AC7 ProxOps CONOPS Appendix

0787-EX-PL-2014 Text Documents

Aerospace Corporation, THE

2015-02-20ELS_159177

AeroCube-7 Proximity Operations CONOPS Joseph Gangestad 14 February 2014 Astrodynamics Department © The Aerospace Corporation 2013

RPO CONOPS Flow Chart 2. Approach “staging point” for RPO 1. Begin with radial/in- • Propulsive correction for orbit-plane differential (inclination, RAAN) 3. Arrive at staging point, track/cross-track offset • Close in-track via differential drag ~2 km in-track from target (>10 km) (bang-bang attitude-control scheme 4. Staging-point tests with 5. Depart staging point for 6. Begin RPO from start warm-gas propulsion RPO start point, ~1 km in- point • Test eccentricity change: reduce track from target • Reduce cross-track excursions below radius of Hill’s orbit • Via differential drag or propulsion, 50 m • Test plane change: reduce cross-track TBD • Reduce radius of Hill’s orbit excursions • Induce small in-track relative motion in • Test evasive maneuvers with direction of target differential drag and propulsion 7. Perform RPO 8. End RPO 9. Repeat RPO as desired • Chaser “corkscrews” around target • Chaser passes target and reaches ~1 • “Corkscrew” back and forth around • Perform radar and imaging tests km in-track offset beyond target target • In-track motion stopped via propulsion joseph.w.gangestad@aero.org 2 Astrodynamics Dept.

RPO CONOPS Notional Diagram 1. Start from distance >10 km Target 2. Use differential drag to AeroCube approach “staging point” 3. Arrive at staging point 2 km from target 4. Perform 6. Begin RPO 8.End RPO propulsion/maneuvering tests at staging point from start point 7. Perform RPO: 5. Depart staging point for chaser AeroCube RPO start point “corkscrews” around target. joseph.w.gangestad@aero.org 3 Astrodynamics Dept.

Initial Conditions • After deployment and during checkout, AeroCubes will drift due to initial deployment dispersions and checkout activities. • Begin RPO with substantial (>10 km) in-track separation between AeroCubes, plus some radial and cross-track separation – Will use differential drag during checkout if available to minimize in-track separation as much as possible • Assumptions for this analysis: – Orbit is 500 km circular, 65 deg inclination – Min drag area: 150 cm2 – Max drag area: 500 cm2 – Mass: 2 kg joseph.w.gangestad@aero.org 4 Astrodynamics Dept.

Approach Staging Point • RPO process begins with approach to a “staging point” to ensure control of the spacecraft and efficacy of planned maneuver schemes. • Use on-board propulsion to correct plane differences between AeroCubes: – Based on AeroCube-4 experience, as much as 0.002 deg of inclination change, costing 30 cm/s of ΔV. – As much as 0.005 deg of RAAN change, costing 75 cm/s. – Budget 2 m/s total, performed in small amounts over many orbits. – Can perform plane change maneuvers at any time. • Use differential drag with a bang-bang attitude-control scheme to approach the target AeroCube within 2 km in-track. This is the “staging point.” – At end of differential drag process, mean motion of chaser and target are matched. joseph.w.gangestad@aero.org 5 Astrodynamics Dept.

Approach Staging Point, In-Plane Motion Preliminary Differential-Drag Motion, Differential drag with a bang-bang attitude- In-Track vs. Radial control scheme brings the spacecraft 110 together within 2 km and holding 100 Begin here Preliminary Differential-Drag Motion, 90 In-Track vs. Radial 80 3.0 70 2.5 In-Track [km] 60 50 2.0 In-Track [km] 40 1.5 In-track motion 30 mostly eliminated at staging point 20 Target 1.0 satellite Converge on 10 staging point at origin 0.5 0 -20 -15 -10 -5 0 5 10 15 20 Radial [km] 0.0 -0.50 -0.25 0.00 0.25 0.50 High-fidelity orbit propagation with TRACE Radial [km] joseph.w.gangestad@aero.org 6 Astrodynamics Dept.

