Lightweight aerobrakes for debris mitigation
Bernasconi, M.C.
MCB Consultants

The concept of removing satellites from their orbits by way of inflatable devices probably is as old as the concept of the artificial satellite itself (see e.g. Leonard, Brooks & McComb, 1960; MacNeal & Kyser, 1966). When the increasing satellite population led to the identification of the risk induced by space debris, suggestions to use inflatable devices for mitigating it soon appeared (see e.g. Anon, 1995; Meyer & Chao, 2000) - we "re-invented" the concept ourselves (Woods & Bernasconi, 1992). Most relevant studies, however, have focused on the orbital characteristics or on the aerodynamic performance of brake shapes (see e.g. Roberts & Harkness, 2007), largely neglecting the actual technology of the brake itself.

We looked at low-load braking systems and at their potential economics. Heat-transfer considerations limit the loads on the expandable structure, because allowable operational temperatures define the needed number of passes; thus, the design accommodates an aerodynamic pressure, for a lifetime to extend over a substantial number of revolutions. Trusses with braking blankets appear to offer the lowest-mass design.

To assess the significance of the spacecraft's mass, we discussed satellites in the range of 50 - 500 kg, assumed to evolve on an 800-km, circular orbit. As the attractiveness of such a space-debris mitigation device decreases with the ballistic coefficient of the spacecraft (without brake), we modeled different numbers of deployed solar paddles and varied the initial propellant load to appraise the economics of such devices. The expandable elements consist of single-ply prepregs and Teflon-glass blankets build the braking surfaces. Given that the blankets alone have an area mass of 0.075 kg/m2, the lowest overall value can be expected at around 0.09 kg/m2. In most cases, the brake takes up less than 2% of spacecraft mass. By comparison with the needs for additional propulsive mass (fuel and tankage), one finds a net mass advantage for the aerodynamic option in all cases. This fact, however,or does not yet guarantee its economic validity.

Accordingly, through an activity-oriented cost estimation model, we estimated the recurring value of the manufacturing activities (for mature items), which depend clearly from the object's size. Over the considered size range, specific costs drop by almost a factor of two for the largest elements. The potential economic value of the brake concept results from (i) a cost reduction for the tank procurement and from (ii) a lower launch cost, against the procurement cost of the device itself. Thus, for varying propellant load factor and initial satellite masses, brakes are competitive with all-propulsive orbit lowering for spacecraft having launch masses of a few hundreds kilograms.

References

Anon (1995). Guidelines & Assessment Procedures for Limiting Orbital Debris. NASA Safety Standard 1740.14.

Robert W Leonard, George W Brooks, & Harvey G McComb jr (1960). Structural Considerations of Inflatable Reentry Vehicles. TN D-457.

Richard H MacNeal & Albert C Kyser (1966). Deployable Tension-Shell Decelerators / Technical Summary Report. NASA CR-66258; Astro Research document ARC-R-229.

KW Meyer & CC Chao (2000). Atmospheric Reentry Disposal of Low-Altitude Spacecraft. JSR 37[05], 670-674.

Peter CE Roberts & Patrick G Harkness (2007). Drag Sail for End-of-Life Disposal from Low Earth Orbit. J Spacecraft Rockets 44[06], 1195-1203.

A.R. Woods & M.C. Bernasconi (1992). Debris Removal & Protection Through the Use of Simple Expandable Structures. Paper TOF PPH-92-007 accepted for presentation at the First European Space Debris Conference, Darmstadt (Germany).

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PPH-08-072