as well as needing an external connection for GSE. However, the idea is to use the same battery type as the main S/C and encase it in the same manner. Even the monitors will be largely the same, albeit much simplified since the cell will not be re-charged. At most, the system will need to be able to switch on and off, perhaps via a photo-sensor, so no logic or commands will really need to be implemented. To better ensure mission success, there will be no modifications made to the tether, so an independent TM power system must be used.