Parametric Design The Design Process Level I Design Example: Low-Cost Lunar Exploration Amplification on Initial Concept Review U N I V E R S I T Y O F MARYLAND 2008 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu 1 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Overview of the Design Process Program Objectives System Requirements Vehicle-level Estimation (based on a few parameters from prior art) Basic Axiom: Relative rankings between competing systems will remain consistent from level to level Increasing complexity Increasing accuracy System-level Estimation (system parameters based on prior experience) Decreasing ability to comprehend the big picture System-level Design (based on disciplineoriented analysis) U N I V E R S I T Y O F MARYLAND 2 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Akin s Laws of Spacecraft Design - #3 Design is an iterative process. The necessary number of iterations is one more than the number you have currently done. This is true at any point in time. U N I V E R S I T Y O F MARYLAND 3 Parametric Design ENAE 483/788D - Principles of Space Systems Design
UMd Exploration Initiative Objective Design a system to return humans to the moon within a decade for the minimum achievable cost. 4
Lunar Mission ΔV Requirements To: From: Low Earth Orbit Lunar Transfer Orbit Low Lunar Orbit Lunar Descent Orbit Low Earth Orbit 3.107 km/sec Lunar Transfer Orbit 3.107 km/sec 0.837 km/sec Low Lunar Orbit 0.837 km/sec 0.022 km/sec Lunar Descent Orbit 0.022 km/sec Lunar Landing 3.140 km/sec 2.684 km/sec Lunar Landing 2.890 km/sec 2.312 km/sec 5
Akin s Laws of Spacecraft Design - #9 Not having all the information you need is never a satisfactory excuse for not starting the analysis. U N I V E R S I T Y O F MARYLAND 6 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Mission Scenario 1 What can be accomplished with a single Delta IV Heavy payload (23K kg)? Assume δ=0.15, Ve=3200 m/sec Direct landing LEO-lunar transfer orbit ΔV=3.107 km/sec Lunar transfer orbit-lunar landing ΔV=3.140 km/ sec Lunar surface-earth return orbit ΔV=2.890 km/ sec Direct atmospheric entry to landing 7
Scenario 1 Analysis Trans-lunar injection r T LI = e V T LI Ve = e 3107 3200 =0.3787 m T LI = m 0 (r T LI δ) = 23, 000(0.3787 0.15) = 5260 kg Lunar landing r=0.3748 m LS =1182 kg Earth return r=0.4053 m ER =302 kg This scenario would work for a moderate robotic sample return mission, but is inadequate for a human program. 8
Mission Scenario 2 Assume a single Delta IV-H payload is used to size the lunar descent and ascent elements Delta payload performs landing and return Something else performs TLI for shuttle payload Assume δ=0.15, Isp=320 sec Direct landing (unchanged from Scenario 1) LEO-lunar transfer orbit ΔV=3.107 km/sec Lunar transfer orbit-lunar landing ΔV=3.140 km/ sec Lunar surface-earth return orbit ΔV=2.890 km/ sec Direct atmospheric entry to landing 9
Scenario 2 Analysis Lunar landing (23,000 kg at lunar arrival) r=0.3748 m LS =5170 kg Earth return r=0.4053 m ER =1320 kg Earth departure Payload mass still too low for human spacecraft. EDS gross mass of 77,600 kg is too large for any existing launch vehicle. r=0.3787 m 0 = m T LI (r T LI δ) = 23, 000 (0.3787 0.15) Mass of Earth departure stage m EDS = m 0 m T LI = 77, 600 kg = 100, 600 kg 10
Mission Scenario 3 Assume three Delta IV-Heavy missions carry identical boost stages which perform TLI and part of descent burn Unique Delta IV-H payload completes descent and performs ascent and earth return Boost module inert mass fraction = 0.1 All other factors as in previous scenarios 11
Scenario 3 - Standard Boost Stage m o =23,000 kg m i =2300 kg m p =20,700 kg LEO departure configuration is three boost stages with 23,000 kg descent/ascent stage as payload m LEO =92,000 kg 12
First Boost Module Mtotal=23,000 kg Mprop=20,700 kg Minert=2300 kg Isp=320 sec 13
Scenario 3 TLI Performance Boost stage 1 ( ) m0 m prop V 1 = V e ln V TLI remaining=2291 m/sec Boost stage 2 r=0.70; ΔV 2 =1141 m/sec V TLI remaining=1150 m/sec Boost stage 3 m 0 r=0.55; ΔV 3 =1913 m/sec = 816 m sec Residual ΔV after TLI=763 m/sec Total booster performance=3870 m/sec 14
Alternate Staging Trade Study Three identical stages Serial staging (previous chart) ΔV=3870 m/ sec Parallel staging (all three) ΔV=3597 m/sec (penalty is 273 m/sec) Parallel/serial staging (2/1) ΔV1=1913 m/sec ΔV2=1913 m/sec ΔVTotal=3826 m/sec (penalty is 44 m/sec) Pure serial staging is preferred 15
Ascent/Descent Performance 763 m/sec of lunar descent maneuver performed by boost stage 4 Remaining descent requires 2377 m/sec r=0.4758 m i =3450 kg m LS =7493 kg Earth return r=0.4053 m i =849 kg Return vehicle mass is still significantly below that of the Gemini spacecraft - need to examine other numbers of boost vehicles m ER =1913 kg 16
