LMA Orbiter Design and SHARAD Instrument Accommodation

1. LMA Orbiter Design and SHARAD Instrument Accommodation 18 Oct 2001 Todd Bayer Orbiter System Engineer Jet Propulsion Laboratory This technical data is export controlled under U.S. law and is being transferred by JPL to ASI or its contractors pursuant to the NASA/ASI Agreement which entered into force on September 25, 2001. This technical data is transferred to ASI or its contractors for use exclusively on the NASA/ASI MRO cooperative project, may not be used for any other purpose, and shall not be re-transferred or disclosed to any other party without the prior written approval of NASA.

2. Topics • SHARAD Accommodation on LMA Spacecraft • Reiteration of Payload Accommodation Requirements • Issues and Questions

3. SHARAD Accommodation on LMA Spacecraft • Lockheed Martin Astronautics was selected as the Spacecraft (S/C) contractor on 03 Oct 2001. • The LMA spacecraft design attempts to maximize the science return from all payloads, including SHARAD. • Figure 1 shows the spacecraft as currently envisioned during the primary science phase. • SHARAD antenna assembly located on a 3m deployable boom to: • maximize the field-of-view required by the instrument and • minimize the EMI/EMC impacts on the spacecraft of the pulsed radar operating at 20 Mhz. • Prevent mechanical interference with solar arrays during periapsis passage. • SHARAD transmitter & receiver are located on spacecraft bus • Figure 2 shows the spacecraft in the launch configuration. • SHARAD antenna stowed in box • Boom in undeployed position, attached to nadir panel

4. Spacecraft Configuration - Primary Science Orbit Downtrack Nadir SHARAD Antenna Assembly SHARAD Transmitter and Receiver Figure 1

5. Spacecraft Configuration - Launch SHARAD Antenna Stowed in box SHARAD Antenna Boom Figure 2

6. Key Spacecraft Requirements • Launch in August 2005 Mars window, arrival March 2006 • Launch vehicle capability: 1800 kg • Achieve mapping orbit using ~180 days of Aerobraking • 3 PM mapping orbit (30 minutes of eclipse per orbit), 400 x 200 km sun synchronous orbit, • primary mission one Martian year from time of turn on of the instruments in orbit • Radar must accommodate heating and pressure forces resulting from aerobraking • ~5 year spacecraft design lifetime • with propellant for 10 years • No single point failures • With “Normal” exceptions (structure, single high gain antenna, etc.) • No radioisotope materials • Science ops during extended mission require NASA approval • Design reference mission for one day of orbital operations is shown in Figure 3

7. Primary Science: One Day of Operations Figure 3

8. Instrument Accommodations • The LMA spacecraft proposal meets or exceeds these requirements • Power • Unregulated 28 Vdc power (+8 Vdc, -6 Vdc) • One power on/off switch (single fault tolerant), separate replacement heater switch • Pointing (3 sigma, per axis) • Accuracy: < 0.7 mrad roll (140 arc-sec) < 1.0 mrad pitch (200 arc-sec) < 1.0 mrad yaw (200 arc-sec) • Stability: < 0.0015 mrad (0.3 arc-sec) over 3 msec < 0.05 mrad (10 arc-sec) over 100 msec < 0.25 mrad (50 arc-sec) over 1 sec < 1.0 mrad (200 arc-sec) over 2 sec < 3.0 mrad (200 arc-sec) over 16 sec • Telecom • X-band up and down • Data rate of 280 kbps min, 2.2 Mbps max • At max distance of 2.67 AU • Using 34 m DSN antenna

9. Instrument Accommodations (cont’d) • Command / Data Handling / Storage • Data interfaces (high speed [20 Mbps] LVDS and low [9600 bps] RS422) • Serial interfaces, discrete digital I/O and mass memory • 20 MIPS processing capability for the entire payload (not including CCSDS downlink formatting provided as orbiter service) • 36 Gbit volatile mass memory for the entire payload • 10 Mbytes of non-volatile memory for the entire payload • Payload engineering telemetry for incorporation into the science data stream • (pointing attitude, temperatures, etc.) • Up to 4 analog temperature sensor channels per instrument • 2 programmable, general purpose digital I/O channels (5V TTL) • Time tag service (+ 30 ms relative to orbiter clock) and 1 Hz time tick • 2 Mbytes of instrument command storage for the entire payload • Mounting alignment services and cubes (mounted by the instrument) • “Star” ground trees (exact design to be negotiated) • Electrical connectors (both sides) and appropriate connector savers

