Space Environmental Hazards For Space and Launch Systems

Transcription

1 Space Environmental Hazards For Space and Launch Systems Dr. Joseph E. Mazur The Aerospace Corporation Presentation to the 2012 FAA Commercial Space Transportation Conference Physical Sciences Laboratory Engineering Technology Group 15 February The Aerospace Corporation

2 Outline Introduction Three main messages Space environment hazards for launch Single event effects Vehicle charging Actions for the launch operator Summary This briefing stresses the need to understand the susceptibility of the space and launch vehicles to environment hazards before launch. PSL/SSD 2

3 Introduction The Aerospace Corporation s vision is to be the leading architect of the country s national-security space program and a principal technical resource for programs of a national significance I am Associate Director of the Space Sciences Department in The Aerospace Corporation My background is in space science and the effects of the space environment on robotic systems My Department works to insure mission success in the area of space environmental effects on satellite systems Our focus is on pre-flight: Specifying the hazards with exploitation of existing space science data and acquisition of new space science data Mitigating the hazards with engineering techniques Developing ways to obtain the correct situational awareness PSL/SSD 3

4 Three Main Messages 1. The space environment is not the same everywhere. 2. The best way to mitigate space environment hazards is through design, but one must first know what the hazards are and how the design might be susceptible to them. 3. There are few tools or data feeds to inform a launch operator about the actual hazards that the launch vehicle will encounter. We next show the hazards for satellites because they are the source of most of our information about how the space environment can become a hazard. PSL/SSD 4

5 Space Environment Hazards Solar array power decrease due to radiation damage False signals in sensors CCD image before & during exposure to multi-mev protons Before After Surface degradation from radiation Single event effects in microelectronics Electronics degrade due to total radiation dose Spacecraft components become radioactive Solar array arc discharge Electromagnetic pulse from vehicle discharge (on surface, behind thin shielding, or deep inside) Induced Voltage Time PSL/SSD 5

6 Impacts To Launch Vehicles There are fewer space environment concerns for launch vehicles mainly because of the short time they spend performing their missions (an exception: the Centaur upper stage that carried LCROSS operated for 4 months) For launch vehicles the hazards are: Single-event effects in microelectronics Surface charging Neither of these hazards may be relevant if the design isn t susceptible to them or if the launch vehicle trajectory doesn t expose it to the relevant environment Limited exposure to the space environment means that launch vehicles have fewer hazards to mitigate. PSL/SSD 6

7 Single Event Effects (SEE) SEE range from non-destructive upsets, transients or interrupts, to destructive failures Environmental causes Galactic cosmic rays Solar energetic particle events Inner Van Allen belt protons PSL/SSD 7

8 SEE Environments Galactic cosmic rays Ubiquitous Primary particles always present above ~100 km Solar energetic particles Not present ~93% of the time Hazard level not predictable Not relevant at low altitude & latitude Inner belt protons Always exist Important below ~6000 km Solar particles Inner belt protons Galactic cosmic rays PSL/SSD 8

9 SEE Mitigation Steps 1. Specify worst-case environment 2. Measure piece-part susceptibility 3. Use 1 and 2 to infer system susceptibility 4. If susceptibility is not acceptable, mitigate with Shielding (not possible with GCR or inner belt protons) Redundancy A redesign using parts that have lower upset rates S. Crain & R. Koga, Crosslink, Summer 2003 The mitigation steps are well-defined in the satellite community; the same steps apply to launch vehicles. PSL/SSD 9

10 Surface Charging The hazard is electrostatic discharge (ESD) from free charge accumulated on the outside surfaces of the vehicle If neighboring surfaces charge at different rates, then the differential voltage can exceed the limit for breakdown The resulting ESD can damage the surfaces and induce hazardous signals in vehicle electronics Environmental causes Friction during ascent through the atmosphere Plasmasheet electrons Auroral electrons PSL/SSD 10

