MSE Status LIST Dec10v1 MS1

LISA Mission System Engineering: 

LISA Mission System Engineering LIST Meeting Roger Diehl Tupper Hyde Marcello Sallusti December 10, 2005

Agenda: 

Agenda Error Budgets & Technical Performance Measures Trade Studies Status Technical Baseline

MRD Requirements (Jan 05): 

MRD Requirements (Jan 05) This allocation slightly misses Hard point at 5 mHz

Look at moving IMS low end up: 

Look at moving IMS low end up This allocation also slightly misses Hard point at 5 mHz

Astrium Performance Outlook: 

Astrium Performance Outlook 0.65 * SRD 3.0 science requirements Makes hard point at 5 mHz

IMS Error Budget Needs Work: 

IMS Error Budget Needs Work

CBEs for DRS: 

CBEs for DRS

CBEs for IMS: 

CBEs for IMS

Technical Performance Measures: 

Technical Performance Measures

Telemetry Budget: 

Telemetry Budget

Trade Studies Completed: 

Trade Studies Completed Strap Down : Old Baseline : One proof mass to proof mass measurement New Baseline : Three measurements (proof mass to optical bench in first sciencecraft, optical bench to optical bench between two sciencecraft, optical bench to proof mass in second sciencecraft) Rationale : Decouples inertial sensor and inter-spacecraft interferometry Optimizes each functional assembly for its prime objective Strong heritage from LTP Impact : Requires point-ahead-angle actuator on optical bench Optical Readout : Old Baseline : None New Baseline : “Minimum” design- 3 axis (x,theta-y,theta-z) from “back side” bench interferometer Rationale : Relax stiffness and crosstalk requirement, no extra hardware Impact : Minor increase in interface complexity

Trade Studies Completed: 

Trade Studies Completed Photodiode Sampling : Old Baseline : None New Baseline : 50 MHz Rationale : Provides require 2.5 times factor to 20 MHz max expected doppler frequency. Impact : Implies orbit design requirement of 15 m/s max arm length rate (with margin to 20 MHz). Implies frequency management scheme where doppler is only 1 times rate effect. Arm Locking : Old Baseline : None New Baseline : Direct arm locking without reducing requirements on laser, cavity, phasemeter, clocks or TDI. Rationale : Provides technology off-ramps (risk reduction) for reference cavity stability, clocks, and phasemeter dynamic range Impact : No new hardware needed. Detailed simulations are underway to define hardware requirements implied by armlocking (method of cavity tuning).

Trade Studies Completed: 

Trade Studies Completed Science Data Rate : Old Baseline : 1500 bps to TDI master though inter SC comm (TDI ver I on board) New Baseline : 400 bps per sciencecraft (allocation), TDI on ground Rationale : Interpolation allows resampling for TDI processing on ground. Impact : 400 bps includes margin on top of “front”, “back” and “LO-LO” phasemeters (each with two redundant quad output photodetectors). Telemetry Rate Old Baseline : 0.45 kbps per SC continuous New Baseline : 5 kbps per SC continuous Rationale : Housekeeping “reality” and sciencekeeping first cut estimate, (first cut bottoms up telemetry estimate showed 4.1 kbps with margin) Impact : relook at comm hardware (see next trade)

Trade Studies Completed: 

Trade Studies Completed End-to-End Data Architecture : Old Baseline : 30 cm HGA, 5 W X-band SSPA, DSN 8 hours/2days, inter S/C comm over laser link New Baseline : 30 cm HGA, 25W Ka TWTA (TBD), DSN 8 hours/2days, inter S/C comm over laser link using spread spectrum on carrier Rationale : Meet telemetry allocation. Inter SC comm required to support ranging and clock tone transfer. No extra hardware. Impact : Software to support spread spectrum mod and demod. Dynamics Parameters : Old Baseline : Multiple sets of simulation parameters with no CM. New Baseline : Database of parameters agreed to by lead dynamicists at both Astrium and NASA. Rationale : All simulation should reference a common baseline. Impact : Parameter database kept under CM by MSE (Tupper).