10. Payload Constraints: SHARAD • Mass 12 kg (MRO Project holding 30% (3 kg) margin) • Volume Receiver/Trans. 22 x 25 x 20 cm, 70 x 25 x 5 cm Dipole Stowed 45 x 25 x 10 cm Dipole Deployed 700 cm • Field of View Omni-directional • Power 50 W Average, 60 W Peak, 10 W cruise • Power Switches 2 (one on/off, one replacement heater) • Data Rate 1 High Speed LVDS (Low Voltage Differential Signaling) with commandable clock rates of 1, 5, 10, 20 and 30 Mbps • Discrete Ins & Outs 2 and 2 • Temperature Sensors 4 (AD590s) • Operations - Operations occur only (1) during local night (7pm to 5am) and (2) when Orbiter is not communicating with the DSN - 4 daily opportunities of 50 min each, for daily data volume of 2Gb

11. Payload Constraints: SHARAD (cont’d) • Assumed data rates for SHARAD, data rates assumed to vary between 34kbps and 1Mbps • Thermal Isolation Assumed transmitter & receiver are thermally isolated from bus (spacecraft can accommodate thermally conductive interface if needed)

12. Key Instrument Responsibilities • Design to operate within specification for 5.4 years • Accommodate heating / pressure forces resulting from aerobraking • Remain within mass / power / volume / field-of view and other allocations • Stay within EMI / EMC, contamination, disturbance, and other limits • Develop thermally isolated interface between instrument and orbiter bus • Handle all their own computing demands (Baseline) • Identify cost / resource savings if orbiter provides added computing capability • Maintain min. natural freq. (fixed base) of 80 Hz in launch configuration • Maintain Deployed Appendage min. natural freq. (fixed base) of 0.1 Hz • Limit induced vibration disturbances from deployments / mechanisms • Deliver Engineering Model (EM) with same form, fit and function as the flight unit EMI: Electromagnetic Interference EMC: Electromagnetic Control

13. Deployment Concept • Current SHARAD Deployment Concept • Boom to be released from spacecraft hold-down soon after launch (but not articulated) • Keep boom next to body until completion of aerobraking • During aerobraking, boom and antenna box will be subjected to the atmospheric free stream during each drag pass (lasting approximately 15 minutes) with heating rates of approximately 0.17 W/cm2 (over approximately 570 aerobraking orbits). • After MOI and Aerobraking, boom is articulated to operational position and antenna is deployed from box. • If instrument checkout during cruise is desired, then early deploy and articulation is required. The following issues arise in this case: • Is antenna compatible with MOI loads and thruster plume impingement? • Is antenna compatible with aerobraking heating? • Is there a way to eliminate the boom?

14. Questions for SHARAD Team 1. Can you provide any update to the number of boxes, the physical dimensions, and the mass of the instrument system? 2. Do you have any special test considerations (additional EMC, deployment testing, etc) 3. What are your drivers, tall poles, and sensitivities.. If we give you another kg or another Watt does this help you? 4. How much on-board processing do you envision.. Are you planning to process the return with your own processor or on-board the flight computer? 5. How is it envisioned for the organization working between LMA, JPL and ASI? 6. Can you tell us as much as possible about the antenna… Some of the items of interest would be: a. Deployed frequency (requirement is 0.1 Hz, but can we get it ~1-2 Hz?). b. Do you have a problem with the pre-deployment condition and aerobraking c. Is it important to checkout SHARAD during cruise? (early deployment) c. How does the antenna deploy, d. Is the antenna pattern consistent with the current spacecraft design, e. Is it OK to “tilt” the antenna as we perform cross-track slews, etc. 7. Is the LVDS Serial i/f the best choice for the instrument, or is there some other type of electrical interface you would prefer

15. Questions for SHARAD Team 8. We have assumed the radar would produce source field strengths of 100 v/m at 20 Mhz at the base of the dipole. Is this correct? a. Field produced by spacecraft not yet modeled, but note that Electra transmits at UHF over 4 steradians. Does SHARAD have special EMI/EMC requirements? 9. Are our assumptions on data rate correct? 10. Does the Design reference mission seem reasonable to you? Do you see wanting to operate the instrument more/less than we are currently assuming? Is the assumption that we will operate it primarily in eclipse correct? Do you envision the instrument cycling between an operational and stand-by mode.. Or do you see us powering it off/on? If off/on, is there any warm-up time required?

16. Topics for Future Discussion • Instrument Mounting, Location, Orientation, Alignment, Accuracy, Special tools • Instrument / radiator field(s)-of-view • Command / Data Handling interface • Induced vibration disturbances: Moving Mechanisms, Deployments • Limiting radar interference with S/C telecom, power & other instruments • Engineering Model fidelity • Design approaches for contamination control • Ground support equipment