11 Surface Charging Environments Tribocharging Not a space effect but due to collisions with ice crystals in clouds Relevant from ~few to 30 km & speeds below 3000 ft/sec Plasmasheet High latitudes and altitudes above ~18000 km Not always present Hazard level unpredictable Aurora Narrow latitude range Not always present Hazard level unpredictable Plasmasheet Aurora P. Anderson, 6th SCTC, AFRL-VS-TR , 2000 PSL/SSD 11

12 Surface Charging Mitigation Steps 1. Conduct a top-level overview of the vehicle from charging perspective 2. Ground thermal blankets and use conductive paints and charge dissipative materials on surfaces 3. If a required surface has uncertain charging susceptibility, then test the materials in appropriate electron beams to demonstrate charge dissipation capability 4. Test box-level susceptibility to ESD using MIL-STD-1541A Surface charging requires a systems-level approach because the surfaces in question often are part of thermal control or power systems or have other mission-related requirements. PSL/SSD 12

13 Actions For the Launch Operator Ideally, the space environment would require no action on the part of a launch operator because all the hazards would have been assessed and mitigated through design This ideal also applies to spacecraft operators, but on-orbit satellite histories show that the environment will likely remain a hazard in spite of community efforts If the launch vehicle has a known susceptibility, Make sure the hazard is quantified Set environment limits based on the susceptibility Establish the launch campaign decision methodology Launch when the environments are GO However, there are problems with assessing whether launch environments are GO. PSL/SSD 13

14 Actions For the Launch Operator There are several problems when using existing near-real-time data to decide GO/NO-GO : It is not clear how to accurately project these data to a particular launch and early-orbit mission profile The data feeds are not available for surface charging GOES data do not show the heavy ions responsible for most SEE Reprinted courtesy of NOAA As a result, data such as these have been incorrectly interpreted, incorrectly applied, and sometimes largely misunderstood GEO data are mostly relevant to GEO hazards, but space is not one place. PSL/SSD 14

15 Can t We Predict What Will Happen Before Launch? The inability to effect on-orbit repair and the cost of replacement has led to the industry s emphasis on pre-flight mitigation Also, something always has to function on orbit regardless of the hazard levels so powering off is not an option Within the community of National Security Space operations, predictions have little value apart from the promise of enhanced situational awareness There are no accurate predictions of SEP environments out to many hours, except maybe for an all-clear assessment or estimates based on persistence Examples of the common misconception that shutting a satellite off will protect it With advance warning, engineers can power down satellites and turn them away from the sun, delay launches of craft and make sure astronauts are not out spacewalking, and mitigate widespread damage to electronic systems on Earth. -The Sun s Halo in 3-D, by Ron Cowen, Science News, vol. 170, August 19, 2006 For now, scientists can only turn off satellites and power grids to prevent electrical damage from the incoming particles. They lose a little data or service in the process but save the satellite or grid in the long run. opstory/2003/0411tadpoles.html PSL/SSD 15

16 Mitigation Through Delay of Launch If the launch vehicle has a susceptibility and redesign is not cost-effective, the only mitigation is through delay of launch We studied this for launch and early orbit activities without specific flow-down of system susceptibility The approach avoided launch into the 99-percentile environments with delays that did not exceed the 10% chance of a delay due to terrestrial weather J. Mazur, P. O Brien, & T. Guild, ATR-2008(8073)-3 PSL/SSD 16

17 Summary We have shown the main space environmental hazards that have been gleaned from years of spaceflight experience The hazards are not the same everywhere and their effects have to be assessed for every piece of space hardware The primary lesson we can apply to launch is that best way to mitigate space environment hazards is through design before flight Even though the near-real time particle and fields data from NOAA and NASA are difficult to use to estimate the actual hazards, without them we would have no indication of the near-earth environment. Solar imagery cannot be extrapolated to the hazards of single-event effects and vehicle charging. PSL/SSD 17

18 2012 The Aerospace Corporation