AC5 Lifetime v2

0339-EX-PL-2013 Text Documents

Aerospace Corporation, THE

2013-10-24ELS_142188

AeroCube 5 Drag Enhancement Device • In order to comply with the 25-year LEO de-orbit requirement, a passive electrodynamic tether is deployed from AeroCube 5 bus. – Orbit decays faster due to electrodynamic force – Increase in surface area also increase orbit decay rate (atmospheric drag) • The tether has an end mass plate for stabilization. The electrodynamic forces should passively stabilize the spacecraft and deployed tether system in a gravity gradient configuration. g – Device provided by a commercial company Tethers Unlimited Inc. – Total device mass = 83 grams – Tether tape dimensions (16 m length, 75 mm wide) – End plate dimensions (100 mm x 83 mm x 6.5 mm) – Deployed two years after spacecraft operations are complete A-010813-1

AeroCube 5.0 Case Descriptions Case 1 • 4 cases were considered: C Case 2 1. Aerocube body only (assumes average tumble configuration) • Assumes tether is not deployed. ram direction 2. Aerocube and tether device deployed (assumes gravity gradient stabilization) • Tether system is fully deployed and in a gravity gradient nadir stabile orientation until reentry. Case 3 3. Aerocube and tether device deployed (gravity gradient stabilization with libration of the tether of ~30 degrees from nadir) • Tether system deployed but uncertainty in the stabilization 30 degrees effects ff t – Assumption taken from conversations with Nestor Voronka ram direction and Rob Hoyt of Tethers Unlimited 4. Aerocube and tether device deployed (alignment with velocity nadir vector with libration of the tether of ~30 degrees from the velocity vector ) • A different orientation to determine the range of lifetimes. Case 4 ram direction 30 degrees A-010813-1

AeroCube 5.0 Initial Conditions • Area estimation: The AeroCube 5 satellite core body is 10.26 x 10.26 x 17.02 cm – Case 1: Aerocube body (assuming tumble) area = 0.023 m2 – Case 2: Aerocube body + tether system (gravity gradient alignment) with = 0.79 m2 – Case 3: Aerocube body + tether system (gravity gradient alignment with 30 degree libration about nadir)= 0.74 m2 – Case 4: Aerocube body + tether system (velocity vector alignment with 30 degree libration about ram direction) = 0.41 m2 – All areas with tether take into account twist twist. • Ref. Noord, J.L., West, B., Gilchrist, B., “Electrodynamic Tape Tether Performance with Varying Tether Widths at Low Earth Altitudes.”, AIAA, 39th Aerospace Sciences Meeting & Exhibit, Reno, NV, 2001 • Mass estimate: 2.2 kg – includes CubeSat + tether drag device • Atmospheric Assumption: Considered 50th percentile (nominal) level of solar flux (F10.7 ) and geomagnetic index (Ap) – U Used d NASA Marshall M h ll S Space Fli Flight ht C Center t monthly thl predictions di ti (b (based d on NOAA data) d t ) from f November 2012 to 2030; for years after 2030, repeated last 11-years (2019-2030) of Marshall predicted data • Initial orbit (provided by David Hinkley) o – 469 x 972 km perigee/apogee altitude, altitude 120 Inclination, Inclination Epoch: December 1 1, 2013 A-010813-1

Lifetime Case 1: AeroCube5.0 Body (only) • A 50th percentile atmospheric assumption (nominal solar activity) was used to determine the orbit lifetime • The satellite by itself will de-orbit within 25 years after launch A-010813-1

Lifetime Case 2: Aerocube 5 and Tether System (gravity gradient stabilized)) g • A 50th percentile atmospheric assumption (nominal solar activity) was used to determine the orbit lifetime • AeroCube will de-orbit well within 25 yyears after tether deployment p y at the 2 yyear mark Drag Device Deployment A-010813-1

Lifetime Case 3: Aerocube 5 and Tether System (gravity gradient stabilized w/ 30 degree libration) • The orientation of the spacecraft and drag device are assumed to oscillate about the nadir direction with an amplitude 30 degree (cone about nadir). • 50th percentile atmosphere assumption (nominal solar activity) Drag Device Deployment A-010813-1

Lifetime Case 4: Aerocube 5 and Tether System (velocity vector aligned w/ 30 degree libration) • The orientation of the spacecraft and drag device are assumed to oscillate about the negative velocity direction with an amplitude 30 degree (cone about negative velocity). • 50th percentile atmosphere assumption (nominal solar activity) Drag Device Deployment A-010813-1

Conclusions • Case 1, where the AeroCube 5 satellite does not deploy the tether, results in an orbital lifetime of ~23 years • Cases 2 - 4, significant reduction of orbit lifetime with successful deployment of the tether drag device – Independent of orientation if successful tether deployment • Results are conservative since electrodynamic forces were not modeled. • All cases comply with U U.S. S Debris Mitigation Standard Practice requirement of an on-orbit lifetime less than 25 years A-010813-1

Long-Term Orbit Propagation Tools • Used precision integration code TRACE for orbit propagations – Developed by Aerospace (TRACE is used throughout the industry, but we used the most recent Aerospace version) – MSISE-86 atmosphere p model – 70 x 70 modified EGM-96 Earth gravity model – Sun and Moon gravity – Solar radiation pressure (assumed reflectivity coefficient = 1.3) • AeroCube will perform operations for 2 2-years years prior to deploying the drag device; this is accounted for in the propagation. • Did not model electrodynamic force (conservative assumption for lifetime) A-010813-1


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Document Modified: 2013-10-23 22:16:45
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