SNAP Strawman Spacecraft Bus Structure: SNAP Strawman Spacecraft Bus Structure 11 March 2005


Structural Functions: Structural Functions Houses and supports spacecraft functions including: Avionics. Electrical power. Communications. Guidance. Propulsion, including fuel. Current estimated mass of above items is 465kg. Provides mechanical support between launch vehicle and: Optical telescope assembly (OTA)/instrument (~550kg). Stray light baffle/cover/solar array/radiator (~479kg).


Structural Requirements: Structural Requirements Launch environment: Minimum observatory natural frequencies: 10Hz lateral (current design > 18Hz). 27Hz axial (current design > 31Hz). Minimum secondary structure natural frequency = 35Hz (OTA natural frequency > 39Hz). Current limit design loads: 12.5g axial. 8g lateral. Current design has safety factors >5 at limit loads. On orbit Observatory free-free natural frequencies high enough for ACS req’ts (current design > 15Hz). Thermal/dimensional stability to minimize influence on OTA. For integration & test, and on orbit, spacecraft must have minimal distortion influence on OTA. Tight tolerance on interface between spacecraft and OTA. Instrument base ring stiffness dominates spacecraft stiffness. Thermal isolators between spacecraft and OTA/Baffle.


Baseline Design Description: Baseline Design Description Central thrust tube: 4mm thick aluminum hollow cylinder. Diameter approximately 1666mm to match EELV payload adapter. Approximately 500mm tall. Spacecraft equipment deck: ~2.6m outside diameter, ~1.7m thru hole. Aluminum honeycomb construction: 1.25mm Al skins, 32mm thick core. Supports spacecraft equipment on ‘bottom’ side between gussets. 12 gussets between thrust tube and spacecraft equipment deck: Equispaced in a polar array around thrust tube. Aligned with mounting points for OTA and baffle supports. 4mm thick aluminum plates. 12 load spreaders: Spread concentrated loads at OTA and baffle mounts and distribute them more evenly at the level of the EELV payload mount ring. Essentially in the form of a truncated cone, with 12 cutouts that allow access and cooling to deck-mounted equipment. 4mm thick aluminum plates. Internal fuel deck: Support up to 8 420mm dia tanks plus plumbing and rocket motor. Aluminum honeycomb with 0.5mm Al skins. Spacecraft structure mass ~158kg.


Telescope/Baffle/Array/Radiator Config.: Bipod Mounts for Telescope Structure Solar Array & Thermal Radiator Mount on Baffle (adiabatic) Pedestal Mount for Light Baffle Structure Telescope Ring & Deck Ring is Primary Load Path Stiff enough for OTA tests Modest Light Closeout Deck Telescope/Baffle/Array/Radiator Config.


Strawman Spacecraft Config.: Aluminum Honeycomb Equipment Deck Internal Fuel Deck 8 – 16.5”f Tanks will Fit (257 kg) w/ Pressurant Tanks for Slosh Aluminum Central Thrust Tube (1666 PAF) Aluminum Load Bearing & Spreading Gussets Avionics Mount as Desired Radiant Box Cooling is Baselined Strawman Spacecraft Config.


Optional Expandability: 2.5 m Diameter Primary Light Baffle Significant radial clearance from baseline S/C to EELV shroud. IMDC / Team X Avionics Comfortably Fit 0.5m Tall Bus Box Details are in the Solid Model Deck & Boxes can Grow Outward to ~3.5 m dia. , If Needed Optional Expandability