Earlier this year, the Meteoroid Environment Office (MEO) presented three papers at the 7th European Conference on Space Debris in Germany, sharing findings and updates related to comparison studies on the damage caused by meteoroids versus Orbital Debris (OD), meteor shower forecasting and NASA’s Meteoroid Engineering Model (MEM).
Bill Cooke, MEO lead; Althea Moorhead, aerospace technologist for planetary studies; and Steven Ehlert, astronomer with Jacobs ESSSA Group (all located at Marshall Space Flight Center) presented “A Comparison of Damaging Meteoroid and Orbital Debris Fluxes in Earth Orbit,” “Meteor Shower Forecasting for Spacecraft Operations,” and “A Comparison of Results From NASA’s Meteoroid Engineering Model to the LDEF Cratering Record,” respectively.
“OD has been universally acknowledged as a problem, and because it can be mitigated that’s the focus [of the conference],” explained Cooke.
“Overwhelmingly people were talking about Orbital Debris, so it was important that we were there to remind them about the risk from meteoroids as well,” added Moorhead.
Even though the conference is OD-focused, it’s still geared towards spacecraft operators and engineers who design and operate the spacecraft affected by MEO’s work.
“It’s really important we share our results and share the overall spacecraft risk with that community,” said Ehlert.
“A Comparison of Damaging Meteoroid and Orbital Debris Fluxes in Earth Orbit”
For MEO’s study captured in “A Comparison of Damaging Meteoroid and Orbital Debris Fluxes in Earth Orbit,” the team worked with members of the Orbital Debris Program Office to look at the number of meteoroids capable of damaging spacecraft and compared it to the amount of OD capable of damaging spacecraft at different altitudes in Earth orbit.
The study, which was the first-ever OD and meteoroid comparison as a function of altitude, found that for altitudes below the International Space Station and above 4,000 kilometers, meteoroid damage is the greater risk to spacecraft, while the altitude from between the space station to that 4,000-kilometer mark has a higher risk of OD damage. (The space station itself shows roughly equal impacts from meteoroids and OD.)
That being said, there are certain sun synchronous altitudes from 800 to 1,000 kilometers where NASA and other government and industry organizations frequently place spacecraft, and in that zone the debris caused by man-made crafts is by far the biggest threat. In this zone, OD sometimes generates 500 times the risk that meteoroids do.
“Certain altitudes in Earth orbit we trash very effectively,” explained Cooke, referencing the heavily cluttered zone. “Unfortunately, it’s a very popular space.”
A few examples of spacecraft at this altitude include commercial imagers, A-Train and NASA’s Iridium NEXT satellites.
“It’s a very popular place to put satellites, in part because you can maintain the same sun angle and resulting shadows,” explained Cooke. “[But] when the risk from what you put up there is over 500 times what the natural environment is, you have a problem.”
Whether or not an organization plans to put a spacecraft in this high-risk zone or at another altitude, it’s important that designers understand the risks posed by both meteoroids and OD so they can take proper precautions to protect the spacecraft. Meteoroids move faster than OD, so smaller pieces can cause damage.
“A meteoroid can be much smaller and still inflict the same amount of damage,” said Cooke.
In fact, the effect of being hit by a 1-centimeter meteoroid can be equivalent to getting hit by a truck, resulting in catastrophic damage.
Despite the damage meteoroids can do, there’s also nothing that can be done to reduce their quantity, so designers must always take this into account and put protection in place for vulnerable spacecraft. Cooke acknowledges that unlike meteoroids, there is something that can be done to reduce OD, or at least prevent a further increase of it, which is why the conference focuses primarily on space junk.
“Meteor Shower Forecasting for Spacecraft Operations”
This paper, presented by Moorhead, highlights NASA’s forecasting methods and presents improvements in the forecasts based on flux measurements from the Canadian Meteor Orbit Radar. The paper also discusses the application of the meteor shower forecast to risk assessments for spacecraft.
Although MEO has produced meteor forecasts for years, this paper is the office’s first publication that goes over how NASA does forecasting, and the conference was a unique opportunity to present meteor shower forecasting to a pre-dominantly engineering based community.
“Besides just explaining it [forecasting], we also talked about some recent improvements we made,” explained Moorhead. “We took a look at the code and made some improvements there and we improved the descriptions of the meteor showers that we input into the forecasting code.”
The goal is to understand the flux of meteoroids occurring during the shower as well as the duration of elevated risk during the shower. According to Moorhead, normally there is a rise and fall to each shower, but some peaks and dips last longer than others. A paper from 1993 was the last time activity profiles of meteor showers were quantified. With this recent re-evaluation, MEO found that in many cases current predictions based on the newer data has resulted in big improvements in the forecast accuracy. Using new data, MEO made significant changes in the timing of some meteor showers, particularly for daytime showers. As a result of the study, new shower parameters were determined and incorporated into the 2017 forecast.
“A Comparison of Results From NASA’s Meteoroid Engineering Model to the LDEF Cratering Record”
Ehlert’s paper, “A Comparison of Results From NASA’s Meteoroid Engineering Model to the LDEF Cratering Record,” covers MEO’s investigation of impact craters on an old spacecraft: the Long Duration Exposure Facility (LDEF).
Impacts on LDEF are indicative of underlying velocity distribution and directionality of the OD and meteoroid environment. LDEF, a school-bus sized facility that hosted science experiments, was in Low-Earth Orbit from April 1984 to January 1990, when space Shuttle Columbia retrieved it so that NASA could observe how the space environment affected the experiments inside. MEO compared the data on the observed impact craters to predictions made by NASA's MEM Release 2 meteoroid environment model over LDEF’s operational lifetime.
“It’s an actual in-space detector,” explained Ehlert.
MEO started by determining how many impacts it expected to see on LDEF based on the existing model and then compared that to reality. According to Ehlert, the model predictions were a pretty good match for those surfaces on which meteoroids were expected to dominate over OD. The biggest surprise to Ehlert was that despite LDEF being in space during the 80s and 90s (when fewer spacecraft were in orbit), there were a lot of OD hits. This information will help MEO understand how well the current version of MEM is working and improve future models.
The 8th European Conference on Space Debris will be in 2021 in Germany.