Approach Staging Point, Out-of-Plane Motion Motion at 2-km Staging Point, At the staging point, the target Cross-Track vs. Radial has some cross-track motion. 0.20 0.15 Target's line The line of motion (the orbit of motion at velocity vector) of the target 0.10 origin AeroCube goes into/out of the Cross-Track [km] screen in this plot. The chaser 0.05 AeroCube “orbits” around that line of motion 0.00 -0.05 Risk mitigation: by following this -0.10 trajectory, the chaser never Chaser corkscrews crosses the path of the target, -0.15 around target preventing collisions. -0.20 -0.20 -0.10 0.00 0.10 0.20 Radial [km] High-fidelity orbit propagation with TRACE joseph.w.gangestad@aero.org 7 Astrodynamics Dept.

Tests at Staging Point: Eccentricity Reduction Small burns (~10 mm/s) performed in the Eccentricity Reduction Test radial direction reduce the radius of the Hill’s orbit (left). These burns can occur as often In-Track vs. Radial as every half-orbit. In practice, will use 3 longer lead times. Note that the cross-track motion (below) is not affected; the chaser Finish, 5 burns and 2.5 orbits later still never crosses the path of the target. 2.5 Eccentricity Reduction Test 2 Cross-Track vs. Radial In-Track [km] 0.2 0.15 1.5 Start 0.1 Cross-Track [km] 0.05 1 0 -0.05 0.5 -0.1 -0.15 0 -0.2 -0.5 -0.25 0 0.25 0.5 -0.2 -0.1 0 0.1 0.2 To Earth Radial [km] To Earth Radial [km] Rule of thumb: ~10 mm/s of DV reduces radius of Hill’s orbit by ~20 m. joseph.w.gangestad@aero.org 8 Astrodynamics Dept.

Tests at Staging Point: Cross-Track Reduction Small burns (~10 mm/s) performed in the cross-track direction reduce the cross-track Cross-Track Reduction Test excursions of the Hill’s orbit. These burns Cross-Track vs. Radial can occur as often as every half-orbit. In 0.2 practice, will use longer lead times. 0.15 0.1 Cross-Track Reduction Test Start Cross-Track [km] Cross-Track vs. In-Track 0.05 0.1 0.08 0 0.06 -0.05 0.04 Finish, 4 burns and Cross-Track [km] 0.02 -0.1 2 orbits later 0 -0.15 -0.02 -0.2 -0.04 Each burn reduces the -0.2 -0.1 0 0.1 0.2 -0.06 out-of-plane component To Earth Radial [km] -0.08 of the Hill’s orbit -0.1 1.7 1.8 1.9 2 2.1 2.2 2.3 In-Track [km] joseph.w.gangestad@aero.org 9 Astrodynamics Dept.

Note on Risk from Staging-Point Tests • In the event that a test burn is misaligned entirely in the in-track direction, the chaser will continue to corkscrew around the line of motion of the target due to cross-track motion. Closest approach to target’s line of motion >50 m. • If a test burn is misaligned in the cross-track direction, the change in cross-track motion is minimal. • No individual burn is sufficient to put the chaser AeroCube on a collision course with the target. – Until we have high confidence in the performance of the thruster later in the mission, each burn will be followed by orbit determination and thruster-performance analysis to ensure that the new desired orbit was achieved. – In the event of an anomaly or undesired behavior, no further burns will be performed to ensure the safety of both spacecraft. joseph.w.gangestad@aero.org 10 Astrodynamics Dept.