Work In-Progress: 

Work In-Progress Orbits : Old Baseline : NASA and ESA trajectories based on different launch dates with different delta-Vs Recommended New Baseline : Select delta-V that envelopes all launch dates Rationale : Provide flexibility to launch any day of the year Impact : Operations orbits will either lead or trail Earth depending on launch date. Getting-To-Orbit : Old Baseline : Solar electric propulsion, Delta IV Med (4,2) (4045 kg capability) Recommended New Baseline : Chemical (Dual-Mode) propulsion, Atlas V 531 (5185 kg capability) Rationale : Chemical propulsion less risk due to less complexity and lower cost. Atlas family has more “steps” due to strap-on options. Impact : Will stay on intermediate launch vehicle. Further LV options to be considered after further mass and delta-V reduction studies.

Work In-Progress: 

Work In-Progress PAA Actuator : Old Baseline : No PAA Rejected option : rotating wedges (Risley prisms), periodic operation. Recommended New Baseline : 1 DOF actuator, TNO Design (Ti-6Al-4V integral structure with piezo actuation and front face centered cross blade flexure). Continuous operation. Rationale : the strap down concept do not allow to use the PM to steer the incoming laser beam on the science photodiode Impact : Addition of actuator, delta mass on optical bench of 75g, additional noise due to actuator in the measurement path Pointing (TA) Mechanism : Old Baseline : 2-stage linear actuator with pivot bearings (FTR) Options: 2 lever “tiller” with OTS linear actuators, rotary piezo stepper motors. Recommended New Baseline : TBD Rationale : TBD Impact : TBD

Work In-Progress: 

Work In-Progress Wave Front Error Impact : Old Baseline : far-field effect budgeted to 8 nrad/rtHz, 30 nrad offset, periodic calibration (TBD), flat spot centering. Rejected Options: continuous dither, bright spot (not flat spot) centering, no on-ground correction. Recommended New Baseline : periodic calibration (2 weeks), flat spot centering, near field pointing (phase center moment arm) budgeted, near and far field effects cancelled on ground Rationale : flat spot centering results in only 2 % loss of power, pointing knowledge is 2-40 times better than pointing error Impact : send down quadrant info from “front” science phasemeters, two tone dithering during calibrations to pick out near and farfield effect, PAA pointing noise directly degrades pointing knowledge Telescope : Old Baseline : Dall-Kirkham 40 cm (up from 30 cm in FTR), optical assy articulation Rejected options: Off axis, Three mirror anistigmat, in-field pointing (+/- 1.5 deg), telescope only pointing. Recommended New Baseline : Cassegrain 40 cm, optical assy articulation Rationale : Cassegrain is least complex but still allows for placement of pupils at PAA steering mirror and at quad science photodetector. Potential for larger FOV to support option of through telescope natural star tracking (TBD). Impact : Additional reflective or transmissive optics required between secondary and first beamsplitter

Trade Studies In-Progress: 

Trade Studies In-Progress Redundancy Philosophy Old Baseline : No credible single point failure shall degrade the mission below the minimum mission performance. Rejected Options: A single failure cannot degrade the mission below the minimum mission success criteria (assuming two arm LISA is still a success). Recommended New Baseline : No credible single point failure shall degrade the mission below the full science requirements. LISA system must be one failure tolerant (fail safe). Rationale : Such a philosophy is appropriate for the scale of the LISA mission. Impact : Design has to implement full redundancy. Failures must be detected before extant capability is damaged. Waivers are required for credible single point failures which are prohibitively expensive to make redundant and whose failure would degrade but not end the mission. The GRS may require such a waiver since there is no redundant GRS and it’s loss still allows two arm science operations).

Trade Study (Dec 05- Feb 06): 

