Abort Black Zones
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Abort Black Zones NASASpaceflight.com 191 Agenda • Introduction • Bigelow Mission Design Recommendation • Designing a Trajectory for Human Flight • Black Zones from Unsafe Landing • Black Zones from High-G Re-entry • Trajectory Shaping to Close the Black Zones for 401 • Performance Impacts from Black Zone Closure • Backup Charts NASASpaceflight.com 192 Introduction • The concept of flying people on the Atlas has been assessed at various times over the years. • The most in-depth study (aside from Project Mercury) was during the Orbital Space Plane (OSP) study. • Atlas worked closely with NASA and the OSP contractors (LM, Boeing, and Northrup Grumman) to perform detailed trajectory studies and assess every aspect of crew deliveries to orbit. • The Bigelow mission will be able to benefit from the extensive analyses that have already been done to make sure the ascent is safe for human spaceflight. NASASpaceflight.com 193 Background • For any Atlas flight, the mission requirements are evaluated and a trajectory is designed that meets those requirements. • For a typical GTO or satellite delivery mission, the most obvious parameter is performance (mass to orbit), however there are numerous additional constraints that we design to meet – Maximum Dynamic Pressure, G-level limits, Angle of Attack constraints, Time at specific throttle levels, etc. • For human missions, the over-arching design parameter is safety for the passengers. • The trajectory design is modified for human missions so that all safety concerns are addressed. NASASpaceflight.com 194 The Bigelow Mission Our Recommendation for the Bigelow Mission: • Mission orbit of 489 km (264 nmi) circular, 41° inclination • Atlas will deliver the capsule to a low-perigee transfer/phasing orbit (131 x 489 km or 71 x 264 nmi), capsule will perform circularization – This stable delivery orbit will allow several revs before re-entry (time to react/plan) should a return be required NASASpaceflight.com 195 The Bigelow Mission (Cont) • Mission orbit is a repeating ground track orbit • Provides daily launch opportunities to Bigelow station with minimum phasing, which reduces on- orbit capsule mission duration requirement • Provides 4 daily landing opportunities at Utah Test & Training Range, and Edwards AFB compatible with low capsule cross range • Inclination is high enough to allow tourists to see most populated parts of Earth and allow communications links to US-based tracking facilities, but lower than ISS for improved launch vehicle performance NASASpaceflight.com 196 Ground Track Plot The same ground track repeats each day NASASpaceflight.com 197 Sub-vehicle Trace NASASpaceflight.com 198 Instantaneous Impact Point Trace NASASpaceflight.com 199 Designing for Human Flight • During the OSP work, NASA identified a term that is used for human flight - Black Zones. • Black Zones are any period of flight when an abort would be unsafe for the passengers • Threats to passenger safety takes different forms: – Unsafe landing conditions if the aborting capsule falls into hostile terrain – High-g loads which occur during a re-entry • Deceleration can exceed human tolerance if the aborting capsule falls from too high an altitude, and hits the dense lower atmosphere too fast and too steeply • A great deal of effort was spent during OSP identifying potential black zones and modifying the mission or trajectory design to eliminate them. NASASpaceflight.com 200 Black Zones from Unsafe Landing Conditions • Black zones from unsafe landing conditions – The location of the vehicle impact point at the time of an abort will determine whether the capsule will have unsafe landing conditions • Capsule impact points from any given abort is determined by the timing of the abort • The resulting impact point is predictable pre-launch • When a capsule aborts, the re-entry impact point is already set (high L/D vehicles have greater flexibility) • Unsafe landing conditions are largely a result of the launch site and the final orbit desired – Orbital inclination is a key parameter of the final orbit • High inclinations such as ~50 degrees requires impact points that cross the North Atlantic and could cross the Alps NASASpaceflight.com 201 Black Zones from High-G Re-entry • Capsule altitude, flight path, and velocity determine the re-entry deceleration profile – Capsule altitude, flight path, and velocity of any given abort is determined by the timing of the abort – The resulting re-entry deceleration profile is predictable pre-launch • When a capsule aborts, the re-entry geometry is already set Ascent Trajectory 18 16 14 12 Abort Entry 10 Trajectory 8 Altitude (ft) 6 4 Load Factor (G's) 2 0 750 775 800 825 850 Range (nmi) Mission Time (sec) NASASpaceflight.com 202 Causes of High-G Black Zones • The combination altitude, flight path, and velocity which result in black zones can often be seen in lofted trajectories – Lofted trajectories are associated with high orbits, low Thrust/Weight upper stages • High orbits require the vehicle to achieve high altitudes for insertion – Limited burn durations require the vehicle to loft to achieve those altitudes before the final stage burns out (time to orbit) • Low thrust to weight vehicles require the boost stage to loft the upper stage and allow it the time required for its full burn – Low time to orbits from high thrust upper stages or high orbits can result in lofted trajectories – Low thrust/weight upper stages can result in lofted trajectories • Low L/D re-entry vehicles also increase the likelihood of black zones (results in steeper re-entry) • The boost phase trajectory and the resulting re-entry trajectory determine high-g black zones NASASpaceflight.com 203 Abort G Level Requirements • G Requirements come from NASA-STD-3000, Volume 8, Feb 1, 2005, “Human- Systems Integration Requirements.” Project Constellation using CXP-70024– (Same Requirement) +Gx Eye Balls In OSP Crew Loads Limits for sustained or short term plateau accelerations 100 Maximum allowable for automated crew abort /escape Design limit for nominal ascent & entry (conditioned crew) Design limit for deconditioned, ill, or injured crew References: 198, p. 13; 415; 418; NASA-STD- 3000-50 10 Acceleration (g's)Acceleration 4 sustained 1 0.1 1 10 100 1000 Duration (sec) Figure 5.3.3.1-1 Linear Sustained Acceleration Limits NASASpaceflight.com 204 Closing the High-G Black Zones Assumptions: • Launch Vehicle – Injection Orbit 131 x 489 km (71 x 264 nmi) at 41 deg – Maximum boost acceleration of 4 g's – Impact point trace • No North Atlantic, no Alps – No constraint on Q and heating (covered by capsule) • Capsule – L/D = ~0.3; conservative – Capsule has control during re-entry – Assumed ~350 fps Delta V required for capture/ circularization (provided by abort escape system) – Seat angles were varied to improve re-entry loads NASASpaceflight.com 205 Shaping the Boost trajectory • Depressing the boost trajectory reduces the altitude from which the capsule will fall, and provides a less steep re-entry flight path angle • The Atlas V 402 has a higher thrust Dual Engine Centaur and flies a more depressed trajectory which causes no black zones • A lower thrust Atlas V 401 flies a more lofted trajectory which requires re-shaping to close black zones 402 Already Satisfies Black Zone Requirement 401 Requires Shaping to Close Black Zones NASASpaceflight.com 206 Abort Load and Black Zone Analysis Process CAD Model NASA Human Factors Limits Capsule Generic Abort Tables of G, q, and Aerodynamic Trajectories for load margin Analysis all Starting Conditions vs Altitude, Velocity, (EVADE) (POST) Flight Path Angle Cl, Cd, L/D G = f (h, v, γ) Ballistic Coefficient Target CG Location Seat Angle Atlas Ascent Mission-specific Adjust for Dispersions & Trajectory Shaping Abort Trajectories Crew Orientation, (POST/TRAJEX) (POST) Validate Against Reqt’s Payload to Orbit Load vs Time Approximate abort load 18 Loads vs Duration in the +Gx direction ("Eyeballs in") 100 16 14 12 10 10 8 Loads (G's) G G Load 6 G Limit for Abort/Escape G Limit for Nominal Ascent/Entry 4 Predicted G Exposure During Abort 2 1 0 0.1 1.0 10.0 100.0 1000.0 700 750 800 850 900 Duration (sec) Time (sec) NASASpaceflight.com 207 Black Zones Elimination • Abort loads can be reduced by “depressing” the launch trajectory to fly lower and flatter – This is more easily done by upper stages with higher thrust/weight ratios • Trajectory shaping using a flattened ascent profile successfully eliminated black zones NASASpaceflight.com 208 Simulation Re-entry Acceleration Re-entry simulated from worst point on the ascent profile. Trajectory Trajectory Shaped for Shaped to Optimum Close Black Zones Performance (Bigelow Orbit) Trajectory (GTO) Shaped for Optimum Performance (Bigelow Orbit) NASASpaceflight.com 209 GTO Mission - High Re-entry Loads Abort Limit for loads taken into chest Loads vs. Duration (Assumes seat is oriented such that all loads are Loads vs. Duration taken through chest) 100 +Gx Accel, Eyeballs In GTO Design violates Maximum abort g-limit 10 Re-entry Acceleration Loads (G's) Loads +15% for Disp. 1 Simulation Re-entry Acceleration 0.1 0.1 1 10 100 1000 Duration (sec) NASASpaceflight.com 210 MPG Shaped - Marginal Re-entry Loads Reentry Loads, Shaped with MPG Rules (Assumes seat is oriented such that all loads are Abort Limit for loads taken into chest taken through chest) Loads vs. Duration 100 MPG Shaped Design just touches +Gx Accel, Eyeballs In Maximum abort g-limit – no additional margin 10 Re-entry Acceleration Loads (G's) Loads +15% for Disp. 1 Simulation Re-entry Acceleration 0.1 0.1 1 10 100 1000 Duration (sec) NASASpaceflight.com 211 Shaped to Close Black Zones – Re-entry Loads with Margin Re-entry Loads, Shaped to Close Black Zones Abort Limit for loads taken into chest (Assumes seat is oriented such that all loads are taken through chest) Loads vs. Duration 100 +Gx Accel, Eyeballs In Extra Margin Desirable to account for RSS Effect of Gy and Gz loads 10 Re-entry Acceleration Loads (G's) Loads +15% for Disp.