Transfer: Staging Point to RPO Start Point Transfer: Staging Point to Transfer: Staging Point to RPO Start Transfer from the RPO Start staging point to the In-Track vs. Radial In-Track vs. Radial RPO start point can 3 occur over different 3 timescales. The longer 2.5 the transfer takes, the 2.5 cheaper it is in ΔV. 2 2 In-Track [km] In-Track [km] 1.5 Start: Staging point 1.5 1 1 End: RPO start point 0.5 0.5 0 0 -0.5 -0.25 0 0.25 0.5 -0.5 -0.25 0 0.25 0.5 To Earth Radial [km] To Earth Radial [km] 1 orbit transfer, ΔV = 12 mm/s 3 orbit transfer, ΔV = 4 mm/s joseph.w.gangestad@aero.org 11 Astrodynamics Dept.

RPO: Initiate In-Track Drift and Approach Target RPO: In-Track Drift to Target A small burn (~10 mm/s) induces in-track motion relative to the target. The chaser corkscrews In-Track vs. Radial around the target over the course of several orbits, 1.5 passes the target, and then performs another burn (~10 mm/s) to stop 1 km beyond the target. Start 1 RPO: In-Track Drift to Target Cross-Track vs. Radial 0.5 0.1 In-Track [km] 0.08 0 0.06 0.04 Cross-Track [km] 0.02 -0.5 0 -0.02 -1 -0.04 End -0.06 -0.08 -1.5 -0.1 -0.5 -0.25 0 0.25 0.5 -0.2 -0.1 0 0.1 0.2 To Earth Radial [km] Radial [km] Because of out-of-plane motion, the chaser never crosses the target’s path. joseph.w.gangestad@aero.org 12 Astrodynamics Dept.

RPO: Chaser-to-Target Range The duration of the RPO depends on the amount of in-track drift induced. For this ΔV = 20 mm/s (start and stop) example, the RPO takes about one day, with closest approach halfway. AeroCube-OCSD RPO: Chaser-to-Target Range 1.2 1.1 1 0.9 0.8 Range [km] 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Time [min] In this example the closest approach is ~50 m. As confidence grows, the radius of the Hill’s orbit will be reduced. joseph.w.gangestad@aero.org 13 Astrodynamics Dept.

RPO: Chaser-to-Target Relative Velocity In this example, the relative velocity between the chaser and target does not exceed 0.35 m/s (<1 mph). AeroCube-OCSD RPO: Chaser-to-Target Relative Velocity 0.35 0.3 Relative velocity [m/s] 0.25 0.2 0.15 0.1 0.05 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Time [min] Even is a collision did happen, these relative velocities are not high enough to cause fragmentation or a catastrophic breakup. joseph.w.gangestad@aero.org 14 Astrodynamics Dept.

ΔV Budget Event ΔV [m/s] Comment Plane corrections 2 Staging-point test: eccentricity 0.1 ~10 mm/s per maneuver reduction Staging-point test: cross-track 0.1 ~10 mm/s per maneuver reduction Transfer from staging point to 0.12 Maximum possible cost (for RPO start point transfer in 1 orbit) RPO: start and stop in-track drift 0.02 RPO: modify radius of Hill’s orbit 0.01 Changes radius by ~20 m A full RPO cycle, including Hill’s orbit modifications, costs ~30 mm/s. Even with this conservative DV budget, the 10 m/s capacity of the AeroCube-7 system should permit dozens of RPO cycles with considerable propellant margin. joseph.w.gangestad@aero.org 15 Astrodynamics Dept.

Summary • The AeroCube-7 RPO CONOPS has been designed to minimize risk to both vehicles and to build maximum confidence via incremental testing of maneuver schemes. – “Dress rehearsal” maneuvers at a staging point will characterize control authority on chaser AeroCube without risk to target. – Cross-track amplitude is always maintained to ensure that the chaser AeroCube never crosses the path of the target, preventing collision. • During RPO, chaser “corkscrews” around target – Radius of Hill’s orbit will be reduced incrementally over several RPO cycles. • ΔV budget has considerable margin – Each RPO cycle costs ~30 mm/s – Can perform dozens of RPO cycles joseph.w.gangestad@aero.org 16 Astrodynamics Dept.


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Document Modified: 2015-02-19 21:29:19
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