Trade Study (Dec 05- Feb 06) The “2 million km arm” Study: ESA and NASA quick-look to find “significant” mass/complexity/risk/cost reductions Goal to maintain full science performance Evaluate cost payoff of slight relaxation at 5 mHz requirement point Reduce Arm Length to 2 million km Cruise deltaV reduced from ~1000 m/s to under ~700 m/s, 500 kg savings, opens monoprop option again Use PM forcing on sensitive axis (~1x10-9 m/s2) to “buck out” earth induced perturbation Max doppler reduced from 15 to ~1 MHz Triangle breathing angle reduced from 1.5 deg to ~0.15 deg Eliminate optical assy articulation Removes large structural stage, large mechanism and launch locks Replaced with in-field pointing (perhaps periodically) Phasemeter bandwidth reduced from 50 Mhz to 3 Mhz Laser power reduced from 1 W to just meet requirements (~300 mW?) Reduce electronics box count (combine functions) Payload mass, power, and size savings SC diameter reduction from 2.7m to ~2.0 m Average thruster force reduced from 9 to 5 micronewtons Bus mass savings due to size reduction and smaller payload Prop module mass savings due to smaller SC and less delta V Overall goal: Max wet stack mass of 3425 kg…. drop two “sizes” in launch vehicle (~$40 M (RY, FY 15 launch) saved) Technology development cost/risk savings… phasemeter, laser, telescope mechanism (~$ 30 M saved) Flight system cost savings… hardware, structure, testing (~90 M saved)

Short Arms (full science): 

Short Arms (full science)

Short Arms (missing 2 points): 

Short Arms (missing 2 points)

Future Trade Studies : 

Future Trade Studies Trade Studies due Feb 06 Spacecraft Mass Reduction Acquisition No Vacuum Optical Bench Layout Arm Locking Details Trade Studies due April 06 Thermal Interfaces Grounding/Power Distribution Frequency Plan Avionics Arch Flight SW Arch Magnetic Zones/PM mag reqs Ranging/Clock DRS Cal Critical Alignments

Timeline for Chemical Transfer: 

Timeline for Chemical Transfer

Optimal Chemical Transfer: 

Optimal Chemical Transfer

Structural Baseline: 

Structural Baseline Sciencecraft mass estimate down to 550 kg (including 30 percent margin) Analyzed several spacecraft/prop module configurations Electric (SEP) and Chemical Prop Module Versions Chem Prop Module looks promising with spaceframe construction Outer cylinder of prop module is the main load up the launch path Spacecraft not required to carry full launch stack Spacecraft designed for 40cm telescope Y-tube opening housed inside of tuna can, providing thermal protection from sunlight and contamination shielding during launch and cruise phase. Develop spacecraft to prop module and PM to PM separation systems Only six separation systems are required (3 PM to PM and 3 S/C to PM) Eliminate release mechanisms on top deck

LISA Spacecraft Configuration: 

LISA Spacecraft Configuration Volume and mass are design drivers!! Coordinated electronics boxes in solid model with agreed to mass/power budget Currently 35 electronic boxes are housed inside of the Sciencecraft Redundancy philosophy needs to be worked (combine functions) Placement of electronics boxes need to address self gravity, thermal, magnetics (adopt zone philosophy) Consider requirements carefully! VIEW: Top of structure with Solar Array and Top Panel removed

Top Hat/Redundant Thruster Clusters: 

Top Hat/Redundant Thruster Clusters Current design puts redundancy in cluster (there are only 3 clusters, not 6 as shown)

Welcome to crowded “LISAapolis”: 

Welcome to crowded “LISAapolis”

Telescope to Bench Options: 

Telescope to Bench Options Astrium MAR (Oct 05) design Astrium lightweight (Dec 05) design NASA Large FOV (Nov 05) design

Laser Subsystem Configuration: 

Laser Subsystem Configuration Old Baseline: 2 + 2 laser subsystems (everything out to fiber to bench) Switching to backup laser was by TBD fiber positioner mechanism Under evaluation: 3 laser units + modulators to provide redundancy A single box serving the three laser heads and amplifiers A single box serving the three modulators electronics A single box for switching the lasers (switchyard) A single box for the electronics needed for the cavity and power stabilization of each laser Total mass of system unchanged at 29 kg

Slide31: 

laser Frequency distribution Out to distant Sc/C In from distant Sc/C Phase Measurement S/C Bus Laser Freq. offset Clock tone Ranging tone InterSc/C comm signal Laser phase lock signal (inc. armlocking) InterSc/C comm demod signal Inter-Sc/C Comm message; Ground commands; Acquisition commands LIMAS Avionics GRS 3 phase msrmts Laser freq. GRS tilt GRS position Clock msrmnt Range msrmt Comm message (all to ground) Phase/range/clock/comm/GRS LIMAS Functions Overview