Effect of Number of Boost Stages Earth Return Payload 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 3 4 5 6 7 Number of Boost Modules 17
Creating a Baseline Need to use Scenario 3 calculations to provide more than 3500 kg of Earth return mass (Gemini-class spacecraft) Select 6 boost modules based on trade study performed (mer=3719 kg) Establish as an early baseline: something to use as a standard, vary parameters to identify promising modifications Often termed strawman design It wonʼt last!!! Design iteration will continue 18
Initial Configuration Sketch 19
Baseline System Schematic TEI TEI TEI TEI TEI Landing Landing Descent Descent Ascent Ascent Mass Mass Mass Mass Mass Mass Crew Cabin 20
Akin s Laws of Spacecraft Design - #20 (von Tiesenhausen's Law of Engineering Design) If you want to have a maximum effect on the design of a new engineering system, learn to draw. Engineers always wind up designing the vehicle to look like the initial artist's concept. U N I V E R S I T Y O F MARYLAND 21 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Transport Architecture Options Transportation node at intermediate point (low lunar orbit, Earth-Moon L1) Leave systems at node if not needed on the lunar surface, e.g.: TransEarth injection stage Orbital life support module Entry, descent, and landing systems Will increase payload capacities at the expense of additional operational complexity, potential for additional safety critical failures 22
Akin s Laws of Spacecraft Design - #10 When in doubt, estimate. In an emergency, guess. But be sure to go back and clean up the mess when the real numbers come along. U N I V E R S I T Y O F MARYLAND 23 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Variation 1: Lunar Orbit Staging Assume same process as baseline, but use lunar parking orbit before/after landing Additional ΔVʼs required for LLO stops Lunar landing additional ΔV=+31 m/sec Lunar take-off additional ΔV=+53 m/sec Low lunar orbit waypoint changes baseline payload to 3579 kg (-3.8%) Not useful without taking advantage of node to limit lunar landing mass 24
Lunar Orbit/Landing Trade Study Delta V for lunar landing = 2706 m/sec Delta V for launch to lunar orbit = 2334 m/ sec Assumptions: inert mass fraction = 0.15, exhaust velocity = 3200 m/sec 3.58 kg of mass in lunar orbit is required to land 1 kg of payload on the surface 10.8 kg of mass in lunar orbit is required to land 1 kg of payload on the surface and return it to orbit 25
Variation 2: Lunar Orbit Rendezvous What donʼt we need on the lunar surface? Trans-Earth injection stage Heat shield Parachutes Landing systems Structure stressed for Earth launch Leave unnecessary stuff parked in LLO Only take to the surface what needs to be on the surface 26
Variation 2 System Schematic TEI Mass TEI Mass TEI Mass TEI Mass TEI Landing Mass Landing Mass Descent Descent Ascent Ascent Lander Cabin Descent Descent TEI ER Cabin TEI 27
Orbital vs. Landed Mass Trade Study Lunar Landing Cabin Mass (kg) 6000 5000 4000 3000 2000 1000 0 0 2000 4000 6000 8000 10000 12000 Earth Return Vehicle Mass (kg) 28
Other Analyses Youʼve Already Seen Reliability and spares analysis (Lecture 6, pgs. 19-22) Boost module tank trade study (Lecture 9, pgs. 12-13) Cost trade-offs (Lecture 10, pgs. 13-21) 29
The Next Steps From Here Perform parametric sensitivity analyses mass fractions Specific impulse More detailed studies of crew cabins to determine minimum masses for lunar and Earth entry spacecraft Perform more trade studies, e.g. 2 crew cabins vs. 1 Different propellant choices Consider other alternatives (e.g., Direct) Reach decision(s) on revision of baseline Detailed configuration design 30
Initial Concept Review - Details Post slide files prior to class on ELMS/ Blackboard site under ICR forum Bring PPT files to class on USB drive - will use classroom PC for presentations Must have at least two speakers (plan handoffs) Must use microphone during talk Ten minutes/group (rigidly enforced), two minutes for questions during transitions U N I V E R S I T Y O F MARYLAND 31 Parametric Design ENAE 483/788D - Principles of Space Systems Design
Initial Concept Review - Grading Algorithms Grade on ICR (equal weightings) Originality/critical thought Number and detail of analyses Quality of oral presentation (clarity, energy, engagement) Overall technical merit Grade on Problem 5 (equal weightings) Overall quality of presentation (organization, slide design, appropriate information density Quality and use of graphics U N I V E R S I T Y O F MARYLAND 32 Parametric Design ENAE 483/788D - Principles of Space Systems Design